THE STRUCTURE OF HIGHLY ORIENTED HIGH MODULUS POLYETHYLENE

A comparative study of the structure of uniaxially-oriented bulk samples of linear PE of various molecular weights over a wide range of draw ratios has been carried out by means of small and wide angle X-ray analysis, NMR-spectroscopy and DSC. The structure of oriented high molecular weight PE samples, prepared by drawing single crystal mats to draw ratios up to 200, have also been studied. A large number of unfolded tie-molecules have been found to exist in the trans-conformation in PE amorphous regions. These tie-molecules, which connect the adjacent crystallites along the axis of orientation, and are not large crystals, account for the high mechanical proper-ties of these samples. It has been shown that in the course of the orientation process, chain unfolding in the amorphous regions is accompanied by the formation of continuous linear systems consisting of several coherent crystallites and tie-molecules. These are coherently aligned along the macromolecular axis.