Entry pressure and elastic behavior of a branched polyethylene

Die entry pressures and elastic parameters derived from these have been determined for one low-density polyethylene (LDPE) at four temperatures using three dies having different entry angles. The elongational viscosity shows a somewhat different behavior with respect to temperature than the shear viscosity. Mostly the elastic parameters show a temperature-independent relation to the shear stress but only if the data at the lowest temperature used (130°C) are ignored. The latter data show that the material is much more elastic at this temperature than at higher ones; this is so even when the temperature is increased by only 20°C, after which any further increase gives negligible difference in elasticity. This behavior is probably due to a structural difference which may be a result of increased crosslink sites created by flow-induced crystallization. © 1995 John Wiley & Sons, Inc.