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 that is shown to enable the monitoring of the structural relaxation process in a polyester-based thermoset (Tg∼95°C). Thermal sampling experiments are able to isolate the contribution of a narrow window of relaxation times assigned to the strain of the material at different temperatures. Such experiments were performed after an ageing period at the same creep temperature. Three ageing temperatures and several ageing times were investigated. Characteristic parameters of the obtained TSR curves are observed to vary with Ta and ta. Such variations are discussed on the basis of the general variation of the viscoelastic response upon structural relaxation, namely the shift of the distribution of relaxation times associated with the glass transition, towards longer times.