Microwave-functionalized natural tannic acid as an anticorrosive UV-curable coating

Corrosion causes serious steel deterioration with consequent negative impacts on the environment and economy. Organic coatings are widely exploited to provide corrosion protection on low-carbon steel. However, the raw materials and preparation methods for common anticorrosive coatings are not sustainable. In this framework, the efficient microwave-assisted methacrylation of a natural polyphenolic compound, tannic acid (TA), provided a UV-curable monomer with a high degree of substitution. The produced methacrylated tannic acid (MTA) was characterized by means of 31P NMR and FTIR spectroscopies. The UV-curing of MTA by radical photopolymerization was deeply investigated via the real-time FTIR, photo-DSC, and photo-rheological analyses, confirming the high photo-reactivity of MTA with a conversion of 80 % and a gel point at 2.5 s. The UV-cured MTA showed good thermal stability and a glass transition temperature (Tg) of 133 °C. Furthermore, UV-cured MTA coating exhibited high hardness and hydrophobicity. The zeta potential measurement indicated a negatively charged surface with an isoelectric point (IEP) at pH 2.7. Finally, the good corrosion protection performance of UV-cured MTA coating on plasma pre-treated steel surface was assessed through electrochemical impedance spectroscopy.