The Crystallinity of Nanocellulose: Dispersion-Induced Disordering of the Grain Boundary in Biologically Structured Cellulose

Abstract

In trees, a-few-nanometers-wide crystalline fibrils of cellulose are tightly bundled with other biopolymers, such as lignin and hemicelluloses, to form robust cell walls. Cellulose nanofibers (CNFs) are obtained by successive treatments including the purification, modification, and disintegration of cell-wall cellulose. Herein, we report that the crystallinity of CNFs is governed by the interface between the bundled cellulose fibrils. The cellulose molecules at the interface or at the surface of the individual fibrils are ordered when the fibrils are more densely bundled upon removal of hemicelluloses. In turn, the interfacial molecules become disordered when bundled fibrils disperse upon disintegration as CNFs. Morphological analysis of the dispersed fibrils supports a model where single-cellulose fibrils in trees are composed of 18 molecular chains. Considering the 18-chain model, the surface molecules of the dispersed fibrils are disordered in the conformation of carbon atoms as analyzed by NMR, while all of the 18 chains are fully ordered in molecular sheet stacking to diffract X-rays.

Anisotropic Thermal Expansion of Transparent Cellulose Nanopapers

“…However, the out-of-plane CTE of our nanopapers (44.6 ppm/ • C) can only be explained by the cross-sectional expansion of crystallites (53 ppm/ • C). This result indicates that the inter-CNF interactions are dominated by hydrogen bonding; as discussed above, the CTE of the hydrogen bonding sheet along the b-axis of the unit cell is nearly zero (Wada, 2002) or even negative (Hori and Wada, 2005), whereas the CTE of the hydrophobic sheet-stacking in the a-axis direction is as large as 43-136 ppm/ • C. Note that XRD profiles of woodderived CNC films and nanopapers show no orientation of the crystal planes to the film surface (Elazzouzi-Hafraoui et al, 2008;Daicho et al, 2018). Figure 3 summarizes our interpretation for the anisotropic nanopaper expansion.…”

Cross-polarization dynamics and conformational study of variously sized cellulose crystallites using solid-state 13C NMR

“…Another possibility of the existence of heterogeneity is also conceivable. It was previously found by some of us that the crystalline C4 signal decreased when the bundled fibers dispersed as microfibrils and, correspondingly, the noncrystalline signal increased [18]. Indeed, the cellulose molecules at the interface between bundled fibrils or at the surface of the microfibrils are partially crystallized.…”

“…The cotton linters and tunicate cellulose (0.1 g for each) were acid-hydrolyzed with a 2 M HCl solution at 105 °C for 4 h. The residual solid hydrolysates were washed with distilled water by filtration. Amorphous cellulose was prepared from the cotton linters according to the method described in a previous report [18]. All the chemicals were of laboratory grade (FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan) and used as received.…”

Nanocellulose Film Properties Tunable by Controlling Degree of Fibrillation of TEMPO-Oxidized Cellulose

“…where the true density of 1.6 g/cm 3 was used for wood TOCNs (Daicho et al, 2018). The surface roughness values of the films were measured for the film/air interface side, which formed during the film preparation process, from the atomic force microscopy (AFM) images (Wu et al, 2014).…”