Preparation and Characterization of TEMPO-Oxidized Cellulose Nanofibers

Isogai, A.

Selective conversion of primary hydroxyls of polysaccharides to carboxyl groups can be achieved by TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxyl radical)-mediated oxidation in water under moderate conditions. Fundamental and application studies of TEMPO-oxidized cellulose nanofibers and their related researches are reviewed primarily based on the results obtained in our laboratory and by collaborations. When TEMPO-mediated oxidation in water is applied to bleached wood kraft pulps for papermaking, C6-carboxylate groups are efficiently and position-selectively formed on the surfaces of wood cellulose microfibrils. TEMPO-oxidized wood celluloses having sufficient amounts of sodium carboxylate groups can be converted to individualized cellulose nanofibers with almost uniform widths of 4 nm and lengths >1 micro m by mild mechanical disintegration in water. Electrostatic repulsion and/or osmotic effect efficiently work between anionically charged TEMPO-oxidized wood cellulose microfibrils, resulting in the formation of the individual nanofibers with high aspect ratios and high crystallinity. Cast films prepared from the TEMPO-oxidized cellulose nanofiber (TOCN)/water dispersions have high optical transparency, extremely low oxygen permeability, low thermal expansion coefficients, high strengths and other unique properties. The new cellulose-based nanofiber films are expected to be applied as transparent packaging materials with high oxygen barrier for foods and medicines, flexible display panels, electronic devices, health care and others. Thus, TOCNs prepared from abundant wood biomass have great potential as novel bio-based nanofibers in state-of-the-art material fields required for the establishment of sustainable society.

Preparation and Characterization of TEMPO-Oxidized Cellulose Nanofibers

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