Effect of Surface Modification for β-Nucleating Agent on Its Nucleation-Inducing Capability and Crystalline Structure of Polypropylene

Abstract

In this paper, the crystalline modification of isotactic polypropylene (PP) based on rare earth β‑nucleating agent (WBG) with surface modification were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). First, the relationship between the different functional additives for WBG surface modification and nucleation-inducing capability of WBG in PP matrix, as well as the possible reason for the change of nucleation-inducing capability of surface-treated WBG with different functional additives in PP matrix were further studied. It revealed that surface treatment can significantly improve the nucleation-inducing capability of WBG, especially silane coupling agent was more beneficial to increase the nucleation-inducing capability of WBG. Compared with titanate coupling agent and stearic acid, the aliphatic chain length of silane coupling agent was suitable to effectively entangle with the surrounding large molecular chain of PP, and not enough to dilute the large molecular chain of PP near it. In addition, the alkoxysilane groups can react with the carbonyl group of PP main chain so that the interaction between WBG and PP matrix was further enhanced and affinity was greatly improved between them. Hence the nucleation-inducing capability was improved. Second, the influence of WBG with surface modification on the crystalline structure and the stratified crystalline structure of PP was also studied. The results showed that silane coupling agent in three functional additives could further improve the β-crystal induction ability of WBG for PP modification. In view of the stratified crystalline structure of PP, the surface-treated WBG with coupling agent, especially with silane and stearic acid, could weaken the effect of cooling environment and was beneficial for further promoting the β-crystal formation in skin layer but also in core layer.