Critical conditions for the onset of unstable flows of molten polymers

摘要

A simple method to predict the critical shear stress and the critical shear rate for the onset of melt flow instabilities in capillary flow is presented. The method, earlier reported for polyisoprene, employed a bulk stable viscoelastic constitutive equation that contains a hardening parameter #beta#. The parameter #beta# is solely determined by the molecular characteristics of the polymer. Below we compare predictions of the critical shear stress with experimental data for some common polymers.