Viscoelastic non-isothermal modeling of film extrusion for membrane production including flow induced crystallization

Abstract

In this work, a viscoelastic non-isothermal extrusion film casting model utilizing 1.5-dimensional kinematics according to Silagy et al. [“Study of the stability of the film casting process,” Polym. Eng. Sci. 36, 2614–2625 (1996)] modified Leonov's constitutive equation, crystallinity-dependent relaxation time and elastic modulus, and flow-induced crystallization considering chain stretch, actual temperature, and cooling rate was developed and validated by using an appropriate numerical scheme and relevant experimental data for linear isotactic polypropylene. The model was used in a parametric study to understand the effect of draw ratio, heat transfer coefficient, and flow-induced crystallization on final film crystallinity and neck-in phenomenon using two different approaches to control the stretching intensity: first by adjusting the speed of the chill roll and second by changing the mass flow in the extrusion die. It is believed that the proposed model and results obtained may help to understand the optimal process conditions for the production of polymeric energy storage membranes, which are increasingly important due to their use in rechargeable lithium-ion batteries, disposable lithium batteries, and specialty energy storage.