Water resistance and corrosion protection properties of waterborne polyurethane coating enhanced by montmorillonite modified with Ce3+

Abstract

In this study, waterborne coatings containing modified montmorillonites were investigated to enhance water resistance and corrosion protection on steel substrates. It is considered to use Ce3+ for substituting Na+ because directly adding Na-montmorillonite (Na-Mt) into coating would cause weak water resistance of coating due to its water absorption and swelling properties. Further, in order to increase the loading capacity of montmorillonite to Ce3+, it was pretreated by chitosan (CS) and was modified by Ce3+. Subsequently, Na-Mt and two modified montmorillonites (Ce-Mt, Ce-CS-Mt) were added to the waterborne polyurethane (WPU) matrix. The modification results of montmorillonite samples were examined by XRD and SEM/EDS. The results showed that Ce3+ was successfully loaded to the montmorillonite. Chitosan pretreatment increased Ce content in montmorillonite particles and improved their dispersion stability in the WPU matrix according to the Zeta potential results. In comparison, coating containing the Ce-CS-Mt particles exhibited the lowest water absorption, which indicated that adding Ce-CS-Mt particles had a significant improvement for the water resistance of WPU coating. Results of salt spray test revealed that no obvious corrosion products were found on the composite WPU coating after 768 h of exposure to salt spray, and it showed the highest |Z|f=10mHz in EIS measurement. These results indicated that the Ce-CS-Mt particles also enhanced the corrosion protection property of WPU coating.