Abstract
Advances in nanotechnology have changed conventional concepts in materials science. This has aloso strongly influenced natural biomass products with hierarchically built-up structures. In general, hierarchical structures in bio-based materials are built up by molecular self-assembly, followed by nanoassembly to form higher-level structures. Key to each step is the formation of interactions at each individual scale. Nature usually achieves such fabrication through a bottom-up process. However, fabrication can also be achieved through a top-down process, with various such downsizing methods now in development. This review article aims to describe trends in nanofiber technology among downsizing processes applied to cellulose as a representative biomass, ranging from fundamentals to recent techniques. The advantages of our recently developed technique, nanopulverization by aqueous counter collision, are also discussed. This method successfully decomposes interactions selectively without damaging the molecular structure, finally liberating components of various sizes into water to provide a transparent and homogeneous component–water system. As nanocellulose research is a broad area involving various fields, the cited references are limited to the scope of the author’s knowledge.
Highlights
Nanotechnology, which is based on clarification of the surface structure of substances on the nanoscale and their interface interactions, has changed conventional concepts in materials science
We have proposed an aqueous counter collision (ACC) method involving the collision of opposing high-pressure water jet streams of aqueous suspension samples
Using an enzyme derived from Trichoderma, Hayashi et al attempted to hydrolyze microbial cellulose crystalline nanofibrils with a width of 40–60 nm secreted from Gluconacetobacter bacteria and natural cellulose fibers derived from seaweeds, which have both crystalline forms of cellulose (Iα and Iβ)
Summary
Nanotechnology, which is based on clarification of the surface structure of substances on the nanoscale and their interface interactions, has changed conventional concepts in materials science. Owing to its sustainability and wide-ranging applications, the use of nanocellulose will contribute to the conservation and maintenance of the global environment In this context, technology for the preparation of nanocellulose has rapidly developed in the last 10–15 years, as described below. In Canada, Marchessault et al (1959) reported that the dispersed water suspension became a gel-like substance at a concentration of ≥13 wt%, indicating a nematic-order sequence, while Revol et al (1992) confirmed the formation of a chiral nematic structure during evaporation of this dispersion This historical research is closely related to the aforementioned Canadian ISO proposal. The production of cellulose nanofibrils and cellulose nanocrystals has been facilitated, and research and development sites are considering how to use such nanosized natural materials in society. 2 and 3, the nanocellulose surface obtained by TEMPO oxidation and the grinder method exhibit high hydrophilicity similar to that of conventional natural cellulose fibers. The nanocellulose surface obtained by the ACC method is more hydrophobic and amphiphilic (Kondo and Kasai, 2015; Tsuboi et al, 2014; Tsuji et al, 2021)
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