Investigation of the formation of epoxy-imidazole adducts and the kinetic triplets during thermal curing of a biobased and petrochemical epoxy with anhydride

The development of new advanced materials based on biobased feedstock is required to achieve more sustainable growth while addressing environmental concerns. The substitution of bisphenol-A-based epoxy (DGEBA), a conventional epoxy with bio epoxy resin, epoxidized linseed oil (ELSO), an anhydride-based hardener and mass percent changes in 2-Ethyl imidazole (2-EI), a catalyst were all studied and compared. The DGEBA and ELSO have molecular weights of 362 and 1166 g mol⁻¹, respectively. In the present investigation, two predictions were made: (1) the generation of the epoxy imidazole adduct was followed by multivariate data analysis and (2) the kinetic triplet was estimated using Isoconversional kinetic analysis techniques and compensation effect. By using Real-time FTIR measurement, the formation of either pyrrole or pyridine type intermediate when the accelerator reacts with epoxy (in the absence of hardener) is examined at different temperatures. Differential scanning calorimetry (DSC) detects an effective change in curing in an epoxy-hardener-accelerator combination. Model free and model fitting approaches are used to calculate the kinetic triplets (apparent activation energy for curing-E_a; reaction model-\(f\left( \alpha \right)\); and pre-exponential factor-A). Both epoxy resin shows nearly similar E_a value (60 kJ mol⁻¹) but the low E_a in the initial stage for bioepoxy indicate low reactivity. The approach of kinetic triplet prediction, which represents the whole understanding of the reaction, will be relevant for selecting acceptable strategies for the research of curing reactions in epoxy resins. The DSC and kinetic findings of the petroleum-based bisphenol-A epoxy and the bio epoxy composite point to the possibility of replacing bio epoxy in standard resins.

Graphical abstract