Fully Bio-based, Degradable and Tunable Epoxy Thermosets from Homogenized Acids and Epoxidized Vegetable Oils

Epoxy resins continue to be seen as desirable materials for high-performance applications given their excellent thermomechanical properties. However, commercial epoxides are generally derived from non-renewable feedstocks and highly resistant to chemical decomposition. Accordingly, the provision of readily degradable, bio-derived alternatives offering both high performance and tunable thermomechanical properties is urgently necessary for the development of sustainable composite materials. In this work, such materials are prepared by reaction of epoxidized linseed oil (ELO) with different quantities of organic acid hardeners, comprising eutectic mixtures of (trifunctional) citric acid (CA) and various concentrations of different linear aliphatic diacids, pimelic (PA) and glutaric acid (GA). Variation of both acid chain length and diacid:triacid ratio permit controlled manipulation of the resulting materials’ thermomechanical properties, with extensive crosslinking in high-triacid systems yielding increases in both glass transition temperature and mechanical strength. The presence of diacid species ensures homogeneity of the reaction mixture during resin curing, without requiring exogenous solvents or other diluents to solubilise the CA, and all materials are shown to be readily degradable under aqueous basic conditions. Finally, preliminary studies indicate that replacement of ELO with glycerol triglycidyl ether (GTE) yields materials with further enhanced thermomechanical properties comparable to Bisphenol A diglycidyl ether-derived materials.