Akira ISOGAI: Department of Biomaterial Sciences, The University of Tokyo

JAPANESE
Laboratory of Cellulose Chemistry

Contact us

Department of Biomaterial Sciences
The University of Tokyo
1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
Phone:+81 80-4154-1362
E-mail:akira-isogai[at]g.ecc.u-tokyo.ac.jp

  • The University of Tokyo
  • Laboratory of Bionanomaterials and Cellulose Sciences
  • The University of Tokyo Biomaterials Sciences
  • Graduate School of Agricultural and Life Sciences, The University of Tokyo
  • Advanced Characterization Nanotechnology Platform
  • RISM|Shinshu University Research Initiative for Supra-Materials

Research Project

Fundamental and Application Researches of Cellulose using Chemistry and Structural Analyses

Real-time observation of microcrack growth in nanocellulose/rubber composite sheets during tensile deformation process

 Rubber/nanocellulose composite sheets improve tensile properties compared with neat rubber sheets, when nanocellulose materials are suitably compounded with rubber matrices. First, two oven-dried nanocellulose materials containing different additive components were prepared from nanocellulose/water dispersions, and the oven-dried nanocellulose-containing materials were compounded with rubber sheets under high shear forces by using a two-roll mill. The tensile moduli and strength of the rubber/nanocellulose composite sheets were clearly better than those of the rubber sheet prepared without nanocellulose, while the elongations at break were similar. Thin films were cut from the rubber/nanocellulose composite sheets, and their real-time tensile deformation processes were observed by transmission electron microscopy (TEM) to understand the time-dependent patterns of crack propagation, void formations, and fusion between cracks and voids in the composites during tensile deformation. TEM observations showed that the composite sheets consisted of individual rubber/nanocellulose clusters. Voids initially formed inside the rubber/nanocellulose clusters, propagated to form cracks, fused with other voids or secondary cracks. There were slight differences between the crack-propagation patterns of the two rubber composites, probably because of differences in the morphologies, sizes, distributions, and structures of the rubber/nanocellulose clusters, and surface chemical structures of individual nanocellulose elements between the composites.

Real-time observation of microcrack growth in nanocellulose/rubber composite sheets during tensile deformation process

(Jinnai et al., Polymer Composites, 2022)

A systematic study for the structures and properties of phosphorylated pulp fibers prepared under various conditions

 A bleached softwood kraft pulp was phosphorylated with (NH4)2HPO4 and urea at 150 °C for 0‒40 min, and the structures and properties of the resulting phosphorylated pulps were systematically investigated for the first time in terms of reaction time and the amount of (NH4)2HPO4 added. The phosphorous and weak acid group contents, and the weight recovery ratio increased with increasing reaction time, and were 1.9 and 4.5 mmol/g, and 114%, respectively, when the reaction time was 20 min. Therefore, numerous phosphate ester and weak acid groups were introduced into the pulp, maintaining its fibrous morphology and cellulose I crystal structure. It was found that almost all the ammonium phosphate groups in the phosphorylated pulp behaved as weak acids. The solid-state carbon-13 nuclear magnetic resonance (13C-NMR) spectrum of the phosphorylated pulp showed that neither carboxy nor carbamate groups were formed in the phosphorylated pulp; only phosphate ester groups were introduced into the pulp under the conditions used in the present study. The X-ray photoelectron spectra of the phosphorylated pulp surfaces suggested that ammonium phosphate groups were introduced into the pulp by phosphorylation. A longer reaction time or a greater amount of (NH4)2HPO4 added during phosphorylation resulted in lower water swelling behavior, indicating that some intrafiber and/or interfiber crosslinking occurred in the pulp under these conditions. The results obtained in the present study show that phosphorylated pulp fibers are suitable for the preparation of new functional cellulosic sheets and materials, in which large amounts of weak acid groups can be used as scaffolds for diverse ion-exchange sites.

