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WOOD FIBER Because of the potential of improved mechanical properties with fillers of greater I/d ratios, there has been a continuing interest in the use individual wood fibers rather than wood flour as reinforcement in WPC. Recently, two wood-pulp fiber suppliers, Rayonier Corp. composite wood fencing for sale (Savannah GA) and Creafill Fiber Corp. (Chesterton, Md) have been marketing wood-pulp fibers for use as reinforcements for thermoplastics. The fibers that they supply have been promoted for use in WPC of higher performance potentials. Adding fibers rather than flour increases mechanical properties such as strength, elongation, and unnotched lzod impact energy. However, processing difficulties, such as feeding and metering low-bulk-density fibers, have limited the use of fibers in WPCs. There have been some developments in pelletizing fibers for ease of handling and processing (Jacobson et 2002). THERMOPLASTIC MATRIX MATERIALS The WPC presently consumes over 685,000 tonnes of thermoplastic resins annually (Morton et There are some differences in processing technologies between Europe and North America and this is reflected in the consumption totals for the various resins. Polyethylene resin (PE) is the dominant resin in North America amounting to 83% of the 685,000 tonnes consumed. Nine percent of the total is polypropylene (PP), and 7% of the thermoplastic resin used in the WPC industry is polyvinyl chloride Only about 1% of other resins are used. ADDED COMPOUNDS Wood and thermoplastic are not the only components in WPCs. cheapest outdoor flooringThese composites also contain additional materials that are added in small amounts to affect processing and performance. Although formulations are highly proprietary, additives such as coupling agents, light stabilizers, pigments, lubricants, fungicides, and foaming agents are all used to some extent. Some additive suppliers are specifically targeting the WPC industry (Mapleston 2001 a). COMPATIBILIZERS Since the wood component of a wood-thermoplastic composite is hydrophilic and the plastic is hydrophobic, a compatibilizer is often used to improve interfacial bonding of the two different phases. Many compatibilizers have been investigated and are reviewed elsewhere (Lu et However, one of the CHAPTER 6 WOOD THERMOPLASTIC COMPOSITES | 145 most common compatibilizers used for wood-thermoplastic composites are maleic anhydride grafted polypropylenes (MAPPs). wpc floor for saleThey differ in molecular weight and the degree of maleic anhydride substitution but those used for compatibilization typically have a number-average molecular weight of about 20,000, a weight-average molecular weight of about 40,000 and contain approximately 6 weight percent maleic anhydride. The anhydride portion of the compatibilizer reacts with a hydroxyl group of the wood cell .