Cellulose Nanofibers Prepared by TEMPO-Mediated Oxidation of Native Cellulose

TLDR

Never‑dried and once‑dried hardwood celluloses were oxidized by a TEMPO‑mediated system and then mechanically treated to produce highly crystalline, individualized cellulose nanofibers dispersed in water. At a carboxylate loading of ~1.5 mmol g⁻¹, the oxidized cellulose/water slurries became transparent, highly viscous dispersions of 3–4 nm wide, micron‑long nanofibers, with no difference between never‑dried and once‑dried celluloses, and viscosity changes mirrored the dispersion state.

Abstract

Never-dried and once-dried hardwood celluloses were oxidized by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated system, and highly crystalline and individualized cellulose nanofibers, dispersed in water, were prepared by mechanical treatment of the oxidized cellulose/water slurries. When carboxylate contents formed from the primary hydroxyl groups of the celluloses reached approximately 1.5 mmol/g, the oxidized cellulose/water slurries were mostly converted to transparent and highly viscous dispersions by mechanical treatment. Transmission electron microscopic observation showed that the dispersions consisted of individualized cellulose nanofibers 3−4 nm in width and a few microns in length. No intrinsic differences between never-dried and once-dried celluloses were found for preparing the dispersion, as long as carboxylate contents in the TEMPO-oxidized celluloses reached approximately 1.5 mmol/g. Changes in viscosity of the dispersions during the mechanical treatment corresponded with those in the dispersed states of the cellulose nanofibers in water.