MOLECULAR-WEIGHT DEPENDENCE OF MORPHOLOGY AND MECHANICAL-PROPERTIES OF ULTRAHIGH-MOLECULAR-WEIGHT POLYETHYLENE GEL FILMS

Films of three kinds of ultrahigh-molecular-weight polyethylenes (UHMWPE) with molecular weights of 6 x 10(6), 3 x 10(6) and 1 x 10(6) were produced by gelation/crystallization from dilute solutions. The dried gel films were stretched up to their maximum draw ratios. The molecular-weight dependences of morphology and mechanical properties of the drawn films have been examined using wide-angle X-ray diffraction, small-angle X-ray scattering, birefringence, crystallinity and stress relaxation modulus. It turned out that the long period, molecular orientation and crystallinity were hardly affected by molecular weight, while the stress relaxation modulus was strongly affected. The master curves indicated that the decrease in the stress relaxation modulus was more pronounced as the molecular weight of the test specimens decreased. This was thought to be due to a drastic increase of the slippage of molecular chains, leading to the disappearance of tie molecules and/or entanglement meshes under the external applied stress.