Preparation and anticorrosion performance of graphene-reinforced epoxy powder coating

Existing studies have reported that graphene can enhance the corrosion resistance of solvent-based organic coatings. However, the role of graphene in organic powder coatings remains to be obscure. In the present study, the graphene powder was prepared through liquid-phase exfoliation of graphite followed by freeze drying and the effects of graphene on structures, anticorrosion performance and adhesion strength of epoxy powder coatings were investigated. Scanning electron microscopy (SEM) demonstrated that graphene reduced surface micropores and enhanced structural compactness of the epoxy powder coatings. Electrochemical impedance spectra, Tafel polarization measurement and salt spray test indicated that a small amount (0.0125, 0.025 and 0.05 wt%) of well-dispersed graphene powder would be sufficient to effectively reinforce the anticorrosion performance of the epoxy powder coatings, especially for the coating with 0.025 wt% graphene, of which the impedance modulus maintained the highest values of nearly 107 and 105.8 Ω cm2 after immersion in 3.5 % NaCl solution for 21 and 30 days. Pull-off test confirmed that graphene enhanced the adhesion strength of coatings after salt spray test for 240 h, while the coating with 0.025 wt% graphene exhibited the highest adhesion strength up to 3.88 MPa. In addition, differential scanning calorimetry (DSC) indicated that graphene sheets could improve the thermal conductivity and promote curing reactions of epoxy powder. The mechanism for the reinforcement of epoxy powder coating by graphene has also been proposed.