13Ohjelmatunnukset

Efficient NetworkingTowards Novel Products and Processes

Programme Report 2010–2013

Efficient NetworkingTowards Novel Products and Processes

Programme Report 2010–2013

13Ohjelmatunnukset

Copyright Finnish Bioeconomy Cluster FIBIC 2013. All rights reserved.

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Content

Foreword ........................................................................................................................................................5

High consistency forming of microfibrillated composite webs ................................................ 14

Foam Forming ...........................................................................................................................................30

Fiber-based products for new applications ....................................................................................48

Microcelluloses and their characteristics ........................................................................................66

Resource-efficient papermaking concepts ....................................................................................90

Management of web uniformity based on imaging measurements ................................... 108

Expanded operating window for printing process enabling efficient use of

newly engineered fiber-web substrate .......................................................................................... 130

Optimizing structures and operation of entire production systems ................................... 146

5

FoReWoRD

The Finnish forest industry is undergoing radical changes. The decline of the graphic paper sector means urgent efficiency improvements in existing products and proces-ses are needed together with the establishment of a new earnings base from novel products and processes. In 2008 these needs initiated the Forestcluster research pro-gramme Intelligent and Resource Efficient Production Technologies (EffTech), of which the three-year research programme Efficient Networking towards Novel Products and Processes (EffNet) was a direct extension.

The high business volumes of the forest industry’s existing products presents a big challenge for any new product to reach similar volumes. Transformation of the industry will, for this reason alone, take time. All possible means to improve the competitiveness of current production must therefore be taken in the meantime, as it is this competiti-veness that will enable the risky, but necessary, renewal of the industry.

The overall goal of EffNet was to improve the competitiveness of the whole forest cluster by developing radically new energy- and resource-efficient production techno-logies and by finding means to reduce capital intensiveness. The focus was twofold: firstly to develop new energy- and resource-efficient web production technologies and, secondly, to re-engineer the product concept of fibre-based products with nanocellu-lose. The target was to develop and demonstrate new types of products manufactured from wood-based fibre material and to expand the current product portfolio offered by forest cluster companies.

New technologies always carry risk. Cooperating across the whole value chain in a com-mon programme towards a common goal, however, gives us the combined force needed to create and evaluate new ideas and to bear the development and implementation risks. EffNet has created bright opportunities to improve raw material efficiency and develop new products. Our goal now is to carry these forward as successful innovations.

Jyrki HuovilaMetso PaperChairperson of Programme Management Group

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Raw material, energy and water efficiency are increasingly dominant drivers of forest indus-try investment. Incremental changes and lin-ear extrapolation of current practices will no longer guarantee a healthy and robust indus-try. Future paper machine concepts will far out-perform current technologies in resource and capital efficiency. The most competitive prod-ucts of today must be used to bridge the gap to the renewed forest industry of tomorrow.

The EffNet programme addressed these challenges by exploring novel applications for new materials, particularly nanocellulose. The aim was to improve resource efficiency and create a wider product space also within exist-ing product categories.

New ideas, successful product concepts

The EffNet programme targeted research ar-eas of key strategic importance to the paper industry, the renewal of which requires high-risk research towards achieving radical devel-opment steps. EffNet succeeded in delivering this calibre of research.

In the EffNet research programme new knowledge, practicable ideas for new products

and use of new raw materials and novel fibre-based product concepts were created. Several technologies demonstrated at laboratory and pilot scale show remarkable techno-economi-cal potential.

Raino Kauppinen, Stora Enso:

“The high applicability of the results reflects

the quality of the research and a clear

understanding of real-life challenges.”

Sharper competitiveness through foam forming

The technology with the highest value crea-tion potential was foam forming. The method was shown to significantly reduce capital inten-siveness and resource consumption and thus improve the competitiveness and sustainabil-ity of current paper and board products. The technology also paves the way for forest in-dustry renewal by enabling raw materials to be combined in revolutionary new ways, creating unique opportunities for companies to enter new value chains.

NEW SOLUTIONSAND

ADDED VALUEFROM THE EFFNET PROGRAMME

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The development of foam forming in EffNet has opened up a totally new research track for the development of novel products. This impor-tant achievement may not have been possible without the combined force of a sizeable con-sortium and public support. Foam forming pre-sents exciting opportunities for the use of ex-isting raw materials and current production infrastructures, but also offers fertile ground for new, competitive applications beyond conven-tional paper and board. Foam forming brings a fundamental change to the way fibre webs can be formed and enables milestone improve-ments in raw material efficiency. The technology opens up new product property windows and is set to make significant inroads in board making.

Knowledge and cost optimization

In today’s cost-pressure environment, the need for new solutions is acute. In EffNet, the biggest innovations in papermaking have been achieved with high-filler concepts. Re-search into microfibrillated cellulose filler ag-gregates and starch-based biominerals also showed high potential for achieving good pa-per properties and cost savings. The develop-ment of binding fillers and novel utilization of cellulose fibrils opens opportunities to develop new paper grades and bring cost benefits.

Printability research achieved important new findings, expanding current knowledge and supporting the further development of printing papers. The printing efficiency results have proven useful and practical. The partici-pating companies have been able to utilize the results in their existing business, for example by providing new pillars of customer support. From the viewpoint of printing companies, one of the most promising results came from the development and test runs of a novel printing paper. The test runs demonstrated good run-nability of the new paper and the concept pro-vides a firm basis for future development.

Novel tools to improve production efficiency

Image-based measuring systems were devel-oped to improve the process efficiency of both existing and potential production systems, such as foam forming. The image-based quali-ty monitoring technologies enable process op-timization and lead to direct improvements in production efficiency. A developed new image analysis method for tissue paper provides fast and accurate information for optimizing crep-ing in tissue production. The new method en-ables evaluation of the effect of chemicals in the creping process, thus leading to radical process efficiency improvements. Fast imag-ing technologies can improve competitiveness in both current and future paper processes.

Marjatta Piironen, Kemira:

“Innovative image-based technologies were

developed in the EffNet programme. Without

EffNet this would have been very difficult or

even impossible.”

Big potential from microfibrillated celluloses

New technologies and utilization of microfibril-lated cellulose (MFC) in paper and board man-ufacturing will impact the paper chemicals industry in the future. The new knowledge cre-ated by EffNet will help companies design their future chemical portfolios. MFC has consider-able application potential through combining various materials and techniques. One prom-ising future application for MFC is in the fast-growing industry of super-absorbent polymers.

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Power through networking

Close collaboration between companies and EffNet researchers created new opportunities, broader insight and networks for the future. According to the participants, networking has been valuable and productive both within and outside the research consortium. Close and open cooperation between key players and experts generated a broad pool of expertise and was considered an essential aspect of the programme.

The networks established in product safety and characterization of nanocellulose were a valuable addition to the programme, and com-pany seminars were also highly appreciated. Participants also gained insights into interna-tional research in several leading areas, such as process design, image-based measurement, nanocellulose applications and foam chemis-try. The networking opportunities and contacts built during the programme will be of significant value in future development projects. Knowl-edge of the competence areas of researchers in different universities and institutes will also greatly facilitate future cooperation.

Jyrki Huovila, Metso:

“ Networking means having more power to

create new ideas and evaluate them throughout

the value chain, and to share the risks of new

technologies.”

Creating value and new business

The EffNet programme has contributed to new value and business creation in key areas of the forest sector. These valuable results must now be carried forward with further testing and eval-uation, for example at the pilot scale. Sever-al participating companies have already based their future business and development projects on the research areas of the EffNet programme and will implement these projects in collabora-tion with one or more EffNet partners.

The results and technology concepts devel-oped in the EffNet programme provide a sol-id basis for further development towards new industrial solutions, generating value and new business opportunities for the forest industry.

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The EffNet programme has had two impor-tant strengths: effective networking between partner companies, research institutes and academia in Finland, and a sufficiently long funding period. These have enabled serious research efforts to generate radical solutions to improve the competitiveness of Finnish for-est industry companies.

The role of VTT Technical Research Centre of Finland in the EffNet programme has been cen-tral and in line with VTT's objectives of creat-ing high-level scientific and techno-economic knowledge and know-how and generating tech-nology and innovations for industry and society.

Erkki Hellén, VTT:

“Without the five-year funding period, the next-

generation resource-efficient technology with

the highest potential, foam forming, would have

not been developed to the level it is at now.”

The research strategy of the Measurement In-formation Group at Tampere University of Tech-nology is to develop generic design and oper-ational methods for dynamic systems whose behaviour includes stochastic aspects. There has been a strong synergy between programme objectives and research objectives: the prob-lems specified by the programme have provided practical test benches for generic research.

Human technology, one of the strategic re-search areas of the University of Jyväskylä, plays a central role in the interactive method-ology for multi-objective optimization devel-oped by the university’s industrial optimiza-tion research group. The research conducted in EffNet supports this major research area. The industrial optimization research group participated in the Effnet programme in devel-oping and applying theory and methods and software development for decision support.

Kaisa Miettinen,

University of Jyväskylä, Department of

Mathematical Information Technology:

“The programme provided interesting and

novel research problems and gave valuable

experience in dealing with the challenges of

complex real-world problems.”

The EffNet programme has demonstrated how companies can collaboratively use Finnish world-class research environments in effec-tive and iterative ways to develop new prod-ucts, leading to fruitful and continuous dia-logue between researchers and industry. The programme has activated international collab-oration, built new contacts, educated young researchers, created novel information and generated strategic opportunities for future research and solutions development.

Risto Ritala, Tampere University of Technology:

“The combined scientific and application oriented research has provided us good opportunities for

publishing results and advancing the doctoral studies of our researchers.”

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1. Background

The National Research Strategy of the Finnish forest-based sector was published in 2006. To help implement the strategy, the public-private partnership Forestcluster Ltd was es-tablished in 2007 with the main goal of taking forward the research priorities outlined in the strategy. Today, the Finnish Bioeconomy Clus-ter (FIBIC) has activities in three strategic fo-cus areas: Intelligent, Resource-Efficient Pro-duction Technologies, Future Biorefinery and Sustainable Bioenergy Solutions.

Research programmes are the core of FIBIC’s operations. Their aim is to foster collaboration between end-users, companies and research-ers in creating opportunities for research and new business through open innovation and new ways of networking, and to speed the transition from research results to commercial products.

Intelligent and Resource Efficient Produc-tion Technologies (EffTech) was the first re-search programme launched by Forestcluster in 2008. In the second phase (2010-2013), the EffTech programme was divided into two in-terlinked programmes in order to sharpen the research focus and to diversify the number of research participants. The three-year re-search programmes, Value Through Intensive and Efficient Fibre Supply (EffFibre) and Effi-cient Networking Towards Novel Products and Processes (EffNet) together cover the whole value chain from forest to printing press. The EffFibre programme focuses on improving the availability and supply of high-quality raw ma-terial from Finnish forests and developing new production technologies for chemical pulping.

The focus of the EffNet programme is on de-veloping radically new energy- and resource-efficient web production technologies and designing nanocellulose-based production concepts and novel, innovative products.

The overall goal of the EffNet programme was to develop sustainable solutions to en-sure the leading position of the Finnish for-est cluster in the large-scale production of fi-bre-based printed and packaging products. The three-year research programme had total budget of 15 million euros. The Finnish Funding Agency for Technology and Innovation (Tekes) provided 60% of the financing, with the re-mainder sourced from the participating com-panies and research institutes.

2. Programme portfolio and goals

The Efficient Networking Towards Novel Prod-ucts and Processes (EffNet) programme aimed to enhance the competitiveness of the whole forest cluster by developing radically new en-ergy- and resource-efficient production tech-nologies and by finding ways to reduce the capital-intensiveness of the cluster. The pro-gramme portfolio for the three years included ten work packages (see Figure 1).

One half of the programme was targeted at demonstrating new products and technolo-gies based on the utilization of microfibrillat-ed cellulose (MFC). The main emphasis was on next-generation resource-efficient forming technologies to expand paper and board prop-

intRoDuCtion

11

erties and to allow the development of new fi-bre-based products outside traditional value chains. The research focused on the two high-est potential technologies: foam forming and ultra-high consistency forming. In addition, the processability of microfibrillated cellulos-es, development of binding fillers for paper applications, and demonstration of new, val-ue-added products were addressed. Special attention was given to the sustainability and product safety of microfibrillated cellulose.

The second half of the EffNet programme developed production system concepts for the existing printed products and packaging markets. The concepts seek efficiency excel-lence in total cost of ownership and sustain-ability performance, such as water and carbon footprint. Three core concepts were identified and analysed: novel fines-coated printing pa-per, high filler content SC paper based on a bindable filler concept, and reduced material consumption in folding boxboard production based on a foam-formed middle ply. The re-search went beyond the boundaries of current business models by analysing opportunities for optimal efficiency throughout the whole supply chain, including intensive analysis of the processes involved in producing customer

solutions, most notably the printing process. Concept generation by the participating com-panies orchestrated the detailed research or-ganized into studies on unit processes, quality control and management, image-based meas-urements, and the printing process.

3. Management of the programme

The EffNet programme was administered by a Management Group (MG) comprising repre-sentatives from industry and academia. The execution of was headed by Programme Man-ager together with Industrial and Scientific Co-ordinators. The daily management tasks were performed in each Work Package (WP) under the leadership of the WP manager.

The main tasks of the Management Group have been to supervise the progress of the programme with respect to the objectives of the national forest cluster research strategy and the EffNet programme plan, and to assess the scientific progress and techno-economic feasibility of the results. In 2011, the MG’s main tasks included mid-term evaluation of the pro-gramme, organization of the discussions with

Figure 1. EffNet programme portfolio.

Efficient Networking towardsNovel Products and Processes

High consistency

forming

Foamforming

Fibre-based products for

newapplications

Micro-cellulosesand their

charasteristics

Production system

concepts management

Resource-efficient

papermaking

Image basedmeasurements Printing

Optimizing structures and

operation of entire

productionsystems

Verification of conceptsNew processes and productbased on nanocellulose

Efficient mill conceptswith new unit processes

12

the shareholder companies of Forestclus-ter Ltd in order to harmonize the EffNet pro-gramme with the companies’ research strat-egies and to define the most important focus areas for the second period of the program. MG had the following members:

• JyrkiHuovila,MetsoPaper,Chairman• ErkkiHellen,VTT,ScientificCoordinator• MikaHyrylä,UPM-Kymmene• RainoKauppinen,StoraEnso• MarkkuLeskelä,FIBIC (Lars Gädda until April 2012)• MarjattaPiironen,Kemira• AriPelkiö,Andritz• ErkkiPeltonen,Myllykoski• RistoRitala,TampereUniversityof

Tehnology, Scientific Coordinator• HannuSaarnilehto,SanomaNews• PauliinaTukiainen,VTT, Programme Manager• LauriVerkasalo,MetsäBoard (Ari Kiviranta until September 2011)• SeppoVirtanen,UPM, Industrial Coordinator• MikkoYlhäisi,Tekes

Dissemination of EffNet programme resultsis achieved with a number of different tools, the most important being the FIBIC research por-tal, accessible to EffNet programme partici-pants, and the FIBIC Ltd website (http://fibic.fi/programmes/effnet). Detailed project reports and publications are available via the FIBIC por-tal. Programme seminars have also been held annually, bringing together experts from ac-ademic and industrial fields and providing a comprehensive overview of the programme’s research activities and results.

4. Participants and international cooperation

The EffNet research programme brought to-gether the leading forest cluster companies and research organisations related to paper-making technology, material science, modelling and simulation and machine vision research in Finland. Eight companies and eight Finnish uni-versities and research institutes participated in the programme. In addition, research was also subcontracted from external partners.

Industrial partners:

• Andritz• Kemira• Metso• MetsäBoard• Myllykoski• SanomaNews• StoraEnso• UPM

Research organizations:

• AaltoUniversity• LappeenrantaUniversityofTechnology• TampereUniversityofTechnology• UniversityofEasternFinland• UniversityofHelsinki• UniversityofJyväskylä• UniversityofOulu• VTTTechnicalResearchCentreofFinland

International cooperation was built into the EffNet programme and plays an important role in the de-velopment of novel resource-efficient production technologies. Research organizations were en-couraged to pursue international collaboration for this purpose with the aim of strengthening the position of Finnish research groups in in-ternational communities and opening up new cooperation opportunities. The programme participated in cooperation with six countries:

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Canada, Germany, Ireland, Sweden, the UK and the USA. Close links with the internation-al scientific community are maintained, par-ticularly in the areas of foam forming, multi-parameter optimization, image analysis and nanocellulose research. The cooperation initi-ated during EffTech was continued and broad-ened in EffNet.

Programme participants have been active in presenting the programme results at inter-national conferences and researchers have arranged international workshops and con-ferences, such as the 21st International Con-ference of Multiple Criteria Decision Making, at which EffNet research groups held a special session on multi-objective process design for systems with multi-objective operation. The session generated valuable input from numer-ous international methodology experts. EffNet participants have also been active participants in international workshops aimed at promoting the standardization of nanocellulose safety and characterization test methods.

The EffNet programme was designed to mini-mize research overlap with related projects and to maximize synergy between other research activities. Many of the programme’s research-ers were also involved in other related projects, which ensured active information exchange and rapid application of results. EffNet research groups participated, for example, in the Euro-pean Community's 7th Framework Programme projects and several COST actions.

The EffNet programme’s core research also supports several industry-driven projects aimed at developing industrial applications. While many of these projects are confidential, active par-ticipation of industrial partners within the pro-gramme has ensured active information flow, in turn speeding the development process.

HIgH cONSISTENcy fOrmINg Of

mIcrOfIbrILLATEDcOmPOSITE WEbS

pa r t n e r s

a a l t o U n i ve r s i t y

M e t s o p a p e r

M e t s ä B o a r d

c o n tac t p e r s o n

Thad Maloney, thaddeus.maloney@aalto.fi

14

The purpose of this project was to develop a high consistency forming process suitable for microfibrillated cellulose (MFC) composite webs and to outline a pa-radigm for manufacturing such webs. A MFC composite furnish was evaluated, and a modular high consistency headbox and suitable approach flow system were constructed. It was found that 8-10% solids was a suitable forming consistency. Webs as low as 150 g/m2 were formed. It was also found that under certain condi-tions the web could be vacuum dewatered to as high as 33% solids with retention close to 100%. Lab pressing studies showed a solids content of around 45% to be achievable with a single shoe press. Excellent physical properties were attained, including good formation, smoothness and light scattering. The results show it should be possible to manufacture composites of this nature in large scale, both the furnish cost and the investment costs look very attractive, and desirable pro-duct properties can be achieved.

This project demonstrates the manufacture MFC composite papers to be both rational and feasible. The excellent intrinsic properties of MFC composite webs means that it should be possible to find many viable new products in this cate-gory. The manufacturing solution is very different, and in many ways superior, to traditional papermaking. There is ample value creation potential across the raw material supplier–machinery manufacturer–producer–converter value chain.

Keywords:microfibrillated cellulose composites, high consistency forming, MFC dewatering

AbstRACt

15

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1. Background

This project has its roots in the “Reengineer-ing Paper” philosophy. Simply put, this says that by rethinking the architecture of paper on a fundamental level we can design a new gen-eration of paper products. More specifically, we are interested in the use of microfibrillat-ed cellulose, not as a functional additive, but as a major structural component in paper. The vast majority of current paper and board prod-ucts are essentially produced from mixtures of various pigments and pulp fibres. The func-tional performance of paper is largely limited by the relatively large size of fibres. Moreover, the product and property space of the fibre/pigment furnish approach has been largely ex-ploited and existing products are mature. By including microfibrillated cellulose as a major structural component in paper, the structure is fundamentally altered and the potential prop-erty space is greatly expanded.

By the time this project started it was already clear that various MFC/pigment/fibre compos-ites could achieve interesting properties. How-ever, it was not clear whether large-scale man-ufacture of the composites would be possible.

In order for MFC composites to become an industrial reality, several problems must be solved. 1. The MFC must be manufactured in a robust process with a rational cost structure; 2. Suitable forming technology must be found; 3. An energy efficient process must be devel-oped to dewater the web. This project did not deal with point (1), but focused instead on the forming technology. Sufficient evidence was gathered to show that dewatering was possi-ble, and to outline a water removal strategy.

For composite webs containing a large amount of MFC, dewatering is a potential problem. It is therefore important to form at high consisten-cy in order to reduce the amount of water that

must be removed, improve energy efficiency, and simplify the manufacturing process. The starting point of our investigation into the po-tential forming technology was a process pre-viously developed for traditional furnishes called ultra-high consistency forming (UHC), in which applied shear is used to deflocculate the suspension before forming the web. The form-ing strategy investigated here has its origin in the earlier UHC work of Professor Gullichsen and co-workers. The possibility to use the UHC technology for a traditional furnish was also investigated.

2. Objectives

The objective was to develop a semi-pilot scale high consistency forming technology suitable for forming MFC composite webs and establish a paradigm for manufacturing such webs. This involved the following specific goals: 1) Con-struct a modular high consistency headbox and approach flow system for the Aalto pilot ma-chine, 2) Develop the forming technology for MFC/pigment/fibre webs, 3) Outline a means for large-scale manufacturing, i.e., determine the forming solids content and develop a water removal strategy after forming, and 4) Test the UHC concept on a folding box board (FBB) fur-nish to identify any structural or potential pro-cess advantages to this forming method.

3. Research approach

1. Laboratory rheometer and former con-struction and tests. A lab device was built which allowed a suspension to be fluidized and a web formed from the fluidized furnish. Sev-eral different slice arrangements for the lab former were constructed and tested. Torque and energy values could be collected from the rheometer. This gave valuable information for the construction of the headbox. The objec-

17

tives of this study were to determine the upper solids content at which webs could be formed, identify possible speed limitations, quantify web characteristics, and investigate 3-phase systems to determine whether dispersed air could help web forming.

2. Design and construction of the headbox. A modular UHC headbox was designed and built. The headbox has segments that can be tak-en off, modified and reattached. Two slice ar-rangements were constructed, and a third was later added.

3. Design and construction of the approach flow. An approach flow was added that al-lowed handling of the high consistency fur-nish, introduction of gas or other chemicals and in-line high shear mixing.

4. Lab studies on composite sheet structure. The property spaces for combinations of pig-ment/MFC/fibre blends were examined. Need-ed sheet preparation methods were devel-oped. From this work a 70/20/10 mixture was defined as the test furnish for process devel-opment.

5. Lab studies on the dewatering/rheology of MFC composite furnish was carried out using an immobilization cell rheometer. The idea was to better understand factors govern-ing the rheology at high consistencies and de-termine how MFC swelling and other factors control dewatering. Lab pressing studies were done with a press simulator.

6. Pilot studies with the UHC former. The first pilot studies were done with traditional fibre furnishes – bleached hardwood (BHW) and BHW/BSW blends. Here we learned to use the equipment and ironed out many practi-cal problems. 3-phase systems were also in-vestigated in which 10% dispersed air was used to reduce viscosity, improve formation

and increase bulk. Two MFC composite trials were carried out at the end of the project. A bent blade bevelling system was added to the headbox for the last trial.

The combination of lab and pilot studies was used to determine whether the manufacture of pigment/MFC/fibre composites was rational and feasible and, if so, how it could be done.

4. Results

4.1 Defining the property space

In traditional papers, the main structural com-ponents are fibres, with length dimensions of 1-5 mm and pigments usually in the range of 1-3 µm. The forming concept, dewatering strat-egy and unit operation design are all based on this broad raw material concept. In this pro-ject, we introduce the use of microfibrillated cellulose as a major structural component. In doing so, we are fundamentally changing the furnish characteristics, the product proper-ties and the needed manufacturing concept. A key problem faced is the fact that the range of furnish mixtures is almost infinite, leading to very different rheological and dewatering characteristics and thus different forming and manufacturing strategies. In order to narrow the 3-component furnish to a more workable concept, a laboratory study on various pig-ment/MFC/fibre mixtures was carried out. For this work the usual laboratory sheet forming method was modified by: increasing the form-ing solids, using a very fine wire, adding over-pressure to the sheet mould, and using a press drying method to prevent sheet shrinkage.

The raw materials used were scalenohedral PCC with 2.4 µm average particle size, VTT coarse MFC, bleached birch Kraft, lightly re-fined. The experimental design is shown in Figure 1. A sample of the results for certain

18

strength properties is shown in Figure 2. The important conclusions from this study are:

• Therearenon-obvioussynergisticeffectsof the components, such as maximum stiffness at 20/60/20 pigment/MFC/fibre.

• Therearesynergisticopticaleffectsbetween the MFC and pigment. Scalenohedral precipitated calcium carbonate (SPCC) prevents the MFC from collapsing in consolidation, thus leading to high light scattering for certain mixtures.

• MFCcontributestobonding,lightscatteringand surface smoothness; pigment to light scatter and surface properties; fibre mostly to tear strength.

• Thecombinationofhighpigment/modestMFC quantity/low fibre was of specific interest to our study. This combination delivers excellent optics, high smoothness, reasonable tensile and tear strength and very good bulk/smoothness. We therefore specified a composite mixture of 70/20/10 SPCC/MFC/fibre. The furnish cost structure is also attractive due to the high amount of pigment. In later work, the BHW was changed to a previously dried, unrefined bleached softwood Kraft to further improve tear strength and dewatering properties.

It should be noted that in this study we are tak-ing a snapshot of only one particular solution. There are a huge range of pigments, fibrillated celluloses and fibres that can be brought to-gether to meet various end-use requirements. We would also like to emphasize that the role and requirements of each of the main compo-nents can be very different to classical paper-making systems. In this project, the idea was to find a furnish concept that would allow web formation and dewatering and lead to a prod-uct with desirable intrinsic properties. This puts certain restrictions on the needed com-ponents and the workable mixtures. For ex-ample, a high degree of pigment structure is desired to give bulk and to maintain poros-ity throughout water removal (a requirement for efficient dewatering, pressing and drying). Thus, highly structured PCC was chosen. Even with suitable components, not all mixtures will be workable. For example, in cases where the fibre content becomes too high the formation may deteriorate, and if the MFC content is too high, water removal can be a limiting factor.

4.2 Headbox design

Our initial hypothesis was that when high amounts MFC are used, dewatering limitations

Figure 1. The experimental design used to define the property space of pigment/MFC/fibre composites.

19

were likely to be the most serious obstacle to developing an industrially feasible process. This implies that the forming process should be carried out at high consistency. The higher the consistency at which we could form, the less water that needed to be removed in sub-sequent operations.

As a starting point, we focused on the earlier work of Gullichsen et al., who developed ultra-high consistency forming (UHC). This concept has its roots in the development of medium consistency pulp technology, which is based on the deflocculation of a fibre suspension by the application of sufficient shear. In several projects, UHC headboxes were constructed and tested with traditional furnishes of up to 10% solids content. The technology met with some degree of success. Based on this earlier work a UHC headbox was designed which was suitable for the Aalto pilot machine. We made

certain simplifications to the headbox design and made the headbox modular in nature. The headbox design is shown in Figure 3.

The basic idea in UHC forming with classical furnishes is to deflocculate the pulp suspen-sion with a spinning rotor. If enough ener-gy is applied, the viscosity of the suspension approaches that of water and the fibre flocs completely break up. This, in principle, pro-vides a route for forming webs at high consist-ency with good formation. The difficulty is that it is rather challenging to form a coherent web with an even velocity profile from a highly tur-bulent suspension. Thus, the design and relat-ed flow phenomena around the slice are cru-cial considerations.

Two different slice arrangements were con-structed for evaluation (Figure 4). The “wedge” arrangement was conceived by Gullichsen et al.

Figure 2. Results for strength properties from the experimental design.

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In this arrangement, the distance from the fluid-ized suspension to the slice is very short, which has a potential benefit in minimizing the refloc-culation time. With the wedge assembly, the web is formed in the gap between the bottom of the headbox and the moving wire. The shear from the wire can potentially rearrange the fibres and improve formation. The wedge space also effec-tively attenuates disturbances arising from the turbulent mixing conditions inside the headbox.

The second slice geometry constructed was a converging geometry with an adjustable slice opening. The idea in this arrangement is to form

a coherent free jet which would then impinge on the forming wire. The distance from the turbu-lent zone to the slice exit should be sufficient to attenuate disturbances and create the required pressure drop to ensure an even flow profile. The design was based on the best results of lab tri-als where, somewhat surprisingly, a converging slice gave the best free jet formation for both fi-bre and MFC composite furnishes.

The rotor in the headbox is capable of a max-imum speed of 4500 rpm and is driven by a 22 kW motor. The pattern on the rotor is 3mm high diamonds.

Figure 3. The high consistency headbox. The headbox is modular and can be taken apart and refitted.

Figure 4. The two slice arrangements. Right: A converging geometry with controllable slice profile; Left: The “wedge” concept.

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4.3 Approach flow and wet end

The approach flow that was designed and built is shown in Figure 5. A 1-cubic metre, well-mixed delivery tank is used as both the make-down and machine chest. A number of pumps were tested. The most suitable for our system was a flexible impeller pump with variable speed control. This system can han-dle fibre furnishes in the range 1-5% and MFC composite furnishes up to 10% solids. A high shear mixer was installed before the headbox. Prior to the mixer, gas or chemical additives could be added. A recirculation line after the mixer could be used for basis weight control or for mixing the furnish before the trials. Three-phase forming experiments can be done by adding air and a suitable surfactant and then forming microbubbles either in the high shear mixer or directly in the headbox.

The headbox contact and position relative to the wire can be adjusted. Furthermore, the vacuum box positions can be adjusted to allow forming either directly on the vacuum zone, or prior to vacuum. Since the main experimental work will be done at elevated consistencies, no provision for capturing or recirculating white water was made. It was planned that MFC composite trials would utilize the former sec-

tion only and pressing and drying of samples would be done in lab devices. The UHC experi-ments with BHW furnish also utilized the press and dryer section of the pilot paper machine.It was originally planned that the forming ex-periments would be done at low speed, 5-10 m/min. It was our initial hypothesis that the forming dynamics would be fairly decoupled from the machine speed, since the turbulence is generated by external means. However, this turned out not to be correct – the forming me-chanics were strongly coupled to speed and generally improved as the speed increased. The operating speed was thus often 30-40 m/min. A method for capturing samples off the wire at this higher speed was developed.

4.4 Lab-scale forming studies

The above concept presented a number of de-sign challenges. Various mechanical designs needed to be tested with different furnishes, each with different rheological characteris-tics. This required focusing in from a range of furnish characteristics and possible headbox design solutions to a more narrowed forming and furnish concept. To facilitate the design of the pilot headbox and investigate web forming mechanics for a range of furnishes, a small-scale lab former was constructed.

The principle of the former was that several li-

Figure 5. Approach flow for the UHC former.

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tres of stock could be fluidized in a chamber. The torque, rotor speed and temperature were recorded. The suspension could then be ex-truded through a slice (different slice geom-etries were constructed) forming a free jet. The condition of the free jet could be exam-ined with a high speed camera. A system for evaluating the quality of the free jet was put in place. With this set-up it was possible to ex-amine what types of furnishes, conditions and slice geometries would lead to the best qual-ity jets (Figure 6). The limitations of the device were that it did not allow web capture, the web speed could not be controlled, and the flow duration was short, so that steady-state con-ditions were not really achieved.

The lab rheometer/former was used to test a

number of different furnishes (Figure 7). The experiments with BHW explored whether small amounts of dispersed air could be used to im-prove the flow and web forming characteristics. The MFC composite furnish experiments con-centrated on finding the upper solids content at which jet forming was still achievable. At this stage we were certain that dewatering the fur-nish would be extremely difficult, so emphasis was placed on maximizing the solids content. The main findings from the experiments are:

• FromtheBHCfurnishescoherentjetscould be achieved at 6% and lower solids. The presence of 10% dispersed air (0.02% sodium dodecyl sulphate SDS dispersant) improved jet formation.

• Thejetspeedwas200-300m/min,

Figure 6. Schematic and actual lab rheometer/forming device. The various possible slice openings are shown on the right (slice opening 2mm). On average, the “modified long narrowing lip” gave the best web forming characteristics.

Figure 7. Examples of free jets formed under high shear conditions from the lab rheometer. On the left is a poor jet formed from a BHW suspension at 6% solids with one of the less successful slice geometries. On the right is an excellent coherent jet of MFC composite furnish at 9.3% solids.

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indicating that sufficient machine speed is needed to form good webs. Pilot trials later confirmed this.

• Theapplicationofhighsheergenerallyimproved jet formation.

• Thejetqualityofthe70/20/10MFCcomposite furnishes was excellent.

• Thehighestsolidscontentatwhichwebforming was possible for MFC composite furnish was 15% in the case of PCC as a filler and 18% in the case of dispersed filler-grade ground calcium carbonate (GCC). Because the GCC had poorer dewatering properties than PCC, the pilot trials were conducted with 2.4 µm SPCC.

• Whiletheseexperimentsshowthatmaximum forming solids could be as high as 15-18%, practical pumping difficulties limited the pilot trials to around 10% solids in the case of MFC composite furnishes.

4.5 Lab rheology/dewatering studies

Common experience is that the addition of just a few per cent of MFC to a handsheet or pilot paper machine can often have a severe neg-ative impact on all stages of water removal. In deploying 20% MFC, we therefore expect-ed water removal to be highly problematic. Indeed, handsheets formed for the 70/20/10 furnish required overpressure and several minutes to drain the water. However, forming and removing water from a high consistency furnish is very different to a handsheet and the furnish is so completely different to traditional fibre stock that poor water removal could not be assumed. Practical experience proved this to be the case.

The first clues that the 70/20/10 furnish could be dewatered came from studies performed with a Physica MRC-300 rheometer. This in-strument allows simultaneous application of shear and vacuum dewatering, so that infor-mation about the relationship between rhe-

ological properties and dewatering can be gathered. In these studies, a couple of differ-ent MFC grades were used, with either high or low swelling. The influence of the fibre fraction was studied, as was the solids content. A sam-ple of the results is shown in Figure 8.

The main findings from these experiments are summarized below (note that further descrip-tion of this work and related publication can be found in the Processability and preservability of microcelluloses section of this report).

• Thefurnishbehavesasagelandishighlyshear thinning.

• Thegelrheologyisgovernedbyitswaterbinding, which in turn is controlled by the swelling of the MFC. Thus, although MFC is only 20% of the furnish, it governs the rheological characteristics.

• MFCswellingalsostronglyinfluences

Figure 8. Immobilization cell dewatering experi-ment with different composite furnishes. Low-er gap position corresponds to easier dewater-ing. The upper curves use a highly swollen grade of MFC (24 ml water/g solids swelling), the lower curves a less swollen grade, VTT course MFC (9 ml/g swelling), used in machine trials. The closed simples show the effect of 10% fibre in the furnish, which increases dewatering for the furnish with VTT course MFC.

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dewatering of the furnish. The VTT coarse MFC with a network swelling of 9 ml/g (measured in a modified WRV test) had much better dewatering characteristics than a fine oxidized MFC with a swelling power of 24 ml/g.

• Theapplicationofshearhelpsdewatering• Thepresenceofpulpfibresappearstohave

a small positive influence on dewatering by helping to open flow channels.

Further studies were begun at the end of the project to examine the press dewatering of the composite furnish. These studies are being carried out with a MTS press simulator which can simulate fairly realistic pressing condi-tions. The results are shown in Figure 9. The results show that for this furnish at 100 g/m2 and 20% initial solids content, 45% solids con-tent can be achieved with a single shoe press. Thus, if the web can either be formed at about 20% solids or at lower solids and vacuum de-watered to 20% solids then pressing is com-pletely feasible. Although we have not yet be-gun the drying experiments at the time of this report, it is unlikely that the drying will be a problem. If the web permeability is sufficient to allow water transport in wet pressing, then it will allow steam transport in drying. In addi-

tion, the PCC does not bind any water. The net bound water in the web is less than traditional paper, even when considering that MFC has a higher bound water content than Kraft fibres.Although our wet pressing research is still in its early stages, it is worth commenting that the pressing characteristics of the composite web material are very different to traditional paper. The composite web is compressible to the point where the filler network does not al-low further compression and does not re-ex-pand. In ordinary paper, the web is highly com-pressible, but expands and draws water back into the structure in the nip-rewetting phase. It is clear from both the vacuum and press dewatering experiments that water remov-al from this kind of furnish can be surprisingly easy if the furnish characteristics and appro-priate water removal strategy are understood. Clearly, this is an area for further research.

