Studies of epoxy resin systems: Part C: Effect of sub‐Tg aging on the physical properties of a fully cured epoxy resin

Abstract The effect of sub‐T g aging on the properties of an epoxy resin system, diglycidyl ether of butanediol, DGEB, cured with 4‐4′ diaminodiphenyl sulfone, DDS, has been studied. Aging was found to increase the DSC (differential scanning calorimetric) endothermic peak, the density, and the upper yield point. In contrast, the lower yield point was relatively unchanged. This result, together with the observation of the elimination of the DSC endothermic peak by deformation and the absence of a yield point after deformation, suggested that the aging effect was eliminated by deformation. The thrermally stimulated depolarization (TSD) α‐peak was found to decrease in strength with aging time. All of the observations were best rationalized on the basis of the free‐volume concept.