Transition from the hierarchical distribution to a homogeneous formation in injection molded isotactic polypropylene (iPP) with dynamic mold temperature control

There is an increasing demand to produce injection molded thermoplastic parts with high performance and more uniform microstructure. In this study, an injection mold with dynamic mold temperature control was developed to create a thermo-mechanical environment in which a high mold temperature and slow cooling rate were retained. Two-dimensional wide angle X-ray diffraction (2D-WAXD) and polarized optical microscopy (POM) studies were carried out to investigate the morphological distribution of isotactic polypropylene (iPP) through the depth. Due to the fast relaxation of polymer chains at a high temperature, the macroscopic orientated structure of iPP in conventional injection molding was eliminated, that is transited from the hierarchical morphology distribution to a more homogeneous formation. A homogeneous appearance without layer boundary was shown and many radial spherulites with loosely packed lamellae distributed uniformly throughout the sample.