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This study attempted to prepare a single cellulose nanofiber, "nanocellulose", dispersed in water from 3D networks of nanofibers in microbial cellulose pellicle using aqueous counter collision (ACC), which allows biobased materials to be down-sized into nano-objects only using water jets without chemical modification. The nanocellulose thus prepared exhibited unique morphological properties. In particular, the width of the nanocellulose, which could be controlled as desired on nanoscales, was smaller than that of just secreted cellulose nanofiber, resulting in larger specific surface areas. Moreover, ACC treatment transformed cellulose I(α) crystalline phase into cellulose I(β) phase with the crystallinity kept >70%. In this way, ACC method depending on the treatment condition could provide the desired fiber width at the nanoscale and the different ratios of the two crystalline allomorphs between cellulose I(α) versus I(β), which thus opens further pathways into versatile applications as biodegradable single nanofibers.

Nanofibrillated bacterial cellulose (NFBC) is produced by culturing a cellulose-producing bacterium (Gluconacetobacter intermedius NEDO-01) with rotation or agitation in medium supplemented with carboxymethylcellulose (CMC). Despite a high yield and dispersibility in water, the product immediately aggregates in organic solvents. To broaden its applicability, we prepared amphiphilic NFBC by culturing strain NEDO-01 in medium supplemented with hydroxyethylcellulose or hydroxypropylcellulose instead of CMC. Transmission electron microscopy analysis revealed that the resultant materials (HE-NFBC and HP-NFBC, respectively) comprised relatively uniform fibers with diameters of 33 ± 7 and 42 ± 8 nm, respectively. HP-NFBC was dispersible in polar organic solvents such as methanol, acetone, isopropyl alcohol, acetonitrile, tetrahydrofuran (THF), and dimethylformamide, and was also dispersible in poly(methyl methacrylate) (PMMA) by solvent mixing using THF. HP-NFBC/PMMA composite films were highly transparent and had a higher tensile strength than neat PMMA film. Thus, HP-NFBC has a broad range of applications, including as a filler material.

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A desirable size of cellulose fibers for enhancing the crystallization of poly(lactic acid) (PLA) in composites was investigated by comparison among cellulose nanofibers with different widths on nanoscales. Namely, the crystallization behaviors of PLA in the presence of cellulose nanofibers were monitored with differential scanning calorimetry and polarized optical microscopy in terms of the crystallization rates of PLA. The smallest width of cellulose nanofibers was found to not necessarily provide better enhancement for the crystallization, presumably because of the preferential self-assembly of smaller cellulose nanofibers in PLA. Namely, when the width was smaller, the better effect expected for nanofibers did not appear in the composites. It is possible that an optimum width range of 60 nm, more or less, in the cellulose nanofibers may exist in balance between the favorable self-assembly as an enthalpy effect and the tendency toward dispersion as an entropy effect.

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