ß-(1 → 4)-Polyglucuronic acids with C2/C3-ketones prepared from regenerated cellulose by catalytic oxidation using solid NaOCl·5H2O.

Three commercial regenerated cellulose samples were subjected to TEMPO-catalyzed oxidation using solid NaOCl·5H2O as the primary oxidant for structural analyses of the oxidized products (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl). The regenerated cellulose/water slurries became transparent solutions after oxidation for 60 min. The yields of the oxidized products were almost 100 % when they were isolated as precipitates in ethanol/water mixtures. The solution-state NMR spectra revealed that the oxidized products were almost pure water-soluble ß-(1 â†’ 4)-polyglucuronic acids; the reaction conditions described herein ensured the complete oxidation of the C6-OH groups in the regenerated cellulose samples to C6-carboxy groups. However, the solid-state 13C NMR spectra of the oxidized products indicated that C2/C3-ketones (<20 % of the total units) were formed during side reactions, which is characteristic for oxidized products prepared from regenerated cellulose with the C2/C3-glycol structure. These ketones were likely to form intermolecular hemiacetal linkages in the oxidized products. During conductivity titration of the oxidized products, it is necessary to control the sample masses to accurately determine the carboxy contents. The mass-average degree of polymerization decreased from 330 to 890 for the original regenerated cellulose samples to 65-79 for the oxidized products; substantial depolymerization is inevitable during TEMPO-catalyzed oxidation of the regenerated cellulose samples.

Molecular mechanisms of self-incompatibility in Brassicaceae and Solanaceae.

Self-incompatibility (SI) is a mechanism for preventing self-fertilization in flowering plants. SI is controlled by a single S-locus with multiple haplotypes (S-haplotypes). When the pistil and pollen share the same S-haplotype, the pollen is recognized as self and rejected by the pistil. This review introduces our research on Brassicaceae and Solanaceae SI systems to identify the S-determinants encoded at the S-locus and uncover the mechanisms of self/nonself-discrimination and pollen rejection. The recognition mechanisms of SI systems differ between these families. A self-recognition system is adopted by Brassicaceae, whereas a collaborative nonself-recognition system is used by Solanaceae. Work by our group and subsequent studies indicate that plants have evolved diverse SI systems.

Structural analyses of supernatant fractions in TEMPO-oxidized pulp/water reaction mixtures separated by centrifugation and dialysis.

Side reactions occurring on cellulose during 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TMEPO)-catalyzed oxidation have not been considered to be significant. Then, TEMPO-oxidized hardwood and softwood bleached kraft pulps (HBKP and SBKP) were prepared with an excess NaOCl·5H2O. Supernatant fractions (SFs) were obtained in the aqueous reaction mixtures of TEMPO-oxidized pulps by centrifugation and dialysis. The SFs with carboxyl contents of 5.0 and 4.2 mmol/g were obtained in the yields of 19 % and 30 % from HBKP and SBKP, respectively. These carboxy contents are much higher than those (2.6-2.7 mmol/g) of the precipitate fractions in the TEMPO-oxidized pulps. Solid-state 13C NMR spectra and other analyses revealed that the water-soluble ß-(1 â†’ 4)-polyglucuronic acids were predominantly present in the SFs. In addition, water-insoluble TEMPO-oxidized cellulose nanocrystals were present in the SFs, but they constituted less than ~10 % of the SFs. The mass-average degrees of polymerization (DPw) of the SFs obtained from HBKP and SBKP were 166 and 155, respectively, whereas the original HBKP and SBKP had DPw values of 1990 and 2140, respectively. These substantial depolymerization and formation of the water-soluble ß-(1 â†’ 4)-polyglucuronic acids occur on cellulose and oxidized cellulose molecules as side reactions during TEMPO-catalyzed oxidation, which should be considered for structural analyses of TEMPO-oxidized products.

Correction to "Comprehensive Study of Preparation of Carboxy Group-Containing Cellulose Fibers from Dry-Lap Kraft Pulps by Catalytic Oxidation with Solid NaOCl".

[This corrects the article DOI: 10.1021/acssuschemeng.3c04750.].

Polyglucuronic acids prepared from α-(1 → 3)-glucan by TEMPO-catalytic oxidation.

