Encapsulation of Linseed Oil and Tung Oil in urea-formaldehyde shells was performed using in-situ polymerization technique. Optimization of process parameters for preparation of microcapsules were carried out using calculated amounts of oil and urea-formaldehyde, that were subjected to formation of spherical microcapsules of 25-45 µm size, that depend on the reaction time and stirring speed. The microcapsules thus prepared were analyzed using optical microscopy (OM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), for ensuring the encapsulation of oil in the thin shells of urea-formaldehyde. Thin film self-healing coatings with uniform and quick self-healing ability were achieved with microcapsules at an optimized concentration of 3 wt%. The anti-corrosive performance was evaluated using immersion test and electrochemical impedance spectroscopy (EIS).
Application of organic coatings is the most economical and common approach to combat corrosion. However, being the outermost layer on the component, these coatings are prone to suffer micro/nano level damages in service, either due to mechanical or chemical actions, failing the coating to last the estimated service life. These issues can be addressed, by using coatings that are tailored to have active functionality to respond against such damages and heal the damages autonomously. Such coatings are generally termed as self-healing coatings [1-8].
Self-healing coatings mimic natural healing process, similar to the healing of damaged skin . Therefore, self-healing coatings are very attractive as they can assure durability of the coated components even after damages in the coating due to chemical or mechanical reasons. Basic principle of self-healing coating is to heal the damaged area utilizing a buffer stock of either the raw materials, or quick healing materials. Three main methods of achieving barrier restoration in self –healing coatings are; (i) intrinsic self-healing; (ii) capsule based self-healing and (iii) vascular self-healing . Encapsulation of reactive materials and incorporating them in a suitable coating system is the most versatile method of self-healing coatings. Also, considerable literature is available on the synthesis methods and parameter optimization for encapsulation. There are different techniques available for encapsulation of reactive materials, which can be classified on the basis of a wall formation mechanism as reported by Pascault et al. .