A computational model for processing of semicrystalline polymers : the effects of flow-induced crystallization

A computational model for the combined processes of quiescent and flow-induced crystallization of polymers is presented. This modelling 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. Rather then the shear rate as the driving force, a viscoelastic approach is proposed, where the viscoelastic stress (or the equivalent recoverable strain) with the highest relaxation time, a measure for the molecular orientation and stretch of the high end tail molecules, is the driving force for flow induced crystallization. Thus, the focus is on the polymer that experiences the flow, rather then on the flow itself. Results are presented for shear flow, extensional flow and for injection moulding conditions of an isotactic Polypropylene (iPP)