Lignin self-assembly and auto-adhesion for hydrophobic cellulose/lignin composite film fabrication

Large amounts of lignin are produced as a by-product of paper pulping, resulting in a tremendous waste of natural resources with potential uses across various areas. To achieve the value-added utilization of agricultural waste and lignin, we developed a method for the fabrication of a lignin structure-designed hydrophobic film (LSHF) directly through solvent/anti-solvent self-assembly (acetic acid aqueous solution/n-hexane) and auto-adhesion of acetic acid lignin (AL) on the surface of a lignocellulose film (LCF). As the morphology structure revealed, the LSHF had a rough surface composed of lignin colloidal spheres, which significantly improved the water contact angle (WCA) from ~80° to ~130°. Furthermore, benefiting from the auto-adhesion of lignin, the WCA was more stable in 240 s, demonstrating that the LSHF had a lower WCA decrease (15.53 % - 25.55 % decrease) than the LCF (41.97 % - 61.11 % decrease) and the sample without auto-adhesion (100 % decrease). Simultaneously, auto-adhesion endowed the LSHF with a ~50 % increase in tensile strength. This work provides a novel strategy for the fabrication of hydrophobic cellulose/lignin composite films via lignin self-assembly and auto-adhesion.