wood as a composite material with other polymers

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1 WOOD AS A COMPOSITE MATERIAL WITH OTHER POLYMERS First of all, I would like to express my deepest gratitude to Allah, the almighty for his mercy extended to me to complete this report manages each and everything soundly. As a part of the fulfillment of honors’ degree from the department of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, project work is included as a unit course. With a view to make the project report, I tried my best to collect required documents and other essential requirements. It is an immense pleasure for me to express my deepest sense gratitude and indebtedness to my respectable supervisor S.M. Abdur Razzaque, Department of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, for his constant supervision and inspiring guidance, active help, indispensable suggestions, proper directions and untold kindness throughout the progress of this project profile. His technical knowledge had helped me to prepare such quality of project profile and I shall remain so much grateful to him. I really owe to him very much for giving me such an opportunity to work in close association with his effort and guidance, otherwise it would be impossible for me to have a successful completion of this dissertation. Also I would like to express my deepest respect and grateful thanks to professor Dr. M. Alauddin, professor Dr. M.A. Sattar, professor Dr. Bhupesh Chandra Roy, professor Dr. Md. Shamsul Alam, Tanzima Parvin, Md. Mamun Al-Rashid and all other respected teachers of Department of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, for their high co-operation and intellectual suggestions. .

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Wood, Classification of woods, wood composite types.

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Page 1: Wood as a Composite Material With Other Polymers

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WOOD AS A COMPOSITE MATERIAL WITH OTHER

POLYMERS

First of all, I would like to express my deepest gratitude to Allah, the almighty for his mercy extended to me to complete this report manages each and everything soundly. As a part of the fulfillment of honors’ degree from the department of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, project work is included as a unit course. With a view to make the project report, I tried my best to collect required documents and other essential requirements. It is an immense pleasure for me to express my deepest sense gratitude and indebtedness to my respectable supervisor S.M. Abdur Razzaque, Department of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, for his constant supervision and inspiring guidance, active help, indispensable suggestions, proper directions and untold kindness throughout the progress of this project profile. His technical knowledge had helped me to prepare such quality of project profile and I shall remain so much grateful to him. I really owe to him very much for giving me such an opportunity to work in close association with his effort and guidance, otherwise it would be impossible for me to have a successful completion of this dissertation. Also I would like to express my deepest respect and grateful thanks to professor Dr. M. Alauddin, professor Dr. M.A. Sattar, professor Dr. Bhupesh Chandra Roy, professor Dr. Md. Shamsul Alam, Tanzima Parvin, Md. Mamun Al-Rashid and all other respected teachers of Department of Applied Chemistry & Chemical Technology, Islamic University, Kushtia, for their high co-operation and intellectual suggestions. .

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CONTENT 1. Abstract……………………………………..........................................................3 2. Introduction………………………………………………………………………4-5 CHAPTER 1 1.1. Wood and it’s classification……………………………………………………...6 1.2. Structure of wood………………………………………………………………...6-10 1.3 Properties of wood………………………………………………………………..10-16 1.4. Chemical composition of wood………………………………………………….16 1.5. Wood polymer composite………………………………………………………..16-17 CHAPTER 2 2.1. High density polyethylene (HDPE) wood-plastic composite & their properties..18-20 2.2. Modeling of wood composite……………………………………………………21-24 2.3. Development of thick mountain pine beetle (MPB) strand based wood composite……………………………………………………………………………..24-32 2.4. Wood-polymer composite using a binder based Polyurethane Recycling product………………………………………………………………………………..33-39 2.5. Wood-Polypropylene composite & it’s temperature dependent behavior………39-53 2.6. Plywood & composite wood product industries………………………………...54-63 2.7. Medium density fiber board (MDF) production………………………………...63-65 2.8. Recycled wood plastic lumber composite……………………………………….65-68 2.9. Powder coating wood composite………………………………………………..68-72 CHAPTER 3 3.1. Physical & chemical properties of some wood composites impregnated with Styrene & Methyl methacrylate………………………………………………………………73-78 CHAPTER 4 4.1. Conclusion……………………………………………………………………….79 4.2. References……………………………………………………………………….80-81

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1. Abstract:

A polymer wood composite material comprises a polymeric component, wood flour, a coupling agent, a thermal stabilizer component, a plasticizer, a foaming agent, and a pigment. Preferably, the composite material exhibits better hardness than natural wood, as well as less water absorption (< 5% by weight) and less thickness swelling (< 1%) than natural wood when submerged in water for at least 24 hours, wherein the thickness swelling is measured as a percentage of original thickness. The composite material may be used to form a building component for use in the production of furniture and buildings, such as a doorjamb. In addition, a method of producing an extrudable mixture for an extrusion process to produce a polymer wood composite material is disclosed, wherein the method preferably does not include any pre-drying, pre-treatment or pelletizing processes.

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2. Introduction: This article gives an extended introduction on the state of the art of wood modification worldwide and then zooms on the variability in degree of formation of composite wood products using pieces of wood. Wood is a three dimensional polymeric composite made up primarily of cellulose, hemicellulose and lignin. These polymers make up the cellwall and responsible for most of the physical and chemical properties shown by wood. Various composite wood products are now employed which are preferred as engineering materials because they are economical, low in processing energy, renewable, strong and aesthetically pleasing. However, they may have some disadvantageous properties such as biodegradability, flammability, changing dimensions with moisture contents, degradability with UV light, acids and bases. Even though wood has been used as a building material for ages there are still several uncertainties when it comes to design of wood structures. Wood is a natural material with natural imperfections such as knots and varying growing conditions that makes it more difficult to decide the strength of the material. As a result of these imperfections a grading system was introduced to predict the material properties. A further attempt to improve the quality of wood products was done by combining wood from several trees of different qualities. This new ‘Engineered wood product’, EWP, has an improved quality due to the spreading of imperfections over a larger area or over several products. The most common EWP today is the glued laminated timber, glulam beams. Thanks to its variety in length and shape this product is today widely used. Timber has good properties in both tension and compression of the fibres when compared to concrete for instance. Concrete has a low tensile strength that would cause it to fail when loaded in bending if reinforcement was missing on the tension side. The use of steel reinforcement bars in the concrete improves the tension capacity of the reinforced concrete. Wood has the disadvantage of a low stiffness which cause timber beams to a rather high deflection when loaded. This is often the limitation when using timber beams as load bearing members. Another problem is that the deflection of timber members increases with time. For the last decade several efforts to reduce the decrease of stiffness has been made. Presence of moisture and especially moisture variation causes the increase of creep deflection. This can be controlled with several methods of treatment of wood. The magnitude of deflection with time is probably directly related to the initial deflection directly after load is applied. By reinforcing timber with material that has superior qualities when it comes to short- and long-term stiffness, the behaviour after long time could be improved and deflection could be reduced. It has been documented by Jobin, Olga (2007) that reinforced timber could very well be improved in ultimate limit state. The question is if these improvements could last over the entire service life of the structure and if the long-term creep which effects timber could be reduced. Another question that is of great importance for the future use of timber reinforcements is the economic aspect of reinforced timber. Now a distinction can be made between preparing various composite wood products by treating them with different polymers. In all experimental treatments of wood, the variability in the material plays a key role. This variability exists between species,

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between growing areas , between individual trees, but even in wood of the same tree and furthermore on an anatomical and ultrastructural level.

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1.1. Wood and it’s classification: Wood is a natural anisotropic material with variations in material parameters in different directions. To be able to understand the behaviour of wood it is of great importance to understand the composition of the material. Wood can generally be divided in to hardwood and softwood. Examples of hardwood Oak, Ash, Cherry and Walnut. Hardwood trees are generally angiosperms, plants produce seeds with some kind of covering. Softwood on the other hand is often gymnosperms (conifers), with seeds without covering that falls down to the ground. Typical softwoods are: pines, firs etc.

1.2. Structure of wood: 1.2.1. Microstructure: Every year trees has an annual growth in both the longitudinal and the radial direction.In the radial direction the growth of new cells expands the diameter of the tree. For softwood the growth of new cells can be divided in two types of new cell depending on the growth time of the year. Earlywood grows during spring and early summer when both the temperature and the moisture content are high and the conditions for growing are good. These fast growing cells has a thin cell wall and a large area of lumen (air) which makes the

earlywood cells pale coloured and large. Latewood grows during late summer and fall until the climate is to cold for any growth to take place. Due to less favourable growing conditions the latewood cells have a thicker cell wall which makes the latewood denser and dark coloured. Earlywood and latewood together makes one anural ring. Hardwood is more varied and complicated in its anatomy than softwood. Most of the structural concepts are analogue with softwood except that hardwood has a denser structure of libriform fibres. Within this tissue there are long pores, often with large lumina. Hardwood has thicker cell walls and smaller area of lumen then softwood generally has. The difference between earlywood and latewood is not as extreme as for softwood. For hardwood it is the diameter of the lumen that varies with the growing season. (Blass et al. Ed., 1995)

Fig.1 Timber from hardwood (left) and softwood (right), adopted from Blasset Ed.al.

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1.2.2. Ultra structure: Almost all species of wood have the same features of wood cells. Elementary fibrils consist of cellulose formed into larger units. Several elementary fibrils together form thread like entries called microfibrils. Microfibrils contain an estimated number of 100 to 2000 cellulose chains embedded in a matrix of hemicelluloses and enveloped by lignin. (Blass et al. Ed., 1995) Between all individual cells in wood there are a middle lamella (ML) which contains lignin and pectic substances. The most outer layer of the cell is called the primary wall (P). This layer consists of cellulose microfibrils which are arranged in an irregular pattern. After the primary wall there is a secondary wall, this normally consists of three layers S1, S2 and S3, Figure 2.2. In the very thin first layer (S1) the angle of microfibrils has an average of 50-70°. In the second layer, which is rather thick compared to the other two, the slope of microfibrils is about 5-20°. In tension of fibres this layer is the most important one since most of the tensile force has to be taken by this layer. Closest to the lumen core, layer (S3) has microfibrils with a smaller slope but not in a defined order. In compression the S2 layer will act as a column. To prevent the layer from buckling the S1 and S3 layer acts as reinforcement since the microfibrils has a larger slope then the middle layer. (Blass et al. Ed., 1995)

Figure-2.2. Cell structure of wood adopted from Nakano; ML- middle lamella, P- primary wall; S1,S2 & S3- layers of secondary wall. 1.2.3. Sapwood and heartwood: There are two types of wood tissue, sapwood and heartwood. Sapwood is the living part that supports the trees with nutrition and water upwards. Heartwood has no influence on the physiology of the tree but both sapwood and heartwood has influence on the mechanical properties. (Bengtsson, 1997) In most species a darker colour appears in the heartwood as an effect of incrustation with organic extractives. This also results in a better resistance against decay and wood boring

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insects. A loss in moisture content also takes place which leads to plugged vessels in the wood. Heartwood looses most of its permeability and can not be chemical preserved in the same manner as sapwood. (Blass et al. Ed., 1995) 1.2.4. Juvenile and reaction wood: Juvenile wood is formed in the first 5-20 years of a trees life. Mechanical properties of juvenile wood can differ a lot from normal wood. Especially the forming of short, thin walled tracheids in the S2 layer makes the juvenile wood experience much greater longitudinal shrinkage but also reduced strength and stiffness. External forces acting on trees over long time will result in formation of reaction wood. For softwood trees compression wood will be formed, while hardwood trees instead will develop tension wood. Tension wood seldom causes any problems in timber engineering but compression wood is of much greater concern. When growing in compression the microfibrils in the S2 layer will develop a large slope of the micro fibrils, sometime as large as 45°. Also the inner S3 layer will be missing entirely. This will cause great longitudinal shrinkage and a greater density of the compression wood. This is not to be confused with the improved mechanical properties the high density brings. High density in compression wood will not improve the mechanical properties. Instead compression wood has a tendency to break in a brittle manner when dried out. (Blass et al. Ed., 1995; Bengtsson, 1997) 1.2.5. STRUCTURE OF WOOD ON THE BASIS OF CELLULOSE, HEMICELLULOSE & LIGNIN: Softwood consists of hollow tubular cells organised in sequential earlywood, transitionwood and latewood tracheids. In addition to longitudinally orientated tracheids there are radially orientated ray cells. The main components in cell walls are cellulose, hemicellulose and lignin. Cell walls are layered (M, P, S1, S2, S3) composite structures with varying composition and orientation of structural units (elementary fibrils, microfibrils). In the middle of two adjacent cell walls there is a middle lamella gluing cells together and forming a double cell wall. Especially the arrangement of cellulose in different layers has a strong impact on the mechanical and physical properties of wood. In transverse direction the cell structure and its variation are important. Ray cells have also an important effect on mechanical behaviour of wood substance. Pit pores are mainly located in the radially orientated cell walls and they are essential to control liquid flow between tracheids and ray cells but pits may also affect the strength properties.

1.2.6. Cellulose:

The crystalline cellulose is common in all lignified plant cell walls and the cellulose content in wood is 40…55%. The longitudinal elastic constant of cellulose has been theoretically estimated based on the molecular structure by several researchers. The theoretical values have a large scattering from 56.5 GPa to 319 GPa. Sakurada et al. [35] has measured the value 137 GPa for ramie fibres. Mark’s theoretical value 111.3 GPa is the closest (17% lower) to the Sakurada’s value. The measurements and theoretical analysis of Page et al. (1977) on black spruce fibres, Preston’s data (1960) as a function of S2-fibril angle for sisal fibres and Cave’s [13,14] modelling indicated that the

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Sakurada’s experimental value fits best to the modelling purposes. Salmén’s [35] calculation results verified that the longitudinal modulus of cellulose is close to data presented by Sakurada.

The only values available for the transverse stiffness (Ey, Ez) and shear modulus (G) are theoretical ones. Most of the cell wall models are based on Mark’s [29] values (Ey =27.2 GPa, Gxy=Gyz=4.4 GPa, Gxz=6.6 GPa).

1.2.7. Hemicellulose: Although cellulose is a dominating constituent (amount and orientation) affecting longitudinal modulus of elasticity and strength of wood, hemicellulose and lignin are important in the11/23 transverse behaviour. Hemicellulose content of wood is 20…25 %. According to Bergander et al. [6] properties of hemicellulose are dominating the ransverse cell wall modulus. In the most of the cell wall models the value of 8 GPa in longitudinal (Ex) and value of 4 GPa for transverse (Ey, Ez) modulus of elasticity have been used in dry conditions. The longitudinal value and the effect of moisture are taken into account based on Cousin’s [19] measurements. Transverse value is estimated robably based on the lignin properties. Glass transition temperature of dry hemicellulose is about 200°C and at room temperature it becomes rubbery at moisture content of 25 % [19].

1.2.8. Lignin: The lignin properties are based on the measurements by Cousins [18]. The modulus of elasticity at dry state is 4 GPa and lignin is assumed to be isotropic. Bodig et al. [7] have used value of 2 GPa. Commonly amorphous lignin is assumed to behave as an isotropic material but according to Åkerholm et al. [49] aromatic units of lignin are not distributed in the structure in an isotropic way. The properties of lignin depend on the moisture and temperature. Glass transition temperature of dry lignin is about 200°C and in wet condition it is 80-90°C.

1.2.9. Cell wall layers:

Cell wall consists of primary wall (P) and secondary layers (S1, S2, S3), (Figure 1). In the middle of the two adjacent cells (double cell wall) there is also a middle lamella (M). Thicknesses of cell walls (2…10 μm) and sizes of cells (porosity) affect the wood density. The thickness of double cell wall affects also bending behaviour and buckling resistance in transverse and longitudinal compression. S2-layer (thickness and micro-fibril orientation) has strong effect on longitudinal properties. Differences between S1- and S2-layer structure have been related to the failure modes observed in longitudinal tension tests. Middle lamella and primary wall affect the transverse tension strength especially at high moisture content and elevated temperature. The shear strength of softwood in LR-direction is often limited by the properties of the middle lamella between latewood-earlywood boundary. This might be due to the sudden change in the density of wood causing more brittle failure type or due to the freezing defects.

According to Brooker there are not clear borders between cell wall layers and he pointed out that it is commonly accepted that the change from one layer to another is smooth and

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there is intermediate layers S12 and S23. In these layers microfibril orientation is between those of main layers. Brooker referred to work done by Abe et al. and noted that in S1-layer the microfibril orientation changes stepwise in a counter clockwise direction from the outside to the inside, from roughly –45° to about +70° at S12 boundary. S2 has microfibril angle from 20° to 0°. In S2-layer microfibrils are closely packed, but not in the other layers. S2 forms 80…90 % of the double cell wall thickness. Sell et al. and Guet al. observed that in S2-layer agglomerations of microfibrils are orientated radially. Tangential thickness of agglomerations is 0.1…1 μm. However, according to the most of the earlier and current studies S2 is layered tangentially.

1.3. Material properties of timber: Material properties of wood are determined by several factors, e.g. density and moisture content of the material. All properties are determined by the growing condition and what type of tree that is used. Also the appearance of knots and defects will influence the material properties. 1.3.1. Density Density is the single most important factor that determines the mechanical behaviour. Several mechanical properties are positive correlated to density; see Figure 2.3.(Hansson & Gross, 1991)

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Density is defined as

where m is the mass (kg) and V is the volume (m³). This can also be written as density at specific moisture content ω (%).

