Corrosion inhibition of a polyurethane-based coating defect with lanthanum or imidazolinium 4-hydroxycinnamate

The advantageous properties of steel result in it being in high demand for structural applications. Unfortunately, it does have some limitations, such as susceptibility towards corrosion and, depending on the service conditions, microbiologically influenced corrosion. A simple strategy for protecting steel from such detrimental environments is through the incorporation of corrosion inhibitors into the coating system that can combat both corrosion and the microbial attachment that exacerbates the degradation. This work examines the effectiveness of combining a proven corrosion inhibitor for steel, lanthanum 4-hydroxycinnamate (La(4OHCin)3), with a candidate microbial inhibitor, imidazolinium 4-hydroxycinnamate (IMI-4OHCin), into a polyurethane-based coating to stifle corrosion on mild steel. Artificial defects have been made on each sample and exposed to a salt spray environment to induce corrosion attack. The coatings are visually compared and subsequently characterized with methods such as SEM/EDS. Of the materials tested, La(4OHCin)3 demonstrated significant inhibition of corrosion at the defect site and potentially provides evidence for inhibitor migration towards exposed steel surfaces. The IMI-4OHCin inhibitor appeared to be detrimental to the durability of the polyurethane coating. The La+IMI mixture demonstrated a relatively higher adhesion to the steel substrate compared to the coatings containing each inhibitor separately.