A systematic study for the structures and properties of phosphorylated pulp fibers prepared under various conditions

(Hou et al, Cellulose, 2022)

Cellulose nanofibril/polypropylene composites prepared under elastic kneading conditions

 An aqueous dispersion of 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibrils (TEMPO-CNFs) was mixed with diethylene glycol (DEG) and dodecyltrimethylammonium chloride (DTMACl) with or without silane coupling agents. The mixture was heated at 40 °C for 1 d to prepare an oven-dried TEMPO-CNF/DEG/DTMACl, which was added to maleic anhydride-modified polypropylene (MA-PP) and kneaded at 165‒175 °C with high shear forces to prepare TEMPO-CNF/MA-PP master batches. Various amounts of TEMPO-CNF/MA-PP master batch pieces were mixed with PP to prepare TEMPO-CNF/MA-PP/PP composite sheets. The yield stress and storage modulus at 25 °C of the composite sheets increased almost linearly with an increase in TEMPO-CNF content. However, the elongation at break decreased clearly with TEMPO-CNF content because of partial formation of TEMPO-CNF aggregates in the composites. The presence of TEMPO-CNFs restricted flow behavior of the MA-PP/PP components above 160 °C, although the crystallinities and melting behavior of MA-PP/PP in the composite sheets at ~160 °C were unchanged. The apparent aspect ratios of TEMPO-CNF components in the composite sheets were 5‒13 by partial aggregation of TEMPO-CNFs in the PP matrix, although the aspect ratio of the original TEMPO-CNFs dispersed in water was ~183. The aggregation behavior of TEMPO-CNFs in the PP matrix may have resulted in brittle tensile properties of the composite sheets. The TEMPO-CNF-containing PP sheets have better printability and adhesion performance between sheets using glues. These results indicate that the oven-dried TEMPO-CNFs can be used as fillers for improvement of mechanical, thermal, and printing properties of recycled and low-quality PP and for quantitative expansion of recycled PP.

Cellulose nanofibril/polypropylene composites prepared under elastic kneading conditions

(Noguchi et al., Cellulose, 2022)

Structures, molar mass distributions, and morphologies of TEMPO-oxidized bacterial cellulose fibrils

 2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation has been applied to bacterial cellulose (BC). The TEMPO-oxidized BC (TO-BC) gel particles were subjected to ultrasonication in water to prepare mechanically fibrillated TO-BC (TO-BC-U) samples. The carboxyl contents of the TO-BC samples were 1.5‒1.6 mmol/g. X-ray diffraction patterns and solid-state 13C-nuclear magnetic resonance (NMR) spectra of the BC, TO-BC, and TO-BC-U samples showed that cellulose Iα was the dominant crystalline structure. The crystallinities of the samples calculated from the carbon signal areas in the NMR spectra were approximately the same between the BC and TO-BC samples, showing that TEMPO-mediated oxidation selectively occurred on the crystalline BC fibril surfaces. However, the crystallinities of the TO-BC-U samples were lower than those of the BC and TO-BC samples, indicating that ultrasonication of the TO-BC samples in water caused partial decreases in crystallinity. The TO-BC-U samples contained both single fibrils and fibril bundles; completely individualized TO-BC-U fibrils with homogeneous widths was not obtained. The average widths of the single TO-BC-U fibrils were ~3 nm, which are close to those of TO-cellulose nanofibrils prepared from wood-cellulose samples. Thus, the crystalline BC fibrils with widths of ~3 nm were the smallest crystalline elements. The lengths of the TO-BC samples were greater than 2‒3 µm, whereas the weight-average cellulose chain lengths of the cellulose/TEMPO-oxidized cellulose molecules in TO-BC-U samples were <800 nm. Hence, each TO-BC-U fibril consisted of multiple cellulose and oxidized cellulose molecules, which were packed along the longitudinal direction.

