Study on the self-lubrication and corrosion resistance of the epoxy coatings containing microcapsules with poly urea-formaldehyde/ nanozirconia as nanocomposite shell

<h2>Abstract</h2> Realizing the healing agent in the self-healing polymeric coatings is the most important factor, which can directly influence on the self-healing ability. Considering this viewpoint, nanocomposite shell was used for synthesizing microcapsules containing linseed oil to create bi-functional (self-healing and self-lubrication) features in the epoxy coatings. To do so, the hybrid microcapsules made of poly urea-formaldehyde (PUF)/ZrO₂ nanoparticles were created through in-situ polymerization. After that, a self-healing epoxy coating, filled with 5 wt% linseed oil-loaded microcapsules were applied to a steel substrate. The coatings' self-lubrication and corrosion resistance were evaluated using pin-on-disk and polarization tests. Additionally, the structure of the microcapsules and the worn samples were examined using images obtained by field emission scanning electron microscopy (FESEM). The study found that the size and distribution of the microcapsules depended on the ZrO₂ nanoparticles content in their shell. Increasing the ZrO₂ concentration improved the uniformity of the microcapsules' size. The optimal ZrO₂ nanoparticle content in the microcapsule shell was determined to be 3 wt%. Friction and wear tests demonstrated that incorporating microcapsules with PUF/3 wt% ZrO₂ nanoparticles shell reduced the friction coefficient and wear rate of the epoxy coating by 82 % and 93 %, respectively. The self-healing coatings that were scratched demonstrated remarkable abilities to heal and prevent corrosion in microcracks. Polarization tests revealed significant enhancements in the corrosion resistance of steel substrates with the application of the scratched self-healing coatings, reducing the corrosion current density by approximately 98 % through the incorporation of microcapsules with PUF/3 wt% ZrO₂ nanoparticles shell.