The analysis of Aging Processes of EPDM Elastomers using low field NMR with Inverse Laplace Transform and Stress Relaxation Measurements

With regard to the long-term stability of seals, "stress-relaxation" testing is known to deliver important information. The mechanism of stress relaxation is, however, difficult to interpret, as several effects take place simultaneously, with each effect itself dependent on external and internal parameters. This paper draws on a combination of stress relaxation experiments and low field NMR measurements. NMR relaxation curves as a function of aging time were analyzed using inverse Laplace transform. The resulting distributions of transversal relaxation times (T-2) shows that during thermal oxidation the network structure and the chain mobility of cured EPDM, with and without carbon black filler, changes differently.