Structures, molar mass distributions, and morphologies of TEMPO-oxidized bacterial cellulose fibrils

(Ono et al., Cellulose, 2022)

Changes in neutral sugar composition, molar mass and molar mass distribution, and solid-state structures of birch and Douglas fir by repeated sodium chlorite delignification

 NaClO2-treated residues or holocellulose samples were prepared from birch and Douglas fir wood powders by repeated cycles of delignification. These delignified samples were characterized from their weight recovery ratios, neutral sugar compositions, size-exclusion chromatograms (SECs) using 1% (w/v) lithium chloride/N,N-dimethylacetamide as eluent, and solid-state 13C nuclear magnetic resonance (NMR) spectra. Neutral sugar composition analysis revealed that the weight ratios of cellulose and xylan fractions were almost constant irrespective of the number of repeated delignification cycles for up to seven and eight cycles for birch and Douglas fir, respectively. The contents of acetyl ester groups were constant between the delignified samples. The glucomannan molecules present in Douglas fir were partly removed from the delignified residues as the number of delignification cycles increased. The SEC analysis showed that the high-molar-mass (HMM) cellulose fractions of birch samples decreased slightly in molar mass with increased number of delignification cycles. The molar mass values in the HMM fractions of Douglas fir samples were much higher than those of the birch samples because of the presence of branched structures with glucomannan, and were mostly unchanged as the number of delignification cycles increased. Solid-state 13C NMR analysis of the NaClO2-treated residues and their acid-insoluble fractions showed that carboxy groups were formed in the residual lignin fractions by the oxidative delignification treatment with NaClO2. Thus, neutral sugar composition, SEC analysis, and solid-state 13C NMR analysis can be used for comprehensive and manifold characterization of NaClO2-treated residues or holocellulose samples prepared from various plant samples.

Changes in neutral sugar composition, molar mass and molar mass distribution, and solid-state structures of birch and Douglas fir by repeated sodium chlorite delignification

(Ono et al., Cellulose, 2022)

Silver-nanoparticle-containing handsheets for antimicrobial applications

 Development of self-sanitizing cellulose and cellulose paper-based products will increase human safety and hygiene. In the present work, a softwood bleached kraft pulp (SBKP) was oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation in water at pH 10 at two NaClO addition levels (3 and 5 mmol g−1 based on the dry weight of SBKP). The fibrous TEMPO-oxidized SBKPs (TO-SBKPs) were subsequently incorporated with silver nanoparticles (AgNPs) by soaking in aqueous silver nitrate (AgNO3) solution and subsequent thermal reduction. The C=O absorption band in FTIR spectra of AgNP-containing TO-SBKPs increased with increasing Ag content, showing that the C2/C3 hydroxy groups in TO-SBKPs were oxidized to ketones by reduction of Ag+ ions to AgNPs during heating at 100 °C for 1 h. Scanning electron microscopy images showed that the AgNPs were almost homogenously distributed on the surface of each TO-SBKP fiber with an average diameter of 32–40 nm regardless of different Ag contents. Handsheets were prepared from SBKP and the AgNP-containing TO-SBKP at various weight ratios. The handsheets showed sufficient antimicrobial activities against a Gram-negative Escherichia coli strain and a Gram-positive Staphylococcus aureus strain. The tensile strength of the handsheets was significantly improved by mixing the AgNP-containing TO-SBKP with SBKP. The 20% TO-SBKP/Ag-containing SBKP sheets were optimal in terms of efficient antimicrobial activities and good mechanical properties. Thus, the AgNP-containing TO-SBKP sheets have potential for use as antimicrobial paper and related packaging materials produced using the conventional papermaking process.

Silver-nanoparticle-containing handsheets for antimicrobial applications

(Puangshin et al., Cellulose, 2022)

