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 (1-2) to include samples constrained at elevated temperatures. Samples of polyurethane, polyethylene and polyimide, representing 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 approximately 100 kg nr 3 density. 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.