Investigation on the Corrosion Resistance of Polyurethane-Urea Hybrid Coatings Using EIS

Low VOC coatings are becoming increasingly important in the paint industry due to environment concerns. The aim of this work was to develop two formulations of polyurethane-urea hybrid coatings with zero VOC content. The main difference between the formulations was the NCO/OH ratio. This ratio influences both flexiibility and crosslinking density of the coatings. The values employed for the coatings were 1.0 and 2.0. The corrosion resistance of these materials was evaluated using electrochemical impedance spectroscopy (EIS). The electrochemical behavior was accompanied during 60 days of immersion in 3,5wt% NaCl solution at room temperature. The capacitance variation of the coatings along the test was determined in order to estimate the electrolyte absorption. The results showed that the coating with higher NCO/OH ratio was less prone to water absorption and presented better corrosion resistance.