Biofriendly vegetable oil healing agents used for developing self-healing coatings: A review

Corrosion in the metallic structures has been a significant economic concern, with corrosion degradation estimated to cost between 2-5% of the gross national product of all countries each year. There have been several methods proposed and deployed to reduce and mitigate corrosion damage. Among the various approaches, applying an organic coating to cover the surface of the metallic structure has risen to prominence due to their effectiveness, cost efficiency, and the relatively benign environmental impacts associated with their use. However, the main drawback related to the use of such organic coatings is their sensitivity to aggressive environments, which damages the coatings and compromises their protective performance. Self-healing coatings, part of an advancing field of polymer science, has shown remarkable development over the recent number of years and demonstrated great promise in extending the service life, reducing maintenance costs, thereby improving the durability and reliability of conventional protective organic coatings over metallic structures. Of the strategies used to imbue self-healing capabilities in the next generation of organic coating materials, the incorporation of healing agents has been widely acknowledged to be the most applicable approach to realizing autonomous self-healing performance. In particular, the deployment of vegetable oils as healing agents has received considerable attention due to their ecologically-safe nature. Therefore, a comprehensive review of the developments in the scientific literature on bio-friendly vegetable oils as healing agents is presented in this paper. The paper will first describe and define self-healing in polymeric materials, then subsequently delve into the introduction and classification of the various vegetable oils and their healing applications. The methodologies for achieving the encapsulation of healing agents in various structures such as nano/microcapsules are then reviewed, with the healing performances of the various healing agents presented and evaluated. Lastly, at the conclusion of the review article, the challenges of using vegetable oils as healing agents will be discussed, along with a brief perspective on the future of vegetable oil based self-healing in scalable industrial implementation.