Influence of the crystallinity on the transport properties of polyethylene

Abstract

Transport properties of dichloromethane were analysed in high- and low-density polyethylene films, obtained with different thermal treatments, 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%. From the X-ray diffractograms the reciprocal of the width at half-height for the strongest reflection was derived for all the samples; it was considered as an order parameter. It was found that the sorption depends only on the fraction of amorphous phase; in fact, the specific sorption, normalized for the crystallinity of the sample, is constant for all the samples. However, the zero concentration diffusion coefficient,D ₀, varies with the sample crystallinity, but there is no simple correlation between these two parameters; rather a transition seems to separate two ranges in which the diffusion coefficient decreases with the crystallinity. At variance, a linear decrease of the diffusion parameter with the order parameter, derived from the X-ray diffractograms, was found in the whole range of crystallinity.