Graphene oxide enhanced aqueous epoxy composite coating derived from sustainable cardanol resource for corrosion protection

Conventional self-emulsified curing agent mainly focus on its stability, yet the contamination of raw materials are scarcely noted. Herein, a waterborne cardanol-based epoxy resin curing agent with emulsifying function was prepared by using the natural renewable biological material cardanol, and a waterborne biological epoxy resin coating was obtained by curing epoxy resin E51. The dual-functional product was synthesized by a two-process reaction (Mannich reaction and ring-opening reaction), as proved via FTIR and NMR techniques. In the curing process, the long alkyl chain in the curing agent molecule can shield the hydrophilic chain, thus improving the hydrophobicity and corrosion resistance of waterborne epoxy resin coating. With the help of this curing agent, graphene oxide (GO) is further used to improve the barrier effect of waterborne epoxy resin coating. The electrostatic interaction among curing agent, epoxy resin and GO improve the stacking dispersion and compatibility of GO in the coating. When the addition amount was 0.5 wt%, the thermal stability of the coating improved and the defects also reduced. The excellent corrosion resistance of the composite coating was verified by EIS. The results suggest that it is a potential candidate low-volatile organic compounds coatings for extending service life of metallic materials.