A slip-link model for rheology of entangled polymer melts with crystallization

Many industrial polymer melts are entangled and undergo crystallization during processing. Several recent studies have reported experimental data for the rheology of crystallizing entangled polymers. Meanwhile, over the past few years, slip-link models have been demonstrated to describe the rheology of entangled melts under a variety of nonlinear deformation conditions. In this work, we present a modification of the slip-link model to describe the rheology of an entangled melt undergoing crystallization. The partially crystallized melt is represented by a blend of linear chains with free ends and cross-linked, bridgelike chains with fixed ends that resemble the tie molecules between developing crystallites. Two new parameters are introduced: the fraction of cross-linked chains and a modulus shift factor, both of which are functions of the degree of crystallinity. The model captures the evolution of viscosity and elasticity simultaneously over the whole range of available frequencies in the linear regime. The model is validated using experimental datasets for isotactic polypropylene.