compounding pvc with renewable materials
TRANSCRIPT
Compounding PVC with renewable materials
D Martinz1
J Quadros2
1
Solvay Indupa do Brasil Ltda
Address: Rua Urussui, 300, São Paulo, SP, 04542-903, Brazil
Email: [email protected]
2 Nexoleum Bioderivados Ltda.
Address: Estrada do Capuava, 1650, #2, Cotia, SP, 06713-630, Brazil
Email: Email: [email protected]
ABSTRACT
In the wake of the recent technological pursuit of renewable and sustainable solutions, PVC
(Polyvinyl Chloride) compounds appear as an additional alternative. This paper covers the
review of PVC compounding with renewable materials, including raw materials production
technology, market dynamics, and the technical aspects of the finished products when
compared to current solutions. The objective is to demonstrate the viability of a renewable
PVC compound, observing technical and commercial aspects, based on existing literature
and recent developments. The paper covers the description and evaluation of PVC resins
produced from renewable ethylene and plasticizers obtained from vegetable oils.
This paper will cover commercial aspects, with an overview of the market dynamics
changes that enabled the competitiveness of bio-based materials as a global phenomenon.
It will also outline the agricultural technology breakthroughs and challenges and the
existing state of the art of the chemical processes to obtain renewable components for PVC
formulating. The market overview will also include indicative costs of current materials.
Additionally the paper will cover a technical review of the existing literature on PVC
formulating, compiling the existing options to formulate with renewable components. It
will also reveal recent evaluations and a comparison of existing commercial materials,
tabulating the results of well known test methods, covering S-PVC compounds mechanical
properties, plastisols rheology and ageing, and compatibility. It will also present a table
comparing one example of a renewable solution to a current traditional compound.
The paper concludes that a PVC compound formulated with renewable resin and plasticizer
is not only viable, but it arises as a natural evolution in the direction of a more sustainable
PVC supply chain. As a sample calculation, 1 ton of a clear flexible vinyl formulation with
100 phr resin and 60 phr plasticizer would remove 4.3 tons of CO2 from the atmosphere.
Keywords: renewable compound, green PVC, sustainable, resin, vegetable plasticizer, bio-
ethanol
INTRODUCTION
This paper intends to address the question of technical, environmental and commercial
viability of a renewable PVC compound.
In the past years, the scientific community has invested significant amounts of time and
resources to evaluate the impact of human activities on climate change and the
environment. At the same time, crude prices have soared to high levels, similar to those
observed during the great petroleum crisis of the decade of 1970 [1]
. The recent rise of the
petroleum prices can be explained by a series of market forces, such as political instability,
increased demand and changes of the strategic positioning of major producers.
The last 20 years have also seen a continuous evolution of agriculture technology, including
the areas of soil enrichment through fertilizers, reduction of losses with improved
agrochemicals and storage, yields with irrigation, and species through genetic selection and
modification[2] [3]
.
After the first petroleum crisis, many companies and governments concerned with raw
material availability invested in the development of renewable, sustainable alternatives.
The result of this movement was the creation of new markets, such as the ethanol fuel in
Brazil. In this second wave of the search for renewable alternatives, motivated by high
petroleum prices and environmental concerns, many other fronts have been opened to
explore vegetables as energy and raw material alternatives. The number of bio-based
products related patents issued has increased significantly in the past years[4]
.
Figure 1: Historical evolution of bio-based product patents
The technology to obtain petroleum substitutes from vegetable and animal sources is not
new. It is, in many cases, older than the processes that use petroleum as raw material.
What is new is that vegetable originated materials are becoming more and more
competitive and relevant to the needs of our global society. As a consequence, the
technology to extract useful materials from vegetables is improving significantly, resulting
in improved final quality and productivity.
