Imaging and analysis of wave type interfacial instability in the coextrusion of low-density polyethylene melts

A modified Leonov model and Flow 2000™ software was used to simulate the LDPE melt flows through these geometries. There was reasonable agreement between modelled at experimentally determined stress fields. Modelling however provided far more detailed stress gradient information than could be resolved from the optical techniques. A total normal stress difference (TNSD) sign criterion was used to predict the critical layer ratio for the onset of the interfacial instability in one die arrangement and good agreement between theory and experiment has been obtained.