4.6 FBB trials

The aim of this part of the project was to test the UHC forming method with a fibre fur-nish to determine whether suitable formation could be achieved and bulk could be improved. About 10 trials were run with a BHW or BHW/BSW furnish. Overall, the technology proved

Figure 9.Moisture ratio after pressing for a 100 g/m2 70/20/10 MFC composite web with 20% initial solids content. The MFC used was MF-Daicel.

25

challenging with fibre furnishes. However, the following findings were also made:

• Severaltrialswereconductedwiththewedge arrangement shown in Figure 4. In these trials, it was found that a web could be formed in the solids range 1-5%, but the formation of the web was not acceptable. Figure 10 shows that when the headbox is lifted from the wire and the rotor is on, the condition of the jet is chaotic. The wedge attenuates pulsation, but formation is limited if the velocity flow through the slice is not even. In these trials the application of shear helped the forming somewhat.

• Thelowspeedofourpilotmachinegaveasomewhat misleading picture, especially at higher solids contents. Forming conditions clearly improved as the machine speed increased.

• Basedonthesetrialsitwasdecidedthatthe headbox needed to be rebuilt with a free jet geometry and that the furnish flow and flocculation characteristics should be improved. This was achieved by dispersing 10% gas into the furnish stabilized with 0.01% SDS dispersant.

• Theuseofthefreejetimprovedtheforming, but low machine speed was still a problem. When 10% air was dispersed in the headbox with the high shear mixer, the formation and bulk improved markedly and were at a good level for this machine type (Table 1). In our opinion, the 3-phase forming solution has potential and further improvements can be made by adjusting the headbox turbulence conditions and attenuating flow disturbances.

Figure 10. Left: Jet condition with the headbox lifted from the wire; Right: The web formed with the head-box against the wire.

Test point SDS(% stock)

Added Air(%)

Deflocculation Bulk(cm3/g)

Formation(g/m2)

1 0 0 before HB 1,99 352 0 0 In HB 1,96 483 0 10 before HB 1,92 374 0 10 In HB 1,94 435 0,01 10 before HB 2,15 20

Table 1. Sheet bulk and formation for 3-phase forming at 1.8% solids content with free jet arrangement. Samples were pressed and dried on machine.

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4.7 MFC composite trials

The aim of this project was to demonstrate the feasibility of producing MFC composite webs in a reel-to-reel operation. The lab work, equip-ment construction and the fibre furnish trials were conducted in preparation for the com-posite forming trials. The industrial realization of MFC composite products requires broader research beyond the lab scale. Furthermore, pilot-scale experiments are needed to identify the fundamental issues for in-depth research. Our first MFC trials validate this point.

The MFC trials entailed numerous practical challenges, especially as the target was a high-consistency process. The MFC is produced lo-cally at about 3% solids content, the PCC from a decanter is at 30-35% solids, and ordinary chemical pulp is available at 4%, unless thick stock is used. This limits the solids of the furnish to 9-10%, unless the MFC solids content can be raised. Furthermore, the components must be brought together and thoroughly mixed. Mixing is of paramount concern when using any nano-material, especially MFC-type products. The tri-

als require about 0.5 m3 of material, so a con-siderable quantity of MFC is needed. Note that we have made some modifications that allow trials to be made with about 200 litres of stock. Sample capture is a further challenge.

Three trials were conducted, as summarized below:

Trial 1: The furnish was 70/20/10 PCC/VTT course MFC/BSW unrefined. Machine speed 5-10 m/min. Grammage was about 500 g/m2. Free jet arrangement. Solids 7-8%.

• Awebcouldbeformedthatwasnotvisually very even. Low speed was also a limiting factor here.

• Sampleswerecollectedbyapplyingblottingpaper to the web to remove samples (Figure 11). This proved cumbersome.

• Retentionwascloseto100%andsomedewatering was achieved on the vacuum section with couch solids at 10.5%.

• Whenthesamplewaspressed-dried,bulkwas 1.30 cm3/g and smoothness 3.5 PPS. Formation was also good, showing that the

Figure 11. Taking samples in the first MFC composite trial.

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gelatinous characteristic of the web means that the structure can be greatly altered after forming the web, contrary to a normal papermaking furnish. Fibres in the gel, when well dispersed, do not reflocculate like a normal papermaking suspension.

Trial 2: The purpose of this trial was to push the solids content to 10%. At this point we were still convinced that a high forming solids content was needed due to dewatering limita-tions. The furnish composition was the same, except that Daicel MFC was used. 400 g/m2 grammage. Conclusions:

• At10%solids,trialconditionswereconsiderably more difficult, e.g. pumping, flow through headbox.

• Recirculating1hourthroughthehighshear mixer proved a good way to mix components.

• Amethodologyforcapturingsampleswasdeveloped (see Figure 12).

• Bevellingexperimentsindictedthatboth the grammage and profile could be controlled and any formation issues corrected by appropriate use of a bent blade system after web formation.

• Theroleofboththewireandfeltwereof apparent importance. It seems that different forming fabrics than are normally used for traditional furnishes will be required. This aspect should be included in continuation projects.

• Thewebisstillquiteplasticevenafterwetpressing. Final surface smoothness will likely be controlled by the drying section conditions.

Trial 3. The purpose of this trial was to reduce the Grammage further to the 100-200 g/m2 range, to test the bent blade concept, and to examine wire section dewatering. The furnish was the same as in Trial 2, but the solids con-tent was lowered to 7%.• Abentbladewithadjustablecontactangle

and blade flexibility was added to the headbox, as shown in Figure 13.

• Thefirstsuctionboxwasmovedundertheblade.

• Thesliceopeningwasreducedtoachievea target grammage of 200 g/m2. The grammage in the trial ranged from 150 g/m2 to 250 g/m2.

• Thelateralspreadofthefurnishwasremarkable at high blade pressure: a 15 cm wide web of 300 g/m2 spread to 30 cm and 150 g/m2.

• Couchsolidscontentvariedinthetrialconsiderably from 12% to as high as 33%. Ash retention also varied from 92-100%.

• Thebasicformingconceptismovinginapromising direction, though considerable development is still needed to test and adjust various aspects.

• Basedonobservationsduringthetrial,wedo not believe there are any restrictions on producing low-grammage webs.

Figure 12. Left: The sampling method of placing wire on wire. Right: Bent blade experiments demon-strate the plasticity of the furnish and that extreme lateral movement of the furnish is possible.

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A major aim of this project was to outline a para-digm for manufacturing MFC composites of the type investigated here. Shortly stated, the form-ing consistency should be 8-10% solids content. The forming should include high shear mixing either before or in the headbox, as component mixing and the shear thinning behaviour of the suspension are essential. A bevelling blade or other means can be used to adjust the profile and grammage. The web can be vacuum dewa-tered to a suitable solids content for press entry. Pressing can be done with existing press technol-ogy, though attention must be paid to the press fabric. The web can be smoothed prior to drying to achieve good surface properties. Since web shrinkage and planar deviation are an issue, re-straint during drying via Condabelt technology or some other approach is warranted. The furnish must be designed such that porosity is main-

tained through the consolidation process, other-wise efficient water removal will not be possible.

5. Exploitation plan and impact of results

Nanocellulose is one of the most promising devel-opments in the forest cluster in recent years. The development of industrial processes to produce high-volume composites or next-generation pa-per and board products from fibrillated cellulos-es represents one of the most important manu-facturing challenges of our time. This project did not, and could not, develop such a manufacturing process. This requires a project of much greater scope. However, we did obtain strong evidence that it is very possible to manufacture MFC com-posite webs on a large scale and that it is rational

Figure 13.Bent blade used to

bevel the furnish after forming.

Figure 14. The bent-blade UHC former in use.

Under some conditions the web had a high solids content, was

surprising strong and could be peeled off the table. The web had the

feel of a fabric. The trials gave many surprising

and fascinating insights into the nature of the

new composite.

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and feasible to do so – both from the product and process point of view. While further research is required, we obtained considerable evidence that we are on the right track and gained useful expe-rience in dealing with MFC furnishes and forming on a somewhat larger scale.

The successful development of MFC compos-ite manufacturing technology should not be viewed as an instrument to improve cost struc-ture, but rather as a gateway to an entirely new industry. The bulk of the results have not been widely published yet. Despite this, several inter-national companies are interested in exploiting the results and continuing development work in this area. Discussions are underway.

6. Networking

The project was carried out in cooperation with Aalto University and Finnish forest cluster com-panies. The pilot former was built at the Depart-ment of Forest Products Technology, Aalto Uni-versity. The project was headed by Thad Maloney at the Department of Forest Products Technol-ogy. Professor Kuosmanen at the Mechanical Engineering department lead the former con-struction. Professor Mika Alava at the Phys-ics Department lead the furnish rheology work. Each of the above is located at Aalto University.

7. Publications and reports

Dimic-Misic, K., Puisto, A., Paltakari, J., Alava, M., Maloney, T. The influence of shear on the dewatering of high consistency nanofibrillated cellulose furnishes, Cellulose, 8/6/2013.

Dimic-Misic, K., Sanavane, Y., Paltakari. J., and Maloney, T. Small scale rheological obser-vation of high consistency nanofibrillar mate-rial based furnishes. Journal of Applied Engi-neering Science, ISSN, 1451-4117, 2013

Dimic-Misic, K., Puisto, A., Gane, P., Niemin-en, K., Alava, M., Paltakari. J. and Maloney, T. The role of MFC/NFC swelling in the rheologi-cal behavior and dewatering of high consist-ency furnishes, Submitted to Chemical Engi-neering Journal, 2013.

Rantanen, J., Lahtinen, P. and Maloney, T. (2013): Property Space for Fibre, Microfibrillar Cellulose and Precipitated CaCO3 Composite Sheets, Int. Paperworld IPW,(5).

Rantanen, J., Lahtinen, P. and Maloney, T. (2012): Property space for fibre, microfibril-lar cellulose and precipitated CaCO3 Compos-ite sheets, Zellcheming annual conference and expo, June 26.-28. 2012, Wiesbaden.

Rantanen, J., Lahtinen, P. and Maloney, T. (2012): Strength property space for fibre, mi-crofibrillar cellulose and precipitated CaCO3 Composite sheets, PaPSaT annual seminar 2012, October 2.-3. 2012, Espoo, 48-52.

Rantanen, J. and Maloney, T. (2011): Novel manufacturing method for nanocellulose con-taining web based products, PaPSaT annual seminar 2011, August 22.-24. 2011, Lappeen-ranta, 42-49.

Rantanen, J. and Maloney, T. (2011): Ultra high consistency forming research using novel raw materials, COST Training school - New tech-nologies for treatments in the end-of-use of packaging materials, September 12.-15. 2011, Zagreb, 107-116.

fOAmfOrmINg

pa r t n e r s

VTT

Metso Paper

Metsä Board

Stora Enso

UPM-Kymmene

c o n tac t p e r s o n

Petri Jetsu, petri.jetsu@vtt.fi

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Foam forming shows high resource efficiency potential and great promise as a next-generation technology in the manufacture of fibre products. It enables production of lightweight structures (high bulk) from various raw materials, gives excellent formation independent of fibre length and shows excellent dewatering properties for furnishes containing MFC. All of these offer ways for forest industry companies to improve their competiveness, reduce capital costs, significantly save resources, and promote sustainability. A semi-pilot foam forming environment, built at the Technical Research Centre of Finland (VTT), enables the production of structures with grammages from 15 to 150g/m2 and forming at speeds up to 300m/min with consistencies as high as 4-5%. The results indicate that in the case of folding box board, foam technology together with advanced raw materials (here MFC as the strengthener) could reduce manufacturing costs by 25% and carbon and water footprints by 45% and 38%, respectively. The estimated reduction in total cost of ownership is about 35%. Currently, the technology is being scaled up to pilot scale in anot-her project to ease the adoption of the technology by industry. The potential is huge, but several technological issues, such as an optimal foaming aid concept, automation and control systems, and suitable processes to achieve excellent printing surfaces while maximizing bulk, have to be tackled before foam technology can be transferred to production scale.

Keywords:Foam forming, folding box board, microfibrillated cellulose

AbstRACt

31

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1. Background

The foam forming research continues the work started within the Re-Engineering Paper (REP) project during the first two years of the Ef-fTech programme. The REP project originally aimed at developing resource-efficient means of paper production utilizing microcellulose and at developing advanced multi-scale mod-els to support this aim. The main findings of REP related to foam forming were:

• Foamforminghasbeenidentifiedasthemost potential resource-efficient and sustainable technological alternative to produce microcellulose-containing products. It enables efficient dewatering and production of fibre-based products not achievable with current papermaking technology.

• Lightweightpackagingboardistheproductconcept with highest potential in terms of market size and growth and product value.

• Microcelluloseshavebeendemonstratedto give various novel product properties (e.g. high stretch). These properties have been shown to depend strongly on both microcellulose quality and process conditions.

The main technical challenges in utilizing mi-crocelluloses in product manufacturing re-lated to forming and dewatering. Since mi-crocelluloses bind water efficiently, they are not compatible with current paper machines, where high wire section drainage is important. Therefore, forming at high solids content is a crucial step in solving the dewatering prob-lems inherent in nanomaterial applications.

Foam forming is a potential technology for next-generation paper and board making. It enables forming of web structures at high consistency with closed water systems and offers high en-ergy saving potential in pumping, drying and

refining. Forming structures from a wide varie-ty of raw materials ranging from nanomaterials to centimetre-long fibres and materials of lower density than water make this an attractive tech-nology for new fibre-based products. For exam-ple, foam forming naturally provides excellent formation even with long fibres as well as the possibility to form high-bulk structures. It also enables forming of multilayered structures with excellent layer purity even for lightweight prod-ucts. The technology is already used for non-woven applications on an industrial scale.

2. Objectives

Objectives of the study were to expand paper and board properties with new resource-effi-cient furnish and technology concepts and to offer ways to radically improve energy, water and raw-material efficiency by utilizing foam forming technology with microfibrillated cellu-lose containing furnishes.

3. Research approach

The work is based on the competencies de-veloped in the EffTech programme. In the Re-Engineering Paper (REP) project, two main advantages of foam forming were identified: 1) Possibility to generate extremely uniform webs (very good formation) and 2) Potential to make bulky structures. In the REP project some demo structures were generated, but very little attention was put to control of pro-cess and product properties such as forma-tion, orientation and strength.

In the EffNet programme, a semi-pilot scale foam forming research environment with sin-gle and multi-layer features was constructed at VTT’s KISU facility. Controllability of sheet structure, product properties and process lim-its, such as jet-to-wire ratio, consistency and

33

vacuum levels, were studied in dynamic condi-tions. Laboratory-scale experiments were also carried out. The main focus was utilization of foam forming technology combined with mi-crocellulose (MFC) containing furnishes in mul-ti-layered board making. The target was to in-crease the bulk of the folding box board (FBB) middle ply by 50-100%, which offers radical en-ergy, water and raw material savings and con-siderably reduces carbon and water footprints. Other studied cases were SC and fine paper. Development work also included foam chem-istry research together with the SP Technical Research Institute of Sweden. Research related to manufacturing of MFCs was excluded, so all utilized MFC grades were developed elsewhere.

The foam forming results were highly promis-ing. Significant potential was identified for raw material and energy savings in the manufacture of folding box board. Changing from water-laid technology to foam forming reduces manufac-turing costs and carbon footprint by 25% and 45%, respectively. Investment costs are also reduced by 25% in greenfield installations. In addition, foam forming broadens the range of product properties and products, creating new business opportunities for the forest industry.

4. Results

4.1 Dynamic foam forming environment

The objective was to construct a dynam-ic foam forming research environment to en-able the forming of single and multi-layered web structures at speeds of up to 200 m/min to be studied. During the project a new foam forming research environment was designed and constructed around an existing semi-pi-lot scale forming environment at VTT. Devel-opment work was divided into two phases: 1) construction of single-layer facilities and 2) construction of multi-layering facilities.

The following improvements were carried out during the first modernization of the single-layer foam forming environment:

• Newheadbox• Newheadboxfeedingpump• Improvedfoamrecoverycapacitythrough

additional exhaust pump

As the new headbox and forming section is a closed unit, there is no free slice jet in the head-box area. The headbox was designed on the ba-sis that the same headbox could also be used for forming multi-layered web structures. The new headbox feeding pump enables pumping of foamed suspensions at high consistency lev-els (up to 5%). Start-up of the single-layered web forming environment took place in No-vember 2011. The single-layer foam forming en-vironment modernization was finalized in May 2012 and provides the following features:

• Improvedfoamrecoverycapacity• Improvedpumpingcapacity• Improvedmixingconditionsinthefeeding

pulper• Improvedapproachsystemforfoamed

furnish• Measurementsforprocesscontrol

A schematic picture of the single-layer foam forming process is presented in Figure 1. The main principle of the foam-laid forming process consisted in the process foam being recirculat-ed within the flow loop and the raw materials being mixed with the process foam in a pulper. The quality of new and recovered process foam is controlled on-line by adjusting mixing condi-tions within the foam generator. Mixing condi-tions are then adjusted on the basis of these foam conductivity measurements. In single-layer mode, both open and closed headbox-wire geometries are possible to run (Figure 2).

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Figure 1. Schematic diagram of the single-layer foam forming process.

Figure 2. Left: Single-layer open headbox based forming unit; Right: Closed headbox based forming unit.

Figure 3. Schematic diagram of the multi-layer foam forming process.

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The modernization of the multi-layer foam forming environment was finalized in June 2013 and includes a manifold, a feeding chest and a feeding pump for each layer. The layered web structure is generated within the head-box. A schematic diagram of the multi-layer foam forming process is presented in Figure 3.

Achievements of the developed dynamic foam forming environment:

Single-layer structures in a continuous process• Grammagesupto150g/m2

• Headboxconsistencyupto4-5%• Speedupto300m/min• Openandclosedheadbox-wiregeometry

Multilayer structures in batch mode• Formingoftwo-andthree-layerweb

structures

4.2 Enhanced product properties

One of the inherent properties of foam-formed products is their excellent formation. Figure 4 illustrates this for three types of fibres. Most notable is that with foam forming the forma-tion is independent of fibre type. Especially, the specific beta formation was enhanced by 69% when spruce chemithermomechanical pulp (CTMP) was used. The experiments were done with a dynamic, single-layer former.

One consequence of the excellent formation is enhanced strength at low grammage, as shown in Figure 5. The tensile index of water-

formed samples typically starts to decrease when the grammage decreases below a cer-tain value (typically 50 – 60 g/m2) as the flocks start to dominate the lateral strength behav-iour. As foam prevents flocculation to a great extent, the tensile index remains constant even at very low grammages. This can have an important impact on low-grammage products. The experiment was conducted with both dy-namic foam and water formers.

Sheets made in the laboratory (static forming) were compared with dynamic foam and water-formed samples and sample data from the Finn-ish Pulp and Paper Research Institute (KCL) pilot paper machine. The data for the static and dy-namic samples is shown in Table 1.

Figure 4. Formation in foam forming is independ-ent of fibre type and of superior quality to water laying.

Static (laboratory sheet mould) Dynamic

Pulp: CTMP spruce Pulp: CTMP spruceMFC: Daicel MFCGrammages: water 230 g/m2; foam 75, 105 and 150 g/m2 Grammage: 105 g/m2

Pressing: no pressing, 1 pin roll and 10 pin roll Pressing: no pressing, 0.5, 1.5 and 3.5 barDisintegration: hot and cold Disintegration: hot

Table 1. The data for the static and dynamic foam and water formed samples.

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The most important outcome of our research is shown in Figure 6: structures with the same strength can be produced with half the raw material. Without MFC a clear trend can be seen. Scott Bond values decrease rapidly as bulk increases from 2 cm3/g to 4 cm3/g. Howev-er, if the bulk is greater than 4 cm3/g, increased bulk lowers the Scott Bond values only slowly. Very high bulk (> 6 cm3/g) can be achieved only with foam forming. Thus, without any strength additives, the only way to obtain a strong enough structure (Scott Bond > 100 J/m2) is to compress the structure sufficiently.

When MFC is added to the foam-forming fur-nish we enter brand new territory in terms of the bulk – Scott Bond relationship. We can make lightweight structures that are strong enough with high bulk. Such structures are unattaina-ble with water forming because high bulk lev-els cannot be reached. Figure 7 further illus-trates this by showing that with a 10% addition of MFC, all of the critical strength properties of the 54% lighter laboratory-scale sheets are at the same level as the water-laid reference.

As a consequence of the positive effect of MFC, a test series using six different grades of MFCs were run at the laboratory scale in order to de-termine their effect on both z-directional and in-plane strength properties. The pulps used in the study were pine kraft and spruce CTMP pulp and the amount of MFC added was 0% (a reference), 5% and 15%. The sheets prepared were dried after forming without wet pressing. The results from the test series are shown in Figure 8.

According to the results, different MFC grades seem to behave rather similarly in bulk vs. strength comparisons. However, in the case of modified Scott Bond, the coarser and cheaper

Figure 5. At low grammages the tensile strength of foam-formed sheets is clearly higher due to im-proved formation.

Figure 6. Scott Bond values of CTMP sheets as a function of bulk. Board properties can be expanded through a combination of foam forming (for high bulk) and strength additives. The green triangles are typical values for CTMP sheets made on the KCL pilot paper machine. The blue squares and brown dia-monds are values from static and dynamic water-formed and foam-formed studies, respectively. The circles show the values of the foam-formed samples with different Daicel MFC contents.

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Figure 7. With a combination of foam forming and MFC it is possible to make sheets at the laboratory scale that are 54% lighter but have the same strength values as water-formed, heavier sheets. Wa-ter-formed sheets of grammage 230g/m2 (red squares), foam-formed sheets of grammage 105g/m2 with MFC (purple circles) and without MFC (blue diamonds). The green triangles indicate the estimated strength values achievable with wet pressing for foam-formed sheets.

Figure 8. Effects of addition of six different MFC grades to pine and spruce CTMP pulps. Above: Modified Scott Bond as a function of bulk. Below: Tensile index as a function of bulk. The right end points of the lines equate to 5% addition and the left end points to 15% addition.

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VTT MFC gave slightly higher values compared to the more refined and expensive VTT MFC. On the other hand, the more refined VTT MFC gave a higher tensile index value. This exam-ple illustrates that the choice of MFC should depend on the required paper properties.

In order to study the dimensional stability of water-laid and foam-laid papers and sol-ids content, the next test series were run us-ing pre-refined pine kraft pulp and VTT coarse MFC. The characteristics were measured af-

ter laboratory wet pressing (3.5 bar, 5+2 min). The shrinkage potential study was based on a free shrinkage drying method allowing in-plane shrinkage, but partly constraining curl-ing (drying between wires). The results of the shrinkage potential measurements are shown in Figure 9 (Left). According to the results, the shrinkage potential of foam-laid papers is smaller compared to water-laid papers. Foam-laid papers are also not as sensitive to MFC content as water-laid papers. The dryness lev-el of foam-laid papers is also higher after wet

Figure 9. Left: Foam-formed samples shrink less in free drying than water-formed samples at MFC con-tents of 0, 2.5, 5, 10, 15 and 20% and wet pressing conditions 0, 1.5 or 3.5 bar. Right: The solid content of foam-formed sheets is higher after wet pressing (3.5 bar 3+2 min) than that of water-formed sheets at MFC contents of 0%, 2.5%, 5% and 10%. The MFC used in the test series was VTT coarse MFC.

Figure 10. Left: In-plane strength properties of foam and water-laid samples (geometric average of ten-sile index values of foam samples) as a function of bulk (variables: MFC content and wet pressing pres-sure). Right: Z-directional strength of unpressed foam and water-laid samples as a function of bulk (vari-able: VTT coarse MFC content).

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pressing (Figure 9, right). The MFC amounts used can be reasonably high due to the open structure of the foam-formed samples. This is not an option in water forming, because the water drainage properties would be deterio-rated excessively. In our foam forming stud-ies the solids content after wet pressing varied from 45 to 55% also at high levels of MFC ad-dition (10%, 15% and 20%).

In summary, foam-laid technology enables the production of high-bulk structures. When this is combined with its good water drainage prop-erties, allowing the addition of high levels of strengthening agents such as MFC, products with both very high bulk and adequate strength can be made. Figure 10 shows the possibili-ties for strength compensation in foam-formed samples for different wet pressing levels. 4.3 Process research

In the process research, refined chemical pine pulp was used as the fibre raw material and the average grammage of the samples was 80 g/m2.

The vacuums in the forming section for dy-

namic water-laid and foam-laid forming meth-ods are presented in Figure 11. Water is removed more easily than viscous foam, leading to lower vacuums in water-laid forming. Corresponding-ly, vacuums were higher in the removal phase of process foam. After the removal phase, vac-uums were approximately at the same level in both forming methods. In the closed headbox based forming process vacuum levels were still higher. This was mainly because most of the process foam was dewatered under the deck of the closed headbox and the quality of the paper web was better with the closed headbox, thus leading to higher vacuum levels.

The tensile strength ratio and specific beta-formation behaviour in the case of the closed headbox former is presented in Figure 12. The results show that a wide tensile strength ratio can be achieved. The minimum tensile strength ratio was around 3 and, correspondingly, the maximum tensile strength was around 8. The achieved maximum tensile strength ratio was exceptionally high compared to normal wet-forming values. The specific-beta formation values were also at a very good level, varying between 0.35 √g/m – 0.60 √g/m.

Figure 11. Vacuums in the forming section.

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Figure 12. Tensile strength ratio can be controlled extensively in foam forming by altering the jet-to-wire ratio without affecting the excellent formation.

Figure 13. Geometric tensile index and specific beta-formation as a function of forming consistency.

Figure 14. Geometric tensile index and specific beta-formation as a function of density of the process foam.

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The geometric mean of tensile index and spe-cific beta-formation as a function of forming consistency is shown in Figure 13. As can be seen, paper quality deteriorates with higher consistency. The maximum forming consist-ency achieved was ~ 4.5%. The limited mixing capacity in the foam chest (foam pulper) and the limited dewatering capacity in the form-ing section prevented the attainment of higher forming consistencies.

The geometric mean of tensile index and specif-ic beta-formation as a function of density of the process foam is shown in Figure 14. Paper qual-ity was weakened significantly when the aver-age density of the process foam was increased.

4.4 Foam chemistry

Much is known about the properties of pure aqueous foams. However, extremely little is known about the chemical interactions be-tween foaming agents and papermaking raw materials in aqueous foam-fibre systems. The objective of the study was to increase under-standing of the basic mechanisms related to fibre-foam chemistry, foamability and foam stability. In particular, gaining an understand-ing of the chemical interactions between foam-

ing agents and papermaking raw materials in aqueous foam-fibre systems was of great inter-est. The research was carried out in close coop-eration between SP (Technical Research Insti-tuteofSweden,formerlyYKI)andVTT.

Foaming aid screening and foaming testsThe foaming behaviour of pulp formulations, in the presence of three ionic and four non-ion-ic foaming aids, was tested with a tailor-made foaming testing device and procedure devel-oped by VTT. Foaming aids for testing were chosen based on their reported good foam-ing properties, availability as bulk chemicals, as well as insensitivity to changes in tempera-ture and pH within limits relevant to the foam-forming process. The results from foaming tests indicated that, of the foaming aids test-ed, three enabled relatively rapid generation of the required foam-fibre volume. The list and molecular structure of the most rapidly foam-ing chemicals are shown in Table 2.

Foam-formed handsheets with different fur-nish recipes (44 different recipes) were made and tested to evaluate the effect of the select-ed foaming agents on the formation and re-tention processes, the technical properties of the handsheets and the performance of other

Table 2. The most rapidly foaming chemicals and their molecular structures.

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chemicals used in paper/board manufacturing in the presence of the foaming aids. The results obtained from the handsheet tests showed that the type of foaming aids used has signifi-cant effects on the mechanical properties and quality of paper. The main findings of the hand-sheet tests can be summarized as follows:

1. Foam-formed handsheets are bulkier than water-formed handsheets after constant wet pressing conditions. The type of foaming aid has a significant effect on bulk.

2. The formation of foam-formed sheets was better than that of water-formed sheets. In the presence of ionic polymers, the charge of the used foaming aid has a significant effect on formation.

3. The in-plane mechanical properties (tensile strength) of foam-formed samples were somewhat similar to water-formed sheets at a given bulk level. However, the out-of plane properties (Scott Bond delamination energy and Z-directional strength) of foam-formed samples, which are crucial for the functionality of board, were clearly lower than for water-formed sheets at a given bulk level.

4. Sizing with alkyl ketene dimer (AKD) was greatly dependent on the type of foaming aid used. Ionic sodium lauryl ether sulfate (SLES) and SDS required significantly higher AKD dosage to achieve similar Mini-Cobb30 values to non-ionic alkyl polyglucoside

(see Figure 15, left). Furthermore, at AKD dosages ≥ 3 kg/t, the water absorbency of water-formed handsheets was higher than that of foam sheets made using the non-ionic surfactant.

5. Foam-formed sheets gave higher dryness after forming and wet pressing than water-formed sheets. Foaming type and dosage had a significant impact on dewatering (see Figure 15, right). Foaming aid dosage had no effect on the mechanical properties of the samples.

6. Filler retention was significantly higher with foam-formed sheets utilizing a non-ionic foaming aid than an anionic foaming aid.

7. The effect of cationic strength additives on the strength increase of foam-formed handsheets was lower in the presence of anionic foaming aids than with non-ionic foaming aids.

The potential of utilizing the selected foaming aids in the practical foam forming of paper was verified in a semi-pilot trial based on a fine pa-per recipe. The results obtained during the tri-als indicated that the findings made in the lab-oratory tests were also valid in more dynamic surroundings. It was also noticed that the se-lection of utilized foaming aids must be done together with the selection of the utilized re-tention system. In conclusion, understanding and control of fibre-foam chemistry is a key for successful tailoring of final product properties.

Figure 15. Left: The effects of AKD dosage on Mini-Cobb30 value of foam- and water-formed hand-sheets. Right: The effects of foaming aid type and dosage on dryness after wet pressing for foam (and water) formed handsheets.

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4.5 Foam forming concept and evaluations

The financial impacts and costs of adaption of the foam technology are discussed in this sec-tion. Folding box board (FBB) is used as a ref-erence case. The main changes required to re-build a FBB machine are illustrated in Figure 16. A foam forming rebuild costs in the region of EUR 10 million. The main changes to the system are the conversion to a closed head-box (which might, in some cases, not even be necessary) and installation of a foam genera-tor for mixing and dispersing, vacuum pumps and a vacuum line for foam removal. In addi-tion, minor automation updates are expected. The consistency is assumed to increase from 1% to 2.5%, so existing tank volumes are suf-ficient. Fresh water intake and outgoing wa-ter quality are assumed to remain unchanged.

There were two main outcomes of the FFB case. Firstly, significant resource savings were expected for both new forming technologies, especially if microcellulose was used to in-crease the strength properties. Secondly, the savings potential is realized only if the value is calculated per unit area (€/km2). Using the as-

sumptions underneath of figure 17, a 25% re-duction in production costs can be expected (Figure 17). The calculations are based on the laboratory and semi-pilot scale results. Pro-duction in square metres is assumed to be the same, i.e., the volume of the reference water forming machine is 400,000 t/a and the foam forming machine 245,000 t/a (same speed, width and efficiency).

Assumptions to achieve these results are: Fibre: Reduction of basis weight from 270 g/m2 to 166 g/m2. Basis weight of the middle lay-er is reduced from 192 g/m2 to 88 g/m2. MFC is considered as fibre, a dosage of 20% is used in calculations. It is also assumed that MFC re-places chemical pulp. This results in a total fi-bre cost of 496 €/t.

Energy: Total energy consumption reduction is estimated to be 20% (per tonne). This arises from higher consistency (2.5%) as lower mass flows are needed but also due to lower basis weight needed for the final product. Use of the same energy levels in forming results in higher solids content before pressing. For example, for the reference case an increase from 19% to 24% is obtained using the same pulp mix (Birch/pine/

Figure 16. Foam rebuild FBB concept with changes highlighted.

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CTMP). The same energy used in pressing re-sults in higher solids content after pressing. This results in a total energy cost of 31 €/t.

Water: 13 m3/t water needed for production (4€/t). This is based on forming at higher con-sistency (2.5%) and improved retention.

Chemicals: Chemical cost per tonne for the reference are assumed to be 86 €/t. For foam-ing chemicals the cost is assumed to be 8€/t (SDS: 0.31% dosage, 2700€/t)

For carbon footprint, the reduction is 45%, as shown in Figure 18. Water footprint reduction is

38%. Reductions are realized mainly through re-duced basis weight. For water footprint, the wa-ter scarcity is different in different regions of the world; in Finland, where water resources are readily available, the water scarcity footprint is low in both cases (reference and foam FBB).

During the estimated 20-year lifetime of a ma-chine line, with 9% interest, the reduction in total cost of ownership (TCO) can be about 35%. This estimation arises from savings in operating, investment, interest (shorter pay-back of machine when operating cost savings are assumed to be used to reduce loans fast-er), logistics and insurance costs.

Figure 18. Carbon (left) and water footprints (right).

Figure 17. Estimated savings potential for foam-formed folding box board.

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5. Exploitation plan and impact of results

Foam forming technology can significantly im-prove competitiveness, reduce capital intensive-ness, reduce consumption of resources and im-prove the sustainability of current products. At the same time, it paves the way for the renew-al of the forest industry by enabling raw materi-als to be combined in new ways, thus opening up opportunities for companies to create novel value chains. This will create new business op-portunities for large companies as well as small and medium sized enterprises (SMEs). Within this programme the concept was demonstrated at the laboratory and semi-pilot scale. The next step – validating the achievements at the pilot scale – has already started in one project, SMEs are seeking value-added applications in another project, and several companies are also taking active steps in this area through their own pro-

jects. Based on the results, we strongly believe that foam forming will lead to a new manufac-turing platform for fibre-based products as it 1) requires significantly less raw materials, water and energy than conventional manufacturing, 2) remarkably improves many product proper-ties, 3) enables exploitation of new raw mate-rial combinations, 4) offers a sustainable solu-tion for manufacturing a wide range of products, such as paper, board, tissue, hygiene products, insulation materials, filters and other added val-ue products from bio-based, long fibres and 5) offers possibilities for both large companies and SMEs to create novel value chains.

6. Networking

The research was carried out jointly by VTT and Finnish forest cluster companies. Table 3 presents the research partners and their roles.

Role

Foam forming research, demo products manu-facturing, fibre network modelling and concept evaluation

Process knowhow, demo products specifica-tions, commercialization perspective

Demo products specifications, concept evalua-tion, commercialization perspective

Demo products specifications, concept evalua-tion, commercialization perspective

Demo products specifications, concept evalua-tion, commercialization perspective

Foam chemistry research, understanding of basic mechanisms related to fibre-foam che-mistry, foamability and stability

Partner

VTT Technical Research centre of Finland, Fibre Process Knowledge Centre

Metso Paper

Metsä Board

Stora Enso

UPM-Kymmene

SP Technical Research Institute of Sweden (formerYKI)

Table 3. Partner organisations and their research roles.

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7. Publications and reports

Publications:

Al-Qararah, A. M., Hjelt, T., Kinnunen, K., Be-letski, N., Ketoja, J. A., Exceptional pore size distribution in foam-formed fibre networks. Nordic Pulp Paper Res. J. 27, 226-230 (2012).

Al-Qararah, A. M., Hjelt, T., Koponen, A., Har-lin, A., Ketoja, J. A., “Bubble size and air content of wet fibre foams in axial mixing with macro-instabilities, Colloids and Surfaces A: Physic-ochemical and Engineering Aspects, Volume 436, 5 September 2013, Pages 1130-1139.

Lappalainen, T. and Lehmonen, J., “ Determi-nations of bubble size distribution of foam-fi-bre mixture using circular Hough transform”, Nordic Pulp and Paper Research Journal, 2012, Vol 27, no. 5, 930-939.

Lehmonen, J., Jetsu, P., Kinnunen, K. and Hjelt, T., “Potential of foam-laid forming tech-nology in paper applications”, approved to Nordic Pulp and Paper Research Journal.

Kinnunen, K., Lehmonen, J., Beletski, N., Jet-su, P. and Hjelt, T., “Benefits of foam technol-ogy and its applicability in high MFC addition structures”, approved to FRC.

Presentations:

Al-Qararah, A. M., Hjelt, T., Kinnunen, K., Belet-ski, N., Ketoja, J. A., “Exceptional pore size distri-bution in foam-formed fibre networks”, Int. Pa-per Physics Conf. 2012, Stockholm, Sweden.

Hellén, E., ”Resource efficiency with foam forming”, Tissue World, Barcelona, 2013.

Hellén, E., “Lightweight fibre materials through foam technology”, Biomaterials - Towards In-dustrial Applications –seminar, Espoo, 2013.