Copper-coordinated cellulose ion conductors for solid-state batteries

 Although solid-state lithium (Li)-metal batteries promise both high energy density and safety, existing solid ion conductors fail to satisfy the rigorous requirements of battery operations. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact with electrodes. Conversely, polymer ion conductors that are Li-metal-stable usually provide better interfacial compatibility and mechanical tolerance, but typically suffer from inferior ionic conductivity owing to the coupling of the ion transport with the motion of the polymer chains. Here we report a general strategy for achieving high-performance solid polymer ion conductors by engineering of molecular channels. Through the coordination of copper ions (Cu2+) with one-dimensional cellulose nanofibrils, we show that the opening of molecular channels within the normally ion-insulating cellulose enables rapid transport of Li+ ions along the polymer chains. In addition to high Li+ conductivity (1.5 × 10−3 siemens per centimetre at room temperature along the molecular chain direction), the Cu2+-coordinated cellulose ion conductor also exhibits a high transference number (0.78, compared with 0.2–0.5 in other polymers) and a wide window of electrochemical stability (0–4.5 volts) that can accommodate both the Li-metal anode and high-voltage cathodes. This one-dimensional ion conductor also allows ion percolation in thick LiFePO4 solid-state cathodes for application in batteries with a high energy density. Furthermore, we have verified the universality of this molecular-channel engineering approach with other polymers and cations, achieving similarly high conductivities, with implications that could go beyond safe, high-performance solid-state batteries.

Copper-coordinated cellulose ion conductors for solid-state batteries

(Yang et al., Nature, 2021)

TEMPO-catalyzed oxidation of polysaccharides

 2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-catalyzed oxidation enables efficient and position-selective conversion of primary hydroxy groups in water-soluble and water-insoluble polysaccharides to sodium carboxylate groups under mild conditions in water. TEMPO/NaBr/NaClO in water at pH 10 is an advantageous system in terms of the degrees of oxidation and reaction rates. TEMPO and NaBr behave as catalysts, and NaClO acts as the primary oxidant. However, oxidative depolymerization that is caused by the presence of NaBr and NaClO and the occurrence of side reactions on the polysaccharide molecules are unavoidable during oxidation. An alternative system is 4-acetamido-TEMPO/NaClO/NaClO2 in pH 5–7 buffer at 35–60 °C for 1–3 d, in which catalytic amounts of TEMPO and NaClO are used with NaClO2 as the primary oxidant. This oxidation system significantly inhibits depolymerization and yields oxidized products that contain no aldehydes. Various new water-soluble TEMPO-oxidized polysaccharides that contain significant amounts of sodium carboxylate groups have been prepared by TEMPO-catalyzed oxidation, and they have unique properties and functionalities. When crystalline native cellulose and chitin are oxidized by the TEMPO/NaBr/NaClO system under suitable conditions, the obtained water-insoluble oxidized products can be converted to various characteristic nanomaterials by mechanical disintegration in water, depending on the oxidation and disintegration conditions.

TEMPO-catalyzed oxidation of polysaccharides

(Isogai, Polymer Journal, 2021)

Cellulose-nanofiber-reinforced rubber composites with resorcinol resin prepared by elastic kneading

 A resorcinol resin/water dispersion and a rubber latex are added to 1% 2,2,6,6,-tetramethylpyperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TEMPO-CNFs) dispersed in water, followed by oven drying at 40 °C for 20 h to prepare a dried TEMPO-CNF/resorcinol resin/latex rubber (DTRL) mixture with a weight ratio of 1/0.5/3. DTRL is then added to a nitrile-butadiene rubber (NBR) or a carboxy group-containing NBR (X-NBR) sheet, and the mixture is kneaded by a two-roll mill at 20–30 °C with high shear forces. The tensile strength and Young’s modulus of the crosslinked DTRL/rubber composite sheets remarkably increased from 10 and 12 MPa, respectively, for the reference sheet to 24 and 82 MPa, respectively, for the DTRL/rubber composite sheets containing ≈10 vol% TEMPO-CNFs. Scanning electron microscopy revealed that no TEMPO-CNF agglomerates are present in the DTRL/rubber composite sheets. The tensile properties of the composite sheets are the best when a X-NBR sheet and NBR latex are used as the matrix rubber and latex in DTRL preparation, respectively. When water-extracted DTRL (WDTRL, mass recovery ratio ≈94%) is used in place of DTRL, the WDTRL/rubber composite sheets show sufficient water resistance, while the tensile properties are almost the same as those of the DTRL/rubber composite sheets.