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-catalytic oxidation was applied to a water-insoluble α-(1 â†’ 3)-glucan in water at pH 10 and room temperature (∼24 °C), with solid NaOCl·5H2O as the primary oxidant. Oxidation with NaOCl at 15 mmol/g gave a water-soluble TEMPO-oxidized product at a mass recovery ratio of 97 %. The carboxy content of the TEMPO-oxidized product was 5.3 mmol/g, which corresponds to a degree of C6-oxidation (DO) of 93 %. A new water-soluble α-(1 â†’ 3)-polyglucuronic acid with a nearly homogeneous chemical structure was therefore quantitatively obtained. X-ray diffraction and solid-state 13C NMR spectroscopic analyses showed that the original α-(1 â†’ 3)-glucan and its TEMPO-oxidized product with a carboxy content of 5.3 mmol/g had crystalline structures, whereas the oxidized products with DOs of 50 % and 66 % had almost disordered structures. The carboxy groups in the oxidized products were regioselectively methyl esterified with trimethylsilyl diazomethane, and analyzed by using size-exclusion chromatography with multi-angle laser-light scattering and refractive index detections. The results show that the original α-(1 â†’ 3)-glucan and its oxidized products with DOs of 50 %, 66 %, and 93 % had weight-average degrees of polymerization of 671, 288, 54, and 45, respectively. Substantial depolymerization of the α-(1 â†’ 3)-glucan molecules therefore occurred during catalytic oxidation, irrespective of the oxidation pH.

Fluoride ion adsorption isotherms, kinetics, and thermodynamics on iron(III) oxyhydroxide powders containing cellulose nanofibrils.

The adsorption isotherms, kinetics, and thermodynamics of fluoride ions (F-) on FeOOH powders in water were investigated to obtain fundamental information on FeOOH powders, which are used as F- adsorbents in drinking and industrial water, and industrial wastewater. FeOOH powders were prepared as precipitates by mixing aqueous FeCl3 and NaOH solutions (1:3 mol/mol) in the presence of 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibrils (TOCNs), carboxymethylcellulose (CMC), or TEMPO-oxidized cellulose (TOC) fibers (without nanofibrillation), and subsequent drying and pulverizing. The FeOOH:TOCN, FeOOH:CMC, and FeOOH:TOC dry mass ratios were controlled at 87:13. The amount of F- adsorbed by the FeOOH/TOCN powder per FeOOH mass was higher than those adsorbed by FeOOH, FeOOH/CMC, or FeOOH/TOC. The F- adsorption isotherms on the FeOOH-containing powders showed higher correlation coefficients with the Langmuir model than with the Freundlich model. This indicates that F- adsorbed on FeOOH initially formed a monolayer, predominantly via physical adsorption. Pseudo-second-order kinetics fitted well to the time-dependent F- adsorption behaviors on the FeOOH-containing powders. Thermodynamic analysis of F- adsorption on the FeOOH-containing powders showed that the ΔG values were negative, which indicates that F- adsorption on the FeOOH-containing powders proceeded spontaneously in water. The negative ΔG value for FeOOH/TOCN was higher than those for FeOOH, FeOOH/CMC, and FeOOH/TOC at the same temperature. This shows that the FeOOH/TOCN powder can be used as an excellent and efficient F- adsorbent in water.

Mechanically robust, flame-retardant phosphorylated cellulose films with tunable optical properties for light management in LEDs.

Biodegradable cellulose films with excellent mechanical, optical, and functional properties have attracted considerable attention as promising alternatives to plastics for photoelectronic devices. In this work, mechanically ductile, flame-retardant cellulose films with tunable optical properties were prepared by simple mechanical disintegration of phosphorylated cellulose (PhC) fibers, vacuum filtration of as-prepared dispersions, and subsequent pressing of the wet PhC films to prepare dried films. When mechanical disintegration conditions were optimized, the resultant PhC films exhibited an average density, tensile strength, Young's modulus, tensile toughness, and folding resistance of 1.4 g/cm3, 150 MPa, 8.5 GPa, 8.2 MJ/m3, and 4580 times, respectively. The PhC film hazes were widely controllable from 9 % to 91 %, while they maintained high light transmittances (>90 %) at a 550-nm wavelength. The PhC films were used for light management of light-emitting diodes by controlling mechanical fibrillation conditions of the PhC fiber/water slurry, showing that the films effectively improved the luminescence uniformity of the devices.

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 chains1-3. 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 polymers2) 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.

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.

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.

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.

Rate-Limited Reaction in TEMPO/Laccase/O2 Oxidation of Cellulose.

