The effects of physical aging in a polyetheramine-cured DGEBA epoxy

As amorphous polymers are cooled, a temperature (T_g) is reached where molecular rearrangements are no longer possible on the time scale of the temperature change. Below T_g, only gradual structural rearrangements (physical aging) are possible as the polymer tries to approach its thermodynamic equilibrium. Samples of a polyetheramine (Jeffamine T-403)-cured digylcidyl ether of bisphenol A (DGEBA) resin (EPON 828) were aged isothermally to examine the effects of physical aging on the mechanical and calorimetric responses. Physical aging was probed through uniaxial compression tests to observe changes in the stress-strain response, and differential scanning calorimetry to observe the evolution of the endothermic peak in the heat capacity. The compressive yield stress substantially increased with aging time, as did the magnitude of the peak in heat capacity and the temperature at which the peak occurred. It is important to understand the implications of these changes on the lifetime of engineering devices that utilize the 828/T-403 material.