Interpretation of the Stress Relaxation Behaviour of Plasticized PVC Using a Cooperative Model

Abstract

It has been reported earlier [1–3] that the stress relaxation behaviour of different materials is largely the same. For instance, the initial part of the relaxation process obeys an exponential relation between rate and stress (σ), while at longer times a power type relation is observed. The slope (F) of the relaxation curves when plotted as stress vs. In (time) is, in the exponential region, related to the initial stress (σ₀) as

$$F = o.1({\sigma _0} - {\sigma _i}), $$

((1))

the scatter of the constant being ca. 10 %. In eq.(1) σ₁- denotes the internal stress, which in this context is equivalent to the equilibrium stress reached after a sufficiently long measuring time. Eq.(l) has been found to be valid for metals, polymers and a number of other materials [1–3].