Tung Oil-Derived Epoxy Vitrimers with High Mechanical Strength, Toughness, and Excellent Recyclability

The application of diglycidyl ether of bisphenol A (DGEBA) is severely limited due to the poor toughness of its thermosets, and the growing concern for sustainability calls for materials with recyclability. Thus, two tung oil-based compounds (DA-MA and TA) with different contents of carboxylic acid and anhydride were prepared and used to cure DGEBA to fabricate vitrimers, a kind of thermoset cross-linked through reversible covalent bonds. Test results show that vitrimers derived from tung oil (EP-DA-MA and EP-TA) exhibit excellent mechanical strength and toughness. In particular, the tensile strength, elongation at break, bending strength, bending toughness, and impact strength of EP-DA-MA are 63.17 MPa, 5.34%, 92.96 MPa, 1.09 kJ·m^–2, and 7.73 kJ·m^–2, respectively, while these parameters of the control, DGEBA cured with commercial methyl nadic anhydride, are 60.86 MPa, 1.77%, 78.94 MPa, 0.14 kJ·m^–2, and 4.42 kJ·m^–2. Meanwhile, high content of reversible ester bonds and secondary hydroxyl groups may facilitate the transesterification in the recycling process; thus, the crushed vitrimers of EP-DA-MA and EP-TA can be remolded without additional catalysts, and the tensile strength of the recycled samples can reach almost 100% of the original sample size, suggesting excellent malleability and recyclability. Therefore, the tung oil-derived epoxy vitrimers are promising candidates for utilization as adhesives, coatings, and matrix resins.