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ABSTRACT
Wood pallets and shipping crates represent a large source of raw material available for use in value-added composites. To determine the feasibility of using wood fibers derived from pallets in wood-plastic composites, this study compared the mechanical properties of polypropylene (PP) composites combined with either wood flour or wood fiber. Wood flour is the most common wood-derived filler used in the plastics industry. Moving from a particulate filler like wood flour to a reinforcing fiber results in property enhancements. In this study, the use of fiber derived from wood pallets and shipping crates as a filler for PP resulted in tensile and flexural strength improvements compared with wood-flour-filled PP. The addition of stearic acid to these composites to increase dispersion of the wood filler in the PP did not improve properties; however, the addition of maleated PP to improve the interfacial adhesion between the two phases resulted in strength improvements.
As the plastics industry becomes more receptive to the use of wood-derived fillers for thermoplastics, further effort is required to improve upon the properties of these materials. Although wood flour (WF), a commercially available resource derived from post-industrial scrap, is the most commonly used wood-derived filler in thermoplastics today, opportunity exists for other sources of wood to be used as filler materials for thermoplastics. These sources may include fibers derived from post-consumer waste, woodwaste such as standing dead and small-diameter trees, or agricultural residues. Filled thermoplastics achieve better strength properties as the aspect ratio of the filler increases; therefore, moving from a particulate filler such as WF to a reinforcing wood fiber should result in strength improvements.
A large source of wood fiber is available in the form of used pallets and shipping containers. Recycling is already a large part of the pallet business. As early as 1992, 44 percent of U.S. pallet manufacturers were involved in recycling (2). However, there continues to be considerable volumes of pallets in municipal solid waste. In 1995 alone, landfills processed around 880 x 103 metric tons of pallets from the municipal solid waste stream. That same year, construction and demolition sites processed approximately 162 x 10^sup 3^ metric tons of pallets (3). This represents a large amount of material that can be used in such...