Eco-friendly carboxymethyl cellulose nanofiber hydrogels prepared via freeze cross-linking and their applications

Sekine, Yurina   ; Nankawa, Takuya ; Yunoki, Shunji*; Sugita, Tsuyoshi   ; Nakagawa, Hiroshi   ; Yamada, Teppei*

We developed a cross-linking method using freeze concentration and used it to synthesize a new type of carboxymethyl cellulose nanofiber (CMCF) hydrogel with high compressive strength ( 80 MPa) and high compressive recoverability. The hydrogels were prepared by adding an aqueous solution of citric acid (CA) to a frozen CMCF sol and then thawing the sol. The reaction between the freeze-concentrated CMCF and CA created a rigid porous structure that reflected the ice crystal structure. Their cross-linked structure has a high stability to compressive stress. Bentonite was immobilized on a CMCF hydrogel by adding bentonite to the CMCF sol before freeze cross-linking. The CMCF-bentonite hydrogel showed high adsorptivity for chemical dyes. The physically cross-linked CMCF hydrogels are non-toxic, metal-free, and simple to prepare, and thus they may be useful as sustainable materials in various fields.