Water resistance and corrosion protection properties of water-borne polyurethane coating

In the study, water-borne coatings containing modified montmorillonites were investigated to enhance water resistance and corrosion protection on steel substrates.

It has been 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 water-borne polyurethane (WPU) matrix. The modification results of montmorillonite samples were examined by XRD and SEM/EDS.

Significant improvement for the water resistance

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. 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. These results indicated that the Ce-CS-Mt particles also enhanced the corrosion protection property of WPU coating.

The study has been published in Progress in Organic Coatings, Volume 136.

Event tip

The EC Technology Forum | Water-based Coatings on 10 March will look at the whole market, showing isocyanates that enable faster drying of wood coatings, additives for easier production and application, and also how machine manufacturers can help with the transition to water-based systems.