New understanding of the hierarchical distribution of isotactic polypropylene blends formed by microinjection-molded poly(ethylene terephthalate) and β-nucleating agent

Abstract

Blends of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET) were prepared by using a special injection molding process named microinjection molding (MIM). Interestingly, a strong continuous shear flow imposed on the melt of iPP/PET directly promotes the formation of the in situ PET microfibrils under microinjection molding. The hierarchical structures, including the shish-kebab-like structure, β-cylindrite, β-spherulite and α-spherulite are simultaneously formed in the iPP/PET microparts, which are closely related to formation of row-nuclei induced by the strong shear flow that is further amplified by incorporating in situ PET microfibrils. A surprising synergetic effect is observed between PET microfibrils and β-NA, resulting in the coexistence of shish-kebab, shish-kebab-like β-cylindrite, β-cylindrite and oriented β-crystal epiphytic on the surface of PET fibers in PP/0.1/15 microparts for the first time. Mechanical properties (e.g., tensile strength increased by 10.4 MPa) of the specimen are significantly improved compared with that of the iPP microparts because of the abundant hierarchical structures. A schematic model of the formation of hierarchical distribution of β-crystals via PET and β-NA addition is thus proposed.