Where 0 0 0 m , V and ρ are mass, volume and density at zero moisture content. ω β is a coefficient defining the volumetric swelling with unit of percent of swelling per percent of moisture change, Blass et al. Ed. (1995). Density of pure timber (only the cell wall and not the lumen from the cell) is about 1500 kg/m³. This density is not relevant when relating to timber for structural purpose. The most common definition of density is the weight of the timber at 0 or 12 percent moisture content. In Eurocode 5 (1993) density is given as the mass and volume at equilibrium at 20°C and a relative humidity of 65%. Density is often compared to the width of one growth ring. This relationship is not really clear and there is a great scatter in experiments with density and growth ring width. There are several other factors influencing the density of wood. According to Hansson & Gross (1991) these factors are: • Temperature: warmer climate gives wood a higher density at a certain growth ring width • Moisture: dryer climate results in wood with a lower concentration latewood, and therefore a lower density • Stand concentration: stands with larger amount trees per area will grow slower then culled stands. Culling results in a higher growth rate and therefore increased density • Position in tree: wood at the same growth ring width has a higher density near the root of the tree then at the top. Trees develop wood with higher density in parts with high strain due to wind loads

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• Fertilise: trees growing in soil with low amount of nitrogen can be fertilised to increase the growth rate without decreasing the density • Genetically properties: trees from same stand under same growing conditions but with different genetically properties can have a great variety in density. 1.3.2. Moisture content Wood has very good water transportation properties because it needs water to grow. After the tree is cut down and sawn in to timber many of these water transportation properties remain. Wood is a hygroscopic material which means that it absorbs and desorbs moisture from the surrounding air. The moisture content (MC) in wood is therefore dependent on the relative humidity (RH) of the surrounding air. Moisture in wood can either be found as moisture in the cell wall or as free water inside the lumens. Increased MC in the cell walls will decrease the mechanical properties of wood. This is due to water penetrating the cell wall which will weaken the hydrogen bonds that hold the cell wall together. Wood has a fibre saturation point of approximately 30% MC. In Figure 2.4 an example of how the MC varies with the RH for both absorption and desorption. There are different curves depending of the type of wood and temperature of the surrounding air. It takes a long time for wood to adapt its MC from the surrounding RH. Studies like Bäckström (2006) show that for a timber stud with cross section dimensions 45x70 mm² it will take up to 60 days to change the MC from 19% to 9%. After approximately two weeks the surface has reached 9% in MC while the middle of the cross section is still at 15-16% MC. The change in MC throughout the cross section can be seen in Figure 2.5.

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Variations of mechanical properties can be said to have a linear relationship for clear wood in the range of an MC between 8% and 20%. In Table 2.1 the change in mechanical properties per change in percent MC is shown. Some changes of the material properties will not be as important for timber as it would be for clear wood. Several experiments have been carried out to find out how mechanical properties varies with MC. Results from these experiments show that the tensile strength of low quality wood is independent of the MC while both bending and compression strength is highly dependent of the MC. (Blass et al. Ed., 1995)

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To ensure sufficient strength of the material there are three service classes defined in Eurocode 5 (1993) depending on the RH of the surrounding where the timber is placed: • Service class 1: is characterised by moisture content in the material corresponding to a temperature of 20°C and the relative humidity of the surrounding air only to exceeding 65% for a few weeks per year • Service class 2: is characterised by moisture content in the material corresponding to a temperature of 20°C and the relative humidity of the surrounding air only to exceeding 85% for a few weeks per year • Service class 3: climatic conditions leading to high moisture content then in service class 2 1.3.3. Shrinkage and swelling Moisture in air has such similarities as the substance in the cell wall that it can even penetrate the almost non-porous wood material. Moisture finds its way into the wood cell which pushes the microfibrils apart. When wood cells swells the volume of the lumens stays constant. The volumetric swelling of the cell has the same volume as the moisture absorbed. When moisture is removed from the cells shrinkage occurs in the opposite manner as swelling. The shrinkage and swelling of timber are called movements. The size of movement in timber is mainly dependent on the microfibrillar angle in the S2 layer. For normal timber the layer S2 has a rather small angle which causes small movements in the longitudinal direction but greater movements in the transversal

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direction. For juvenile and compression wood the transversal and longitudinal movements are equal. Normally the movement in radial direction is ten times as large as the movement in the longitudinal direction. The tangential movement is twice the magnitude of radial movements. Shrinkage and swelling can differ on both sides in sawn timber. This causes distortions. This variation between the top and the bottom layer of a beam causes a curvature on the beam, usually called spring or bow. (Kliger et al., 1994) 1.3.4. Duration of load Wood loaded under a long period of time will experience an instant deformation right after load is applied. With time creep deformations will develop in the loaded specimen. Part of the deformation will be elastic and disappear right after the load is removed. The other part is a plastic deformation that is due to viscous flow within the molecules that leaves a permanent deformation. Several studies have shown that with a stress level beneath the failure stress, longterm effects can cause failure of wood, Figure 2.6. It has also been shown that longterm loading does not affect short-term strength and elasticity if the long-term load is kept underneath the proportional limits. For decreasing rate of creep failure due to creep will not occur. (Hoffmeyer, 1990)

The most important of the early studies of long-term behaviour of wood is carried out by Madsen in 1947 and 1951. He performed long-term bending test under constant load with 1x1x22” test specimens and could show that the relation between stress level until failure and logarithmic time has a linear relationship. These curves are called “The Madison Curve” and are still used today to define the duration of load capacity. (Hoffmeyer, 1990)

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Duration of load is taken into concern in Eurocode 5 (1993) by dividing the load time in to 5 categories: • Permanent load has an accumulated duration of load for more then 10 years, for example self weight • Long-term load is defined as 6 months to 10 years, for example storage • Medium-term load is defined as 1 week to 6 months, for example imposed loads • Short-term load is duration less then one week. Wind, temporary load and snow load for some countries • Instantaneous load is usually accidental loads 1.4. Chemical composition of wood: The dicotyledons, on the other hand, are composed of cells of more varying shapes and sizes. Most dicotyledon cells are long and narrow, with pointed and closed ends – the fibers. Other important constituents are the parenchyma and, in relatively small quantities, the vessels that, in transversal cuts, are called pores. These cells have open ends and are usually shorter than fibers, varying considerably in shape and size. Wood cells are connected to each other through a cemented substance called intercellular layer or medium lamella. A mature cell is made up of two layers: the primary wall – a thin external layer, and the secondary wall – a thicker internal layer composed of three other layers. The interior of the cell contains the cellular lumen which, in most mature cells, is completely empty1.The main wall constituents of xylem cells are cellulose, hemicellulose and lignin1. In addition to these structural components, wood presents inclusions of organic and inorganic matter with high and low molecular weights. 1.5. Wood polymer composite: 1.5.1. Polymers: Polymers are a large class of materials consisting of many small molecules (called monomers) that can be linked together to form long chains, otherwise known as macromolecules. Polymerization is the chemical process whereby monomers are joined to form a polymer. Polymers are widely used in composites as fibers or as the matrix. 1.5.2. Wood-polymer composites: Wood-polymer composites (WPC) result from the polymerization of liquid monomers or oligomers already impregnated in the wood. Wood porous structure, composed of lignin, cellulose and hemicellulose, is filled with a solid, plastic and fairly hard substance. In principle, WPCs should display superior mechanical properties, dimensional stability, greater resistance to chemical and biological degradation, and less moisture absorption than non-impregnated wood. WPC production necessarily goes through two different phases: impregnation with a monomer/oligomer, followed by its polymerization inside the wood. Wood is impregnated injecting certain chemical products (liquids), which can be done by immersion, vacuumimmersion and vacuum-pressure. In so far as impregnation with natural resins is concerned, it is worth mentioning the improvement of some physical properties of White Fig (Ficus monckii) impregnated with natural resin

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from Jatobá (Hymenaea courbaril)11. The impregnated monomer/oligomer can be polymerized through two different processes: by the incidence of radiation or by the thermal decomposition of initiators. In thermal polymerization processes, the thermal dissociation of initiators is the most commonly used method to generate radicals to start the reaction. These initiators are compounds which decompose easily into free radicals as temperature rises. The preliminary study carried out in Brazil presents few information related to modulus of rupture and hardness parallel to grain, in Pinus Elliottii (Pinus elliottii) specimens impregnated with methyl methacrylate. The results showed the good potential of WPC but only now circumstances turned possible the research continuation.

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2.1. HDPE wood plastic composite and some of their properties: Historically, preservative-treated wood timber has been utilized for structural elements within marine fender systems. However, as waterways have become less polluted, the traditional wood members are subjected to increasing degradation generated by marine borers. Furthermore, public concerns about water pollution in harbors have resulted in restrictions on the use of wood preservatives. As a result, an alternative material to replace the traditional wood material is required. The U.S. Office of Naval Research funded this research project with the Department of Civil and Environmental Engineering, Washington State University to investigate the feasibility of using a wood-plastic composite material (WPC) as an alternative for components of fender systems. Wood-plastic composite materials (WPC) have several benefits compared to the traditional wood material. First, it is resistant to insects, marine borers and rot when used for structural members. Without the preservative treatments, there is no environmental impact. Also, reduced production costs make wood-plastic economical for many structural applications. The information presented is High Density Polyethylene (HDPE) material development and the other is the use of Finite Element analysis software ABAQUS to model the nonlinear behavior of the HDPE material. The experimental testing was performed on extruded wood-based composite material, which was approximately composed of 70% wood and 30% high-density polyethylene (HDPE) that wood/plastic composites display a nonlinear constitutive behavior in hyperbolic tangent form. This is known as HDPE wood plastic material. 2.1.1. The Properties and Mechanical Behavior of the HDPE Material: In this case, the high-density polyethylene (HDPE) composite material was chosen to be modeled. Specifically, the HDPE composite was composed of 58% maple flour (American Wood Fiber #4010), 31% HDPE (equistar LB0100 00), 8% inorganic filler, and 3% processing aids. For specimen tests, the HDPE material was extruded using a conical twin-screw extruder (Cincinnati-Milicron CM80) and a stranding die (Lockyear, 1999). Tensile, compression, bending and torsion tests were performed on small HDPE composite specimens to determine its properties. Interested readers can find detailed information on experimental methods from the reports of Haiar (2000) and Lockyear (1999). Here, examples of testing specimens are given. Figure 1-1 shows typical extruded wood/plastic hollow test sections, which were used in uniaxial and five-point bending tests.

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Figure1-1:Extruded wood/plastic hollow section(left) Figure1-2 shows torsion

specimen.(right) The shear modulus used as input for the HDPE model was obtained from torsion tests. Through the compression and tension tests of small specimens, the properties of the HDPE composite material have been obtained. Stress strain relationships are similar in shape, no matter how loads were applied. Such relationships can be represented by a hyperbolic-tangent function (Cofer, 1999): σ = a tanh(bε ) ,……………………………….(1) And

2cosh ( )ab

bσε ε

∂=

∂………………………………(2)

Also when ε=0

abσε

∂= =

∂MOE (Modulus of Elasticity)………(3)

Here, σ and ε are uniaxial stress and strain, respectively, and a and b are constants. A typical stress-strain relationship of the HDPE material is shown in Figure 1-3, which was obtained when the load was applied in tension parallel to the material grain. From the physical specimen tests, it was found that the HDPE composite material behaves differently in tension cases versus compression cases with respect to different values of tiffness and strength. One of the differences is the maximum strain, which is defined by the onset of softening or fracture. Table 1-1 and Table 1-2 show the tensile and compressive maximum strain values and hyperbolic tangent constitutive parameters. Another interesting phenomenon observed is that the HDPE composites are quite flexible in shear, with a shear modulus obtained from torsion tests. Table 1-3 shows the maximum strain and strength values obtained from torsion tests.

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From these experiment results, some constitutive assumptions were made for this material model and they are given below: 1. The HDPE material model is appropriate for plane stress conditions. 2. The stress-strain relation obtained from test data of the HDPE material is known to be nonlinear, and it appears to follow a hyperbolic tangent curve. All nonlinear effects of the constitutive behavior are attributed to damage. 3. The orientation of the eigenvectors remains unchanged after damage initializes. 4. The damage variable for the shear mode is only available through the coupling of damage variables for the normal eigenmodes.

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2.2. Modeling of wood composites: Engineered wood industry products are boards, panels and other composites which have been manufactured by gluing. Traditionally these products have been developed based on experience and experiments. Modeling research widens the use of physical models and numerical simulation to the development of wooden composites, the areas of application being: • Manufacture of plywood so that plywood boards would keep their plane form after moisture equilibrium of various end-uses has been reached • Drying of veneers to optimal final moisture content in terms of veneer characteristics • Optimal manufacture of particleboard: correct raw material and chips to each end-use. The research includes a wide experimental programme, and development of testing methods. Different factors affecting the warping and twisting of plywood panels were studied experimentally both in laboratory and on industrial scale. Most of the studied factors of the raw material and production did not have an effect on the magnitude of warping or twisting. The most important factors found were the difference of moisture content of different veneers, which affected warping, and the slope of grain of the veneers, which affected twisting. 2.2.1. Background Dimensional stability and straightness are important factors affecting the usability and quality of panel products. However, distortions of plywood panels have been observed soon after manufacturing and during the storage and use of panels. The amount of distortions is affected by the thickness and the lay-up of the panel, but the actual reasons for warping and twisting are not well understood. There are large differences in the behavior of individual panels. Drying of the veneers is a critical stage in plywood production significantly affecting the product quality and wastage in the later stages of the manufacturing process. A key issue is the control of final moisture content of veneers and their distribution. At present, the control of the final moisture content, and of the other drying quality factors depending on it, is somewhat inadequate, because there are several contributing factors, and the drying process conditions and the effect of changes in them are not well known. Thus, process control is largely based on experience, and no systematic data are collected about the effects of controlling actions on the drying machine operation. Particleboard characteristics are dependent on the quality of chips (particles), glue, amount of glue and manufacturing conditions. Chip quality is affected by the raw material, chipping method and screening. Development of better particleboard and maintaining the product’s competitiveness on the market require better knowledge of chip quality, quicker analysis methods, and especially, deeper knowledge of the relationship between particles and particleboard to be able to correctly direct the development of analysis methods. 2.2.2. Objectives The objective of modeling exp.1 is to find out the reasons for twisting and warping of plywood panels, to analyze the possibilities for preventing twisting and warping in production, and thus to establish the preconditions for producing straight plywood at even

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quality. The study focuses on the raw material and the moisture changes during the production process, swelling and stresses in veneers and how they cause distortions in the end product. The effect of the formation of the glue bond on the warping of plywood panels is also studied. Numerical methods are developed for the determination of changes in moisture content and swelling, as well as deformations caused by them. The methods developed can be applied also to predicting deformations during the use in different end-use conditions. The sample material is birch plywood panel. The experiment on the drying of veneers (expt.2) aims to optimize the drying process in terms of total productivity of plywood panel production. This leads to an optimal quality of veneer and end product, minimal loss in the manufacturing process and low energy consumption. Another objective is to create a simulation tool for generating drying models that lead to production of high-quality veneer. The parameters used in the model are veneer moisture and quality characteristics. In the experiment on particleboard (expt.3), the effect of particles (chips) on the most important particleboard properties are defined. Usable interpretations are looked for in order to better utilize the results of the methods used for analyzing the chip characteristics. The most characteristic chip properties in terms of particleboard properties are defined on the basis of the correlation between the chips and the board. Key particleboard properties are modeled using the chip characteristics and fast analysis methods are developed for these characteristics. Methods are developed in order to better understand the most important particleboard properties in further processing. The effects of raw material and chipping machine on particle characteristics are also examined. 2.2.3. Results and discussion The experiment on warping and twisting of plywood studied the effect of process parameters on plywood deformation (warping and twisting) experimentally by varying the selected variables in six test phases in laboratory and industrial scale. Most of the studied raw material and production factors did not have any significant effect on warping or twisting. The most important factor was the difference in veneer moisture content, which affected warping and the slope of grain, which affected twisting. If the veneers at the opposite surfaces of the panel had differences in moisture content, this resulted in significant warping of the panel. When the two veneers next to each other at the surface had a 3%difference in moisture content compared to the other surface, this resulted in a 30 to 40% increase in warping as compared to a case where all veneers had similar moisture content. The difference in moisture content above is that of individual veneers before assembling or pre-pressing. After pre-pressing, during a 1 to 2-hour period, the moisture content of the assembly stabilizes to a level of 12 to 15%, excluding the surface veneers. After pre-pressing, it appears that little can be done to affect the straightness of the panel. The slope of grain in the veneer varied between –7° and +9°. The average value for different veneer qualities used was between 1.5°and 2.5°. When the slope of grain was eliminated from the test veneers, the twisting of a laboratory panel reduced to a third. In industrial conditions, similar improvement could not be reached. This was probably because the slope of grain was limited in factory panels, on an average, only to less than 1.5°, since the slope of grain of the veneers could not be measured reliably in the production process. If the end-use moisture content of the panel is assumed to be 7–8 % (RH 45 %), they should be produced to be as straight as possible

