Development of Advanced New Bio - Nanofibers from Wood Pulp - Preparation and Application of TEMPO-Oxidized Cellulose Nanofibers

Native cellulose forms hierarchical structures in plant cell walls from molecular chains to fibers and plant tissues through nano-sized and highly crystalline cellulose microfibrils. We have developed some methods to prepare individual cellulose nanofibers by TEMPO-mediated oxidation of native celluloses followed by gentle mechanical agitation in water. The cellulose nanofibers thus obtained have high crystallinity of 74%, almost uniform widths of 3-4 nm and lengths of at least a few micrometers. Because significant amounts of C6 carboxylate groups are selectively formed on the cellulose microfibril surfaces by the oxidation, bundles of cellulose microfibrils forming numerous hydrogen bonds between them can be converted to individual cellulose nanofibers dispersed in water by electric repulsions between highly anionic cellulose microfibrils, whose zeta potentials are around -80 mV. Transparent and flexible films with high strength and extremely low oxygen permeability were obtained by casting the TEMPO-oxidized cellulose nanofiber/water dispersions on a PLA film. The new cellulose nanofiber films are expected to be used as transparent packaging materials with high oxygen barrier for foods and medicines, flexible display panels, electronic devices and others.