Ageing of Natural Rubber under Stress

摘要

We report a dynamical-mechanical study of stress relaxation at smalldeformation in a natural (polyisoprene) rubber well above its glass transitiontemperature Tg. We find that an almost complete relaxation of stress takesplace over very long periods of time, even though the elastic network integrityis fully retained. The relaxation rate and the long-time equilibrium modulusare sensitive functions of temperature which do not follow time-temperaturesuperposition. Many characteristic features of non-ergodic ageing response areapparent at both short and very long times. We interpret the observed behaviourin terms of the properties of rubber crosslinks, capable of isomerisation understress, and relate the results to recent models of soft glassy rheology.