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in this condition. This was attempted by using glue film with no moisture and veneers of moisture content 6 %. When these panels were conditioned to 7 % moisture content, they were as twisted as the other panels. The warping in film-glued panels was, however, very small. To produce a straight panel, it is necessary that the veneers have an even moisture content and a small slope of grain. This is particularly important for surface veneers and veneers close to the surface. Reliable methods to measure and control the moisture content in the veneers do exist. If, in addition to moisture control, the slope of grain of the veneers could also be measured and veneers with a minimal slope of grain could be separated, straighter panels could be produced. In the veneer drying experiment, the effects of wood raw material and the drying process on the veneer characteristics were studied and a simulation model for veneer drying was developed. A measurement device was developed and made for studying veneer waviness (i.e. deviation of the veneer from the plane). Drying was carried out both in a laboratory dryer and in an industrial dryer. On the basis of the laboratory drying, the effects of changes in drying conditions were studied with regard to tensile strength, waviness and adhesion, and a simulation model for veneer drying was developed. On the basis of the industrial drying, the moisture variations of veneers and factors affecting them were studied. In both laboratory and industrial drying, the effects of the drying temperature and drying air moisture content on the final veneer moisture content were studied. The wood species used in laboratory drying were spruce and birch. In industrial drying spruce was used. With spruce veneer, also the differences between sapwood and heartwood and the effect of veneer thickness were examined. Veneers having undergone a different drying process had differences in waviness and tensile strength. In waviness, there were differences in shape and height of waves as well as in the force needed to press the waves down. The most significant factor affecting tensile strength was final moisture content. The effects of the veneer drying process on the veneer adhesion properties were studied by measuring the contact angles with a water drop. Veneers dried under different process conditions had differences in adhesion properties. The most important factor affecting adhesion was final moisture content. On the basis of the industrial drying tests, the veneer final moisture content variance is, as expected, affected by the initial moisture content variance and the average final moisture content of veneers. Drying tests were also made on a paper machine press felt during the development of the veneer drying simulation model. The drying of the veneer has been simulated using the new model developed. In the particleboard subproject, a laboratory method for analyzing particle length, width and aspect ratio on the basis of optical image processing was developed. Also, new analysis methods and parameters have been developed for particle size analysis used by the industry. The method developed for characterization of chip surface is being tested. Further, an analysis method for chip surface porosity important for further processing is ready or testing. The so-called model chips used in the second phase of the study emphasized the effect of chip screening on particleboard properties. The differences between the chips were increased according to the raw material and chipping method used. It seems that the sorting method influences the quality of the chips. The modeling of the correlation between particleboard and chip characteristics is being completed. On the basis of the results received, key

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characteristics of chips seem to be related to whether the emphasis is on particleboard strength or surface properties. 2.2.4. Capabilities generated and utilization of results The results of the plywood part of the study can be utilized in the industry manufacturing birch plywood for demanding end uses, where the dimensional accuracy requirements are high. Such end uses are to be found in furniture manufacturing and in laser cutting of plywood. The users of the results are Koskisen Oy, Finnforest Oy and Schauman Wood Oy. The results can, however, best be utilized only if the veneers can be screened on the basis of the slope of grain. A follow-up study is suggested on this subject. The research group is now capable of mathematically simulating veneer drying. The industry manufacturing veneer drying equipment can use the results in designing next-generation drying machines. 2.3. Development of Thick mountain Pine Beetle (MPB) Strand Based Wood Composites: Glues have been around for a long time; the ancient Egyptian used them in veneering the treasure of Tutankamun and the ancient Greek word for glue is κоλλα, from which we got colloid. In all centuries up to and including the 19th glues originated from plants and animals; during the 20th century synthetic chemical have largely taken over and the more respectable name of adhesives has been introduced. Adhesion is essential for printing inks, sealants, and paints and other surface coating, and at interface in composite materials such as steel or textile fibers in rubber tyres and glass- or carbon fibers in plastics. Mother natures uses adhesion rather than mechanical fasteners (nuts and bolt, nails staples, etc.) in constructing plants and animals, and some animals are masters at exploitation of adhesion. Adhesives are not the only materials that must stick or adhere. A definition for adhesive is a material which when applied to the surface of materials can join them together and resist separation. The term adherent and substrate are used for a body or material to be bonded by an adhesive. Adhesive must wet the surface, spread and make a contact angle approaching zero. Intimate contact is required between the molecules of adhesive and atoms or molecules of the substrate in the surface. The adhesive must then harden to a cohesively strong solid. This can be by chemical reaction, loss of solvent or water or by cooling in the case of hot melt adhesives. Nowadays adhesives are used in all types of manufacture, in the construction of aircraft or plywood and in many cases have displaced other means of joining. The use of adhesives is a daily occurrence in many wood-processing industries as well, such as in the particleboard, plywood, and finger joints field. Adhesion is an important physicochemical phenomenon that has attracted considerable attention from many researchers in many fields of science. Advantage of adhesives as a mean of joining is that they are generally weakened by water and its vapor. Also, their service temperature ranges are less than for metal fasteners, being limited by their glass transition temperature and chemical degradation. Advantages include their ability to join dissimilar materials and thin sheet materials, the spreading of load over a wider area, the aesthetic and aerodynamic exteriors of joints and application by machine. Any materials that are bound to each other by an adhesive form a system

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that includes adhesion and cohesion. Adhesion is established between two surfaces due to intermolecular forces whereas cohesion is the bonding of molecules together in the bulk. Adhesion refers to the interaction of the adhesive surface with the substrate surface. It must not be confused with bond strength. Certainly if there is little interaction of the adhesive with the adherent, these surfaces will detach when force is applied. However, bond strength is more complicated because factors such as stress concentration, energy dissipation, and weakness in surface layers often play a more important role than adhesion. Consequentially, the aspects of adhesion are a dominating factor in the bond formation process, but may not be the weak link in the bond breaking process. It is important to realize that, although some theories of adhesion emphasize mechanical aspects and others put more emphasis on chemical aspects, chemical structure and interactions determine the mechanical properties and the mechanical properties determine the force that is concentrated on individual chemical bonds. Thus, the chemical and mechanical aspects are linked and cannot be treated as completely distinct entities. In addition, some of the theories emphasize macroscopic effects while others are on the molecular level, Thus, the mechanism of adhesion can be different for various materials. In general the principal theories describing the phenomenon of the adhesion are the followings: � Mechanical Entanglement/ Interlocking theory � Diffusion theory � Electronic theory � Adsorption/Specific Adhesion theory And the covalent bond theory.

Adhesives may be defined as any substance capable of attaching materials together by means of surface attachment. This property is not necessarily an intrinsic characteristic of the substance itself since the adhesive may be much weaker than the materials joined together, but it is developed as the adhesive interacts with the adherends under certain

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conditions of temperature and pressure. Most observations of adhesive interaction with wood are concentrated on scales of millimeter or larger. However, the wood-adhesive interaction needs to be evaluated in three spatial scales (millimeter, micrometer, and nanometer). The millimeter or larger involves observations by eye or light microscopy. The use of scanning electron microscopy allows observations on the micrometer or cellular level. On the other hand, the size of the cellulose fibrils, hemicellulose domains, and lignin regions are on the nanometer scale. The nanometer level is also the spatial scale in which the adhesive molecules need to interact with the wood for a bond to form. Tools, such as atomic force microscopy, developed for making observations on the nano scale can be difficult to use with wood because its surface is rough on the micrometer scale. For the most part, adhesives used to bond wood together may be separated into two distinct groups, those adhesives such as animal, vegetable, casein, and blood glues which are formulated from materials of natural origin, and those adhesives which are based on synthetic resins derived from petroleum, natural gas, and coal, i.e., products of the petrochemical and related industries. The properties of various adhesives are discussed below separated according to these two categories, natural and synthetic adhesives. Natural adhesives have been replaced in many uses by synthetic polymers; but animal glues, starches, gums, cellulose and natural rubber cements continue to be used in large volumes. Organic adhesives derived from animal proteins made from collagen, constituent of the connective tissues and bones of mammals and fish; blood albumen glue, used in the plywood industry; and glue made from casein, a protein constituent milk, are employed in wood bonding and in paint. Vegetable adhesives include starch and dextrin derived from corn, wheat, potatoes, and rice used for bonding paper, wood, and textiles. Gums such as agar and algae when moistened provide adhesion for such products as stamps and envelopes.35,36 The five groups of natural adhesives considered are: � Animal Glues: � Vegetable based adhesive- � Protein based adhesives-Soybean and Casein: � Flavonoids wood based adhesive-Tannin: and � Wood based adhesive- Lignin: 2.3.1. Synthetic Resin Adhesives Synthetic resins are man-made polymers which resemble natural resins in physical characteristics and can be tailored to meet specific woodworking requirements. These resins impart to glue lines and joints the highest water resistance attained to date. In contrast to the natural adhesives which at the best can resist only a moderate amount of moisture, properly formulated synthetic adhesives appear able to withstand repeated direct wetting. Synthetic resins were introduced as woodworking adhesives during the early 1930's. Synthetic resin adhesives are separated into two distinct categories thermosetting adhesives and thermoplastic adhesives. Thermosetting adhesives during cross-linking reaction, undergoes an irreversible chemical and physical change which render them insoluble. Thermoplastic resins are pre-polymerized and set by loss of dispersing solvent. They do not undergo a chemical cross-linking reaction while curing, therefore, remain in a reversible state and can readily be softened by heating.

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Development of Thick MPB Strand Based Wood Composites: 2.3.2. Thermoset Adhesive � Urea-Formaldehyde (UF): Urea-formaldehyde resins are the most important and probably the most widely used thermosetting resin for wood. UF resins are polymeric condensation products of the reaction of formaldehyde with urea. Urea is reacted with formaldehyde, which results in the formation of addition products such as methylol compound. Further reaction and the concurrent elimination of water leads to the formation of low molecular weight condensate UF that is still soluble in water. Higher molecular weight polymer, which are insoluble are obtained by further condensing the low molecular weight of UF.44 The reaction between urea and formaldehyde is complex and combination of these two chemical compounds results in three dimensional network in cursed resin. This is due to functionality of four in urea and functionality of 2 in formaldehyde. The most important factors determining the properties of the reaction products are the relative molar portion of urea and formaldehyde, temperature and PH values. The rapid initial addition reaction of urea and formaldehyde is followed by a slower condensation, which results in the formation of polymer. The rate of this condensation polymerization of urea is PH dependent and decreases exponentially from a PH of 2 to 3 and to neutral PH value. No condensation occurs at alkaline PH values. It is very important in the commercial production of UF resins to be able to control the size of the molecules by condensation reaction, since their viscosity increases continuously as they grow larger. The most common method for the preparation of commercial UF resin adhesive is the addition of a second amount of urea during the preparation reaction. This consists of reacting urea and formaldehyde in more than equivalent proportions. Methylolation can in be carried out in much less time by using temperature of up to 90 to 95 °C. The reaction is completed under reflux by increasing the PH as soon as right viscosity is reached.45 The advantage of UF adhesives are given below- 1) initial water solubility, 2) hardness, 3) no flammability, 4) good thermal properties, 5) absence of color in cured polymers, and 6) easy adaptability to a variety of curing condition. They are widely used for the manufacture of interior grade plywood and also for the manufacture of particleboard. In particular, they are extensively used in producing hardwood plywood for furniture and interior paneling and for furniture assembly. Urea-formaldehyde resins may also be fortified with melamine resins to improve both their moisture and temperature resistance.

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� Melamine-Formaldehyde (MF): The condensation reaction of melamine with formaldehyde is similar to but different from the reaction of formaldehyde with urea. As with urea, formaldehyde first attacks the amino groups of melamine, forming the methylol compounds. However, formaldehyde addition to melamine occurs more easily and completely than addition to urea. The amino group in melamine easily accepts up to two molecules of formaldehyde. Thus complete methylolation of melamine is possible, which is not case of urea. Up to six molecules of formaldehyde are attached to a molecule of melamine. Because melamine is less soluble than urea in water, the hydrophilic stage proceeds more rapidly in MF resin formation. Therefore, hydrophobic intermediates of the MF condensation appear early in the reaction. Another important difference is that MF condensation to give resins and their curing, can occur not only under acid conditions, but also under neutral or alkaline condition. The mechanism of the reaction of ethylol melamine to from hydrophobic intermediate is the same as fro UF resins, with splitting off of water and formaldehyde. Methylene and ether Bridge are formed and the molecular size of the resin increase rapidly and final curing process transforms the intermediate MF to insoluble resin.

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Melamine resins are used primarily to improve the moisture resistance of urea resin adhesives. In this respect, they are substantially more resistant than urea resins but not as resistant as phenol and resorcinol resins. Melamine resins must be cured at temperatures of at least 240° F for most applications. They are also quite expensive relative to the urea resins. These two factors have limited the use of straight melamine-resins to a few special applications such as marine plywood where the need for a light-colored water-resistant adhesive justifies their cost. � Phenol-Formaldehyde (PF): Phenolic resins are poly-condensation products of phenol and aldehyde particularly formaldehyde. Phenolic resins are the first true synthetic polymers to be developed commercially. In initial attack, poly-functional phenols may react with formaldehyde in both the ortho and para positions of the hydroxyl group. The second stage of the reaction involves the reaction of methylol groups with other available phenol or methylol phenol, (fig.6) leading first to the formation of linear polymers and then to the formation of hard-cured highly branched structures.

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Figure 6: Phenol-formaldehyde chemistry involves first formation of the hydroxymethyl group, followed by partial polymerization to the oligomer that makes up the adhesive. After applying adhesive to the substrate the polymization is completed to form a cross linked polymer network PF-resins are classified into two groups: Resols and Novolaks. Resols are made by base catalysis (caustic, amine) with an excess of formaldehyde cutting off the reaction at a certain condensation degree where PF resins are still liquid or soluble. The curing is done by heating and/or addition of catalysts. In the case of Novolaks the poly-condensation is brought to completion. The molecular growth is limited by the low molar ratio F/P (<1). Novolaks can be cross-linked by adding of curing agents such as formaldehyde and hexamethylenetetramine. The difference between acid and base catalyzed process is in the rate of aldehyde attack on the phenol, in the subsequent condensation of the phenolic alcohols and to some extent in the nature of the condensation reaction. With acid catalysis, phenolic alcohol formation is relatively slow. Therefore, this is the step that determination the rate of the total reaction. The condensation of phenolic alcohols and phenols forming compounds of the dihydroxydiphenylmethane type is, instead, rapid. The latter are therefore predominant intermediate in novolak resins.The application field of PF-resins is wide spread. Phenol-formaldehyde resins are widely used to produce softwood plywood for severe service conditions. These resins are dark reddish in color and are available as liquids and powders or in film form. Their use is almost mandatory in plywood to be used in severe service conditions. Most types used in the United States are alkaline catalyzed. Acid catalyzed systems are also available, primarily for use at curing temperatures of 70° to 140° F, but are used little in the United States. Principal limitation is the possible damage to wood by the acid catalyst.

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� Isocyanates: The isocyanate group reacts with any hydroxyl group to form a urethane bridge. The reaction between isocyanate and hydroxyls extends to water, which the isocyanate group reacts readily with the liberation of carbon dioxide and simultaneous formation of substituted urea groups.

As primary and secondary amines are the other favorite group with which isocyanate react, the amine formed by the reaction above reacts immediately with additional isocyanate to form a substituted urea as follows: The secondary amine groups present in the urethane bridge and in the substituted urea formed react further with available iso-cyanate groups to continue cross-linking and hardening of the material by the formation of allophenate and biuret bridges:

As to reach R belongs at least two –NCO groups, a hard, cross-linked network is formed rapidly.

