Bio-Based Dual-Layer UV-Cured Oil- and Water-Resistant Paper Coating for Food Packaging Applications

Fluorine-free paper coatings with water- and oil-resistance properties have gained considerable attention for sustainable food packaging applications. In this study, a dual-layer coating based on chitosan (Chi) and acrylated epoxidized soybean oil (AESO), both derived from renewable and natural resources, was applied to kraft paper. The ultraviolet-cured AESO top layer formed a dense crosslinking network, while the Chi interlayer promoted strong interfacial adhesion with the kraft paper through hydrogen bonding, effectively restricting fluid penetration. The Chi/AESO₄₀/kraft paper showed markedly enhanced water repellency and oil resistance, with a reduced Cobb₆₀₀ value of 16 g m^-2 and kit rating of 12. Thermogravimetric analysis demonstrated improved thermal stability, and mechanical testing results revealed enhanced packaging-relevant strength, with the tensile strength increasing from 33 to 40 MPa and tensile index increasing from 45 to 60 kPa·m² g^-1; furthermore, the burst strength and index improved from 260 to 330 kPa and from 3.2 to 4.0 kPa·m² g^-1, respectively. Food contact tests conducted using French fries confirmed the effective barrier performance of the Chi/AESO/kraft paper, highlighting its potential for use in sustainable paper-based food packaging applications.