Accelerated Compression Set at Elevated Temperature in Rigid Polymer Foams

We have extended our study of the recovery behaviour of rigid polymer foams following long periods of compression (Miller Tate and Talal, 1999) to include samples constrained at temperatures above ambient. Samples of polyurethane, polyethylene and polyimide, which represented highly crosslinked, lightly crosslinked and uncrosslinked foams respectively, were maintained under a range of compressive strains for periods ranging from three days to one month and their dimensional recovery followed at ambient temperature after release. All materials were of similar density (~100 kg m-3).The different materials showed markedly different behaviour, suggesting that the dominant effect of elevated temperature testing is to induce minor phase changes in the polymer, thus incrementally reducing the mechanical resilience of the polymer chain to applied stress and yielding results which do not accord with an Arrhenius (or other simple) model.