IMPROVING THE UNDERSTANDING OF ENVIRONMENTAL STRESS CRACKING IN POLYETHYLENES

Abstract

One of the most common failures of plastics while in use is environmental stress cracking (ESC). Studies were conducted in this thesis to improve our understanding of ESC, through experimentation to modify the existing and most-used standardized test for ESC, namely the Bell Test (ASTM D-1693). Given the large variability of failure times associated with the Bell Test, the first study consisted of developing a novel heat notching technique. This technique consisted of a heated blade used for notching and showed decreased variability compared to the standard method of notching. Given the success, this work further highlighted a growing theory that the local phase morphology of the notch was critically important to assessing environmental stress cracking resistance. The second study in this thesis explored the ESC failure mechanism on this new viewpoint that the local region of the notch and the structural arrangement of polyethylene therein was critically influential. The work related the failure mechanism to the localized absorption of the typical stress cracking agent, IGEPAL CO-630, in conjunction with the localized stress development in the notch, using an organic dye tracer and computer vision aided analysis. The study reinforced the importance of the local amorphous and crystalline regions, seen in the heat notch study, and found a two-stage stress-dependent absorption mechanism for IGEPAL occurring as cracking developed in the polyethylene samples.