Compression creep of molten low‐density polyethylene

Abstract

SYNOPSISViscoelastic parameters of low-density polyethylene melt ( LDPE) in compression creep have been measured. Volume deformation ( k% ) increases as pressure ( P ) increases and temperature ( T ) decreases. Plots of the bulk creep compliance B ( t ) vs. time ( t ) may be shifted to provide master curves. As the pressure and the temperature increase, the pressure shift factors (b, and a,) increase almost linearly [activation volumes ( AV * ) varying from 1.0 to 15.0 cm3 moll, while the temperature-shift factors (bT and aT) decrease. The steadystate creep compliance ( B ' ) describes the recoverable storage of elastic energy ( B e ) and seems to be related to the extrusion die-swell ( B : / B z ) . Volume viscosity (vK) decreases with increasing stress ( P ) and increasing temperature ( T ) .