Sulfonated graphene-reinforced waterborne cardanol epoxy coatings: Green synthesis and exceptional corrosion resistance

With the growing global emphasis on environmental protection and sustainable development, the development of environmentally friendly anti-corrosion coatings has become a significant research direction in the field of materials science. Based on the principles of green chemistry, this study successfully developed a waterborne bio-based epoxy anti-corrosion coating that combines environmental friendliness with outstanding protective performance. The coating was synthesized using cardanol-derived epoxy resin as the raw material, employing a phase inversion emulsification process, and incorporating sulfonated graphene (SG) as a nanofiller. The materials were characterized using NMR, FTIR, XRD, XPS, and SEM, while mechanical property tests, electrochemical impedance spectroscopy (EIS), and salt spray tests were conducted to evaluate the influence of SG content on the coating's comprehensive performance. Experimental results indicate that the coating system with 0.5 wt% SG exhibited improved mechanical properties and corrosion resistance compared to other formulations. The experimental results demonstrate that when the SG content is 0.5 wt%, the low-frequency impedance (|Z| 0.01 Hz ) of the coating reaches 2.96 × 10 9  Ω·cm 2 , which is one order of magnitude higher than that of the unmodified coating. Moreover, the impedance remains stable at this high level even after 720 h of EIS testing. Additionally, during the 360-h scratch salt spray test, this coating exhibits the least noticeable corrosion propagation, indicating that the coating system possesses excellent anti-corrosion performance. This study provides novel design insights and technical pathways for the development of high-performance, environmentally friendly anti-corrosion coatings.