Simulation of the Flow-Induced Crystallization of Polypropylene Based on Molecular Kinetic Model

A model for the isothermal flow-induced crystallization (FIC) of polypropylene melt in a simple shear flow is developed. The model is based on the molecular kinetic theory. The first normal stress difference of the stress tensor, calculated according to a molecular model, is assumed as the driving force of the flow-induced nucleation. Crystallization is described as a spherulitical nucleation and growth process. The theoretical predictions of the evolution of the viscosity in steady shear flow of iPP are in agreement with the experimental findings. The relative influence of the mechanical and thermal phenomena on the crystallization development is then analyzed as a function of the shearing intensity in terms of nucleation density. The results show the enhancement of the crystallization kinetics due to the shearing.