Bio-based polyurethane coatings from sugarcane bagasse acetosolv lignin with enhanced anticorrosive performance

Polyurethane coatings are widely used in the anticorrosive protection of metals due to their high adhesion, durability, and chemical resistance, despite their dependence on non-renewable raw materials. In this study, acetosolv lignin from sugarcane bagasse was evaluated as a renewable polyol in the synthesis of polyurethanes for application as anticorrosive coatings. Polyurethanes containing different proportions of lignin and PEG1500 as polyols, ethylene glycol as a chain extender, and HMDI as a diisocyanate were synthesized using a two-step method and applied onto phosphated carbon steel to form coatings. The synthesis of the polyurethanes was confirmed by FTIR. Thermogravimetric analysis and adhesion testing indicated that the incorporation of lignin ranging from 25 to 75 % w/w relative to the polyol, improved the thermal stability of the polymers (>220 °C) and provided good adhesion of the coating to the substrate, respectively. In addition, an increase in glass transition temperature (Tg) and hydrophobicity of the polyurethanes was observed with increasing lignin content as a polyol. The best anticorrosive performance was obtained for coatings containing 50 and 75 % w/w lignin as a polyol, which showed an impedance modulus (|Z|) greater than 10⁷ Ω·cm² after 68 days of immersion in 3.5 % (w/v) NaCl. These results demonstrate the potential of acetosolv lignin from sugarcane bagasse as a renewable polyol to produce polyurethane anticorrosive coatings.