Nonionic Emulsifier with Lipophilic–Hydrophilic–Lipophilic Structure for Preparing Waterborne Epoxy Coatings with High Corrosion Resistance and Thermal Stability

Although the environmentally friendly waterborne epoxy (WEP) coatings exhibit high adhesion to substrates, the abundant hydrophilic groups in those coatings always bring about poor anticorrosion performance. Herein, a nonionic WEP emulsifier with the lipophilic–hydrophilic–lipophilic (L-H-L) structure has been successfully prepared to enhance the anticorrosion performance of the WEP coating. After the hydrophilic chains formed between polyethylene glycol (PEG) and hexahydrophthalic anhydride (HHPA) are terminated by epoxy resin (E51), the WEP emulsifier with the L-H-L structure can be obtained, which is then used for preparing the WEP emulsion with regular shape, small particle size, uniform distribution, and high stability by the phase inversion method. The WEP coatings of uniform thickness (110 ± 15 μm) without anticorrosion fillers can be prepared by spraying. The results of electrochemical impedance spectroscopy (EIS) show that the WEP-PEG2000-10% coating exhibits high anticorrosion performance with the low-frequency impedance value as high as 7.47 × 109 ohm·cm2 after being immersed in 3.5 wt % NaCl solution for 60 days. Actually, the L-H-L structure effectively reduces the free hydrophilic groups in the WEP coating, thus significantly improving the anticorrosion performance. This study provides new insight on developing novel inherent WEP coating with high anticorrosion performance.