Marine Algae (Caulerpa lentillifera) Extract as a Green Corrosion Inhibitor in Epoxy Coatings

Corrosion poses a serious threat to marine structures, leading to rapid degradation of metal components through their interaction with aggressive environments. One effective strategy to mitigate corrosion is the use of inhibitors incorporated into protective coatings. This study investigates the anticorrosive properties of a green inhibitor derived from sea grapes (Caulerpa lentillifera), a marine ulvophyte algae commonly found in the Indo-Pacific. Extracts of sea grapes were incorporated into epoxy resin coatings at concentrations of 0%, 4%, 8%, and 12%, and applied to mild steel specimens immersed in artificial seawater. Corrosion performance was evaluated using weight loss measurements, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The maximum extract concentration (12%) resulted in the highest protection, achieving approximately 70% inhibition efficiency via weight-loss measurements and 64% via EIS, compared to the uninhibited control. This formulation exhibited the largest impedance semicircle in the Nyquist plots and a smooth, defect-free surface under SEM analysis. These findings highlight the role of adsorption and film formation in enhancing protection. In conclusion, epoxy coatings modified with 12% sea grapes extract provide superior corrosion resistance, offering an eco-friendly and effective solution for marine applications.