A mussel-inspired lignin micro-nanospheres/epoxy composite coating with superhydrophobicity, ultraviolet resistance, and photothermal conversion performance for excellent corrosion control

Abstract

Developing epoxy (EP) anti-corrosion coatings with ultraviolet (UV) resistance by incorporating natural fillers remains a significant challenge. Herein, a functionalized biomass filler (LMNS@PDA/ODE) is synthesized via sequentially grafting polydopamine (PDA) and low surface energy substances (ODE) on the surface of lignin micro-nanospheres (LMNS) and further preparing a multifunctional LMNS@PDA/ODE-EP coating for corrosion protection of carbon steel. As expected, LMNS@PDA/ODE exhibits excellent dispersion stability in EP and endows the composite coating with a high adhesion strength (5.9 MPa). Benefiting from the reinforced physical barrier (a water absorption rate of 0.55 %) and superhydrophobic performance (a surface free energy of 4.65 mJ∙m⁻²), the initial impedance modulus (|Z|_{0.01 Hz}) of 2LMNS@PDA/ODE-EP coating (8.05 × 10⁸ Ω∙cm²) is significantly higher than that of EP coating (8.91 × 10⁴ Ω∙cm²) after immersing in 3.5 wt% NaCl solution for 50 days. In addition, 2LMNS@PDA/ODE-EP coating exhibits excellent UV-blocking properties, as demonstrated by the high |Z|_{0.01 Hz} of 4.86 × 10⁹ Ω∙cm², as well as the low gloss loss (11.0 %) and minimal color difference (2.2). Furthermore, the superhydrophobicity of the 2LMNS@PDA/ODE-EP coating is capable of restoration after simulating sunlight exposure for 10 min under 200 mW·cm⁻² owing to the efficient photothermal conversion performance. Therefore, this work provides a multifunctional coating for long-term corrosion protection, facilitating the value-added utilization of lignin and the development of environmentally friendly coatings.