Chemiluminescence monitoring during an epoxy curing reaction

• Chemiluminescence offers a simple way to monitor the curing reaction of an epoxy resin. • Both the temporal data and the spectral distribution of the luminescence can reflect the stage of the reaction. • New emissive molecular groups formed during the curing reaction could be identified. • The exothermicity of the reaction might explain the observed phenomenon. Chemiluminescence is one of the ways to monitor chemical reactions, and notably the curing of epoxy resins. The kinetics and conversion of the reaction are classically monitored using total light emission without consideration of the emission spectrum. In the present work, we investigated the chemiluminescence of an imidazole catalyzed epoxy resin during its curing at 90°C. Attention is paid to the change in the chemiluminescence spectrum with the extent of the reaction. The spectral distribution changes with curing time and exhibits a non-monotonous behavior that correlates well with the chemiluminescence intensity monitored with a photomultiplier. The curing chemiluminescence is attributed to the oxidation of the material in an evolving environment and is promoted by the exothermicity of the curing reaction. After a short period of time where only the oxidation of the catalyst and the hardener are revealed, the reaction rate accelerates and peaks after 40 min of curing at 90°C. Then, the chemiluminescence spectrum progressively evolves toward the one characteristic of the fully cured resin. This study demonstrates that analyzing the spectral distribution of luminescence can effectively determine the curing reaction stage of a given resin.