Preparation of strong, tough and highly ion-conductive nanocellulose hydrogels based on freeze–thaw cycles: performance evaluation under different freezing temperatures

Abstract Rapid and effective preparation of hydrogels with excellent properties by cyclic freezing–thawing has remained an enormous challenge as hydrogels prepared using traditional freeze–thaw methods demonstrate poor, unstable and unalterable mechanical properties. In this study, an innovative method was introduced to develop a nanocellulose hydrogel with excellent properties via cyclic freezing–thawing and ionic cross-linking, and various methods were used to characterise the structure and properties of the hydrogel. The results showed that hydrogen and ester bonds existed in the soy hull nanocellulose–sodium alginate–calcium chloride (SHNC/SA/Ca 2+ ) hydrogel and that the internal structure of the hydrogel changed from a lamellar to three-dimensional network structure owing to low temperature, increasing the cross-linking density of SHNC and SA and enhancing the mechanical strength of the hydrogel. Meanwhile, the SHNC/SA/Ca 2+ -4 hydrogel demonstrated excellent elongation (804 %), viscoelasticity (storage modulus = 89.6 kPa), mechanical strength (tensile strength = 0.59 MPa, compressive strength = 1.52 MPa), ionic conductivity (3.84 S/m), transparency (54 %), anti-ultraviolet properties and fatigue resistance. The simple preparation process, excellent performance and three-dimensional porous network structure of the nanocellulose hydrogel offer broad application prospects in many fields.