Structural relaxation in a polyester thermoset as seen by thermally stimulated recovery

The thermally stimulated recovery technique (TSR), also known as thermally stimulated creep, is a low-frequency mechanical spectroscopic technique tha t is shown to enable the monitoring of the structural relaxation process in a polyester-based thermoset (T-G similar to 95 degreesC). Thermal sampling experiments are able to isolate the contribution of a narrow window of rel axation times assigned to the strain of the material at different temperatu res. Such experiments were performed after an ageing period at the same cre ep temperature. Three ageing temperatures and several ageing times were inv estigated. Characteristic parameters of the obtained TSR curves are observe d to vary with T-a and t(a). Such variations are discussed on the basis of the general variation of the viscoelastic response upon structural relaxati on, namely the shift of the distribution of relaxation times associated wit h the glass transition, towards longer times. (C) 2001 Elsevier Science Ltd . All rights reserved.