Methods for predicting more confident lifetimes of seals in air environments

We have been working for many years to develop improved methods for predict ing the lifetimes of polymers exposed to air environments and have recently turned our attention to seal materials. This paper describes an extensive study on a butyl material using elevated temperature compression stress-rel axation (CSR) techniques in combination with conventional oven aging exposu res. The results initially indicated important synergistic effects when mec hanical strain is combined with oven aging, as well as complex, non-Arrheni us behavior of the CSR results. By combining modeling and experiments, we s how that diffusion-limited oxidation (DLO) anomalies dominate traditional C SR experiments. A new CSR approach allows us to eliminate DLO effects and r ecover Arrhenius behavior. Furthermore, the resulting CSR activation energy (E-a) from 125 to 70 degrees C is identical to the activation energies for the tensile elongation and for the oxygen consumption rate of unstrained m aterial over similar temperature ranges. This strongly suggests that the sa me underlying oxidation reactions determine both the unstrained and straine d degradation rates. We therefore utilize our ultrasensitive oxygen consump tion rare approach down to 23 degrees C to show that the CSR E-a likely rem ains unchanged when extrapolated below 70 degrees C, allowing more confiden t room temperature lifetime predictions for the butyl seal.