Effect of coating process on the properties of multi-walled carbon nanotubes/waterborne polyurethane anticorrosive and conductive coating

A thicker layer of multi-walled carbon nanotubes (MWCNTs)/waterborne polyurethane (WPU) anticorrosive and conductive coating was respectively prepared on the Q235 steel substrate by brushing (Br) and electrostatic spraying (ES) in this work. The effect of coating process on the dispersion of the MWCNTs and the electrical conductivity, corrosion resistance, and bond strength of the coating was investigated. It was shown that the coating prepared by ES (ES coating) had a smooth surface, few defects and evenly dispersed MWCNTs. The coating prepared by Br (Br coating) had a rough surface, some defects and obviously agglomerated MWCNTs. The electrical conductivity, corrosion resistance, and bond strength of the ES coating were higher than those of the Br coating with the same MWCNT content. As the MWCNT content increased, the electrical conductivity of the ES coating increased, however, its corrosion resistance and bond strength first increased and then decreased. The resistivity of ES 0.3 wt% MWCNTs/WPU coating (12808.4 Ω·m) met the standard requirement of the conductive coating. Its corrosion rate was 3.50×10-5 mm/a immersed in 3.5 wt% NaCl solution. Its bond strength to the Q235 steel substrate was higher than that of ES pure WPU coating. As the MWCNT content increased, the electrical conductivity of the Br coating increased, however, its corrosion resistance and bond strength decreased. When the MWCNT content was 0.6 wt%, the Br coating would conduct electricity. Its corrosion rate was 5.24×10-2 mm/a.