High Aspect Ratio Carboxycellulose Nanofibers Prepared by Nitro-Oxidation Method and Their Nanopaper Properties

High aspect ratio carboxycellulose nanofibers (NOCNF), having typical length over 1000 nm, width ∼4.6 nm, thickness ∼1.3 nm, and carboxylate content of 0.42 mmol/g, were extracted from jute fibers using a modified nitro-oxidation method. The extracted nanofiber was found to possess crystallinity of 69% (measured by wide-angle X-ray diffraction, WAXD), relatively higher than that of raw jute fibers (crystallinity ∼61%). Gelation of NOCNF in aqueous suspensions was observed due to the high aspect ratio of the fiber even at a relatively low concentration. Rheological studies on the NOCNF suspensions at different concentrations (0.01–1 wt %) revealed the shear-thinning behavior with increasing shear rate. The corresponding viscoelastic moduli (G′ and G′′) results indicated that the NOCNF suspension at concentration between 0.1 and 0.2 wt % possessed a liquid–gel transition. The rheological data near the gelation point could be fitted by the Winter–Chambon model, where the results confirmed the formation of a percolated fibrous network. The flow behavior of the NOCNF suspensions in the chosen concentration range could be further described by the concept of the crowding factor. Nanopaper prepared using these high aspect ratio carboxycellulose nanofibers exhibited good mechanical properties with tensile strength of 108 ± 2 MPa and Young’s modulus of 4.1 ± 0.2 GPa.