Study of Micro-Injection Moulding: Factors Affecting the Content of the β-phase in Isotactic Polypropylene with β-nucleating Agent

Abstract

The special processing conditions of micro-injection moulding will affect the micro-structure of polymer microparts processed by micro-injection moulding. In this article, two-dimensional wide-angle X-ray diffraction (2D-WAXD) and differential scanning calorimetry (DSC) were used to study the influence of nucleating agent concentration, mould temperature and injection pressure on content of the β-phase in isotactic polypropylene (iPP) with β-nucleating agent in micro-injection moulding. It was found that the high shear stress during micro-injection moulding could induce the formation of β-phase crystals in pure iPP, but which could restrain the formation of β-phase crystals in iPP with β-nucleating agent. The β-crystal content in micro-injection moulded samples decreased continuously with increasing the mould temperature from 130°C to 160°C. Besides, the shear stress that could restrain the nucleating efficiency of β-nucleating agent in β-nucleated iPP increased with the rise of the injection pressure and resulted in the decrease of β-phase crystals in the sample.

Keywords:

• Isotactic polypropylene
• β-nucleating agent
• β-phase content
• Micro-injection moulding
• Processing factors

ACKNOWLEDGMENTS

We would like to express our sincere thanks to the National Natural Science Foundation of China (51010004) and the Sichuan Science and Technology Support Project (2011FZ0033). We are indebted to the National Synchrotron Radiation Laboratory (NSRL) in University of Science and Technology of China and Prof. Guoqiang Pan (NSRL) for his help in synchrotron WAXD experiment.