Epoxy thermosets comprised of plant oils along with simple curing agents are sustainable and environmentally friendly polymers. The curing agent selected, and its compatibility with epoxy monomers, strongly affects the curing kinetics, the extent of curing, and the final properties of an epoxy polymers. The goal of this work is to expand the application of epoxidized oils in formulating biobased thermoset polymer systems. Epoxidized hemp oil (EHO) was produced with 8% oxirane oxygen content (OOC) after 24 hours using in situ generated performic acid. Two model curing agents-one aromatic (trimellitic anhydride, TMA) and one biobased nonaromatic (citric acid, CA)-with similar molecular weights were selected to study the cure behavior of EHO in acetone. Both curing agents are insoluble in EHO. The prepolymerization curing reaction behavior was monitored via the OOC, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and gel permeation chromatography. It was demonstrated that at 50 C, the reaction of EHO with TMA was extremely fast to form esters of TMA, while the reaction of EHO with CA was slower and followed different pathways. The cured EHO/TMA epoxy network is rigid and has a high alpha relaxation temperature (T α ) of 89 C, which is associated with the glass transition temperature (T g ), while the cured EHO/CA network system is semirigid with a T α of 40 C. In addition, TGA analysis showed that the EHO/TMA resin system represents a more homogenous structure compared to the EHO/CA system, as indicated by the presence of lower-temperature decompositions of citric acid derivatives.Keywords Biobased epoxy thermosets Á Epoxidized hemp oil Á Citric acid Á Trimellitic anhydride Á Epoxy cure behavior J Am Oil Chem Soc (2019) 96: 1389-1403.

This work describes a model biobased epoxy thermoset resin incorporating epoxidized linseed oil fatty acid methyl esters (ELOMEs) with trimellitic anhydride (TMA) as a curing agent. Unlike epoxidized linseed oil (ELO), ELOME acts as a solvent at moderate temperatures and can dissolve the curing agent. Thermosets were prepared using a range of molar ratios of ELOME, or ELOME/ELO mixtures, to TMA. It was found that the storage moduli and glass-transition temperatures of the resulting thermosets increase with the increasing concentration of the curing agent due to enhanced crosslinking. On the other hand, the dynamic mechanical analysis demonstrated that an increase in the curing agent content, especially above the stoichiometric ratios of reactive moieties, hinders the formation of the cross-linked network when an excessive amount of TMA esters of ELOME are formed. These consume a large proportion of the available epoxy moieties and consequently limit further cross-linking and polymer network growth. The glass-transition temperature (T g ) of these resins was between 80 and 86 °C, depending on the stoichiometric ratio of the reactive moieties. In thermoset systems prepared with ELOME/ ELO mixtures, an improvement in the thermomechanical properties (increase of T g up to 102 °C) was observed, which was associated with the increase in cross-linking density resulting from the branched triacylglycerol structure of epoxidized linseed oil.