Physical aging of an epoxy/cycloaliphatic amine resin

The physical aging of a system containing a diglycidyl ether of bisphenol A (DGEBA) resin and the hardener 1,3-bisaminomethylcyclohexane (I,3-BAC) has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The effect of the enthalpy relaxation Juring DSC heating scan is shown by the presence of an endothermic peak whose position and intensity depends on the aging conditions, both temperature and time. Samples fully cured were aged at temperatures between 110 and 140 degrees C, for periods of time from I h to a maximum of 168 h. Furthermore, the dynamic mechanical relaxation behaviour of the system annealed at temperature of 100 degrees C was studied, aging during 24 and 168 h. DSC studies suggest that enthalpy relaxation increases gradually with aging time to a limiting value for each temperature where structural equilibrium is reached. DMA results show that the effect of aging is to cause chain stiffening and a decrease in the height of the peak value of the loss factor. (C) 1998 Elsevier Science Ltd. All rights reserved.