Molecular weight dependency of β phase formation in injection-molded isotactic polypropylene

The influence of beta-nucleating agents and the molecular weight of isotactic polypropylene (iPP) on the formation of beta phase in the injection-molded iPP were explored using wide-angle X-ray diffraction technique. Without the beta-nucleating agents, the molecular weight of iPP was the dominant factor controlling the production of beta phase during injection. A higher molecular weight could promote the orientation of molecular chains in the skin layer of injected sample, bringing out a larger content of beta phase in the corresponding region. Although the beta-nucleating agents had a profound effect on the formation of beta phase, it was only efficient for the iPP with moderate molecular weights. The systems of the lowest and highest molecular weight iPP samples compounded with beta-nucleating agents still performed the same with the corresponding ones without beta-nucleating agents. Such performances can be interpreted as a result of the competition between the beta-nucleating agents and the orientation degree of molecular chains. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48555.