Cellulose nanofibrils, which attract extensive attention as a bio-based, sustainable, high-performance nanofibril, are believed to be predominantly hydrophilic. This study aimed to prove the presence of an amphiphilic “Janus-type fiber surface” in water with hydrophobic and hydrophilic faces in a cellulose nanofibril (ACC-CNF) that was prepared by the aqueous counter collision method. We clarified the surface characteristics of the ACC-CNF by confocal laser scanning microscopy with a carbohydrate-binding module and congo red probes for the hydrophobic planes on the cellulose fiber surfaces and calcofluor white as hydrophilic plane probes. The results indicated the presence of both characteristic planes on a single ACC-CNF surface, which verifies an amphiphilic Janus-type structure. Both hydrophobic probes adsorbed onto ACC-CNFs for the quantitative evaluation of the degree of ACC-CNF surface hydrophobicity by Langmuir’s adsorption theory based on the optimal maximum adsorption amounts for various starting raw material types.

Cellulose nanofibrils (CNFs), which are attracting increasing attention as sustainable biomass nano-objects, are believed to be hydrophilic. Recently, aqueous counter collision (ACC) has been used to produce Janus-type amphiphilic cellulose nanofibrils (ACC-CNFs) from various cellulosic raw materials. In the current study, ACC-CNFs were preferentially adsorbed onto hydrophobic isotactic polypropylene (i-PP) microparticles and linear low-density polyethylene (LLDPE), which demonstrated their characteristic amphiphilicity. This was achieved by simply mixing the constituents together in aqueous media. The products were visualized by confocal laser microscopy (CLMS). Thermodynamic measurements obtained by differential scanning calorimetry revealed that the melting points of i-PP/ACC-CNFs and LLDPE/ACC-CNFs were lower than those of the untreated polymers, which indicates interactions between the ACC-CNFs and the polymer surfaces. Coating the polymer particles with the ACC-CNFsas confirmed by CLMSappeared to reduce their melting points. This finding demonstrates the possibility of a novel fusion between synthetic polymeric materials and biomass nano-objects.

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Naturally occurring polysaccharides, such as cellulose, hemicellulose, and chitin, have roles in plant skeletons and/or related properties in living organisms. Their hierarchically regulated production systems show potential for designing nanocomposite fabrication using engineered microorganisms. This study has demonstrated that genetically engineered Gluconacetobacter hansenii (G. hansenii) individual cells can fabricate naturally composited nanofibrils by simultaneous production of hyaluronan (HA) and bacterial cellulose (BC). The cells were manipulated to contain hyaluronan synthase and UDP-glucose dehydrogenase genes, which are essential for HA biosynthesis. Fluorescence microscopic observations indicated the production of composited nanofibrils and suggested that HA secretion was associated with the cellulose secretory pathway in G. hansenii. The gel-like nanocomposite materials produced by the engineered G. hansenii exhibited superior properties compared with conventional in situ nanocomposites. This genetic engineering approach facilitates the use of G. hansenii for designing integrated cellulose-based nanomaterials.

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