Biowaste extract-sourced eco-friendly inhibitive pigments in waterborne anticorrosive coatings for structural steel in marine environment

The study aimed to develop an environmentally benign inhibitive pigment for waterborne epoxy coatings based on polyphenols extracted from waste Chinese Keemun black tea leaves. The water extraction process was best fitted to follow the Elovich’s model. The extracted tea polyphenols were complexed with cerium cations to address the high water solubility issues while implementing them in coatings. Characterization results showed that the complex derived from tea polyphenols (Ce-TP) shared similar physiochemical properties with the one synthesized from commercial tannin (Ce-CT), including morphology, composition, oil absorption, and thermal stability. The solubility test revealed that Ce-TP has a higher solubility in 3.5 wt% NaCl solution, with 131 ± 3.00 mg/L of released Ce3+ ions compared to 57.6 ± 0.115 mg/L from Ce-CT. Further, both pigments were incorporated into waterborne epoxy coatings. Electrochemical impedance spectroscopy measurement on scratched coatings displayed higher charge transfer resistance compared to the reference unpigmented coating. Coatings containing Ce-CT and Ce-TP achieved inhibition efficiencies of 78.8 % and 71.6 % respectively after 5 days of immersion in 3.5 wt% NaCl solution