Self-healing, recyclable, and removable UV-curable coatings derived from tung oil and malic acid

Authors: ZHANG, JINSHUAI - Chinese Academy Of Forestry; HUANG, JIA - Chinese Academy Of Forestry; ZHU, GUOQIANG - Chinese Academy Of Forestry; YU, XIXI - Chinese Academy Of Forestry; CHENG, JIANWEN - Chinese Academy Of Forestry; Liu, Zengshe - Kevin; HU, YUN - Chinese Academy Of Forestry; SHANG, QIANQIAN - Chinese Academy Of Forestry; LIU, CHENGGUO - Chinese Academy Of Forestry; HU, LIHONG - Chinese Academy Of Forestry; ZHOU, YONGHONG - Chinese Academy Of Forestry

Submitted to: Green Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2021
Publication Date: 7/6/2021
Citation: Zhang, J., Huang, J., Zhu, G., Yu, X., Cheng, J., Liu, Z., Hu, Y., Shang, Q., Liu, C., Hu, L., Zhou, Y. 2021. Self-healing, recyclable, and removable UV-curable coatings derived from tung oil and malic acid. Green Chemistry. 23(16):5875-5886. https://doi.org/10.1039/d1gc01726h.
DOI: https://doi.org/10.1039/d1gc01726h

Interpretive Summary: Materials that we use every day usually require a coating to provide long lasting protection from the elements and an overall satisfactory appearance. However, conventional coatings, varnishes, and waxes often contain volatile organic compounds (VOCs) that can be emitted from the final product. These gasses can have short term health effects such as eye, nose and throat irritation with headaches, or even more serious long-term adverse health effects on the liver, kidneys and central nervous system. In this work, we report a coating system that is both non-volatile, and primarily from renewable resources. The key to the technology is the combination of Tung oil with a biobased reactive additive called malic acid and a new zinc-based catalyst. The material can be applied and cured with a simple process using ultraviolet (UV) light to form a coating with excellent properties. We report a formulation that is up to 58% biobased. This work will benefit those looking for an outlet for commodity oils, as well as any manufacturer looking for a new, strong and versatile, renewable coating material.

Technical Abstract: This study reports the development of super "green" smart coatings by integrating renewable resources, microwave-assisted synthesis, and dynamic covalent chemistry into UV-curable coatings. First, a novel UV-curable oligomer (TMG) was synthesized from renewable tung oil (TO) via microwave technology, and a biobased reactive diluent (MM) was derived from malic acid under ambient conditions. Afterward, a set of UV-curable coatings containing plentiful hydroxyl and ester groups were prepared by photo-polymerizing the TMG oligomer with the MM diluent. The resulting coatings demonstrated a high biobased content (49.2%–58.1%), good mechanical and thermal properties (e.g. Tg of 70.6–78.6 °C), and excellent coating adhesion and flexibility. Furthermore, by activating dynamic transesterification reactions at elevated temperatures with a zinc catalyst, the resulting UV-curable materials exhibited excellent repairability, removability, recyclability, malleability, and shape memory property. For instance, the TMG material containing 10% of MM demonstrated a crack repair efficiency of 92.5%, a welding efficiency of tensile strength up to 171.8%, a recycling efficiency of tensile strength up to 404.3%, and a shape fixity ratio of 98.2%.