Effect of ChCl:Glycolic Acid Molar Ratio and Plant Extract Incorporation on the Structure–Property Relationships of Chitosan Active Packaging Films

The influence of choline chloride:glycolic acid (ChCl:GA) stoichiometry and plant extract incorporation on the properties of chitosan-based active packaging films was investigated. A deep eutectic solvent with a ChCl:GA molar ratio of 1:2 (DES_GA2) was used both as a chitosan plasticizer and an extraction medium for neem and hawthorn compounds. Films containing 44–70 wt% DES_GA2 were characterized to establish composition–structure–property relationships. The 50 wt% formulation showed a favorable balance between mechanical flexibility and water vapor barrier performance and was selected for plant extract incorporation. Neem extract showed higher radical-scavenging activity than hawthorn despite its lower total phenolic content. Extract incorporation enhanced UV shielding and reduced water vapor permeability, with the hawthorn-containing film showing an approximately 41% reduction in WVP. Extract-containing films retained antioxidant functionality and showed antibacterial activity against Escherichia coli. Comparison with the previously investigated ChCl 1:3 system revealed stoichiometry-dependent behavior. At 50 wt% NaDES, increasing the ChCl:GA molar ratio to 1:2 increased elongation at break from 90.5% to 120.1% and reduced Young’s modulus from 131.0 to 48.0 MPa. Comparison of neem-loaded films based on different NaDES systems further demonstrated the influence of the NaDES composition. These results identify the NaDES composition and botanical source as relevant formulation variables for tailoring CS–NaDES active packaging films.