The morphological evolution and β-crystal distribution of isotactic polypropylene with the assistance of a long chain branched structure at micro-injection molding condition

Long chain branching polypropylene (LCBPP) has good application prospect but the synergistic effects of the long chain branching (LCB) structure and complex flow field on the crystallization behavior of LCB polymers are still elusive. In the present work, microparts of isotactic polypropylene (iPP)/LCBPP blends were prepared by microinjection molding (MIM). The effect of the LCB structure on the morphology evolution and the β-crystal distribution in microparts were investigated. Interestingly, adding LCBPP facilitates the formation of oriented β-crystals along the shear direction in the core layer of the microparts but unexpectedly, decreases the relative content of β-crystals due to the heterogeneous nucleation effect of LCBPP. Moreover, the introduction of LCBPP can also improve the orientation degree of the molecular chains and shrink the thickness of the core layer thereby inevitably suppressing the “skin–core” structure which might optimize the properties of MIM parts.