Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion

During the capillary extrusion with several different polyethylenes, we observe an abnormal rheological behavior. The nominal viscosity of polyethylene melt in the gross melt fracture regime does not change with a temperature. All polyethylenes tested show same behaviors. More interestingly, the nominal viscosity in the gross melt fracture regime shows even no molecular weight dependency when PEs have similar molecular structures (degree of branching and co-monomer content). From various experiments, we conclude that this abnormal phenomenon is relevant to the structural change with the melt temperature.