Thermal History Effects on DSC Kinetic Analysis of DGEBA–DICY Epoxy Curing

Abstract The curing behavior of diglycidyl ether of bisphenol A (DGEBA) epoxy resin with dicyandiamide (DICY) was evaluated using differential scanning calorimetry (DSC) and standard industrial kinetic methods. Melt-extruded powder samples were analyzed at heating rates of 5–20 °C min–1, under isothermal conditions from 180 to 210 °C, and through combined isothermal–dynamic experiments to assess residual curing. The Borchardt–Daniels method yielded apparent activation energies that depended on the heating rate, ranging from 177 ± 2 kJ/mol to 127 ± 4 kJ mol–1. The ± values correspond to the confidence limits reported by STARe for the numerical fit and should not be interpreted as measures of experimental reproducibility. A peak-based Kissinger analysis resulted in an apparent activation energy of about 108 kJ mol–1, whereas the isothermal Arrhenius analysis yielded approximately 84 kJ mol–1. Both values had relatively wide confidence intervals because of the limited number of experimental conditions. The nonextruded reference sample, analyzed at 10 °C min–1, showed a lower reaction enthalpy (89.45 versus 118.54 J g–1) and a higher peak temperature (234 versus 203 °C) than the extruded material. This suggests that melt processing changed the initial state of the formulation. However, the DSC results alone do not allow us to determine whether this was mainly due to better dispersion, partial dissolution of DICY, or some early-stage reaction during processing. The glass-transition temperature increased with conversion but remained well below the isothermal curing temperature, indicating that classical vitrification was not observed. The linear relationship between ln(A) and Ea (R2 > 0.99) is interpreted as a correlation between the fitted Arrhenius parameters and may reflect both changes in the material and covariance between the parameters. Overall, the kinetic values obtained here should therefore be regarded as protocol-dependent phenomenological descriptors rather than intrinsic mechanistic constants.