To produce a renewable PVC compound, this paper will focus the analysis on two major
formulation elements (resins and plasticizers), demonstrating the technology of production,
commercial and environmental sustainability and the quality in the final applications. The
Number of Industrial Biotech Patents IssuedSelected Industrial Bio-Products/Processes
22300
18900
1600011800
6200
103000
19800
0
25000
50000
75000
100000
1900 1999 2000 2001 2002 2003 2004 2005 Total
detailed evaluation of fillers and other additives, due to time and space limitations, should
be the object of a later study.
GREEN PVC
PVC Polymerization – Generals
Two of the most important raw materials to obtain PVC intermediates are salt, which
provides the chlorine source, and ethylene, the hydrocarbon source. Salt comes from the
seas or mines and ethylene is obtained from oil. Chlorine coming from salt electrolysis is
reacted with ethylene in order to produce 1,2-dichloroethane (DCE). DCE is then pyrolyzed
to split into vinyl chloride (VCM) and hydrogen chloride (HCl), which are separated
afterwards via distillation columns. VCM is fed into reactors to be converted into PVC and
HCl is sent to the oxychlorination unit, where it is combined with oxygen and ethylene to
obtain extra dichloroethane, which is fed into the pyrolysis unit. The whole process is
illustrated on figure 2.
Figure 2. PVC manufacturing process (adapted from Nass and Heiberger, - Encyclopedia of
PVC – 2nd
Edition)
From Sugar and Salt to PVC
PVC is known to be a polymer consisting of 43% hydrocarbons and 57% chlorine. This
characteristic gives a natural advantage when it comes to fossil fuels supply, mainly
ethylene. With the increasing prices of oil, alternative routes to produce ethylene became
more and more attractive. One of them is the so called bio-ethylene route or ―green route‖,
i.e., the generation of ethylene from ethanol coming from sugar cane.
The process itself consists in dehydrating ethanol obtained from fermented, distillened
sugarcane juice (see fig 3). Ethanol is evaporated and fed into a multi-stage adiabatic
reactor, composed of a series of four catalytic beds. Ethylene and water are then separated
through distillation in a column. Ethylene is compressed and dried via molecular sieve. A
further purification is necessary in order to comply with the specifications for 1,2-
dichloroethane production. This last stage involves one extra distillation. Overall reaction is
described below and 1.9 ton ethanol produces 1 ton of ethylene.
Chlorination
Oxychlorination
DichloethanePyrolysisPurification
Chlorine
Ethylene
Oxygen
DistillationHCl Stream
Vinyl Chloride
PolymerizationPVC
This bio-ethylene is then pumped into the reactor to combine with chlorine, and the process
follows as in figure 3.
Figure 3. Ethylene manufacturing process from Ethanol (Solvay Indupa technology)
Brazilian Ethanol
Brazil has a total arable surface of approximately 360 million hectares (52% of its territory,
and 22% of the total arable area of the world[5] [6] [7]
), 5.0 million[8]
of them indented for
sugar cane crops. In other words, only a small portion of the arable Brazilian surface
(~1.2%) is used for sugar cane plantations. Besides being renewable, ethanol is known to
remove and fix CO2 from the atmosphere.
Bioethanol-based Vinyl Brazilian Project
In South America, Solvay Indupa is one of the leading PVC manufacturers, with one plant
in Brazil (Santo Andre) and one in Argentina (Bahia Blanca), presenting a total capacity of
500 kt (thousand metric tons) of PVC/ year. The Brazilian affiliate has just announced an
investment program to expand vinyls production from current 300 to 360 kt/year of PVC,
including the creation of an integrated plant to produce bio-ethylene with ethanol coming
from sugar cane.
The project will be finished in the first half of 2010 and forecasts a production of 60 kt/year
of bio-ethylene and 55 kt/year of green PVC, i.e., PVC produced from an entirely
sustainable source. It is expected a consumption of 100 kt of ethanol/ year. This will be
then the first industrial facility in Americas using renewable resources for PVC production.
This innovation is cost-effective and will prevent the emission of 300 kt/year of CO2 into
the atmosphere, generating carbon credits.
