Effect of the gradient distribution of multiwalled carbon nanotubes on the bond strength and corrosion resistance of waterborne polyurethane conductive nanocomposites

To make the conductive anticorrosive coating containing low conductive filler content meet the requirements for antistatic applications, and improve the bond strength and anticorrosive ability of the coating, a series of eco-friendly waterborne polyurethane (WPU) graded conductive nanocomposites with low contents of multiwalled carbon nanotubes (MWCNTs) were prepared by two special multilayer coating processes on the basis of the gradient distribution of MWCNTs. Effects of the gradient distribution and the content of the MWCNT on the electrical conductivity, bond strength, and corrosion resistance of the nanocomposites were investigated. The graded conductive nanocomposites prepared by casting the upperlayer coating on the uncured underlayer coating can conduct electricity when the MWCNT content in the underlayer coating was only 0.4 wt%. The coating resistance of the obtained graded conductive nanocomposites exhibiting good properties of adhesion and anticorrosion met the requirements for antistatic. SEM tests showed that the high MWCNT content in the upperlayer coating could penetrate into the underlayer coating, leading to that the MWCNTs formed a gradient distribution of “low content–high content–low content–high content” in the whole coating. As the MWCNT content in the upperlayer coating increased, the dispersion of the MWCNTs in the whole coating became uniform.