Hellén, E., “Renewal by combining novel form-ing technologies with advanced raw materi-als”, EffFibre&EffNet Workshop, 2012.

Hellén, E., “Beyond paper and board - Leap in resource-efficiency with nanocellulose and new forming techniques”, Forestcluster Annu-al seminar, 2011.

Hjelt, T., Kinnunen, K., Lehmonen, J., Beletski, N., Hellén, E., Liljeström, V., Serimaa, R., Miet-tinen, A., and Kataja, M., ”Intriguing structur-al and strength behaviour in foam forming”, PPPS 2011, Graz.

Lehmonen, J., Jetsu, P., Kinnunen, K. and Hjelt, T., ”Potential of microfibrillar cellulose in water-laid and foam-laid papers” 2013 Tappi International Conference on Nanotechnology for Renewable Materials.

Mira, I., Andersson, M., Boge, L., Blute, I., Salminen, K., Lappalainen, T., Kinnunen, K., “Foaming behaviour of cellulose pulp fibre-surfactant systems used for novel production of fibre-based materials”, Formula VII, 1 July 13 - 4 July 2013, Université de Haute Alsace, Mul-house, France.

Poranen, J., Kiiskinen, H., Salmela, J., Asi-kainen, J.,Keränen, J., Pääkkönen, E., “Break-through in papermaking resource efficiency with foam forming”, PaperCon, Atlanta, 2013.

Poranen, J., “Resource efficiency with foam forming”, EffFibre & EffNet Seminar, 2012.

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Posters:

Lappalainen, T., Salminen, K., Kinnunen, K., Järvinen, M., Mira, I., Boge, L., Andersson, L., M. and Carlsson, G. ”Laboratory scale inves-tigation of foam forming”, EffFibre & EffNet Seminar, 20.11.2012.

Lehmonen, J., Kinnunen, K., Hjelt, T., “Signifi-cant process improvements using foam form-ing”, Forestcluster Annual seminar, 2011.

Kinnunen, K., Lehmonen, J., Hjelt, T., Jetsu, P., “Foam forming facilities and demonstrations”, EffFibre & EFFNet Seminar, 2012.

Kinnunen, K., Hjelt, T., Lehmonen, J., Jetsu, P., Hellén, E., Kiiskinen, H., Poranen, J., ”Foam forming - renewal of fibre products”, SHOK Summit, 2012.

Salminen, K., Lappalainen, T., Kinnunen, K., Andersson, M., Isabell, M., ”Foam chemistry”, EffFibre & EFFNet Seminar, 2012.

EffNET PRogRAmme RePoRt48

pa r t n e r s

VTT

Aalto University

Helsinki University

Kemira

Stora Enso

Tampere University of Technology

UPM

c o n tac t p e r s o n

Erkki Hellén, erkki.hellen@vtt.fi

fIbrE-bASED

PROducTsfOr NEW APPLIcATIONS

EffNET PRogRAmme RePoRt 49

AbstRACt

Demonstrations of new fibre-based products focussed on utilizing microfibril-lated or microcrystalline celluloses in various applications and determining the potential of foam forming technology to manufacture value-added products. Filler-MFC composites were shown to offer a cost-effective substrate for printed electronics applications with a superior temperature tolerance that only special plastics can compete with. The performance of four different demonstrators printed on the composite were comparable to those printed on plastic reference substrates: conductors by inkjet, a LC resonator by screen printing, a near field communication RFID tag by screen printing, and transistors by flexo printing. Lightweight structures (densities 8-26 kg/m3; bulk 38-120 cm3/g) having thermal conductivities comparable to commercial mineral and stone wool insulation ma-terials were made from basic papermaking raw materials using foam forming. Similar structures were also shown to perform well as lightweight, sustainable sound absorption materials at challenging low frequencies (~500Hz). The best structures were comparable to commercial sound insulation materials with a density as low as 20 kg/m3. Finally, it was demonstrated that a new type of microcellulose, namely carboxymethyl cellulose grafted microcrystalline cellulo-se, can act as an efficient strength additive in paper.

Foam forming clearly has the highest value creation potential of the concepts studied in this section. Foam forming opens the way for a new manufacturing platform for fibre-based products, as it 1) enables exploitation of unprecedented raw material combinations 2) offers a sustainable solution for the manufacture of a wide range of products like paper, board, tissue, hygiene products, insulation materials, filters and other added value products from bio-based, long fibres, and 3) offers possibilities for both large companies and SMEs to create novel value chains. The substrate for printed electronics also shows good value creation po-tential but, although the market potential for printed electronics is high, the mar-ket itself is still most probably too small for large companies to enter. The same applies to the other demonstrations, which, however, may offer viable market op-portunities for small and medium size enterprises. Overall, these demonstrations show that it is possible to manufacture value-added products from wood fibres.

Keywordsprinted electronics, MFC, foam forming, sound absorption, lightweighting, thermal insulation

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1. Background

The main driver behind the work is renewal: finding ways to generate new business from sustainable raw materials. This directly sup-ports the Research Strategy of the Finnish For-est Cluster, which says “…The objective is to double the value of the forest cluster’s prod-ucts and services by 2030. Half of this value would come from new products…”. These new products are seen to arise by developing new products utilizing a wide raw material base, especially microfibrillated celluloses, and new production technologies such as foam forming. The actions described here are largely based on the research started within the Re-Engi-neering Paper (REP) project during the first two years of the EffTech programme. The REP project originally aimed at developing re-source-efficient paper production by utiliz-ing microcelluloses and developing advanced multi-scale models to support this aim. Based on discussions with industrial partners, the experimental focus was extended to identify the potential of microcelluloses also in other applications than paper, both from the product and process point of view. This section out-lines the main achievements.

2. Objectives

To demonstrate product concepts and technol-ogies to replace current, non-fibre-based prod-ucts. The target is to develop 2-4 new prod-uct concepts outside the existing business of paper and board making companies. To pro-vide microfibrillated celluloses (MFCs) for pro-gramme partners and develop modelling tools.

3. Research approach

The starting point for new product demonstra-tions has been the unique properties of micro-fibrillated celluloses and the novel possibili-ties provided by foam forming. The properties of microfibrillated celluloses range from high-stretch packaging applications to transparent barrier films and thermally stable and smooth substrates for electronic applications. For ex-ample, it is possible to make 1) transparent, non-porous films, 2) paper-like, flexible sub-strates, and 3) plastic-like, hard plates from the same raw material just by changing the processing conditions. This is far beyond what can be achieved with ordinary fibres. Here we have modified microcelluloses for paper appli-cations as well as for superabsorbents. When making substrates for printed electronics, MFC has been used to glue cheap filler particles to a flexible sheet. Foam forming has been used to manufacture low-density structures from tra-ditional papermaking raw materials at unpar-alleled high performance/weight ratios. To decrease product development costs and speed up development times, we started to develop multi-scale modelling and simulation tools to examine new resource-efficient paper structures and different ways that they can be produced. The modelling tools were developed collaboratively by several top research teams. Here, the aim was to elevate to an entirely new level the way microscopic structures are de-picted and to utilize several models togeth-er. However, covering in detail all the relevant scales and phenomena related to MFC pro-cesses and applications proved too challeng-ing within a single research programme. The developed models were therefore used to help in interpreting experimental results. The mod-els also led to important findings beyond cur-rent experimental capabilities.

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4. Results

4.1 Cheap, temperature-tolerant substrates for printed electronics

Filler-MFC composites have been shown to of-fer a cost-effective substrate for printed elec-tronics applications at high temperatures that only very special plastic films can nowadays withstand (see Figure 1). The composites con-sist typically of 80% filler and 20% MFC. The properties of the substrates can be varied with-in a relatively large range by the selection of raw materials and their relative propositions.

The substrates performed well in printing tests. The conductivity values of patterns were simi-lar to those printed on PET film (Mylar A). The best conductivity was obtained with silver na-noparticle patterns, which were inkjet printed on kaolin-based sheets. Most interestingly, curing temperatures as high as 220 °C could be used without causing any damage to the sheets.

Thermogravimetric analysis (TGA) showed that the substrates can tolerate short exposure to temperatures up to 270°C and over 12 h expo-sure to 230°C. These temperatures are much higher than the current substrates for printed electronics, enabling, for example, high sintering temperatures and increased production speeds.

Four demonstrations were successfully print-ed on the substrates: The above-mentioned conductors by inkjet, an LC resonator by screen printing, a near field communication RFID tag by screen printing, and transistors by flexo print-ing. In all cases the components performed as well as on plastic reference substrates.

The LC resonator was screen-printed using silver-microparticle paste for bottom and top conductors and UV-cured dielectric paste (Fig-ure 2). The obtained resistivity of the printed pattern complies closely with the ink manu-facturer specifications. However, the printed resonator did not provide the needed func-

Figure 1. Filler-microcellulose composites (yellow) offer a cost-effective substrate for printed electronics ap-plications with a superior temperature tolerance that only special plastics can compete with. Plastic film my-lar A (PET 1), electronic grade paper substrate (PEL) and polyimide Kapton film (PI).

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tionality. This is not due to the substrate mate-rial, but rather the need for optimization of the printing process.

The functional near field communication RFID demo consisted of an antenna screen printed with silver ink on a filler-MFC sheet and a com-mercial RFID chip (strap) attached using silver epoxy. The tags for near-field communication are a more sophisticated version of the infor-mation previously stored in bar codes. This information is readable using many smart-phones and, for example, in consumer goods they can be used for gathering information about products or for making payments. The DC resistance of the printed antenna, 33Ω (33 m Ω /sq sheet resistance), is similar to those printed on PET film (30-45Ω depending on the sintering temperature) and lower than those printed on copy paper. Benefits of the filler-MFC substrate include better temperature tol-erance compared to PET film. This enables the use of higher sintering temperatures and opens the way towards achieving even lower resistance levels. When compared to copy pa-per, the filler-MFC substrate is less sensitive to moisture changes. Organic field-effect transistors (OFET) were chosen as the most challenging test compo-

nent to be processed on filler-MFC substrates. OFETs fabricated on the filler-MFC substrate were compared to ones fabricated on selected plastic substrates (polyimide) and on a “Lumi-Press Art” coated paper substrate provided by Stora Enso. Transistors made on the smoothed paper substrate showed excellent output char-acteristics (Figure 3). Only the gate leakage current was slightly high. Transistors made on a polyimide plastic substrate had similar per-formance, as well as those printed on MFC-kaolin substrates. However, with MFC-kaolin substrates the transistors could be made in air at 240°C (even with flexographic printed base coat), whereas for the other substrates mul-tiple coating layers were needed and the Lu-miPress Art paper could be processed only at 200°C and in N2 conditions. Upscaling the production. Several methods to upscale the production of MFC-filler sub-strates were tested. Optimizing the drying conditions proved to be of extreme impor-tance. Quick drying of the filler-MFC web re-sulted in cracks and the dried structure was hard and brittle. Slow drying at room temper-ature resulted in a smooth and more flexible structure. The best results were obtained by pressing the formed web before/during dry-ing. The smoothest surface was obtained by

Figure 2. Demonstrators made on filler-MFC substrates. Left: An LC resonator. Right: A RFID tag, hot-laminated into a plastic pocket. The content of the tag can be read with a mobile phone supporting the near-field communication technology. Both demos have been screen printed.

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oven drying under pressure. Interestingly, ex-cess water can be easily pressed out of the structure, which clearly speeds the drying pro-cess. Pressing also further improved the flex-ibility of the formed structure.

Techno-economic feasibility of the sub-strate for printed electronics. The following assumptions based on the experiments have been made in the analysis: The substrates are printable with inkjet, flexo and screen printing at good enough quality for low-cost applica-tions. The structure consists of 80% pigment filler (e.g.CaCO3, kaolin) and 20% microfibrillat-

ed cellulose (MFC) and is formed by vacuum fil-tration, dried under pressure and calendered. These assumptions result in a total produc-tion line cost of about EUR 10 million with a production capacity of 3000 t/a, whereas PET film production lines typically cost EUR 40-75 million and produce 10,000-20,000 t/a. New product opportunities and markets can be captured through the use of filler-MFC sub-strates for printed electronics applications. However, this concept still requires develop-ment and drying conditions, in particular, are critical. The environmental performance of these products is excellent (Figure 5), based

Figure 3. Example of an organic transistor printed on coated paper ”LumiPress Art” (left), which shows excellent output characteristics (right).

Figure 4. Production cost estimates of printed electronics substrates.

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on evaluations using the standardized LCA approach, including fossil greenhouse gases (CO2, CH4 and N2O), expressed as carbon diox-ide equivalents (CO2 eq). No water consump-tion data were available for the reference product.

4.2 Conductive materials for fuel cells, sensors and indicators

The carbon-containing sheets were formed using a similar method as for preparing filler-MFC sheets, and calendered. The sheets con-tained 80% carbon (Printex carbon black or G1 graphite) and microfibrillated cellulose was used to form a network that binds the carbon particles into the structure. The surface re-sistivity of the printed carbon black contain-ing sheet was at same level as that of a print-ed current collector (~1 Ohm). Benefits of the substrate include high porosity, high surface area, flexibility, low cost and biodegradability. These are properties desirable for, e.g., biofu-el cells and sensors. However, the conductivity turned out to be sensitive to moisture content. This issue was not further studied. Moisture sensitivity could, however, be overcome by pre-treatment of cellulose fibrils. On the oth-er hand, moisture sensitivity offers potential uses for the substrates as intelligent seals or moisture indicators.

4.3 New microcelluloses for increasing the tensile strength of paper

Laboratory tests showed that carboxymethyl cellulose (CMC) can be produced from micro-crystalline cellulose (MCC) using the chloroacet-ic acid method. Although the product is slightly yellowish and contains some fibre flocks, it is a technical grade. Within this study, CMC was made from 1) MCCs produced from softwood bleached pulp with degrees of polymerization (DP) of 300, 400, 500 and 2) MCC produced from eucalyptus bleached pulp with DP 500. By varying the DP of the MCC it is possible to affect the properties of CMC, making MCC an interest-ing raw material for CMC production.

Microcrystalline cellulose was modified to pro-duce different kinds of microreticulated cellu-loses (MRCs), see Figure 6 for an example. The MCC was produced via acid hydrolysis of Kraft pulp at the pilot scale at Kemira using cook-ing times of 20 and 120min, and further refined with varied setups to produce MRCs. Scan-ning electron microscope (SEM) imaging and viscosity measurements clearly indicated that different kind of MCCs and MRCs were suc-cessfully produced. Longer-cooked MCC had smaller particle size, and refining of MCC par-ticles caused more fibrillated and smaller parti-cles. The differences in viscosity between MRCs

Figure 5. Environmental performance screening for the substrates of printed electronics: Carbon (left) and water scarcity (right) footprints.

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produced from 120 min cooked MCCs were neg-ligible. Addition of CMC to refining seemed to cause a more fibrillated and loosened structure compared to refining without CMC.

The potential to increase the tensile strength of paper using these new celluloses was test-ed using a dosage of 50 kg/t. Pure MCC did not increase tensile strength notably. A 10% increase in tensile strength with MRC was ob-tained when the refining was done at pH 7, but at the same time the drainage time increased. The best increase in tensile strength was ob-tained with MRCs or MCCs that were graft-ed with CMC. The highest increase in tensile strength was obtained with 20 min cooked CMC grafted MCC that was refined once at pH 7. However, while the tensile strength in-creased by 32%, the drainage time increased by more than 30%.

The best combination of strength, drain-age and bulk was obtained with non-refined, CMC grafted MCC, see Figure 6 (right). The 120 min cooked CMC grafted MCC increased ten-sile strength by over 29% and had a negligi-ble effect on drainage time (5% increase). Bulk decreased by 2.6%. For comparison, a 4 kg/t dosage of pure CMC increased tensile strength by 25%, but at the same time the drainage time increased by nearly 20%. The decrease

in bulk with CMC was around 1%. Interesting-ly, the smaller particle size 120 min cooked and grafted MCC gave better drainage than 20 min cooked and grafted MCC, even though it is known that smaller particle size normally causes longer drainage times. The dosage of the MCC (5%) responds to 1 kg/t of pure CMC.

4.4 Thermal insulation and sound absorption materials by foam forming

Lightweight structures were prepared at labo-ratory scale from basic papermaking raw ma-terials with target grammages of 200, 400 and 800 g/m2 using foam forming (Table 1, Figure 7). The density of the samples varied from 8 kg/m3 to 30 kg/m3 (bulk 34–126 cm3/g). Compressibil-ity and reversibility were measured to under-stand the response to external load. Samples were compressed to 50% initial thickness and the maximum load was measured. Thicker 800 g/m2 sheets showed much higher compression loads than thinner 200 and 400 g/m2 sheets. Pure pine pulp sheets seemed to have higher compression strength, but also better revers-ibility than CTMP sheets. Microcellulose made the structures a lot less compressible, especial-ly for CTMP-based structures, and also greatly improved their reversibility. The results showed that all foamed samples reversed quite well after compression (62–83%) and, after 1 min,

Figure 6. Left: SEM image of a microreticulated cellulose. Right: Carboxymethyl cellulose grafted micro-crystalline cellulose significantly increases tensile strength and decreases drainage time.

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they had reversed by a further 3–6%. Thus, the bulky structure is maintained well even if some external load exists.

The thermal conductivity values of foam-formed sheets were compared to commer-cial thermal insulators (Table 2). The thermal conductivities of pure pine pulp sheets, CTMP with 20% microcellulose addition and CTMP with 20% PCC addition seem very promis-ing. The values are comparable to mineral and stone wool insulation materials of similar den-sity. CTMP sheets with 50% pine pulp addi-

tion do not show as good thermal conductiv-ity as stone or mineral insulation, but slightly better conductivity than, e.g., flax insulation. The thermal conductivity of pure CTMP sheet is slightly high, but still comparable with some flax insulation. Naturally, there are other re-quirements for insulation materials than mere-ly thermal conductivity, but other application areas, such as packaging, could also be con-sidered for these kinds of foamed, low-density materials.

The lightweight, foam-formed structures also

Figure 7. Left: Foam-formed, low-density pine pulp sheets. Right: Structures made from different wood fi-

bres: 200 and 400g/m2 samples shown on the left and 800g/m2 samples on the right.

Sample Grammage Thickness Density Bulk

[g/m2] [mm] [kg/m3] [cm3/g]

100 CTMP 800 32 25 40

100 Pine pulp 885 34 26 38

80/20 CTMP/MFC 820 34 24 41

80/20 CTMP/PCC 760 59 13 78

50/50 CTMP/pine 845 39 22 46

80/20 CTMP/PCC(1 720 87 8 120

Commercial Styrofoam 530 25 21 48

(1 Water and surfactant was foamed at the 1st stage, and fibres and other substances were added at the 2nd stage.

Table 1. Basic properties of foam-formed sheets.The values for typical Styrofoam are shown for reference.

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act as good sound absorbers. The results in-dicate that thicker samples with a grammage of 800 g/m2 had a much higher sound absorp-tion coefficient than thinner 200 g/m2 sheets. Pine pulp sheets, CTMP with 20% MFC addition and 50/50% mixture of CTMP/pine, had the best overall absorption coefficient in all meas-ured (0, 10 and 30 mm) air spaces. At the chal-lenging 500 Hz frequency, the absorption coef-ficient of the foamed samples was 0.3, whereas

Table 2. Comparison of foam-formed sample with commercial thermal insulators (source: TM

Rakennusmaailma 06/2012). U-values were calculated.

Trade name Material Density Thermal U-value 1

conductivity

kg/m3 10 W/(m·K)

Commercial Isover KL-33 glass 21.8 0.033 0.66

glass and stone Ursa Lasivilla lambda 37 glass 18.3 0.035 0.70

wool insulators Knauf Space Slab 035 glass 23.1 0.035 0.70

Paroc eXtra stone 31.1 0.035 0.70

Rockwool Flexi-Batts stone 34.5 0.035 0.70

Commercial Hunton Flex wood 62.2 0.038 0.76

natural fibre Ekovilla paper 38.6 0.038 0.76

insulators Konto peat+wood 54.2 0.037 0.74

Foam-formed Foamed pine pine pulp 28.0 0.035 0.71

1 Calculated value: U = 1/R, where R = d/λ. Thickness (d) of the samples was 50 mm. For foam-

formed sample also 50 mm thickness value was used and expected that thermal conductivity is

same than with 31.5 mm sample.

Figure 8. Concept line for making low-density foam-formed sound insulation materials.

the values for the commercial products varied from 0.1 to 0.6. Interestingly, the absorption co-efficient measured from the denser side of a CTMP sheet gave the highest value, 0.5, of the foamed structures at 500 Hz frequency.

A potential production line for making low-density sound insulation materials with foam forming is shown in Figure 8. The concept is still web-like, although the super-bulky and

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thick materials would most likely be formed using non-continuous processes. The cost of such a line is estimated to be approximately EUR 20-30 million (15 000 t/a) with a width of 1.5m, speed of 30m/min and annual produc-tion of 20 km2/a. The production cost is esti-mated to be about 1.7 €/m2, whereas compet-ing products are in the order 9-14 €/m2. When comparing this, e.g., with cylinder drying used for a typical folding box board machine, more energy is needed (increase 200%) due to through air drying and as no press water re-moval is made. Water usage is at the same level, chemical costs increase by 20% (more binding chemicals) and investment is assumed to cost 170% of the original, mainly due to the longer dryer section requirement.

The environmental performance of foam-formed sound insulation materials is better than that of competing products (Figure 9) based on standardized LCA evaluation, includ-ing fossil greenhouse gases (CO2, CH4 and N2O) expressed as carbon dioxide equivalents (CO2 eq). No water consumption data were availa-ble for the reference product.

In conclusion, the results indicate that foam-formed structures could have great potential

in sound absorption applications as, without any optimization of the structure, they showed mediocre results compared to commercial products on the market. For thermal insulation applications, the production of bulky struc-tures economically enough, i.e., drying them in a manner that preserves their bulk, should be addressed as well as their flammability and water absorption properties.

4.5 Modelling of material interactions, rheology and structure New models describing the basic properties of cellulose nanofibrils and their product ap-plications were developed at several different scales, as indicated in Figure 10. With the help of modelling, it is possible to re-think the be-haviour of MFC in very short time and spatial scales. Although the process size is huge, the short time and spatial scales often drive mac-roscopic behaviour. For example, amorphous nano-scale regions in elementary fibrils domi-nate the macroscopic viscoelastic properties of not only MFC films, but also those of wood fi-bre networks and thus conventional paper. As a second example, fibril floc formation within microseconds affects the rheology of MFC sus-pensions and the macroscopic strength prop-

Figure 9. Environmental performance screenings for foam-formed, low-density sound absorption ma-terials at 800 gsm: carbon (above) and water (below) footprints.

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erties of MFC re-enforced materials. There are also rheological and structural properties, such as plug flow in pipes or optimal composition of a multi-layer structure, that can be understood only by looking at sufficiently large, sometimes even macroscopic scales.

It is impossible to comprehensively cover all relevant scales and phenomena related to MFC processes and applications within a sin-gle research programme. Therefore, the ini-tial multi-scale modelling objective, in which models developed by different groups would be combined into a coherent analysis package, was too challenging. However, the developed models not only helped in interpreting the ex-perimental results, but also led to important findings beyond current experimental capabil-ities. A few key examples of such findings are given in Figure 10.

Viscoelastic behaviour of elementary fibrils affects the stiffness of MFC films

Experimental studies have shown that micro-cellulose films are not as stiff as could be ex-

pected based on the very high elastic modu-lus of 120-150 GPa of a single cellulose crystal. This discrepancy could be caused either by im-perfections in the fibrils or by the inability of the fibrils’ networks to utilize the full strength potential of individual fibrils. Thus, it is impor-tant to systematically investigate the effect of various structural factors on different scales to gain a fuller understanding of the causes of the observed mechanical behaviour. Atomis-tic simulations provide great insight into the dominant molecular-level factors that may drive macroscopic behaviour. Previous atom-istic molecular dynamics simulations of cel-lulose have focused on its crystal structure and elastic behaviour, whereas in the EffNet programme this approach was extended to non-crystalline regions formed within the fi-bril in zones where a large part of the cellulose chains were broken (Figure 11). X-ray diffrac-tion data suggests such regions to be common in cellulose fibrils, with up to 50% of the mate-rial being in an amorphous state.

The simulated elastic modulus for crystal cellu-lose compared well with the values obtained ex-

Figure 10. Modelling groups and topics related to MFC in the EffNet programme. The operation scales of the models are indicated on the horizontal axis.

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perimentally. However, non-crystalline regions were found to decrease the modulus significant-ly. Different numbers of connecting chains be-tween the crystallites were examined, and it was found that the elastic constants, inelastic defor-mations, and strength of the fibril depended on this number. For example, the elastic modulus for the whole fibril can be estimated to increase

by 4 GPa for each additional connecting chain. The molecular dynamics simulations are closely related to the fibril network simulations of Ku-lachenko et al. (2012, Cellulose 19, p. 793). Our at-omistic simulations confirmed a number of their speculations on the role of non-crystalline re-gions in fibril stiffness.

Microrheology of nanocellulose suspensions is dominated by consistency and fibril length

Nanocellulose fibres in suspension/gel states are known to have complex structures, de-pending on, for example, concentration and ionic strength. These complex structures pose both opportunities and challenges: creating novel functional structures is challenged due to the difficult rheology and processability of MFC suspensions. To better assess the chemi-cal and rheological impacts on the formation of nanocellulose structures, a novel particle-based method based on smoothed dissipative particle hydrodynamics was developed. This numerical approach treats both fluid and sol-id phases in a unified way. The fluid and sol-id phases are described as a set of particles exchanging momentum and/or interacting through Derjaguin-Landau-Verwey-Overbeek (DLVO) potentials. Furthermore, nanocellulose fibres are represented as strings of solid par-ticles connected through extensional/bending springs. This model was used to simulate the microrheology of MFC suspensions.

The simulations were carried out for the Cou-ette geometry with a gap of 1 µm. The goal was to determine the effect of various properties of cellulose nanofibre and its interaction strength on forming micro-flocs and on local viscosity. The parametric effects on the micro scale are expected to be reflected in the observed mac-roscopic flow behaviour, as this behaviour de-pends critically on the local aggregation dy-namics. In the simulations, at very large shear rate 0.3 106 1/s floc formation was seen to take

Figure 12. Dependence of simulated viscosity on various model parameters. In each case, the other model parameters were fixed at the values shown in the middle of each block (consistency 1.0%, length 0.30µm etc.).

Figure 11. Relative sliding of cellulose chains with-in an amorphous region, leading finally to breakup of the fibril at high tensile stress. The images are snapshots of fibril structure in atomistic molecu-lar simulations at different phases of straining.

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place very rapidly, within microseconds. More-over, due to slippage, the local shear rate be-comes higher than average close to the walls. Thus, the effective viscosity has a higher val-ue in the central region of the flow compared to the boundary regions. As regards the varied parameters, suspension concentration and fi-bril geometry (especially length) appear to have much stronger effects on viscosity and floc formation than fibril interaction (double layer thickness) or bending stiffness (Figure 12).

Surface pore structure underlies conductivity of printed lines on filler-microcellulose substrates

Composites made from cellulose microfibres and inorganic filler particles can be applied as substrates for printed electronics. The struc-tural properties of these substrates have been studied both experimentally at VTT and with a particle-level modelling approach developed at Helsinki University. The model describes the skeleton structure formed by pigment particles of varied shape and size distribu-tion. Microcellulose is assumed to fill voids of the structure. In order to compare the mod-el results with experiments, it was important to also simulate the profilometer measure-ment of surface roughness. The model simu-lations predict quite well the relative changes in measured density, porosity and roughness for kaolin and precipitated calcium carbon-ate (PCC) pigments. Small-scale roughness turned out to be higher for kaolin than for PCC. However, the measured conductivity of print-ed lines on kaolin surfaces was higher than on PCC surfaces. The simulations reveal a more open surface pore structure for PCC than for kaolin, which leads to stronger absorption of the silver ink, and thus explains the differenc-es in the measured conductivities. These re-sults have been published by Penttilä et al. (2013, Cellulose 20, pp. 1413-1424).

5. Exploitation plan and impact of results

The achievements directly support the goal of demonstrating new types of products that can be produced from wood-fibre based materials and that expand the current product portfolio offered by forest cluster companies. Micro- and nanofi-brillated cellulose raw materials will have a high impact on the future paper- and board-making industry through the introduction of new prod-ucts. Filler-MFC composites show good potential for low-cost printed electronics substrates, but market penetration will require investment in de-veloping the production technology.

Foam forming clearly has very high value cre-ation potential as it can both considerably in-crease the competiveness of current fibre products and offer a sustainable solution for manufacturing a large range of value-added products. This opens opportunities for both large companies and SMEs to create novel val-ue chains. The examples of lightweight struc-tures demonstrated in this section represent only the tip of the iceberg. Good sound ab-sorbance properties achieved with lightweight structures made from sustainable raw materi-als is an intriguing combination to be addressed further. Similarly, the microcrystalline cellulose applications show potential both as superab-sorbent polymers and strength additives in pa-permaking. The modelling results can be ap-plied, for example, when tailoring micro- and nanocelluloses for specific applications.

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Table 3. Partner organisations and their research roles.

Role

Simulations of the flocculation of microcellulose, also in the

presence of filler particles. Investigation of the mechanical

properties of particle-MFC packings.

Optical simulations and particle packing simulations in the virtual

product development environment.

Specialized in structural characterization of materials and

products using X-rays. Team responsible for x-ray scattering and

x-ray microtomography measurements of cellulose microfibers

and structures.

Evaluating both the quality and properties of microcellulose,

focusing on P&P applications.

NFC processing and fractionation, substrates for printed

electronics.

Development of atomistic, molecular and coarse-grained models

for nanocellulose.

Microcellulose polymer interactions in water suspensions.

Production of microcelluloses, demonstration of new product

concepts, implementation of virtual product model environment

and coordination of networking activities.

Partner

Aalto University, Complex

Systems and Materials,

Prof. Alava

Helsinki University,

Department of Physics,

Penttilä

Helsinki University,

Department of Physics,

Prof. Serimaa

Kemira

Stora Enso

Tampere University of

Technology, Biological Physics

and Soft Matter,

Prof. Vattulainen

UPM

VTT Technical Research

Centre of Finland

6. Networking

The research was carried out jointly by re-search organisations and Finnish forest clus-ter companies. Table 3 presents the partners and their role in the research.

VTT has collaborated with FPInnovations (Can-ada) on modelling the rheological properties of micro/nanocellulose suspensions and forming micro-scale fibre networks. The Department of

Solid Mechanics at the Royal Institute of Tech-nology (Sweden) has assisted VTT in the devel-opment of the advanced fibre network model.

The Tampere university of Technology group has collaborated with the Royal Institute of Technology (KTH, Stockholm) on coarse grain-ing of cellulose nanofibril systems using the Martini model. The modelling work of the Bio-logical Physics and Soft Matter team are also coupled to the ESF network SIMBIOMA in terms

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of developing coarse-graining techniques and coarse-grained models for complex biomolecu-lar systems. In addition, the research benefits fromtheESFnetworkFUNCDYN,theobjectiveof which is to link detailed models to large-scale networks for the examination of functional dy-namics in complex chemical systems. The team also belongs to the Norforsk-funded networks “Refining Lignocellulosics to Advanced Poly-mers and Fibers” (headed by Maija Tenkanen, Finland) and “Nordic Network of Soft Matter Physics (headed by Jon-Otto Fossum, Norway).

7. Publications

Illa, X., Puisto, A., Mohtaschemi, M., Alava, M. J., Transient shear banding in time-dependent flu-ids. Phys. Rev. E 87, 022307 (2013).

Paavilainen, S., Róg, T., and Vattulainen, I., Analysis of Twisting of Cellulose Nanofibrils in Atomistic Molecular Dynamics Simulations. The Journal of Physical Chemistry B, 2011, 115, 3747-3755

Paavilainen, S., McWhirter, J.L., Róg. T., Järvi-nen, J., Vattulainen, I., Ketoja, J.A., Mechanical properties of cellulose nanofibrils determined through atomistic molecular dynamics simula-tions. Nordic Pulp Paper Res. J. 27, 282-286 (2012).

Penttilä, A., Sievänen, J., Torvinen, K., Ojan-perä, K., Ketoja, J.A., Filler-nanocellulose sub-strate for printed electronics: experiments and model approach to structure and conductivity. Cellulose 20, 1413-1424 (2013).

Puisto, A., Illa, X., Mohtaschemi, M., Alava, M. J., Modeling the viscosity and aggregation of sus-pensions of highly anisotropic nanoparticles. Eur. Phys. J E 35(6) (2012).

Puisto, A., Illa, X., Mohtaschemi, M., Alava, M., Modeling the rheology of nanocellulose suspen-sions. Nordic Pulp Paper Res. J 27(2), 277-281 (2012).

Torvinen, K., Sievänen, J., Hjelt, T., Hellén, E., “Smooth and flexible filler-nanocellulose com-posite structure for printed electronics appli-cations”, Cellulose 19, Issue 3, pp 821-829. doi: 10.1007/s10570-012-9677-5

Conference presentations and posters:

Hellén Erkki., “Filler-nanocellulose composite as a substrate for printed electronics”, Indus-trial Biomaterials seminar, November 22, 2012. Espoo, Finland.

Illa, X., Puisto, A., Mohtaschemi, M., Lehtinen, A., and Alava, M. J., “Simple rheological models and fluidization in complex fluids”, 2nd Edition on Materials Deformation: Fluctuations, Scal-ing, Predictability, February 17-22 2013, Les Houches, France.

Illa, X., Puisto, A., Mohtaschemi, M., and Ala-va, M. J., “Transient Shear Banding in Attractive Colloids”, The 2nd Workshop on Fluctuations in Materials Properties: Physics, Geoscience and Environment, January 31- February 1, 2011, Courmayeur, Italy.

Ketoja, J., Hellén, E., Lappalainen, J., Kulachen-ko, A., Puisto, A., Alava, M., Penttilä, A., Lumme, K., Paavilainen, S., Róg. T., Vattulainen, I., Vid-al, D., Uesaka, T., “Multi-scale modeling envi-ronment for nanocellulose applications”, 2010 TAPPI International Conference on Nanotech-nology for the Forest Products Industry 27 – 29 September 2010, Espoo, Finland

McWhirter, J.L., Paavilainen, S., Järvinen, J., Róg, T., Vattulainen, I., “Atomistic modeling of cellulose nanofibrils: Elastic Properties”, 2010 TAPPI International Conference on Nanotech-nology for the Forest Products Industry 27 - 29 September 2010, Espoo, Finland.

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Mohtaschemi, M., Puisto, A., Alava, M. J., “Con-tinuum mechanics modeling of suspensions with elongated nanoparticles”, 2nd Edition on Materi-als Deformation: Fluctuations, Scaling, Predicta-bility, February 17-22 2013, Les Houches, France.

Paavilainen, S., McWhirter, J.L., Orlowski, A., Róg, T., Vattulainen, I., “Computational perspective to cellulose nanofibrils through atomistic simula-tions”, 2010 TAPPI International Conference on Nanotechnology for the Forest Products Industry 27 - 29 September 2010, Espoo, Finland.

Paavilainen, S., McWhirter, J.L., Róg, T., Vattu-lainen, I., “Atomistic modeling of cellulose na-nofibrils and their interactions”, 2010 TAPPI In-ternational Conference on Nanotechnology for the Forest Products Industry 27 - 29 Septem-ber 2010, Espoo, Finland.

Puisto, A., Mohtaschemi, M., and Alava, M. J., “Rheological model for unstable colloidal sus-pensions in pipe flow”, International Soft Mat-ter Conference, July 5-8, 2010, Granada, Spain.

Puisto, A., Mohtaschemi, M., Illa, X., and Ala-va, M. J., “Modeling the rheology of nanocel-lulose suspensions”, International Soft Matter Conference, July 5-8, 2010, Granada, Spain.

Puisto, A., Illa, X., Mohtaschemi, M., and Ala-va, M. J., “Modeling the rheology of nanocellulose suspensions”, 2010 TAPPI International Confer-ence on Nanotechnology for the Forest Products Industry 27-29 September 2010, Espoo, Finland.

Puisto, A., Illa, X., Mohtaschemi, M., and Ala-va, M. J., “Modeling the rheology of nanocel-lulose suspensions”, International Paper Phys-ics Conference & 8th International Paper and Coating Chemistry Symposium, June 10-14 2012, Stockholm, Sweden.

