Continuous heating transformation (CHT) cure diagram of an aromatic amine/epoxy system at constant heating rates

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Abstract
The overall reaction kinetics of a high‐Tg tetrafunctional aromatic diamine/difunctional epoxy system (maximum glass transition temperature, Tg∞ = 182°C), which can satisfactorily describe the rate of the reaction in both kinetically and diffusion‐controlled regimes, had been determined earlier from isothermal conversion/Tg data by differential scanning calorimetry (DSC). The mathematical expression of the kinetics, together with the unique one‐to‐one relationship between Tg and chemical conversion, is used to calculate the material's Tg vs. time under heating at constant rates. For a heating scan from below Tg0 (the glass transition temperature of the unreacted material), initial devitrification corresponds to the reaction temperature (Tcure) first passing through the Tg of the reacting material; vitrification corresponds to Tg becoming equal to the increasing Tcure after initial devitrification; and finally, upper devitrification corresponds to Tg eventually falling below the rising Tcure. The results of the calculation correlate well with the available experimental data of the dynamic mechanical behavior of the material during temperature scans at constant rates that were obtained by the torsional braid analysis (TBA) technique. Tg is calculated to remain slightly higher than Tcure after vitrification due to the influence of diffusion control, the difference being greater for lower heating rates. The limiting heating rate with no initial devitrification and that with no vitrification are also calculated.