A stable ‘‘island’’ in the slip-stick region of linear low-density polyethylene

Abstract

A stable ‘‘island’’ has been discovered in the slip-stick region of a linear low-density polyethylene. Within this region, which exists only in a narrow temperature range, pressure oscillations cease, the pressure drop falls by a substantial amount, and the extrudate becomes reasonably smooth. Unstable oscillating flow persists at throughputs on both sides of this island. The existence of this intermediate stable flow challenges all current theories of extrusion instabilities. The phenomenon resembles observations of a drop in extrusion pressure for which a mesophase transition has been suggested.