Photo – DSC and real time – FT-IR kinetic study of a UV curable epoxy resin containing o-Boehmites

Nanocomposite coatings based on a cycloaliphatic epoxy resin (3,4-epoxycyclohexylmethyl- 30,40-epoxycyclohexane carboxylate – CE) with two different o-Boehmites (content ranging from 5 to 10 wt.%) were prepared by cationic photopolymerization. Two different in situ monitoring techniques, photocalorimetry (p-DSC) and real time FT-IR spectroscopy (RT-IR) were used in order to investigate the kinetics of the photopolymerization process. A theoretical approach for establishing the equivalence of the irradiation conditions in the two experimental set-ups was developed in order to compare the obtained results. A substantial correspondence of the two techniques was found for the qualitative trend of the final conversion of the epoxy groups of the filled formulations relatively to the pure CE resin. Conversely, the final conversion of the epoxy groups and the reaction rate were found to be quite different. Higher kinetic profiles were obtained in RT-IR experiments, in which were also observed lower final conversions of the epoxy groups relatively to the p-DSC measurements. The presence of the nanofillers resulted in a decrease in the reactivity of the epoxy system, which was attributed to the light absorbance of Boehmites due to scattering from the clusters in the micron-size range. All the nanocomposites exhibited a high level of transparency and high Tg values, which were found to decrease slightly with increasing the nanofiller content.