Development of waterborne anticorrosive coatings by the incorporation of coumarate based corrosion inhibitors and phosphate functionalization

Waterborne coatings are more industrially appealing for corrosion protection due to their low toxicity when compared to traditional solvent based coatings. In waterborne latex systems, the presence of surfactants is crucial, which can nevertheless contribute later to a poor performance of the final films in terms of barrier protection. This can be avoided by the use of polymerizable surfactants covalently bonded to the polymeric chains. In this work, particles of a latex loaded with an organic corrosion inhibitor, methoxy p-coumaric acid (H1), are further functionalized by the incorporation of a polymerizable surfactant, Sipomer® PAM-200 (SIP), by semibatch emulsion polymerization. The proposed system was hypothesized to ideally have higher barrier and corrosion protection properties due to the combination of H1 and SIP. However, the Electrochemical Impedance Spectroscopy results of the latexes cast on metal substrates indicate an antagonistic effect on the corrosion inhibition process rather than synergistic, as both species compete for the same moieties of the metallic surface. Thus, while the control coating with SIP (13.3 mg of SIP/g of polymer) showed impedances of 107.1–106.4 Ω and phase angles of 84–88 degrees over 24 h, the coating with H1 (3.3 mg of H1/g polymer) and SIP (13.3 mg of SIP/g of polymer) showed a less stable behavior with changes in impedances with time from 107.1 to 105.5 Ω and in phase angle from 86 to 72 degrees. The production of a bi-layer system avoids this antagonistic effect.