Schiff's base crosslinked gelatin-dialdehyde cellulose film with gallic acid for improved water resistance and antimicrobial properties

Gelatin is a versatile biopolymer for bio-packaging, but its poor water resistance and susceptibility to deterioration limit its application. This study addresses these limitations by forming a Schiff's base through crosslinking gelatin with dialdehyde cellulose (DAC) to enhance mechanical properties and water resistance. The crosslinking degree was investigated using the ninhydrin method and, also visually identified through a yellow-brown color formation. Crosslinking increased tensile strength (TS) from 30.2 ± 1.6 MPa to 37.3 ± 3.9 MPa and improved UV barrier properties, with a 30% increase in UV-B and UV-A protection compared to the pure gelatin film. Gallic acid (GA) was incorporated at concentrations ranging from 1% to 5% to improve the antimicrobial properties and shelf life of the film. Films with GA inhibited E. coli and S. aureus and resisted fungal growth on the film for more than 20 months. Furthermore, incorporation of GA further enhanced TS, elongation of break (EBA), barrier and hydrophobic properties of the composite film. The highest tensile strength was achieved with 3% GA (49.4 ± 4.5 MPa). EBA improved with higher GA concentrations, reaching a 44% improvement at 5% GA compared to the non-GA film. Oxygen permeability dropped from 5.7 ± 0.1 to 4.3 ± 0.1 cm 3 /m 2 d 0.1 MPa, and water vapor permeability decreased from 6.7 ± 0.75 × 10 −11 to 4.2 ± 0.07 × 10 −11  g m/m 2 s Pa at 5% GA. Despite these benefits, the films remained vulnerable to high acidic conditions. This study demonstrates that Schiff's base crosslinking of gelatin with DAC, combined with GA, results in durable, antibacterial bio-based packaging films with enhanced strength and barrier properties.