| Abstract: | The influence of morphology in a low density, high melt index polyethylene was studied with particular reference to environmental stress cracking (ESC). Test samples of the polyethylene were molded under constant conditions, only the subsequent rate of cooling to room temperature being changed. Several techniques were used to study the resultant polymer including ESC tests, X-ray diffraction, optical microscopy and constant strain rate stress/strain tests. It was found that the faster the polymer was cooled after molding, the smaller was the typical diameter of the spherulites and the greater the resistance to stress cracking. A hypothesis is proposed to explain the differences in terms of the ease with which a crack can propagate, assuming that propagation is easier in amorphous material than within spherulites. |
