Development of a curcumin-based antifouling and anticorrosion sustainable polybenzoxazine resin composite coating

Polybenzoxazine is an outstanding and highly promising resin for many advanced applications. This paper reports on a series of sustainable high-performance coatings made of benzoxazine monomer synthesized via the Mannich reaction of curcumin, 3-aminopropyltriethoxysilane and paraformaldehyde. This curcumin-based polybenzoxazine resin was experimentally demonstrated for the first time to be an effective barrier layer, which could evidently reduce the corrosion rate of the substrate metal, and significantly resist the fouling attachment. In addition, it was found that an increased content of PEG in the resin could further improve the antifouling performance of the coating. Molecular dynamics (MD) simulations suggested that a carefully selected density of PEG molecules in the polybenzoxazine framework could critically affect the hydration layer and the interaction energy. The benzoxazine monomer and polymer were characterized by Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), proton nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopy, different scanning calorimetry (DSC), and thermogravimetric technique. The anticorrosion and antifouling of the developed polybenzoxazine resins were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and attachment of protein, bacteria and microalgae. The results showed that the polybenzoxazine coatings (PCB or PCBG-X) performed excellently in anticorrosion even after long-term exposure in corrosive environments, and some of the polybenzoxazine coatings, like PCBG-10 and PCBG-15, possessed a superior antifouling capacity. To simultaneously enhance the anticorrosion and antifouling, a double layer coating system was designed using the PCB resin as the sub-layer and the PCBG-10 or PCBG-15 film as the uplayer. The great long-term corrosion resistance of the coatings was confirmed by electrochemical measurements in salt immersion and salt-spray. It is expected that this new design of the promising polybenzoxazine resin coating system will find wide applications in marine industry and relevant fields.