Effect of water absorption on the thermal–mechanical properties of HTPB modified DGEBA-based epoxy systems

Abstract

Three DGEBA-based epoxy systems modified by the incorporation of hydroxyl-terminated polybutadiene (HTPB) were aged by water immersion. These systems have different macromolecular structures, and comprise a monophasic system (EPI) and two biphasic systems (EPH and EPA) differing in the size of the elastomeric domains. The diffusion coefficient and the water saturation value were successfully determined using the Fickian diffusion model. Both parameters were larger for the monophasic system. The effect of water absorption on the glass transition temperature was evaluated by DMA. The results show that at the beginning of the immersion process the absorbed water forms strong dipole–dipole interactions, increasing the values of Tg. Plasticization follows for longer immersion times. From the DMA results, it was also observed that the monophasic system has a more rigid structure. The biphasic system with small elastomeric domains (EPA) has a flexible network, indicating that the HTPB domains are chemically linked to the epoxy matrix. The small value of tan- δ for the biphasic EPH formulation was attributed to poor elastomeric–matrix interaction.