Cellulose-nanofiber-reinforced rubber composites with resorcinol resin prepared by elastic kneading

(Noguchi et al., Composite Science and Technology, 2021)

TEMPO/NaBr/NaClO and NaBr/NaClO oxidations of cotton linters and ramie cellulose samples

 Dried cotton linters and ramie cellulose samples were oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/NaBr/NaClO and NaBr/NaClO (i.e., TEMPO-free) in water at pH 10. The carboxy contents, degrees of polymerization (DPs), X-ray diffraction patterns, and solid-state 13C NMR spectra were measured or obtained for the oxidized products with and without subsequent NaBH4 reduction. Cellulose nanofibrils were prepared from the oxidized cellulose samples by sonication in water and observed by atomic force microscopy and transmission electron microcopy. Because the cellulose molecules were depolymerized with NaBr/NaClO, the depolymerization behavior of the cellulose samples with TEMPO/NaBr/NaClO can be mainly explained by depolymerization with NaBr/NaClO (i.e., not TEMPO-related compounds or reactions). However, because C6-aldehydes formed in the disordered regions periodically present along the longitudinal direction of each cellulose microfibril, the viscosity-average DP values of the TEMPO/NaBr/NaClO-oxidized cellulose samples decreased to 200–300, while those with subsequent NaBH4 reduction exhibited much higher DP values. The nanofibrils prepared from the TEMPO/NaBr/NaClO-oxidized cellulose samples had smallest fibril heights or widths of 5–6 nm. However, significant amounts of unfibrillated bundles with heights of 10–40 mm were present in the nanofibril/water dispersions. The high carboxy contents of the TEMPO/NaBr/NaClO-oxidized cellulose samples (1.62–1.63 mmol/g) indicated that significant amounts of carboxy groups were likely present in the disordered regions, probably forming tail-like polyglucuronate chains. Solid-state 13C NMR analysis revealed that some of the glucosyl units originally with the tg C6–OH conformation were transformed to other conformations by TEMPO/NaBr/NaClO oxidation, while the crystalline C4 signal areas remained constant.

TEMPO/NaBr/NaClO and NaBr/NaClO oxidations of cotton linters and ramie cellulose samples

(Ono et al., Cellulose, 2021)

Nanocellulose-containing cellulose ether composite films prepared from aqueous mixtures by casting and drying method

 A TEMPO-oxidized cellulose nanofibril (TEMPO-CNF)/water dispersion was mixed with an aqueous solution of hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), methyl cellulose (MC), or carboxymethyl cellulose sodium salt (CMC). The mixtures were converted into TEMPO-CNF/cellulose ether composite films containing 0–5% TEMPOCNFs by casting and drying of the aqueous mixtures. All the composite films had high light transparency. However, the tensile properties of the composite films of a given TEMPO-CNF content differed for the HPC and HEC, MC, and CMC matrices. The nanoreinforcing effect owing to TEMPO-CNFs was evident in the TEMPO-CNF/HPC composite films, which became strong but brittle. In contrast, the TEMPOCNF/HEC composite films did not exhibit this nanoreinforcing effect. Transmission electron microscopy observation of the film cross-sections revealed that the TEMPO-CNF elements were homogeneously distributed in the 5% TEMPO-CNF/HPC composite film. In contrast, the TEMPO-CNF elements were densely present on the top and bottom surfaces of the 5% TEMPO-CNF/HEC composite film; the TEMPOCNFs were heterogeneously distributed in the HEC matrix. The low gelation or aggregation concentrations of TEMPO-CNFs in water may have resulted in the different distribution states of TEMPO-CNFs, depending on the cellulose ether matrix used, and hence the different tensile behaviors.

