Polystyrene wood composites

Currently marketed wood composites are based on 30% to 70% natural-fibre-filled polypropylene, polyethylene, polystyrene and PVC. Formulations have high performances and are more expensive than the virgin material. 

U.S. Pat. No. 6,903,149 [58] discloses a plastic-wood composite comprising 100 parts by weight of a thermoplastic resin such as PVC, polyolefin, polystyrene, a polyester resin, and a polyamide resin, 5-400 parts by weight of wood flour, and 0.05-20 parts by weight of a dibasic polyol ester having at least one hydroxyl group esterified with fatty acid. 

When used as substitutes for asbestos fibers, plant fibers and manmade cellulose fibers show comparable characteristic values in a cement matrix, but at lower costs. As with plastic composites, these values are essentially dependent on the properties of the fiber and the adhesion between fiber and matrix. Distinctly higher values for strength and. stiffness of the composites can be achieved by a chemical modification of the fiber surface (acrylic and polystyrene treatment [74]), usually produced by the Hatschek-process 75-77J. Tests by Coutts et al. [76] and Coutts [77,78] on wood fiber cement (soft-, and hardwood fibers) show that already at a fiber content of 8-10 wt%, a maximum of strengthening is achieved (Fig. 22). 

Figure 12. Thermomechanical behavior of an acetylated-propionylated wood sample and the acetylated-propionylated wood-polystyrene composites prepared by the y-ray induced graft copolymerization in a pyridine medium. Numerical values on the curves represent the total dose of the irradiated y-ray. Key (total irradiation, resultant weight increase based on the weight of wood) A, 0.1 Mrad, 4.2% , 0.5 Mrad, 12.2% , 1.9 Mrad, 49.1% A, 2.4 Mrad, 66.0% and ,...

Figure 13. Thermomechanical behavior of O, the acetylated wood and , the acetylated wood-polystyrene composite prepared by the y-ray induced graft copolymerization in a pyridine medium. Conditions total dose, 2 Mrad resultant...

Bonding of hydrophobic plastic materials to wood to create new wood-plastic (polystyrene) materials with improved mechanical and physical properties that incorporate the desirable features of each constituent is difficult to achieve. This is due to poor interfacial adhesion between the wood and polystyrene components because of their inherent incompatibility. New, well-defined, tailored cellulose-polystyrene graft copolymers have recently been prepared using anionic polymerization techniques. Preliminary bonding studies showed that these graft copolymers can function effectively as compatibi-lizers or interfacial agents to bond hydrophobic plastic (polystyrene) material to wood, evolving into a new class of composites. 

It may also be possible to eventually extend this bonding concept to the preparation of flakeboards and other wood-base composite materials. If plastics like polystyrene are incorporated into the composite matrix, and successful bonding between the wood and plastic is developed through the graft polymers, the three-dimensional network of plastic material throughout the composite matrix may lead to enhanced physical and mechanical properties as well as improvements in dimensional stability (Figure 2). 

Results from the initial resin studied are also being employed in the development of additional experimental procedures. Plans are currently being drafted to prepare three-ply test specimens that are similar to the specimens used in the initial study, with the middle ply consisting of solid polystyrene. Comparing specimens with and without the graft polymers introduced to the ply interfaces should provide additional information on the ability of the cellulosic graft polymers to facilitate bonding between wood and plastic materials. If this approach proves successful, additional procedures will then be developed for the production of simple composite specimens. 

This research project represents initial studies into a new approach to blending thermoplastic materials like polystyrene with wood materials, leading to a new class of wood-plastic composites. Traditional wood-plastic composites have involved the impregnation and subsequent in situ polymerization of vinyl monomers. This procedure has been adopted for selected products for which improved physical properties justify increased production costs. While producing mixtures or blends of wood and plastics, these types of composites do not demonstrate significant chemical bonding between the wood and plastic components. 

This specification covers the composition and physical properties of insulating boards composed of wood-fiber insulation board laminated to rigid cellular polystyrene insulation boards, flat or tapered, used principally above structural roof decks for thermal insulation as well as for a base for roofing in building construction. 

U.S. Pat. No. 3,875,088 [29] describes a composite material comprising 50-75% of a thermoplastic resin binder (ABS or rubber-modified polystyrene) and 20-40% of wood flonr (40 mesh and 100 mesh), with the ratio of plastic to wood flonr being between 1.5 and 3.0. 

