Stress Relaxation and Creep of Several Vulcanized Elastomers

Abstract

Abstract It is well known that polymeric materials in general creep with increasing time under a given constant stress and that stress relaxes with increasing time under a given constant strain. Recently, theoretical studies en these phenomena have been made in detail for polyisobutylene, vulcanized natural rubber and polymethylmethacrylate. Both properties for any vulcanized elastomer depend on the molecular structure of the network, the temperature and the amount of original stress or deformation, but it can be deduced from the Tobolsky and Eyring theory of viscoelasticity for polymers that both properties are linearly related to log time. In fact, however, the polymers begin to deviate rapidly from such a linear relationship if they are placed in air at high temperature for a long time, because thermal degradation by oxidation occurs. For elastomers used in electrical machinery and for other industrial uses, for example rubber packaging, diaphragms, or vibration and shock absorbers, it is required that we understand thoroughly the behavior of both properties at each temperature and each time for individual materials in order to make a proper choice of material suitable in behavior for each purpose. The author has studied these properties experimentally for natural rubber as well as for several synthetic elastomers and then investigated the relation between thermal life and the temperature employed. This paper describes a few results obtained up to the present.