Evaluating environmental stress cracking thresholds by contact angle measurements
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This work probes a hypothesis for predicting a critical stress associated with of environmental stress cracking (ESC). The hypothesis is based on a thermodynamic criterion for localized swelling induced by stress on the polymer. The surface-active liquids chosen for study are oleic acid and dibutyl phthalate and the polymer is polycarbonate (PC). An experimental technique involving contact angle measurements of a sessile drop as a function of stress is used to probe the hypothesis. A new method for measuring contact angle using refraction is also introduced. No significant change in contact angle as function of stress is observed in either system, though the kinetics of craze initiation and inelastic strain at craze initiation do show a shift in response to stress at levels similar to those predicted by the hypothesis.
KeywordsContact Angle Solubility Parameter Sessile Drop Hydrostatic Stress Inelastic Strain
We would like to acknowledge the generous support given this work by the Materials Research Science & Engineering Center on Polymers at the University of Massachusetts (MRSEC) and Cluster M of the Center for University of Massachusetts-Industry Research in Polymers (CUMIRP). Cluster M member companies include: Atofina, Essilor USA, Henckel Loctite, International Paper and Meadewestvaco.
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