Dynamically Co-assembling Guaiacol Glyceryl Ether and Cellulose Nanocrystals for Iridescent Films Construction: The Visualized and Sensitive Monitoring for Food Spoilage

With the increasing demand for food safety and quality monitoring, sustainable and intelligent packaging that enables real-time, visual, and non-destructive indication of food freshness has become a key research direction. However, most existing indicators rely on synthetic dyes, which raise safety concerns and environmental issues. In this work, cholesteric cellulose nanocrystals (CNCs) served as chiral building blocks to construct the liquid–crystalline skeleton, and chitosan (Cs), xylose (Xyl), and guaiacol-glyceryl ether (GGE) were introduced to construct a multi-component composite iridescent film via evaporation-induced self-assembly. Chitosan and xylose modulate the internal hydrogen-bonding network, while GGE acts as a co-assembly regulator to endow the film with stimulus-responsive optical evolution. The microstructure, mechanical properties, thermal stability, and pH-responsive behavior were systematically investigated. The optimal formulation achieved a tensile strength of up to ∼5.7 MPa and a toughness of ∼44 MJ/m3, which were 4.5 MPa and 42 MJ/m3 higher than those of pure CNC films. Meanwhile, its peak thermal decomposition temperature increased by around 40 °C relative to pure CNC films. The CXCG-4 film exhibited distinct, reversible pH-responsive iridescent color changes from orange to deep red (ΔE ≈ 23.3), enabling real-time visual monitoring of grape freshness. In an 8-day grape storage test at 25 °C, the CXCG-4 group retained the highest soluble solids content (12.8%) and ascorbic acid content (3.0 mg/100 g), with the lowest weight loss (24.6%), confirming its superior comprehensive performance. Unlike traditional CNC-based films, this work achieved responsive color variation relying on multi-component co-assembly rather than extrinsic dyes. The present dye-free, green, and degradable structural color film may provide a promising strategy for intelligent food packaging applications.