5. Effect of Temperature on Mechanical Property Degradation of Polymeric Materials

Proton Electrolyte Membrane (PEM) fuel cell is a promising energy source because of its high efficiency and zero emission. One of the most important unresolved problems of PEM fuel cells today is the durability issue of its components. For example, the polymeric gasket material of PEM fuel cell must be durable enough to hold the liquid and gas inside the fuel cell channel, as its sealing force decreases gradually with time and also changes with temperature. Liquid Silicone Rubber (LSR) is commonly used as gasket or seal material in many industrial applications including PEM fuel cells. This paper discusses the compression stress relaxation of LSR under temperature cycling, which is to simulate the actual fuel cell operation. It is found that (a) in addition to stress relaxation, thermal expansion or contraction of the material contributes the most in the observed stress variation during temperature change, and (b) the stiffness of LSR appears to change according to temperature history, and (c) the Maxwell stress relaxation model can be used to predict the sealing force only after a correction of the change of material stiffness is implemented into the model.