Enhanced UV resistance and antioxidant efficacy of chitosan films through synergistic Schiff base crosslinking of dialdehyde cellulose and gallic acid

Chitosan is a biodegradable, renewable, and biocompatible polymer with promising potential for food packaging. However, its practical use is limited by poor mechanical strength and insufficient antioxidant capacity. This study addressed these drawbacks by introducing dialdehyde cellulose (DAC) as a crosslinker and gallic acid (GA) as a bioactive additive to prepare chitosan/DAC/GA composite films. Varying the GA content (0–20 %, w /w) significantly enhanced the mechanical strength, UV barrier properties, and antioxidant activity. The composite film with 10 % GA (CDG-5) achieved a tensile strength of 32.31 MPa, a 17 % increase over pure chitosan film, and showed near-complete UV-blocking properties, with UV transmittance <0.1 % at wavelengths below 400 nm. Furthermore, the film exhibited high radical antioxidant activity (94.97 % DPPH and 92.31 % ABTS) and significant antibacterial efficacy, reducing Escherichia coli and Staphylococcus aureus colony counts by 86.82 % and 86.52 %, respectively. GA incorporation lowered moisture content, water solubility, and swelling ratio while increasing opacity. These results demonstrate the synergistic effects of DAC and GA in improving the structural and functional properties of chitosan films, supporting their use as active packaging materials in food and pharmaceutical applications.