Modeling morphology evolution during injection molding of thermoplastic polymers

Abstract

The effect of temperature, pressure and flow on relaxation time (or spectrum), crystallization time, nucleation density and rate, spherulite growth rate, the interrelation among these quantities and the distributions of deformation rate and cooling time during the process all together determine the morphology distribution in the final object. A simple model linking all these quantities was developed to describe morphology evolution during polymer processing. The effect of flow on nucleation density and growth rate of an isotactic polypropylene (iPP) is described on the basis of a molecular stretch parameter and the stretch evolution is described by a simple nonlinear Maxwell model, whose relaxation time, in its turn, is determined by the molecular stretch and, obviously, temperature pressure and crystallinity [1]. The model is applied to the description of morphology evolution during the injection molding process of a very accurately characterized iPP as far as rheology, quiescent crystallization and effect of flow on nucleation and spherulitic growth rates. Main characteristics of final morphology are reproduced by the simulations.