Nanocellulose-containing cellulose ether composite films prepared from aqueous mixtures by casting and drying method

(Okahashi et al., Cellulose, 2021)

Emerging nanocellulose technologies: recent developments

 Nanocelluloses have unique morphologies, characteristics, and surface nanostructures, and are prepared from abundant and renewable plant biomass resources. Therefore, expansion of the use of CO2-accumulating nanocelluloses is expected to partly contribute to the establishment of a sustainable society and help overcome current global environmental issues. Nanocelluloses can be categorized into cellulose nanonetworks, cellulose nanofibrils, and cellulose nanocrystals, depending on their morphologies. All of these materials are first obtained as aqueous dispersions. In particular, cellulose nanofibrils have homogeneous ≈3 nm widths and average lengths of >500 nm, and significant amounts of charged groups are present on their surfaces. Such charged groups are formed by carboxymethylation, C6-carboxylation, phosphorylation, phosphite esterification, xanthation, sulfate esterification, and C2/C3 dicarboxylation during the pretreatment of plant cellulose fibers before their conversion into cellulose nanofibrils via mechanical disintegration in water. These surface-charged groups in nanocelluloses can be stoichiometrically counterion-exchanged into diverse metal and alkylammonium ions, resulting in surface-modified nanocelluloses with various new functions including hydrophobic, water-resistant, catalytic, superdeodorant, and gas-separation properties. However, many fundamental and application-related issues facing nanocelluloses must first be overcome to enable their further expansion.

Emerging nanocellulose technologies: recent developments

(Isogai, Advanced Materials, 2021)

Recent advances in cellulose-based piezoelectric and triboelectric nanogenerators for energy harvesting: a review

 Cellulose is the most earth-abundant natural polymer resource, which with combined eco-friendly and extraordinary sustainable properties such as renewability, biodegradability, low cost and excellent biocompatibility has been widely used by humans for thousands of years. In the past few years, many novel cellulosic materials and their unique applications have been developed including the recent research focus on energy harvesting. The high crystallization and plentiful polar hydroxyl groups endow cellulose with a large number of dipoles and strong electron donating capacity, resulting in a promising potential of piezoelectric and triboelectric effects. However, there is no review about cellulose-based nanogenerators until now. In this paper, the most recent developments of designing, modification, processing and integration of cellulose-based piezoelectric nanogenerators (PENGs), triboelectric nanogenerators (TENGs) and hybrid piezo/triboelectric nanogenerators (PTENGs) for energy harvesting and other applications are reviewed in detail. For cellulose-based PENGs, representative basic piezoelectric cellulose and recent research on PENG devices are discussed. For cellulose-based TENGs, several effective strategies including rough modification of contact surface, addition of electronic functional fillers and chemical modification for improving the output performance are further summarized. Meanwhile, the latest cellulose-based hybrid PTENG is also introduced from the fundamental design to the investigations on enhanced strategies. The opportunities and challenges of these cellulose-based nanogenerator devices are put forward in the final part, which could enable this upto-date and state-of-the-art review to be an effective guidance for the future research on cellulose-based nanogenerators in energy harvesting.

Recent advances in cellulose-based piezoelectric and triboelectric nanogenerators for energy harvesting: a review

(Song, et al., Journal of Materials Chemistry A, 2021)

Developing fibrillated cellulose as a sustainable technological material

 Cellulose is the most abundant biopolymer on Earth, found in trees, waste from agricultural crops and other biomass. The fibres that comprise cellulose can be broken down into building blocks, known as fibrillated cellulose, of varying, controllable dimensions that extend to the nanoscale. Fibrillated cellulose is harvested from renewable resources, so its sustainability potential combined with its other functional properties (mechanical, optical, thermal and fluidic, for example) gives this nanomaterial unique technological appeal. Here we explore the use of fibrillated cellulose in the fabrication of materials ranging from composites and macrofibres, to thin films, porous membranes and gels. We discuss research directions for the practical exploitation of these structures and the remaining challenges to overcome before fibrillated cellulose materials can reach their full potential. Finally, we highlight some key issues towards successful manufacturing scale-up of this family of materials.

