Comparative investigations of surface instabilities ("sharkskin") of a linear and a long-chain branched polyethylene

TL;DR

This study investigates the physical mechanisms behind sharkskin surface instabilities in polyethylene extrusion, comparing linear and branched types through experimental flow and stress measurements.

Contribution

It provides detailed stress distribution analysis in extrusion flows of different polyethylene types, enhancing understanding of sharkskin instability origins.

Findings

Stress distributions differ between linear and branched polyethylene.

Tensile and shear stresses correlate with surface instabilities.

Experimental methods reveal mechanisms behind sharkskin formation.

Abstract

An experimental study of the physical origin and the mechanisms of the sharkskin instability is presented. Extrusion flows through a slit die are studied for two materials: a linear low density polyethylene (LLDPE) and a low density polyethylene (LDPE). By combining laser-Doppler velocimetry (LDV) with rheological measurements in both uniaxial extension and shear, the distributions of tensile and shear stresses in extrusion flows are measured for both materials.