Flow Properties of a Partially Crystalline Polyethylene

Abstract

This study defines experimentally the steady flow of a partially crystalline polyethylene. The polymer has been exposed to high and variable shear rates at temperatures from about 40°C above to about 40°C below the polymer melting point. The polymer tested was a branched polyethylene, specific gravity 0.92 (20°C), melting point 103°C with a viscosity‐average molecular weight of 2800. Viscosities measured above the melting point were independent of shear over the experimental shear rate range, $\text{30–10,000\hspace{0.17em}}{\sec }^{\text{−1}}.$ Viscosities measured below the melting point became progressively more shear dependent with decreasing test temperature. A rotational concentric cylinder viscometer and a pressure capillary viscometer were used. The results have been interpreted in terms of temperature and shear dependence in order to evaluate possible mechanisms in flow such as orientation and destruction of crystalline regions. Estimates of the magnitude of molecular associations from several approaches have been made. Flow activation energies were calculated for the melt and as a function of shear rate for the partially crystalline state.