The environment-friendly oxidation of cellulose by the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)/laccase/O2 system is an alternative route with huge potential to prepare cellulose nanofibers. It is found that the concentration of TEMPO significantly affects the oxidation efficiency. An effective method for improving the oxidation effect is to increase the TEMPO concentration and prolong the oxidation time. To clarify the rate-limited step of TEMPO/laccase/O2 oxidation of cellulose, the academically accepted oxidation process is divided into individual pathways. A series of experiments is conducted with laccase and the three forms of organocatalyst (TEMPO, oxoammonium (TEMPO+), and hydroxylamine (TEMPOH)) to simulate individual reactions and calculate the reaction rates. The concentrations of TEMPO and oxoammonium are monitored by EPR spectroscopy. The oxidation rate of TEMPO by laccase varies at different pH conditions, and laccase activity is much higher at pH 4.5. Other reactions without laccase involved express a higher reaction rate when the pH value increased. TEMPO is mainly regenerated through a comproportionation reaction between oxoammonium and hydroxylamine. The acceleration of TEMPO regeneration by laccase is not obvious. The results indicate that the rate-limited reaction in TEMPO/laccase/O2 oxidation is cellulose oxidation by TEMPO+.

Primary structure of gum arabic and its dynamics at oil/water interface.

Gum arabic (GA), an arabinogalactan-based gum, is a well-known powerful emulsifier. However, the poor stability of emulsion has often been pointed out. In order to clarify the origin, the structure-property relationship of GA, especially the interfacial property at oil/water interface, needs to be investigated. Here, we tried to correlate the primary structure with interfacial property at oil/water interface. A series of structural analyses by SEC-MALLS, SAXS, etc. showed that the primary structure of GA was a disk-like star shaped nanoparticle. The dynamic interfacial tension measurement showed that GA molecules adsorb onto oil surface in 2 steps: Firstly, the micron-aggregates of GA approach onto the oil surface, and then the aggregates are dissociated into nano-particles so that they cover the oil surface. Therefore, the emulsification and emulsion stability are controlled not by the property of the primary structure of GA but by the higher-order molecular network structure made of GA molecules.

Controlling Miscibility of the Interphase in Polymer-Grafted Nanocellulose/Cellulose Triacetate Nanocomposites.

The miscibility at the interphase of polymer-grafted nanocellulose/cellulose triacetate (CTA) composite films was tailored using different casting solvents. The polymer-grafted cellulose nanofibrils were prepared by modifying surfaces of 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized nanocellulose with amine-terminated poly(ethylene glycol) (PEG). The PEG-grafted nanocelluloses were individually dispersed in dichloromethane, 1,4-dioxane, and N,N-dimethylacetamide. The PEG-grafted nanocellulose/CTA composite films were prepared by mixing the nanocellulose dispersion and CTA solution and subsequent casting-drying. The miscibility of PEG and CTA at the interphase of the composite was controlled by controlling the solvent, which was confirmed by dynamic mechanical analysis. All the composite films showed high optical transparency. However, the mechanical properties of the composites differed because of the difference in the PEG/CTA interfacial miscibility. The composite films with better PEG/CTA interfacial miscibility showed higher Young's modulus, strength, and toughness. This interfacial design technique paves the way to exploiting the reinforcing potential of highly transparent and hydrophobic surface-grafted nanocellulose/polymer composite materials.

Nanocomposite desalination membranes made of aromatic polyamide with cellulose nanofibers: synthesis, performance, and water diffusion study.

Reverse osmosis membranes of aromatic polyamide (PA) reinforced with a crystalline cellulose nanofiber (CNF) were synthesized and their desalination performance was studied. Comparison with plain PA membranes shows that the addition of CNF reduced the matrix mobility resulting in a molecularly stiffer membrane because of the attractive forces between the surface of the CNFs and the PA matrix. Fourier transform-infrared spectroscopy and X-ray photoelectron spectroscopy results showed complex formation between the carboxy groups of the CNF surface and the m- phenylenediamine monomer in the CNF-PA composite. Molecular dynamics simulations showed that the CNF-PA had higher hydrophilicity which was key for the higher water permeability of the synthesized nanocomposite membrane. The CNF-PA reverse osmosis nanocomposite membranes also showed enhanced antifouling performance and improved chlorine resistance. Therefore, CNF shows great potential as a nanoreinforcing material towards the preparation of nanocomposite aromatic PA membranes with longer operation lifetime due to its antifouling and chlorine resistance properties.

Changes to the Contour Length, Molecular Chain Length, and Solid-State Structures of Nanocellulose Resulting from Sonication in Water.

