High-barrier and antibacterial polyvinyl alcohol/chitosan composite films reinforced by deep eutectic solvent-modified cellulose nanofibers for grape preservation.

Abstract

Deep eutectic solvents (DES) demonstrate unique advantages as green media in the modification and preparation of cellulose nanofibers. In this work, uniformly dispersed carboxylated cellulose nanofibers (DCNF) with enhanced surface charge and improved polymer compatibility were successfully prepared from microcrystalline cellulose via a DES pretreatment coupled with ultrasonication. The prepared DCNF were then incorporated into multifunctional composite films with polyvinyl alcohol (PVA) and chitosan (CS). Systematic evaluation showed that the optimal composite (PCDCNF3, containing 1.5 wt% DCNF) possessed a tensile strength of 17.5 MPa (133% higher than pure PVA film), along with significantly improved thermal stability and outstanding barrier performance against water vapor, oxygen, and carbon dioxide. Moreover, the film exhibited strong antibacterial activity, inhibiting E. coli and S. aureus by 93.06 ± 1.10% and 89.00 ± 1.35%, respectively, owing to a synergistic effect between CS and DCNF predominantly through enhanced electrostatic attraction and hydrogen bonding. Density functional theory calculations revealed that the enhanced properties originated from intensive hydrogen-bonding and electrostatic interactions, particularly between carboxyl groups on DCNF and amino groups on CS, as further visualized through reduced density gradient and atoms-in-molecules analyses. In grape-preservation tests, the composite film effectively retarded weight loss, maintained firmness, and suppressed microbial decay, with fruit showing markedly better visual and textural integrity after 10 days of storage compared to controls. This work demonstrates a sustainable and rationally designed material strategy, underscoring the promise of DES-modified nanofibers for active packaging of perishable fruits.