The thermal degradation of an epoxy system consisting of diglycidyl ether of bisphenol-A and 1,2-diamine cyclohexane (BADGE n = 0/1,2-DCH), immersed in hydrochloric acid for 30 days, was studied by thermogravimetric analysis, to determine the reaction mechanism of the degradation process. The results were compared with experimental data corresponding to the same epoxy system without exposure to the acid. It was found that the kinetic reaction mechanism changed with the immersion in HCl. The average activation energy of the solid-state process was determined by using the Flynn-Wall-Ozawa method, resulting in 81 2 kJ/mol. Different integral and differential methods and different reaction mechanisms reported in the literature were used and compared to this value. Analysis of experimental results suggests that in the conversion range studied, 5-20%, the reaction mechanism is somewhere between the different types of phase boundary controlled reaction and random nucleation with one nucleus on the individual particle.