The final resins, produced from ethanol shall present no difference when compared to the
oil based resins, since the specifications of the raw materials (ethylene, chlorine) are
exactly the same in both cases. This quality similarity has been widely verified in the past,
from previous productions of ethanol based PVC by Solvay from 1962 to 1982.
RENEWABLE PLASTICIZERS
Some well known renewable plasticizers, such as epoxidized soybean oil and epoxidized
linseed oil have been present for more than 50 years in flexible PVC formulations.
Although not considered to be primary plasticizers, these two materials are well known for
improving the weathering and thermal stability of the final compound, since the synergy
with metallic salt thermal stabilizers (especially Ba/Ca/Zn) greatly improves the protection
of PVC against degradation in high temperature[9]
and Ultra Violet (UV) exposure[10]
.
The main concern with these materials was their compatibility (exudation) and long term
stability. Wickson and Lutz[10]
also indicated that the compatibility retention of epoxidized
oils is inversely related to the iodine index. A reduction of the iodine index from 13 to 3
resulted in a useful life three times longer for the product formulated with Epoxidized
Multi-stageDehydration
EthanolPurification Ethylene
Ethylene, H2O and Others
Soybean Oil (ESO). A further reduction of the iodine index to 1 resulted in another two
times compatibility retention. The oxirane content is directly related to compatibility, since
it indicates the concentration of molecules that have effectively been epoxidized. A low
oxirane content may indicate that the reaction was incomplete or that oxirane rings started
to open, forming less compatible hydroxyl groups. The conclusion, verified by weathering
experiments, is that the efficiency of the epoxidation process, maximizing oxirane content
and minimizing iodine index, is vital to obtain a compatible, long lasting vegetable
plasticizer.
Another problem with the traditional epoxidized vegetable oils was the limitation of use,
due to their higher molecular weight. Depending on the application and the components of
the formulation, both ESO and Epoxidized Linseed Oil (ELO) may be limited to a
maximum percentage, to avoid the risk of exudation. Also, both materials are not sufficient
to provide enough flexibility for the formulators to achieve the desired physical and
chemical properties of the compound. Traditional plasticizers, such as phthalates and
adipates would be necessary to provide additional degrees of freedom.
In past and recent years, researchers[11] [12]
found that epoxidized esters obtained from the
transesterification of various alcohols with vegetable oils were fully compatible with PVC
resins, as much as well known phthalates such as DOP or DINP, with the added advantages
of the improved UV resistance and higher thermal stability. Good compatibility has also
been observed for the acetylation of castor oil[13]
. These materials have been extensively
tested in the recent years and have been used commercially for many applications. The
freedom of choosing the alcohols and the vegetable oils offers a huge range of possibilities
Figure 4: Theories of Compatibility
Key:
2: DOA (Dioctyl Adipate)
6: BES (Butyl Epoxy Stearate)
7: OES (Octyl Epoxy Stearate)
18: DOP (Dioctyl Phthalate)
21: DIDP (Diisodecyl Phthalate)
30: ESO* (Epoxidized Soybean Oil)
31: MES* (Methyl Epoxy Soyate)
32: ACO* (Acetylated Castor Oil)
* theoretical only
to obtain useful renewable products, that can be appropriately tailored to each application
and need of the formulator, giving the necessary degrees of freedom to formulate PVC
compounds that will comply with the demands of the final users.
Considering the Hildebrand Parameters as a theoretical measure of compatibility, the curve
below, extracted from Sears and Darby[14]
, compares some vegetable and traditional
plasticizers. The phr of plasticizer absorbed is an indication of compatibility, and the curve
represents the theoretical value versus the actual results.
The market dynamics for renewable plasticizers follows the recent trend where vegetable
derived materials are becoming increasingly more competitive versus the traditional
petroleum based products. The chart below demonstrates prices of crude oil over the
years[15]
, DEHP (or DOP, di-octyl phthalate)[16]
, and soybean oil[17]
. The cost of soybean
oil have recently seen significant increases, but even in this scenario, vegetable derived
materials are presenting a cost advantage over petroleum derived materials.
