Lignin-Based Anticorrosion Coatings for the Protection of Aluminum Surfaces

New renewable lignin-based coatings with anticorrosion properties are presented in this work. These materials are based on the silanization of a tetrahydrofuran (THF) soluble fraction of a technical softwood kraft lignin through urethane linkages and its subsequent thermal cross-linking on metallic substrates using different cross-linking promoters. Spectroscopy analyses confirmed silanization of lignin meanwhile the thermal analyses indicated an increase of the glass transition temperature and the thermal stability after the functionalization process. The silanized (LF-S) and nonsilanized (LF) lignins were used as main materials for the preparation of thermally cross-linked coatings in the presence of different promoters, namely tetraethyl orthosilicate (TEOS) as a cocrosslinker and/or acetic acid (AcH) as a catalyst. The coatings prepared from LF-S presented improved thermal stability and hydrophobic character compared with those obtained from unmodified LF. Moreover, the adhesion strength of the coatings on aluminum increased when the cross-linker promoters were incorporated to the coating formulation. Finally, the corrosion inhibition effect of these coatings was assessed through the evaluation of the corrosion current density on aluminum, finding important improvements on the electrochemical stability of the metal. The results of this study clearly demonstrate a straightforward approach for the production of high-lignin-content coatings that may find direct industrial application in the field of corrosion prevention for metals.