Sustainable and Robust Cellulose-Based Core–Shell Hydrogels Recycled from Waste Cotton Fabrics as High-Performance Food Coolants

Ideal temperature condition is one of the essential determinants that critically impact the quality of food products. Conventional water-based ice cubes present challenges from meltwater being breeding grounds for microorganisms and heightening the risk for cross-contamination. Hereby, the presented cellulose-based hydrogels crosslinked by epichlorohydrin are dip-coated with alginate/calcium chloride to form a core–shell structure for achieving the critical benchmarks of an ideal food coolant with limited meltwater production, high-water retention capacity, and high mechanical strength. The structures and properties of the hydrogels before and after freeze–thaw cycles are characterized by scanning electron microscopy, compressive test, water retention test, and differential scanning calorimetry. All formulated hydrogels demonstrate promising compressive strength, latent heat of fusion, and water retention properties. Notably, the C2A10Cl hydrogel exhibits a maximum compressive strength of 144.7 kPa and high latent heat of fusion of 272.5 J g^–1, which is better than previously reported sustainable hydrogel coolants. Furthermore, comparison studies reveal that the cellulose-based hydrogels demonstrate a similar thawing pattern to conventional ice cubes but without the generation of any meltwater. The temperature of blueberries can be cooled down from 22 to 3.9 °C in 32 min by the hydrogels and in 26 min by ice cubes, respectively.