Pricing Evolution
0
500
1000
1500
2000
2500
jan
/03
jul/
03
jan
/04
jul/
04
jan
/05
jul/
05
jan
/06
jul/
06
jan
/07
jul/
07
$/t
Brazil Soybean Oil (Export)
DOP WE (domestic)
WTI Crude
DOP and Soybean Oil Price Evolution
0%
50%
100%
150%
200%
250%
300%
350%
jan
/03
jul/
03
jan
/04
jul/
04
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/05
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/06
jul/
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jan
/07
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07
0
200
400
600
800
1000
1200
1400
$/t
Ratio DOP WE domestic /SOYBEAN OIL
Gap DOP WE domestic -SOYBEAN OIL
Figure 5: Price evolution charts
The long term competitiveness of vegetable derived plasticizers will depend greatly on the
price differential between petroleum and oilseeds. These two markets are not directly
related, since they depend on significantly different drivers. It is the opinion of many
analysts [18] [19] [20]
, the petroleum price should continue to rise through 2010, stabilize until
2013 and then rise again in the following years. In a recent evaluations regarding oilseeds
markets[21]
, the expected trend is still upwards, but no conclusion was drawn regarding the
maximum forecasted price nor the expected long term effects. It seems that the oilseed
prices, as renewable fuels increase their participation in the overall demand, will be more
and more influenced by the energy demand, moving naturally to a dynamic similar to
petroleum in the long term.
RENEWABLE PVC COMPOUND
Based on the two main raw materials described previously, a renewable PVC compound
can be produced, both in rigid or flexible PVC. The renewable PVC resins, as explained
earlier, will have exactly the same behavior as traditional resins, since the building blocks –
ethylene and chlorine – have exactly the same specifications in both cases. Figures 6 and 7
and Table 1 show some of the evaluations of currently commercial renewable plasticizers
in comparison with traditional oil based materials.
The tests of foam formation for spread coatings presented a significant improvement of
foam quality and reduction of kicker contents for the plastisol formulated with MES when
compared with one formulated with DOP. Also, UV ageing tests demonstrated significant
improvement of UV protection of MES when compared to DOP – the samples with DOP
became brown and sticky, while the samples with MES presented yellowing and no
stickiness. Printability was also improved with the use of MES, due to the higher surface
tension of the compound, resulting in better ink adhesion[24]
.
Figure 6: Fusion Temperatures [22]
Table 1 is a compilation of various results comparing one commercially available and
competitive vegetable plasticizer with DOP (dioctyl phthalate). The results indicate that
the product presents significant similarity to DOP and would be a valid replacement in
many applications. Field tests have confirmed this perception and, as of February/2008,
MES presented a lower market price than DOP in Brazil, and would also be competitive in
Europe, according to published market prices[16]
.
Key:
HES: Epoxy Hexyl Stearate
MES: Methyl Epoxy Stearate
Plastisol Fusion Temperature (°C)
60
80
100
120
140
160
14 16 18 20 22 24 26 28 30 32 34
Number of Carbons
Adipates
Epoxidized Esters
Phthalates
DIDADINA
DOA
DTDP
DIDPDINP
DOP
DBP
BES
EHS
OES
BBP
MES
Figure 7: Thermal Stability, Metrastat @175 °C/min[23]
Table 1: Performance comparison
Compound properties[24]
, adjusted to same hardness DOP MES
Elongation, % 264 357
Tensile Strength, MPa 14.8 16.2
Weight Loss (144 hrs, 40°C), % 0.16 0.51
Weight Loss (72 hrs, 70°C) , % 1.16 3.67
Viscosity of Plastisol (0h, low shear, 1.4 s-1
), Pa.s 3.1 3.5
Viscosity of Plastisol (48h, low shear, 1.4 s-1
), Pa.s 4.8 5.7
Water extraction (75 °C, 1% soapy water, 48h), % 0.13 1.82
Solvent extraction, (Isoparaffin, 48h), w% 14.4 3.36
Butane extraction (48h), w% 18.5 9.7
Fish Eyes, counts/dm2 29 21
Air entrapment measurement, (volume of foam), cm3 53 65
Resin Absorption (max uptake @ 74 °C), minutes 25 8
Low Temperature (Brittleness), °C -20 -23
SUSTAINABILITY
The term renewable in this paper refers to materials obtained from vegetable sources, such
as soybean oil, castor oil, sugar cane, etc. Ethanol based PVC resin and renewable
plasticizers are an obvious improvement in terms of reduction of green house gases in the
atmosphere. Because of their vegetable origin, a certain quantity of CO2 is sequestered
from the air through photosynthesis, resulting in a reduction of total CO2 in the atmosphere.
