Towards sustainable steel corrosion protection: expanding the applicability of natural hydrolyzable tannin in epoxy coatings via metal complexation
Chunping Qi, Ziyou Li, Huichao Bi, Kim Dam‐Johansen
Abstract
The study aimed to develop inhibitive pigments based on the natural biopolymer tannin through metal complexation, as an effective and eco-friendly alternative to conventional inhibitive pigments in epoxy coatings for steel protection in marine environments. Initial screening of metal cations for tannin complexation was conducted via steel immersion tests in 3.5 wt% NaCl solution. The combination of tannin with Zn2+ and Ce3+ both exhibited outstanding corrosion inhibition performance. After a 14-day immersion period, the inhibition efficiency reached 79.0% and 74.0% respectively, compared to 53.9% for pure tannin. The more uniform formation of iron-tannin complexes and the co-deposition of metal hydroxides/oxides are believed to contribute to a synergistic effect, as confirmed by ATR-FTIR and SEM-EDS analysis. Further, considering both inhibition efficiency and eco-friendliness, the cerium(III)-tannin complex (CeTA) pigment was successfully synthesized and incorporated into anticorrosive epoxy coatings. Salt spray exposure and electrochemical impedance spectroscopy (EIS) measurements consistently demonstrated improved pigment compatibility with the epoxy matrix and reinforced coating anticorrosive performance.