Isocyanate based adhesives were first used in the 1940's, but their high cost, along with technical difficulties and associated health hazards, largely prevented their commercial application. Technical improvements (copolymerization), along with the demand for board products which are totally free of formaldehyde emissions, subsequently lead to the use of isocyanate binders for particleboard manufacture. Many numbers of co-polymer of polymeric di-isocyanates (MDIs) with a variety of other resins exist to yield thermosetting wood adhesive with excellent performance. These copolymers decrease cost, toxicity, ease of handling the resins and use for plywood. Some of these di-isocyanate copolymerized resins are MDI-PF, MDI-MF and MDI-UF. They have excellent resistance to moisture and hence are well-suited for exterior applications. In addition to wood, isocyanates may also be used to bond agricultural cellulosic. The basic bonding mechanism consists of forming urethane bridges with the hydroxyl groups of the cellulose. This results in an extremely strong wood to adhesive bond, which is resistant to moisture. Isocyanates are also used to assemble glues, but the cost of the adhesive limits their use at the present time. 2.3.3. Thermoplastic Adhesives � Polyvinyl Acetates (PVAc): The synthesis and patenting of vinyl acetate monomer by Dr Fritz Klatte in 1913 (fig. 8), in Germany, provided the foundation for many valuable and now essential plastic products. He found that the catalyzed reaction of acetylene with

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acetic acid gave a polymerized low boiling liquid (vinyl acetate) to yield a potential range of dense solid materials. These are now often denoted as PVAc polymers. Klatte found that PVAc was compatible with other polymers and plasticizers which could give valuable adhesives and coatings for cellulose and textile products

Figure8- Polyvinyl Acetate Polyvinyl acetate (PVAc) is an important type of industrial glue. Also in the wood working industry the direction is toward industrial use of glued materials and construction instead of nailing or screw joints. The most rapid development is taking place in the building product area, where a more efficient joining technique is needed. The use of glued-laminated timber (glulam), particle, and fiberboards (MDF, OSB) is becoming increasingly popular. Wood is also extensively used as curved laminated veneer in furniture. The properties and durability of adhesives exposed to different climates are becoming more and more important. However, polyvinyl acetate is nonresistant to moisture and if such adhesive joints are exploited in moist environment its strength substantially decreases. Sufficiently moisture resistant adhesive joints are obtained by modifying PVAc dispersion with special compounds characterized by high reactivity. Such monomers have chemically active groups with the aid of which spatial structures of molecules are formed. Polyvinyl alcohol is known as having high reactivity with hydroxylic groups, including polyvinyl acetate, acting as netting agents. They are applied seeking to reduce the solubility of poly(vinyl alcohol), to change OH groups by hydro-phobic ones, to make induce the netting of molecules. Other example, as modifying the dispersion additive is suggested monoaldehyde-formaldehyde. However, the drawback of this method lies in free formaldehyde in isolation of a poisonous substance from adhesive joints. There is another method to modify PVAc dispersion by dialdehyde – glyoxal, which is an expensive product. Other substances to modify PVAc dispersion are known as well, such as isoprophylene alcohol, iron trichloride, potassium bichromate, butyl acrylate, methyl methacrylate, alkoxysilane, polyisocyanate.

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2.4. WOOD POLYMER COMPOSITES USING A BINDER BASED ON POLYURETHANE RECYCLING PRODUCTS:

A new type of binder for wood particles or fibres was developed using a recycling polyol from polyurethane wastes and a polyisocyanate as raw materials. The binders developed with various ratios of hydroxyl and isocyanate groups are solid at room temperature with melting points between 45and 80 C. Sand2O o of these were added to wood products and this mixture compression moulded to give the composites materials Composites based on wood and various binders are frequently used in design and construction where a broad range of properties is established both by the type and shape of the wood particles and the binder used [1]. Phenolic resins, urea formaldehyde resins, acrylates, epoxies or polyurethanes are used as binders [2-5]. Recent developments favour aqueous dispersions of acrylics or polyurethanes instead of urea or phenolic resin due to the supposed elimination of formaldehyde from these polymeric binders. In another application polyisocyanates are used as liquids and directly combined with the wood particles in a spray and pressing process [6]. Handling of the polyisocyanates and their use in a spraying process constitutes always some safety problems. In the present paper we report another opportunity of such processes by the use of specially developed solid and easy and low melting polymeric binders with multitude of reactive groups. The process is based on the development of two new types of reactive precursors, i. e.

• specially designed polyol components derived from industrial polyurethane wastes and produced by a new solvolysis process ;

• solid, low melting isocyanate containing prepolymers with free isocyanate groups being stable over at least one year and containing catalysts to promote the reaction of the isocyanate and hydroxyl groups of the wood. The process to produce the composites is based on the properties of the solid prepolymers and is applied in the following stages:

• mixing of the powdered prepolymer with the wood particles in the appropriate proportion in a dry process;

• forming the mixture to the shape and magnitude of the composite intended; • applying pressure and temperature to the mixture in a mould

The preparation of the reactive intermediates and the process to produce such composites of various properties and fields of application is described below:

2.4.1. Experimental materials:

Dipropylene glycol (DPG) was obtained by Fluka AG and used without further purification, polypropylene glycol 2000 was a gift of Elastogran AG, Germany, di-n-butyl amine (DBA) was purchased from Merck KGaA, Darmstadt, Germany, and used without further treatment. The polymeric 4,4’-diphenylmethane diisocyanate (Lupranate® M20S) was a gift from Bosig Baukunststoffe GmbH. The types of

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polyurethanes used were samples from producers of Germany, Japan, Mexico, Poland, USA, Bulgaria, or Portugal. For the experiments to follow, mainly high resiliency foam (HR foam) of a German producer was used.

2.4.2. Method to obtain a recycling polyol—

The composition, the reaction condition and the characteristics of the recycling polyol are given in Table 1. The polyol was derived from flexible polyurethane foams by solvolysis [7]. The experiments were performed in a three necked glass flask with stirrer, thermometer, reflux and solids inlet. The liquids were placed into the reactor, heated to 180C, and the PUR foam was introduced with stirring as fast as possible while the temperature was slowly increased to the final reaction temperature of 220C and was kept after completion of the addition for another 30 minutes. The reaction mixture was cooled down, recovered and subjected to analysis for determination of the hydroxyl number (DIN 53 240), amine number (DIN 16 945) and viscosity (DIN 3219) using a Rheo Stress 300 (Haake GmbH). The polyol was used without further purification.

2.4.3. Method of obtaining of prepolymers--

The preparation of the prepolymers [8] was performed in a stainless steel vessel with oil heating mantle, stirrer, nitrogen inlet, column, condenser, and bottom outlet. The polyisocyanate was introduced into the vessel, nitrogen applied for about 5 minutes and the temperature raised to 45C. The polyol was added in steps not to exceed a temperature of 80C. After completion of the addition, the temperature was kept at 80C for three hours. After this phase, the prepolymer was recovered from the vessel by recovering through the bottom outlet onto Teflon® coated steel plates and cooled to ambient temperature. After

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conditioning for 24 hours it was milled using a lab mill to receive a powder with average particle diameter of less than 1 mm. The main parameters of prepolymers thus obtained are presented in Table 2. The isocyanate content was determined according to DIN 53 185.

The prepolymers obtained were used without further treatment. Under ordinary conditions they are stable up to two years.

2.4.4. Method of obtaining and characterisation of the composites -- Composites were prepared using a two-step process. The first step was mixing the wood particles with the calculated amount of powdered prepolymer in a drum. In the second tep the mixture was placed into a mould (100 / 200 / 20 mm). The mould with the mixture was heated to the desired temperature of moulding and the predetermined pressure applied by a lab press type RSR 200 for the time given. After cooling the mould to 50CC the composite was removed. Mechanical tests, i. e. tensile strength, elongation at break, elastic modulus, ere performed ith a Zwick Z20 Universal prófmaschine (DIN EN 527-1) after conditioning the samples for seven days at room temperature. Melting points were determined using a Netzsch DSC 102 with a heating rate of 1 K/mm between —100 and +200 C.

Now, from the above discussion, we can see that The polyols used in this investigation were recycling polyols derived from HR foams. Their characteristic parameters are depicted in Table 1. They generally have a completely different structure and composition as virgin polyols and, hence, unique properties. Consequently, also the polyurethanes produced on their basis will have mechanical or thermal properties which differ from such polyurethanes being produced from ordinary polyols. The main components of the recycling polyols are:

• the polyether polyol originally used to prepare the polyurethane (main component), • any short chain glycol, e. g. poly(ethylene glycol) 600 used in the formulation,

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• all catalysts used, i.e. tertiary amines and tin compounds (the latter are fully active), • silicones used as cell stabilizers,

• the short chain glycols of the reaction mixture,

• co-hydroxyl-urethanes from the trans-esterification of the hydroxyl component at the urethane group,

• trisubstituted polyureas derived from the originally used isocyanate and the amine used in the reaction.

The recycling polyols constitute thus a mixture of various components which were controlled only by the composition of the solvolysis mixture. One essential feature is that the originally present isocyanates were first reacted to the urethanes and by the solvolysis process converted to trisubstituted polyureas with chain length up to several nanometers. These form a kind of nanofillers with some reactive (amino) groups left. They will further react with any isocyanate added. The catalysts originally present are further fully active in the mixture. This could result in instable liquid prepolymers leading to gelation.

The properties of the recycling polyol (BP 1), e.i. hydroxyl number 301 mg KOH/g, amine number 53 mg KOH/g, viscosity at 25CC 3810 mPas are suitable for preparation of solid prepolymers. The hydroxyl and amine content are balanced to the amount of isocyanate to be used to establishe the melting areas useful in further processing

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The prepolymers prepared (Table 2) are powders stable at room temperature. They have an isocyanate content in the range of 4.87 to 11.28 mass The prepolymers still contain the catalysts of the original polyurethane which are fully active as are the isocyanate. It was found that the prepolymers are nevertheless stable at room temperature in a closed container up to two years. Their high reactivity toward hydrogen-active compounds together with the low melting point is of advantage in producing composites from natural resource of various kinds. The prepolymers were prepared at constant conditions reaction so as to measure the effect of the composition on the properties. In this series, the melting peak (determined by DSC) shows a minimum at an isocyanate content of 8.36 mass at about 50°C with increasing values to both lower and higher isocyanate contents reaching in both cases about 65°C. The determination of the melting peaks was rather complex due to the complicated structure of the material having a great number of different species with melting ranges between —65CC (glass transition of the polyurethanes derived from the polyether triol) and +250C (melting point of the polyureas of MDI). The second peak observed usually in the range of 1 30CC degrees maybe attributed to the lower chain length co-isocyanato-oligourethanes of the glycols

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It is essential to keep in mind that despite of various ratios of hydroxyl and isocyanate groups the prepolymers exhibit similar melting points and melting behavior and, thus, having very little effect on further processing conditions. The prepolymer PP 1-3 was used for obtaining composites. From Table 3 it can be seen that with decreasing amount of prepolymer there is a decrease in the tensile strength of the composite simultaneously with a reduction of the elongation at break. It is seen that in the range of 20 to 15 °°mass of prepolymer the mechanical properties show a plateau and do not follow a straight line while with a higher portion of wood particles the decrease in properties is dramatical. This results in the proposal to use for producing high quality wood products a prepolymer amount of about 20 %. In a further series (Table 4) with constant proportions of wood particles and prepolymer the processing conditions were optimized. The effect of pressure in the process is illustrated. The mechanical properties depend on the pressure in such a way as they pass a maximum with a certain pressure, here shown with sample 023, to result in maximum tensile strength and elongation at break. Higher pressure applied will reduce the mechanical properties again, presumably due to a breakdown of the wood structure.

In the following series was investigated the effect of pressing time at fixed conditions (pressure and temperature) and composition on the mechanical properties of the composites (Table 5). The time of pressing of the components in the mould at fixed conditions suggests that a longer pressing time than 20 minutes has nearly no effect on the mechanical properties. Small differences are usually within the range of statistical error. It is seen from the experiments to prepare composites with wood that this new type of prepolymers is ell suited to receive such composites ith high mechanical strength even when employing rather mild conditions. Here, a press temperature of 120C at a pressure of 200 kp/cm2 for 20 minutes was found to be the optimum.

So, as conclusion, we can write that --Recycling polyols from HR PUR foam may be type of stable prepolymers by reacting them with polyisocyanates. It could be shown that the reaction of polymeric MDI results in prepolymers being stable at room temperature and

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having a melting point exceeding 50CC so they are solid at room temperature and may be subjected to typical mechanical processing such as milling. It is surprising that material containing isocyanate groups between 4.87 and 11.28 mass and highly active catalysts are stable over a period of two years even with no protection or nitrogen blanket. A new type of binder material has been developed which may have much more fields of application as was shown here.

The prepolymer binders are highly effective in bonding wood particles even at a rate of 15 % mass added under various of conditions. The composite material obtained by this process has high mechanical properties as was shown by the tensile strength being up to 40 N/mm2 and the elongation at break between 0.27 and 0.77 %. So, the prepolymer binders add to the elasticity of the composites without affecting negatively the properties of wood. All these applications make the developed polyols and the prepolymers valuable new intermediates for the production of composites.

2.5. Wood-Polypropylene composite and it’s temperature dependent behaviors:

Wood-plastic composites (WPCs) are a class of engineered materials comprised mainly of a lignocellulosic (wood) component and a plastic component (Clemons, 2002; Wolcott, 2001). The majority of WPCs employ the use of thermoset plastics such as polyvinyl chloride (PVC), polypropylene (PP), high-density polyethylene (HDPE) or low-density polyethylene (LDPE). Various species of wood have been tested, with the most common being pine, maple, and oak (Clemons, 2002). In addition to wood species variations, the wood component can be integrated into the composite in one of three main ways: as wood flour, short wood fibers or long wood fibers, with wood flour being the most common form (Clemons, 2002; Wolcott 2001). With all the possible combinations of thermoplastics, wood species, and wood form, there is a vast spectrum of mechanical properties for the permutations of the three variables. From their beginning, WPC products have been utilized primarily in light or onstructural applications. For example, the first recorded use of a wood-thermoset composite was as a gearshift for Rolls Royce in 1916 (Clemons, 2002). Currently, they are most commonly found as the superstructure on residential decks, sills for windows and doors, or interior paneling for automobiles. Selection of WPC materials in these markets is based less upon mechanical performance, and more upon water-resistance, durability and/or low-maintenance qualities inherent in this class of product (Wolcott, 2001). WPCs have not been widely used in structural applications because their long term performance is not documented well enough to make suitable engineering assumptions and judgments. However, advantages of WPC products (i.e. moisture resistance, durability and low-maintenance, the ability to easily construct complex cross sections, the efficient nature of extrusion processing, and the ability to use recycled materials) are becoming increasingly appealing for select structural applications.

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2.5.1. Manufacture of Polypropylene-Pine wood plastic composite: 2.5.2. Materials and Methods The WPC was manufactured using a formulation composed of 58.8% pine (Pinus spp.) flour, 33.8% Polypropylene (PP), 4.0% talc, 2.3% maleated polypropylene (MAPP) and 1.0% lubricant by mass (Slaughter, 2004). Manufacturer details for each specific product included can be found in Table 2.1. Commercial 60-mesh pine (Pinus spp.) flour was dried in a steam tube dryer to a moisture content of less than 2%. The formulation components were dry-blended in powder form using a 1.2-m (4-ft) drum mixer in a series of 25-kg (55-lb) batches. An 86-mm conical counter-rotating twin-screw extruder (Cincinnati-Milacron TC 86), operating between 5 to 12 rpm, was used to produce thesections from which specimens were obtained. Barrel and screw temperature profiles were pre-arranged according to previous research (Kobbe, 2005) and are included in Table 2.2.

The formulated WPC material was extruded into a three-box cross-section using a stranding die (Laver, 1996). The section (Figure 2.1) had overall nominal dimensions of 45.7 by 165.1-mm (1.8 by 6.5-in) with nominal wall and flange thicknesses of 10.2-mm

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(0.4-in). Test specimens were machined from 1.22-m (4-ft) lengths of this extruded profile. The dimensions of individual tension and compression specimens were measured using digital calipers, recorded and used in all property calculations (i.e. cross-sectional area). 2.5.3. Determination of various material properties at different temperatures: a) Mechanical Testing Mechanical testing was conducted to determine material properties at various temperatures. To achieve this, a 222-kN (50-kip) servo-hydraulic test frame (MTS 810 with MTS 407 controller) was used for load application. Data was collected during testing by computer at a sampling rate of 2-Hz. Displacement over a 25.4-mm (1-in) gauge length was measured using an extensometer (MTS Model 634.12E-24). Applied loads were determined by a 22.2 and 244.7-kN (5-kip Interface 1210AJ-5k-B and 55-kip MTS 661.22C-01) in-line load cell for tension and compression tests, respectively. A constant strain rate of 0.01-mm/mm was applied by a controlled crosshead displacement rate of 2.03-mm/min (0.08-in/min) for both tension and compression. An environmental chamber was mounted within the test frame to control test conditions at a variety of potential service temperatures. Specifically, tests were conducted at 21.1°, 30°, 40°, 50°, 65.6° and 80°C (70°, 86°, 104°, 122°, 150° and 176°F) within a tolerance of ±2°C (9°F) throughout any given test. It was considered that the mechanical behavior of the material could potentially be affected by molecular rearrangement at higher temperature tests, thereby relaxing potential processing stresses in some, higher-temperature, test temperatures but not all conditions. This concern was addressed by conditioning all specimens at 65.6°C (150°F) for 48-hours prior to testing at any of the prescribed service conditions. This temperature was judged as an appropriate upper bound to the realistic service conditions At each temperature level, 28 specimens were tested to ensure a representative average value and to allow for a valid 5% exclusion limit at 75% confidence level if needed.

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The modulus of elasticity (MOE) of this material was determined using a secant modulus technique, applied between 5% and 10% of ultimate load (Kobbe, 2005). This procedure was adopted to maintain consistency in analyzing the nonlinear stress-strain behavior of this material. b) Tension Mechanical properties in tension were established by following procedures outlined in ASTM D683 with the exceptions of the test temperature and conditioning procedures. Type III dog-bone specimens were sampled from the top and bottom flanges of the three-box boards. During preparation, the flanges were cut and planed to ensure uniform thickness and eliminate surface defects. These planed flanges were then cut to the required dimensions and shaped to their final configuration using a guide and router. c) Compression Mechanical properties in compression were established by following procedures outlined in ASTM D695, except for test temperatures, conditioning procedures, and specimen geometry. Previous experiments testing small-scale compressive specimens according to the ASTM standard have yielded unrepresentative values for full-scale specimen performance. For this reason, a single-box compression specimen 203-mm (8- in) long was cut from the outer boxes of the three-box section (Hermanson, et al., 2001). This specimen was produced by detaching the outer boxes at the two flanges and machining the cut edges until smooth. All specimen dimensions were measured using digital calipers and recorded. These dimensions were used in relevant calculations for section area. The nominal specimen dimensions were 45.7 by 61.0-mm (1.8 by 2.4-in) with four 10.2-mm (0.4-in) thick walls.

