The Morphology and Mechanical Properties of Isotactic Polypropylene Injection-Molded Samples with the Presence of β-Nucleation Agent and Periodical Shear Field

The pressure vibration injection molding (PVIM) method was used to prepare beta-nucleated isotactic polypropylene samples (PVIM beta-iPP samples); a relatively low, periodical shear was imposed on the polymer melt in the mold at the filling and packing stages. The crystal structures and crystal orientation of the PVIM beta-iPP samples were investigated by polarizing light microscopy (PLM), scanning electron microscopy (SEM), and synchrotron two-dimensional wide-angle X-ray diffraction (2D-WAXD). The PLM observations indicated that a cylindrite layer, rather than the transition layer, was found in PVIM beta-iPP samples, which is different from the conventional injection-molded (CIM) samples. In addition, the thickness of the oriented layer of the PVIM samples was obviously greater than that of the CIM samples. The SEM observations demonstrated that a large amount of shish-kebab structures appeared in the shear layer of the PVIM beta-iPP samples; at the same time, numerous beta-spherulites were formed in the core layer. The 2D-WAXD data indicated that orientation homogeneity, to some degree, could be obtained by the periodical shear during PVIM. As a result, the above-mentioned morphology of the PVIM beta-iPP samples leads to potentially useful prominent reinforcement and toughening of the material.