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.