Non-isothermal crystallization during the molding of a viscoelastic polymer film

Abstract

A steady-state non-isothermal process of forming a viscoelastic flat polymer film is considered. The polymer melt is extruded through a flat die, subjected to uniaxial stretching and at the same time air cooling, and then finally cooled down on a chill roll. It is assumed that the film is wide enough and the distance between the extruder die and the cooling roller is minimal to such an extent that the change in the width of a film in the course of longitudinal stretching can be neglected. From a rheological standpoint, a polymer melt is a viscoelastic fluid. The upper-convective Maxwell model is used, for which the viscosity and relaxation time are assumed to be temperature dependent. The mathematical model is supplemented by the equation of non-isothermal  crystallization kinetics. The problem is solved by a numerical method of finite differences.