Flow-induced β-crystal of iPP in microinjection molding: effects of addition of UHMWPE and the processing parameters

Abstract

The flow-induced β-crystal of isotactic polypropylene (iPP) with addition of ultrahigh molecular weight polyethylene (UHMWPE) molded by microinjection and influences of processing parameters on the formation of β-crystal in iPP/UHMWPE microparts were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). It was found that the contents and the dispersion of UHMWE affect the formation of β-crystal in iPP/UHMWPE blend. With the addition of UHMWPE, Kβ values of the blends increased significantly compared with that of the pure iPP and reached the maximum at the content of 2 wt% UHMWPE. In addition, a better dispersion of UHMWPE can facilitate the formation of the β-crystal in the iPP/UHMWPE. The results showed that the thermal stability of the β-crystal was enhanced with increasing the mold temperature. When the mold temperature was increased from 60 to 120 °C, the β-crystal become more perfect. High injection speeds can promote the formation of the β-crystal, but the value of the injection speed must be within a certain range.