Biobased epoxy resins obtained from resorcinol epoxy monomer and anhydrides

Design and development of high glass transition (Tg) biobased epoxy thermosets is a key challenge for several fields of applications. To this aim, in the present study diglycidyl ether of resorcinol (DGER) is proposed as a potentially biobased alternative to diglycidyl ether of bisphenol A (DGEBA) for the synthesis of high-performance epoxy resins. DGER is obtained by diglycidylation of resorcinol, an aromatic diol synthesized by fermentation of glucose or catechin. The curing process of DGER in the presence of various anhydrides as hardeners and several imidazole initiators is studied. The most efficient hardener/initiatior combination, which leads to the resin with the highest degree of reaction conversion and the highest glass transition (Tg > 100 °C) is further studied by chemorheological analysis, and a kinetic model for the crosslinking reaction is proposed. The conversion degree is evaluated by monitoring the disappearing of characteristic peaks of anhydride and epoxy rings in ATR-FTIR spectra collected at different curing temperature, as well as the appearance of the characteristic band of ester groups typically formed in epoxy/anhydride resins. By fitting the conversion data, the autocatalytic crosslinking mechanism is confirmed, and kinetic parameters are calculated. Also, the thermomechanical characteristics and chemical stability of DGER-based epoxy resins are evaluated, confirming the potential use of this epoxy thermosets when high mechanical and thermal properties are required.