Stress relaxation in polymers: a modified site model analysis

Abstract

The site model theory is used to derive an expression for stress relaxation in a polymer governed by a single thermally activated process. Backward jumps of the structural units are taken into account and it is further assumed that when a structural unit executes a jump it does not regenerate a configuration suitable for another jump of a similar kind in the same direction. A limiting “internal stress” is predicted, as obtained in practice, and it is found that the formulation corresponds exactly to the standard linear solid of group I. This correspondence extends to creep, with the retention of the same parametric identities. Consideration is given to the influence of residual stresses and to the aging characteristics of fabricated polymers.