Nanocellulose hydrogels formed via crystalline transformation from cellulose I to II and subsequent freeze cross-linking reaction

Yurina Sekine; Takuya Nankawa; Kosuke Hiroi; Yojiro Oba; Yoshiyasu Nagakawa; Tsuyoshi Sugita; Yuki Shibayama; Tomoko Ikeda-Fukazawa

doi:10.1016/j.carbpol.2023.121538

Nanocellulose hydrogels formed via crystalline transformation from cellulose I to II and subsequent freeze cross-linking reaction

Carbohydr Polym. 2024 Mar 1:327:121538. doi: 10.1016/j.carbpol.2023.121538. Epub 2023 Dec 1.

Authors

Yurina Sekine¹, Takuya Nankawa², Kosuke Hiroi³, Yojiro Oba⁴, Yoshiyasu Nagakawa⁵, Tsuyoshi Sugita⁶, Yuki Shibayama⁶, Tomoko Ikeda-Fukazawa⁷

Affiliations

¹ Materials Sciences Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan. Electronic address: sekine.yurina@jaea.go.jp.
² Planning and Coordination Office, JAEA, Tokai, Ibaraki 319-1195, Japan.
³ Materials Sciences Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan; Japan Proton Accelerator Research Complex (J-PARC) Center, JAEA, Tokai, Ibaraki 319-1195, Japan.
⁴ Department of Mechanical Engineering, Toyohashi University of Technology, Tempaku-Cho, Toyohashi, Aichi 441-8580, Japan.
⁵ Tokyo Metropolitan Industrial Technology Research Institute, Aomi, Koto-ku, Tokyo 135-0064, Japan.
⁶ Materials Sciences Research Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195, Japan.
⁷ School of Science and Technology, Meiji University, Kawasaki, Kanagawa 214-8571, Japan.

PMID: 38171650
DOI: 10.1016/j.carbpol.2023.121538

Abstract

We describe nanocellulose (NC) hydrogels formed from chemically unmodified NC by cellulose crystalline transformation and subsequent freeze cross-linking reaction. The freeze cross-linked NC hydrogel with macropores (~100 μm) was prepared by freezing a mixture of NC and NaOH (0.2 mol L^-1), adding citric acid to the frozen mixture, and thawing it. Using NaOH and freezing together induced the crystalline transformation of NC from cellulose I to II via freeze concentration. After the crystalline transformation, cross-linking between the NC and CA in the freeze concentration layer provided a strong NC network structure, forming NC hydrogels with high mechanical strength. The structural changes in NC caused by NaOH, freezing, and freeze cross-linking on the angstrom to micrometer scale were investigated with FT-IR, SAXS, PXRD, and SEM. The freeze cross-linked NC hydrogel easily retained powder adsorbents in its inner space by mixing the NC-NaOH sol and the powder, and the hydrogel showed high removal efficiency for heavy metals. The results highlight the versatility of chemically unmodified celluloses in developing functional materials and suggest possible practical applications. This study also provides new insights into the efficient use of chemical reactions of cellulose under freezing conditions.

Keywords: Cellulose; Cross-linking; Crystal structure; Freeze concentration; Hydrogen bonding; Ice crystals.