Tetrafunctional epoxy resins: modelling the curing kinetics based on FTIR spectroscopy data

The curing kinetics of two thermosetting systems based on a tetrafunctional epoxy resin was investigated by Fourier transform infrared spectroscopy. Two formulations were studied, in which the hardener was an aromatic diamine and a carboxylic dianhydride, respectively. The quantitative evaluation of the epoxy conversion was based on spectra collected in the near-infrared range (8000-4000 cm-1) as well as in the medium infrared range (4000-400 cm-1). The kinetic parameters evaluated in the above frequency intervals were significantly different. The reasons for such a discrepancy are discussed critically. Several kinetic models, based on the widely employed Kamal approach, were applied to verify their predictive capability. Satisfactory results were obtained for the amine-cured system, particularly with a modified equation taking into account the autocatalytic nature of the process as well as a limiting diffusional effect. Less accurate results were achieved for the anhydride-cured system.