Shear Modification of Polyolefines and its Integration in Polymer Processing

Abstract

Abstract The viscous and especially the elastic properties of polymer melts can be altered by a previously imposed deformation history. This phenomenon, usually termed as shear modification, is caused by the reversible physical disentanglement of the polymer molecule chains. The shearing unit presented in this paper was used to systematically investigate the processing parameters governing shear modification. A set of rheological tests was carried out with the shear modified sample material and the expected changes in the rheological behaviour were detected. The relative change of the storage modulus G’, measured using a Rheometrics On-line Rheometer system, was taken as a measure for the degree of modification and was found to correlate with the specific energy dissipated during sample preparation. The effects of shear modification on product properties were investigated for the tubular film-blowing process. Changes in the optical and mechanical properties of films which can be attributed to the previously imposed shear modification process were found.