Fabrication of chitosan-sodium alginate/polyvinyl butyral composite layers with synergistic oleophobic-hydrophobic properties for eco-friendly water/oil-barrier paper coating

To address the inherent deficiencies in the water and oil barrier properties of paper-based packaging and the environmental risks posed by traditional coatings, this study developed a fluorine-free water/oil-barrier coating using bio-based chitosan (CHI) and sodium alginate (SA), together with polyvinyl butyral (PVB), as raw materials. A two-step modification strategy of cross-linked network construction and hydrophobic capping enhancement was employed. A dense cross-linked polysaccharide network underlayer was fabricated on the paper substrate via electrostatic interactions between CHI and SA combined with Ca 2+ -mediated crosslinking, which filled the substrate pores and imparted oil resistance. This was followed by the introduction of a PVB-based hydrophobic capping layer. The synergistic hydrogen bonding between PVB and polysaccharides significantly enhanced the coating's water resistance and structural stability. The composite coating exhibited excellent water and oil resistance, superior water vapor barrier performance, effectively improved the mechanical strength of the paper substrate, and demonstrated good tolerance to common solvents such as ethanol, hexane, and xylene. Furthermore, the excellent biodegradability of the coating was demonstrated through soil burial tests. The study presents a feasible technical solution for producing green, high-performance water/oil-barrier paper, effectively advancing the application of paper-based packaging in the food industry.