Improved Corrosion Protection of Acrylic Waterborne Coating by Doping with Microencapsulated Corrosion Inhibitors

Herein, a waterborne acrylic coating doped with pH sensitive colophony microcapsules containing corrosion inhibitors was studied on carbon steel plates. The changes in the physical properties of the coatings were studied. The microcapsule coating specimens maintained more noble Ecorr values compared to the control in deionized water and simulated concrete pore solutions with −513 and −531 mVSCE, respectively. Additionally, the microcapsule polarization results for both pH 12.6 and 6.2 electrolyte solutions showed lower icorr values of 1.20 × 10−6 and 3.24 × 10−6 A·cm−2, respectively, compared to the control sample (1.15 × 10−5 and 4.21 × 10−5 A·cm−2). Therefore, the microcapsule coating provided more protection from chloride attack on the substrate as well as the deleterious effects of low pH on carbon steel. The electrochemical impedance spectroscopy analysis corroborated the DC polarization results, showing increased corrosion resistance for the microcapsule coated specimens compared to the control. Moreover, the Rpore and Rct are much higher than the control, indicating the protection of the inhibitors. The Ceff,dl also shows lower values for the microcapsule coating than the control, showing a more protective and less doped double layer.