Grafted triglycerides comprising a triglyceride grafted with a fatty acid residue containing 4 to 30 carbon atoms are reacted with an epoxide resin and an amine curing agent to yield an epoxy thermoset. The grafted triglyceride is prepared by reaction of an epoxidized triglyceride with a fatty acid. By varying the length of the fatty residue, the number of fatty residues per triglyceride, the identity of the epoxy resin and the amine curing agent, it is possible to prepare epoxy thermosets that exhibit superior physical properties compared to the properties of epoxy thermosets prepared without the grafted triglyceride, or as compared to epoxy thermosets wherein the epoxidized triglyceride is used in place of the grafted triglyceride.