Fabrication of Chia oil encapsulated biobased poly (Urea-formaldehyde) microcapsules for corrosion-resistant coatings

In the present study, Chia oil (CO) was successfully encapsulated within poly(urea-formaldehyde) (PUF) shells via in situ polymerization, and the resulting microcapsules were incorporated into epoxy to develop sustainable microcapsule-based anticorrosive coatings. The fabricated microcapsules were characterized by optical microscopy, Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and particle size analysis to evaluate morphology, chemical composition, thermal stability, and size distribution. Successful encapsulation of chia oil within the PUF shell was confirmed by FTIR spectral analysis, while satisfactory thermal stability of the developed microcapsules under elevated temperatures was demonstrated by thermal analyses. The formation of both nano- and micro-sized capsules with relatively uniform size distribution was revealed by particle size analysis. The anticorrosive performance of microcapsule-loaded epoxy coatings was investigated through long-term immersion tests conducted in 3.5 wt% NaCl and 0.2 M HCl media using scratched mild steel panels. Improved corrosion resistance and delayed degradation behavior were exhibited by microcapsule-containing coatings compared with neat epoxy coatings. Under saline conditions, comparatively superior resistance against corrosion progression over prolonged immersion periods was demonstrated by the 3.0 wt% microcapsule-loaded coating, whereas under acidic conditions, enhanced stability and delayed coating failure were exhibited by the 7.0 wt% formulation. The improved protective behavior has been attributed to the combined effects of enhanced coating barrier properties and the potential release of encapsulated chia oil at damaged regions, which may contribute to the formation of a secondary protective layer through oxidative polymerization. However, while enhanced corrosion resistance was indicated by immersion studies, direct experimental evidence of autonomous self-healing behavior was not established in the present work; the observed performance should therefore be interpreted as improved corrosion resistance with potential healing functionality. The developed microcapsule-based coatings are demonstrated to hold promising potential as environmentally sustainable, corrosion-resistant protective coatings for metallic substrates exposed to aggressive saline and acidic environments.