Cellulose Nanofibers as New Bio-Based Nanomaterials

Abstract

Nanocelluloses have attracted much attention as new bio-nanomaterials, which are prepared from abundant wood biomass resources by downsizing of cellulose fibers with or without pretreatments by mechanical disintegration in water. In this review paper, fundamental and application researches of fibrous TEMPO-oxidized celluloses (TOCs) and TEMPO-oxidized cellulose nanofibers (TOCNs) primarily carried out in our laboratory are reviewed for future prospects of nanocelluloses. The characteristic points of TOCNs different from other nanocelluloses are (A) wood TOCNs are crystalline nanofibers with homogeneous widths of ~3 nm and high aspect rations, (B) TOCNs have abundant sodium carboxylate groups exchangeable to other metal carboxylate groups and alkylammonium carboxylate groups by simple ion exchange, and (C) TOCNs are dispersed at the individual nanofiber level in water, forming nematic-like liquid crystalline or self-aligned structures caused by electrostatic repulsions between TOCN elements. From these aspects, self-standing films, hydrogels, aerogels, and composite materials have been prepared with TOCNs, and some of them showed unique and excellent properties.