Fourier transform IR and differential scanning calorimetry study of curing of trifunctional amino-epoxy resin

The curing process was studied for a trifunctional epoxy resin, triglycidyl-p-aminophenol, using the hardener 4,4′-diaminodiphenylsulfone. Two curing cycles were carried out: one following the manufacturer's guidelines (2 h at 80°C, 1 h at 100°C, 4 h at 150°C, and 24 h at 200°C) and another proposed in this study, in which the two stages at low temperatures were excluded. Fourier transform IR spectroscopy was used to quantify the conversion of different functional groups (primary amine, secondary amine, epoxide, hydroxyl and ether functional groups), and these conversions could be used to infer the type of reactions that took place. These results allowed us to analyze the evolution of the curing process over time and the influence of the curing cycle. Furthermore, the enthalpy of the curing process was determined using differential scanning calorimetry, and from this the thermal conversion for the whole process was evaluated. By taking into account the autocatalytic kinetic model, the rate constants were evaluated. The glass-transition temperatures were also estimated by applying different curing cycles to the resin.