Puisto, A., Niemi, M., Illa, X., and M.J. Alava., “Multicomponent Population Balance for Ag-gregating Suspensions”, The 2nd Workshop on Fluctuations in Materials Properties: Physics, Geoscience and Environment, January 31- Feb-ruary 1, 2011, Courmayeur, Italy.

Puisto, A., Illa, X., Mohtaschemi, M., and Ala-va, M. J., “Modeling the rheology of colloidal suspensions”, Materials Deformation: Fluctu-ations, Scaling, Predictability, 22-28 January 2012, Les Houches, France.

Puisto, A., Illa, X., Mohtaschemi, M., Lehtinen, A., and Alava, M. J., “Rheological models of complex fluids”, 2nd Edition on Materials De-formation: Fluctuations, Scaling, Predictabil-ity, February 17-22 2013, Les Houches, France.

Sievänen, J., Torvinen, K., Hjelt, T. and Hellén, E., A New Type of Filler-Nanocellulose Com-posite Substrate for Printed Electronics Appli-cations. 2011 International Conference on Na-notechnology for Renewable Materials, June 6-8, 2011, Arlington, VA (Washington, DC), USA.

Sievänen, J., Torvinen, K., Hjelt, T. and Hellén, E., “Smooth and flexible filler-nanocellulose sub-strate for printed electronics applications, Spe-ciality Paper Industry conference 2012, March 12-13, Amsterdam, The Netherlands.

Sievänen, J., Torvinen, K., Hjelt, T. and Hellén, E., “A new type of filler-nanocellulose composite substrate for printed electronics”, The 8th Bien-nial Johan Gullichsen Colloquium, 22 November 2011, Espoo, Finland.

Torvinen, K., Sievänen, J., Hjelt, T. and Hellén, E., “Flexible filler-nanocellulose structures”, 2010 TAPPI International Conference on Nanotech-nology for the Forest Products Industry 27 – 29 September 2010, Espoo, Finland

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Torvinen, K., Sievänen, J., Hjelt, T., Hellén, E., “Smooth and flexible filler-nanocellulose com-posite substrate for printed electronics”, Print-ed Electronics Europe 2011, 5-6 April 2011 Düs-seldorf, Germany

Torvinen, K., Sievänen, J., Mattila, T., Alastalo, A. and Hellén, E., “Flexible bio-based pigment-nanocellulose substrate for printed electron-ics”, ICFPE2012 conference, September 6-8, 2012, Tokyo, Japan.

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mIcrO-cELLULOSES

AND THEIr cHArAcTErISTIcS

pa r t n e r s

VTT

Aalto University

Andritz Oy

Kemira

Stora Enso

University of Oulu

University of Helsinki

UPM

c o n tac t p e r s o nHeli Kangas, heli.kangas@vtt.fi

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Different types of microcelluloses were produced in a quality-controlled way, characterized and distributed to programme partners. MicroFracon showed promise as a method for analysing the amount of nanomaterial in microcellu-loses, although further development of the method is needed. Analysis meth-ods suitable for routine quality control of microcelluloses, namely low shear viscosity and transmittance measurements, were harmonized and can now be used routinely in different laboratories.

A method to determine both the retention and distribution of microcelluloses in the final product in real papermaking process conditions was developed and successfully demonstrated at pilot scale trials. Deeper understanding of the rheological properties of suspensions of microfibrillated celluloses was gained. Together with the results on the processability, i.e. pumping and mixing, and dewatering of microfibrillated cellulose suspensions, this information can help in designing future industrial processes. Up-to-date information on progress in research, legislation and recommendations related to product safety of microcelluloses was gathered, and REACH requirements for microcelluloses were clarified. International and national cooperation was established related to both the characterization and product safety of nanocelluloses.

AbstRACt

Keywordsmicrocellulose, nanocellulose, fibrillated celluloses, characterization, product safety, processability, pumping, mixing, rheology, dewatering

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1. Background

The overall goal of the EffNet research pro-gramme has been the development of re-source-efficient production technologies through the renewal of production processes and by developing new unit processes based on advanced raw materials and desired end-product characteristics. Bio-based nanoma-terials are promising candidates for improv-ing the performance of many products in the near future due to their unique properties and to the fact that they originate from renewa-ble resources. Among the most abundant and sustainable nanomaterials are micro- and na-nocelluloses, which have a wide industrial ap-plication potential, including, for example, novel composites and construction materi-als, new kinds of porous materials, biomedical materials, value-added paper and board prod-ucts, intelligent packages, barrier materials, as well as functional surfaces and additives.

As with any new materials, proper characteri-zation of micro- and nanocelluloses is critical, both for their trade and for their safety assess-ment. However, characterization, especially of fibrillated celluloses, is challenging due to their heterogeneous nature and the fact that they mostly consist of long, slender fibrils with a high degree of branching. Research in this area is very actively pursued in several re-search projects around the world, but despite the characterization work done already, there is still a need to find new methods and develop existing ones in order to better describe mi-cro- and nanocelluloses and their distribution in web-like end-product or composite struc-tures. In particular, reliable characterization methods are needed to determine the quali-ty of micro- and nanocelluloses. Validation of the characterization methods to enable com-parison of material properties is also a key fac-tor. In addition, product safety is an essential aspect when developing new products and is

very closely related to accurate and reliable characterization of raw materials used. The safety of bio-based nanomaterials depends on many still poorly understood factors, as well as on the exposure route (via respiratory, gastronomic track, skin or eye). The size and shape of the particles, their aggregation prop-erties, degree of branching and specific sur-face properties, among others, may affect the interactions of bio-based micro- and nanoma-terials with cells and living organisms.

It is known that the rheological properties of suspensions containing micro- and nanocel-luloses differ a great deal from those in to-day’s papermaking operations. In order to pro-cess these suspensions, their rheology must be known. In addition, due to their high swell-ing, micro- and nanocelluloses are inherent-ly difficult to dewater. Up-scaling will require re-thinking of the whole papermaking process from wet end to drying of the porous struc-ture. Therefore, unit operations involved in the processing of micro- and nanocelluloses, such as pumping, mixing and dewatering, need to be carefully studied.

2. Objectives

The objectives were to gain information about the characteristics of microcelluloses with variable properties as well as their behaviour in different processing environments. Activi-ties related to the product safety of microcel-lulose, such as research projects and guide-lines given by the authorities, were actively followed to obtain up-to-date information. The specific objectives of the work were:

• Preparationoftailoredrawmaterials• Toachievealeadingroleintheproduct

safety and characterization of micro- and nanocelluloses

• Toensurethesafetyofnewmaterials,

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processes and product concepts based on microcellulose

• Toevaluatetheeffectsofmicrofibrillatedcellulose on forming and dewatering characteristics

• Togaindeeperunderstandingoftherheological properties of microfibrillated cellulose suspensions, in order to have necessary knowledge for eventual scale-up of MFC processes; production, paper manufacture, etc.

3. Research approach

For successful research on the characteristics and safety aspects of microcelluloses, as well as on their behaviour and performance during pro-cessing, the production of the studied materials must be performed in a quality-controlled way. The fundamental issues critical to the produc-tion of micro- and nanocelluloses were therefore studied. As a result, seven different types of mi-crocelluloses were successfully made, charac-terized and delivered to partners.

Based on the results from the first phase of the programme, characterization of the mi-crocelluloses was considered both essen-tial and challenging. Identification of suitable methods was therefore required. A survey of published micro- and nanocellulose charac-terization methods was performed to gain in-formation on their most important properties and state-of-the-art characterization meth-ods. Active discussion with the industrial part-ners of EffNet led to proposals both for materi-al specification and a classification scheme for micro- and nanocelluloses. Start-up work for standardization included participation in the preparation of a standardization workshop and allowed us to contribute to the roadmap for in-ternational standardization of cellulose nano-materials. Method development was success-fully performed in areas considered important

for quality control and safety assessment of micro- and nanocelluloses. As a result, viscos-ity and transmittance measurement methods were harmonized and can now be used in dif-ferent laboratories to obtain comparable re-sults. An estimate of the size distribution of particles in microcelluloses can be obtained by fractional analysis.

Product safety is an essential part of the de-velopment of new products and very close-ly related to accurate and reliable character-ization of the raw materials used. As there were many national and EU FP7 projects re-lated to safety issues of microcelluloses al-ready on-going at the beginning of the pro-ject, their activities were intensively followed in order to avoid parallel research in the field as well as to gain state-of-the-art knowledge on product safety. In addition to this, relevant and up-to-date information on the product safety of micro- and nanocelluloses was con-tinuously collected by following the develop-ment of legislative requirements and recom-mendations given by authorities, scientific advisory bodies, and international organiza-tions in EU member states and North Ameri-ca. The REACH requirements for nanomateri-als were clarified and simplified based on the new RIP-oNs (Reach Implementation Project on Nanomaterials) guidelines and ECHA (Eu-ropean Chemicals Agency) recommendations. In addition, application-specific requirements for nano- and microcelluloses were evaluated. Information needed for material safety data sheets (MSDS) for micro- and nanocelluloses was gathered, and the main knowledge gaps identified. International cooperation was es-tablished in the field of nanomaterial safety, for example with COST action FA0904 and the Canadian research centre FPInnovations. Na-tional cooperation between two SHOKs (Finn-ish strategic centres for science, technology and innovation), FIBIC’s EffNet programme and CLEEN’s MMEA programme was practiced

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under the title “Environmental management and sustainable use of nanocellulose”. The discussions of a two-day workshop were pub-lished in a public report.

In studying the processability of microcel-luloses, the main aim was to clarify the pro-cessability of high-water binding furnishes in-cluding rheological properties, pumping and mixing with the applied chemistry. The behav-iour of suspensions of microcelluloses at dif-ferent consistencies between 1% and ~20% was studied, including studies of both UHC (ul-tra-high consistency) and foam suspensions. Suspension rheology was measured with state-of-the-art devices and the studies on flow rheology at various chemical conditions were supported by simulations. The effect of microcellulose quality was analysed with new meso-scale models for colloidal interactions, which was applicable even at very high con-sistencies. Simulations were used to extrap-olate the process operating window beyond laboratory scale, for example by simulating a faster process, which would be impossible ex-perimentally. This supports the design of scal-able forming concepts.

In the dewatering studies, the target was to determine the limitations of initial dewater-ing and press dewatering for microcellulose-containing furnishes. The material behaviour in dewatering operations was studied at lab scale with a moving belt former. The effect of furnish type was studied based on the water removal efficiency of the furnish recipes, the main variables being furnish composition, re-tention control, and type and amount of micro-cellulose. The effect of papermaking additives and fines on dewatering was also studied.

4. Results

4.1 Production and characteristics of microcelluloses

Production of microcellulosesDifferent types of microcelluloses were either acquired or produced for research purposes in EffNet. The microcelluloses used in the project are described as follows:

• Daicel MFC (Celish KY-100G) According to currentknowledge,CelishKY-100Gconsistsof dissolving pulp with high cellulose content. The dissolving pulp is originally from softwood. The material was delivered at 10% consistency.

• VTT coarse and fine MFC: Both VTT grades are made of bleached hardwood kraft pulp. They are ground to different coarseness levels having a viscous structure higher than other grades. These grades also have the highest transmittance levels. The material was delivered at 3% consistency unless otherwise stated.

• P-1 MFC: Pilot-scale microfibrillated material consisting of stiff fibre fragments and fibrils, having medium viscosity compared to the other available grades.

• P-2 MFC: Pilot-scale microfibrillated material consisting of a wide selection of unfibrillated and fibrillated material and having medium viscosity compared to the other available grades.

• MCC and MRC: Microcrystalline cellulose (MCC) is produced via acid hydrolysis of kraft pulp cellulose polymer. The produced MCC is refined with varied setups to produce microreticulated cellulose (MRC). The samples have relatively low viscosity and MRC has smaller reticulated particle size compared to MCC.

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Basic characterizationThe basic characteristics of the microcellulos-es were defined using the following methods:

• Opticalmicroscopy(OM)–visualinspectionof microcellulose sample type (coarse/fine) and assessment of homogeneity.

• Scanningelectronmicroscopy(SEM)–evaluation of detailed fibril structure. Thickness and branching of the fibrils.

• Low-shearviscosity–evaluationofgelstrength and flow behaviour as a measure of product quality and processability.

• Transmittance–evaluationoftheamountof larger-size fibrils in the suspension.

• Stabilityanalysis–transmissionmeasurement combined with measurement of the specific volume of sedimentation at a certain time frequency, providing information about the stability of the system (e.g. phase separation, sedimentation).

The basic characteristics of the EffNet mi-crocellulose samples are summarized in Ta-ble 1 and their optical microscopy images are shown in Figure 1.

Low shear viscosity and transmittance meas-urements were both considered good methods

for evaluating the product quality of microfibril-lated celluloses. In order for the results to be comparable regardless of the place of meas-urement or type of sample, efforts towards harmonization of these measurement methods were made. The harmonization included both the sample preparation and the measurement procedure. The methods were then tested with the same samples between different labora-tories. The introduced viscosity measurement method is now routinely used in at least six lab-oratories and the transmittance measurement method in three laboratories.

Strength potential of microcellulosesAs part of their characterization, the strength potentials of the EffNet microcelluloses were evaluated. The strength measurements were done both for 100% microcellulose films and for blend sheets, in which microcellulose addi-tion levels of 0, 1 and 5% and two different fur-nishes, spruce CTMP (CSF=570 ml) and chem-ical pine (19 °SR), were used. The results for 100% microcellulose films showed that the type of microcellulose has an impact on the strength potential of the films, as do the film forming and drying procedures. The elastic modulus of the films increased with density, but for fine microcellulose grades, the brittle structure of the films with no plastic behaviour

Shear viscosity, Transmittance, Stability analysis Transmittance of mPa·s % Sedimentation volume, sediment, % (10 rpm, 1.5%) (800 nm, 0.1%) mm

Daicel MFC 15 777 8.1 26 2

VTT coarse MFC 23 176 34.3 35 7.5

VTT fine MFC 22 502 60.2 42 15

P-1 MFC 2 784 24.9 23 <1

P-2 MFC 3 654 26.2 13 11.5

MCC NA 0.2 9 <1

MRC 400 0.5 32 <1

Table 1. Basic characteristics of the EffNet microcelluloses.

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resulted in low tensile values. For handsheets with microcellulose addition, the effect of mi-crocellulose type was insignificant. A 1% ad-dition of microcellulose did not notably influ-ence the wet and dry strength properties of the handsheets. However, with 5% microcel-lulose addition, a substantial increase in ten-sile index was observed for CTMP, even 73% with VTT coarse (Figure 2). In addition, the z-directional strength increased for both pulps and the increase in wet tensile strength was remarkable in both pulps.

Fractional analysisFractional analysis of microcelluloses was per-formed at the University of Oulu with a Micro-Fracon device (Metso Automation, Finland), which utilises a tube flow fractionation prin-ciple (Figure 3). In the tube flow technique,

the particles are separated axially so that the largest ones accumulate at the front end of the flow plug and the smallest ones at the rear end. In MicroFracon, a defined quantity of sample is mixed with water flowing through a long tube wound onto a wheel. The pulp sam-

Figure 1.Optical microscopy images of the EffNet microcelluloses. Scale bar: 200 µm.

Figure 2. Tensile index for CTMP handsheets with microcellulose addition.

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ple is fractionated into different size catego-ries as it flows through the tube, and when the pulp-water mixture exits the long tube, it is di-vided into size fractions according to the setup of the device. The different fractions can then be analysed, for example with image analysis software or various microscopic methods.

The EffNet microcellulose samples were frac-tionated into four different fractions according to their size, primarily according to the long-est dimension of the particles. The fractions obtained were FR1 (largest particles), FR2, FR3 and FR4 (smallest particles). The mass per-

centages of the fractions were determined by filtration (in the presence of flocculent) on a membrane, followed by precision weighing (Table 2). The largest particles in the fraction-ated particle-water suspension were visual-ised with a high definition camera unit. How-ever, the sensitivity of the image analysis is around 1 µm, and particles with dimensions smaller than that could not be reliably meas-ured. The aspect ratio (AR) of particles – the relation of the longest dimensions (LD) and the shortest dimensions (SD) – were obtained from optical image analysis (fractionation im-ages) (Table 3).

LD FR1 LD FR2 LD FR3 SD FR1 SD FR2 SD FR3 AR AR AR [µm] [µm] [µm] [µm] [µm] [µm] FR1 FR2 FR3

Daicel MFC 141 55 20 4.5 2.1 1.5 31.3 26.2 13.3

VTT coarse MFC 34 19 11 2.2 1.5 1.3 15.5 12.7 8.5

VTT fine MFC 49 12 9 2.7 1.2 1.1 18.1 10.9 8.2

P1-MFC 41 22 * 3.0 1.7 * 13.7 12.9 -

P2-MFC 178 17 8 4.5 1.7 1.2 39.6 10 6.7

MCC 139 17 11 10.3 2.5 1.7 13.5 6.8 6.5

MRC 21 16 10 3.4 2.9 1.6 6.2 10 6.3

Table 3. Dimensional data of fractions from EffNet microcelluloses.* not enough particles for MicroFracon image analysis (see mass percentages in Table 2).

FR1 [%] FR2 [%] FR3 [%] FR4 [%]

Daicel MFC 31.4 53.6 13.7 1.3

VTT coarse MFC 27.0 59.7 9.8 3.5

VTT fine MFC 1.8 63.8 29.7 4.8

P1-MFC 46.0 50.9 3.2 0.0

P2-MFC 57.2 23.2 14.9 4.7

MCC 48.0 35.8 12.0 4.2

MRC 5.5 77.2 13.6 3.7

Table 2. Mass percentages of the EffNet microcelluloses in different fractions.

Figure 3. Principle of tube flow fractionation.

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Direct measurement of MFC retentionand distribution in paper by labellingDetection of individual MFC fibres in paper is difficult using any measurement method avail-able because the density and chemical com-position of the pulp and MFC fibres are the same. A method to increase the average den-sity of MFC using a selective labelling meth-od was therefore developed, enabling the de-tection of the spatial distribution of MFC and providing a method to study its retention in paper. The labelling method is based on at-taching Iron-Cobalt-nanoparticles onto the surface of the MFC. The spatial distribution of the MFC can be evaluated from the X-ray mi-crotomographic images and the retention can be studied by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS) analysis and inductively coupled plasma optical emission spectrophotometry (ICP-OES) measurements (Figure 4).

Tests showed that labelling does not change the strength properties of the samples. The concept was tested in pilot-scale SUORA tri-als with good success. The trial showed that is possible to directly measure the effect of MFC addition on paper strength properties, as well as monitor retention and distribution in real papermaking process conditions.

Structural analysisThe research group at the Department of Physics, University of Helsinki, is specialized in structural analysis of soft materials using x-rays, especially synchrotron radiation based methods. In this project, the structure of cellu-losic materials, including microcelluloses, was studied using x-ray scattering and microto-mography. Specifically, the preferred orienta-tions of cellulose fibres were determined us-ing both x-ray microtomography and x-ray diffraction, and similar results were obtained. Wide-angle x-ray scattering (WAXS) was used for determining the crystallinity and size of

Figure 4. Visualization of paper cross sections by SEM (a, b) and X-ray microtomography (c). In im-age a) dense, labelled MFC was thresholded from the image and denser areas are emphasized with red colour. In image b) (reference with original MFC), the contrast between fibres and MFC can-not be seen. Image c) illustrates four paper sam-ples with different amounts of labelled MFC and d) shows the distribution of MFC in a paper produced in the SUORA environment.

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cellulose crystallites in the studied samples (Figure 5). In addition, WAXS gave information on the crystal structure (cellulose I, II). Small-angle x-ray scattering (SAXS) was found to be useful in studies of nanometre range porosity and short range order of cellulose microfibrils.

Standardization of micro- and nanocellulosesAt the beginning of the project, standardization of micro- and nanocelluloses was considered important both in Finland and internationally, and preparatory work for standardization was included in the project plan. First, the most im-portant aspects for the industrial programme partners were clarified and a suggestion/road-map for continuation of the standardization was drafted. Internationally, a proposal to the ISO to form a nanocellulose task group under TC-229 nanotechnologies, which would coor-dinate ISO standardization of nanocelluloses, was made. In addition, participation in organiz-ing an international Workshop on Internation-al Standards for Nanocellulose, held in Wash-ington DC on June 9, 2011, was accomplished.

Following the start-up work on standardiza-tion in EffNet, the international standardiza-tion regarding nano- and microcelluloses is being currently managed by Kemesta ry (For-est and Chemical Industry) and METSTA (Na-notechnology).

4.2 Product safety aspects of microcelluloses As product safety is an essential part of new product development, the safety aspects of nano- and microcelluloses must be taken into account as early as possible. During EffNet, the current knowledge on the safety of nano-materials was reviewed as well as the current regulations related to nanomaterials.

At present, there are no detailed regulations re-garding nanomaterials, and nanocelluloses are regulated as bulk cellulose. Any nanomaterial is thus required to fulfil current regulations, such as REACH, occupational health related instruc-tions, and regulations based on its intended use, such as regulations related to food contact materials (FCM), food legislation, cosmetics, etc. However, authorities worldwide are currently evaluating the existing regulations in order to determine whether they are applicable or ad-equate for nanomaterials, or whether there is a need for further nanomaterial-specific rules. It remains to be seen whether such specific regu-lations will be announced and if they will be ap-plied also to nano- and microcelluloses. Some scientific opinions and guidelines have already been published, such as the OECD’s Guidance Manual for the Testing of Manufactured Nano-materials and the REACH Implementation Pro-ject on Nanomaterials (RIP-oNs). Based on the extensive RIP-oN reports, the European Chem-icals Agency (ECHA) has released the Guidance on Information Requirements and Chemical Safety Assessment on nanomaterials, provid-ing endpoint-specific guidance for registrants preparing REACH dossiers on nanomaterials.

Figure 5. Crystallinity of VTT fine and coarse MFC, measured from 100% microcellulose films. Crys-tallinity of VTT fine MFC was 42±3% and that of VTT coarse MFC 40±3%. The crystal width (200 reflection in Iβ) was 4.4±0.1 nm for VTT fine MFC and VTT coarse MFC 4.5±0.1 nm.

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The guideline is relevant to physico-chemical and ecotoxicological endpoints. In addition, guidelines on the characterization of dose-response for human health and the environ-ment, and occupational exposure estimation are given by the ECHA. The main guideline is now in hearing by CARACAL (an expert advi-sory group to the European Commission and ECHA on questions related to REACH and CLP (Classification, Labelling and Packaging) of sub-stances and mixtures) and in all likelihood will be included in the EU’s chemical legislation in the near future. In addition, specific applica-tion areas have specific requirements that the materials applied should fulfil, for example the European Food Safety Authority (EFSA) has re-leased guidance on risk assessment concern-ing potential risks arising from applications of nanoscience and nanotechnologies to food and feed, and in the USA the Food and Drug Admin-istration (FDA) has published guidelines for the food and food packaging industry. The require-ments also vary depending on the application area, such as food, food contact materials, cos-metics, etc. For example in the US, the FDA has published guidelines for industry on the safety of nanomaterials in cosmetic products.

The main question regarding legislation re-quirements on micro- and nanocelluloses in the future will be whether they are considered nanomaterials according to the Commission definition 2011/696/EU (Figure 6). Today cellu-lose pulp is exempted from the registration re-quirements based on Article 2(7)a; Annex IV, if not chemically modified, and as there are no specific requirements for nanomaterials, cel-lulose micro- and nanomaterials are exempted also. However, there is a possibility that this will change, since REACH is currently under revision and new guidance documents and possibly amended annexes will be published after June 2013. Chemical modification may also bring mi-cro- and nanocelluloses under the REACH reg-ulation and under registration requirements.

Published studies of the health effects of mi-cro- and nanocelluloses as well as their envi-ronmental effects and occupational health is-sues were first reviewed in the research report “Characterization and safety aspects of nano-celluloses” and, more recently, in the Hand-book of Green Materials; Processing Technolo-gies, Properties and Applications (Chapter 12, Toxicity and health issues). The results pub-

Is thenanocellulosenanomaterial

accordingdefinition?

Registrationrequirements

apply

Registrationrequirements

apply

Registrationwith current rules

Is thenanocellulose

chemicallymodified?

Current REACHregulations

stands

No registration

New recommendations published by ECHA

Registration with additional

nanomaterialspecific

requirements

Figure 6.Current status of nanocellulose and possible future vision.

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lished so far indicated that nano- and micro-celluloses do not pose risk to human health or to the environment, but more research and toxicity tests are needed to guarantee their safety, especially if the finest particles will be applied in high concentrations. In addition, even though there is no related safety con-cern, these materials cannot be considered in-ert either, since inflammation reactions have been observed in many cases.

As mentioned above, more research and toxic-ity tests are needed to guarantee the safety of nano- and microcelluloses, especially if the fin-est particles will be applied in high concentra-tions. In order to also guarantee the safety of the finest particles, their amount in microfibril-lated cellulose (MFC) was studied, along with their properties and health effects as part of the safety assessment. VTT fine MFC was fraction-ated with MicroFracon into 4 fractions of differ-ent size. The two smallest fractions (FR3+FR4) were collected and subjected to toxicity testing. Using In vitro toxicity testing, the effect of the fractions (FR3+FR4) on human cervix carcino-ma (Hela229) cells was studied. Cytotoxicity was assessed by short-term studies including esti-mates of highest tolerated dose (HTD) and to-tal protein content (TPC). Sublethal toxicity was assessed by RNA inhibition testing, and geno-toxicity was evaluated by the Ames test. By In vivo toxicity testing, the effect of the fractions (FR3+FR4) was studied on a living organism. The test was performed with the Nematode Caeno-rhabditis elegans as an egg-laying assay. The results showed no indication of toxicity in the majority of the tests. Slight indication of cyto-toxicity was observed in the TPC test with the highest sample concentration. However, the cy-totoxicity test result should be considered only indicative, since the toxicity test results should always be addressed in relation to the other tox-icity test results, which showed no indication of toxicity. Most importantly, there was no indica-tion of toxicity in the in vivo test.

The environmental behaviour of microcellulos-es is important when considering both their fu-ture production and the utilization of products based on them. Therefore, the biodegradation of two EffNet microcelluloses, VTT fine MFC and P-2 MFC (produced at laboratory scale), was studied according to OECD test methods commonly used in chemical testing. The ready biodegradability was determined according to OECD 301 B Ready Biodegradability CO2 Evolu-tion (Modified Sturm Test) measuring CO2 pro-duced during the test (28 days). The criterion of ready biodegradability is 60% ThCO2 within 10 days. Based on the results, VTT fine MFC is readily biodegradable. P-2 MFC did not reach the criterion for ready biodegradation, but can be considered as rapidly biodegradable. The difference in the biodegradability was proba-bly due to the finer structure of VTT fine MFC.

The most critical product safety, environmen-tal efficiency and regulation challenges of MFC production and its use were identified in a pre-study “Environmental management and sustainable use of nanocellulose”. The Finn-ish national study was jointly conducted by the EffNet programme of the Forest Cluster/Finnish Bioeconomy Cluster (FIBIC) and the Measuring, Monitoring and Environmental as-sessment (MMEA) programme of the Cluster for Energy and Environment (CLEEN). In the study, information needs and possible obsta-cles to utilization of nanocelluloses were iden-tified. The main issues identified were the lack of and confusion over regulation for nanoma-terials; risk for over-regulation, especially for natural, unmodified materials; and challenges in the communication chain. However, pro-ac-tive regulation was found to be a possible tool. The report “Piecing together research needs: safety, environmental performance and regu-latory issues of nanofibrillated cellulose (NFC)” was published in June 2012.

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Guidance documents relevant to the safety of nanomaterials:

• GuidanceManualfortheTestingofManufactured Nanomaterials: OECD’s Sponsorship Programme. First Revision, 02-Jun-2010, Series on the Safety of Manufactured Nanomaterials 25 (2012). Available in Internet (21.12.2012): http://search.oecd.org/officialdocuments/displaydocumentpdf/?cote=env/jm/mono(2009)20/rev&doclanguage=en

• REACHImplementationProjectonNanomaterials (RIPoN) final reports (RIPON2 and RIPON3). Available in Internet (17.12.2012): http://ec.europa.eu/environment/chemicals/nanotech/

• EuropeanChemicalAgency(ECHA).Guidance on information requirements and chemical safety assessment. Available in Internet (8.10.2012): http://echa.europa.eu/guidance-documents/guidance-on-information-requirements-and-chemical-safety-assessment

• EuropeanFoodSafetyAuthority(EFSA).Guidance on the risk assessment of the application of nanoscience and nanotechnologies in the food and feed chain, 10 May 2011. EFSA Journal 9(5): (2011) 2140, 36 pp. DOI:10.2903/j.efsa.2011.2140 Available in Internet (21.12.2012): http://www.efsa.europa.eu/en/efsajournal/pub/2140.htm

• U.S.FoodandDrugAdministration(FDA).DraftGuidance for Industry: Assessing the Effects of Significant Manufacturing Process Changes, Including Emerging Technologies, on the Safety and Regulatory Status of Food Ingredients and Food Contact Substances, Including Food Ingredients that are Color Additives. Available in Internet (8.10.2012): http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredientsandPackaging/ucm300661.htm

• U.S.FoodandDrugAdministration(FDA). Draft Guidance for Industry. Safety of Nanomaterials in Cosmetic Products. Available in Internet (8.10.2012): http://www.fda.gov/Cosmetics/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/ucm300886.htm

4.3 Processability and preservability of microcelluloses

Pumping and mixing characteristics of microfibrillated celluloseThe objective of this study was to clarify the behaviour of MFC grades in mixing and pump-ing through pipes. It was found that mixing of MFC (into pulp) is difficult with a tradition-al tank mixer. Due to the shear thinning flow behaviour of MFC a fluidized cavity is formed around the impeller, while the material near the tank walls remains stationary. With the tested centrifugal pump, the characteristic curves of MFC grades were identical to those of water, but, due to the high loss in MFC flow, there was an upper limit to the consisten-cy at which centrifugal pumps may be used. Screw pumps, on the other hand, are favour-able when pumping high-consistency MFC at low or moderate flow rates, as shown by the red patch in Figure 7.

In a pipe flow, MFC has two distinct flow re-gimes. At low flow rates, MFC undergoes lami-nar, shear thinning flow with high energy loss as compared with water flow. At high flow rates the flow of MFC is very similar to turbu-lent water flow, i.e. it is in fluidized state, as il-lustrated by the green patches in Fig. 7. Due to various flow-induced instabilities that may be present in the shear thinning flow, the fluidized regime is preferable while pumping MFC with a centrifugal pump. Thus the experimental data presented here provides a simple tool in de-signing pipe flow systems for MFC.

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Preservability of microfibrillated celluloseExperimental laboratory and semi-pilot scale studies were carried out to evaluate the pre-servability properties of microfibrillated cel-lulose and to demonstrate the effects of ma-terial spoilage on its quality and usability. The main focus was to study the effects of MFC spoilage in papermaking applications. At start-up, the batch of VTT coarse MFC used in the study was clean (aerobic and anaerobic bacte-ria counts were less than 10 cfu/ml); the batch was then contaminated by diluting it with pro-cess water to 1% consistency.

The results indicate that microbes can eas-ily utilize MFC as a nutrient. Microbial activi-ty caused spoilage of MFC within a few days of storage. This spoilage can be detected as changes in chemical parameters (e.g. pH and redox potential drop) as well as increase in mi-crobial counts (Figure 8). The spoilage of MFC directly affected its performance: phenome-na such as dewatering and bonding were af-fected, causing deterioration in viscosity and strength properties.

Biocide treatment can inhibit the microbi-al growth. However, the recovery of spoiled MFC using biocides is difficult. Therefore, good

housekeeping, including storage and trans-portation, as well as a carefully planned bioc-ide strategy should be applied to ensure opti-mal performance for MFC.

Laboratory-scale processability of MFC at various consistenciesInformation on the laminar, mixed, or turbulent suspension flow behaviour is typically used as initial data for equipment design and process engineering. To that end, MFC and kraft pulp mixing and turbulence tests were performed. The measurements were carried out with a medium-consistency laboratory mixer. The re-lationship between power consumption and rotor speed provides the basis for determin-ing the processability of MFC. Mill-produced northern SW kraft pulp (NBSK) was used as a reference pulp for the measurements. In the MFC tests, VTT coarse and VTT fine MFC grades were used as the raw materials.

In the tests, each sample exhibited three dis-tinct phases: laminar flow with minor pow-er dissipation at low speeds, mixed flow with temporal fluctuations at moderate speeds, and finally a turbulent flow with high power dissipation at high speeds. The power dissipa-tion increases with increasing consistency. At 1% consistency, both MFC and SW kraft pulp

Figure 7. Operating window graph showing pref-erable flow rates and pump types.

Figure 8. Evolution of redox potential (continuous on-line data), anaerobic bacteria count (samples), and filtration time (samples) during the preserv-ability trial of VTT coarse MFC.

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behave like water but, already at 2% consist-ency, the power dissipation in MFC is higher than in the pulp. At 3% consistency, the differ-ence between MFC and SW pulp is clear (Fig-ure 9). MFC requires significantly higher ener-gy in the mixing process than SW kraft pulp (50% more at 3% consistency), and there is no major difference between the VTT coarse and VTT fine grades. Moreover, after the suspen-sion has been mixed using high dissipation en-ergy, the suspension properties are equal to those of pulp.

Dynamic rotational rheometer as a tool to identify and characterize MFC suspensionsMFC as a heterogeneous fibre material is chal-lenging to characterize with conventional dy-namic rotational rheometers. MFC also has a tendency to flocculate depending on, for ex-ample, the flow conditions. As such, measur-ing its rheology must be performed carefully, as many errors may occur during measure-ment, such as wall slip or wall depletion, shear localization, or other heterogeneities in the flow profile. These phenomena are a problem in flow measurements, in particular. To study and overcome these problems, different im-

aging methods were combined with rheome-try. Firstly, the floc structure in different shear conditions was studied by photographing the suspension under shear. The results showed that the floc size is dependent on the flow rate above the apparent yield stress of the mate-rial. On the other hand, certain polymers can be used to prevent flocculation, whereas ex-cess ions in the suspension enhance floccula-tion, in a similar manner to pulp suspensions. Secondly, in collaboration with VTT, optical co-herence tomography (OCT) was employed to analyse the flow in the rheometer gap. These studies revealed the occurrence of wall deple-tion, which has to be taken into account when analysing the rheological data from this kind of measurement. Contrary to flow measure-ments, the oscillation measurements are not as prone to wall depletion, since the materi-al is analysed at very low stresses and defor-mations. Oscillation measurements, such as amplitude sweep or frequency sweep, proved to be a good characterization method for the MFC suspensions, giving information about the gel strength of different kinds of MFC sus-pensions. An example of this is given in Figure 10, where different size fractions of the same

Figure 9. Power consumption of MFC and NBSK at 3% consistency as a function of mixer rpm.

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MFC (VTT coarse MFC) give different storage moduli, which can be considered as the gel strength of the material. The finest fraction had the highest storage modulus, whereas the coarsest fraction had the lowest storage mod-ulus. This can be attributed to the denser net-work of fibrils in the finest suspension.

Models for the rheology of MFC suspensionsTraditional continuum rheological models are suitable when simulating the steady-state flow of complex fluids, which can exhibit, for example, shear thinning, shear thickening or yield stress. However, these models offer no information on more complex flow behaviour, such as thixotropy, rheopexy, or other flow transients. More advanced structural models have to be used to describe the real physical microscopic processes underlying these mac-roscopically observed rheological phenomena. Of such models, a colloidal aggregation model was used to simulate the flow of MFC suspen-sions under various conditions. In this model, the collisions of particles lead to growth of ag-gregates, thus increasing the flow resistance, i.e. viscosity. Forcing the flow, on the other hand, tends to break the aggregates, thus de-creasing the viscosity. Using the model, an ad-equate reproduction of experimental rheology data measured for MFC was obtained (Figure 11a). A plausible reason for the differences be-tween the model and the experiments may be heterogeneous shearing during the ex-periments, which was not explicitly taken into account in the model. To that end, the model was solved in conjunction with a flow solution in the Couette geometry, and the results indi-cate that the heterogeneous flow can indeed cause problems in the experimental setting.

During the shear transients, the aggregation model showed stress overshoots (Figure 11b). These transients are typical for viscoelastic fluids, and the origins of such a phenomenon were traced to the delayed response of the ag-

gregate size distribution. This clearly demon-strates that the time-dependent behaviour of these unstable suspensions can be easily con-fused with an elastic response of the material. However, the difference between the two cas-es, although both appear during shear tran-sients, is from the model point of view clear. In the experiments it might be difficult, or even impossible, to distinguish between the two.