2.5.4. Result and discussion for static mechanical properties:

The temperature dependence of tension and compression properties (σult, εmax, and E) are presented in Figures 2.2-2.4; respectively. In general, increases in service temperature resulted in decreased values for σult and E, while εmax showed an increase, indicating a more ductile response. Representative mean curves were computed by averaging the load values at common strain levels from the 28 specimens in each loading condition. These curves, along with the fit constitutive relation curves, are found in Figures 2.7 and 2.8 for tension and compression, respectively.

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For both tension and compression, σult decreased linearly with increasing temperature. At 21.1ºC (70ºF), the ultimate tensile strength of this material was found to be 18.14-MPa (2.631-ksi) and decreased to 12.03-MPa (1.745-ksi) at 80ºC (176ºF). A similar trend is found in compression, however the σult at ambient temperature was approximately 4x greater at 48.91-MPa (7.094-ksi). Again, as temperature increased to 80ºC (176ºF), σult decreased linearly to 24.90-MPa (3.611-ksi).

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When examining εmax values, the tension and compression gain differed in magnitude, with compression displaying a much more ductile response. For tension the εmax linearly doubled from a value of 0.00901-mm/mm at 21.1°C (70°F) to 0.01925- mm/mm at 80°C (176°F). The compression strains were nearly 3.5x larger than tension strains at ambient temperatures. The temperature dependence for εmax in compression was more modest than the tensile trend, however, and remained nearly constant at 0.035- mm/mm regardless of temperature tested. A decreasing trend for E is expected due to decreasing strength and increasing ductility with respect to temperature. At ambient temperature E values for both tension and compression were nearly identical with values of 3489-MPa (506-ksi) and 3447-MPa (500-ksi) for tension and compression, respectively. In both modes of loading the values of E decreased. In tension, E decreased according to a second-order function to a value of 1593-MPa (231-ksi) at 80ºC (176ºF). In compression, a linear decrease was found and at 80ºC a value of 1751-MPa (254-ksi). Summary statistics for σult, εmax, and E at each temperature level can be found in Table 2.3. For εmax, coefficient of variation (COV) values were between 10% to 16% for tension and 10% to 22% for compression. There was slightly less scatter for the E data where COVs ranged between 9% and 18.5% in tension and 7.5% to 13% in compression. The least scatter among the groups of data is found in ultimate strength. COV values for this were all below 10% with only one exception at 21.1ºC in tension where the value is 11.2%.

Detection of the α-phase transition prompted an investigation into the behavior of polypropylene over the temperature range of interest. Previous research has conducted DMA testing on specimens of neat polypropylene and polypropylene-binder composites that show glass transition at -8ºC (17.6ºF) and an α-phase transition between 70 and 100ºC (158 to 212ºF). These phase transitions of the composite materials at 70ºC exhibit less pronounced changes in the DMA results than neat PP. This decrease in prominence is thought to be a “masking” effect due to including the thermally stable wood phase. It is proposed that at the α-phase transition a lamellar slip mechanism and rotation of the

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crystalline phase begins (Amash and Zugenmaier, 1996). Detection of the α-phase transition is important because it indicates a change in microstructure response to stress and could manifest itself in significant changes in mechanical properties at 75ºC. 2.5.5. Constitutive Relations: The non-linear nature of this material requires a more complex relation than materials where linear proportionality exists. Separate works by Conway (1967), Lockyear (1999), Murphy (2003) and Kobbe (2005), have investigated expressions using hyperbolic functions to describe constitutive relations for non-linear materials. Two possible constitutive relations could be appropriate for modeling this material, one utilizing the arc-hyperbolic sine and the other using the hyperbolic tangent functions. Previous research on this specific formulation by Kobbe (2005) has indicated that the archyperbolic sine function with two curve fitting parameters (a and b) most accurately represents the initial stress-strain behaviour. sinh( )a a bσ ε= − − ………………………………………………………………. (eq. 1) Values for the constants a and b were determined for mean stress-strain curves at all emperatures and are presented in Table 2.4. Values for these constants were determined by minimizing the residual sum of the squares between the predicted and experimental data. The quality of fit can be judged in Figure 2.7 and Figure 2.8, where the constitutive relations are plotted against experimental data.

Clear trends for these empirical parameters can be seen in Figure 2.5 and Figure 2.6 showing a decreasing trend for a and an increasing trend for b with increasing temperatures. Because of the wide range of temperatures tested, the likely in-service high temperature condition of any user-end application should fall within this range. Therefore, appropriate constitutive equations can be interpolated from this data to arrive at reasonable predictions.

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2.5.6. Development of Design Factors: The mechanical testing results indicate that performance of WPCs is strongly dependent upon temperature. This dependence should therefore lead to adjustments in the allowable design process when elevated in-service temperatures are expected. Temperature effects for civil engineering materials other than timber do not provide much guidance for expected service temperatures. For steel, concrete, and masonry design, no reductions are

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proposed for the temperature range studied in this work (Salmon and Johnson, 1996; MacGregor, 1997). Decreases for steel and concrete are only assessed at much higher temperatures for fire-resistance and welding considerations. Because timber construction is the only material widely used within the civil engineering community with temperature-dependent strength, and WPC products are likely to be used as replacements for timber components, an approach similar to timber design is logical to develop. For this reason, the same ranges for temperature factor limits are considered for WPCs as in the timber code; T < 37.8°C, 37.8°C < T < 51.7°C, and 51.7°C < T < 65.6°C (T < 100°F, 100°F < T < 125°F, and 125°F < T < 150°F). Interpretation of the results presented here suggests that the decrease in E with temperature should also be addressed to appropriately deal with some load-bearing phenomena (i.e. buckling of columns, serviceability limits, etc.). Both strength and material stiffness degradation can be addressed using a factor-based design methodology with timber design as a model to develop these procedures. 2.5.7. Proposed Design Factors: To arrive at an appropriate allowable design value for a given loading property (Fx), the mean value of the property must be first adjusted for variability to arrive at a characteristic value (B), that is then further modified by a series of adjustment factors (Ci) which account for service conditions that differ from testing conditions. The following equation has previously been proposed for WPC materials and is similar in form to the NDS method for timber design:

Where: B represents the characteristic allowable property modified for variability C indicates various property adjustment factors Subscripts a, t, m, v, d represent adjustments for safety, temperature, moisture, volume, and load duration; respectively. From strength and MOE trends found in this investigation, an equation to calculate specific Ct factors for specific thermal loads has been found. This equation takes a quadratic polynomial form to encompass second-order effects that are found in material stiffness degradation:

Where: Ct is the temperature adjustment for a specific thermal load β1,2 are empirical coefficients (Table 2.5) ΔT is the difference in thermal load temperature from ambient (21.1°C or 70°F) Equation 4 can be applied to calculate reduction factors for both strength and E. Furthermore, investigating the reduction of these properties indicated unique decreases in properties between tension and compression. Therefore, different empirical factors should be applied to calculate the thermal reduction parameter depending on the mode of loading

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that a member will experience. Table 2.5 contains the empirical β-coefficients that apply to Equation 4 above.

A more simplified approach can also be employed to determine the Ct factor for these materials. This approach considers temperature ranges over which a single reduction factor is calculated. Values of Ct have been calculated for the same temperature intervals as the NDS approach for timber design and are presented in Table 2.6. It is important to mention that this approach is always conservative by converting the prevailing temperatures to the low end of the interval.

Comparing the approach developed here with previous attempts to determine temperature adjustment factors offers four obvious differences. First, this study has determined a strong dependence between loading mode and degradation path. This is most clearly illustrated in Figures 2.9 and 2.10 by the difference between tension and ompression values for Ct. Secondly, is the ability to calculate a case-specific thermal adjustment by presenting an equation-based method to determine the temperature reduction factor. This will allow for full utilization of these materials rather than only providing an approach that may unduly penalize the performance of the material at the low end of a temperature range. Next, a method to determine thermal loads follows in this work to determine thermal loads where no approach had previously been suggested to the knowledge of the author. Lastly, the magnitudes of the reduction factors found here are different than those previously proposed for the same temperature intervals proposed by the NDS and similar to the ranges previously approximated for WPCs (Haiar, 2000; NDS, 2001).

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2.5.8. Considerations for Thermal Loads: Reductions to WPC strength and material stiffness with increased temperature are more severe than for timber because a stronger temperature dependence exists. Furthermore, because the loss in strength and MOE for timber at high temperatures is often offset by gains from lower moisture contents, most residential construction assesses no adjustment (Breyer, et al., 1999, NDS 2005). Application of temperature factors in timber design

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focuses upon sustained temperatures upon a member due to the slow strength degradation wood undergoes at high temperatures. Degradation in timber is due to hydrolysis of the hemicellulose components and is non-recoverable due to the chemical breakdown of components. A different approach is appropriate for WPCs because strength and material stiffness degradation occur quickly. Mechanical performance decreases with temperature in WPCs because of a softening of the thermoplastic matrix, rather than chemical degradation as in the case of timber. Strength and MOE of WPCs is recoverable then as the temperature decreases and the polymer matrix hardens. It is still unclear the degree to which these properties recover after heating. Transient periods of high temperature must therefore be evaluated in the design process to coincide with the worst-case performance of the material, rather than a sustained load approach where appreciable short-term decreases in strength and MOE may be overlooked. It is important then to address what temperature should be considered a design level temperature. Many design loads are considered on a 50-year recurrence timeframe (i.e. snow loads in the International Building Code (IBC)). This will provide a temperature that should be exceeded only once every 50-years, and probabilistically should only have a 2- 24 percent annual likelihood of being exceeded. This approach is recommended to find a thermal load for WPCs based on air temperature with regard to geographical location. One credible source for data to calculate the 50-year temperature is the ASHRAE Fundamentals Handbook (ASHRAE, 2001). This source includes extreme air temperature annual daily maximums, the standard deviation of those maximums with respect to all historical data present for a given location, and the equation used to alculate the 50-year maximum temperature. This extreme annual mean and standard deviation data is presented in tabular form for hundreds of cities in the United States and Canada, as well as for select other cities worldwide. Following are example calculations for two locations in the United States with very different climate considerations:

The temperature load to consider for design is calculated using the following equation found in ASHRAE and is based upon an assumed Gumbel distribution fitted with the method of moments:

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appropriate engineering judgment must be employed when considering temperatures at which loads will be applied. At high temperatures when solar incident heating would occur, oftentimes the application will not see full design loads. The difficulty in addressing issues such as solar incident heating and assessing non-uniform thermal gradients within a cross-section is a lack of a standardized method to address these issues. Until a standardized process is established to account for these influences, the judgment of competent design engineers must be trusted. So, a designer must consider the probability of experiencing both solar incident heating and full design load, keeping in mind that reductions for strength and material stiffness are temporary while high-temperature conditions exist. Furthermore, in applications such as decking superstructures, to achieve a full design load on the deck would effectively block the sunlight from the members themselves and negate any incident effects. Heating effects beyond ambient air temperature must be considered on an individual application basis, 26 with reasonable assessment for the application of loads and applicability of additional heating 2.5.9. Considerations for Implementation Final implementation of temperature factors should include some consideration for the mode of failure for the designed member. When members are constructed for only compressive loadings, factors based on the compressive testing here would recommend values of 0.80, 0.70, 0.60, and 0.50 for the respective temperature ranges of the previous section (Section 2.4.3). This would apply to situations like deck foundation columns where only compressive axial forces are of interest. Similarly, calculations for buckling stress and other performance issues relating to stiffness should be checked using a reduced E in order to ensure adequate stiffness during high temperature conditions. If the mode of loading is a flexural or pure tensile application, the σult temperature factors should more closely resemble the tensile factors of 0.80, 0.80, 0.70, and 0.60. At a “design level” stress, a flexural member would be designed such that maximum tensile and compressive stresses are less than or equal to approximately 40% of their respective ultimate strengths. At this loading level, compressive and tensile behavior should be roughly equal in magnitude (Kobbe, 2005). However, the disparity between compressive and tensile capacities is such that a load level equal to the ultimate design level stress in tension (40% of 2630 psi or 1052 psi) would only be 15% of the compressive capacity on the opposite extreme fibers in the member. Thus, failures will initiate in the tensile face of flexural members (Kobbe, 2005). The factors developed for the tensile failure mode would then be the appropriate mode to combat flexural failure. Applying the more 27

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conservative (smaller in magnitude) compressive factors would create an overly conservative case because of the disparity in strength between tension and compression. 2.5.10. Conclusion Experimental results have provided the opportunity to track the performance of a pine-polypropylene composite material over a temperature range of 21.1ºC (70ºF) to 80ºC (176ºF). Different magnitudes of σult were measured for tension and compression, but the trend for both loading modes with respect to increasing temperature both decrease linearly. Tension loadings for εmax increased appreciably with temperature, whereas a nearly constant maximum strain was determined for compression regardless of temperature. E in both tension and compression both measured near 3447-MPa (500-ksi) at ambient temperatures and decreased by nearly half of that at 80ºC (176ºF), with a linear inverse relationship in compression and a quadratic relationship for tension. The nonlinear behavior of this material class dictated that an arc-hyperbolic sine function with two empirically fit parameters be used to adequately describe the constitutive behavior of this material. An inverse relationship between the first empirical parameter, a, while a direct relationship for the second parameter, b, was determined to occur with increasing temperatures. Correct determination of constitutive relations with respect to temperature will allow for more accurate analytical results from finite element, moment curvature or other analytical tools. One possible method for determining thermal loads upon a structure based upon geographical location was explored, and sample calculations were presented. This method is based on historical climactic data in the ASHRAE Handbook and has solid engineering principles supporting it. A 50-year extreme maximum temperature is recommended for design. However, proper engineering judgment and consideration of competing factors (i.e. reduced live loads at high temperatures and issues regarding solar incident heating) should be taken into account by the individual designer for appropriate use of these materials. Based upon the test results and trends over this temperature range, adjustment factors were proposed at temperature levels similar to timber design for both ultimate stress and material stiffness in tension and compression. Considering ultimate stresses, for ambient temperature to 37.5ºC (100ºF) a reduction of 0.80 is appropriate for both tension and compression members. The next temperature range is between 37.8ºC (100ºF) and 51.7ºC (125ºF) and factors of 0.80 and 0.70 for tension and compression, respectively were determined. The next range found factors of 0.70 for tension and 0.60 for compression and applies between 51.7ºC and 65.6ºC (125ºF to 150ºF). Above 65.6ºC (150ºF) a factor of 0.60 for tension and 0.50 for compression will appropriately reduce the allowable stress allowed on a member to account for the reduction of strength at the elevated temperature condition. MOE reductions similar to those for σult are also proposed for the same temperature levels to address decreases in E. From ambient to 37.8ºC (100ºF) factors of 0.70 and 0.80 were determined for tension and compression, respectively. Above that, for temperatures between 37.8ºC (100ºF) and 51.7ºC (125ºF) reduction values of 0.50 and 0.60 apply for tension and compression. Lastly, at temperatures greater than 65.6ºC (150ºF), factors of 0.40 and 0.50 are recommended to adequately reduce E.

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2.6. Plywood and composite wood product industries: Several industries that comprise the plywood and composite wood source category fall into three categories based on their Standard Industrial Classification (SIC) or North American Industry Classification System (NAICS) classifications and they are: • Softwood plywood and veneer • Reconstituted wood products • Structural wood members . Here, three categories of plywood and wood composites production: plywood and veneer; particleboard, strand and fiber composites; and structural wood members are given. The construction of plywood, consists basically of combining an odd number of layers of veneer, with each layer having one or more plies. Hardwood plywood is generally made by applying a hardwood veneer to the face and back of a softwood plywood, MDF, or particleboard panel. The differences between the hardwood and softwood processes occur because of different inputs and markets. Particleboard, oriented strand board, fiberboard, and hardboard are all processed similarly. These three types of reconstituted wood products are manufactured by combining fragmented pieces of wood and wood fiber into a cohesive mat of wood particles, fibers, and strands. Structural wood members are the products of multiple manufacturing techniques. This section describes the production of glue-laminated timber and the three types of structural composite lumber: laminated veneer lumber, parallel strand lumber, and laminated strand lumber. While there is a broad range of plywood and wood composites and many applications for such products, this section of the profile groups the production processes of these products into three general categories: plywood and veneer; particle board, strand and fiber composites; and structural wood members. Further descriptions of the production processes for each of these categories are provided in this section. 2.6.1. Manufacturing of Plywood and Veneer: a) Plywood and Veneer Construction of plywood relies on combining an odd number of layers of veneer. Layers consist of one or more than one ply with the wood grain running in the same direction. Outside plies are called faces or face and back plies, while the inner plies are called cores or centers. Layers may vary in number, thickness, species, and grade of wood. To distinguish the number of plies (individual sheets of veneer in a panel) from the number of layers (number of times the grain orientation changes), panels are sometimes described as three-ply, three-layer, or four-ply, three-layer. As described above, veneer is one of the main components of plywood. Most softwood plants produce plywood veneer for their own use. Of facilities reporting drying of veneer, 86 percent of the veneer produced was used for in-facility plywood production. Only approximately 7 percent of the facilities in the ICR survey produced veneer solely for outside sales and non-internal plywood use (EPA, 1998).

