Performance of red grape pomace extract as a bio-based corrosion inhibitor in primer to protect steel

This research evaluates the use of red grape pomace extract (GPE) as a sustainable and eco-friendly alternative for the corrosion protection of steel in solution and in wash primer, being this last application a novelty for the use of plants extract. The GPE was characterized by its total phenolic content, antioxidant capacity, and phenolic profile, identifying syringic acid and (-)-gallocatechin as the most abundant compounds. Electrochemical tests in a 0.17 M NaCl solution revealed that the addition of GPE increased the polarization resistance of the steel, with an inhibitory efficiency of 92%. Scanning electron microscopy (SEM) confirmed that the extract promotes the formation of a less porous protective film through the adsorption of organic compounds. Subsequently, GPE was incorporated into polyvinyl butyral wash primers (pTO), exhibiting excellent dry adhesion to the substrate. Although traditional exposure tests in salt spray and humidity chambers showed that pTO provided moderate protection, electrochemical impedance spectroscopy (EIS) demonstrated that the pTO primer surpassed the protective behavior of traditional zinc tetroxychromate primers (pZn) by showing higher polarization resistance and lower corrosion currents. The reduction of the corrosion current maybe due to the organic film formed on the substrate, a typical mechanism of metal protection by polyphenols. The results suggest that winery by-products are effective "green" inhibitors that can replace toxic substances or used as additives in primer formulations, contributing to the circular bioeconomy of agricultural products.