Local Crystallinity in Twisted Cellulose Nanofibers

Abstract

Cellulose is crystallized by plants and other organisms into fibrous nanocrystals. The mechanical properties of these nanofibers and the formation of helical superstructures with energy dissipating and adaptive optical properties depend on the ordering of polysaccharide chains within these nanocrystals, which is typically measured in bulk average. Direct measurement of the local polysaccharide chain arrangement has been elusive. In this study, we use the emerging technique of scanning electron diffraction to probe the packing of polysaccharide chains across cellulose nanofibers and to reveal local ordering of the chains in twisting sections of the nanofibers. We then use atomic force microscopy to shed light on the size dependence of the inherent driving force for cellulose nanofiber twisting. The direct measurement of crystalline twisted regions in cellulose nanofibers has important implications for understanding single-cellulose-fibril properties that influence the interactions between cellulose nanocrystals in dense assemblies. This understanding may enable cellulose extraction and separation processes to be tailored and optimized.

Recovery of the Irreversible Crystallinity of Nanocellulose by Crystallite Fusion: A Strategy for Achieving Efficient Energy Transfers in Sustainable Biopolymer Skeletons**

“…We assumed no speci c orientation of the crystal planes to the sheet surface by considering: 1) the similarity of the experimental pro le in Figure 3 with that obtained by the re ection method for sample iv in Figure 1a, and 2) the twisting structure of the CNFs around the crystallographic c axis. [24][25][26] In the simulation, the structure of the single CNFs was assumed to be composed of 18 cellulose chains with a stacking mode of 2/3/4/4/3/2, based on previous reports on the morphological analyses of single CNFs. [11,27] This 18-chain model has at two-molecule-wide (2 0 0) surfaces, enabling the CNFs to stably stack on the (2 0 0) plane (see the results for TBA-bearing CNFs in Figure 2).…”

“…The experimental profile was obtained by azimuthally integrating an XRD diagram of a sample iv sheet set parallel to the beam. We assumed no specific orientation of the crystal planes to the sheet surface by considering: 1) the similarity of the experimental profile in Figure 3 with that obtained by the reflection method for sample iv in Figure 1 a, and 2) the twisting structure of the CNFs around the crystallographic c axis [24–26] …”

Application of nanocellulose composites in the environmental engineering: A review

“…The cellulose chains possess a large surface area and are twisted and flexible. NFCs are different from CNCs in that they are composed of many amorphous domains and soft, long chains with widths and lengths often to a few hundred nanometers and several micrometers, respectively [40,41]. Before converting the fibers to CNF, a vigorous mechanical disintegration should be exerted to the cell wall of the plant because of the sophisticated cellulose fiber structure.…”

Crystallite fusion in nanocellulose aggregates

“…It is well known as a phenomenon "hornification" in the field of wood pulp and paper sciences that the crystallinity of cellulosic samples including CNFs slightly increases by the repeating cycle of wet-dry states 22,23 . This phenomenon has been ambiguously interpreted to result from enhancement of the degree of hydrogen bonding in samples by drying, and its mechanism remains unclear.…”