Enhancing mechanical and anti-corrosion properties of waterborne epoxy coatings with (+)-catechin and tea polyphenol copolymerized nanosheets

Mild steels are essential in marine engineering, but their susceptibility to electrochemical corrosion in high-salt, high-humidity environments poses significant challenges. With the functional fillers addressing hydrophilic nature and enhancing barrier integrity, waterborne epoxy (WEP) coatings have emerged as a promising solution. Tea polyphenols (TPs) and (+)-catechins as bio-derived fillers offer unique advantages, including antioxidative properties, excellent compatibility with epoxy resins, and alignment with circular economy principles. However, their particulate monomers fail to establish durable barriers due to discontinuous passivation layers and weak resin interactions. Herein, we design two-dimensional copolymerized nanosheets (CTPNS) derived from TPs and (+)-catechins via Mn(II)-catalyzed oxidative polymerization to optimize their application capability. The optimized CTPNS_0.5/WEP composite coating demonstrated exceptional anti-corrosion performance, retaining a low-frequency impedance modulus of 2.25 × 10¹⁰ Ω·cm² after 70 days of immersion in NaCl solution, which is four orders of magnitude higher than pure WEP. Remarkably, mechanical performances are simultaneously elevated, outperforming conventional biocomposites. Mechanistic studies reveal a dual protection mechanism: CTPNS forms self-passivating Fe-O coordination layers on substrates, while its aligned nanosheet structure prolongs the diffusion pathways of corrosive species, collectively ensuring durable barrier performance. By pioneering bio-derived 2D nanosheets as dual-functional additives, this work establishes an eco-conscious paradigm for anti-corrosion coatings, paving the way for the use of renewable biomaterials in anti-corrosion technologies.