Physical aging of a tetrafunctional/phenol novolac epoxy mixture cured with diamine -: DSC and DMA measurements

The physical aging of a system containing tetraglycidyl-4-4'-diaminodiphenylmethane (TGDDM), with a multifunctional novolac glycidyl ether resin hardened by 4,4'-diaminodiphenylsulphone (DDS) has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Samples fully cured were aged at temperatures between 200 and 250 degrees C, during periods of time from 1 to a maximum of 336 h. Furthermore, the dynamic mechanical relaxation behaviour annealed at temperature of 220 degrees C, was studied, aging during 24 and 168 h. The effect of the enthalpy relaxation during 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. 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.