The role of MFC swelling in the rheology and dewatering of high-consistency furnishesThe studied microfibrillated cellulose suspen-sions and furnishes were evaluated in the con-sistency ranges of 1–2%, 3%, and 5–15% with the Åbo Akademi gravimetric dewatering de-vice (ÅA-GWR) and MCR 300 rheometer ac-companied with and an immobilization cell (IMC). The furnish composition was 70% fill-er, 20–30% VTT coarse MFC or P-2 MFC, and 0–10% cellulose fibres. All labels followed the notation: ratio of pigment / ratio and type of MFC / ratio of pulp / consistency. The surface charge of the fibrillated cellulose was found to influence the rheological and dewater-ing properties of the evaluated suspensions and furnishes due to its impact on swelling and effectively bound water; the higher sur-

Figure 10. Frequency sweep for the VTT coarse MFC suspension and its fractions at a concen-tration of 0.5% (weight/weight). G’ is the storage modulus and G’’ the loss modulus.

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face charge of P-2 MFC resulted in lower stor-age modulus (G`) and higher WRV due to the more swollen fibrillated cellulose particles. The flow curves of both the VTT coarse MFC and P-2 MFC suspensions and furnishes showed a gel-like structure and shear thinning behav-iour, and had a high yield stress. All the fur-nishes showed shear thinning behaviour with the power law exponent n ≈ -1; the actual fit-ted exponents varied between -1.02 and -0.94. The yield stress, as an indicator of the floccu-lated network strength, was found to increase with the consistencies, following the increase in elastic moduli (G`), which indicated a gel-like strongly flocculated matrix of VTT coarse MFC and P-2 MFC.

Complex systems, such as the materials used in this study, i.e. microfibrillar and nanofibrillar cel-luloses as well as colloidal particulates, undergo multiple structural configurations during dewa-tering. A modified method for determination of immobilization times was developed. The meth-od is based on a rheological analysis, adopt-ing the rate of change in viscoelastic loss factor (tan δ) over time, as first and second zero of d (tan δ). It was shown that it is possible to char-acterize the immobilization of these materials (VTT coarse MFC and P-2 MFC) without a direct measure of MFC surface swelling. Information

on the rheological properties of high-consist-ency microfibrillated cellulose (VTT coarse MFC and P-2 MFC) based furnishes can be utilized for improving dewatering. It was found that when the studied furnishes were dewatered under vacuum conditions, the final solids content was increased with the application of shear, which was applied between oscillation intervals with the application of vacuum dewatering. The im-plementation of rotation cycles between oscil-lation vacuum cycles was found to increase the final solids content of the samples. Complex vis-cosity (λ*) in an oscillation cycle had a non-linear dependency on the solids content of the furnish cake, shear thinning during the rotation interval, shearing history in previous oscillation cycles, and the Weissenberg effect (Figure 12). A minute difference in final solids content was obtained with respect to the MFC type and the presence of cellulose fibres (Figure 13).

4.4 Dewatering of microcelluloses

Forming and dewatering analysis with the Moving Belt FormerThe target of this study was to show how mi-crofibrillar cellulose and fines material from TMP pulp affect forming and dewatering of mechanical pulp furnishes. A dynamic form-

Figure 11 a) The steady shear rheology of MFC water suspensions with different concentrations as re-ported in experiments (dots) and predicted by the model (lines). b) The transient shear response of the model showing stress overshoots related to the delayed response of the aggregate size distribution.

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ing device, the Moving Belt Former (MBF), was used to form the sheets under pulsating vac-uum dewatering. An important research ques-tion was how fibrillated celluloses and fines interact during vacuum-assisted pulsating de-watering.

The furnish components were TMP long fibres mixed with different amounts of TMP fines (0, 10 and 20%) and MFCs (VTT coarse and fine, 1 and 3%). The retention components and ad-ditives used were cationic-PAM (7 mil. g/mol 1meq/g , 600 g/t, added 10 s prior to dewater-ing) and starch (Raisamyl 50021, addition 1% from dry matter). A fractional factorial design with 34 trial points was carried out.

The following measurements were taken dur-ing the forming process: dry solids after form-ing, total retention, vacuum levels during forming, surface level curves from the forming chamber (dewatering speed), dewatering time (both initial and high-vacuum dewatering) and apparent thickness of the wet fibre mat.

The effects of different factors on dewatering time are summarized in Table 4.

Effect of papermaking additives and fines on dewateringThe objective of this set of experiments was to clarify how different types of MFCs affect drainage when different papermaking addi-tives are present in the system. The main fo-cus was on studying how the amount of fines affects dewatering when MFC is used in com-bination with different retention aids. De-watering was studied with the Åbo Akademi Gravimetric Water Retention (ÅAGWR) and Dy-namic Drainage Analyser (DDA) devices. With the ÅAGWR device, the purpose was to eval-uate how different MFC properties influence water holding capacity and how the addition of different polyelectrolytes affects this. In ad-dition, the effect of fines on dewatering was studied. With the DDA device, the purpose was

Figure 12. Development of dynamic and complex viscosities during measurement of 5% consistency P2-MFC-furnish without cellulose fibres, subjected to a rotation rate of 200 s-1 during the CSR cycle.

Figure 13. Solid content increase, ∆λ, for different dewatering schemes vs. shear rates in CSR inter-vals 0, 40 and 200 s-1, and the flow index K for all furnishes.

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to study how dewatering of the pulp changes when different MFCs are added to the system in the presence of polyelectrolytes and fines.

Dewatering of the MFC was significantly changed when different polyelectrolytes were added to the MFC suspension. With low mo-lecular weight cationic polyelectrolyte, dewa-tering of the MFC was improved, while addition of high molecular weight polyelectrolyte led to deteriorated drainage, the biggest effect being observed with high molecular anionic polyelec-trolyte. The amount of fines also had a signif-icant effect on dewatering: as the amount of fines increased, pulp dewatering deteriorated significantly (Figure 14a). In addition, the MFC grade used had an effect on dewatering. The more refined VTT fine MFC deteriorated dewa-tering to a large extent, whereas the less re-

Factor Initial dewatering High vacuum dewatering

Fraction of long fibres increases Decrease (---) Slight decrease (-)

Fraction of TMP fines increases Increase (+++)

Amount of added CPAM increases Slight decrease (-)

Interaction of fines x MFC amount Clear increase (++)

Interaction of fines x starch Slight increase (+)

Table 4. Effect of different factors on dewatering time.

Figure 14. Effect of a) MFC amount and fines content and b) addition of CPAM on dewatering.

fined VTT coarse MFC had no significant ef-fect on dewatering. The effect was emphasized when a higher amount of fines was present in the pulp. Dewatering of the pulp could be im-proved by adding high molecular weight cati-onic polyacrylamide (CPAM) (Figure 14b). When the amount of MFC increased, a higher amount of CPAM was also needed to improve dewater-ing, especially with the more refined VTT fine MFC grade.

5. Exploitation plan and impact of results

Micro- and nanocelluloses are among the most important developments in the forest cluster in recent years. Current research in this field is vast and conducted mostly outside of the pre-

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sent programme. As companies begin com-mercializing these products, issues of product safety, environmental efficiency, regulato-ry challenges and the need for standardiza-tion are becoming centre stage. Knowledge of the general properties of microcelluloses and suitable characterization methods will help the industry to plan its own analytical pro-cedures. Harmonized viscosity and transmit-tance measurements are ready to be used for quality control purposes. This programme has created several new networks, both national and international, to support these themes. Understanding the rheological properties of microcellulose suspensions and their process-ability and dewatering characteristics will help in up-scaling unit operations and in designing industrial processing.

The manufacturer is always responsible for the safety of its products. The product safe-ty information gathered here helps companies to plan and realize appropriate and sufficient safety testing programmes for their future products, and could thus accelerate the place-ment of future products on the market.

6. Networking

The research was carried out jointly by re-search organisations and Finnish forest clus-ter companies. Table 5 presents the research partners and their roles.

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Table 5. Partner organisations and their research roles.

Role

Production of EffNet microcelluloses and their

basic characterization, product safety aspects of

microcelluloses, organizing the harmonization of

viscosity and transmittance measurements, start-

up work for standardization, assessment of safety

aspects of microcelluloses, engineering studies on

the flow behaviour, pumping, mixing, and storage

of MFC suspensions

Participation in the activities for harmonization of

viscosity and transmittance measurements

Participation in the activities for harmonization of

viscosity and transmittance measurements, parti-

cipation in biodegradability and toxicity testing

Method development and fractional analysis of

EffNet microcelluloses

X-ray scattering and microtomography measure-

ments of cellulose samples

SEM imaging of EffNet microcelluloses, production

of MCC and MRC samples, method development

and characterization of MCC and MRC samples,

participation in the activities for harmonization of

viscosity and transmittance measurements

Laboratory-scale processability of MFC at various

consistencies

Rheology and flocculation of MFC suspensions at

low concentrations

Aggregation models of MFC suspensions

Forming and dewatering analysis with the Moving

Belt Former

Dewatering methodology of high consistency

furnishes

Partner

VTT Technical Research Centre of Finland

Stora Enso

UPM

University of Oulu,

Fibre and Particle Engineering Laboratory

University of Helsinki,

Department of Physics

Kemira

Andritz Oy

Aalto University, Polymer Technology

Aalto University,

Complex systems and Materials

Aalto University,

Paper Converting and Packaging

Aalto University,

Bio-based Materials Technology

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7. Publications and reports

Scientific journals:

Leppänen, K., Pirkkalainen, K., Penttilä, P., Sievänen, J., Kotelnikova, N., Serimaa R., Small-angle x-ray scattering study on the structure of microcrystalline and nanofibril-lated cellulose. Journal of Physics: Conference Series, 247 (2010):012030, doi:10.1088/1742-6596/247/1/012030.

Mohtaschemi, M., Karppinen, A., Saarinen, T., Puisto, A., Lehtinen, A., Illa, X., Alava, M., Shear Banding and Colloidal Models, Annual Transactions of the Nordic Rheology Society 20 (2012):113-116.

Puisto, A., Illa, X., Mohtaschemi, M., Alava, M.J., Modeling the viscosity and aggregation of sus-pensions of highly anisotropic nanoparticles, Eur. Phys. J. E 6 (2012) 35:

Puisto, A., Illa, X., Mohtaschemi, M., and Ala-va, M.J., Modeling the viscosity and aggre-gation of suspensions of highly anisotrop-ic nanoparticles, Nordic Pulp Paper Res. J. 27(2):277-281 (2012).

Rämänen, P., Penttilä, P.A., Svedström, K., Maunu, S.-L., Serimaa, R., The effect of dry-ing method on the properties and nanoscale structure of cellulose whiskers. Cellulose 19(3):901-912, 2012.

Saarinen, T., Karppinen, A., Seppälä, J., Evolu-tion of Floc Structure as Function of Time. An-nual Transactions of the Nordic Rheology So-ciety 20 (2012): 113-116.

Book chapters:

Kangas, H., Cellulose nanofibrils – a material with unique properties and numerous poten-tial applications. In: Production and Applica-tions of Cellulose Nanomaterials. M.T. Postek, R. Moon, M. Bilodeau, A. Rudie (Eds.), June 2013. Accepted.

Pitkänen, M., Kangas, H., Vartiainen, J., Chap-ter 12. Toxicity and health issues. In: Handbook of Green Materials; Processing Technologies, Properties and Applications. Vol 1. Bio Based Nanomaterials: Separation Processes, Char-acterisation and Properties. Accepted.

Conference presentations/posters:

Forsström, U. and Hellén, E., Finland’s opin-ion: Standardization of micro- and nanocellu-loses. Oral presentation in Workshop on Inter-national Standards for Nanocellulose, June 9, 2011, Washington DC (Arlington VA), USA.

Forsström, U. and Harlin, A., International co-operation for the standardization of nano-scale cellulose materials. Oral presentation in 2011 TAPPI International Conference on Nano-technology for renewable Materials, June 6-8, 2011, Washington DC (Arlington VA), USA.

Jäsberg, A., Gorshkova, E., Kiuru, J., Kouko, J., Lampinen, H., Liukkonen, J., Luukkainen, V.-M., Tukiainen, P., Salmela, J., Syrjänen, J., Process-ability of nanocelluloses. Oral presentation in EffFibre&EffNet Seminar 2012, Nov. 20, 2012, Helsinki.

Jäsberg, A., Kouko, J., Luukkainen, V-M., Salmela, J., Processability of microfibrillated cellulose. Proceedings of Papercon 2012. Tap-pi, Apr. 22 – 25, 2012, New Orleans, LA, USA.

Jäsberg, A., Kouko, J., Luukkainen, V.M., Pro-cessing of nanocellulose. Poster presentation in Forestcluster Ltd’s Annual Seminar 2011, No-vember 16, 2011, Helsinki.

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Laitinen, O., Niinimäki, J., Fractional analysis and characterization of microfibrillated cellu-lose. Accepted for oral presentation in 2013 Tappi International Conference on Nanotech-nology for Renewable Materials, June 24-27, Stockholm, Sweden.

Leppänen, K., Lucenius, J., Immerzeel, P., Mel-lerowicz, E., Fagerstedt, K., Saranpää, P., Seri-maa, R., Effect of moisture on cellulose structure in juvenile hard- and softwood as revealed by X-ray diffraction. Oral presentation in COST Action FP0802 Workshop “Wood Structure/Function-Re-lationships”, Oct. 5-8, 2010, Hamburg, Germany.

Leppänen, K., Peura, M., Kallonen, A., Pent-tilä, P., Lucenius, J., Sievänen, J., Sneck, A., Serimaa, R., Characterization of nanofibrillat-ed cellulose samples using x-ray scattering, microtomography, scanning and transmission electron microscopy. Oral presentation in 2010 TAPPI International Conference on Nanotech-nology for the Forest Products Industry, Sept. 27 – 29, 2010, Espoo, Finland.

Kangas, H., Pitkänen, M., Laitinen, O., Niinimä-ki, J., Amount, characteristics and safety of na-no-scale cellulose fibrils. Accepted for oral pres-entation in 2013 Tappi International Conference on Nanotechnology for Renewable Materials, June 24-27, Stockholm, Sweden.

Kangas, H., Nanoselluloosa – Mahdollisuuk-sien materiaali. Kemian päivät, March 21, 2013, Helsinki.

Kangas, H., Pitkänen, M., Sneck, A., Tanaka, A. and Forsström, U., Assessing the charac-teristics and safety of nanocellulose – con-sensus and co-operation on national, Europe-an and international level, Oral presentation in 2012 Tappi International Conference on Nano-technology for renewable materials, June 4-7, 2012, Montreal, Canada.

Kangas, H., Pitkänen, M., Hellén, E., Micro- and nanofibrillated celluloses – Characteriza-tion, classification and safety. Poster presen-tation in Forestcluster Ltd’s Annual Seminar 2011, November 16, 2011, Helsinki.

Peltonen K., Vehmaa J., Henriksson, A., and Tirri, T., Laboratory scale processability of na-nocellulose in various consistencies, compar-ison to bleached softwood kraft pulp. Poster presentation in EffFibre&EffNet Seminar 2012, November 20, 2012, Helsinki.

Pitkänen, M., Kangas, H., Current views on na-nocellulose product safety. Poster presenta-tion in EffFibre&EffNet Seminar 2012, Nov. 20, 2012, Helsinki.

Pitkänen, M., Vartiainen, J. Kapanen, A., Health & environmental safety aspects of na-nofibrillated cellulose. Oral presentation in COST FA0904 International Workshop “Novel nanostructured polymeric materials for food packaging and beyond”. September 15-16, 2011, Espoo, Finland.

Serimaa, R., Cellulose nanostructures in wood cell wall and in wood based materials. Invit-ed talk in ACS Spring meeting, April 7-11, 2013, New Orleans, USA.

Serimaa, R., Nanocomposites of natural pol-ymers. Oral presentation in Workshop ‘Soft matter physics and complex flows’, May 22-24, 2012, Lofoten.

Sneck, A., Lahtinen, P., Viscosity measure-ment – a valuable tool for routine quality con-trol of fibril cellulose. Accepted for oral presen-tation in 2013 Tappi International Conference on Nanotechnology for Renewable Materials, June 24-27, Stockholm, Sweden.

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Sneck, A., Pitkänen, M., Kangas, H., Tammelin, T., Hellén, E., New approach to classification of cel-lulose fibrils and suitable methods for their char-acterization. Oral presentation in COST FA0904 International Workshop “Novel nanostructured polymeric materials for food packaging and be-yond”. September 15-16, 2011, Espoo, Finland.

Sneck, A., Pitkänen, M., Kangas, H., Tamme-lin, T. and Hellén, E., New approach to classifi-cation of cellulose fibrils and suitable methods for their characterization. Oral presentation in 2011 Tappi International Conference on Nano-technology for Renewable Materials, June 6-8, 2011, Arlington, VA (Washington, DC), USA.

Sorvari, A., Puisto, A., Mohtaschemi, M., Lehtinen, A., Saarinen, T., Jäsberg, A., Seppälä, J., Alava, M.J., Characteristics of microfibrillated cellulose. Poster presentation in EffFibre&EffNet Seminar 2012, Nov. 20, 2012, Helsinki.

Sorvari, A., Saarinen, T., Seppälä, J., Time de-pendent rheology of MFC. Poster presentation in BioEnvironmental Polymer Society Annual Meeting, Sept. 18-21, 2012, Denton, Texas, USA (Best student poster award).

Vartiainen, J., Kunnari, V., Kaljunen, T., Tamme-lin, T., Backman, U., Vikman, M., Pitkänen, M., Kangas, H., Roll-to-roll production of nanofibril-lated cellulose films for food packaging applica-tions. Poster presentation in 5th International Symposium on Food Packaging Scientific Devel-opments Supporting Safety and Innovation, ILSI Europe, Nov. 14 – 16, 2012, Berlin, Germany.

Vartiainen, J., Pitkänen, M., Lahtinen, P., Kaljunen, T., Kunnari, V., Kangas, H., Vikman, M., Salminen, A., Tammelin, T., Nanofibrillat-ed cellulose films - environmentally safe al-ternative. International workshop, COST Ac-tion FA0904, Development of new safe PNFP, Workshop WG1, 7 - 8 February, Prague, Czech Republic, Book of Abstracts (2013), 20.

Thesis:

Jarovisky, M., Wet pressing strategies for mi-crofibrillated cellulose based furnishes, Bioma-terials Technology, Aalto University, Feb. 2012.

Liljeström, V., Kuituverkon rakenteiden orien-taation tutkiminen röntgenmenetelmin. Mas-ter’s thesis, Department of Physics, University of Helsinki, 28. 5. 2012.

Svedström, K., Hierarchical structure and dy-namics of plant cell wall studied using x-rays. PhD thesis, Department of Physics, University of Helsinki, 2. 5. 2012.

Public reports:

Lähtinen, K., Pitkänen, M., Valve, H., Jouttijär-vi, T., Kangas, H., Kautto, P., Koskela, S., Leski-nen, P., Silvo, K., Tukiainen, P., Piecing together research needs: safety, environmental perfor-mance and regulatory issues of nanofibrillated cellulose (NFC). CLEEN Ltd. Research report no D2.5.2. Helsinki, 2012. http://www.ymparisto.fi/download.asp?contentid=139228&lan=fi

Kangas, H., Nanoselluloosa – Mahdollisuuk-sien materiaali. In: Työelämäyhteyksiä vah-vistamassa insinöörikoulutuksen satavuotis-juhlaviikolla. Mustonen, A. (toim.). Tampereen ammattikorkeakoulun julkaisuja. Erillisjulkaisu. Tampere, 2013. ISBN 978-952-5903-31-7(PDF), 102-109. http://www.tamk.fi/cms/kirjasto.nsf/pages/tamk_julkaisut.html

Kangas, H. Soveltajan opas mikro- ja nano-selluloosille, Espoo, 2012. http://www.jklin-novation.f i/default/?__EVIA_WYSIWYG_FILE=5350&name=file

rESOUrcE-EffIcIENT

PAPErmAkINg

c o n tac t p e r s o n

Juha Salmela, juha.salmela@vtt.fi

pa r t n e r s

VTT

Aalto University

Metso Paper

University of Jyväskylä

90

This research was aimed at achieving radical improvements in the resource efficiency of papermaking. Specifically, the goals were to reduce paperma-king raw material consumption by 25% and to improve the energy, water and raw-material efficiency of paper- and board-making processes. Novel production concepts for printing paper, fine paper and for board grades were developed and demonstrated. All concepts show good potential for impro-ving resource efficiency and profitability. In all cases, the research was done from laboratory scale to pilot scale and end products were tested for all relevant properties, including print quality where necessary.

Optimal use of raw materials is key to the global competitiveness of the Finnish papermaking industry. Reduced basis weight, increased filler content, and optimized dewatering offer the potential to decrease product costs and improve product properties significantly. The cost savings of the printing pa-per concept were calculated to be ~23% and the use of advanced fillers may improve this further. An optimized dewatering profile will save energy in the forming, press and in drying sections. The cost savings for a typical LWC pa-per machine between traditional and optimized dewatering are around EUR 500,000 per year for the dryer section alone, representing ~0.3% of total production costs with a 1.5% increase in dryness after the press section.

AbstRACt

Keywords:Resource efficiency, printing paper, board, layering, dewatering, fillers

91

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1. Background

This part of EffNet programme is focused on radical improvement of the resource efficien-cy of papermaking. The main goals are to re-duce papermaking raw material consumption by 25% and to improve the energy, water and raw-material efficiency of paper- and board-making processes. Traditionally, paper has been sold by weight, but future paper pricing will change from weight- to area-based. Area-based pricing enables production of lighter pa-per or board grades that meet current paper demands. This, together with increased use of novel fillers, will enable radical savings in ma-terial costs. Future paper and fibre compos-ite products will involve much more sophisti-cated integration of mineral and fibrous and polymeric material compared to today’s filled papers. Savings will also come from optimiz-ing de-watering and from reduced drying and pumping costs. Another important goal is to find optimal means for forming section and press section cooperation. Improved dryness after the press section requires optimization of the forming section de-watering profile so that paper solid content is maximized after press section. Modelling of these processes is also included in this study.

2. Objectives

The main goal is to reduce raw material con-sumption by 25% and to improve the energy, water and raw-material efficiency of paper-making processes. For fine paper grades, the goal is to find a viable solution to increase fill-er content by 5% (thus reducing variable costs by 10%) and to integrate inorganic components and organic material to produce novel fillers. Together with these goals, product properties should also be either retained or improved. This calls for the development of new raw materi-al concepts, advanced web forming techniques

and novel surface treatment methods that will provide the functional product properties re-quired for the existing marketplace of consum-er applications with radically less material. The main research topics and their motivation are:

• Fractionationandlayeringoffibres •stifffibrestoproducebulkylayer •finesforsmoothprintingsurface• Optimizeddewateringandretention• Novelfillerparticles• Optimizationofsurfaceandprinting

process

3. Research approach

The project utilized a unique research chain in which the initial research hypothesis was first demonstrated and then improved at VTT’s re-search laboratories. The laboratory-scale re-sults were verified in VTT’s SUORA environ-ment and produced samples were calendered (Metso / Kemira), finished (VTT, Espoo) and printed (KCL). From each of these unit pro-cesses feedback was collected and new reci-pes and technologies were tested at the labo-ratory scale before the next pilot-scale round. Up to five test loops were required to achieve a good-quality novel printed paper product from KCL pilot printing tests.

Material efficiency was achieved by reducing LWC paper grammage by using stiff, long-fibre TMP furnish to produce bulky base paper and by replacing LWC coating with layering of TMP fines on the surface of the bulky base paper at the end of the forming section.

Developing the binding of MFC-PCC aggregates and starch-based biominerals raises the pos-sibility to increase the filler content of papers. The research hypothesis for high-binding fillers was that they have better filler and MFC reten-tion and high shear resistivity. The optimal ag-

93

gregate size distribution was studied to obtain sufficient strength and printing properties. The developed new material combinations also of-fer possibilities outside paper applications.

To study dewatering efficiency, an improved version of the laboratory-scale experimen-tal 1D filtration device was developed. Using this method, it is possible to determine opti-mal dewatering conditions in terms of ener-gy consumption (i.e. water removal efficiency) for different furnish types. Experiments with a dynamic wet pressing simulator indicated that increased solid content achieved using opti-mal initial dewatering conditions remains also after wet pressing. Based on the filtration re-sults, a novel phenomenological model for the time-evolution of sheet flow resistivity during filtration was developed.

At the University of Jyväskylä, a two-phase (water + fibre) volume-averaged model for the filtration of fibre suspensions has been devel-oped. The model includes a novel viscoelastic sub-model for structural stress in the consoli-dating fibre network. The model was first ap-plied to simulation of dewatering in the wet pressing section of VTT’s SUORA environment with relatively accurate results. Secondly, the model has been used for simulating fibre con-solidation in VTT’s fibre suspension filtration device, resulting in plausible estimates of the dynamic behaviour of the fibre suspension.

The filtration device itself has been improved such that it can be used to accurately deter-mine parameters for the model. The modifica-tions include, e.g., fitting a new set of ultrasound Doppler anemometer sensors and refurbished control and analysis software. The device can now produce repeatable experimental results on the temporal evolution of local velocity, vol-ume fractions and stresses of fibre and liquid phases inside the consolidating network during the filtration process. This provides significant-

ly better possibilities for validating dewatering models than the conventional methods based on measuring various bulk properties (e.g. total pressure loss and average volume fraction of fi-bres in a filtrated cake).

4. Results

4.1 Dewatering modelling and efficiency

Filtration models for fibre suspension in the paper machine former section have to include the effects of air in addition to fibres and water. Thus, a three-phase (water+fibre+air) model has been developed. The model has been for-mulated as a generalization of the two-phase model, such that model parameters found in the filtration device could be exploited as much as possible. The model developed by the Uni-versity of Jyväskylä has been successfully used for simulating fibre consolidation in VTT’s fibre suspension filtration device (Figure 1). Knowledge gained from the laboratory experi-ments was successfully applied in VTT’s SUO-RA environment to develop an optimal initial dewatering profile for maximizing solids con-tent after the press section. Overall, our new concept can be used for improving the effi-ciency of the forming and press sections. The detailed results have been published by Ko-ponen et.al (PaperCon, 2012).

The effect of vacuum profile on dewatering ef-ficiency was studied using a modified filtration device. Figure 2 shows how an optimal dewa-tering profile can be found for any paper fur-nish at the laboratory scale. Dewatering was shown to be up to three times more efficient after optimization.

Dewatering profile can be expressed as the to-tal impulse of the vacuum on the web. Figure 3 shows at pilot scale how an optimal dewatering

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Figure 2. Left: Water removal efficiency E of LWC furnish for different dewatering profiles. Here efficien-cy E=C/Wend where C is final sheet consistency and Wend is the total pressure work during the filtration process. Right: An example of a measured and modelled time-evolution of the paper sheet resistivity K during the filtration process. The water flow rate v through the sheet is v=P/Kb, where P is pressure loss, b is basis weight and K is resistivity (Filtration device, LWC furnish, grammage 80 g/m2).

Figure 3. Left: Impulse on the fourdrinier forming board and total impulse on the forming section to-gether with the consistency after the forming section for different dewatering profiles. Right: Solid con-tent after the press section for different dewatering profiles. The results resemble those acquired at the laboratory scale: the highest pressure impulse does not necessarily give the highest dewatering effi-ciency (SUORA environment, OCC furnish, grammage 90 g/m2).

Figure 1. Fibre pathlines in a filtration experiment where the flow has been stopped between 8.5 and 12.5 s. Solid lines represent measured results; dashed lines are given by the mathematical model. Colours represent the pathlines of fibres from different initial positions.

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pressure profile and impulse gives the highest solid content also after the press section.

In the SUORA dewatering trials it was found that addition of MFC decreases the initial de-watering rates (as indicated by many labora-tory-scale tests), but as the solid content in-creases in the forming section MFC actually improves dewatering and increases the final solid content after the forming section and press section (see Figure 4).

4.2 Novel printing paper

In the novel printing paper study, the poten-tial of the layered structure concept to achieve the assigned target of 25% raw material sav-ings was investigated. Initially, TMP pulp was separated into fines and coarse fractions. The base paper was produced from the coarse frac-tions and the surface layers from a mixture of fines and pigments. The coarse furnish of the base paper increased the bulk and the fines smoothened the surfaces to meet the quality demands. The object was to verify the potential of the novel printing paper concept by produc-ing one-side coated reels in the SUORA envi-ronment and printing them at KCL on a heatset web offset (HSWO) printing press. This object

was finally fulfilled at the end of the project. In the concept development, an iterative research process from laboratory scale to pilot produc-tion and printing was employed (Figure 5).

The research was divided into three tasks: base paper recipe, surface layer recipe and surface layer application method. The novel printing paper concept study started with a laborato-ry-scale study of the paper recipe. Based on

Figure 4. Relative web solid content before the hybrid unit for different NFC addition amounts. Values are scaled according to the reference case solids content. Smaller values represent lower solids.

Figure 5. Iterative research process used in the novel LWC concept study.

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the laboratory-scale results, the initial surface layer recipe for the SUORA trial was:

– Base paper 35 g/m2: 95% coarse fraction of TMP & 5% MFC

– Surface 5 g/m2: 60% TMP fines & 40% calcined clay pigment and binder chemicals

One interesting avenue studied was the use of SOS (self-organizing structure) polymers to in-crease surface strength and print quality. The polymers were synthesized from native pota-to starch (Periva, Kokemäki) at VTT Rajamäki. Native potato starch was modified using vari-ous functional groups (acetate group, hydroxy-propyl group, carboxymethyl group and octenyl succinate groups). The emphasis was on low or moderate degree of substitution of the select-ed substituent in order to keep the modifica-tion as simple as possible. Six different water-soluble modified potato starches were selected and synthetized, using know-how and meth-ods developed in other projects. The most suit-able SOS starch at the laboratory scale was se-lected for pilot-scale testing. Selected octenyl succinate starch polymer with a low degree of substitution (0.1) is anionic and hydrophobic and was synthesized as described in the pat-ent application by Kataja et al. (2007) in order to achieve water-soluble derivatives.

SOS polymers were tested with respect to im-proved surface strength. They increased IGT surface strength by over 300% in laboratory-scale tests (Figure 6). At the pilot scale, SOS treatment increased the surface strength by 106% or 41%, depending on the used base pa-per and polymer amount. The amount of pol-ymer was notably lower at the pilot scale to prevent an excessively hydrophobic surface for offset printing. It should be noted that the surface layer recipe was changed during the project, whereas the SOS polymer was not changed. The fundamentals of SOS polymer selection are described by Anttila et al. (2012).

The results showed that surface treatment with SOS polymer also had potential to en-hance print gloss and diminish mottling.

In pilot scale studies, on-line fractionation of the coarse fraction and fines gave good re-sults. Initially, application of fines to the sur-face was done by spraying with tongue-type nozzles. The nozzles are shown in Figure 7.

Paper samples produced with this technique were calendered at Metso Järvenpää and their paper properties were tested. The roughness and bulk behaviour of the novel LWC paper and the IGT strength results are presented in Figure 8.

In the following lab and pilot trials, the focus was on improving the surface properties of the paper. An improved recipe with good surface strength and optical properties was eventual-ly achieved. Cationic starch and SB-latex com-binations gave the best IGT surface strength (Figure 9) and use of GCC together with cal-cined clay gave the most even ink transfer.

The new surface layer recipe:

– Raw materials: 60% TMP fines, 20% calcined clay pigment & 20% carbonate pigment

– Binders: 3% starch & 6% SB-latex of solids content of surface

To further improve surface coverage, the tongue nozzles were replaced with air-atom-izing nozzles. Four reels of the novel printing paper were successfully produced and HSWO printed. Although visual observations of the paper were very promising, SEM images re-vealed the surface layer coverage to be slight-ly uneven (Figure 10). The sprayed particles have filled the pores between the fibres, but have not attached to the fibres. Surface lay-er application, and probably also grammage, need further optimization.

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Figure 6. Effect of SOS polymer on the novel LWC surface strength.

Figure 7. Five tongue-type nozzles in operation during SUORA trials

Figure 8. Left: Roughness and bulk development of the novel LWC paper with sprayed surface during Gekko calendering test. Right: IGT surface strength of the novel LWC compared with the commercial LWC gloss paper. Both surface layer application methods, spraying and water forming, are presented.

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Figure 9. IGT surface strength results of two surface layer recipe optimization series.

Figure 10. SEM images of the novel LWC base paper and layered novel LWC paper.

Table 1. Target and achieved values for critical properties of the unprinted novel LWC paper.

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The achieved paper properties are present-ed in Table 1 together with the target values. The roughness and thickness were almost at the target level in the trial, despite the limit-ed calendering conditions of the narrow web. The tensile, z-directional and surface strength properties of the novel LWC paper are also at acceptable levels. It should be noted, howev-er, that in this trial MFC was not used in the base paper, only cationic starch was added to the coarse fibres as a strength additive. The bending stiffness of the product was relatively low. Optical properties can be improved by us-ing better quality TMP raw material. For bet-ter gloss, optimization of pigment quality is re-quired; varnishing is one option for improving the gloss of the novel LWC paper. Print quality of the novel LWC was general-ly lower compared to commercial LWC gloss. The printed gloss of the novel LWC was sig-nificantly lower and the surface was rougher after printing. The print density was lower due to deeper penetration or greater spread of ink on the novel LWC. Performance of the novel LWC paper web was nevertheless fairly good in printing, with HSWO runnability and print-ability at acceptable levels. The print quality of the novel LWC can be further enhanced by op-timization of surface layer material spreading, adding surface layer on both sides, optimiza-tion of the surface layer recipe, and applying surface varnish after or during printing.

Overall, the layered novel LWC concept seemed to be a potential option for producing printing paper using 25% less raw material and with 15% lower production costs.

4.3 High filler content papers

The aim of this task was to develop the bind-ing properties of fillers by using microfibrillat-ed cellulose (MFC), starch and other bio-based materials. Savings in costs, materials and en-

ergy are striven for by increasing the filler con-tent of the studied paper grades. The research hypothesis is to create mechanically stable and durable aggregates or biominerals that si-multaneously enhance dry and wet strength properties, filler retention and dewatering compared to traditional fillers. By developing the binding MFC-PCC aggregates and starch-based biominerals it is possible to increase the filler content of papers. The new developed material combinations also open up possibili-ties beyond paper applications.

PCC-MFC aggregatesPromising results were achieved using the MFC-PCC aggregates in high filler (40%) con-tent PGW-based SC laboratory handsheets, and also at the semi-pilot scale (KISU envi-ronment). The final content of VTT fine MFC in the sheets was approximately 2-2.5% de-pending on the retention. Calendered sheet dry strength properties, optical properties and predicted printing properties (density, print gloss and wet pick) improved when aggregates were used compared to the reference PCC. The RPA (retention process analyzer) device was used to study the fibre and ash retention and also dewatering of PCC-MFC aggregates in the SC paper furnish. Use of either dispersed or undispersed PCC was observed to be the most important variable affecting both ash reten-tion and fibre retention. With undispersed cat-ionic PCC, both ash and fibre retention were remarkably better than with dispersed anionic PCC. The effect of the PCC-MFC aggregation was slightly negative for retention and uncer-tain with respect to ash retention compared to direct dosage of the same materials to the furnish. With the finest VTT fine MFC ash re-tention was the lowest, and with the roughest P2-MFC ash retention was the best with the tested MFC types. The RPA laboratory-scale tests showed no significant advantages relat-ed to ash and fibre retention from using PCC-MFC aggregates. Furthermore, in the laborato-

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ry handsheet tests no significant improvement in dry strength properties were obtained using PCC-MFC aggregates compared to direct dos-age of raw materials in TMP-based SC paper. Because of these results, a new research di-rection was needed and a larger floc size hy-pothesis was developed in cooperation with VTT and Aalto University.

The semi-pilot trials (KISU environment) were done with on-line PCC-MFC aggregates and starch dosing, which was a different approach to any previous off-line aggregate dosing. With on-line dosing significant improvements were ob-tained in strength properties, ash retention, IGT

surface strength and other relevant papermaking properties (See Figures 11 and 12). The finer VTT fine MFC provided better strength potential than the courser P2-MFC grade, especially Scott Bond and IGT surface strength increased remarkably. The finer MFC has more specific surface area and the potential to form suitable flocs and microfilms between filler agglomerates and fibres.

