Influence of molecular weight on impact fracture behavior of injection molded high density polyethylene: Scanning electron micrograph observations

A group of high density polyethylene with different molecular weight was prepared by melt blending two kinds of HDPE with weight average molecular weight of 3.2 X 10(5) g/mol and 7.2 X 10(5) g/mol, respectively. The fracture behavior of injection molded specimens of these samples was investigated by Izod impact test and scanning electron microscopy. The results show that the variations of impact toughness of injection molded HDPE could be reflected directly by the evolution of morphology of fracture surface as molecular weight increases. Higher molecular weight led to higher impact toughness, due to both thickened oriented shear zone which could enhance the crack resistance and depressed two types of fracture behavior (tearing-brittle fracture and heat softening/melting fracture) with low energy consumption. Fracture behavior in different position of injection molded HDPE shows different molecular weight dependence. The impact toughness at far-gate-end increases with increasing molecular weight, while the impact toughness at near-gate-end, especially for the blends, almost keeps constant within a certain range of molecular weight. (c) 2008 Wiley Periodicals, Inc.