TTT - Cure diagram of an anhydride-cured epoxy system including gelation, vitrification, curing kinetics model and monitoring of the glass transition temperature
The curing reaction of an epoxy resin [diglycidyl ether of bisphenol A (DGEBA)] combined with a methyl-hexahydrophtalic anhydride (MHHPA) hardener and a benzyldimethylamine (BDMA) accelerator was studied over a temperature range of 60140°C to build its isothermal time-temperature-transformation (TTT)cure diagram. This includes gelation and vitrification measurements using rheological measurement techniques, monitoring of the glass transition temperature and the reaction kinetics by differential scanning calorimetry, and determination of the following critical glass transition temperatures: Tg0, GelTg, and Tg.. A new curing kinetics model, based on the Sesta´k-Berggren model, was developed including both chemicaland diffusion-controlled stages of reaction. Then, the TTTcure diagram was built by numerical integration of the kinetics model, and good agreement was obtained by comparison with experimental data. Additionally, for the first time, this model takes into account the incomplete cure, which occurs when the thermosetting system is cured below its ultimate glass transition temperature, leading to a more realistic description of the cure evolution after vitrification.