The Morphology Evolution Of Injection Molded IPP Parts

As the main kind of plastics, Isotactic polypropylene(iPP) has good processing properties and application properties. Because of its good crystallization ability and the important industrial application background, iPP is applied in more and more field. Injection molding is the most widely employed forming method. Because of its processing characteristics, the parts show specific morphology distribution. The morphology distribution determines product performances (such as mechanical properties, optical properties, chemical properties, shrinkage, etc.), and becomes one of the polymer research focus. In recent years, people have widespread interest and attention on the relationship of process conditions and microstructure evolution, and has made great progress. Therefore, deeper study not only has certain academic significance, but also has extensive engineering background.In this work, one-dimensional flow plate mold and commercial iPP were chosen for the study. Polarized light microscopy (PLM), small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD) were used to investigate the influence of injection molding process parameters on morphology evolution. The work includes:1. Significance of processing parameters on morphology of the parts. The orthogonal experiment was used to investigate the effects of processing parameters on morphology of the injection molded parts. The results indicated that the melt temperature is the most influential factor of the skin thickness, followed by injection rate, and the influence of mold temperature, packing pressure and packing time was unobvious.2. The influence of melt temperature on morphology of the parts. Single-factor experiments were conducted to investigate the influence of the melt temperature. The results show that both crystallinity and the average grain size of spherulites at the same distance from skin increase gradually with the melt temperature increasing from 210 degrees to 250 degrees; the skin thickness of the products decrease; The content of P crystal at the junction of Skin-core, the maximum degree of orientation and lamellae thickness decrease with the melt temperature increasing.3. The influence of injection rate on morphology of the parts. Single-factor experiments of were conducted to investigated the influence of the flow rate at the inlet on morphology of the injection molded parts. The results indicate that the skin thickness of the products, the content ofβcrystal at the junction of skin-core and the average grain size of spherulites decrease with the injection rate increasing from 30 cm 3/s to 70 cm 3/s; While both crystallinity and the maximum degree of orientation change unobviously with the injection rate increasing.