Viscous flow of molten polyethylene resins

A screw extruder and capillary dies of different length radius ratios were used to measure melt flow and end effects for three commercial polyethylene resins, two of low density and one of high density. The apparent melt viscosities of the low density resins decreased faster with increasing shear and temperature than that of the high density resin. Zero shear activation energies for viscous flow were 11.6 and 12.7 kcal./mole for the low density resins and 7.0 for the high density resin. Apparent activation energies at fixed shear stresses were independent of shear stress while apparent activation energies at fixed shear rates decreased with increasing shear rate. End effects and recoverable shear strain were smallest for the high density resin. The differences between the melt flow characteristics of the two types of polyethylene are tentatively correlated with structure.