The SUORA environment pilot-scale trials were run successfully. The main goal of the trials was to verify on-line dosing of aggregates and the benefit of using them when the filler con-tent of SC paper was increased. Possible bottle-necks were also investigated. Based on knowl-

Figure 11. All main properties of printing papers can be improved with the use of filler-MFC aggregates. Results from the KISU environment semi-pilot scale tests. The strength properties are scaled to 30% filler content. MFC dosing amount was ~2.8% of total product.

Figure 12. Left: IGT surface strength WS results for different filler contents; Right: Scott Bond results for different filler contents. The mill reference sample was included in the calendering trials.

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edge from the semi-pilot trials, the selected trial points were chosen for the pilot-scale tests. The long paper rolls were reeled for pilot calendering and heatset web offset (HSWO) printing tests.

All of the most critical properties, i.e. strength, retention, dewatering, formation, smoothness, optical and predicted printing properties, either improved or achieved similar levels compared to the reference PCC in the pilot SUORA trials. In particular, IGT surface strength and Scott Bond improved significantly when aggregates were used. This gives the possibility to raise the filler content from 30% to 40% or even more. No major bottlenecks occurred in the trials.

The high filler content SUORA SC paper reels were pilot-calendered at Metso Paper. The calendered paper rolls were HSWO printed at KCL. These full-scale printed novel SC papers were compared to mill reference paper, which was also pilot-calendered with the same pilot machine and also to commercial production-scale SC paper. The performance of the novel SC papers in HSWO printing was quite good, no breaks or picking occurred and accept-able runnability and printability levels were achieved. No significant differences occurred between the SUORA reference and the aggre-gate trial points in print gloss, printed smooth-ness, print trough, dot gain or print density. Print trough, dot gain and print density were of similar levels compared to the commercial SC paper. Sight mottling and graininess tenden-cies were observed in aggregate trial points in some measured colour areas, but, in general, no significant differences were observed com-pared to the reference samples. Calendering with higher nip pressure reduced the mottling.

4.4 Biominerals An experimental framework for starch-PCC bi-ominerals was built around coprecipitation of calcium carbonate from milk of lime and super-saturated carbon dioxide systems. The work

was conducted at the laboratory scale with a 4-litre adiabatic reactor with suitable control system. A major focus of the project was on combining existing low-cost raw materials in new ways. Thus, besides simulated flue gas and commercial lime, natural starch, cationic and anionic starches and carboxymethyl cel-lulose were used in many experiments. Some experiments were conducted with microfibril-lated cellulose and with chitosan, which are not common commercial additives for paper. The main technical approaches were:

1. To precipitate calcium carbonate on top of a polymer. The purpose of the polymer was to a) help direct the morphology of the pigment and b) form a polymer reinforced microcomposite with desirable properties. The crystallization conditions were explored in some detail.

2. The surface treatment of commercial PCC with polymer and polymer/calcium carbonate complexes. In this case, the problem was to increase the polymer adsorption beyond the natural monolayer levels so that a significant improvement in sheet bonding potential could be realized. It is known that when pigments are added to paper the elastic modulus (thus stiffness, strength) is lowered because ordinary pigments interrupt the fibre-fibre hydrogen bonds. In this work we attempted to counteract this affect by clever adsorption of polymers and polymer/PCC complexes.

3. In some experiments, the use of microfibrillated cellulose as a substrate for calcium carbonate growth was explored. The target was to improve both optical and strength properties simultaneously, which is difficult to do in polymer systems. In other experiments, precipitation of calcium carbonate was used to reduce swelling and improve the dewatering properties of microfibrillated cellulose.

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Calcium carbonate on top of polymerThe experiments involved the precipitation of PCC on top of starch(es), CMC, chitosan and cmc/cationic starch complexes. The crystalliza-tion conditions were varied so that crystalliza-tion was done under acid and alkali conditions, at different concentrations and temperatures. Extensive particle analysis and handsheet ex-periments were carried out for each of the bi-ominerals produced. The main conclusions are:

1. Composite pigments were produced with pigment structures (particle size, distribution, surface area, morphology, pigment strength) that would be hard to achieve with classical pigment synthesis routes. In particular, it was possible to engineer higher-order structural levels by precipitating in polymer solutions. The work showed that by altering both the crystallization conditions and polymer chemistry it was possible to engineer paper properties in new beneficial ways.

2. The aggregates, being polymer-reinforced microcomposites, were quite strong and capable of withstanding wet-end shear conditions (in simulated lab measurements), contrary to classical filler flocculation systems, which are sensitive to electrostatic interactions and shear conditions.

3. Several pigments were found that led to superior paper strength properties and bulk/strength relationship compared to the reference pigments and thus could be used to increase filler content.

4. The improved paper strength was believed to derive from the aggregate structure, as the added polymer was mostly covered with PCC and not available for hydrogen bonding.

5. Low light scattering was somewhat problematic, especially for the starch-based pigments. This was due to the formation of an undesirable amorphous PCC morphology. This problem should still be solved before full- scale implementation, at least with natural corn starch as a substrate.

6. Both the value proposition and the technical feasibility warrant further pilot- and full-scale research of this concept.

Surface treatment of PCC Commercial PCC bonding characteristics were studied using a couple of novel routes. In one pathway, a technique for precipitating CMC onto the pigment surface under high Ca++ concentra-tion was developed. In a second pathway, starch (cationic/anionic/natural corn) was adsorbed to the pigment. A technique was developed for co-precipitating the unadsorbed starch from the solution. Thus, the starch adsorption could be increased and the wet end kept clean even at el-evated starch levels. The main results are:

1. PCC surfaces treated with CMC and CMC/cationic starch gave desirable strength, stiffness and other properties consistent with a 5-7% filler content increase. It is notable that in many experiments with CMC optical properties were improved compared to reference or starch-based treatments.

2. Natural starch and cationic starch surface treatment also increased strength significantly. The results show that paper properties can be manipulated in a non-obvious way by changing the coprecipitation conditions. For example, by changing the pH of coprecipitation, very different improvements to different paper strength properties could be achieved.

3. Starch adsorption was found to be improved by cooking the starch in a pigment slurry. It was also found that while natural starch has higher adsorption under some conditions, under other conditions cationic starch had the best adsorption. Cationic starch is probably the most feasible surface treatment polymer considering performance, cost and wet-end behaviour.

4. The results show that by using the right combination of starch chemistry, adsorption conditions and coprecipitation it is possible to increase the starch content,

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strength properties and filler content of paper (by 5-7%) in a cost effective manner.

5. The technology opens opportunities for increased filler content in various printing and writing grades of paper, eliminating the size press, as well as other potential board applications. The technology is untested in large scale, but there are no major roadblocks to scale-up.

Microfibrillated cellulose/PCC complexesExperiments were conducted to determine whether microfibrillated cellulose could be a useful substrate on which to grow PCC. Oth-er experiments were done to determine if the swelling of oxidized MFC could be altered by coprecipitation of PCC. The results were:

1. MFC/PCC gave good strength, retention, low roughness and also good light scattering and appears to be an excellent substrate for building PCC/cellulose biominerals.

2. A small amount of PCC precipitated to the surface of oxidized microfibrillated cellulose could reduce its swelling from 40 ml/g to 8 ml/g, showing that dewatering of microfibrillated cellulose can be improved using biomineral systems. This is important in several fibrillated cellulose applications.

4.5 Calcium silicate hydrates on PCC surface

The nucleation effect on the PCC surface was also demonstrated. This concept originated from concrete production, in which concrete reacts with water to produce calcium silicate hydrate (CHS), which provides the concrete its strength, and CSH is formed on the concrete surface. The same treatment was done with PCC, and the treated PCCs were then formed into hand-sheets. Raw materials used in the treatment method were Ca(OH)2 (calcium hydroxide) and SiO2 (silica). As a result, calcium hydrate “hairs” (CSH) were obtained, the length of which can be altered by adjusting the reaction time and condi-tions. As a Figure 13 shows, nanoscale CHS par-ticles were grown on the PCC surface.

Calcium silicate hydrate (CSH) pigments were studied with chemical cement coating treat-ment and additional cement coating treat-ment. VTT fine MFC was also added to these treatment processes. The best growth of CHS on the filler surface was observed with 1% dos-age of cement. The higher dosages produced competitive reactions and less desirable CSH growth. Treatment of the fillers required vig-orous mixing and careful addition of cement when adjusting the length of growth. Ten-

Figure 13. Nucleation treatment of PCC filler. Left: Treated CSH nucleated PCC; Right: Reference non-treated PCC.

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Figure 14. Strength properties of calendered SC sheets improved with cement-treated CSH fillers and with VTT fine MFC. The figure shows how pigment treatment intensity influences the modulus of elasticity.

sile index and modulus of elasticity improved with cement addition, but not with chemical treatment in calendered SC sheets (Figure 14). Strain at break decreased linearly as pigment treatment intensity increased. Interaction with MFC was good, with both treatments improv-ing the mechanical properties significantly. Further optimization of process variables is required in the CSH cement coating of fillers.

5. Exploitation plan and impact of results

Optimized dewatering may change the way ini-tial dewatering is carried out on paper machines, and lowered vacuums may enable the use of blowers instead of vacuum pumps. This, togeth-er with more gradual water removal rates will decrease the cost of de-watering substantially. Development of the de-watering model will in-crease the efficiency of trial planning and, in fu-ture, also enable forming section development.

This work directly supports the goal of the EffNet programme of developing radically new produc-tion systems that make the best use of resources and are energy-efficient so as to reduce capital intensiveness and improve the entire cluster's ef-ficiency and flexibility. The expected impacts on the forest cluster companies include:

• Novellayeredprintingpaperandfoldingbox board products will give substantial competitive advantage

• Improvedformingsectionde-wateringprofile will change the way paper machine forming section de-watering is done and bring vacuum system cost savings

• De-wateringmodellingwillimprovepossibilities to predict needed changes in de-watering elements when furnish properties are modified

• BindableMFC-PCCaggregatesandstarch-based biominerals enable the filler content of papers to be substantially increased.

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Role

Dewatering research, high filler content papers, novel printing paper research

Dewatering research, dynamic wet pressing, finishing and calendering

Modelling of dewatering

Biomineral development

Partner

VTT

Metso Paper

University of Jyväskylä

Aalto University

Table 2. Partner organisations and their research roles.

Expected scientific impacts:

• Effectoffurnishpropertiesonde-watering• Effectofpulsationonfiltrationprocess

dynamics and web consolidation• Novelinformationonwebconsolidationand

structure during the filtration process• MFCdistributioninpaperstructure• Newunderstandingofhowmicrofibrillated

cellulose fibres increase paper strength • Improvedformingsectionandpresssection

de-watering models• Potentialtoreplacevacuumswithblowers

Majority of the results indicated that savings in both energy and raw material consumption can be achieved. The novel layered printing paper concept will reduce costs by 23%. New NFC filler aggregates may further decrease energy con-sumption of different pumping operations. The novel surface layer spraying technique may be used in several applications in the near future.

6. Networking

The research was carried out jointly by re-search organisations and Finnish forest clus-ter companies. Table 2 presents the research partners and their roles.

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7. Publications and reports

Presentations:

Haavisto, S., Liukkonen, J., Jäsberg, A., Ko-ponen, A., Lille, M., Salmela, J., “Laboratory-scale pipe rheometry: A study of a microfibril-lated cellulose suspension”, PaperCon 2011, Vol. 1(2011),357-370,Covington,KY,1-4May2011

Koponen, A., Haavisto, S., Salmela, J., Liuk-konen, J., “Optimization of paper machine ini-tial dewatering”, Papercon 2012. New Orleans, LA, USA, 22 - 25 Apr. 2012. Tappi. New Orleans, LA, USA (2012)

Salmela, J., Ruusuvirta, L., “MFC Labelling, Re-tention and Distribution in Paper”, 2013 TAPPI International Conference on Nanotechnology for Renewable Materials, 24-27 June, Stock-holm, Sweden.

Torvinen, K., Helin, T., Kiiskinen, H., Hellén, E., Hohenthal, C. and Ketoja, J., “Nano fibrillated cellulose as a strength additive in filler-rich SC paper”, 2011 TAPPI International Conference on Nanotechnology for Renewable Materials, 6-8.6. Arlington, USA.

Torvinen, K., Vehmas, T., Kronlöf, A., Hellén, E., ”Binding fillers for paper applications using na-noscale calcium silicate hydrate coating and na-nofibrillated cellulose” 2013 TAPPI International Conference on Nanotechnology for Renewable Materials, 24-27 June, Stockholm, Sweden.

Master Thesis:

Ahonen, M., “Measurement of elastoplastic parameters of fibre networks “, University of Jyväskylä

Ghosh. I., “Starch adsorption onto PCC”, 6/2013, Aalto university

Juusela. L., “Starch modification to increase filler content of paper”, 10.8.2011, Aalto University

Koski, R., "Kontrastin lisääminen puukuidun rakenteen selvittämiseksi ja paikallistamiseksi paperiarkista röntgentomografialla", 2011, University of Jyväskylä

Ruusuvirta, L., “Microfibrillated cellulose – structure, properties and interactions with metals “, 2012, University of Jyväskylä

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ImAgE-bASED mEASUrEmENTS

c o n tac t p e r s o n

Risto Ritala, risto.ritala@tut.fi

pa r t n e r s

Tampere University of Technology

Kemira

Lappeenranta University of Technology

Metso Automation

University of Eastern Finland

University of Helsinki

University of Jyväskylä

University of Oulu

UPM

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AbstRACt

In order to support the quality management of current and future products, imaging-based measurements of fibrous network structures were developed. A device capable of measuring surface topography on-line based on photometric stereo was developed. The device is also capable of measuring surface fibre/floc orientation. The illumination and imaging geometry were optimized for topography inference. The measurement was validated based on X-ray tomography measurements that provide high-resolution 3D information about the fibre network in laboratory conditions. Optical coherence tomography was shown to be a promising technique for a reference measurement as it is much faster than X-ray tomography. Varying the wavelength of illumination, in particular in near infrared, enables the planar distribution of material components on the paper surface to be examined. It was also shown that current web defection imaging systems can be used to assess CD/MD variation of the web for control and monitoring purposes. It was found that with such measurements CD profile estimation is speeded up considerably, which allows some room for improvement in controller performance. The main limiting factor in further control performance improvement is the long delay from actuators at the headbox to measurements at the dry end.

New image-based technology was studied and applied to the monitoring of chemistry in papermaking. For enhancing tissue production and improving tissue quality, two new image analysis methods were developed and tested. The image-based measurement system for tissue structure and quality provides a means to enhance the creping process and production rate in tissue production. For monitoring and controlling chemistry in water streams a new particle analysis method was developed and tested at laboratory and full scale. The method automatically detects particles from images and continuously analyses their properties, such as size, count, shape and type. It also provides distributional information on particle types.

When moving towards higher added value products, papermaking is facing increasingly strict requirements on the uniformity of quality. With current products and production systems, incomplete quality information leads to non-optimal use of raw materials due to “safety margins”. Measurability and controllability affect how new production system concepts should be designed and, hence, the new image-based methods add degrees of freedom to the design.

Keywords:imaging, fibre network structure, topography, orientation, surface composition, printability, to-mography, near infrared, web-wide imaging, 2D control

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1. Background

EffNet has developed production system con-cepts for producing the functional proper-ty combinations of present products more ef-ficiently by reducing raw material costs, use of energy and water, and capital expenditure, and with present or reduced carbon and water footprint. EffNet research is providing means for achieving this by developing new raw mate-rial concepts, advanced web generation tech-niques, novel surface treatments, and studying optimal roles of paper surface preparation and printing. However, for these methods to be ap-plicable in large-scale production, the uniform-ity of the functional properties of printed prod-ucts must be managed. It is well-known that current production systems must operate with considerable and costly safety margins as qual-ity variations would otherwise lead to process-ing problems and poor consumer-perceived quality. Furthermore, many key characteristics cannot be measured on-line; e.g. surface to-pography and mottling tendency are crucial for print quality, and surface orientation and for-mation are critical for out-of-plane mechanics (curl and cockling). As the development of new production system concepts has been largely based on using more tailored material compo-nents and fractions and more delicate surface treatments, the benefits will be limited by how uniform the material composition and structure are in large-scale operation.

The research on image-based measurements continues the work initiated in EffTech’s Qvision project. The objective of this study was to pro-vide means for managing the uniformity of web material in the macro scale, in particular, so that bulk and surface microstructure are consistent-ly produced over time and machine-wide. Until very recently – mostly due to the work of Qvision – wide ranges of product variability have been unobservable. The web needs to be character-ized and managed at the following scales:

- Sub-formation scales of surfaces affecting printing; mottling effects, deep surface pores in uncoated surfaces

- Formation scale structure, including fibre orientation

- Web-wide structures at high resolution (sub mm)

- Fast web-wide temporal structures (residual variation at resolution of 10 cm...1 m in machine direction and 1 mm in cross-direction)

- Slow web-wide temporal structures (MD and CD profiles)

This characterization will be based on digital imaging, which has been the most rapidly de-veloping area of electronics in the last decade. Inference based on images will be supported by advanced use of structural models and oth-er prior information according to the principle of inverse and Bayesian methods. The man-agement of uniformity will consist of a com-bination of feedback control and diagnostics.

QVision-project generated an idea to utilize imaging techniques for evaluating properties of tissue paper and water & pulp quality. Cur-rently, measurements on quality properties specific to tissue are scarce, which is a ma-jor limiting factor for quality management. Im-age-based measurement techniques for char-acterizing web structure may provide new quality measurement opportunities in tissue production, as they have provided in other pa-per manufacturing applications. New imaging techniques together with novel analytical and computational methods can generate deeper understanding needed for improved chemistry control in papermaking.

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2. Objectives

The objectives of the study were to develop new on-line characterization methods for web structure and to develop image technology based chemistry control concepts to manage wet end chemistry and tissue paper properties.

The specific objectives were to:

- Develop on-line measurements for topography and surface orientation,

- Analyse the feasibility of on-line surface orientation measurement, and to identify opportunities for spectral surface imaging in paper surface chemistry applications

- Develop continuous web-wide imaging as a variability analysis tool in all relevant length scales, and to assist scanner-based quality control by optimizing the scanner path based on transmittance variability

- Study methods of 2D control based on continuous web imaging, supported by scanner measurements

- Develop a crepe bar analyser for tissue paper structure and an analysis method for evaluation of tissue softness

- Apply and evaluate new imaging technologies for improving papermaking chemistry and process efficiency

3. Research approach

The research hypothesis was that many highly relevant structural properties of fibre networks can be inferred from images of paper. As a rap-id-response measurement method, imaging can be applied on-line and web-wide and can im-prove the performance of on-line quality control.

The research questions were:

1. Which structural properties of the fibre network can be inferred by imaging and

to what accuracy (varying illumination and imaging geometry and wavelength of light)? The ground truth of the fibre network structure was assumed to be provided by X-ray tomography.

2. Which image-based measurements can be implemented on-line with CD scanning? Which measurements can be implemented web-wide with time-wise snapshot sampling? Which measurements can be implemented web-wide continuously in time?

3. To what extent do such measurements improve the performance of CD/MD control?

In particular, the following structural properties were considered:

1. Surface topography (photometric stereo)2. Orientation (on surface and through the

web)3. Basis weight variation in scales relevant for

CD/MD control4. Small-scale basis weight variations5. Surface composition (NIR illumination)6. Web shrinkage

The main outcomes were:

1. A device capable for simultaneous surface topography and surface orientation measurement on-line has been constructed and applied on webs at realistic production speeds.

2. Measurement setup (illumination angle, number of lights) and computational methods (gradient methods, curvelets, SIFT) for surface topography/orientation have been analysed and optimized.

3. Traceability from X-ray tomography to imaging surface measurements has been established.

4. Optical coherence tomography provides a fast reference measurement for structural measurements. The measurement results

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provide required accuracy with well-stabilized laser.

5. Spectral imaging is feasible for analysis of small-scale variations in surface composition.

6. New set of web-wide mill data was collected and analysed for quality variations and actuator responses. Although the data set was rather limited due to production problems at the site, overcoming the real-time and huge data flow requirements has been proved feasible.

7. Comprehensive diagnostics functions for 2D transmittance variation have been implemented.

8. A method for extracting actuator step responses from image data has been developed.

9. Dynamics of 2D control has been analysed to analyse the importance of dead time as the leading limiting factor in control performance based on 2D quality measurement.

10. Simulations to validate the performance improvements of 2D control using web-wide measurements were continued and a new multiple-property controller was developed and tested.

11. Formation measurement and control opportunities explored in the SUORA environment.

12. Two new image analysis methods for enhancing tissue production and improving tissue quality were developed and tested. A developed new image-based measurement system for tissue structure and quality opens opportunities for enhancing the creping process and tissue production rate.

13. For monitoring and controlling chemistry in water streams, a new particle analysis method was developed and tested in laboratory and full scale.

The work was organized into five tasks as follows:

• Characterizationmethodsofpaperstructure aiming at scanning or point-wise measurements.

• Characterizationofweb-widevariabilityofoptical transmittance.

• Managementoffunctionalwebpropertieswith control and chemicals.

• Imageanalysisforenhancingtissueproduction

• Imageanalysismethodforwaterandpulpquality

4. Results

4.1 Paper structure characterization methods based on scanning or point-wise measurements

Measurements for surface topography and sur-face orientation were developed; improvements in bulk formation and orientation measurements were made; the feasibility of surface chemical composition measurement was analysed; and dot gain measurement concepts were proposed.

The general goal was to develop a tracea-ble measurement chain from first-principles structural laboratory measurements to im-aging measurements made at full speed on-line. Tomography measurements are consid-ered the ground truth. At present, tomography measurements are X-ray based and are highly accurate but time-consuming. Simultaneous-ly sub-micron resolution spectral domain op-tical coherence tomography (OCT) has been developed. OCT measurement provides meas-urement speeds of 1-140 kHz, which is suffi-cient for fast laboratory measurements and may even have on-line potential. However, spectral OCT requires more advanced data analysis and signal processing. Spatial meas-

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urements were initially noisier than the time domain method. The new measurement setup, based on spectral domain analysis, was devel-oped and the resolution was confirmed. Sensi-tivity problems were solved towards the end of the project by a new laser. The laser is sealed and thus not sensitive to environmental vari-ations. EffNet samples were measured with a measurement time of 1-2 seconds per sample, see Figure 1. The penetration depth was 40 um. The data is of the order of 40 MB. The de-velopment of OCT continues in other projects. OCT appears to be a good and fast reference

measurement method for image-based struc-tural measurements of paper.

An on-line device (see Figure 2) capable of measuring surface topography and orien-tation was designed, built and installed to measure at speeds corresponding to the re-alistic web speeds of new production system concepts. The measurement area is 1 cm x 1 cm and pixel size roughly 10 λm. The method is based on simultaneously illuminating the sample with three different wavelengths and imaging it so that the main response of each

Figure 1. Reconstruction of paper structure using OCT. Measurement area 1 mm x 1 mm x 1.4 mm.

Figure 2. Structure of the on-line surface orienta-tion and topography measurement device.

Figure 3. Surface topography of a sample. Left: Reconstruction using photometric stereo. Right: Recon-struction using X-ray tomography. The correspondence is good, although X-ray tomography (ground truth) has higher spatial resolution.

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light has its own response channel in a red-green-blue (RGB) camera.

Topography reconstruction using the optical method (photometric stereo) and X-ray tomog-raphy were compared, see Figure 3. The corre-spondence is quite good and has been further characterized by 2D spectral coherence analy-sis. The laboratory optical method is based on a large number of different illumination angles. With the on-line device only a few illumination angles are used, but the effect of varying the number of illuminations has been analysed and the on-line structure has been found to provide good correspondence to the true surface, as evaluated by tomography.

Orientation and formation were analysed both at the surfaces and in the bulk. The main observations are:

- Several efficient methods for extracting orientation distribution were developed. These include Fourier-based, gradient-based, curvelet and Scale Invariant Feature Transform (SIFT) methods. The Fourier and gradient-based methods were implemented in the prototype.

- The number of lights and the illumination angle were analysed and optimized as measurement parameters, see Figure 4.

A pentagon arrangement was found to be better than a three-light arrangement.

- A method for floc orientation was developed and compared with fibre orientation results. The effect of scale on floc orientation was analysed.

- Bulk orientation angle can be estimated even from standard resolution formation images.

- The response of a wavelength to surface gradient depends on the wavelength (the shorter the wavelength the larger the response). This needs to be taken into account in particular in surface orientation analysis. A computational correction for dealing with these problems was developed and implemented.

Surface composition was analysed using IR spectral means. Kaolin, water and paper have specific absorbencies as functions of wave-length. In Figure 5, examples of paper and kaolin absorbencies are shown as spectra measured with a PerkinElmer Lambda 1050 spectrophotometer and two spectral bands λ=1600 nm and λ=2208 nm of a Specim N25E spectral camera (spatial resolution 30 µm and real dimension 10 x 32 mm), where the Metso logo is hand-drawn with kaolin on paper. Ka-olin peaks at wavelength 2208 nm are clear-ly shown. Hence, measuring the uniformity of

Figure 4. Left: The effect of inclination angle on orientation distribution observed; Right: The effect of number of lights on orientation distribution and its repeatability.

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kaolin is feasible by comparing the images at different wavelengths. Similarly, measuring the distribution of water (moisture) in the sur-face was shown to be feasible.

4.2 Characterization of web-wide variability of optical transmittance

The Qvision project and the EffNet programme planned two mill data collection campaigns of web-wide measurements, carried them out on a full-scale paper machine, and pre-processed and analysed the data in order to assess the possibilities to estimate basis weight varia-tions. Such studies need to be carried out in a full-scale environment as real-time issues and huge data flows are important technologi-cal challenges of such systems. The data was analysed with tools developed earlier to clas-sify and diagnose the 2D variations in the Qvi-sion project and in EffNet. Unfortunately, the quality of the data from the second campaign

was rather poor due to production problems at the site of data collection. The data collec-tion was planned for the start-up of the line. However, the start-up was delayed and not all data specified could be obtained. The follow-ing data was obtained:

- Calibration measurements for identifying uneven illumination effects and geometric disturbances

- Two sets of line data of duration 10 min each; including step response tests

- Some reference paper samples for the Tapio web analyser

Due to practical limitations caused by the de-layed start-up of the line, no full image data or data in which the reference scanner meas-urements were stationary were obtained. The analysis focussed on on-line data. Line data required considerable preprocessing. In par-ticular, the alignment needed considerable

Figure 5. (Left) Absorbance of kaolin and paper in near infrared. The Metso logo was drawn by hand with kaolin on the surface of the paper. (Middle) at spectral band 1600 nm the logo cannot be observed, but at 2208 nm (right) it is clearly visible.

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correction compared to the image metadata. Preliminary indication of actuator respons-es was observed, but response identification from the data was not possible.

A method for identifying actuator step respons-es from web-wide images was developed based on principal component analysis (PCA) and test-ed with simulated data, see Figure 6. Response forms can be obtained from far shorter tests than at present with scanners. The method re-quires a scanner for response gain identification.

4.3 Management of functional web properties with control and chemicals

This study sought to assess the potential for quality improvement if continuous 2D imaging is used as the primary measurement signal in CD/MD control. At present, it is conjectured that the limiting dynamic factor of CD/MD control is the scanner measurement and CD/MD estima-tion of the scanned signal. This limitation would be obviously removed if the 2D image data gave perfect quality information, primarily on basis weight. Then, the dynamic limits would be set by the dead time from actuator to measure-ment and the actuator speed.

Simulations with a simplified process mod-el show that imaging measurements may in-crease the dynamic bandwidth of the cross direction control system substantially. It can also be expected that errors in actuator re-sponse identification and shrinkage estima-tion can be decreased. It was found that the imaging measurements may provide means for removing cross direction profile distur-bances with wavelengths larger than 400 s, whereas with scanner-based control, all dis-turbances with wavelengths under 1000 s are practically uncontrollable. With perfect model knowledge and measurements, the limit is al-most an order of magnitude smaller than with the more practical case simulated with the scanner measurements. Also, higher sampling rates and shorter control intervals provided by the imaging measurements indicate that actu-ator dynamics will not necessary be an unim-portant factor in paper machine control, espe-cially if the dynamic part of CD profiles is to be controlled. The results also indicate the impor-tance of accurate approximation of time delay in order to maximize control performance.

The results presented underscore the impor-tance of developing new sensing techniques in paper machines and, hence, call for con-tinued development. We assumed rather fast CD profile changes to be present in the pa-per machine. Therefore, it should be exam-ined whether such dynamic patterns in cross direction variation really exist. A large number of control algorithms for CD problems can be found from literature and, with minor chang-es, these might be applicable also with fast-er measurements. The controller structure applied in this paper showed good computa-tional performance, which surely is an impor-tant, perhaps even limiting factor when bring-ing the sampling and control interval from one scan time closer to one second.

Analysis of the potential of 2D control with im-

Figure 6. (Left) Simulated step response on the mill web-wide transmittance data. The CD re-sponse identified for a number of durations (10–60s) of response test.

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aging measurements has continued with dy-namic response modelling only, thus enabling control performance to be determined across a wide frequency range, with different actua-tor scenarios and with varying quality of the es-timated model. The control loop is construct-ed using the estimated process model in the controller, but then simulated with a “true” re-sponse model as a process model. The estima-tion process is modelled as the difference be-tween the true and the estimated response, including the dead time difference. Two types of simulated actuators are studied, one with sufficiently fast response dynamics and anoth-er with slower response. These actuators can be considered as the dilution valve and slice lip used in basis weight control in a paper machine. The simulated dead time remains the same, as the actuator position with respect to the meas-urement position is not changed. The time con-stant and the delay of the control model are al-tered in order to demonstrate how the quality of the image-based estimate may affect the achievable control potential, see Figure 7.

The results show that, mainly due to dead time, but partly also due to actuator speed and to the mismatch between true response dynamics and estimated dynamics, there are

considerable limitations so that dynamics faster than, say, 300s cannot be affected. The results are in accordance with the 2D simula-tor results. This comparison justifies our use of the simpler SISO models in the analysis.

Successful web-wide measurements make it possible to extend the CD control strategy to multiple property control, i.e. to combine the control of several paper properties and sever-al actuators in an optimal control strategy that takes the interactions into account. This kind of new control strategy has been tested by simu-lations. The results show that as the benefits of multiple-property CD control we can expect more uniformity when observing all properties of interest and with less actuating energy. The controller presented is a computationally ef-ficient option and is expected to be a feasible control method for use with the higher sam-pling frequencies provided by imaging meas-urements. The automated tuning procedure developed offers a way to avoid severe input saturation, although further development and analysis of the method is required.

The web-wide measurements enable coordi-nation of CD actuators effectively also in MD control. Simulations indicate that a substantial

Figure 7. Limiting disturbance wavelength as a function of control model dynamics, in s, when the esti-mated model and true model differ. Estimated models are (1-a)z-d/(z-a)). Results are given as functions of a and d. On the left, with fast actuator (true model: 0.6916z-10/(z-0.3084)). On the right, with slow ac-tuator (true model: 0.1z-10/(z-0.9)).

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performance increment in MD control, both in disturbance rejection and setpoint following, could be expected if CD assistance is taken into action (Figure 8). The variance of the MD profile is decreased 55% compared to conven-tional PI control and Smith predictor by using scanner-based estimation. The effect of im-age-based estimation solely is more moder-ate, at around 12% degradation in variance.

In order to analyse the MD control opportunities of features extractable from image-based meas-urements, data was collected from the VTT SUO-RA environment in experiments in February 2011. The correspondence between on-line and off-line image analysis was studied (see Figure 9), reveal-ing on-line and off-line measurement to be close-ly comparable. Although formation changes were observed when the jet-to-wire ratio or water re-

moving element vacuums were changed, the in-terpretation of the results is somewhat cum-bersome due to numerous other parameters, in particular basis weight, changing at the same time. Moderate correlations were found between the image features and reference values. The effect of retention chemicals on formation ap-peared to be small.

4.4 Image analysis for enhancing tissue production

Tissue structure analysisFor analysing the crepe structure of tissue pa-per, an image-based measurement system was developed. The system captures four re-flectance images and one transmittance im-age from tissue paper. In the reflectance imag-es the light sources were located at an angle to the tissue surface. The optimum angle be-tween the light source and the tissue surface was found to be 55 degrees. An example im-age and mechanical drawing from the off-line measurement system are shown in Figure 10.

The 3D surface and gradient fields were recon-structed from four reflectance images based on photometric stereo. The gradient field es-timates the steepness of ascent and decent from the tissue paper, and the 3D surface es-timates the shapes and height of the crepes in millimetres. The crepe bar distributions from reflectance, gradient field and 3D surface im-ages were computed. Computation of crepe

Figure 8. MD control performance for disturbance rejection. (a) MD profiles, (b) Power spectrum. The dotted line is disturbances, the gray dashed line is image-based control and solid line is CD assisted control.

Figure 9. Comparison of on-line and off-line im-aging results (standard deviation of illumination).

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Figure 10. Off-line image-based measurement system.

Figure 11. Image-based estimation of tissue properties.

density from gradient field in MD was found to be the most robust method.

The crepe length distribution in CD was stud-ied from the gradient fields and the amount of defects from the reflectance images was

obtained. Figure 11 illustrates how the tissue properties were estimated from the images.

To validate the tissue analyser, several tissue samples were analysed. Cross-dimensional samples were collected from the top of a ma-

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chine reel, each sample consisting of one ply. Basis weight data was collected with an online quality control system. The scanner measured basis weight, moisture and dry weight. The off-line and on-line profiles were aligned uniformly in CD according to maximized correlation.

The CD samples were measured with the im-age analyser, which captures light reflectance imagesfromtheYankeesideofthetissueweb.The most important property evaluated was crepe frequency, which describes the number of crepe folds per unit length. An ideal crep-ing mechanism would generate uniform crepe frequency profiles in CD. However, with real tissue samples it can be seen that the crepe frequency is not constant in CD. Figure 12 also shows the basis weight profiles computed from the same reels from which the crepe fre-quency profiles were measured.

Figure 13 shows a pair of images captured from the first reel at the CD locations 300mm and 2700mm. The crepe frequency values computed at these locations were 4.1 and 4.6 crepe folds/mm, respectively. As the images show, some ar-eas are not creped. Furthermore, the share of such areas is much higher at the 2700mm CD location, at which the crepe frequency had been

estimated to be higher. These areas do not in-clude crepe folds, which increases the crepe frequency value computed from such image. It appears that high basis weight increases the probability of uncreped areas.

The crepe frequency profiles of bath tissue were also measured. The profiles are shown in Figure 14. The samples were cut from the same reel with an approximately 10-metre MD sam-pling interval. It can be seen that the amount of crepe folds per mm varies between 2.9 and 3.3.

The crepe frequencies computed from the bath tissue grade are much lower than the napkin grade. The image pair captured at CD locations 900 mm and 1900 mm is shown in Figure 15. The crepe frequency values at these locations were 2.85 and 3.33 crepes/mm, re-spectively. The images show a visually ob-servable difference in crepe frequency value, as indicated by the crepe frequency estimate, as opposed to the presence of uncreped areas, which caused the crepe frequency difference with the napkin samples.

It was observed that the crepe frequency varies in CD on tissue machines. The main reasons for the crepe frequency profile are the condition of

Figure 12. Basis weight and crepe frequency profiles from consecutive reels.

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Figure 13. Images captured from napkin tissue at CD locations 300mm and 2700mm.

Figure 14. Crepe frequency profiles measured from bath tissue.

Figure 15. Images captured from bath tissue at CD locations 900mm and 1900mm.

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the blade and CD variation of web properties such as bulk and basis weight. It was observed that the basis weight and crepe frequency pro-file correlate significantly. It was conjectured that the variation in basis weight profile pro-duces variations in the crepe frequency profile.

Ordinary measurement devices on tissue ma-chines are not able to detect crepe frequen-cy or other properties related to the struc-ture of crepe folds or the creping mechanism. Thus, there is a need for optical measurement devices for measuring and controlling crep-ing. Although the method developed here has been tested for tissue only under laboratory conditions, it is based on technology that has been proven in other applications to be direct-ly transferable to on-line applications at web speeds of up to 30 m/s.

Free fibre end (softness) analysisFor the end user, softness is among the most desired properties of tissue paper. Tissue soft-ness can be divided into bulk softness and sur-face softness. Bulk softness can be measured quite reliably by measuring the thickness and elasticity of the sheet. However, the measure-

ment of surface softness is not straightforward. One factor influencing surface softness is the fibers extending from the surface of the paper.

