Mechanical properties of ultra‐oriented polyethylene

Abstract

AbstractSemicrystalline polymers generally exhibit moduli well below their theoretical limit due to chain folding and to lack of crystal alignment. Modulus increases attainable through standard drawing procedures are limited by sample fracture before large draw ratios are reached. Using an Instron capillary rheometer which allowed a draw ratio of > 300, transparent polyethylene strands of unusually high c‐axis orientation have been produced by a combination of pressure and shear. The virtually perfect crystalline orientation and evidence for extended chains confirm that a significant improvement in modulus can be realized by this technique. The dynamic tensile storage modulus was measured by Vibron over the temperature range −160°C to +120°C. Room‐temperature moduli were 7 × 1011 dyne/cm2, higher than any reported values for drawn polyethylene. Values also remained above 1011 dyne/cm2 even at 120°C. The moduli and morphological data have been related by a model consisting of an extended‐chain component in paralled with a conventional drawn morphology. Experimental and calculated moduli are compared and related to available theory.