INFLUENCE OF THE CRYSTALLINITY ON THE TRANSPORT-PROPERTIES OF POLYETHYLENE

Transport properties of dichloromethane were analysed in high- and low -density polyethylene films, obtained with different thermal treatment s, in order to correlate sorption and diffusion with the crystallinity of the samples. The crystalline fraction of all the analysed samples was evaluated from density and X-ray data; it ranged from 40%-85%. Fro m the X-ray diffractograms the reciprocal of the width at half-height for the strongest reflection was derived for all the samples; it was c onsidered as an order parameter. It was found that the sorption depend s only on the fraction of amorphous phase; in fact, the specific sorpt ion, normalized for the crystallinity of the sample, is constant for a ll the samples. However, the zero concentration diffusion coefficient, D-0, varies with the sample crystallinity, but there is no simple cor relation between these two parameters; rather a transition seems to se parate two ranges in which the diffusion coefficient decreases with th e crystallinity. At variance, a linear decrease of the diffusion param eter with the order parameter, derived from the X-ray diffractograms, was found in the whole range of crystallinity.