Development and Validation of a Recoverable Strain-Based Model for Flow-Induced Crystallization of Polymers

Abstract

A model for the description of the combined process of quiescent and flow-induced crystallization of polymers is presented. The model allows to predict in detail the spatial distribution of the crystalline structure in semi-crystalline products. Based on this structure, the final mechanical properties, shape and dimension stability of those products can be modeled. For quiscent crystallization kinetics we use the Schneider rate equations.[1] For flow-induced crystallization we have modified the Eder rate equations.[2] Where Eder used the shear rate as the driving force for flow-induced nucleation and crystallization, the modification proposed here adds a viscoelastic equation to account for molecular orientation, in particular that of the high-end tail of the molecular weight distribution. This is expressed in terms of the elastic Finger tensor with the highest relaxation time. The second invariant of this tensor, equivalent to the order parameter for a nematic phase, is used as the driving force for flow-induced nucleation and crystallization and, consequently, a coupling between rheology and structure formation is obtained.