Time-temperature-transformation (TTT) diagram of a dual-curable off-stoichiometric epoxy-amine system with latent reactivity

The time-temperature-transformation (TTT) diagram of the curing an off-stoichiometric amine-epoxy formulation with intermediate latent reactivity has been elaborated. The first curing stage is an epoxy-amine polycondensation taking place at low temperatures, while the second curing stage is an anionic homopolymerization of the excess epoxy groups, taking place at high temperatures and catalyzed by a latent base. The curing kinetics of the first and second curing stages have been analyzed separately by integral isoconversional procedures, and the kinetics data has been used to plot the isoconversion lines in the TTT diagram. The relationship between the glass transition temperature (Tg) and conversion has been determined experimentally and theoretically and used to determine the vitrification line in the TTT diagram. The results reflect the clearly different kinetic behaviour of both curing stages and a significant intermediate storage stability, which makes these curing systems highly attractive for multiple stage processing. The shape of the vitrification line also reflects the occurrence of different curing processes with different structure build-up. Safe processing and storage conditions can be easily defined on the basis of the TTT diagram. This is the first time the curing behaviour of dual-curing formulations is illustrated in such a clear and concise way thanks to the TTT diagram.