To detect the amount of such fibers in tissue paper, a novel imaging method was developed (Figure 16). The method is based on the detec-tion of shadows caused by free fibre ends. The shadows cannot be detected directly from the reflectance image due to the rough and wavy surface of tissue paper. Therefore, the surface normals of the tissue paper were first estimat-ed based on the photometric stereo method. The reflectance intensities of the surface were then reconstructed based on the surface nor-mals and the result was subtracted from the original reflectance intensities. The shadows were then detected from the difference image. The paper surface can be divided roughly into specular and diffuse based on the surface re-flection. The photometric stereo method as-sumes that the surface reflection is diffuse. The surface of paper is nearly diffuse. The unwant-ed effect of specular reflection was reduced by passing the light through two linear polarizers positioned at 90 degrees to each other, one in front of the LED light source and one in front

Figure 16. The polarizers block the specularly re-flected light from the sample surface.

Figure 17. Close-up of the original image (a), re-constructed image (b), difference between the im-ages (c) and the processed image in which shad-ows are amplified (d).

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of the camera. The light which passes the first polarizer is blocked at the second polarizer if the light is specularly reflected. Both polariz-ers were attached to a supporting arm, so that the polarizer in front of the camera lens rotated, thus keeping the orientation between the po-larizers constant during measurement.

The shadows caused by the fibres can be seen as faint dark curves in the difference image. De-tection of the shadows is based on line detection in all orientations across the image. The shadow lengths vary depending on the angle and exten-sion from the paper surface of the free ends of the fibres, which are usually shorter than the ac-tual fibre length. Figure 17 illustrates the differ-ent steps in the image processing.

The number of free fibre ends in three tissue grades was estimated with the new imaging system. The fibres were counted from the side of tissue paper which had been in contact with theYankeecylinder.

Grade 1 Grade 2 Grade 3

Average 36.3 40.1 64.5

Std 6.1 5.4 2.7

Table 1. Free fibre end count estimated with the novel imaging system

Based on the results, significant differences in free fibre end count were observed between each tissue grade tested. The standard devia-tion of the fibre counts was small, which indi-cates good repeatability of the measurement. The result of this research provides a good starting point for development of off-line or on-line softness measurement systems.

4.5 Image analysis method for water and pulp quality

An image analysis method was developed for monitoring particles in water suspension. The method was implemented as two prototype

systems, one for laboratory use and one for on-line mill tests. The systems contain a flow-through cuvette, a CCD camera equipped with a high-magnification objective achieving mi-crometer resolution per pixel, and back-light illumination (Figure 18). The software in sys-tems automatically analyses the morpholog-ical properties of particles with a size range from micrometres to millimetres.

The method automatically detects particles from images and continuously analyses their properties, such size, count, shape and type. It also provides distributional information on particle types.

Shape properties describe the morphology of particles. These properties are aspect ra-tio, roundness, and coarseness. Aspect ratio is computed as the ratio between the major and minor axes of the particle image. The princi-pal axes are computed from the particle image with principal component analysis (PCA). The aspect ratio of an infinitely thin line goes to in-finity, whereas a sphere’s aspect ratio is one. Roundness determines how circular the par-ticle is. Round objects have 100% roundness, and the roundness percentage decreases with increasing the complexity of the particle shape. Roundness thus indicates the degree to which a particle outline deviates from a cir-cle. Coarseness is computed as the sum of discrete curvatures along the perimeter di-vided by the length of the outline (degrees/pixel). Only the discrete curvatures of spikes (i.e. rapid turns) are counted in the coarseness computation. Therefore, coarseness increases with the increasing number density and sharp-ness of spikes along the perimeter. Bubbles, droplets and other blobs have low coarseness values, whereas fibres and flocs have higher coarseness values.

Particles can be classified as fibres, flocs or oth-er particles based on measured size, roundness

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Figure 18. The flow-through cuvette with optical setup and CCD camera.

Figure 19. Images of water and pulp suspensions.

Figure 20. Examples of images from pulp treatment tests.

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and coarseness values. Flocs are distinguished based on their high coarseness value. Fibres have a low roundness value and a correspond-ingly high aspect ratio. Other particles are more or less round and have smooth outlines.

Laboratory test resultsImage analysis was applied to measure the quality of various water and pulp samples from paper mills as well as a number of samples from high-filler and printing house trials. Figure 19 shows some example images from the analysis.

The effect of chemical treatment of pulp in a laboratory-scale system is illustrated in Fig-ure 20. The original pulp sample contains a lot of small colloids and fibres. The sample was treated with two different types of cati-onic polymer (A&B). The reaction mechanisms of the two polymers are different, as can be discerned from the images. Polymer A has a longer chain length and decreases the colloid

count by bridging them with larger flocs and with fibres. Polymer B forms smaller flocs by neutralizing the surface charge of particles. The choice of chemical depends on the appli-cation and target quality.

Another chemical treatment example is pre-sented in Figures 21 and 22. In this example, the original water sample contains only a small amount of particles. At low chemical dosage the particle count increases due to the precipi-tation of dissolved substances. Flocculation of particles starts at higher chemical doses. The size and coarseness of particles increase and the particle count decreases as the chemical doses increase. The performance of the chem-icals also differs with, for example, better floc formation achieved with chemical A.

On-line prototype test resultsThe on-line prototype was tested in a paper mill. Three different types of water sample

Figure 21. Example water treatment analysis using the image analysis method: particle count and mean size as a function of chemical dose.

Figure 22. Example water treatment analysis using the image analysis method: particle coarseness and floc count as a function of chemical dose.

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were measured: white water and two filtrates (pulp, water circulation). The white water and pulp filtrate samples required dilution of the sample flow. An automatic cleaning sys-tem was also required to prevent fouling and blocking of the system.

The first successful mill test result is presented in Figure 23. The results from a three-month test period revealed that circulation water quality varies considerably. Mean particle size varied in the range 4-10 µm and the maxi-mum particle count was 600 pc/image. Circu-lation water includes several water streams, the quality of which can vary significantly. In this case one stream brings varying amount of small particles to the water circulation. There-fore the particle count increases and average size decreases cyclically in water circulation.

Chemical response tests were carried out in the mill to investigate how to reduce colloidal par-ticles in the water circulation. A clear chemi-cal response was seen with respect to particle counts. The tests showed that chemical treat-ment could be improved by controlling chemi-cal doses using the new image-based analyser.

5. Exploitation and impact of results

The developed technologies can be implemented in existing production systems with appropriate cooperation between end users, large automa-tion suppliers and SMEs specializing in imaged-based measurements and machine vision.

Radically improved management of the materi-al flow of webs – achieved through continuous transmittance imaging and 2D control support-ed by it – is expected to be a component of the management in all concepts considered in the EffNet programme. Surface characterization for printing is obviously of importance for all

production concepts for printed products, and the methods developed are imperative when the concept analysis is extended to include the optimization between functionalities generat-ed at the paper machine and printing press.

Image-based measurement system for tissue structure and quality opens a way to enhance the creping process and production rate in tis-sue production. Today, the crepe ratio is con-trolled on the basis of unreliable, subjective and slow measurements. New image analysis based measurement provides fast and accurate infor-mation for optimizing the creping process.

One important goal in the creping process is to achieve the desired sheet quality with the low-est possible crepe ratio. In addition, the frequen-cy of creping blade changes has a direct impact on the production rate of tissue machines. The novel image analysis method enables the effect of chemicals on the creping process to be evalu-ated, leading to a radical improvements in pro-cess efficiency in tissue production.

The image-based analyser can provide spe-cific information on particles in water and pulp suspensions for chemical testing, anal-ysis and optimization of chemical treatments in papermaking. By utilizing this new method-ology more specific chemistry and phenom-ena based information can be provided ei-ther to develop new chemical products or to improve papermaking process performance through more optimal selection of chemicals. The image analysis system can also be used to improve colloidal chemistry in papermaking. Current commercial systems and sensors are more or less indirect (e.g. turbidity, cationic de-mand) and not feasible for efficient chemistry management. This new approach facilitates the direct observation of colloids by imaging.

For immediate utilization of image-based measurements, EffNet actively pursued the

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Figure 23. Particle count and size in circulating water during mill tests.

involvement of partner SMEs in the project. LabVision was included in all project activities to develop laboratory-level technologies for current production systems. Metso is active-ly analysing opportunities for commercializing the technologies developed, both scanning image based surface property measurement, and continuous web imaging based on tech-nology acquired from Viconsys, a partner in the earlier Qvision project.

6. Networking

The research was carried out jointly by re-search organisations and Finnish forest clus-ter companies. Table 2 presents the research partners and their roles.

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Partner

Tampere University of Technology,Department of AutomationScience and Engineering

Kemira

Lappeenranta University of Technology,Information technology

Metso Automation

University of Eastern Finland, Optics

University of Helsinki,Department of Mathematics

University of Jyväskylä,Department of Physics (P),Department of InformationTechnology (IT)

University of Oulu,Control (C), Optoelectronics (O)UPM

Role

Imaging for topography, surface orientation and dot gain measurement. Diagnostic analysis methods for web-wide images. Image-based measurement technology in tissue structure analysis and control of tissue machine.

Image-based measurement technology for water and pulp quality analysis and control of chemistry. Image-based measurement technology in tissue structure analysis and tissue machine control.

Imaging and analysis methods for topography, surface orientation and formation. Imaging for on-line control of formation/orientation.

Development of on-line scanning image-based measurements for topography and surface orientation/formation. Web inspection systems for web-wide imaging solutions.

Spectral imaging for surface chemistry applications.

Inverse methods and wavelet transforms for surface orientation measurements. Inverse methods in estimation for diagnostics and control.

(P:) X-ray tomography measurements as references for paper structure measurements. Wavelet and related methods for surface orientation analysis. (IT:) Image correction, calibration and stitching methods for web-wide imaging solutions. Feature extraction methods for diagnostics based on web-wide images.

(C:) 2D control methods and their performance (O:) Optical tomography measurements as references for paper structure measurements. Providing a case for full-scale studies of web-wide imaging.

Table 2. Partner organisations and their research roles.

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7. Publications

Ihalainen, H., Marjanen, K., Mäntylä, M., Ko-sonen, M.J., Developments in camera-based measurement of paper, presented as an invit-ed paper in Control systems 2012 conference in New Orleans, USA, April 2012.

Isokangas, A., Leiviskä, K., Analysis of forma-tion and flock size on the basis of optical trans-mittance. Report series A, Control Engineering Laboratory, University of Oulu.

Kälviäinen, H., "Machine vision based quality control from pulping to papermaking for print-ing", Presentation as an invited speaker in 10th International Conference on Pattern Recogni-tion and Image Analysis (PRIA-20-2010), St. Petersburg, Russian Federation, and accept-ed to Pattern Recognition and Image Analysis.

Mettänen, M., Jukola, M., Miettinen, A., Ihalainen, H., ” Comparison of registered pa-per surface representations from microto-mography and photometric stereo”, accepted to 2011 Paper Physics Seminar, Graz, Austria, 5-8.9.2011.

Ohenoja, M., "Application feasibility study of 2D control methods", Report series A, Control Engineering Laboratory, University of Oulu.

Ohenoja, M., Leiviskä, K., Multiple property con-trol in cross direction in a sheet-forming process, Journal Modelling, Identification and Control.

Ohenoja, M., Leiviskä, K., Potential of imaging measurements in paper machine control. Con-trol systems 2012 conference in New Orleans, USA, April 2012.

Pant, P., Mutanen, J., Mankki, A., Hauta-Kasari, M., Parkkinen, J., Spectral Analysis and Classi-fication of Dirt Particles in Pulp, Nordic Pulp & Paper Research Journal, 2012, pp.577–589.

Seppänen, J., Utilizing Online topography Measurement on LWC papermachine, Master’s thesis, University of Oulu, 2013

Raunio, J.-P., Ritala, R. and Mäkinen, M., (2012): Variability of crepe frequency in tissue paper; relationship to basis weight profiles, In-ternational Control systems Program 2012, New Orleans, USA, 2012.

Raunio, J.-P. and Ritala, R., (2012): Simulation of creping pattern in tissue paper, Nordic Pulp and Pap. Res. J., Vol. 27, No. 2, pp. 375-381.

Raunio J.-P., Tirronen, V., Lehtoranta, I. and Ritala, R., (2013): Web-wide imaging of paper; Analyzing the potential of on-line light trans-mittance measurement in quality control and diagnostics of paper, Nordic Pulp and Pap. Res. J., Vol. 28, No. 1, pp. 137-146.

Raunio, J.-P. and Ritala, R., (2013): Potential of full-web imaging in measuring web structure on-line, J-For, Vol. 3, No. 1, pp. 6-12.

Raunio, J-P. and Ritala R., (2013): Method for de-tecting free fiber ends in tissue paper, accepted to Measurement Science and Technology.

Takalo, J., Timonen, J., Sampo, J., Siltanen, S., and Lassas, M., “Evaluation of the areal mate-rial distribution of paper from its optical trans-mission image”, Eur. Phys. J. Appl. Phys. 55 (2011) 20701.

co n tac t p e r s o n

Markku Parola, markku.parola@vtt.fi

pa r t n e r s

VTT

Sanoma News

Stora Enso

UPM

ExPANDED OPErATINg WINDOW

fOr PrINTINg PrOcESS

ENAbLINg

EffIcIENT USE Of NEWLy ENgINEErED

fIbrE WEb SUbSTrATE

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This research explored the key printing materials and press adjustments affecting press runnability and productivity through finite element modelling, laboratory work and printing trials. Finite element modelling enables the prediction of the operating window in a heatset press: how the key paper and printing material parameters affect press runnability. With the help of modelling and measurements in the laboratory and in printing presses, the web tension formation mechanism between printing units was determined for the first time. This helps both papermakers and printers to achieve better productivity. Here, printing blankets and nip loads play a crucial role in affecting the web strain between printing units. The most important paper property affecting web tension is tensile stiffness.

Accumulation build-up (piling) starts with the interaction between the ink and the printing plate. A slight increase in fountain solution feed in the printing press decreases build-up tendency. The use of novel topography measurement in the printing press helps the printer to optimize washing cycles and leads to better press productivity.

Key paper parameters of novel webs regarding printing are: surface strength, absorption, tensile stiffness and hygroexpansion. Accurate selection of press material combinations and optimized press settings enabled printability of the novel webs produced in EffNet. A novel printing concept in which the web is varnished after printing was studied. Laboratory varnishing tests gave promising results, as varnished uncoated and printed SC papers gave as good printed gloss levels as the reference LWC paper.

AbstRACt

Keywords:heatset printing, runnability, web tension, accumulation, blanket, web release, novel web, varnishing, build-up, piling

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1. Background

The push towards efficiency enhancement and cost reduction continues to dominate the printing industry. Good print quality is also no longer a competitive asset, but a bare neces-sity. Common runnability problems faced in-clude, for example, material accumulation on the blanket (piling) and problems related to web tension. Blanket accumulation, in turn, results in vanishing dots, ghosting and de-creased print density. In addition, short wash-ing intervals decrease press productivity, and web tension variations through the press af-fect printed waste, web breaks, colour register, web movements, web release in the nip area, waviness, fluting, etc.

VTT has conducted extensive research on printing process interactions and runnability. Studies have focussed on a specific stage (e.g. drying) or phenomenon (e.g. accumulation, web tension) at a time. Printing research with-in EffNet summarizes the knowledge gained in earlier studies and clarifies in further detail those phenomena that are expected to be the most significant when optimizing the efficien-cy of the heatset printing process.

The overall goal of the Efficient Networking To-wards Novel Products and Processes (EffNet) programme is to improve the competitiveness of the whole forest cluster by developing rad-ically new energy and resource efficient pro-duction technologies and by finding means to reduce capital intensiveness. The printing component of the EffNet programme studied the critical interactions between the fibre web, printing materials and the press in order to op-timize the printing process for novel fibre webs developed in EffNet Programme. In addition, possibilities to perform surface finishing of the fibre web with existing technologies during the printing stage were explored. One impor-tant goal was to expand the operating window

of the current printing process to accommo-date cost efficient printing of novel webs.

2. Objectives

The main objective of the printing research was to maintain the newly engineered fibre web properties throughout the printing phase, thus increasing the efficiency of the whole val-ue chain. Furthermore, the aim was to identi-fy in which phases of the value chain actions towards efficient production could be feasibly taken, and whether the printing process could replace certain fibre web manufacturing phas-es (e.g. surface treatment). The research thus contributes to overall optimization of the whole value chain, from paper making to printing.

The research focussed on heatset web off-set printing because demanding process con-ditions apply high stresses on the fibre web during printing. As the newly engineered fibre products require a new approach to the print-ing process, the printing research concentrat-ed on how different components of the print-ing process influence the fibre web. One goal was also to expand the operating window of the current printing process to accommodate the novel webs, drawing on the valuable con-tribution of the graphic industry and its suppli-ers. Furthermore, the novel webs and new im-age-based measurement method developed in EffNet Programme enabled exploration of the printing process.

The knowledge gained from the printing research and the validated characterization methods can be turned into services, sharing the knowledge throughout the value chain of printed products, and thus increasing competitiveness.

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The objectives of the printing research were to:

• Studytheprintabilityofthenewlyengineered fibre web substrates

• Optimizetheprintingprocessfornewsubstrates (operating window of presses)

• Increaseknowledgeoftheinteractionsbetween the fibre web and the printing process

• Clarifythekeypaperandprintingparameters affecting runnability and accumulation in printing

• Predicttheeffectsofmaterialchangesonrunnability and printability => efficiency throughout the value chain

• Predictwhethertheprintingprocesscanreplace some fibre web manufacturing phases

• Createpracticaltoolsandservicesforimproving printing productivity and for future implementations

3. Research approach

The printing research was considered essential for the development of novel paper concepts for the printing market. Better understanding of the printing process, especially printing nip phenomena, is needed to determine how nov-el fibre webs should be printed and how the re-quired print quality can be achieved. The printing research within the EffNet programme focussed on heatset web offset printing, because the de-manding process conditions of HSWO printing apply high stresses on the fibre web during print-ing. The newly engineered fibre products require a new printing approach; the study therefore fo-cussed on how different printing process com-ponents affect the fibre web.

The research set out to clarify two important aspects of heatset printing: the web tension formation between printing units and inside the printing nips, and the mechanisms leading

to ink build-up on printing blankets (accumula-tion). Finite element modelling was successful-ly used to model the effect of the printing nips on the paper web. The papers, inks and print-ing blankets were characterized in laborato-ry studies. Commercial materials were used in the study: six paper grades, two inks and four different printing blankets. Printing trials and measurements were carried out on the KCL heatset press and on two commercial printing presses (Hansaprint and Sanomapaino).

Furthermore, the aim was to identify the stag-es in the value chain in which actions towards efficient production of printed end products could be feasibly implemented, and whether the printing process could replace certain fibre web manufacturing phases (e.g. surface treat-ment). As part of the novel printing concept, the influence of varnishing on the printed sur-face was also studied.

4. Results

4.1 Modelling printing nips and the paper web

The novel webs developed under the EffNet pro-gramme have different structure and bulk com-pared to currently used paper grades. It is there-fore essential to determine how these novel structures perform during printing, especially under high nip loads. Nip phenomena are, how-ever, not yet well understood, and no definitive results have been reported in the literature.

The goal of this study was to increase our un-derstanding of the stresses occurring in the printing nip and how they affect web tension formation by means of modelling. The model-ling was carried out using the finite element method with the Abaqus software.

The two-dimensional finite element model

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consists of four printing units. Each printing unit consists of two rubber-covered cylinders through which the paper web passes (Figure 1). The web tension was kept constant before the first unit. The paper web and rubber blankets were considered to be in plane strain state. The friction between contact surfaces was mod-elled using Coulomb’s friction law, with a con-stant coefficient of friction. In all simulation cases, the radius of the cylinders was 100 mm and the thickness of the blanket 2 mm. The be-haviour of the web was assumed to follow the orthotropic linearly elastic constitutive law.

Rolling contact is a well-investigated area. Rolling contact with respect to multi-layered cylinders has been reported in the literature mainly with regard to strains and stresses in the nip area. In the present study, the rubber blankets were represented as a three-layer

structure. The surface and compressible lay-ers were modelled as hyperelastic material, whereas the bottom fabric layer was modelled as linearly elastic material. For the compress-ible middle layer, the elastomeric foam mate-rial model was used.

The actual simulation consists of three steps. In the first step, a tractive infeed tension is creat-ed. At this stage, the cylinders are not touching the paper web. In the second step, the oppos-ing printing cylinders are pressed together to generate the nip. In the final step, the printing process is activated by rotating the cylinders at a prescribed angular velocity. The cylinders are rotated until a steady state is attained.

The forces and strains acting inside the print-ing nip were modelled to analyse how the nips affect the web tension. Figure 2 presents an

Figure 1. The printing nip and different blanket layers used in the modelling.

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example modelling result, in this case the ve-locities (MD direction) of the blankets inside the printing nip are modelled.

The nip modelling results are presented in the next chapter together with web tension results.

Further on, the modelling has been pushed forward to analyse the fibre network behav-iour under loading inside the printing nip. The finite element method was used to create the fibre network, with the bonds between differ-ent fibres modelled as springs that can fail. Figure 3 presents a fibre network created us-

ing the finite element method (FEM). The fig-ure shows the simulated stress-strain test re-sult for a network in which the bonds do not break (blue line), and for a network modelled with spring-like bonds that can fail (red line).

It can be seen that a network with spring-like bonds gives quite a realistic stress-strain curve.

The developed modelling allows adjustment of the fibre shape and orientation, as well as ap-plication of a coating layer on the surface of the network.

Figure 2. Modelled velocity fields in printing blankets in a printing nip.

Figure 3. Left: A fibre network created with FEM. Right: Results of the modelled stress-strain test for a network in which the bonds do not break (blue line) and for a network modelled with spring-like bonds that can fail (red line).

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4.2 Web tension

Comprehensive understanding of web tension formation in the heatset offset printing pro-cess facilitates the introduction of novel webs into the printing process. The web tension for-mation mechanisms and the key parameters affecting them were studied through model-ling and measurements both in the laborato-ry and on actual printing presses (KCL press and a commercial press). Figure 4 presents the measurement setup at the KCL heatset press.

Web tensions were measured with weighing rollers between all printing units. Web tension was also measured at the infeed unit, before the dryer and before the folder.

The results show that press draw adjustments explain a large part of the tension formation before and after the printing nips. These ad-justments include the infeed control, chilling roller and folder draws.

As the web tension formation between the first and last printing units is complex, mod-elling is needed to support its analysis. Mod-elling was especially used to understand how

stresses and strains in different directions build up inside a printing nip, as they cannot be measured on line. In this study, three dif-ferent blankets types with different feeding properties were used: neutral (n), negative (N) and positive (P) feeding. Trials were carried out on the KCL press with three different blanket combinations, n-n-n-n; n-P-N-n and n-N-P-n, where n-P-N-n means that the printing units had neutral, positive, negative, and neutral blankets, respectively. In this way, all blanket combinations could be studied.

Modelling revealed that different blankets affect the strains between the printing units, leading to tension changes between printing units. Figure 5 presents the modelled strains and modelled and measured web tensions on the KCL press with different blanket configurations.

As the figures show, the measurements and the modelling results correlate well. It was concluded that tension changes are due to strain differences, and that the degree of pa-per tensile stiffness determines the magni-tude of the change. Figure 6 presents the ten-sion and tensile stiffness measurements for the studied paper samples.

Figure 4. Web tension and other measurement locations in the web tension trial run on the KCL press.

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As the figure shows, the n-P-N-n blanket set in-creases the draw between the 1st and 2nd print-ing units (neutral – positive blanket). It can also be seen that the tensile stiffness of the differ-ent paper grades (violet line) correlates with the web tension change. Between the 2nd and 3rd printing units (positive – negative blanket), the blankets decrease the draw. In this case, the web tension drops more when tensile stiffness is higher, as indicated by the green columns. The measured tension changes and their correlation with paper tensile stiffness also strongly sug-gest that strain changes occur between printing units, thus verifying the modelling results.

The other key parameters affecting web ten-sion were: fountain solution feed level, print-

ing nip load, and drying temperature. As expected, increased fountain solution feed de-

Figure 5. Left: Modelled strains of the paper web through the printing units; Right: Modelled (blue line) and measured web tensions (green spots). The blankets sets are marked above the figures, n-P-N-n above and n-N-P-n below.

Figure 6. Effect of tensile stiffness of paper (blan-ket set n-P-N-n) on web tension between printing units 1 and 2 and between printing units 2 and 3.

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creased web tension, but the effect was quite small. Nip load has a clear effect on web ten-sion as it affects the feeding property of the blanket. Within the operating window of heat-set printing, dryer temperature changes had only a small effect on web tension.

High web tension peaks were measured during printing press start-ups. Such tension peaks can lead to web breaks during start-up. The peaks are most likely due to the start-up sequence, in which the paper is first run without ink and foun-tain solution during warm-up of the dryer.

Web tension is not normally measured be-tween the last printing unit and the chilling rollers. However, with heatset presses it is rec-ommended that web tension should also be measured (after the dryer and before 1st chillig roller) and controlled in this part of the press in order to avoid start-up problems.

Trials were also carried out on Sanomapaino and Hansaprint presses. These results were in line with the results of the KCL press.

4.3 Web release

Web release from the printing blankets was studied in the laboratory and with on-line measurements on the KCL press. Web release has an effect, for example, on dot gain, accu-

mulation, register errors and on web handling. Poor web release also leads to high release forces, which, in turn, lead to a higher surface strength requirement of the paper. The web release angle was measured after the fourth printing unit in the KCL press trials (Figure 7).

The results showed that the release angle in-creases with higher ink tack and higher nip load. Conversely, increased fountain solution feed lowers the release angle: a higher amount of fountain solution in the ink emulsion low-ers the internal cohesion of the ink, leading to easier emulsion splitting at the nip exit and to easier web release.

Blanket manufacturer has developed easy-release blankets. The release property of the blankets is controlled by surface chemistry (po-larity) and/or by controlling the surface rough-ness of the blanket. Test results showed that the easy-release blankets achieved a lower web release angle compared to normal release blankets. Figure 8 presents the effect of blanket type, paper and ink type on web release angle.

The results are in line with the laboratory measurements, in which easy-release blan-kets achieved lower release forces than nor-mal release blankets. The easy-release blan-kets also produced less lint and dust than the normal blankets.

In general, the paper grade determined the level of release angle: in all printing material combinations and press settings LWC gloss had the biggest, and LWC matt lowest release angles. It is yet not clear what is behind this phenomenon as there are many paper prop-erties affecting release angle. It is presumed that the high ink setting speed, high surface smoothness and low porosity (small pore size distribution) of LWC gloss paper leads to a large contact area between the inked blanket and paper surface in the nip, thus leading to a

Figure 7. Measured and calculated points for de-termining release angle.

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higher force needed to separate the inked pa-per from the blanket surface.

4.4 Accumulation build-up

The accumulation build-up of ink and paper particles on the printing blanket, leads to de-teriorated print quality. This accumulated ma-terial has to be washed from blankets typical-

ly between every one or two hours in heatset web printing, leading to high printed waste and lowered printing productivity.

The accumulation mechanism was studied in heatset printing trials at KCL and in a commer-cial press using on-line devices including a mi-croimaging system and various IR and UV-VIS measurements. A high-resolution colour cam-

Figure 8. Effect of blanket release property, paper and ink tack on release angle in the KCL press trial. Release angles at 300 N/m web tension.

Figure 9. On-line instrumentation and additional measurements for studying build-up tendency on KCL’s HSWO press.

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era was used to take still images from the ro-tating plate and blanket cylinder surface during printing. On-line measurement systems were used to monitor the amount of water, ink binder and ink pigment on the rotating blanket cylinder. Figure 9 shows the used on-line instrumentation during the piling trial on the KCL press. The addi-tional off-line analyses are also listed in Figure 9.

Samples from the fountain solution and cyan and magenta emulsions were taken during the accumulation trial and analysed in the lab. Lint and dust were measured from adhesive tape samples taken from the blanket surface of the first printing unit. The composition of the accu-mulated material was analysed using scanning electron microscope/energy dispersive spec-troscopy (SEM/EDS) and pyrolysis gas chroma-tography/mass spectrometry (GC/MS) meth-ods from blanket samples cut after printing.

Microimaging results showed that non-image area accumulation starts from the printing plate conditions; impurities originating from fountain solution cycle as well as uneven split-ting of emulsion between the plate and blanket cylinder cause ink transfer to non-image are-as on the printing plate and further on to the blanket (Figure 10). Moreover, ink from back-

trapping image areas transfers to the plate by micro-toning or by migration. These ink impu-rities are then transferred to, and accumulated on, the non-image areas of the blankets of the next printing units. The image area accumulation build-up took place at the edges of the images. Uneven splitting of emulsion in the printing nip induc-es ink tailing at the edges of the image area on the printing plate. These ink tails transfer to the blanket, increasing the accumulation on the trailing edges of the image areas (Figure 11). Nip pressure further enriches the amount the accumulation on the leading and trailing edges of the image areas in both the ink trans-fer and back-trapping areas. It was found that the distribution of accumulat-ed material between image and non-image ar-eas depends on the printed paper grade. With coated grades the ink transfer areas are clean, while the non-image areas are covered with accumulated material. Accumulated material at the edges of the images areas forms sharp dense edges that prevent efficient ink transfer, leading to reduced dot size and vanishing dots on the printed paper. With uncoated grades accumulation is detected on non-image areas and, in some cases, even on image areas. This

Figure 10. Formation of non-image area accumulation; Left: Microimage showing ink spots on the non-image area of a printing plate; Right: Microimage from non-image area accumulation on a printing blan-ket (magenta).

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is especially noted on back-trapping halftone areas. However, with uncoated grades the ac-cumulated material contains sparse fibrous material, thus allowing sufficient ink transfer.

It was found that a slight increase in fountain solution feed is beneficial for heatset print-ing productivity (Figure 12). Higher fountain solution feed decreases accumulation build-up and eases web release, leading to longer washing cycles. A minor increase in fountain solution feed has no notable influence on web tension, drying efficiency or print quality. Analysis of the accumulated inorganic materi-al composition was carried out from the blan-ket samples cut after printing of the coated and uncoated papers. The elemental analy-

sis was carried out using SEM/EDS equipment. Analysis of the printing materials, i.e. papers, inks and blankets, was carried out using the IR method. Both studied inks contained small amounts of clay and calcium carbonate, which are also common compounds in paper coating and fillers. According to EDS elemental map-ping, the accumulated material in magenta ink transfer areas contained both clay (Al, Si) and calcium carbonate (Ca). The calcium carbon-ate and clay are located mainly between dots, indicating that slightly more accumulation oc-curs on the non-image areas. Figure 13 shows an example of an EDS measurement from a blanket. As all of these materials are present in both ink and in paper it is impossible to iso-late the origin of the detected elements.

Figure 11. Formation of edge accumulation. Left: Ink tails on halftone dots on the plate. Middle: Accumu-lation build-up around halftone dots on the blanket. Right: Illustration of accumulation build-up around halftone dots on the blanket.

Figure 12. On-line images from the printing plate. Left = more fountain solution feed. Right = less foun-tain solution feed

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Figure 13. SEM/EDS elemental maps of blanket samples cut after coated paper printing from 15% half-tone area. Accumulation of cyan ink. Left: SEM image showing the accumulation topography on the blan-ket. The elemental maps to the right show the distribution of aluminium (Al), silicon (Si) and calcium (Ca).

Figure 14. Material components and accumulation composition at different trial points. KP 1 is a SC pa-per, KP 3 a LWC paper. Reference points are measurements of used materials (left). The measured com-position of the accumulation is presented on the right.

Figure 15. Accumulation measured from the printing blanket topography (LabVision Technologies Oyj). C15 is Cyan in 15% dot field (see also figure above). M is magenta and K is Black. 100 mean compact ink field.Y-axisisinmicrometres.

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The composition of the accumulated organ-ic material was studied using the methylation pyrolysis GC/MS method. The method shows the organic structure of the accumulation, but does not give quantitative results for the ac-cumulated components. Figure 14 reveals the composition of the used materials and accu-mulation components at different trial points.

The analysis showed that the accumulated ma-terial consists of components from both ink and paper. The results show that the accumulated or-ganic material consists mainly of fatty and resin acids, originating most likely from the used inks.

Topography measurements by LabVision Technologies Oyj clearly show how the accu-mulation occurs in different areas of printed web. Figure 15 shows the accumulation build-up on three printed paper rolls.

Topography measurement enables the optimi-zation of washing intervals in heatset printing.

4.5 Varnishing the paper web

Background research (literature review and in-terviews) was carried out to determine how

improved printed quality could be achieved for uncoated papers in the heatset offset printing process. As a result, the concept of paper var-nishing after the last printing unit was select-ed for closer examination.

Laboratory-scale trials were carried out with the Prüfbau printing apparatus. A SC paper and improved news samples were printed with cyan ink and varnished with an oil-based commercial varnish wet on wet. LWC reference paper was also printed with compact cyan ink. The print-ed gloss was then measured (Figure 16). The amount of varnish used with SC paper was be-tween 3.5 and 3.9 g/m², which is considerably more than in commercial sheetfed offset press, where varnish levels are typically about 2 g/m².

4.6 Micro-scale analysis of paper structural properties for printability prediction

This research evaluated the mill performance of a new on-line paper quality sensor that con-tinuously measures paper surface topography from the moving web (Figure 17). The results clearly indicate that the measurement appli-cation reliably predicts printability and pro-

Figure 16. The effect of varnishing on printed gloss; printed with Prüfbau apparatus at laboratory scale.The results are quite promising, as the printed gloss of the varnished SC paper is quite near to that of the reference LWC papers.

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vides real-time information for process control and troubleshooting purposes. The state-of-the-art imaging system, developed by Metso Automation, is based on topography meas-urement and includes a novel image analysis technology integrated into the process quality control system.

5. Exploitation plan and impact of results

The printing study defined the operating win-dow for novel webs in heatset web offset print-ing, thus supporting the introduction of novel webs to the printing market.

The results revealed the crucial press and pa-per parameters affecting runnability in heatset printing. The results have already been success-fully used by papermakers in troubleshooting customer problems in printing presses, lead-ing to financial benefits through increased pa-per orders. The results suggest that printing press runnability can be increased significantly and systematic exploitation of the results would lead to remarkable cost savings in heatset print-ing. These savings include, for example:

• Longerwashingcyclesduetobetterprocess knowledge and novel topography measurements

• Lessprintedwaste• Fewerwebbreaks• Fewercolourregisterproblems• Quickerprintingstart-ups

Increased printing efficiency will also lead to a smaller carbon footprint.

Varnishing of the printed web substantially improves the printed quality. Varnishing (after the printing units) can be used in the printing of papers developed in EffNet programme as well as in traditional printing.

The research results can also be beneficially used in other web applications, such as paper-making and printed electronics. Cooperation with printed electronics manufacturers has al-ready started. In printed electronics, the regis-ter accuracy between different printed layers remains a key challenge to be resolved.

6. Networking

The research was carried out jointly by re-search organisations and Finnish forest clus-ter companies. Table 1 presents the research partners and their roles.

Figure 17. The on-line topography measurement principle: RGB photometric stereo imaging.

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Table 1. Partner organisations and their research roles.

Role

Contribution of expertise and materials; BALAS modelling of heatset press; adhesion study and trial run on a commercial press to examine the effect of press materials and settings on web release and piling.

Contribution of printing expertise; printing trials on the Sanomapaino printing press; financing of materials, machine time and man-hours.

Contribution of expertise and materials; verification of results in sheet-fed offset press; financing of separate rotogravure study for testing the new Labvision imaging systems ability to predict missing dots.

Responsible for the majority of printing research and reporting.

Conducting and reporting on-line surface topography and on-line dot measurements.

Delivery of printing blankets; expertise in blankets and printing; laboratory analyses of printing blankets.

Partner

UPM

Sanomapaino

Stora Enso

VTT Technical ResearchCentre of Finland

LabVision Technologies

ContiTech AG

7. Publications and reports

Parola, M., Sorvari, J., Ketoja, J., Web tension formation and web deformation in printing process; presented at the 16th International Coating Science and Technology Symposium, September 9-12, 2012, Atlanta, USA.

