Theoretical Study on the Reaction Mechanism of Closed-Loop Recyclability of a Biomass-Derived Epoxy Resin Thermoset by Methanolysis

Abstract Epoxy resin thermosets (ERTs) represent a significant category of polymeric materials. However, ERTs have high cross-linking and are difficult to decompose, leading to unacceptable environmental pollution. It is evident that there is a critical need for the development of inherently recyclable ERTs derived from renewable resources. In addition, the feasibility of related reaction mechanisms of the recyclable routes needs to be investigated. In this work, the potential energy surface information for 13 reaction channels was obtained using density functional theory at the B3LYP/6-311+G(d,p) level based on electronic structure calculations. The curing, methanolysis, and acetolysis routes were identified. The influence of heteroatom electron effects was evaluated. The calculation results show that the reaction Gibbs free energy barrier during the curing process of the DGF/MBCA ERT material is about 0.64 eV higher than that during the methanolysis process, successfully elucidating the experimental phenomenon of high-temperature curing and low-temperature methanolysis. The reaction Gibbs free energy barriers of nucleophilic substitution for the thiophene-like are both lower than those for the furan-like due to the higher conjugation degree of furan-like pentagonal rings. The elucidated reaction mechanism of the recyclable process involves lignin- or lignocellulosic-derived ERT raw materials.