In the case of petroleum based materials, such photosynthesis happened many millions of
years ago, and the sequestering effect is not relevant to our current needs.
Sustainability, however, refers to a much broader perspective about the life cycle of a
product, including the direct and indirect consequences to the environment and the human
DOP
DIBP
MES
Figure 8[25]
: Renewable concept: the faster removal of CO2 from the atmosphere of bio-
based materials when compared to the fossil cycle.
health of its means of production, its application, and its disposal. In this sense, this paper
will briefly describe and analyze the sustainability of a renewable PVC compound.
Availability of Raw Materials
The substitution of petroleum fuels by renewable fuels such as ethanol and biodiesel are a
controversial issue. The core of the debate lies around the effect of the increased demand
for sugar cane and oilseeds on both food supply and deforestation. The benefits of reduced
CO2 emissions may be countered by the negative effects of reduced offer of land for food
and increased deforestation.
José Roberto Moreira indicates[26]
that the technology is in place to have renewable sources,
coupled with wind and solar power, replace the use of fossil fuels completely by year 2100,
even considering the highest forecasted energy consumption. Such study does not take into
account the social and economic difficulties to carry on such change. It does not, either,
consider the high probability of significant improvements in the current technology of
extracting valuable energy from renewable sources.
In the past years, a significant improvement in energy yields has been noted, which
reinforces the idea that the volume of biofuels and bio raw materials extracted per hectare is
still not at its optimum.
Figure 9: Soybean Yield per acre[27]
CO2
Polymers,
Chemicals
and Fuels
Fossil Resources
(Petroleum,
Natural Gas)
Biomass/
Bio-organics
Sunlight + H2O
>106 years1 – 10 years
Bio-Refinery
The yield of ethanol per hectare[28]
have increased from 1.5 m3/ha in the 70’s to more than
7.0 m3/ha in Brazil between 1975 and 2005. Following the same trend, figure 9 shows a
clear improvement of soybean yield. Furthermore, the use of transgenic species, that would
be less controversial for fuel sources, is still not fully developed.
Also, some new technologies that could significantly change the bases for renewable
sources are in early stages of development. Among those it is important to mention the
extraction of ethanol from pulp of any origin and the extraction of useful oils and ethanol
from algae.
Considering the short term, the scientific community is pursuing an equilibrium between
the exploration of renewable sources to replace petroleum with other energy sources, to
properly address the global warming challenge. The issue of preventing renewables from
affecting food supplies and deforestation must be continually controlled, through proper
international policies, regulatory and non-governmental bodies, and the society.
For the purpose of this paper, the volume of renewable raw materials for PVC would
represent a fairly small portion of the total ethanol and oilseeds production of the world.
The total demand for PVC resins in the world is approximately 33,000 kt/yr [29]
, which
would require an ethylene demand of approximately 15000 kt/yr. This volume of ethylene
would require a total of 28000 kt/yr of ethanol, what would represent 2.5% of the Brazilian
arable territory. The total demand for phthalates in the world is approximately 5000 kt/yr.
Assuming, just for the exercise, that all this volume should be replaced by materials
produced from soybeans, the whole plasticizer market would represent a share of 16% of
the total soybean oil global production[8]
. Such volume would be covered by yield
improvements alone, considering estimates from the Brazilian Agriculture Ministry that
production per hectare can be enhanced 25% with improved agricultural technology.
