A fracture mechanics study of polypropylene-wood flours blends

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 mat rix exceeded that of the neat resin at higher filler loading when the compo unds contained the maleic-anhydride-polypropylene (MAPP) copolymer. The Izo d 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 tes t results were then performed to sudy the nature of these increases in impa ct fracture resistance. It was found that both the fracture toughness K-c a nd the critical strain release energy G(c) increase with filler content in blends containing MAPP. In blends without MAPP, however, G(c) decreases sli ghtly with filler content while K-c increases less significantly. The incre ases of G(c) with MAPP and with increasing filler particle size were also o bserved for the blends with a tougher PP as matrix. It is thus the reinforc ing role of cellulosic fibers of the wood hours that contribute positively to the impact resistance of the PP/wood blends. It was thus proposed that h igher wood filler aspect ratio, stronger interface, and tough copolymer mat rix is the better choice in designing the PP/wood compounds.