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The general processes for making softwood includes: log debarking, log steaming and/or soaking, veneer cutting, veneer drying, veneer preparation, glue application, pressing, panel trimming, and panel sanding. Softwood plywood is generally made with relatively thick faces (1/10 inch and thicker) and with exterior or intermediate glue. This glue provides protection in construction and industrial uses where moderate delays in providing weather protection might be expected or conditions of high humidity and water leakage may exist. Logs delivered to a plant are sorted, then debarked and cut into peeler blocks. Almost all hardwood and many softwood blocks are heated prior to peeling the veneer to soften the wood. The peeler blocks are heated by steaming, soaking in hot water, spraying with hot water, or combinations of these methods. Heated blocks are then conveyed to a veneer lathe. The block, gripped at either end and rotated at high speed, is fed against a stationary knife parallel to its length. Veneer is peeled from the block in continuous, uniform sheets. Depending on its intended use, veneer may range in thickness from 1/16 to 3/16 (1.6mm to 4.8mm) for softwood and much thinner for hardwood and decorative plywood uses (Youngquist, 1999). Slicing methods are also used to produce hardwood decorative veneers generally in thicknesses of 1/24 inch and thinner. After peeling, the continuous sheets of veneer are transported by conveyor to a clipping station where it is clipped. In softwood mills and some hardwood mills, high-speed clippers automatically chop the veneer ribbons to usable widths and defects are removed. In many hardwood mills, clipping may be done manually to obtain the maximum amount of clear material. Wet clipped veneer is then dried. Proper drying is necessary to ensure moisture content is low enough for adhesives to be effective. Dryer-- Two types of dryers are used in softwood veneer mills: roller resistant dryers, heated by forced air; and “platen” dryers, heated by steam. In older roller dryers, also still widely used for hardwood veneer, air is circulated through a zone parallel to the veneer. Most plants built in recent years use jet dryers (also called impingement dryers) that direct a current of air, at a velocity of 2,000 to 4,000 feet per minute, through small tubes on the surface of the veneer. Veneer dryers may be heated indirectly with steam, generated by a separate boiler, which is circulated through internal coils in contact with dryer air. Dryers may also be heated directly by the combustion gases of a gas-or wood-fired burner. The gas-fired burner is located inside the dryer, whereas combustion gases from a wood-fired burner are mixed with re-circulating dryer air in a blend box outside the dryer and then transported into the dryer. Veneer dryers tend to release organic aerosols, gaseous organic compounds, and small amounts of wood fiber into the atmosphere. Once dried, veneer is sorted and graded for particular uses. Adhesives-- Plywood manufacturing begins with the veneer sent to a lay-up area for adhesive application. Various adhesive application systems are used including hard rolls, sponge rolls, curtain coaters, sprayers, and foam extruders. The most common application for softwood plywood is an air or airless spray system, which generally uses a fixed-head

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applicator capable of a 10-foot wide spray at a nozzle pressure of 300 pounds per square inch (psi). The phenol-formaldehyde (PF) adhesives typical in softwood plywood manufacturing is made from resins synthesized in regional plants and shipped to individual plywood mills. At the mills, the resins are combined with extenders, fillers, catalysts, and caustic to modify the viscosity of the adhesive. This glue mixing has several additional effects: allowing the adhesive to be compatible with the glue application method (curtain, roll, spray, foam); allowing for better adhesive distribution; increasing the cure rate; and lowering cost. Presses-- Following the application of glue, the panels must be pressed. The purpose of the press is to bring the veneers into close contact so that the glue layer is very thin. At this point, resin is heated to the temperature required for the glue to bond. Most plywood plants first use a cold press at lower pressure prior to final pressing in the hot press. This allows the wet adhesive to "tack" the veneers together, permits easier loading of the hot-press, and prevents shifting of the veneers during loading. Pressing is usually performed in multi-opening presses, which can produce 20 to 40 4x8-foot panels in each two-to seven-minute pressing cycle. Finishing-- After pressing, stationary circular saws trim up to one inch from each side of the pressed plywood to produce square-edged sheets. Approximately 20 percent of annual softwood plywood production is then sanded. As sheets move through enclosed automatic sanders, pneumatic collectors above and below the plywood continuously remove the sander dust. Sawdust in trimming operations is also removed by pneumatic collectors. The plywood trim and sawdust are burned as fuel or sold to reconstituted panel plants. 2.6.2. Particle, Strand, and Fiber Composites: This group of products falls into the SIC or NAICS code category of reconstituted wood products. The impacted facilities in this category manufacture the following products (MRI, 1999). • Medium density fiberboard • Oriented stand board • Particleboard • Hardboard All particle, strand and fiber composites are processed in similar ways. Raw material for particleboard, oriented strandboard (OSB), fiberboard, and hardboard is obtained by flaking or chipping wood. The general process then includes wood drying, adhesive application, and forming a mat of wood particles, fibers, or strands. The mat is then pressed in a platen-type press under heat and pressure until the adhesive is cured. The bonded panel is finally cooled and further processed into specified width, length, and surface qualities. Specific details regarding the production processes for different products are provided below.

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a) Particleboard Generally, particleboard is produced by mechanically reducing wood materials into small articles, applying adhesive to the particles, and consolidating a loose mat with heat and pressure into a panel product. Particleboard is typically made in three layers with the faces consisting of finer material and the core using coarser material. Particleboard can also be made from a variety of agricultural residues, including kenaf core, jute stick, cereal straw, and rice husks depending on the region. EPA does not expect facilities that produce particleboard made from agricultural esidues, also called agriboard, to experience compliance cost impacts associated with the new MACT standard. EPA expects only one facility that produces molded particleboard to experience compliance cost impacts (MRI, 1999). The raw materials, or "furnish," that are used to manufacture reconstituted wood products can be either green or dry wood residues. Green residues include planer shavings from green lumber and green sawdust. Dry process residues include shavings from planing kiln-dried lumber, sawdust, sander dust, and plywood trim. The wood residues are ground into particles of varying sizes using flakers, mechanical refiners, and hammer mills, and are then classified according to their physical properties. After classification, the furnish is dried to a low moisture content (two to seven percent) to allow for moisture that will be gained by the adding of resins and other additives during blending. Most dryers currently in operation in particle and fiber composite manufacturing plants use large volumes of air to convey material of varied size through one or more passes within the dryer. Rotating drum dryers requiring one to three passes of the furnish are most common. The use of triple-pass dryers predominates in the United States. Dryer temperatures may be as high as 1,100 -1,200° F with a wet furnish. However, dry planer shavings require that dryer temperatures be no higher than 500° F because the ignition point of dry wood is 446° F. Many dryers are directly heated by dry fuel suspension burners. Others are heated by burning oil or natural gas. Direct-fired rotary drum dryers release emissions such as wood dust, combustion products, fly ash, and organic compounds evaporated from the extractable portion of the wood. Steam-heated and natural gas-fired dryers will have no fly ash. The furnish is then blended with synthetic adhesives, wax, and other additives distributed via spray nozzles, simple tubes, or atomizers. Resin may be added as received (usually as an aqueous solution), or mixed with water, wax emulsion, catalyst, or other additives. Waxes are added to impart water repellency and dimensional stability to the boards upon wetting. Particles for particleboard are mixed with the additive in short retention time blenders, through which the furnish passes in seconds. The furnish and resin mixture is then formed into mats using a dry process. This procedure uses air or a mechanical system to distribute the furnish onto a moving caul (tray), belt, or screen. Particleboard mats are often formed of layers of different sized particles, with the larger particles in the core, and the finer particles on the outside of the board. The mats are hot pressed to increase their density and to cure the resin. Most plants use multi-opening platen presses.

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Though more popular in Europe, the continuous press is currently being used in particleboard plants in the United States. Primary finishing steps for all reconstituted wood panels include cooling or hot stacking, grading, trimming/cutting, and sanding. Cooling is important for UF-resin-cured boards since the resin degrades at high temperatures after curing. Boards bonded using PF resins may be hot-stacked to provide additional curing time. Secondary finishing steps include filling, painting, laminating, and edge finishing. The vast majority of manufacturers do not apply secondary finishes to their panels; panels are finished primarily by end-users such as cabinet and furniture manufacturers. Panels are also finished by laminators who then sell the finished panels to furniture and cabinet manufacturers.

b) Oriented Strandboard (OSB) OSB is an engineered structural-use panel manufactured from thin wood strands bonded together with waterproof resin under heat and pressure. OSB manufacturing begins with debarked logs usually heated in soaking ponds sliced into wood strands typically measuring 4.5 to 6 inches long (114 to 152mm). Green strands are stored in wet bins and then dried in a traditional triple-pass dryer, a single-pass dryer, a combination triple–pass/single-pass dryer, or a three-section dryer. A recent advance in drying technology is a continuous chain dryer, in which strands are laid between two chain mats so the strands are held in place as they move through the dryer. After drying, blending and mat formation take place, blending of strands with adhesive and wax takes place in separate rotating blenders for face and core strands. Different resin formulations are typically used for face and core layers. Face resins may be liquid or powdered phenolics, while core resins may be phenolics or isocyantes. Mat formers take on a number of configurations to align strands along the length and width of the panel. Oriented layers of strands are dropped sequentially (face, core, face, for example), each by a different forming head. The mat is then transported by conveyer belt to the press. Hot pressing involves the compression of the loose layered mat of oriented strands under heat and pressure to cure the resin. Most plants utilize multi-opening presses that can form as many as sixteen 12-by 24-ft (3.7-by 7.3m) panels simultaneously. Recent development of a continuous press for OSB can consolidate the oriented and layer mat in 3 to 5 minutes.

c) Fiber Composites Fiber composites include hardboard, medium-density fiberboard (MDF), fiberboard, and insulation board. In order to make fibers for these composites, bonds between the wood fibers must be broken. This is generally done through refining of the material, which involves grinding or shearing of the material into wood fibers as it is forced between rotating disks. Refining can be augmented by water soaking, steam cooking (digesting), or chemical treatments as well. Fiber composites are classified by density and can involve either a wet process or a dry process. High and medium density boards, such as hardboard and MDF, apply a dry process. Wet processes can be used for high-density hardboard and low-density insulation

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board (fiberboard). Dry process involves adhesive-coated fibers that are dried in a tube dryer and air-laid into a mat for pressing. Wet processes differ from the dry processes. This process involves the utilization of water as a distributing medium for fibers in a mat. Further differences lie in the lack of additional binding agents in some wet processes. The technology is very much like paper manufacturing in this pulp-based aspect. Natural bonding in the wood fibers occurs in this process. Refining in this process relies on developing material that can achieve this binding with a degree of “freeness” for removal from mats. The wet process involves a continuously moving mesh screen, onto which pulp flows. Water is drawn off through the screen and through a series of press rolls. The wet fiber mats are dried in a conveyor-type dryer as they move to the press. Wet process hardboard is then pressed in multi-open presses heated by steam. Fiberboard is not pressed. Manufacturers use several treatments alone or together to increase dimensional stability and mechanical performance of both wet and dry process hardboards. Heat treatment exposes pressed fiberboard to dry heat, reducing water absorption and improving fiber bonding. Tempering is the heat treatment of pressed boards preceded by the addition of oil. Humidification is the addition of water to bring board moisture content into equilibrium with the air. 2.6.3. Structural Wood Members: Structural wood members, such as glue-laminated timbers and structural composite timber, are manufactured using a number of methods. Glue-laminated timber, or glulam, is an engineered product formed with two or more layers of lumber glued together in which the grain of all layers, called laminations, is oriented parallel to the length of the lumber. Glulam products also include lumber glued to panel products, such I-joists and box beams. Structural composite lumber consists of small pieces of wood glued together into sizes common for solid-sawn lumber. a) Glue-Laminated Timber (Glulam) Glulam is a material that is made from suitably selected and prepared pieces of wood, either straight or curved, with the grain of all pieces essentially parallel to the longitudinal axis of the member. The manufacturing process for glulam involves four major steps: (1) drying and grading, (2) end jointing, (3) face bonding, and (4) finishing and fabricating. b) Structural composite lumber There are three major types of structural composite lumber: laminated veneer lumber, parallel strand lumber, and laminated strand lumber. Each is described in more detail below, however, the general manufacturing process for these composites is similar. Laminated veneer lumber (LVL) is manufactured by laminating veneer with all plies parallel to the length. This process utilizes veneer 1/8 to 1/10 inches. (3.2 to 2.5 mm) thick, which are hot pressed with phenol-formaldehyde adhesive to form lumber of 8 to 60 feet (2.4 to 18.3 m) in length. The veneer used for LVL must be carefully selected to achieve the proper design characteristics. Ultrasonic testing is often used to sort veneer

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required for LVL. Once the veneer has been selected, end jointing occurs followed by adhesive application and continuous pressing. Parallel strand lumber (PSL) is a composite of wood strand elements with wood fibers primarily oriented along the length of the member. PSL is manufactured using veneer about 1/8 inch (3 mm) thick, which is then clipped into 3/4 inch (19 mm) wide strands. The process can utilize waste material from a plywood or LVL operation. Strands are coated with a waterproof structural adhesive, and oriented using special equipment to ensure proper placement and distribution. The pressing operation results in densification of the material. Adhesives are cured using microwave technology. As with LVL, the continuous pressing method is used. Laminated strand lumber (LSL) is produced using an extension of the technology used to produce oriented strandboard structural panels. LSL uses longer strands than those commonly used in OSB manufacturing. LSL is pressed into a billet several inches thick in a steam-injection press, as opposed to an OSB panel pressed in a multi-opening platen press. The product also requires a greater degree of alignment of the strands at higher pressures, which result in increased densification.

2.6.4. Products, By-Products, and Co-Products Exhibit 2-3 presents products, corresponding SIC and NAICS codes, and product examples of the plywood and composite wood products industry. The plywood and composite wood products industries have unique manufacturing processes in their use of waste wood products as an input for additional products. Planer shavings, sawdust, edgings, and other wood by-products are inputs to many wood composites. Structural wood members were developed in response to the increasing demand for high quality lumber when it became difficult to obtain this type of lumber from forest resources. Therefore, many of the by-and co-products from one process may be used in another.

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Exhibit 2-4 provides ratios of specialization and coverage (product mix) calculated by the U.S. Census Bureau for the last three Censuses of Manufacturers. The Census assigns a “primary” SIC code to each establishment which corresponds to the SIC code for the largest (by value) single type of product shipped by the establishment. The products shipped from that establishment that are classified in the same industry as the establishment are considered “primary,” and all other products shipped by the establishment are considered “secondary.” The Census then calculates various measures to illustrate the product mix between primary and secondary products in each industry. The specialization ratio represents the ratio of total primary product shipments to total product shipments for all establishments classified in the industry. The coverage ratio represents the ratio of primary products shipped by the establishments classified in the industry to the total shipments of these products shipped by all establishments classified in all industries.

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2.7. Medium Density Fiberboard (MDF) production: MDF consists of wood fibers (including; tracheids in softwoods, and vessels, fibres, fiber-tracheids and parenchyma cells in hardwood (Evans, 1994)) blended with synthetic thermosetting formaldehyde based resins and then pressed into boards. MDF can be made from a wide variety of lignocellulosic materials and an important implication of this is the use of recycled materials and non-wood fibres in its manufacture. Many softwoods and even bamboo (Wang, 1991), rice husks and waste paper (Dube, 1995) have been used successfully in the manufacture of MDF, although the type of fiber used in its manufacture strongly influence board properties (Myers, 1983). Combinations of wood and non-wood materials are increasingly being used to enhance specific properties, particularly strength, density and sorption characteristics (Park, 1993). MDF is increasingly being used as a replacement for other wood products, and its use in

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engineering fields is increasing. Figure 1.6 illustrates the manufacturing process of MDF.

