Composite Materials of TEMPO-Oxidized Cellulose Single Nanofiber

Abstract

When TEMPO-mediated oxidation is applied to wood celluloses in water at pH 10 under suitable conditions, almost all glucosyl units exposed on crystalline cellulose microfibrils are selectively oxidized to sodium glucuronosyl units. The TEMPO-oxidized celluloses thus obtained have the same fibrous morphologies as those of the original wood celluloses. Mild mechanical disintegration of the fibrous TEMPO-oxidized celluloses in water in turn allows them to be converted to highly viscous and transparent gels consisting of individually fibrillated TEMPO-oxidized cellulose single nanofibers (TOCNs) uniform 3-4 nm in width and over 1 m in length. Because anionically charged sodium carboxy-late groups are present on the crystalline TEMPO-oxidized cellulose microfibril surfaces in high densities, electrostatic repulsion and osmotic effect efficiently work between the microfibrils, resulting in the complete nanofibrillation of wood cellulose microfibrils. The TOCNs and their counter ion-exchanged TOCNs can be converted to self-standing films, hydrogels, aerogels, multi-layered composite films, polymer-nanocomposites, nanoclay-composites and others, which show high mechanical properties, high optical transparencies, high gas-barrier properties, low thermal expansion coefficients, high thermal stabilities, high catalytic behavior, spider web-like nano-networks, and other unique properties, when prepared under adequate conditions. Thus, TOCNs are expected to be used as new bio-based nanofibers for versatile applications in high-tech fields.