Influence of Shear Flow on the Crystallization Kinetics of Isotactic Polypropylene in Nucleation and Crystal Growth Processes

Based on the modified flow induced crystallization model taking into account the effect of shear flow on the crystal growth, a compared study was made on the influence of shear flow on the crystallization kinetics of isotactic polypropylene in nucleation and crystal growth processes. It was theoretically confirmed that shear flow could also accelerate the spherulite growth rate of polypropylene though this effect was small and limited compared with that on the nucleation rate. However, in order to understand and predict the whole crystallization kinetics more accurately and practically, it is essentially necessary to consider the effect of shear flow on the spherulite growth rate especially at high shear rates and low crystallization temperatures. Our theoretic results showed that the shearing effect on the crystal growth rate was relatively large at a high supercooling degree in comparison with that at a low supercooling degree. This could be attributed to the relaxation behavior of macromolecule chains, which vanishes shear history quickly at high crystallization temperatures. The theoretically predicted curves are in good agreement with the experimental data indicating the validity of the modified model.