Use of Hempseed-Oil-Derived Polyacid and Rosin-Derived Anhydride Acid as Cocuring Agents for Epoxy Materials

A poly(carboxylic acid) [hempseed oil (HO)-polyacid] was prepared from the fatty acids of hempseed oil and used as a curing agent for epoxies. Polyunsaturated fatty acid (C18:2 and C18:3) that composed ∼77% of the hempseed oil fatty acid (HOFA) were introduced more carboxylic groups by conjugation followed by Diels–Alder addition with maleic anhydride and hydrolysis. This conversion process was further confirmed using pure methyl linolenate as a model compound. In addition, a rosin-derived anhydride acid, maleopimaric acid (MPA) that has a rigid molecular structure, was used as a cocuring agent. Effects of the HO-polyacid/MPA cocuring agents in different ratios on the curing behavior, dynamic mechanical properties, thermal stability, and flexural properties of a commercial bisphenol A epoxy were studied. The results suggest the balance of stiffness/flexibility of the cured resins was effectively regulated by varying the cocuring agent ratio.