EFFECTS OF IMPACT MODIFICATION ON THE MECHANICAL-PROPERTIES OF WOOD-FIBER THERMOPLASTIC COMPOSITES WITH HIGH-IMPACT POLYPROPYLENE (HIPP)

This paper reports on the effects of impact modification on the mechan ical properties of wood-fiber thermoplastic composites with high-impac t polypropylene (HIPP). Homo polypropylene (PP) was modified through i ts melt blending with HIPP to obtain an inherently tough matrix resin for PP/wood-fiber composites. The resin modification improved the impa ct strength of the composites, while it reduced the stiffness and stre ngth properties acquired by the addition of wood-fibers. The requireme nts of plane strain fracture toughness were not satisfied in this stud y. In order to compensate the nonplane strain fracture toughness, the specimen strength ratio was used as a comparative measure of fracture toughness. The strength ratio depended on impact modifier levels as we ll as on wood-fiber concentrations, The work of fracture measured as t he area under the load-displacement curve increased with impact modifi er levels except at 40% wood-fiber concentration. Microstructural prob ing showed a degree of wood-fiber alignment in the skin and core of in jection-molded specimens and provided some insight into the slight inc rease in the impact strength of composites.