Plastic deformation behavior of polypropylene/calcium carbonate composites with and without maleic anhydride grafted polypropylene incorporated using the essential work of fracture method

Abstract

The plastic deformation behavior and fracture properties under plane-stress conditions of calcium carbonate (CaCO 3) filled polypropylene (PP) composites, with and without maleic anhydride grafted polypropylene (PP- g-MA) incorporated, have been studied using the essential work of fracture (EWF) method. The influence of composition on the strain capacity, the development of plastic zone and plastic energy absorption was investigated in detail. It was shown that at room temperature (23±2 °C) and low tensile speed (5 mm/min), pure PP, PP/CaCO 3 and PP/CaCO 3/PP- g-MA composites all behaved in a ductile-tearing manner, that is, the ligament fully yielded and the crack stably propagated. Moreover, double-plastic zones around the inner fracture process zone, with distinctly different extent of stress-whitening, could be observed for all DDENT specimens of the materials with different composition. With the height of the intense outer plastic zone accurately measured at suitable light intensity, the values of plastic zone shape factor, β and specific plastic work, w p were determined. The specific essential work of fracture, w e, of PP/CaCO 3 composites was appreciably lower than that of pure PP, while the displacement to failure and the total plastic energy dissipation, βw p, decreased markedly with increasing CaCO 3 content. At the same time, it was found that the decrement of w p was more pronounced than that of β as CaCO 3 content increased. For the PP/CaCO 3 composites modified with PP- g-MA in which the mass ratio of PP to CaCO 3 was fixed at 80–20, w e increased remarkably at first and then decreased with increasing amount of PP- g-MA, while the displacement to failure decreased considerably with respect to PP/CaCO 3 (80/20). All βwp values for the hybrid composites with different amount of PP- g-MA were also lower than that of PP/CaCO 3 composites as β decreased further with increasing amount of PP- g-MA, while the w p values were improved.