Hydrophobic Coating of Paperboard Using Oak Wood-Derived Lignin Nanoparticles and Chitosan Composites

This study explores the potential application of lignin nanoparticles and chitosan-lignin nanoparticles (CLNs) as hydrophobic barrier coatings for paperboard. The lignin nanoparticles were initially prepared using a mixed solvent of ethanol and acetone. Their characteristics were examined via scanning electron microscopy (SEM) and dynamic light scattering, which revealed particle sizes in the range of 180-400 nm. The results indicated that the coatings with pure lignin nanoparticles failed to impart hydrophobicity to the paperboard, whereas the CLN coatings significantly enhanced hydrophobicity and reduced water absorption. The water contact angle increased from 109° to over 128° after the first CLN coating, remained at 127° with the second and third coating layers, and was maintained at 119° with four layers. Multilayer coatings were applied to improve barrier performance; however, no further enhancement in hydrophobicity was observed. The CLN-coated paper exhibited a significantly improved surface smoothness, as confirmed by SEM. The results indicate that a single-layer CLN coating is effective for imparting water-barrier properties to paperboard. In contrast, the coating with pure lignin nanoparticles resulted in cracked surfaces and inconsistent coating thicknesses.