Hierarchical Distribution of β-Phase in Compression- and Injection-Molded, Polypropylene-Based TPV

Abstract

The distribution of the β-phase crystals of polypropylene (PP) in different zones of compression and injection moldings molded from PP-based dynamically vulcanized thermoplastic elastomer (TPV) in the presence of a β-nucleating agent (β-NA) was investigated. The influence of shear and cooling conditions and the addition of β-NA on the development of β-phase was examined and discussed based on the one-dimensional heat conduction behaviors with phase change. A hierarchical distribution of β-phase was observed in both compression- and injection-molded TPV/β-NA specimens. For the compression-molded TPV/β-NA specimens, the hierarchical distribution of β-phase induced by β-NA is dominated by the cooling conditions. For the injection-molded TPV/β-NA specimens, the occurrence of β-phase is also mainly induced by the addition of β-NA; the effect of shear on the relative content of β-phase can hardly be observed and the cooling conditions control the hierarchical distribution of β-phase. Both in compression and injection-molded TPV/β-NA specimens, the relative content of β-phase increases from the skin to the core zones, owing to the cooling rate decreasing from the skin to the core zones.

Keywords:

• β nucleating agent
• β-phase
• cooling conditions
• shear

Acknowledgments

The authors gratefully acknowledge the financial support of National Natural Science Foundation of China (Grant No. 20734005), the Program for New Century Excellent Talents in University (NCET-08-0382), and the Doctoral Research Foundation granted by the National Ministry of Education, China (Grant No. 20060610029). We are also heavily indebted to Mr. Zhu Li from the Center of Analysis and Test of Sichuan University for careful observation of SEM.