Parola, M., Sorvari, J., Web deformations in printing; presented at the 2012 International Conference on Flexible and Printed Electron-ics, September 2012, Tokyo, Japan

Parola, M., Sorvari, J., Web tension forma-tion in heatset printing; presented at PTS Im-aging Symposium - Paper and Imaging (20.–21.11.2012, Munich)

Parola, M., Sorvari, J., Modeling web behaviour in printing press and in printed electronics, IWEB 2013, International Web Handling Con-ference, USA, June 2013

Passoja, S., Sneck, A., Hakkila, O., Monitoring heatset performance to control accumulation, Tappi Papercon, April, 2013, Atlanta, USA

Sneck, A., Passoja, S., Monitoring heatset per-formance to control accumulation; presented at PTS Imaging Symposium – Paper and Imag-ing (20.–21.11.2012, Munich)

Sneck, A., Passoja, S., Web release in heatset web offset printing, PTS Coating Conference, Germany, September 2013

Sorvari, J., Parola, M., Effect of printing nips on web tension formation in offset printing; pre-sented at the 6th European Congress on Com-putational Methods in Applied Sciences and Engineering (ECCOMAS) in Vienna, Austria, September 2012.

OPTImIzINgSTrUcTUrES

AND OPErATIONOf ENTIrE PrODUcTION SySTEmS

co n tac t p e r s o n

Risto Ritala, risto.ritala@tut.fi

pa r t n e r

Tampere University of Technology

Aalto University

University of Eastern Finland

University of Jyväskylä

VTT Technical Research Centre of Finland

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A general methodology for concurrently designing processes and their operational practices under several conflicting objectives was developed. The six-stage procedure is based on dynamic modelling of the process, developing a parameterized operational practice and then, by using multi-objective optimization methods, finding the trade-offs between the objectives as functions of operational parameters, process dimensions and structures. The objectives are evaluated in dynamic simulations corresponding to process operation of months to years. The solution is computationally highly intensive. Thus, the design optimization first produces a vast amount of design data, and then makes a computationally light surrogate model to be used in interaction with the design decision maker. The final design candidate is then further analysed with the simulator – first to determine the corresponding design parameters and then to analyse the sensitivity of the choice to the simulation model parameters. Finally, the design is validated with a more detailed simulator.

This design methodology was applied to two of the concept cases. The fines-coated LWC and the binding filler concept (of fine paper rather than SC, which was studied by other WPs). The studies were on retrofit designs, analysing the trade-off between buffer volumes and tolerance to process upsets and non-stationary operating conditions. Due to rather limited degrees of freedom in the cases, the trade-offs involved investment differences of only a few millions of euros. A simulation model and operational optimization were also developed for the foam-formed folding boxboard case. The studies emphasized the importance of efficient management of the foaming chemical in long circulation if a foam headbox is implemented as a retrofit in existing mills.

Keywords:process design, control design, optimization, Pareto optimal, validation, LWC, fine paper, folding boxboard, foam forming.

AbstRACt

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1. Background

Large capital employed and inflexibility of pro-duction systems are the core business chal-lenges of forest-based chemical industries. Design of production systems has been consid-ered from the point of view of material equilib-rium at operating points and with convention-al processing tasks for players in the supply chain, most notably for papermakers and print-ers. The design of production system dynam-ics has been based on rather coarse analyses of production disturbances. Buffer volumes be-tween production departments and mecha-nisms for attenuating disturbances have been designed accordingly, but only after the main production system structures have been deter-mined. Control and operational decision sup-port systems have thus had minimal degrees of freedom in their design and, as a result, dy-namic behaviour and capital efficiency are sub-optimal: many operations that could be dealt with by information, computational and con-trol means are implemented with capital-in-tensive process equipment. Implementing the management of disturbances with equipment has led to long transition times between oper-ating points – i.e. poor flexibility. These factors have resulted in production systems that have high performance when analysed in the steady state, but when dynamics and operational is-sues are included, their performance is severe-ly deteriorated. The effects of poor dynamical performance can vary greatly between produc-tion system structures and concepts, resulting in pure steady-state analyses incorrectly prior-itizing certain concepts as investment targets. Optimization of production system structures has also been constrained by the conventional task descriptions of papermakers and printers. As the EffNet programme seeks major changes to – or entirely new – production system con-cepts throughout the value chain, design com-parisons must be based on concepts that in-clude both structural and operational issues,

and the reallocation of tasks between paper-making and printing must be considered as a design degree of freedom.

Best-practice chemical engineering methods for the integrated design of process structure and control have been developed, but not ap-plied in pulp and paper. Furthermore, recent developments in biorefinery and its integra-tion into conventional pulping and papermak-ing have opened up possibilities to radically rethink material flows and to seek completely different process structures.

2. Objectives

Objectives of optimizing structures and oper-ation of entire production systems research area with in EffNet was to develop multi-ob-jective design optimization methodology ad-dressing the structural and operations design on the basis of results in EffTech programme.

Specific objectives of the research:

• Optimizethestructure,dimensioning,dynamics and operation of conceptual cases defined by EffNet. Two categories of design cases are foreseen: one for retrofit renewal of current process concepts and another for entirely new process concept.

• Multi-objectivedesignoptimizationmethodology addressing structural and operational design developed further based on EffTech results. In particular, scalability issues and multi-objective operational design were addressed.

• Workflowandbusinessmodelforthejoint design of process structures and operations developed to draft level.

The design cases were updated during the re-search with discussions on concept cases in the entire programme. Two cases – the fines-coated

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LWC concept and the high binding filler content fine paper concept – were selected for detailed analysis, and one case, foam-formed folding boxboard, was examined with simulations. All cases studied analyse the entire mill concepts.

3. Research approach

The research hypothesis was that by integrat-ing the design of process structure and oper-ation, the cost of ownership can be reduced considerably.

The research questions were:

1. How can the design of process equipment and process operation, measurement and control be integrated so that the life-time performance of the production system is enhanced from the conventional practice of layout design preceding operational/control design?

2. How can design decisions be based on life-time performance data obtained through time-consuming dynamic simulations?

3. How should multiple contradictory design objectives be dealt with, and how should the trade-offs be presented to the decision maker?

4. Can the model-based, multi-objective design methodology be implemented as commercially viable service business?

These methodological questions were studied through case analyses, the design problems being derived from the envisaged novel concepts in EffNet. In particular, the three cases studied were:

1. LWC paper with a fractionated TMP fines based coating.

2. Fine paper with a high content of filler with binding capability.

3. Folding boxboard with a foam-formed centre ply.

Initially, the scope was planned to include two case studies: retrofitting new unit pro-cess technology in a current mill layout, and designing a radically new process structure (green field). However, in practice, all three of the studied concepts fell into the retrofit cat-egory. Furthermore, the additional third case study was not carried out as a complete de-sign optimization, but rather as a dynamic simulation study.

The main outcomes of the work are the following:

1. The design methodology was developed and tested in the case studies. The methodology is feasible and generic. As the method relies heavily on the process models and their parameterizations, the critical point in the analysis is the quality of models available for the analysis.

2. The service business model was analysed and outlined. The methodology combines knowledge in the application domain, modelling and simulation, and multi-objective optimization. Thus, the challenge for the service business is to acquire the right combination of people with the required knowledge areas and to arrange their communication, which most probably requires “an integrator” with adequate background in all these fields. Furthermore, due to costs and response times, the service is seen as viable for studies of novel process systems rather than as a tool for “standard cases”.

3. The results of the case studies were encouraging, but indecisive regarding benefits with respect to cost of ownership. This is firstly because the cases studied had a rather narrow scope of optimization, and secondly because the effects of model uncertainties could not be assessed in detail as no process implementations were made. The model and parameter uncertainties are

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the main limitation for the credibility of the design optimization results.

The work was organized into three tasks as follows:

Development of methods for multi-objective conceptual design. Conceptual design address-ing both structures and operation in a multi-ob-jective way is an area of research about which rather little literature and methodology exists.

Concept optimization. A set of concepts to be optimized can be defined as a process super-structure, indicating the potential components of the concept and their structural and para-metric options. Multi-objective optimization considers performance criteria set at both the life-cycle level and the operational level.

Work flow and IT infrastructure analysis. The current work flow in conceptual design results from the conventional design practice of first choosing the process structure and only then tackling operability. This study first analyses the current work flow and attitudes of present players towards concurrent structural and op-erational design, and then specifies new ways of working towards concurrent design, pre-senting this as the basis for service provider business planning.

4. Results

This section first describes the methodology, then the results of the three concept case stud-ies and, finally, the business model analysis.

4.1 Methodology for designing process structures and dynamics with multiple contradictory design objectives

The problem of concurrent design of process structure, dynamics and operation can be stated as follows:

Given a set of performance criteria, find the process structure, dimensioning, control structure and tuning so that the life-cycle per-formance of the system under a set of busi-ness scenarios is Pareto optimal.

As there are several performance criteria, the design problem includes an important communication task:

To effectively present the Pareto optimal de-signs and their trade-offs to the decision maker(s) so that person(s) with expertise in the process/business domain but not in the modelling/optimization methods are able to make justified design decisions based on the data produced during the mathematical analy-sis of the design problem.

The design methodology developed in EffNet consists of the following main steps:

1. Mathematical problem formulation. This step translates the process description, objectives and constraints, degrees of freedom, reference process information and long-term business and technology environment scenarios from verbal information into mathematical expressions that can be used in the mathematical (multi-objective) design optimization.

2. Constructing the dynamic process (superstructure) model that allows assessment of the life-time performance of any production system within the scope of degrees of freedom.

3. Implementing operational optimization in the dynamic process model. In this step the control degrees of freedom are included in the analysis. Each production system performance is compared when optimally operated, although the exact form of optimal operation may depend on the system structure and parameters.

4. Multi-objective design and presentation

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of the decision alternatives to the decision maker. At this stage the life-time performance of the system is assessed in order to generate “trade-off surfaces” for the design objectives. This is computationally extremely demanding. Presenting the options to the decision maker is therefore an important part of the methodology.

5. Robustness/sensitivity analysis examines the extent of the changes imposed on the performance of the chosen design when the parameters in the dynamic process model are varied within their uncertainty range.

6. Validation implements the chosen design with a more detailed process simulator in order to safeguard against phenomena neglected in the model used in the computationally heavy design optimization.

The problem formulation includes specifying first verbally and then mathematically the fol-lowing:

(i) Process description (ii) Metrics for process performance,

including constraints and other limitations(iii) Degrees of freedom (iv) Reference process information(v) Long-term scenarios

Models are constructed at three levels:

(i) Validation model; detailed description of the final design candidate, usually implemented on a platform such as APROS; the critical requirement is that it must support both process and control/operations modelling.

(ii) Nominal model; somewhat simplified process model (e.g. tank dynamics, separations with constant retention parameters, etc.) used in estimating the performance of a large number of design

options; the critical requirement is that the computation time must be 1/100000 of real time.

(iii) Model for operational optimization; simplified – typically a linearized version of the nominal model – nests inside the nominal model and is used at each time step to find the optimal sequence of actions over time horizons of hours; the critical requirement is the speed of computation, which must be such that the nominal model including this model satisfies the requirements for computational time.

Operational optimization is a dynamic pro-gramming problem which, for nonlinear mod-els, has been solved using the receding hori-zon model-predictive control approach.

In multi-objective design, the task is to obtain a process structure with good performance in the long-term in all respects. In papermak-ing, the processes considered are dynam-ic and, due to web breaks, stochastic. As the evolution of the process states is stochastic, the process performance over a time period is a random variable. In design optimization, the process performance is evaluated based on long-term simulations with the nominal model with nested operational optimization that includes the prediction model. In an ideal case, the process is simulated over the entire life time; in practice, simulations span a peri-od of months up to a year. Thus each simula-tion provides a sample vector of the process performance. The performance of the process is calculated as the mean of the performance samples from the design simulations.

In order to solve optimization problems while taking into account multiple objectives, multi-objective optimization methods have to be ap-plied. These can be classified as a priori, a pos-teriori, interactive and no-preference methods

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based on the time when the preference infor-mation is taken into account. The interactive methods for solving multi-objective optimiza-tion problems are very useful as they involve the decision maker in the solution process and enable learning about the problem. These methods elicit preference information from the decision maker progressively. At each itera-tion, the decision maker is presented with one or more designs and asked to express prefer-ences relative to them. Interactive methods facilitate comparing performance trade-offs. However, in simulation-based optimization and in design optimization in general, it is time-consuming to compute new solution(s) and the decision maker cannot be realistically expected wait for the next results. Therefore, the multi-objective computationally intensive problem was replaced by a surrogate problem with the same performance objectives. The surrogate problem must be computationally inexpensive in order to eliminate waiting times in the interactive process. The use of a surro-gate problem for real-life decision making con-

sists of three stages. The stages are classified as the pre-decision making stage, the decision making stage, and the post-decision making stage. The decision maker is directly involved only in the decision making stage, whereas all computationally intensive tasks are carried out in the pre- and post-decision making stag-es. The stages along with their main compo-nents and the dependences among them are illustrated in Figure 1.

In the pre-decision making stage an a poste-riori method is applied to the multi-objective design optimization problem to produce a set of Pareto optimal decision vectors that are used to define the surrogate problem. In the decision making stage, the computationally inexpensive surrogate problem is tackled: the decision maker identifies the preferred per-formance vector. In the post-decision making stage, the original multi-objective design opti-mization problem is solved in a scalarized form to project the objective vector (of the surro-gate problem) preferred by the decision maker

Figure 1. A solution approach consisting of three stages (MO: multi-objective, SO: single objective).

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to the Pareto optimal set of the original design optimization problem.

The three-stage solution allows fluent interac-tion with the decision maker regardless of the computational intensiveness of the simulation model. The solution process is motivated by the PAINT method to create a surrogate prob-lem for decision making, and by the availability of multi-objective optimization methods such as ParEGO and SMS-EGO that provide a finite approximation to the Pareto optimal set of a multi-objective optimization problem.

The decision maker requires visualization sup-port to deal with multiple conflicting objec-tives in their search for a preferred solution. For example, simple pairwise projections of the Pareto optimal solutions can be provided to the decision maker, as shown in Figure 2. The solutions for a problem with four objec-tives can be presented as a 3D figure in which the fourth objective is represented by different colours depending on its value (see Figure 3).

The Pareto optimal solutions should be pre-sented in a convenient and understandable way to reduce the cognitive load on the de-cision maker when considering the trade-offs. Therefore, the decision maker has to select the most comfortable visualization.

Interactive methods require active participa-tion of the decision maker. An example inter-active method is the NIMBUS method, which is implemented in the IND-NIMBUS software. The graphical user interface of the NIMBUS method is presented in Figure 4.

After selecting the design candidate, the ro-bustness of the performance of the chosen candidate with respect to the model simplifi-cations and parameter values used must be analysed. Robustness describes the model’s ability to operate in different conditions where the chosen model parameters are not exactly correct. The robustness of the chosen opera-tional optimization is examined by simulating the process using different parameter values

Figure 2. Pairwise projections of objective functions

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in the simulator (nominal model) than in the operational optimizer (prediction model). The parameter values are cross-studied in the sim-ulator and optimizer.

The robustness of the design is studied by var-ying the nominal model parameters slightly and studying the corresponding changes in perfor-mance. The degree of the “slight variation” re-flects the uncertainty of the parameter. When varying the parameters, it should be recog-nized that there are constraints between them.

For example, a nominal quality value may have been defined as a starting point for the design analysis. This is achieved by a combination of material property parameters. If the param-eters are varied one at a time, the reference point changes. Instead, they must be varied so that the nominal quality value is maintained.

Sensitivity analysis assumes linearity of the pro-cess performance with respect to the param-eters in the analysis range. A typical nominal model for the design analysis includes 30-300 parameters, preventing the analysis of cross ef-fects, which scales as the square of the number of parameters. In the paper production system, the parameters of the break probability model are based on rather vague assumptions. Thus, its robustness with respect to the break model parameters needs to be studied carefully.

The nominal model used in the design optimi-zation is based on approximations of the real system, thus it might contain certain inaccu-racies. The validation model is as realistic a model as possible, including more features of the real process. The objective of the valida-tion model is to test with the final design how

Figure 3. 3D Pareto optimal solutions representation, with fourth objective value shown in different colours.

Figure 4. Screen shot of the graphical user inter-face of the NIMBUS method in the IND-NIMBUS software.

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sensitive the process performance estimates are to these finer details of the process.

4.2 Concept cases

Fines-coated LWC (concept case 1, CC1)

The first concept studied was based on applying a TMP fines fraction as a coating for LWC paper.

A dynamical model for CC1 was drawn up on the basis of the diagram shown in Fig-ure 5. The economic performance assess-ment shows that radical improvements can be achieved only if the content of fines in the coating is high, e.g. 40%. As there is currently no unit process technology available for this, the unit process development must be accom-panied with concept optimization.

Figure 5. Model for concept case 1. The key elements are fractionation of the TMP so that the fines frac-tion can be applied to the surface, and surface preparation with the fines-based “coating colour”. Bal-ancing the two parallel TMP lines (fibres and fines) in dynamic conditions (breaks, variable dosage of broke) are the main operational challenges, which also necessitate new chests in the system.

The main dynamic control challenge is that, due to fractionation, there are two parallel mate-rial flow lines of TMP that need to be balanced in dynamic conditions caused by, for example, web breaks and/or a variable amount of broke used in the base paper furnish. The material flow vector was divided into 17 components indicat-ing the proportions of furnish components in the base paper and surface layers. A dynamic oper-ational optimization was implemented with ob-jectives related to quality and constraints relat-ed to tower overflows/running empty.

The dimensioning of the fractionation was giv-en fixed. Structurally, one open question was where to direct the overflow from the fines chest, the options including the broke chests, mixing chest, TMP proportioning chest or TMP tower. After initial assessments, the TMP tow-

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er was chosen due to the high consistency of the fines fraction and the consistency uniform-ity problems presented by the other locations.

The design was given five objectives:

- Investment costs (min)- Average proportion of time spent in

uncoated breaks (min)- Average time till volume overflows/empty (max)- Average deviation of light scattering

coefficient from target value (min)- Average deviation of strength coefficient

from target value (min)

The design degrees of freedom were four tower volumes and two operational parameters:

- Volume of a white water tower- Volume of an uncoated broke tower- Volume of a coated broke tower

- Volume of a clear filtrate tower- Short-term risk of tower overflow- Relative weighting of quality variations in

operational optimization

Over 300 non-dominated solutions were gen-erated in the simulations (stage 1, Figure 6). Each simulation was run till first tower over/underflow or, at most, to a time correspond-ing to approximately 9 months of process op-eration. Each design was simulated 80 times and the averages of the objective values were computed for each design to determine non-dominated solutions. The parallelized compu-tation took some 13 days on a grid consisting of 160 computers (Kivikasa grid, University of Jyväskylä) using the parallelized Matlab com-putation tool. Illustrating the non-dominated points in a five-dimensional space of objec-tives is somewhat challenging. However, Fig-ure 6 gives these in projections to planes of two objectives at a time.

Figure 6. Projections of the non-dominated solutions to the planes of two objectives at a time.

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The set of non-dominated solutions was used to create a surrogate problem using the PAINT method, which was solved by the NIMBUS method implemented in IND-NIMBUS soft-ware. With NIMBUS the decision maker can search for the most favourable design by ex-pressing their preferences, by indicating the desired trade-off among the objectives (as in Figure 4). When the most favourable design in the objective space (of the surrogate prob-lem) is found, then the closest objective vec-tor of the original problem can be sought in two senses: either the closest by to one of the non-dominated designs or closest by to the interpolated set of non-dominated solutions. The first option readily gives the design pa-rameters corresponding to the objective vec-tor of the surrogate problem selected by the decision maker, whereas the second requires further simulations to find the projection of the objective vector of the surrogate problem

selected by the decision maker over the non-dominated solution set of the original problem.

The results were discussed, but no actual de-cision-making exercise was carried out. The following three points of criticism were raised:

- The non-dominated solutions do not have the expected property that the sum of water volumes would equal the sum of broke volumes. This is probably because there was no constraint on water intake/outflow from the balance area. This emphasizes the importance of setting the objectives at the design and at operational level so that they cover all aspects.

- The designs were based on average values of objectives. As Figure 7 shows, the distributions of the objective values are rather wide. Therefore, a more appropriate design would probably be based on a

Figure 7. Distribution of the objectives for a non-dominated design, 80 simulations. Wide distributions suggest that designs should be considered also from the x worst-case percentile approach.

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percentile basis: if x percentage of the worst cases are first eliminated from the analysis, what is the remaining worst case.

- The design aspects were focussed on issues of, at most, moderate economic interest (a few million euros). This is because the degrees of freedom given were rather narrow, e.g. the volume of the fractionation was fixed. In practical decision making, the main issue in CC1 would be the technical feasibility of the application of fines on the paper surface; this could not be analysed with the techniques used in the optimization study.

A more general concern expressed was that as the approach hinges on process models, the ac-curacy/reliability of the models should be as-sessed and the sensitivity to the key model pa-rameters should always be analysed in detail. Sensitivity analysis shows the most critical pa-rameters to be those related to the break model.

High filler content fine paper

The second concept studied was based on fill-ers manipulated to form binding structures for

increasing the filler content of fine paper from the current 30% to 40%. In the analysis it is as-sumed that the retention of binding filler in the short circulation is 0.6 (corresponding typical-ly 0.25..0.3 first pass retention) and that all fill-ers leaving the short circulation area lose their binding capacity. A critical issue in this concept is runnability. The break tendency was assumed to be such that with a nominal (all filler binding) recipe, the time spent in breaks is 3%, whereas with a realistic (non-binding filler recovered and reused) recipe the figure is 7% on balance.

The analysis is based on a conventional fine paper mill layout. The degrees of freedom in the study were the buffer volume (broke and clear filtrate), disc filter capacity, and opera-tional parameters. Either clear filtrate or white water can be used for broke dilution. The main objectives were to minimize:

- Capital employed- Loss of production time due to breaks- Variations in filler content- Solids lost through the broke system

(insufficient capacity)

Figure 8. Process model for the high filler content fine paper concept case. Two options for broke dilu-tion are indicated.

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A dynamic process model for seven material components at 10 min time step was devel-oped for process alternatives, see Figure 8.

The operations were developed as dynamic optimization, characterized by three param-eters related to the aggressiveness of broke volume management. Figure 9 shows two ex-treme ways of operation.

The performance of the design alternatives was studied through simulations corresponding to one year of mill operation. The simulations were repeated ten times and the average was taken as the performance vector. Initial sets consisting of 125/133 (dilution with clear filtrate/white water) Pareto optimal solutions were constructed for a range of performance values, see Table 1. The range was further narrowed on the basis of these

Figure 9. Two extreme ways to manage broke dosage. Top 4 curves: aggressive control causing varia-tions but helping to manage volumes. Bottom 4 curves: conservative control, no variations but volume management problems.

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results and 948/551 Pareto optimal solutions were constructed for a range of performance val-ues, see Table 2. Pairwise comparisons of these are presented in Figure 2 and a three-dimension-al presentation with the fourth objective colour coded in Figure 3 as examples of the methodol-ogy. The results can be analysed either by rotat-ing the 3D presentation or through a surrogate model and decision maker interaction through the NIMBUS programme (Figure 4).

The main observations are that at investments above EUR 9 million, operability becomes quite good in all respects, whereas with invest-ments below EUR 6 million good compromises can be reached, but not completely problem-free operation. The results also show that with constant investment the system with clear fil-trate dilution performs better than that with white water dilution.

If retention in the short circulation falls below 0.6 (and fillers leaving short circulation lose their binding capacity), managing the quality and runnability of the system becomes very difficult, even with large investments in buff-ering volumes and internal water purification. Folding boxboard with foam-formed middle plyThe task was to design a production line for folding box board in which the middle ply is formed using a foam forming technique. Be-cause there is no reference case of mill-scale foam forming, the technique was applied to a mill with a traditional water forming process with the middle ply section modified to corre-spond to foam forming. Technical information of the reference line was provided by Metsä Board. Parameter information of the foam forming technique was based on the laborato-ry and semi-pilot scale trials conducted at VTT Jyväskylä as part of EffNet.

As the study was initially resourced for only two application studies, the third case study was an add-on and thus not all steps of the methodology were worked through in detail. The case study developed a process mod-el and operational optimization suited for de-sign analysis, but no systematic construction of Pareto optimal designs was made.

Figure 10 presents the process structure. The process corresponds to a normal three-ply board line. The most significant revisions are made to the approach system of the mid-dle ply and to the water system. The foam-ing chemical is mixed with the stock just be-fore the forming section. The chemical retains its foaming capacity after the forming sec-tion, with most of the chemical ending up in the water system. To avoid foaming in the wa-ter towers, defoamer is used in the disc fil-ter feed. However, defoamer in the water cir-culation also decreases foaming capacity in the forming section. In the model, any single

Table 1. The initial performance range studied.

Table 2. Narrowed performance space, limited to EUR 5.5-7.5 million investment.

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flow may include only either foaming chemi-cal or defoamer, i.e. the reaction between the chemicals is assumed to be complete. Foam-ing chemical is dosed before the forming sec-tion using a simulated control loop with a real-istic time constant of 30 minutes.

As the phenomena and possibilities of the foam forming were partly unknown, the dry solids content after the forming section can be parametrically tuned in the model to anything between 8% and 25%.

In the model, each flow was defined as a flow vector of fifteen elements: water, CTMP, MFC, filler, pigment, foaming chemical, defoamer, broke (two pulps, CTMP, MFC), broke filler and broke pigment. The dynamic process model was based on a steady-state model in which the nominal state was defined.

The simulator can easily be modified to incor-porate future changes in the model and opera-tional control. Figure 11 shows a simulation case study. This model and the operational optimi-zation within it can be used to compare differ-ent process parameterizations, both concerning

foaming chemical, defoamer and process vol-umes and retentions in separation processes.

4.3 Workflow in conceptual process design based on modelling and multi-objective optimization

The bi-level multi-objective optimization (BLMOO) method in EffNet WP9 was applied to the design of paper manufacturing facilities. This subsec-tion proposes a business process guideline for a business process in a real-scale business en-vironment. The proposed business process was evaluated by expert interviews and critical suc-cess factors based on the concept case projects.

The conventional process plant design process is described with the linear waterfall model. The design process consists of problem anal-ysis, conceptual design, detailed engineering and construction. The BLMOO method mainly addresses the conceptual design phase.

Current practice in forest industry process en-gineering is almost solely based on engineering experience. Mass and energy balances of oper-ating points can be defined with steady-state

Figure 10. Process model for the folding boxboard concept with foam-formed middle ply.

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Figure 11. An example of simulated dynamics of the folding boxboard case.

Figure 12. BLMOO design adds the optimization and modelling organization to the conventional design organization consisting of the end user and engineering. BDM = business decision maker, TDM = tech-nology decision maker, BC = business consultant, D = designer, A = analyst, VM, M1, M2, M3 = modellers.

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simulation. Dynamic simulation is used in the design of unit processes, but less in the design of the process as whole. The process structure is designed in general first and the operation of the plant after that. BLMOO studies the options more widely and may consider various busi-ness possibilities in the design. Plant-wide sim-ulation enables the validation of process struc-ture and control concepts before an investment decision and therefore reduces risks. In BLMOO method, both the process structure and control

concepts are designed simultaneously, which leads to more systematic trade-offs.

The BLMOO method introduces a new element to the engineering organization, the optimi-zation and modeling organization (Figure 12). In particular, the key role of the analyst (A) is added. Furthermore, as the optimization task requires additional nominal and predictive models, two modellers are added (M2 and M3). It should be noted that whereas the designer

Figure 13. Workflow in BLMOO design.

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mostly communicates with the technical deci-sion maker and the business consult with the business decision maker, the analyst must be proficient in both technical and business mat-ters in order to form the optimization task and communicate the results. The iterative na-ture of the design process cannot be avoided, which leads to close cooperation between the designer, analyst and modellers. These can then share common knowledge about process design, mathematical formulation, modelling and optimization, which constitutes a critical requirement for the BLMOO as business; in particular as the changes in the interface be-tween the customer organization and engi-neering organization need to be kept minimal in order to be able to compete with engineer-ing organizations offering traditional design.The workflow of the BLMOO method is de-scribed in Figure 13. This further emphasiz-es the role of the Analyst as being capable of communicating about business, process, modelling and optimization issues.

The organizational structure and workflow pre-sented here provide the basis for a business model for BLMOO consultancy as a service. It is therefore concluded that the main customer of the service business is the engineering organi-zation, which may be a consultant to the end customer or, in some cases, the engineering or-ganization within the end customer.

5. Exploitation plan and impact of results

This study addresses the key economic chal-lenge of the forest-based chemical industries – capital intensiveness. The results are consid-ered essential to the renewal of the industry and are expected to contribute strongly to the selection of future production concepts and their unit process technology.

For technical and economic credibility of the multiobjective bilevel design methodology in-cluding both structural and operational as-pects is crucial for its rapid uptake. The con-cept case studies within EFFNet serve three exploitation/impact purposes. Firstly, the con-cept is expected to be essentially improved by such an analysis, and made more rapidly transferable to the implementation stage as operational aspects are addressed early on. Secondly, the case studies demonstrate the benefits of the approach to the end users and hence create markets for the design method-ology as a service. Thirdly, the concept analy-sis is closely monitored in order to define the work flows and practices involved in the de-sign approach, thus creating the way of work-ing and business model for provision of the model-based design optimization as a service.

Furthermore, the design methodology is quite generic and can be applied not only to the de-sign of papermaking systems but also to pulp production and biointegrates. Cooperation be-tween all FIBIC programmes related to new production systems is a further exploitation avenue to be examined.

The design methodology has been of practical importance also when paving the way for the uptake of new process technology. The meth-od reveals the key issues of concern when im-plementing new technologies in new environ-ments, thus guides the research to cover all relevant aspects. The operational optimization methodology can be readily implemented on existing production systems.

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Role

Work Package Manager. Task Leader for concept case

studies. Formulation of the design optimization prob-

lem and the related operational optimization problem,

participation in solving the case design problems.

Task Leader for work flow analysis. Design work flow

analysis and development of a new work flow for

model-based multi-objective, optimized conceptual

design.

Modelling for the design case studies, participation in

solving the case design problems.

Task Leader in multi-objective optimization methods,

formulation and solvers. Participation in solving the

design case problems.

Modelling for the design case studies, participation in

solving the case design problems, design validation.

Partner

Tampere University of Technology,

Department of Automation Science and

Engineering

Aalto University, Information

Technology in Automation

University of Eastern Finland,

Paper Physics

University of Jyväskylä,

Industrial Optimization

VTT Technical Research Centre of

Finland, Systems Dynamics

Table 3. Partner organisations and their research roles.

6. Networking

The research was carried out jointly by re-search organisations and Finnish forest clus-ter companies. Table 3 presents the research partners and their roles.

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7. Publications and reports

Linnala, M., "Optimization and simulation tools in paper machine concept design", PaP-SaT/FPIRC Annual Seminar, 22.-24.8.2011, Lap-peenranta, Finland

Linnala, M., Hämäläinen, J., "Improvement of the cost efficiency in papermaking with opti-mization tools", was presented at PAPTAC Pa-per week, 2011.

Linnala, M., Hämäläinen, J., "Improvement of the cost efficiency in papermaking with op-timization tools", The Journal of Science and Technology for Forest Products and Process-es, 1(2), 71-76, 2011.

Linnala, M., Hämäläinen, J., "Model-based op-timization in papermaking process design", Progress in Paper Physics Seminar, 5.-8.9.2011, Graz, Austria

Linnala, M., Hämäläinen, J., "Bi-level optimi-zation in papermaking process design", Nordic Pulp and Paper Research Journal, 27(4), 774-782, 2012.

Linnala, M., Madetoja, E., Ruotsalainen, H., Hämäläinen, J., "Bi-level optimization for a dy-namic multiobjective problem", Engineering Optimization, 44(2), 195-207, 2012.

Miettinen, K., Steponavice, I., and Ruuska, S., Challenges of Multiobjective Optimization in Integrated Design and Control: Case Study in Paper Making, 17th International Confer-ence on Mathematical Modelling and Analysis (MMA2012), Tallinn, Estonia, June 6-9, 2012

Rajala, M., Ropponen, A., Ritala, R., "Multi-ob-jective supervisory control of furnish flows", presented at PAPTAC Paper week, 2011

Ropponen, A., Ritala, R., Pistikopoulos, E.N., “Optimization issues of the broke manage-ment system in papermaking”, Computers & Chemical Engineering, 35, 2510-2520 (2011)

Ropponen, A., Rajala, M., Ritala, R., "Multi-objective optimization of the pulp/water stor-age towers in design of paper production sys-tems", ESCAPE-21 conference, Thessaloniki, Greece, June 2011.

Ropponen, A., Ritala, R., "Multiobjective op-timization of process design and operation: a case study on paper production", 21st Interna-tional Conference on Multiple Criteria Decision Making, 13-17.6.2011, Jyväskylä, Finland

Ropponen, A., Ritala, R., "Specifying risk lev-el for constraint violation in stochastic system - a case study on papermaking" ESCAPE-22, London, UK, June 2012.

Ropponen, A., Ritala, R., "Operational optimi-zation of flow management in papermaking”, Control Systems 2012, April 2012, New Orleans, USA.

Ruuska, S., Miettinen, K., Wiecek, M., "Refor-mulations for Bilevel Multiobjective Optimiza-tion", 21st International Conference on Multiple Criteria Decision Making, 13-17.6.2011, Jyväsky-lä, Finland

Ruuska, S., Miettinen, K., Wiecek, M., "Con-nections between Single-level and Bilevel Multiobjective Optimization", Journal of Opti-mization Theory and Applications, 153(1), 60-74, 2012

Ruuska, S., Miettinen, K., Constructing Evo-lutionary Algorithms for Bilevel Multiobjec-tive Optimization, in "Proceedings of the 2012 IEEE World Congress on Computational Intelli-gence", IEEE Press, 374-380, 2012.

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Savolainen, J., Saarela, O., Lappalainen, J. and Kaijaluoto, S., 2011, "Assessment method of dy-namic, stochastic process models with an appli-cation to papermaking", Nordic Pulp and Paper Research Journal, vol. 26, no. 3, pp. 336-348.

Steponavice, I., Miettinen, K., “On Multiob-jective Robustness for Simulation-Based Op-timization”, 21st International Symposium on Mathematical Programming, Berlin, Germany, August 19-24, 2012.

Steponavice, I., Miettinen, K., , “Multiobjective Optimization of Integrated Design and Control of a Paper Mill”, 22nd International Conference on Multiple Criteria Decision Making, 17-21 June 2013, Málaga, Spain

Steponavice, I., Ruuska, S., Miettinen, K., "Ex-pensive Robust Multi-Objective Optimization in Process Design and Operation", 21st Inter-national Conference on Multiple Criteria Deci-sion Making, 13-17.6.2011, Jyväskylä, Finland.

Steponavice, I., Ruuska, S., and Miettinen, K., Decision making in a multi-objective paper mill design problem, 25th European Conference on Operational Research (EURO2012), Vilnius, Lithuania, July 8-11, 2012.

Steponavice, I., Ruuska, S., and Miettinen, K., On Challenges in Simulation-based Multi-objective Optimal Design with an Application in Paper Industry, submitted for publication in Computer-Aided Design

Strömman, M., Seilonen, I., Koskinen, K., “Chal-lenges in Applying Optimization in the Design of Continuous Processes – Case: Collaborative Optimizing Design of Pulp Fractionation Pro-cess”, SIMULTECH 2012 (2st International Con-ference on Simulation and Modeling Method-ologies, Technologies and Applications. Rome, Italy 28-31, July 2012

Strömman, M., Seilonen, I., and Koskinen, K.,”Collaborative optimization based design process for process engineering,” in Simula-tion and Modeling Methodologies, Technolo-gies and Applications, J. Kacprzyk N. Pina and J. Filipe(Eds), Berlin: Springer (In press).

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Strömman, M., Seilonen, I., Peltola, J., Koski-nen, K., “Integration of Optimization to the De-sign of Pulp & Paper Production Processes”, in Simulation and Modeling Methodologies, Tech-nologies and Applications. Nuno Pina, Janusz Kacprzyk, Joaquim Filipe (Eds.). Advances in In-telligent Systems and Computing, Vol 197. ISBN 978-3-642-34335-3. Springer-Verlag 2012

Efficient Networking Towards Novel Products and Processes (EffNet) is one

of FIBIC´s research programmes. The focus of the EffNet programme is on

developing radically new energy- and resource-efficient web production

technologies and designing nanocellulose-based production concepts and novel,

innovative products. The overall goal of the EffNet programme was to develop

sustainable solutions to ensure the leading position of the Finnish forest cluster in

the large-scale production of fibre-based printed and packaging products.

www.fibic.fi