Physical Aging in Anhydride-Cured DGEBA Epoxy

In amorphous polymers, there is a temperature (T_g) reached upon cooling at which the thermal energy is insufficient to allow for molecular rearrangements on the time scale of the temperature change. At this point, the material becomes kinetically trapped in a glassy, non-equilibrium state characterized by excess free volume and enthalpy. Physical aging occurs as a material is held below T_g and begins to relax towards equilibrium. This relaxation can change the properties of the material and is important to understand when considering the long-term reliability in applications. In this work, the physical aging of an anhydride (Aradur 917, Huntsman) cured DGEBA resin (EPON 828, Hexion) was investigated. Four sets of samples were held between 8°C and 35°C below T_g (132°C) for 0 to 4000 hours. The properties of these samples were tested through uniaxial compression and differential scanning calorimetry to observe the changes in yield stress and heat capacity.