EFFECTS OF COMPOSITE PROCESSING METHODS ON WOOD PARTICLE DEVELOPMENT AND LENGTH DISTRIBUTION: CONSEQUENCES ON MECHANICAL PROPERTIES OF WOOD-THERMOPLASTIC COMPOSITES

The relationship between structure and properties of high-density polyethylene (HDPE) filled with wood particles and processing techniques-injection molding, compression molding, and extrusion-was investigated. Wood particles were hammer-milled, sieved, and compounded into pellets at 35% by weight with HDPE using a twin-screw extruder. Coupling agent (ethylene-maleic anhydride copolymer) was added at 2% by wood filler weight. The pellets were used to produce test samples using the three processing techniques. The sensitivity of jack pine and several other wood particles (eastern white cedar, black spruce, and jack pine bark) to composite processing was analyzed. Bark particles showed higher propensity to generate fines than wood particles, possibly because of a higher thermal sensitivity. The major reduction in mean particle length was found to occur in the compounding process. Extrusion and injection molding contributed to particle length reduction to a lesser extent. Conversely, compression molding did not cause significant damage to wood particles. Stiffness and strength increased linearly with weight-averaged length.