Sodium alginate (SA)-based cold-chain packaging films are prone to moisture absorption, embrittlement, and structural instability under high-humidity freeze-thaw conditions. The work aims to develop food-grade sugar-based deep eutectic solvent/sodium alginate (DES/SA) anti-freezing gel films with a wax-based hydrophobic sealing layer introduced to enhance long-term freeze-thaw stability. Four sugar-based DESs were prepared to systematically evaluate their low-temperature thermal behavior and film-forming adaptability. The optimal components were screened to prepare SA-DES gel films. The failure mechanism was revealed through high-humidity moisture absorption, swelling and freeze-thaw cycle experiments. A hydrophobic beeswax-based sealing layer was constructed on the film surface to evaluate its long-term moisture resistance and freeze-thaw stability. The result showed that Pro-Tre was the optimal DES component. The resulting SA-Pro-Tre gel film maintained excellent flexibility at -30 °C, with a fracture strain approximately 30 times higher than that of pure SA films. Further investigation revealed that continuous moisture invasion induced DES dilution and exudation, disrupting the internal hydrogen bond network and leading to reduced anti-crystallization capacity and mechanical degradation. After applying the wax-based sealing layer, the surface water contact angle increased to 130.8°, and BW/SA-Pro-Tre retained 91.03% and 88.58% of its stress and strain after 30 freeze-thaw cycles, significantly outperforming the unsealed counterpart (71.8% and 75.38%). The anti-freezing performance of the SA-DES system stems from the coordinated regulation of the multiple hydrogen bond network among DES, SA and water molecules. The essence of high-humidity freeze-thaw failure is a coupling process of water invasion, DES dilution and outflow, and hydrogen bond network disruption. The synergistic strategy of "internal DES-mediated moisture regulation and external wax-based moisture blocking", offering new insights for the design and failure prevention of bio-based packaging materials in high-humidity cold-chain environments.
Key words
deep eutectic solvent /
sodium alginate /
anti-freezing gel film /
hydrophobic sealing layer /
freeze-thaw stability
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