The role of crystallinity and morphology in the preparation of ultra‐highly oriented polyethylene

Abstract

The influence of the degree of crystallinity and morphology on the drawing behavior of linear polyethylene (LPE) has been investigated on three polymers with molecular weights ranging from 67,000 to over 300,000. Samples of similar crystallinity, but different morphology, were obtained by subjecting the polymers to two distinct preparations: slow cooling from the melt in one case and rapid quenching followed by annealing at 120°C in the other. The resulting isotropic products, characterized by optical microscopy and density measurements were drawn at constant speed and the deformation process monitored by recording the draw ratioldraw time relationship and the stresdstrain curves. The results indicate that crystallinity per se does not have a primary effect in determining the rate of local deformation except in the case of polymers of very low weight average molecular weight and narrow molecular weight distribution. A dominant role seems to be played by the broad features of the sample morphology as detected by optical microscopy. A comprehensive explanation of these results is based on the concept of a network structure whose nature is affected by the annealing treatment to an extent which depends on the degree ofcoupling between adjacent crystalline regions in the isotropic undrawn polymer.