A recoverable strain-based model for flow-induced crystallization

A model for the combined processes of quiescent and flow-induced crystallization of polymers is presented. This modeling should provide the necessary input data, in terms of the structure distribution in a product, for the prediction of mechanical properties and shape- and dimensional-stability. The model is partly based on the work of Schneider et al. ([1]) and Eder et al. ([2]) where the shear rate was taken as the relevant parameter for flow-induced crystallization. Rather then the shear rate as the driving force, a viscoelastic approach is proposed here, where the resulting recoverable strain (expressed by the elastic Finger tenser) with the highest relaxation time is the driving force for flow-induced crystallization. Thus we focus on the polymer that experiences the flow, rather then on the flow itself. For a fully characterized isotactic Polypropylene (iPP), i.e. a polymer for which all data needed as input for the computational model are available, comparison with experimental results from literature shows good agreement. For results from extensional flow, part of this data set is missing and therefore comparison is only qualitative.