Enhancing the water resistance and functional properties of chitosan-based films using a hydrophobic deep eutectic solvent

To enhance the mechanical properties and water resistance of chitosan (CS) films while imparting additional functionalities, this study incorporated a hydrophobic deep eutectic solvent (DES) composed of menthol and pyruvic acid into the CS matrix. At an optimal DES content of 15 %, compared to pure CS films, the elongation at break increased by 77 %, while swelling degree and solubility decreased by 94.44 % and 60.71 %, respectively. The lowest water vapor permeability (11.55 × 10 −11  g·m −1 ·s −1 ·Pa −1 ) demonstrated enhanced moisture barrier properties. These improvements were attributed to the synergistic effects of hydrogen bonding and ionic crosslinking, reinforcing the network structure and restricting water penetration while maintaining molecular mobility. The films also exhibited excellent ultraviolet-shielding (ultraviolet C transmittance of 3 %) with high transparency, making them suitable for light-sensitive packaging. Additionally, they achieved complete biodegradation in soil within 10 weeks, highlighting their potential as sustainable alternatives to petroleum-based plastics. This study presents a novel approach to enhancing bio-based packaging materials through hydrophobic DES, expanding their applications in sustainable food and pharmaceutical packaging.