U.S. Pat. No. 5,153,241 [66] discloses composites made of thermoplastic polymers such as low-density polyethylene, polypropylene or polystyrene (90-60%) and wood pulp or sawdust (10-40% by weight) grafted with a titanium coupling agent (isopropyltri[n-ethylaminoethylamino] titanate) in acetone, along with some inorganic fillers, such as calcium carbonate and Portland cement. 

U.S. Pat, Nos. 6,122,877 [107] and 6,682,814 [108] (both by Andersen Corporation) disclose a cellulosic fiber-polymeric composite comprising 45-70% of thermoplastic polymers such as PVC, polyethylene and its copolymers, polystyrene, polyacrylate, polyester and their mixtures, and 30-65% of wood fiber, such as sawdust. 

U.S. Pat. No. 6,780,359 [109] (by Crane Plastics Company, TimbeiTech) discloses a cellulosic fiber-polymeric composite comprising mixing a cellulosic material, such as wood fiber, with a plastic material, such as HDPE, LDPE, PVC, chlorinated PVC, polypropylene, EVA, ABS, and polystyrene, to form a cellulosic reinforced plastic composite. 

U.S. Pat. No. 7,022,751 [111] describes a fiber-reinforced composite plastic material comprising thermoplastic polymers such as HDPE, LDPE, polypropylene, PVC, and polystyrene a high melting point waste polymer fiber material such as polyethylene terephthalate and nylon, an inorganic filler, such as glass and other material, and an organic filler such as wood or particles of a thermoset plastic, such as rubber and polyurethane foam. 

U.S. Pat. No. 6,255,368 [114] describes plastic cellulosic composite pellets comprising 20-60% by weight of polyethylene, polypropylene or polystyrene, 40-80% of cellulosic fiber (jute, kenaf, sisal, bamboo, rice hulls, corn husks, wood fiber, and wood flour) with an aspect ratio of between 2 and 20 and a trace of mineral coating (talc) dispersed on the surface of the pellet. 

Natural fibers can be classified as seed fibers (such as cotton), bast fibers (like flax, hemp, jute, kenaf, ramie), hard fibers (like sisal), fi-uit fibers (like coir), and wood fibers. The chemical composition and dimensions of some common agro-fibers are presented in Table 5.21. The origin of wood fibers can be sawmill chips, sawdust, wood flour or powder, cutter shavings, pulp or wood residues. As binders for these fibers, both thermosetting (like phenolic, epoxy, polyester) resins and thermosetting matrices [such as polyethylene (LDPE, HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS)j can be used. Thermoplastic composites are, however, less expensive to process than thermosetting composites, in addition to their ability to be manufactured into complex shapes. 

FIGURE 5.97 Effect of plastic type (polyethylene o, polypropylene A, polystyrene X) and wood loading levels on properties of wood plastic composites. (After Chelsea Center for Recycling and Economic Development (CCRED), 2000. Technical Report 19, An Investigation of the Potential to Expand the Manufacture of Recycled Wood Plastic Composite Products in Massachusetts, Univ. of Massachusetts, Massachusetts.)... 

Maldas D, Kokta BV, Daneault C (1989) Thermoplastic composites of polystyrene effect of different wood species on mechanical properties. J Appl Polym Sci 38 413-439... 

Currently, most WPC are made with PE, both recycled and virgin, for use in exterior building components. However, WPC made with wood-PP are typically used in automotive applications and consumer products, and these composites have recently been investigated for use in building profiles. Wood-PVC composites typically used in window manufacture are now being used in decking as well. Polystyrene and acrylonitrile-butadiene-styrene (ABS) are also being nsed. 

Chemically prepared PPy can also be processed in various shapes, and especially a wide variety of micro- and nanostructured composites have been prepared. An important amount of work is due to Armes and coworkers, who systematically studied the formation of PPy composites formed by chemical oxidation of pyrrole, essentially by iron salts, in various colloidal solutions. This results into the formation of colloidal suspensions of the host substrate (sihca, polystyrene, silica-coated magnetite, etc.) impregnated with PPy. However, the conductivity of pressed pellets of these composites is low, mostly below 1 S/cm. More recently, a wood saw dust/PPy composite has been reported, and applied to the selective removal of chromium (VI) from waste water. PPy/Mn02 composite (see above) has been shown to be effective for use as an active material in supercapacitors. 

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