Once the MDF plant has obtained suitable logs, the first process is debarking. The logs could be used with the bark, as could any fibrous material, but for optimisation of the final product the bark is removed to decrease equipment damaging grit, allow faster drainage of water during mat formation, decrease organic waste load by 10-15 %, stabilize pH levels (reduces corrosion of tools ) and increase surface finish. Although some plants accept chips directly from other operations, chipping is typically done at the MDF plant. A disc chipper a plate and the spinning plate is faced perpendicularly to the log feed. The feed speed of the logs, the radial speed of the knife plate, the protrusion distance of the knives and the angle of the knives, control the chip size. The chips are then screened and those that are oversized may be rechipped. The chips can be pulped using a Masonite gun process, atmospheric or pressurized disk refiner. After defibration fibers enter the blow line. The blow line is initially only 40mm in diameter with the fibers passing through at high velocity. Wax, used to improve the moisture resistance of the finished board, and resin are added in the blow line while the fibers are still wet, as dry fibers would form bundles, due to hydro bonding, and material consistency would be lost. The fibers are dried by heating coils warming the blowline to about 6-12 percent moisture content. After drying, mat formation is accomplished by

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means of airlaying. The mat can either be laterally cut to size as it leaves the pendistor or it can be cut half way through its run by a synchronized flying cut off saw. The density profile of the panel is critical to achieving satisfactory strength properties concentrating mass, and hence load bearing ability, at the top and bottom of the board means that inertial properties are maximized and the greatest strength can be obtained for minimal weight. This is achieved by the press acting at impacted pressure initially and then slower pressure application. As an example, for a 16mm board: • Press closed. 20 seconds to bring mat to 28 mm. • 28 seconds at 26mm. • 23 seconds at 25mm. • 125 seconds at 18.3. 2.8. Recycled wood plastic lumber composite: During 1990s, a number of technologies emerged to utilize recycled plastic in products designed to replace dimensional wood lumber. Since that time recycled plastic products have proven to be alternatives for many applications offering high durability and requiring low maintenance. RPLs are resilient, weather resistant, impervious to rot, mildew and termites. They do not need painting and staining. While RPL id widely employed in the construction of outdoor decks, it is also being used to fabricate moldings, doorjambs, window casings, railway tiles, pilings, posts and fencing products. The development of high throughput, low cost processing technologies will afford the opportunities to further close the recycling loop for the PE film and other plastics collected in industrial, commercial and municipal programs.

2.8.1. Properties of Plastic Lumber

In general, plastic lumber products are durable, stable, resilient and weather-resistant. They are impervious to rot, mildew, termites and other wood-eating organisms, and do not require high maintenance or regular repainting or staining. Many plastic lumber products are highly attractive and can be manufactured to meet a wide variety of design and appearance specifications. When wood or some other natural fibre source is incorporated into the material, many plastic lumber products can be painted or stained. The polymer chosen to formulate a wood fibre-plastic composite, as well as the amount of fibre added, will affect the properties (and potential applications) of the end products produced. In addition, increasing the amount of wood fibre can reduce the degree of creep exhibited by a plastic composite. A critical issue with plastic lumber is its low stiffness and low flexural strength when compared with natural wood. This may have limited the use of plastic lumber or wood fibre-plastic composites for structural applications, such as deck joists. To date, most of the extruded plastic or WPC boards produced have been used for deck surfaces where flex modulus is less critical. The new oriented wood-polymer composites may be able to reverse that situation. . As can be seen, conventional WPCs have relatively low flexural strength and stiffness compared to pine. However, the oriented wood fibre- polypropylene composite offers stiffness that is up to 82 percent of the flex modulus of the pine, while more than doubling the flexural strength

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2.8.2. Processing Technologies & Product Type

During the 1990s, a number of technologies emerged to utilize recycled plastics in products designed to replace dimensional wood lumber. While the largest market growth has been in the production of exterior deck boards, recycled plastic lumber (RPL) is also being used to fabricate moldings, doorjambs, window casings, playground equipment, railway ties, pilings, posts and fencing products. Despite a temporary slowdown in demand in 2000-2001, due to generally depressed economic conditions and the accumulation of high inventories by suppliers, the plastic lumber industry remains a growing force in the construction and building sector. Some of the traditional wood lumber companies are investing in new facilities to produce polyethylene wood composites. In addition, a number of Canadian companies have launched plastic lumber products in the past two years (although, for the most part, these recent start-ups have focused on the use of virgin polymers, rather than recycled plastics). Recently, an Ontario firm has updated an earlier extrusion flow molding technology, which had only limited application, to create a low-cost, high-output system that should provide new options for using recycled plastic, including sources that are heavily contaminated, to make railway ties and other large cross-section timbers.

This section briefly reviews the major production systems that are being used to make recycled plastic lumber -- including single polymer systems, extrusion flow molding systems, fiberglass-reinforced RPL, PVC extrusion profiles, wood fibre-plastic composites, oriented wood fibre-polymer composites, and polymer-polymer products. This section also assesses the capacities of the various production technologies to utilize recycled plastics in an effective and economic manner, and investigates the opportunities that might arise through the use of the new extrusion flow mold system developed by SPS Inc. (Tilsonburg, Ontario).

a) Single Polymer Systems

These systems, which use (primarily) continuously-extruded, structurally-foamed high density polyethylene, represent a significant part of the deck board market. The producers tend to use natural HDPE from milk jugs that can be pigmented to produce attractive deck colours. U.S. Plastic Lumber (Boca Raton, Florida) has been the largest and fastest growing company making this product.

b) Extrusion Flow Molding One of the first processes to be utilized to manufacture plastic developed in Europe, these systems can utilize mixed poh costs. However, the earlier versions of the process produced parts of low quality, which resulted in low Ontario company (SPS Inc.) has developed a new flow overcome the shortcomings of the earlier models (see si revolutionizes flow mold technology”). The high thro t SPS produces low-cost, high-

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quality railway ties, marine ties and other profiles with large cross-sections. The system can handle a wide range of recycled plasticADDSsJ’4O

2.8.3. Fibreglass-Reinforced RPL Production

This technology can be used to produce structural components and has a growing list of applications, including: deck joists; marine break walls, bulkheads and pilings; railway ties; and more demanding structural components. U.S Plastic Lumber is the largest producer of this type of material and some is produced under license from Rutgers University. It may be advantageous to place the glass fibre in the outer region of an extruded profiler to maximize stiffness and maintain toughness. A demonstration project (designed by M. G. Maclaren Engineering, for the New York Department of Economic Development) uses fiberglass-reinforced RPL in an arched bridge. The bridge constructed in New Baltimore N.Y. has met the design criteria for load; the tests included driving a heavy truck onto the structure and measuring deflection under load. A polypropylene-composite sheet, manufactured by Elf Products Inc. (Euclid, Arizona), has successfully replaced marine plywood in new boat manufacture. The product is a compression-molded composite composed of polypropylene, glass fibre and cellulose fibre (that is a combination of wood, long fibre flax and kenaf). This new product, under the brand name All-A-Board, is being used by SEA RAY in the manufacture of fibreglass boats. It resists rot better than marine plywood and bonds well to fibreglass. It can be used for bulkheads, transoms, decks and backing plates.

2.8.4. PVC Extrusion Profiles

These profiles are being used in railing and deck board markets. The American Architectural Manufacturers Association is working with ASTM on standards that cover PVC products. At least 14 companies extrude PVC deck boards and railing components. Royal Plastics (Woodbridge, Ontario) offers a complete line of vinyl decking systems in Canada. If fire retardancy is required, then PVC extrusion profiles have an advantage over other plastics (that might require heavy doses of flame retardant to meet flammability requirements).

2.8.5. Wood fibre—Plastic composites

WPCs are the largest and fastest growing segment of the recycled plastic lumber market. In the early 1 990s, products were commercialized using mixtures of polyethylene and wood to manufacture deck boards and other wood replacement products. They were manufactured with mixtures of 50 to 70 percent wood fibre and 30 to 50 percent polyethylene, either high or low density PE or mixtures of the two polymers. The extruded deck boards and profiles exhibit higher modulus than pure (such as those made from HDPE) and can be painted and offered in natural colours that age to a gray shade similar to manufactured with blue, gray or red pigments that sil the major manufacturers in this sector are the Trex C a series of new composite products have been polymers including polypropylene polystyrene, ABS, and PVC.. Other natural fibres have been used in addition to wood fibres, including rice hulls and even straws and flax. The mostly used raw materials for these composites continue to be Polyethylene bags and films,

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waste wood fibres, including high and low density polyethylene. The cost of these raw materials has tended to be lower than the cost of virgin HDPE, providing a manufacturing cost advantage to the composite board stock over the pure polymer extrusions. Despite the cost disadvantage, some companies are opting to use virgin polymers of higher modulus (including PP, PS, and ABS) to meet certain property and appearance specifications. The higher polymer costs are offset, to some degree, by designing engineered profiles that reduce weight while maintaining board stiffness.

2.8.6. Oriented Woodfibre-Polymer Composites

Dramatic improvements in flexural strength and flexural modulus have been emonstrated by cold drawing extruded polypropylene-wood composite. The flexural modulus of an oriented polypropylene composite with 30 percent wood fibre can achieve 82.5 percent of the flex modulus of dried pine. The same material had a flexural strength that was more than double that of pine. While not yet produced on a commercial basis, this new class of woodfibre-polymer composites shows great promise by offering a dramatic improvement in performance.

Polymer/Polymer Systems

This is an interesting new technology developed by Rutgers University, which discovered that specific blends of polymers, normally thought to be incompatible (such as polyethylene and polystyrene), can form composites with properties that dramatically exceed the expected performance of the blend. Under the right conditions of mixing and component levels, an inter-penetrating network of the polymer can achieve a better balance of modulus and impact strength. This discovery is being successfully applied to the manufacture of railway ties by Polywood, a New Jersey manufacturer of composite RPL.

2.9. Powder Coating Wood and Wood Composites: 2.9.1. Technique-- Powder coating is a technique whereby “Dry Paint” is electro-statically applied (by Corona or Tribo techniques) to, in the main Metallic substrates. After electrostatic spraying the ground powder could be described as a high Tg (>40ºC), non cross-linked, non-coalesced particulate film. This loosely coherent layer is then melt fused by thermal energy to form a highly viscous ‘liquid coating’ having a melt viscosity many orders of magnitude greater than for a solvent borne coating processed at the same temperature. his highly viscous material then increases in viscosity as it cross-links to form a three dimensionally cross-linked, tough, chemically resistant film. This film exhibits excellent mechanical properties when all cross-linked functional groups are cross-linked to ca. 90% of conversion.

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Powder coatings have been well established and are ‘mainstream’ for the coating of metallic substrates e.g. Iron, Aluminium, Galvanized Steel and so on. Environmental pressure and impending legislation, technical excellence and economic reasons have forced a huge and extensive developmental programme to realize the goal of powder coating Heat Sensitive Substrates. 2.9.2. Practical and Technical challenges: Powder Coating MDF The coating of metallic substrates and the Powder technology for the coating of metallic substrates is well developed. Some obvious difficulties and differences between powder coating metallic substrates and MDF are as follows: � Metallic substrates are conductive (refer Table One); the surface resistance of MDF needs to be adjusted (by either chemical doping and/or preheating techniques) to enable the substrate to have suitable conductivity for efficient powder coating. To use a straightforward analogy, metallic substrates are efficiently chemically pre-treated for reasons of adhesion, corrosion control and the like. Quality control of this process for metallic substrates is simple- checking chemical concentrations, deposition rates and so on. The ‘pre-treatment’ is to ensure that it can be properly powder coated efficiently, this process just as per the metallic analogy needs control and attention to detail. � Metallic substrates do not exhibit differential stress build up (edge/centre or centre/panel face) upon thermal heating, MDF does. Incorrect or relatively minor variability of heating regimes around the object to be powder coated will result in differential stress and subsequent failure of the cured powder. � Infrared (usually medium wavelength IR) and convection ovens are commonly utilized to provide the energy needed to cross-link powder coatings applied to metallic surfaces. For MDF, IR technology (either Gas IR or Electric IR) is a prerequisite. Infrared emitter technologies differ markedly from convection technology. Convection technology heats the air, which in turn transmits this thermal energy to the part being powder coated (the metallic substrate is, of course, thermally conductive as well). IR energy is either directly absorbed or transmitted through the Powder to the substrate. It heats what it sees – i.e. all surfaces which need to attain cure need ‘to see’ the IR source. Refer to table 1 for a list of some materials and their thermal conductivity values. � The use of convection ovens with highly conductive metallic substrates means that control of the ‘energy source’ is relatively simple. When using IR ovens to cure MDF composite substrates the operator needs to carefully monitor the temperature of all surfaces being painted. This is to ensure that all surfaces are being equally and evenly cured. Incomplete chemical conversion (cross-linking) of the powder coated film manifests itself as differential cure – differential cure will in effect, equate to internal stress building up in the powder coated film – the net result being powder checking and/or cracking. � Conventional powder coatings (as utilized for metallic substrates) are usually cured at higher temperatures and for longer dwell times. I.e. the powder coating traditionally cures @ 180 ºC for 10 minutes or 200 ºC for 10 minutes (metal temperature). MDF substrates will not tolerate these harsh temperatures so lower temperature curing schedules and more reactive powder coatings must be developed.

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� A variety of powder technologies have been investigated in the literature for use on Heat Sensitive Substrates via thermal curing i.e. Anhydride chemistries, Uretdione, Polyacrylate GMA etc. In general terms powder coatings utilize high Tg resin systems (Tg>50 ºC) to ensure that the powder coating material does not undergo agglomeration or pre-reaction at the molecular level during storage conditions. Lower temperature cure powder technologies must still pass standard storage condition protocols to be commercially viable. � Conventional powder coating technologies can be ‘catalyzed’ to cure at lower temperatures. The Powder Coating system needs to have negligible ‘activity’ during melt/shear extrudate processing (for short dwell times at ca. 120-130 ºC). It is expected that there will be some partial cross-linking during pre-reaction in the extruder as typically reaction rates follow classical Arrhenius temperature dependence. (This is a logical statement as we are curing these coatings at temperatures approaching 120 ºC) .The result of this ‘pre-reaction’ will be a building in cross-link density and a subsequent melt viscosity increase. What this means to the customer, of course, is poorer flow or orange peel. (This summary is ‘holistically simplistic’ – Resin and Coating suppliers have spent countless man-hours developing resin systems (I.e. semi crystalline, crystalline, hyper branched polymers etc) with “rapid melt viscosity drop” profiles so that suitable resins can be utilized for coating Heat Sensitive Substrates). � MDF is a highly complex, somewhat variable substrate, this can best be realized when one views the typical specifications of commercial MDF. Some highlights are of interest – MDF differs markedly in density (from ca. 650-850kg/m³) usually this is related to varied MDF thicknesses (typically from 3mm through > 30mm). Humidity content within the MDF board varies considerably with relative humidity, (MDF will reach equilibrium moisture content (EMC) with the surrounding environment); Factors that are of particular concern with powder coating MDF are: a. Type of MDF substrate (MDF, MUF, Particle Board, etc.) and constituents/additives. b. Moisture content, which is known to relate to conductivity and potentially blistering and out gassing issues during the curing process. c. Fibre size/porosity/fibre grain raise related to surface finish. d. If pre-conditioning is too severe then the edges will loose moisture in preference to the centre of the board. e. Rough, routed edges can be hard to dress, and can suffer from porosity issues. Some advantages of powder coatings over other coating materials is as follows: a. Powder is nil to very low in VOC b. Depending upon the formulation the overspray can be recycled, hence utilization of powder can approach 95%+.

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c. Waste from powder coating operations is easily discarded in an environmentally friendly manner. d. Excellent coating properties can be afforded by this technology. e. Single coat systems, high in film build (>100μm) can be processed in one layer on awkward, geometrically complex surfaces. 2.9.3. Commercial Realities created by LTCP-- During the past few years there has been a growing awareness of the need to expand the flexibility of supply of MDF panel products to the furniture & Joinery market segment. Indeed the uptake of powder coated MDF panels has been swift once designers and specifiers saw the inherent flexibility that LTCP brings to the table, particularly where colour choice and minimum run sizes are concerned. Core to this has been the metallic and speckle effect LTCP finished panels now supplied into the market. It has been this aesthetic as well as cost flexibility that has won over the adopters. Whilst powder coated MDF opens up opportunities for edge-finished components, particularly for the Kitchen, office furniture, and POS (point-of-sale) display areas, there are still challenges with industry acceptance. Edge taping (or banding) is universally accepted and there is little financial incentive for fabricators to move away from this lucrative process in their businesses. As New Zealand and Australian companies compete with the influx of product from international countries, particularly Asia based, new manufacturing techniques such as “Nesting” are becoming commonplace in local fabricator plants. Nesting is highly efficient and pre-finished nested components are cheaper to produce than corresponding edge finished components overall. Climate Coating Limited has invested heavily in developing its “Climate Application Process” to successfully apply LTCP to a variety of different variable wood fibre based substrates, including MDF, with out sacrificing the performance properties of the underlying substrate. This has been achieved with out the need to develop specialized expensive substrates. Proprietary new instrumental techniques have been developed with partner companies to measure panel moisture content AND conductivity in a non-destructive, non-contact way. This together with highly sensitive, Resistance spectroscopy instruments enables the successful application of the LTCP’s to the various types of MDF and other substrates. It cannot be more important to note that the success of LTCP over MDF requires the partnership of the LTCP supplier and applications specialists to enable a truly successful solution that meets market acceptability requirements. There is numerous end use applications for the LTCP coated MDF, a few examples of actual Climate Coating Limited element™ panels (LTCP coated MDF) are shown in figs 2-7; Kitchens, interior claddings, POS display, retail store fit outs, residential and commercial furniture.

