Influence of molecular structure on crystallization behaviour and mechanical properties of polypropylene

Two series of polypropylenes with different molar mass—reactor grade (RE) and peroxide-degraded (CR) types—were investigated with respect to mechanical and crystallization parameters. A significant influence of the production process on mechanical parameters was found, which can be attributed to differences in the crystallization behaviour, mainly to the number of nuclei per unit volume. At a comparable average molar mass, RE types crystallize faster and exhibit higher levels of stiffness, combined with lower levels of impact strength, than CR types.