A Sustainable and Room Temperature Curable Sol–Gel Formulation for the Preparation of Corrosion Resistant Hybrid Coatings Cross-Linked with Lignin

This work presents a new sustainable hybrid protective coating obtained by the direct incorporation of modified lignin dissolved in a natural deep eutectic solvent (NADES) into a sol–gel formulation based on a mixture of organosilanes and zirconium alkoxides. Viscosity measurements showed that the presence of lignin improves the shelf life of the initial hybrid formulation. Hybrid coatings with 0% and 3% (w/w) lignin were prepared by dip-coating on Al2024. The presence of lignin lowers the curing temperature and allows preparation of anticorrosion coatings even at room temperature. This was confirmed by FTIR analyses where the cross-linking density in the lignin containing coatings cured at room temperature is comparable to the thermally cured coatings. The formed coatings are homogeneous, defect-free, and hydrophobic. Regarding the electrochemical behavior of the coatings, room temperature cured 3 wt % lignin containing coatings on aluminum surfaces show the best anticorrosion performance even if they are thinner than the lignin-free coatings. Summarizing, the results obtained in this work open the possibility of producing sustainable protective coatings by taking advantage of using natural resources, reusing industrial paper making byproducts such as lignin, and using a room temperature curing process to obtain the protective coatings.