Robust polyvinyl alcohol based multifunctional films with pH-responsive via electrostatic self-assembly of TOCNF and quaternary ammonium chitosan by loading apple polyphenol.

Polyvinyl alcohol (PVA)-based materials with pH-responsive colorimetric properties have attracted increasing attention for sustainable and intelligent packaging applications. Although numerous studies have reported PVA-based pH-responsive packaging films with antioxidant and antimicrobial activities, further optimization is still required in achieving a balanced integration of multiple functionalities, including antioxidant performance, antimicrobial efficiency, and long-term structural stability. Thus, a new kind of multifunctional PVA based composite film was fabricated via direct solvent casting combined with ultrasonication by mixing PVA with TEMPO-oxidized nanocellulose (TOCNF), quaternary ammonium chitosan (QCS), and apple polyphenol (APP). The effects of APP and QCS incorporation on the structural, mechanical, barrier, biological, and intelligent-responsive properties of the films were systematically investigated. The optimized PT-1.5(QA) film exhibited a balanced mechanical performance, with a tensile strength of approximately 8.1 MPa and an elongation at break of approximately 243%, attributed to the formation of intermolecularly associated polymer networks. Meanwhile, APP incorporation significantly enhanced the antioxidant and UV-shielding properties, achieving approximately 92.8% DPPH and 96.5% ABTS radical scavenging activities. Furthermore, the composite film exhibited enhanced barrier properties, strong antibacterial activity against Escherichia coli and Staphylococcus aureus, and distinct pH-responsive color changes over a broad pH range (1-12). Cytotoxicity evaluation confirmed good in vitro biocompatibility. Importantly, the composite film effectively delayed postharvest senescence and quality deterioration of litchi fruit, while maintaining favorable biodegradability. These findings highlight the potential of TOCNF/QCS/APP/PVA films as sustainable active and intelligent packaging materials for food preservation.