CRYSTAL ORIENTATION IN INJECTION MOLDINGS OF FLAKY FILLER-FILLED POLYPROPYLENES

Crystal orientation states in injection moldings of polypropylenes filled with flaky fillers such as glass flake, mica, and talc have been studied. Talc-filled polypropylene injection moldings show a peculiar crystal orientation, in which the plate planes of talc particles are aligned parallel to the mold surface, the c- and a*-axes of polypropylene crystals are bimodally oriented to the flow direction, and the b-axes are oriented in the thickness direction. Although an unfilled polypropylene injection molding basically shows a similar crystal orientation to that of the talc-filled polypropylene injection molding, the b-axis orientation to the thickness direction is much weaker. Glass flake- or mica-filled polypropylene injection moldings show similar crystal orientations to that of the unfilled polypropylene injection molding. Only talc-filled polypropylene injection moldings show the peculiar crystal orientation. Since an injection molding of polypropylene filled with only 0.5 wt.-% talc already shows the peculiar crystal orientation, it is assumed that talc influences a remote interaction on the crystallization of polypropylene.