The Effect of Water Sorption and High Temperature Aging on the Calorimetric Signature of the Aging of an Epoxy Glass

The cure of DGEBA with diethanolamine results in an epoxy that is susceptible to complex aging signatures. We explore the calorimetric signatures resulting from aging under a variety of conditions. Aging at room temperature (~Tg-50°C) and ambient humidity results in distinct features in the DSC thermogram. A broad “post-Tg shoulder” is seen extending from Tg (75°C) to 175°C and centered at ~150°C. A decrease in Cp is seen between 175°C and 200°C, indicating additional chemical aging. The first heating ramp erases the post-Tg shoulder, but the change in Cp is still observed on the second heating ramp. Isothermal holds at 200°C remove the high-T decrease in Cp and increase the Tg. Samples soaked in water at ~20°C show the gradual evolution of the post-Tg shoulder indicating that this epoxy is sufficiently hydroscopic that aging under typical laboratory conditions will yield a “shoulder” that will significantly affect the DSC thermogram and complicate the analysis of physical aging.