A novel method for monitoring chemical degradation of crosslinked rubber by stress relaxation under tension

This paper describes a novel test method for monitoring chemical degradation of a crosslinked rubber by stress relaxation under tension. An accelerated sulphur cured ethylene propylene diene rubber (EPDM) was subjected to stress relaxation under tension while exposing to 50% aqueous solution of nitric acid (HNO3). An experimental set up was designed and built in-house for this purpose. The tensile test specimen was stretched to a constant elongation. The stress decay was monitored upon exposure to the harsh chemical. Stress decay was found much faster in the exposure media than in air. Decrosslinking was the main reason for quicker stress decay as observed by decrease in crosslink density. To compare, experiments were conducted by exposing similar specimens in the same exposure media under unstressed conditions. It was found that monitoring chemical degradation under given stressed condition yielded relatively quicker yet reliable and reproducible results.