Mechanical properties and fracture behavior of injection and compression molded polypropylene/coal gangue powder composites with and without a polymeric coupling agent

Coal gangue powder filled polypropylene composites modified with maleic anhydride grafted polypropylene (PP-g-MA) were prepared. The mechanical properties and fracture behavior of the injection and compression molded composites were investigated, respectively. It was found that the yield strength measured on injection-molded dumbbell specimens and melt flow rate (MFR) varied slightly while the impact toughness measured on injection-molded rectangular specimens decreased with increasing particles loading. With proper amount of PP-g-MA incorporated, both the yield and impact strength of the composites were improved. The essential work of fracture (EWF) results measured on compression-molded thin sheets showed that the fracture toughness decreased considerably at low content of coal gangue (5 wt% in the composites) and then increased markedly with increasing fillers loading, back to appreciably lower than that of pure PP, while the total plastic energy showed gradual decrease due to the reduction of both shape factor and specific plastic work. For the modified composites containing about 5 wt% PP-g-MA, the fracture toughness was higher than that of the base PP/coal gangue (80/20) composites. It was attributed to the remarkable improvement of crack-resistance in necking and subsequent fracture stage. Though the total plastic energy values of the modified composites only showed slight fluctuation, the specific plastic work of fracture was improved markedly with respect to the composites only coal gangue filled into.