(Li, et al., Nature, 2020)

Analysis of celluloses, plant holocelluloses, and wood pulps by size-exclusion chromatography/multi-angle laser-light scattering

 Size-exclusion chromatography with multi-angle laser-light scattering and refractive index detection (SEC/ MALLS/RI) provides the number- and weight-average molar masses, molar mass distributions, conformations, and linear/branched structures of polymers. In the case of pure celluloses including highly crystalline tunicate and alga celluloses, and hemicellulose-rich plant holocelluloses, soaking in ethylene diamine (EDA) and subsequent solvent exchange to N,N-dimethylacetamide (DMAc) though methanol is effective for complete dissolution in ~8% (w/w) LiCl/DMAc. SEC/MALLS/RI analysis can, therefore, be applied to pure celluloses, chemical wood pulps, and plant holocelluloses after dissolution in ~8% (w/w) LiCl/DMAc, dilution to 1% (w/v) LiCl/DMAc and membrane filtration. All pure celluloses and the high-molar-mass cellulose fractions of hardwood and grass holocelluloses have linear and random-coil conformations and various average molar masses and molar mass distributions depending on the cellulose and holocellulose resources. In contrast, Japanese cedar (i.e., softwood) holocellulose and softwood bleached kraft pulp have alkali-stable cellulose/glucomannan branched structures in the high-molar-mass fractions.

Analysis of celluloses, plant holocelluloses, and wood pulps by size-exclusion chromatography/multi-angle laser-light scattering

(Ono and Isogai, Carbohydrate Polymers, 2020)

Branched structures of plant cellulose molecules related to plant evolution

 Plant holocelluloses can be totally dissolved in 8% LiCl/DMAc after ethylene diamine pretreatment. The plant holocellulose solutions are then analyzed by SEC/MALLS/UV/RI system, to investigate branched structures of high-molar-mass (HMM) cellulose fractions. The results show that the HMM cellulose fractions in hardwood and grasses have the same linear structures as those of bacterial, tunicate, and algal celluloses. In contrast, the HMM cellulose fractions in moss, adiantum, and gymnosperm have branched structures with glucomannan via lignin or lignin-like compounds. These cellulose/glucomannan branched structures may contribute to tall and strong gymnosperm trees with long life times.

(Ono et al., ACS Symposium Series, 2017)

Xylem Formation in Trees, Analyzed by NanoSIMS/13C-Labelling

 High lateral resolution secondary ion mass-spectroscopy (NanoSIMS) in combination with 13C-labelling technique is applied to investigation of the formation process of xylem, consisting of cellulose, hemicelluloses, and lignin. When poplar trees are grown in air containing 13CO2 for short time, distribution of 13C-labelled components in xylem is observed with high resolution by NanoSIMS.

(Takeuchi et al., in preparation)

Cellulose Nanofiber/Polymer Composites and their Characterization

 Wood cellulose nanofibers (CNFs) are bio-nanomaterials with high tensile strengths and moduli. Therefore, CNFs are expected as nanofillers for CNF/polymer composite materials with light weight yet high strengths. However, because CNFs are originally obtained as water dispersions and therefore highly hydrophilic, CNFs easily aggregate in hydrophobic polymer matrices during mixing process, resulting that almost no positive properties appear on the composites. In contrast, CNF/elastomer mixtures are mixed under high shear conditions using a three-roll mixer, high tensile strengths, moduli, and ductility concomitantly appear on the composites. STEM and NMR analyses of the composites show that homogeneous distribution of CNFs in polymer matrix is the key factor, influencing the improvement of mechanical properties of the CNF/elastomer composites.

(Noguchi et al., Composite Science and Technology, 2020)

Self-Assembly Behavior of New Cellulose Nanocrystals

 Needle-like new cellulose nanocrystals (CNCs) with aspect (length/width) ratios of <50 can be prepared from TEMPO-oxidized cellulose fibers by sonication in water for long time. When dynamic light scattering analysis is applied to CNC/water dispersions with various CNC consistencies, the transition CNC concentration from homogeneous dispersion to gel state can be determined. When the CNC length decreases to 1/2, the gelation point of the dispersion increases to 4 times as much as that of the original TEMPO-oxidized cellulose nanofiber dispersion.

(Zhou et al., Biomacromolecules, 2019)

Preparation of Cellulose Nanofiber/FeOOH Composites for F-Ion Trapping

 Iron oxyhydroxide (FeOOH) molecule has a unique structure, in which fluoride ion can selectively be trapped. When FeOOH molecules are formed on the TEMPO-oxidized cellulose nanofibers as templates, the FeOOH/cellulose nanofiber composites are expected to efficiently remove fluoride ions for drinking and industrial water grade.

