Surface and interface characteristics of hydrophobic lignin derivatives in solvents and films

Lignin is an abundant macromolecule available in large quantities in the world, but it is under-utilized. In this study, lignin was modified via methylation and grafting with dodecyl glycidyl ether (DGE), and films containing these lignin derivatives were generated following different routes and using solvents (water, ammonium hydroxide, and dimethylformamide). The impact of the solvent type, coating method, and temperature on the characteristics of the prepared films was studied using contact angle (sessile drop experiment), scanning electron microscopy, and Turbiscan stability index (TSI) analyses. Methylation and the subsequent DGE grafting improved the hydrophobicity of lignin by blocking the phenolic active site of lignin, which improved the surface tension, contact angle, and interfacial tension of solvents containing lignin derivatives. Such alternations in the hydrophobicity of lignin substantially decreased the water uptake (90 %) of the lignin derivatives analyzed by the powder test wettability analysis. Quartz crystal microbalance (QCM) analysis revealed that the modifications were successful in reducing the dissolution of lignin derivatives in water, and exhibited the fundamental absorption behavior of water by the films. The methylated and DGE grafted lignin derivative with the highest hydrophobicity may be more attractive than other lignin derivatives to be used potentially in coating and packaging applications.