Deep eutectic solvents based on L-Arginine and glutamic acid as green catalysts and conductive agents for epoxy resins

Abstract

Many engineered epoxy products in the recent years require sustainable materials to be contributive in the coming decades. The efficiency of [DES]Arg/Eg and [DES]Glu/Eg deep eutectic solvents (DESs) on the curing reaction of bisphenol A diglicydyl ether (DGEBA) with the application of differential scanning calorimetry (DSC) at temperatures 313–333 K is assessed. The both DESs studied here can act as the catalyst of epoxy-amine reaction, hardener and conducting agents in a simultaneous manner. Moreover, it reveals different reaction kinetics which strongly depend on the type of hydrogen bonding acceptor of the mixture. It is observed that there exist many fundamental differences between the progress of isothermal curing reaction in the presence of [DES]Arg/Eg and [DES]Glu/Eg considering the conductive ionic liquids and non-conductive conventional hardeners. The [DES]Glu/Eg at lower concentrations exhibits different catalytic behavior in the initial stages of the reaction, in a sense that the reaction progresses at higher rates up to 5 min and hampered afterward. In contrast, [DES]Arg/Eg act as a high-efficient catalyst in a sense that it allows the curing reaction approaches the completion level within 30 min which is comparable to previously reported conducting dopants. From kinetic results it is deduced that the mechanism of curing reaction follows the first-order kinetic in the presence of [DES]Arg/Eg and [DES]Glu/Eg and reaction occurring in the presence of [DES]Glu/Eg is characterized by higher activation energy compared to [DES]Arg/Eg. To analyze the efficiency of DESs as a catalyst for the epoxy-amine reaction, a computational study is run on a simplified model reaction catalyzed by [DES]Glu/Eg revealing a significant decrease in activation energy of the catalyzed reaction.