Lignin-Based Bio Ionic Liquids for Enhanced Corrosion Protection of Metals

The investigation of new corrosion inhibitors based on environmentally friendly biobased derivatives is still an underexplored topic that has gained increased interest in the past years. Recent improvements in separation techniques now allow one to obtain lignin derivatives that are suitable as corrosion inhibitors for different kinds of metals. This work explores the potential of lignin-based ionic liquids (ILs) as new, sustainable corrosion inhibitors, focusing on cinnamate derivatives paired with biobased cations such as choline and methylcholine. Twelve structurally related ILs were tested in 0.01 M NaCl aqueous solutions using electrochemical techniques (potentiostatic electrochemical impedance spectroscopy and potentiodynamic polarization), as well as surface characterization methods like scanning electron microscopy, energy-dispersive X-ray spectroscopy, and optical profilometry. Among the ILs, choline methoxycoumarate and methylcholine methoxycoumarate showed the highest corrosion inhibition efficiencies (98 and 97%, respectively), and therefore, they were subsequently successfully investigated under more aggressive conditions (3.5 wt % NaCl). These results highlight the synergistic effects and structural advantages of lignin-based ILs, paving the way for their use as ecofriendly corrosion inhibitors.