A continuum model for flow-induced crystallization of polymer melts

A macroscopic, continuum model based on the Hamiltonian/Poisson Bracket formalism, combined with the Avrami equation, is developed to simulate flow-induced crystallization of polymer melts in homogeneous flow fields under isothermal conditions. The model predicts crystallization kinetics as well as rheological and rheooptical behavior of semicrystalline systems. The amorphous phase is modeled as a modified Giesekus fluid and the crystalline phase is approximated as a collection of multibead rigid rods that grow and orient in the flow held. The two phases are coupled with crystallinity via the dissipative Poisson brackets. The input parameters of the model can be obtained from experiments. Orders of magnitude reduction in induction times and enhancements in crystallization rates are predicted to occur under flow. Critical deformation rates are captured above which induction times sharply decrease. Calculations show increases in stiffness and strain hardening of the semicrystalline system via dramatic increases in the system stresses during crystallization. Moreover, for the temperature range studied, hydrodynamic forces dominate the undercooling effect in the regime of high deformation rates. The simulations also predict more rapid induction of crystallization following cessation of flow relative to quiescent crystallization. (C) 1999 The Society of Rheology. [S0148-6055(99)00201-1].