Tung oil-derived epoxy vitrimers with high mechanical strength, toughness, and excellent recyclability

Authors: XIAO, LAIHUI - Chinese Academy Of Forestry; LI, WENBIN - Chinese Academy Of Forestry; Liu, Zengshe - Kevin; ZHANG, KUN - Chinese Academy Of Forestry; LI, SHUAI - Chinese Academy Of Forestry; WANG, YIGANG - Chinese Academy Of Forestry; CHEN, JIE - Chinese Academy Of Forestry; HUANG, JINRUI - Chinese Academy Of Forestry; NIE, XIAOAN - Chinese Academy Of Forestry

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2022
Publication Date: 7/17/2022
Citation: Xiao, L., Li, W., Liu, Z., Zhang, K., Li, S., Wang, Y., Chen, J., Huang, J., Nie, X. 2022. Tung oil-derived epoxy vitrimers with high mechanical strength, toughness, and excellent recyclability. ACS Sustainable Chemistry & Engineering. 10(30):9829-9840.
DOI: https://doi.org/10.1021/acssuschemeng.2c01653

Interpretive Summary: Many of the materials that we use today, especially as coatings and adhesives, are made using an ingredient called epoxy resin. This material is known for high mechanical strength, good thermal stability, ease of application, and an overall ability to stick to surfaces. However, if epoxy resin is used alone, it also has problems such as brittleness and low impact resistance. The additives that overcome these problems, called plasticizers, allow the coating to become flexible and give it desired toughness. However, many of them have environmental drawbacks, and more friendly alternatives are needed. We have developed such an alternative from naturally available tung oil. The new family of additives were formulated into a specific epoxy resin which were stronger materials than current commercial materials. Further, the new tung oil-based components contain reversible bonds which will likely increase recyclability of products made with the epoxy resin coatings. This research will lead to broad benefits in the entire product chain, from oil producers, to coating manufacturers, and eventually to recyclers and the overall environment.

Technical Abstract: 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.