COLD-DRAWN MATERIAL AS MODEL MATERIAL FOR THE ENVIRONMENTAL-STRESS CRACKING (ESC) PHENOMENON IN POLYETHYLENE - A RAMAN-SPECTROSCOPY STUDY OF MOLECULAR STRESS-INDUCED BY MACROSCOPIC STRAIN IN DRAWN POLYETHYLENES AND THEIR RELATION TO ENVIRONMENTAL-STRESS CRACKING

Raman spectroscopy was used to study strain-induced molecular stress i n cold-drawn polyethylenes, which were being used as a model system fo r fibrils present in the crazes formed during environmental stress cra ck resistance (ESCR) tests. The molecular stress was measured at 240 K in order to minimize relaxation phenomena. Molecular stress was relat ed to macroscopic strain and, by correcting for differences in E-modul i, to true stress. In this paper, the measured molecular stress is rel ated to ESCR values and sample characteristics. It was observed that g ood ESCR materials showed a lower molecular stress than worse ESCR mat erials at the same macroscopic strain level. It was also observed that the molecular weight has a major effect on the observed molecular str ess per macroscopic strain (molecular stress per macroscopic strain de creases with increasing M-w), whereas the effect of chain branching is smaller (molecular stress per macroscopic strain decreases with chain branching).