Production Processes
Several different processes have been developed to obtain ethanol from sugar cane and
building block molecules from vegetable oils.
The most prevalent process for ethanol is the extraction of the juice of sugar cane,
fermentation and further distillation. Recent improvements eliminated the need for
petroleum solvents in this process, and all the waste is reused: bagasse is burned to generate
electricity and the vinasse is used as fertilizer for the sugar cane crops. To produce 1 liter
of ethanol, 0.2 liters are consumed in planting, harvesting and processing. As mentioned
before, the technology is evolving continually to more efficient systems.
For the production of oilseed derivatives, the production of oils is currently based on
solvent extraction, with reduced solvent losses. Non-solvent or ethanol based extraction is
already available and in the early stages of feasibility studies. The subsequent processes,
which can include hydrolysis, esterification, transesterification, epoxidation, hydrogenation,
are all well known reactions commonly used in the food industry, to obtain various food
additives or derivatives. These processes are also evolving rapidly as they become more
relevant to the production of Biofuels and raw materials for the chemical industry. The
greatest concern for these processes is the generation of glycerin as a by-product. Once
again, there are several researchers [30] [31]
investigating alternative uses for glycerin, such as
composting for fertilizers or biogas generation, as its offer is increasing with the increasing
demand for biodiesel.
Environmental Impact and Toxicology
The immediate benefit of vegetable derived materials is the reduction of the CO2 in the
atmosphere. Considering the current state of the art and the commercially available
products, 1 ton of a fully renewable PVC compound for a clear vinyl calendered sheet, with
100 phr PVC resin, 60 phr vegetable plasticizer, 4 phr ESO, 1 phr Ca/Zn stabilizer, would
represent a net reduction of 4.30 tons of CO2 from the atmosphere. The calculation is
summarized below:
100 kg Green PVC+ 60 kg EMS+4 kg ESO+1 kg Ca/Zn Stabilizer = 165 kg compound
545 kg CO2[32]
141 kg CO2[33]
+ 0 + 0 = 686 kg CO2
4.3 ton CO2 / ton compound
For the resins production from ethanol, the environmental impact of the final product is
exactly the same as with regular oil based resin, as they are exactly the same, chemically.
Naturally, due to the recent nature of the renewable technology, toxicology and
environmental evaluations are still considerably less extensive than the studies conducted
for the major oil based plasticizers. However, some immediate benefits have been noted,
such as biodegradability and toxicology reduced impacts[34]
. Some products have been
thoroughly evaluated, such as ESO or ELO, and some more recent materials are still being
analyzed. The initial results point to very encouraging perspectives, which are in line with
the theoretical expectations, based on the chemical species of such materials.
REACH
All bio-based materials must go through a series of analyses to comply with REACH, the
European Community effort to ensure that all chemicals sold in Europe will be registered
and have their physicochemical, toxicological and eco-toxicological properties well
documented and evaluated. This will require that all these new chemicals have proper
assessment of the associated risks and safety measures derived from the end-uses and the
supply chain.
CONCLUSION
A completely renewable PVC compound, with the term renewable as defined previously in
this paper, can be obtained for almost all applications with the materials that are currently
commercially available and it is economically competitive when compared to petroleum
alternatives. Naturally, with every new chemical, the evaluation and investigation of the
recently introduced raw materials are still underway, but the initial results and the rapidly
evolving agricultural and industrial technologies indicate that renewable PVC compounds
are not only viable, but they arise as a natural evolution in the direction of a more
sustainable PVC supply chain.
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kyoto/artigo.php? segmento=corporatvo&id_artigo=19, accessed Feb/05/2008
[34] Danisco A/S, ―PRODUCT DESCRIPTION, GRINDSTED® SOFT-N-SAFE‖,
http://www.compound-solutions.com/pdf_files/pds_grindsted_softnsafe.pdf,
accessed Feb/15/2008