Rheological properties of long chain branched polyethylene melts at high shear rate

Capillary extrusion experiments involving a number of polyethylenes with emphasis on assessing the effect of long chain branching (LCB) are performed. None of the metallocene catalyzed linear low density polyethylenes (mLLDPE) produced by Dow Chemicals, which are believed to have some level of LCB, show temperature dependence on the viscosity at the gross melt fracture regime. Furthermore, these materials do not show spurt or stick-slip flow, in contrast with most linear polyethylenes. LDPE and blends of LDPE with LLDPE having LCB also show the absence of stick-slip flow, but show temperature dependence on the viscosity. From these observations, we conclude that the stick-slip flow is very sensitive to the existence of LCB.