Investigation on the Self-nucleation Behavior of Controlled-rheology Polypropylene

Abstract

Self-nucleation (SN) behavior is one of the most fascinating behaviors of semicrystalline polymers; it is of great scientific and practical importance. In this study, the crystallization and melting behavior of a series of controlled-rheology polypropylene (CRPP) with different molecular weights were studied by differential scanning calorimetry (DSC) scanning and successive self-nucleation and annealing (SSA) fractionation, and their self-nucleation behavior was studied according to the conventional SN measurement, in order to provide a new understanding on the relationship between the molecular weight and the SN behavior of polymers. The results of DSC scanning and SSA fractionation showed that the decrease of molecular weight led to higher molecular chains mobility, making the crystallization temperature higher and the crystalliation peak narrower; in addition, it significantly restrained the formation of thick lamellae. The results of SN measurements showed that both the upper and lower temperatures of the samples decreased as the molecular weight decreased, which was suggested to be closely related to the reduction of the formation of thick lamellae. The related mechanism is discussed, and it was found that the key parameter determining the occurrence of SN and annealing of CRPP was the ability to form thick lamellae with high melting point, which might be related to the ability for ordered structures to persist at high temperature.