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

Abstract

Abstract The overall reaction kinetics of a high‐ T g tetrafunctional aromatic diamine/difunctional epoxy system (maximum glass transition temperature, T g ∞ = 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/ T g data by differential scanning calorimetry (DSC). The mathematical expression of the kinetics, together with the unique one‐to‐one relationship between T g and chemical conversion, is used to calculate the material's T g vs. time under heating at constant rates. For a heating scan from below T g 0 (the glass transition temperature of the unreacted material), initial devitrification corresponds to the reaction temperature ( T cure ) first passing through the T g of the reacting material; vitrification corresponds to T g becoming equal to the increasing T cure after initial devitrification; and finally, upper devitrification corresponds to T g eventually falling below the rising T cure . 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. T g is calculated to remain slightly higher than T cure 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.