Creep and stress-rupture of Nafion® membranes under controlled environment

Nafion® as a polymer shows time-dependent behavior including creep and relaxation. Application of this material in automotive fuel cells and targeted lifetimes require consideration of time-dependent failure of Nafion® in fuel cell design. In this work, creep tests for Nafion® were conducted in a controlled environment at different hydrations and temperatures. Stress-rupture curves for Nafion® were obtained for different hydrations (RH = 5%, 50% and 90%) at room temperature and also for two different temperatures (25 °C & 80 °C) at 50% relative humidity. Time-dependent failure was observed for all these conditions regardless of temperature and hydration level (state of water in Nafion®). Ionic forces created by cross linkings (by introducing water to membrane) do not seem to prevent disentanglements of the chains since there is no change in rate of time-dependent failure results. A time-hydration/temperature equivalence method (Sherby–Dorn) is suggested as a method to use short-term test data to estimate rupture times for other conditions.