Abstract
Protective coatings are efficient for preventing corrosion, but they may not be sufficient for applications in aggressive and extreme environments, such as in coastal areas that could be subjected to corrosion. Inhibitors can suppress the corrosion rate significantly, but direct addition to the coating is ineffective because the inhibitor is easily soluble in water and can reduce the effectiveness of the barrier properties of the coating. Encapsulating the inhibitor into a nanocontainer is a promising alternative that may lead to a self-healing coating technology. Halloysite nanotubes (HNT) have been successfully reported for their application in smart coatings, and they exhibit superior aerodynamic and hydrodynamic properties and better process ability than spherical capsules for the same amount of load. Therefore, nanotubes are appropriate candidates to be used as nanocontainers for inhibitors over smart coating applications. This research discusses the design of a polyurethane coating loaded with modified halloysite nanotubes for corrosion protection of steel. Halloysite nanotubes were first functionalized using aminopropyltriethoxysilane (APTES) to improve their dispersion in the polyurethane matrix. The modified halloysite nanotubes were then loaded with the corrosion inhibitor 2-mercaptobenzimidazole (IMZ). The loaded nanotubes were incorporated into polyurethane coatings. Various characterization techniques were used to confirm the successful modification and loading of the halloysite nanotubes. The distribution of particles in the matrix was investigated by Transmission Electron Microscopy (TEM) test. The modified nanotubes showed better dispersion in the polyurethane coating, which improved the coating's barrier properties and corrosion resistance. Electrochemical Impedance Spectroscopy (EIS) and salt spray tests showed that the polyurethane coating containing the loaded and modified halloysite nanotubes exhibited the highest resistance to corrosion. The adhesion strength of the coating was also improved after immersion in a saline solution, particularly for the coating with modified and loaded halloysite nanotubes. In summary, the functionalization and loading of halloysite nanotubes improved their dispersion in the polyurethane coating, which in turn enhanced the coating's barrier properties, corrosion resistance, and adhesion strength, making it a promising approach for designing smart corrosion protective coatings.
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