THE MECHANICAL-BEHAVIOR OF ORIENTED HIGH-PRESSURE ANNEALED POLYETHYLENE

Four different grades of polyethylene have been annealed under high pr essures, to transform the morphology, and then oriented by hydrostatic extrusion. The pre-extrusion morphology is shown to have a significan t influence on the mechanical properties of the extrudates. At high cr ystallinities the mechanical behaviour of the extrudates can be interp reted using a simple aggregate model. This model suggests that high me chanical moduli can be obtained by orienting the crystallites more eff ectively and by increasing the crystallinity, which results in a highe r shear modulus. However, the developments of crystallinity and lamell ar size occur at the expense of reducing the integrity of the molecula r network. Eventually this limits the efficiency of the orientation pr ocess and has a detrimental effect on the shear modulus and hence the extensional modulus of these oriented materials. Copyright (C) 1996 El sevier Science Ltd.