Bio-Based, Degradable, and Tunable Epoxy Thermosets from Homogenized Acids and Epoxidized Linseed Oil or Glycerol...

Epoxy thermosets 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 are highly resistant to chemical decomposition. Accordingly, the provision of readily degradable, bioderived 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 the 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 two different linear aliphatic diacids, pimelic acid (PA), and glutaric acid (GA). Variation of both acid chain length and diacid:triacid ratio permits controlled manipulation of the resulting materials' thermomechanical properties, with extensive cross-linking 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 solubilize 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.