Flow Enhancement in the Continuous Extrusion of Linear Low-Density Polyethylene

Abstract

Enhanced throughput and the elimination of sharkskin were observed over an extended temperature range when linear low-density polyethylenes having the same molecular weight, polydispersity, and melt index, one with and one without commercial additives, were extruded through α-brass dies. The additives appear to play a significant role in the detailed flow behavior, however, most notably in an irreversible transition to a “normal” flow curve at stresses on the order of 0.3 MPa. There are indications of a slip-like phenomenon, including the occurrence of electrostatic charge on the extrudate. A high-throughput, low-extrusion-pressure processing window like that associated by Keller with a transition to a mesophase was observed for the polymer containing no additives, but not for the polymer containing additives.