Self-healable corrosion-protective alkyd resin based on microencapsulated natural tung oil

This article introduces a new method in which tung oil is employed as a bio-friendly curative substance enclosed within melamine-urea-formaldehyde microcapsules. Due to the high reactivity of melamine, particle agglomeration can occur. To tackle this issue, this study focuses on optimizing the quantity of emulsifiers to achieve the best microcapsules with 15% melamine in the shell structure without particle agglomeration. The impact of melamine content and the quantity of emulsifier on the morphology of the synthesized microcapsules, the reaction yield, core content, and the hardness of the microcapsule shell were investigated. The presence of tung oil in melamine-urea-formaldehyde microcapsules was proven by Fourier transform infrared spectroscopy (FT-IR). Field emission scanning electron microscopy (FESEM) revealed the spherical morphology of the capsules with a mean diameter of 2.29 μm. UV–vis analysis and nano-indentation tests were used to evaluate the core content and the hardness of the result microcapsules, respectively. Finally, one sample, as the best microcapsule, was dispersed in an alkyd-based resin in the amount of 1, 2.5, and 5 wt% and applied on a steel substrate for its ability to prevent corrosion. The study also highlights the adverse effect of excessive capsule usage in the resin, as demonstrated by reduced resin adhesion to the substrate, according to electrochemical impedance spectroscopy (EIS) and salt spray tests. The study found that the best long-term anticorrosion properties are achieved by including 1 wt% of microcapsules in an alkyd resin.