Fabrication of Fluorinated Tannic Acid-Modified Waterborne Epoxy Resin Coatings and Investigation of Their Long-Term Corrosion Resistance.

Abstract

Waterborne epoxy resin (WEP) has gained attention for its low volatile organic compound (VOC) emissions, making it a key focus in eco-friendly coatings. However, its corrosion resistance still lags behind that of traditional solvent-based coatings. Tannic acid (TA), a natural polyphenolic compound, shows strong metal chelating ability and potential for corrosion protection. Yet, its high hydrophilicity limits its use in coatings. Herein, fluorinated tannic acid (F_xTA) with different degrees of fluorination was synthesized by grafting polyhexafluorobutyl acrylate (PHFBA) onto tannic acid and was introduced into the WEP matrix as a functional filler to enhance its anti-corrosion performance. Electrochemical tests demonstrated that the F₃TA filler in the F_xTA/WEP composite coatings exhibited the most superior performance. When the filling amount of F₃TA was 4.9 mL, the contact angle of the 4.9-F₃TA/WEP composite coating increased to 86.42°, and the water absorption rate decreased by approximately 52.37%. Moreover, this composite coating maintained a basic constancy in hardness and adhesion while having a tensile strength of 2.51 MPa and an elongation at break of 77.80%, demonstrating excellent mechanical properties. The electrochemical impedance modulus of the 4.9-F₃TA/WEP coating is 2.13 × 10⁸ Ω·cm², and it maintains a high value of 2.0⁷ × 10⁷ Ω·cm² even after 20 days of salt spray exposure, demonstrating its excellent corrosion resistance. This study offers novel insights into the functional modification of natural polyphenolic compounds and introduces an environmentally friendly coating system capable of providing excellent long-term corrosion protection.