Optimization of a commercial epoxy curing cycle via DSC data kinetics modelling and TTT plot construction

Abstract

A commercial bio-epoxy resin was investigated by means of DSC experiments. Dynamic ramps of 1, 2.5, 5 and 10 °C/min were used to attain the total heat of curing reaction (ΔHtotal) and glass transition temperatures of the unreacted monomers (Tgo) and the fully cured sample (Tgoo), estimated to be 398.3 J/gr, −46.4 °C and 63.9 °C, respectively. Isothermal measurements at 50, 65, 70 and 80 °C were performed in order to construct Di Benedetto equation, which resulted in the values of −44.1 °C and 61.2 °C for Tgo and Tgoo. Isothermal predictions, based solely on dynamic DSC data, were further conducted. Model-free kinetic analysis revealed a slight decrease in the effective activation energy Eα, which found to vary with conversion in the range of 30–60 kJ/mol. Utilizing Kamal and Sourour (KS) with diffusion reaction model under dynamic conditions, Ea values of 49 kJ/mol and 56 kJ/mol were reported for catalytic and autocatalytic mechanism, while a strong compliance was accomplished between experiment and simulation. Vyazovkin isoconversional method accurately predicted isothermal curing for temperatures exceeding 65 °C, could not however capture curing rate hindrance below Tgoo. Eventually, KS with diffusion model was incorporated in the production of Time Temperature Transformation (TTT) plot. The present comprehensive kinetic analysis, aims for divulging the optimum curing temperature window for the investigated epoxy system, leading the way to materials with advanced properties.