Some structure-property relationships in oriented polychloroprene

Abstract

The deformation, yield and brittle fracture properties of an 84% trans-polychloroprene (Neoprene W) were determined at −180°C for samples prepared with a range of microstructures (including amorphous, row-nucleated and spherulitic morphologies) and a range of pre-orientations from 0 to 300%. Pre-orientation was carried out at room temperature and crystallisation, where required, at −5°C. The degree of crystallinity was low, in the region of 18%, and the crystalline morphology was monitored by thin film electron microscopy and by wide angle X-ray analysis.

The results indicate that in this temperature range a row-nucleated (“type I”) morphology produces little modification of the amorphous properties at a given pre-extension except to inhibit premature fracture after yield. In contrast a distorted spherulitic (“type II”) morphology, raises yield stresses and strains above those for the amorphous material and produces post-yield strain hardening not observed with the other microstructures.

In all cases, pre-orientation exerts a profound effect on elastic moduli, yield stresses and the brittle-ductile fracture transition. Some tentative mechanisms are proposed to explain these features.