Comparison of Birefringence and Mechanical Properties of Injection Molded Metallocene and Ziegler-Natta Based Isotactic Polypropylene

Abstract

Moldings of isotactic polypropylenes (i-PP's) polymerized using metallocene and Ziegler-Natta catalysts and having the same molecular weights are compared in terms of their birefringence and mechanical properties. In particular, the gapwise distribution of birefringence, tensile and impact properties are measured and related to the microstructure of the injection molded samples. The effects of processing conditions on these values are also elucidated. Metallocene based i-PP's show significantly higher birefringence, unnotched Izod impact strength, yield strain and ultimate elongation but lower yield stress, tensile strength and Young's modulus than that of Ziegler-Natta based i-PP.