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

Abstract

Crystallite refers to a single crystalline grain in crystal aggregates, and multiple crystallites form a grain boundary or the inter-crystallite interface. A grain boundary is a structural defect that hinders the e cient directional transfer of mechanical stress or thermal phonons in crystal aggregates. We observed that grain boundaries within an aggregate of a-few-nanometers-wide brillar crystallites of wood cellulose were crystallized by enhancing their inter-crystallite interactions; multiple crystallites were coupled into single fusion crystals without passing through a melting or dissolving state. Accordingly, the crystallinity of wood cellulose, which has been considered irreversible once decreased, was signi cantly enhanced, and the thermal energy transfer in the aggregate was improved. Other brillar crystallites of crab shell chitin also showed a similar fusion phenomenon by enhancing the inter-crystallite interactions. These ndings imply that such crystallite fusion naturally occurs in biological structures with network skeletons of aggregated brillar crystallites.

Single Molecular Layer of Chitin Sub‐Nanometric Nanoribbons: One‐Pot Self‐Exfoliation and Crystalline Assembly into Robust, Sustainable, and Moldable Structural Materials

“…The above results clearly support that the inter-ChNRs (010) stacking and 𝜋-𝜋 interaction are dominant in the mesoscale assembly process. The rebuilding of crystalline structure through such ChNRs' coupling may be substantially the same phenomenon as the fusion of ultrafine cellulose nanofibrils under high temperature and pressure, lately proposed by Daicho et al [18] Further characterization by SEM, the assembled film shows a compact and isotropic morphology on the surface while straight alignment feature on the section, which is analogous to that of homogeneously dried film prepared from 2D materials (e.g., graphene and MXene) (Figure 3D; Figure S18, Supporting Information). [19] Thus, we speculate that lamellate ChNRs' mesocrystals might be first formed before stacking and fusing into a layered structure during the film-forming process.…”

“…The rebuilding of crystalline structure through such ChNRs’ coupling may be substantially the same phenomenon as the fusion of ultrafine cellulose nanofibrils under high temperature and pressure, lately proposed by Daicho et al. [ 18 ]…”

Atomic-scale dents on cellulose nanofibers: the origin of diverse defects in sustainable fibrillar materials

“…This hypothesis is supported by our recent studies on the crystallinity of CNFs; the aggregated bundles of cellulose have a higher crystallinity than the dispersion state, and the grain boundaries within an aggregate of CNFs were crystallized by enhancing their inter-crystallite interactions. 9,34 This means that the boundary between CNFs is partly unclear in the aggregated bundles. Irrespective of the type of mechanical force applied, in the process of dispersion, the CNFs are forced to be torn off from such a fused boundary, which may induce imperfect splitting and/or fragmentation of the CNFs.…”

Nanoscale Mechanism of Moisture-Induced Swelling in Wood Microfibril Bundles

“…When examining the results as lattice parameters of the monoclinic unit cell, the largest discrepancies between the experimental and model-based results were found in the lattice constant b (in the hydrogen-bonded layer, perpendicular to the chain axis) and the monoclinic angle γ (Figure S11b). These observations indicate that the 11̅ 0 and 110 diffraction peaks are sensitive to the molecular configurations at microfibril surfaces and fibrillar aggregation, 47 which thus contribute to the WAXS analysis of cellulosic samples.…”