A FRACTURE MECHANICS STUDY OF POLYPROPYLENE–WOOD FLOURS BLENDS

Abstract

Polypropylene/wood blends were prepared from various resins and wood flours through extrusion compounding and injection molding. It was observed that the notched Izod strength of the blends with a relatively brittle resin matrix exceeded that of the neat resin at higher filler loading when the compounds contained the maleic-anhydride-polypropylene (MAPP) copolymer. The Izod strength of the blends with a tough matrix increased with the content of the interfacial modifier MAPP and is higher in blends with coarser fillers. The fracture mechanics analyses of the instrumented drop-weight Charpy test results were then performed to sudy the nature of these increases in impact fracture resistance. It was found that both the fracture toughness Kc and the critical strain release energy Gc increase with filler content in blends containing MAPP. In blends without MAPP, however, Gc decreases slightly with filler content while Kc increases less significantly. The increases of Gc with MAPP and with increasing filler particle size were also observed for the blends with a tougher PP as matrix. It is thus the reinforcing role of cellulosic fibers of the wood flours that contribute positively to the impact resistance of the PP/wood blends. It was thus proposed that higher wood filler aspect ratio, stronger interface, and tough copolymer matrix is the better choice in designing the PP/wood compounds.