Reinforcing and toughening isotactic polypropylene through shear-induced crystallization and -nucleating agent induced crystallization

In this article, iPP with -nucleating agent was molded by sequential co-injection molding (SCIM), in which skin and core melt were injected into the mold cavity one after the other. The microstructure and mechanical properties of samples were investigated by polarized optical microscope (POM), wide angle X-ray diffraction (WAXD) and mechanical property test. Results show that plastic parts molded by SCIM have double shear layers due to twice shear induced by filling flow of skin and core melt. In the shear layers especially the layer at the overlap of skin and core material, shear promoted the formation of highly oriented structures (shish-kebabs) but inhibited the produce of -form. In core layer of skin material and core layer of core material, crystals are predominant. The combination of oriented structures (shish-kebabs) and crystals endow iPP with high strength and toughness. This work demonstrates a new approach to achieve high-performance polymer materials based on general plastics by manipulation strategy for morphology and structure.