Green synthesis of graphene with the assistance of modified lignin and its application in anticorrosive waterborne epoxy coatings

In this work, the lignin, undervalued sustainable biomaterials, was modified and utilized to produce low-defect graphene from pristine graphite by exfoliation in water. The non-covalently interactions between modified lignin (lignin-OH) and graphene were confirmed to improve the dispersion and stability of the nanocomposites. As an additive, the lignin-OH/graphene dispersion was added into waterborne epoxy resin to enhance anticorrosion of the nanocomposites. By the analysis of the electrochemical impedance spectroscopy (EIS), the nanocomposite coatings displayed higher impedance value at low frequency and bigger phase angle at high frequency with respect to the pure epoxy coatings. By fitting with equivalent circuits, the coating resistance (R-c) and charge-transfer resistance (R-ct) of 0.5% lignin-OH/graphene/WEP coatings are one or two orders of magnitude higher than that of pure epoxy coatings. The better anticorrosion effect should be attributed to well-dispersed graphene with the assistance of lignin-OH which generated the labyrinth effect of corrosive route. Therefore, this work provides a new way to enhance anticorrosive ability of waterborne epoxy resin, and it also gives a noteworthy strategy for development of biomaterial lignin's high value-added applications.