Ambient-densified and polymer-free transparent wood film for smart food packaging window

Wood, with its inherent hierarchical structure, presents opportunities for creating eco-friendly and cost-effective alternatives to petroleum-based plastics. We introduced a top-down and polymer-free method for engineering natural balsa wood into transparent wood film, demonstrating its potential use in food packaging windows. The wood was delignified and then proceeded with 2,2,6,6-tetramethyl-1-piperidinyloxy oxidation to soften the wood structure and introduce carboxyl groups. A robust and transparent wood film was produced by drying the wood under ambient condition without the need for additional polymers or mechanical force. Curcumin was also integrated into the wood using vacuum impregnation. The functionalized wood film with curcumin (WFC) exhibited a distinguishable redness shift in alkaline conditions. We then applied the WFC as an intelligent food packaging window to sense the freshness of shrimp based on the pH-responsive color change. This study provides a simple and scalable approach for developing sustainable and smart food packaging using wood. [Display omitted] •Transparent wood film was fabricated by delignification, oxidation, and air-drying•No external polymers or mechanical forces were used in the film fabrication process•The curcumin-functionalized film enabled a smart window to monitor freshness for food packaging Biotechnology; Biomass; Materials science; Materials chemistry; Biomaterials