(Umehara et al., in preparation)

Determination of dn/dc value of Cellulose in 1% LiCl/DMAc

 When weight- and number average molar masses of cellulosic materials are determined by SEC/MALLS, an accurate dn/dc value of cellulose in 1% LiCl/DMAc used as an eluent should be determined beforehand. In literature, various dn/dc values have been reported, and consequently the calculated molar mass values vary, depending on the dn/dc value. We have made clear the reasons for discrepancy of dn/dc values between publications, and an accurate dn/dc value is obtained as 0.131 mL/g for cellulose in 1% LiCl/DMAc. Because each hydroxy group of cellulose forms an unstable complex structure with LiCl and DMAc, the dn/dc values change, depending on the cellulose concentration. Furthermore, dissolution states of chitin, pullulan, and other polysaccharides and their derivatives in solutions have been clarified, associated with their accurate dn/dc values, by SEC/MALLS.

(Ono et al., International Journal of Biological Macromolecules, 2018; Biomacromolecules, 2018)

Distribution of Carboxylate Groups in TEMPO-Oxidized Celluloses

 Distributions of carboxylate groups in cellulose molecules, which are introduced to cellulose fibers by TEMPO-mediated oxidation, are analyzed by position-selective methyl and methyl-anthracene esterification, and successive dissolution in LiCl/DMAc and SEC/MALLS/UV/RI analysis. In the case of algal cellulose microfibrils with a large crystal size, carboxylate groups are formed selectively in the cellulose microfibril surfaces associated with partial surface-depolymerization. In contrast, in the case of TEMPO-oxidized plant celluloses, carboxylate groups are homogeneously distributed from low- to high-molar-mass regions, indicating that each plant cellulose microfibril has a different cellulose chain packing structure from that of algal cellulose.

(Ono et al., Biomacromolecules, 2019)

Structural Analyses of Plant Cellulose Microfibrils

 Wood cellulose fiber is oxidized by TEMPO-mediated oxidation and successive sonication in water. The kink formation and fragmentation mechanisms of the obtained TEMPO-oxidized cellulose nanofibers and nanocrystals are analyzed by AFM, SEC/MALLS, and solid-state 13C-NMR analyses. The results show that each wood cellulose microfibril consists of 32 fully extended cellulose chains in average, forming a hexagonal cross section structure. Furthermore, TEMPO-mediated oxidation causes not only position-selective oxidation of C6-OH groups to C6-carboxylate groups but also significant side reactions such as depolymerization, partial detachment of surface chains, and formation of homopolymer chains and disordered regions occur simultaneously, which cannot be ignored in TEMPO-mediated oxidation of natural cellulose fibers.

(Zhou et al., Biomacromolecules, 2020)

Related Analytical Apparatuses

CAMECA NanoSIMS 50L
(MEXT project)

JEOL solid-stateCP-MAS 13C-NMR(JST-CREST project)

JEOL solid-state CP-MAS 13C-NMR
(JST-CREST project)

MOCON oxygen and moisture permeability analyzers (NEDO Nanotech project)

MOCON oxygen and moisture permeability analyzers
(NEDO Nanotech project)

SEC/MALLS/UV/RI system (JSPS project)

SEC/MALLS/UV/RI system
(JSPS project)

High-performance liquid chromatogram for sugar composition analysis (JST-CREST project)

High-performance liquid chromatogram for sugar composition analysis(JST-CREST project)

Ultrasonic homogenizer

Ultrasonic homogenizer

Dynamic laser particle size/zeta-potential analyzer

Dynamic laser particle size/
zeta-potential analyzer

High-pressure homogenizer

High-pressure homogenizer

Phase-contrast optical microscopy

Phase-contrast optical microscopy

Electron spin resonance apparatus

Electron spin resonance apparatus

pH stat (automatic pH controller)

pH stat (automatic pH controller)

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