Abnormal crystallization behavior of high impact polypropylene under shear

Publication date: 31 January 2018
Source:Polymer, Volume 136
Author(s): Di Sun, Peng He, Yanfang Wang, Xingbo Shi, Wei Yu
The crystallization of two high impact polypropylenes (HIPP) was investigated under shear flow by online rheo-Raman spectroscopy. Abnormal retardation of crystallization under shear is observed in one HIPP, but the usual shear accelerated crystallization is observed in the other one. Such abnormal phenomenon was understood by thorough investigations on the phase separation behaviors in two HIPPs by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rheology. The slowdown of crystallization under shear can be ascribed to the suppression of the interface and fluctuation assisted nucleation under shear, which cannot be compensated by the acceleration effect due to molecular stretching/orientation under shear. The difference between two HIPP comes from the interplay between the suppression and acceleration effect of shear flow, which is determined by the amount of ethylene-propylene segmented copolymer (EPS) and its selective location in isotactic polypropylene (iPP) and ethylene-propylene random copolymer (EPR).

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