Artificial weathering and physico-chemical characterization of EPON-IPD thermosets with high enthalpy storage of shape memory

Abstract

While thermosetting shape memory polymers (TSMPs) hold great potential in aviation, automotive, and biomedical industries, an understanding of how they degrade under environmental conditions is needed before they can be broadly incorporated into their respective applications. This study includes a characterization of TSMP of notably high-enthalpy storage in response to artificial weathering including UV irradiation and cyclic condensation to simulate aging under terrestrial conditions. The comprehensive characterization includes differential scanning calorimetry, FTIR analysis, scanning electron microscopy with image analysis, nanoindentation, and stress and shape recovery tests after macro-scale compression. Qualitative and quantitative differences between the irradiated samples with and without condensation are observed and discussed. Glass transition temperatures increased due to crosslinking in UV-irradiated samples, while they decreased due to plasticization and hydrolysis under cyclic condensation. Similarly, UV-irradiated samples experience an increase in elastic modulus and hardness, while these properties decreased in cyclic condensation samples with exposure time. UV-irradiated samples had better stress recovery and smaller surface cracks than UV-condensation-weathered samples which had better shape recovery. The mechanisms of these fundamentally different effects are discussed.