Reina Tanaka

Cellulose nanofibrils prepared from softwood cellulose by TEMPO/NaClO/NaClO2 systems in water at pH 4.8 or 6.8

Catalytic oxidation of softwood cellulose using NaClO and either 2,2,6,6-tetramethylpiperidine-1-oxyl (4-H-TEMPO) or 4-acetamido-TEMPO (4-AcNH-TEMPO) was applied with NaClO(2) used as a primary oxidant in an aqueous buffer at pH 4.8 or 6.8. When the 4-AcNH-TEMPO-mediated oxidation was applied to softwood cellulose in water at pH 4.8 and 40 °C, the carboxylate content rose to ∼1.3 mmol/g after reaction for 48 h and the DP(v) value was more than 1100. This 4-AcNH-TEMPO-oxidized softwood cellulose was mostly converted to individual nanofibrils by mechanical disintegration in water, with uniform widths of 3-4 nm and lengths greater than 1 μm.

Influence of Flexibility and Dimensions of Nanocelluloses on the Flow Properties of Their Aqueous Dispersions

We report that the intrinsic viscosity [η] of nanocellulose dispersions can be solely expressed as a function of the aspect ratio p of the nanocellulose. Both short rod-like nanocrystalline and long spaghetti-like nanofibrillated celluloses were prepared as dispersions in water. The influence of the flexibility and dimensions of the nanocelluloses on the flow properties of their dispersions was investigated by experimental and theoretical approaches using seven nanocellulose samples with different widths (2.6-14.4 nm) and aspect ratios (23-376). As the aspect ratio of a nanocellulose increases, it becomes more flexible, and its dispersion has higher viscosity. Irrespective of the flexibility and dimensions of these nanocelluloses, the relationship between [η] and p was ρ[η] = 0.15 × p(1.9), where ρ is the density of the nanocellulose.

Viscoelastic Properties of Core–Shell-Structured, Hemicellulose-Rich Nanofibrillated Cellulose in Dispersion and Wet-Film States

We report the viscoelastic properties of core-shell-structured, hemicellulose-rich nanofibrillated cellulose (NFC) in dispersion and wet-film states. The hemicellulose-rich NFC (hemicellulose neutral sugars 23%, carboxylate 0.2 mmol g(-1)), prepared from Japanese persimmons, had a core crystallite thickness of 2.3 nm and unit fibril thickness of 4.2 nm. A carboxylate-rich NFC (hemicellulose neutral sugars 7%, carboxylate 0.9 mmol g(-1)) with crystallite and fibril widths of 2.5 and 3.3 nm, respectively, was used as a reference. The solid-concentration dependencies of the storage moduli of gel-like water dispersions of the hemicellulose-rich NFC were weaker than those of carboxylate-rich NFC, and the dispersions were loosely flocculated even at high salt concentrations and low pH values. The viscoelastic properties of wet NFC films were similar to those of their dispersions; the hemicellulose-rich NFC films were significantly less sensitive to salt concentration and pH and were soft and swollen at high salt concentrations and low pH values.

Ensemble evaluation of polydisperse nanocellulose dimensions: rheology, electron microscopy, X-ray scattering and turbidimetry

Six types of CNCs with different sizes were prepared from tunicins by sulfuric acid hydrolysis and subsequent sonication in water. The size distributions of CNCs were comprehensively evaluated by turbidimetry, small angle X-ray scattering, and microscopy to predict their intrinsic viscosities. Experimental intrinsic viscosities [η] of the CNC dispersions were evaluated by shear viscosity measurement, and then compared with their theoretical [η] values based on theories for rotational motions of rigid rods. The experimental [η] values for the straight CNCs were in good agreement with their theoretical [η] values, irrespective of the size and distributions. On the other hand, the experimental [η] value of the kinked CNC was higher than the theoretical [η] value, in agreement with a theoretical calculation giving higher intrinsic viscosities for bent fibers.

Changes in the degree of polymerization of wood celluloses during dilute acid hydrolysis and TEMPO-mediated oxidation: Formation mechanism of disordered regions along each cellulose microfibril

Most commercially available plant celluloses, such as kraft pulps and cotton celluloses, have so-called leveling-off degrees of polymerization (LODPs) when subjected to dilute acid hydrolysis. The formation of LODPs is hypothesized to be caused by disordered regions that are present periodically along each cellulose microfibril in plant celluloses. Here, we prepared never-dried wood cellulose, and wood celluloses at different drying stages, and subjected them to dilute acid hydrolysis. The viscosity average degrees of polymerization (DPv) of the wood celluloses decreased in DPv with increasing dilute acid-hydrolysis times. However, the DPv values after 4h of acid hydrolysis differed from those of softwood bleached kraft pulp (SBKP), which showed typical patterns of LODPs. Thus, the disordered regions corresponding to LODPs that were observed for SBKP are probably not synthesized in the native wood. Instead, such disordered regions are formed secondarily or artificially during the isolation/purification and/or drying processes of plant cellulose fibers. The results of the dilute acid hydrolysis and the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of SBKP and softwood unbleached soda-anthraquinone pulp showed that the structures of disordered regions can be controlled via the preparation and drying conditions of wood cellulose used as starting materials.