Simulation of film blowing including flow-induced crystallization

The two-phase microstructural flow-induced crystallization model developed by the authors is applied to the simulation of film blowing. In order to isolate the effects due to crystallinity, a simplified "quasicylindrical" approximation is used for the momentum equations, which neglects the effect of axial curvature in the axial direction. The present simulations include the combined effects of flow-induced crystallization, viscoelasticity, and bubble cooling. In all cases studied, the location of the frost line is predicted naturally as a consequence of flow-induced crystallization. The effects of inflation pressure, melt extrusion temperature, and take-up ratio on the bubble shape are predicted to be in agreement with experimental observations. The combination of these processing conditions determines the shape of the bubble, i.e., whether the bubble contracts or expands. An important feature of our model is the prediction of the locked-in system stresses at the frost line that are related to the physical and mechanical properties of the film. (C) 2001 The Society of Rheology.