Smart lignin-based polyurethane conjugated with corrosion inhibitor as bio-based anticorrosive sublayer coating

Incorporating corrosion inhibitors in the formulation of coatings can yield active coatings which are able to provide a sustained release of the corrosion inhibitor in the case of emergence of microcrack in the structure of the coating. Herein, we developed bio-based polyurethane sublayer coatings with strong anticorrosion performances. First, lignin-corrosion inhibitor (LCI) conjugate was obtained through conjugation of nicotinic acid to lignin through hydrolytically cleavable ester linkage to afford the steady release of low concentrations of corrosion inhibitor in case of the emergence of microcracks. Subsequently, solution polyaddition of LCI with diisocyanates and polypropylene glycol and coating on the stainless steel surface afford the polyurethane coatings. Coating with a thickness of 16 µm increased the E corr from − 481 mV (for bare steel) to + 187 mV and reduced both I corr and corrosion rate more than 6700 times. As an added benefit, after creating artificial cracks on the surface of the coating, the release of corrosion inhibitors gradually increased the impedance value, indicating a thin barrier layer has formed within the cracks.