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Other composite substrates successfully coated with LTCP coatings include plywood and Gypsum panels, both extensively used in the interior claddings markets. So, commercial application of LTCP over composite Plywood is forging its way into the housing interior and exterior claddings market. Other substrates are also soon to be launched into expanded end use markets. LTCP coated MDF is a substrate, which more so is being utilized for a number of cost effective end-use application. .

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3.1. Wood-Polymer Composite: Physical and Mechanical Properties of Some Wood Species Impregnated with Styrene and Methylmethacrylate Brazil has considerable reserves of tropical species. However, selective and predatory exploitation has reduced the offer of traditional species, of which demand still persists. The reserves of some of these species have therefore become almost completely depleted, causing prices to soar prohibitively and making the use of these raw materials unfeasible. In the search for solutions to this issue, the South and Southeastern regions have fallen back on reforested species, particularly the genera Eucalyptus and Pinus. Increasing interest has focused on the study of Wood-Polymer Composites (WPC) obtained from reforested species for the aforementioned reasons. However, for this alternative to be feasible on an industrial scale, it is essential that the performance of WPCs be well characterized, from their production process to the requisites for their various applications in the construction and furniture industries, among others. The work reported on here, developed in the Wood and Timber Structures Laboratory (LaMEM) of the São Carlos School of Engineering (EESC), University of São Paulo (USP), aims at demonstrating the possibility of producing WPC with superior mechanical properties to those of untreated wood, using reforested species of the genera Eucalyptus and Pinus and in situ polimerization of styrene and methyl methacrylate monomers 3.1.1. Materials and Methods Wood Tests were carried out on samples of reforested Eucalyptus grandis and Pinus caribaea obtained from the Itirapina nursery of the São Paulo Forest Institute, some of them not impregnated and others impregnated with styrene and methyl methacrylate monomers. .Eucalyptus grandis Eucalyptus grandis, within the class of the dicotyledons, has a parenchyma that is visible under a hand lens, vasicentric, scanty and occasionally dispersed. Its pores are visible to the naked eye, numerous and of medium size, predominantly solitary, frequently containing resins and sometimes obstructed by tyloses; rays visible under a hand lens in the cross section and the tangential face; and a strong pink colored heartwood. This species occurs in the reforested areas of southern and southeastern Brazil15. .Pinus caribaea Pinus caribaea, classified as a conifer, lacks parenchyma and pores. It has very small tracheids with a slightly radial orientation that are individually indistinguishable to the naked eye but visible under a hand lens, almost indistinguishable rays at the cross section and on the tangential face, growth layers marked by initial and late xylem with variable thicknesses, a medium texture, and a beige colored core slightly resinous and with a pleasant odor15.

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Monomers and initiator Styrene, methyl methacrylate, and benzoyl peroxide were obtained from Companhia Brasileira de Estireno, Companhia Química Metacril and Degussa Initiators Ltda., respectively. 3.1.2. Removal and identification of the test specimens The samples were prepared according to the specifications of Attachment B of the Brazilian NBR 7190:1997 standard16. The test specimens (TP) were taken from twelve pieces of each wood species, with nominal dimensions of 5 cm × 12 cm × 180 cm, each piece yielding three bars. Each bar supplied a set of three samples for each type of impregnation, totaling 576 test specimens, i.e., 12 sets of samples for each of the wood species studied, as illustrated in Fig. 1. Each test specimen was identified with a capital letter (corresponding to the beam), a small letter (corresponding to the type of test) and a number (corresponding to the type of impregnation). The samples identified with the number 1 were tested without impregnation, those displaying the number 2 were impregnated with styrene monomer, and the ones bearing the number 3 were impregnated with methyl methacrylate. 3.1.3. Phases of the test specimens’ impregnation and polymerization process Before the wood was impregnated with the monomer, part of the water had to be removed from its pores due to the wood’s moisture content. The test specimens were therefore oven-dried at a temperature of 40 °C until their moisture content decreased to 12%. The oven’s temperature was gradually raised to 50 °C to reduce the possibility of cracking or warping. The method utilized to impregnate the monomer-initiator solution was vacuum-pressure. The autoclave employed for the impregnation work had a capacity of 159,000 mL. A total volume of 20,520 mL of each wood species was placed in the autoclave, which was then closed and the air removed from its interior. When vacuum was reached, the monomerinitiator solution (20,520 mL of monomer + 255 g of benzoyl peroxide)17, was injected into the autoclave for each wood species. A pressure of 0.66 MPa was then applied for 30 min to complete the impregnation process. The test specimens were then removed from the autoclave and wiped with paper towels to remove any excess impregnation resin. The next step consisted of weighing the test specimens, wrapping them in aluminum foil and placing them in the oven, where they were left for 48 h at a temperature of 60 °C. The samples were then removed from the oven, unwrapped, weighed and put back into the oven for another period of 72 h at 50 °C to consolidate the polymerization process inside the wood. Finally, the samples were removed from the oven, weighed, and their dimensions measured, in preparation for the tests to obtain the desired properties. 3.1.4. Tests to determine the properties of impregnated and non-impregnated wood Tests were carried out to determine the following properties: Density (ρ); Total radial shrinkage (εr,2); Total tangential shrinkage (εr,3); Total radial swelling (εi,2); Total tangential swelling (εi,3); Strength in compression parallel to grain (fc0); Modulus of elasticity in compression parallel to grain (Ec0); Strength in tension parallel to grain (ft0);

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Modulus of elasticity in tension parallel to grain (Et0); Strength in tension perpendicular to grain (ft90); Shear strength (fv0); Toughness (W); Impact bending (fbw); Hardness parallel to grain (fH0) and Hardness perpendicular to grain (fH90). The tests were performed following the specifications of Attachment B of the Brazilian NBR 7190:1997 standard16. The toughness was calculated based on the ASTM D143-52:1981 standard18. 3.1.5. Procedures for analyzing the results The results were analyzed using the pairing test, procedure commonly employed in such cases19. The test consists of making a comparative analysis of the test specimens nonimpregnated and impregnated with styrene and methyl methacrylate monomers to discover whether the difference between the averages of the physical and mechanical properties under study could be null, evidencing that they can be admitted to be statistically equivalent. The first step in order to apply this methodology consists in calculating the difference between two population means (impregnated and non-impregnated specimens). Values obtained in this way are considered as a third population.

The second step consists in estimating the mean and confidence interval of this population, which is obtained through the following expression:

Where: mX is the sample mean of the third population, Sm is the sample standard deviation of this population, n is the sample size, α is the confidence level usually adopted 95% and is the percentage point of the t distribution with n-1 degrees of freedom. Analysis is carried out using this interval. If zero belongs to it, the means of the two populations (impregnated and non-impregnated) can be considered as equivalent. If zero does not belong to the interval, these means can be considered as different.

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3.1.6. Presentation and Discussion of the Results Tests were carried out on a total of 576 samples, 288 of Eucalyptus grandis (EG) and 288 of Pinus caribaea (PC), with 96 samples of each species without impregnation (wi), 96 impregnated with styrene monomer (i-E) and 96 impregnated with methyl methacrylate monomer (i-M). Small variations in the toughness values caused by differences in the nominal dimensions of the samples were corrected20. The results obtained from the tests performed to determine the physical and mechanical properties of the wood at 12% moisture content are listed as follows: Eucalyptus grandis Tables 1 and 2 list the results and pairing tests obtained when comparing samples of Eucalyptus grandis without impregnation and impregnated, respectively, with styrene and methyl methacrylate monomers. The statistical analysis revealed that, except for the hardness parallel (fH0) and perpendicular to grain (fH90), all the other properties studied showed a zero within the confidence interval of the mean differences. Hence, equivalence is admitted between the properties of the wood without impregnation and impregnated with the two monomers involved in this study. The analysis of the microscopic structure of the nonimpregnated samples of Eucalyptus grandis compared with the samples impregnated with the styrene and methyl methacrylate monomers shown in Fig. 2 revealed that there was little penetration and subsequent polymerization of the monomers inside the wood’s anatomical structure. However, some of the pores are clearly filled with polystyrene and with polymethyl methacrylate. The reason for this poor penetration is that, despite the large quantity of fibers, their mall diameter almost completely precludes impregnation. In addition, the interior of the pores may present contents generically called gum-resins.

Pinus caribaea Tables 3 and 4 show the results and pairing tests obtained when comparing samples of Pinus caribaea nonimpregnated and impregnated with styrene and methyl methacrylate monomers, respectively. The statistical analysis indicated that the confidence interval of

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the mean differences did not contain zero for any of the physical and mechanical properties studied. fore, one can Therefore, one can state a statistical non-equivalence

between the properties of the wood without impregnation and impregnated with the styrene and methyl methacrylate monomers. The analysis of the microscopic structure of the nonimpregnated samples of Pinus caribaea compared with the samples impregnated with the styrene and methyl methacrylate monomers shown in Fig. 3 indicated that penetration and subsequent polymerization of the monomers occurred inside the wood’s anatomical structure. This Pine species has a permeable structure, facilitating its impregnation and the subsequent retention of the polystyrene and the polymethyl methacrylate. 3.1.7. Discussion of above topic The results obtained for Eucalyptus grandis showed a statistically non-significant variation in all the properties studied here between impregnated and non-impregnated wood, except for the hardness parallel and perpendicular to grain. This poor outcome can, in principle, be attributed to the merely superficial penetration of the aforementioned monomers as a result of the species’

anatomical peculiarities (small diameter fibers and ends, and vessels or pores frequently containing resins). The presence of styrene and methyl methacrylate in these regions caused minor variations of the measured properties. The comparison between Pinus caribaea impregnated with the aforementioned monomers showed a significant increase in all the physical and mechanical properties related to the non-impregnated samples. The dimensional stability of the composite increased in comparison with the untreated wood, rendering it more impermeable to moisture absorption and retention. The two types of impregnation led to a strong improvement in the wood’s hardness parallel and perpendicular to grain, with an average percent increase of over 400% and 300%, respectively, rendering this composite very interesting for flooring applications, for instance. It is also worth noting that the incorporation of polystyrene and polymethyl methacrylate was also highly satisfactory in Pinus caribaea, reaching an average of 80% and 50%, respectively, in wood mass. Based on these results, it can be concluded that Eucalyptus grandis does not exhibit performance suitable for this type of impregnation, owing to its low permeability. Pinus caribaea, on the other hand, absorbs styrene and methyl methacrylate monomers easily, indicating the efficiency of the wood

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impregnation process and thus allowing for its use in applications that require materials with superior mechanical properties.

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4.1. Conclusion: Composites have attractive mechanical and physical properties that are now being utilized in industry and aerospace on a grand scale world-wide. New fibres, polymers, and processing techniques for all classes of composites are constantly being developed. Research is also ongoing to improve repair techniques, recyclability, and the bonding between fibres and matrix materials. Moreover, standards are being set up for the testing and computerization of mechanical- and corrosion-property databanks. Because of the development of new fire-retarding constituents, the availability of polymers with higher temperature ratings, the relative ease of fabrication, and the fair costs, PMCs are being utilized more in structural and wear-resistant applications in mining and industrial environments. There is no doubt that, if processing costs can be substantially reduced, MMCs, WPCs and CMCs will be increasingly employed in applications that require light weight in addition to toughness and wear- and abrasion-resistant properties. CMCs will increasingly be used for high-temperature, oxidation-resistant, and wear- and abrasion-resistant applications where good corrosion resistance is also required. Leading international companies involved in the traditional manufacture of metal and ceramic parts are already positioning themselves to obtain a market share. The new applications that are being found on an almost daily basis, and the continuous reporting of company investments and new ventures into the manufacture of MMC and CMC parts, tend to indicate that important progress has been made towards the reduction of processing and manufacturing costs. These developments have been noticed by the mining industry in South Africa. However, it is important to realize that the use of composites requires an integrated approach between user and designer/manufacturer to ensure functionality. This entails knowledge of the structural efficiency of the material, its isotropic or anisotropic behavior, environmental effects, and its manufacturing requirements, assembly, and repair. The application of composites to the mining environment and industries in the whole world can result in many long-term cost-related advantages. The question arises as to whether we in the world are being unnecessarily conservative in sticking to tried materials.

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4.2. References: 1. American Society of Testing Materials, (1998) Standard Test Method for Shear Properties of Composite Materials by the V-notched Beam Method, ASTM D5379. 2. Arramon, Y. P., Mehrabadi, M. M., Martin D. W., Cowin, S. C., (2000) A Multidimentional Anistropic Strength Criterion Based on Kelvin Modes, International Journal of Solids and Structures, Pergamon Press, 37, 2915-2935. 3.Wanger J. W., Deaton J. B. and Spicer B., “Generation of ultrasound by repetitively Qswitching a pulsed Nd: YAG laser”, Applied Optics, Vol. 27, pp. 4696-4700, 1988. 4.White, R. M., “Generation of elastic waves by transient surface heating”, J.Applied Phys., Vol. 34, pp. 3559-3567, 1963. White S. R. and Kim Y. K., “Staged curing of composite materials”, Composites Part A, Vol. 27A, pp. 219-227, 1996. 5. Schauwecker, C., Morrell, J. J., McDonald, A. G., Fabiyi, J. S., "Degradation of a woodplastic composite exposed under tropical conditions". Forest Products Journal, Vol. 56, No. 11/12, pp 123-129, 2006. 6. Stark, N. M., Matuana, L. M., “Surface chemistry and mechanical property changes of wood-flour/High-density-polyethylene composites after accelerated weathering". Journal of Applied Polymer Science, Vol. 94, pp 2263-2273, 2004. 7. Pilarski, J. M., Matuana, L. M., “Durability of wood flour-plastic composites exposed to accelerated freeze-thaw cycling. II. High density polyethylene matrix". Journal of Applied Polymer Science, Vol. 100, pp 35-39, 2006. 8. Elias, Hans-Georg. An introduction to plastics.ed. 1, Verlagsgesellschaft, VCH, 1993. 9. Meyer, J.A. Industrial use of wood-polymer materials: state of the art. Forest Products Journal, v. 32, n. 1, p. 24- 29, Jan, 1982. 10. Avilov, A.; Deruyga, V.; Popov, G.; Rudychev, V.; Zalyubovsky, I. Non-waste and resource-saving radiation process of polymer modified wood production. In: Proceedings. v. 4, p. 2549-2551, 1999. 11. Barnes RA, Baglin PS, Mays GC and Subedi NK. “ External steel plate systems for the shear strengthening of reinforced concrete beams.” Structural Engineer, 2001, No. 23. pp 1162 – 1176. 12. Hollaway LC and Leeming MB. “Strengthening of reinforced concrete structures.” Woodhead Pub Ltd. England. 1999. pp 11-45. 13. Jansze W. “Strengthening of reinforced concrete members in bending by externally bonded steel plates.” Deft University of Technology. 1997. pp 1-8.

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14. Jones R, Swamy RN and Ang TH. “Under and over-reinforced concrete beams with glued steel plates.” International Journal of Cement and Composites. 1982. Vol. 4 No. 1. pp 19-32. 15. Jones R, Swamy RN and Charif A. “Plate separation and anchorage of reinforced concrete beams strengthened by epoxy-bonded steel plates.” The Structural Engineers. 1988. Vol. 66 No.5. pp 85-94. 16. Klaiber FW, Dunker KF, Wipf TJ and Sanders WW Jr. “Methods of strengthening existing higway bridges.” NCHRP Rep. 193, Transportation research Board. Washington DC 1987. 17. Mukhopadhyaya P, Swamy N, Fellow, ASCE and Lynsdale C. “Optimizing structural response of beams strengthened with GFRP plates.” Journal of Composites for Construction. 1998. No. 2. pp 87 – 95. 18. Swamy RN, Jones R and Bloxham JW. “Structural behaviour of reinforced concrete beams, strengthened by epoxy-bonded steel plates.” The Structural Engineers. 1987. Vol. 65 No. A2. pp 59-68. 19. Sain, M.M., Balatinecz, J. and Law, S., “Creep Fatigue in Engineered Wood Fiber and Plastic Compositions.” Journal of Applied Polymer Science, Vol. 77, pp. 260- 268, 2000. 20. Schildmeyer, A.J., “Temperature and Time Dependent Behaviors of a Wood- Polypropylene Composite.” Chapter 2, Master Thesis, Washington State University, July 2006. 21. Schildmeyer, A.J. (2), “Temperature and Time Dependent Behaviors of a Wood- Polypropylene Composite.” Appendix A, Master Thesis, Washington State University, July 2006. 22. Slaughter, A.E., “Design and Fatigue of a Structural Wood-Plastic Composite.” Master Thesis, Washington State University, August 2004. 23. Beckers, E.P.J., Militz, H. and Stevens, M. (1994) Resistance of acetylated wood to basidiomycetes, soft rot and blue stain. International Research Group on Wood Preservation. Document no. IRG/WP 94-40021. 24. Bongers, H.P.M. and Beckers, E.P.J. (2003) Mechanical properties of acetylated solid wood treated on pilot plant scale. Proceedings of the first European Conference on Wood Modification, Ghent, Belgium, 341-350. 25. Boonstra, M, Tjeerdsma, B.F. and Groeneveld, H.A.C. (1998) Thermal Modification of Non- Durable Wood Species.