High-Efficiency and Recyclable Green Molten Salt Hydrate Solvent for Cellulose Hydrogels with High Conductivity and Freeze Tolerance

Cellulose, as a sustainable biomass material, has aroused wide attention and has been extensively employed in functional biomaterials. However, due to the strong intra/intermolecular interactions, the dissolution problem has significantly limited its applications. Although different kinds of solvents have been developed, most of them still cannot equilibrate dissolution, recyclability, and functional material preparation, simultaneously. In this work, an efficient and recyclable green solvent─molten salt hydrate (calcium chloride hexahydrate-lithium chloride, CHLH)─was prepared with excellent dissolving ability (high solubility of 7.0 wt %) for cellulose at a low dissolution temperature. Moreover, the CHLH showed good stability and storage properties. The dissolved cellulose could be stored in a solid state at a wide range of temperatures (<65 °C) for more than 3 months while remaining stable. Meanwhile, CHLH exhibited excellent recycling properties. After 5 dissolving–recovering cycles, the recycled CHLH still maintained stable dissolution performance and a high recovery of 92%. More importantly, the advantages of CHLH made the prepared cellulose hydrogel integrate good flexibility, ionic conductivity, and freezing tolerance. When used as a strain sensor, it could not only detect body movements but also identify the motion direction, which would have broad application prospects in flexible electronic devices.