Enhancement of β-nucleated crystallization in polypropylene random copolymer via adding isotactic polypropylene

Abstract

Polypropylene random copolymer (PPR) is one of important polypropylene types for the application fields needing for excellent toughness. Because of the random copolymer chain configuration, the polymorphic behavior of PPR is difficult to be altered even by adding β-nucleating agent (β-NA). In this study, a promising method was developed by adding isotactic polypropylene (iPP) into PPR/β-NA blend, which has leaded to a surprising enhancement in the β-crystallization capability of PPR. At the optimal component condition, the β-crystal content of PPR can reach the highest level of 92 % and the β-crystallization capability is improved by 56%. As a result of high β-crystal contents, a superior mechanical toughness has been attained. On the other hand, the fractional crystallization experiment suggests that the stereoregular chains of iPP could assist the formation of primary β-nuclei at the very early stage of crystallization. This special crystallization event dominates the final polymorphic composition in PPR. Furthermore, it is demonstrated that impact polypropylene copolymer (IPC) can be used to substitute iPP for the improvement of β-crystal content of PPR. This provides a huge possibility to improve the low temperature properties of PPR to enlarge its applications.