Sonication in water reduced the average contour lengths of nanocellulose prepared from wood cellulose fiber and microcrystalline cellulose. Most of the kinks in the wood cellulose nanofibrils were formed during the initial 10 min of sonication. Fragmentation occurred at the kinks and rigid segments associated with depolymerization during subsequent sonication for 10-120 min, resulting in the formation of cellulose nanocrystals with low aspect ratios. Solid-state cross-polarization magic angle sample spinning 13C-nuclear magnetic resonance revealed that the original crystalline regions of the cellulose were partly transformed to fibril surfaces or disordered regions by both pretreatment and the subsequent fragmentation of molecular chains during sonication. The nanocellulose prepared from microcrystalline cellulose had different fragmentation behavior with regard to molecular chain length following sonication. The results indicated that on average the hexagonal 36 cellulose chain structure formed the cross-section of each wood cellulose microfibril.

Nanocellulose Film Properties Tunable by Controlling Degree of Fibrillation of TEMPO-Oxidized Cellulose.

A fibrous 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized wood cellulose/water slurry was disintegrated with a magnetic stirrer or high-pressure homogenizer under various conditions to prepare TEMPO-oxidized cellulose (TOC)/water dispersions with different degrees of fibrillation. The turbidity value of the as-prepared dispersion was used as a measure of the degree of nanofibrillation of the fibrous TOC slurry in water. The fibrillated TOC/water dispersions with low degrees of fibrillation had cellulose nanonetwork (CNNeW) structures consisting of TOC nanofibrils (TOCNs), unfibrillated TOC fibers, and fibril bundles. The original TOC/water slurry and partly fibrillated TOC/water dispersions with low degrees of fibrillation were converted to a sheet and films, respectively, in a short time by membrane filtration, and they had low bulk densities and high porosities. Membrane filtration of an almost completely nanofibrillated TOC/water or TOCN dispersion took a long time, but the as-prepared TOCN films had the highest light transparency, tensile strength, Young's modulus, and work of fracture. The oxygen permeabilities of the films at 23°C and 50% relative humidity were as low as 1-2 ml µm m-2 day-1 kPa-1 among the films prepared from the fibrillated TOC/water dispersions with a wide turbidity range of 0.01-0.45. Therefore, TEMPO-oxidized CNNeW films with the versatile optical, porous, and mechanical properties but similarly low oxygen permeabilities can be prepared by controlling the degree of fibrillation of the TOC/water slurry (Graphical Abstract).

Synthesis of Chitin Nanofiber-Coated Polymer Microparticles via Pickering Emulsion.

Chitin nanofiber (ChNF) has received significant research attention owing to its potential for use in a variety of applications, such as medicine and cosmetics. Here, we synthesize a novel ChNF material, ChNF-coated polymer microparticles, using a Pickering emulsion-templated approach. Two varieties of ChNF with different crystal structures, lengths, and surface charges were used to form the microparticle shells. When ChNFs with a shorter length and greater surface charge were used, the microparticles showed good dispersibility in water and narrow size distribution with number- and volume-median diameters of 1.46 and 1.84 µm, respectively. The microparticles were easily collected by filtration and redispersed in water, even after drying. The surface ChNF shells assembled at the microparticle surfaces showed potential as an adsorption site, effectively capturing anionic dye molecules. This technique offers new opportunities for the development of green nanocomposite materials using a facile aqueous process.

A bacterial endo-ß-1,4-glucuronan lyase, CUL-I from Brevundimonas sp. SH203, belonging to a novel polysaccharide lyase family.

Cellouronate is a (1,4)-ß-D-glucuronan prepared by TEMPO-mediated oxidation from regenerated cellulose. We have previously isolated a cellouronate-degrading bacterial strain, Brevundimonas sp. SH203, that produces a cellouronate lyase (ß-1,4-glucuronan lyase, CUL-I). In this study, the gene encoding CUL-I was cloned, and the recombinant enzyme was heterologously expressed in Escherichia coli. The predicted CUL-I protein is composed of 426 amino acid residues and includes a putative 21-amino acid signal peptide. The recombinant CUL-I specifically depolymerized ß-1,4-glycoside linkages of cellouronate, and its mode of action was endo-type, like the native CUL-I. Sequence analysis showed CUL-I has no similarity to previously known polysaccharide lyases (PLs), indicating that CUL-I should be classified into a novel PL family.

Carboxylated nanocellulose/poly(ethylene oxide) composite films as solid-solid phase-change materials for thermal energy storage.

Composite films of poly(ethylene oxide) (PEO) and 0%-20% surface-carboxylated cellulose nanofibrils (CNFs) were prepared by mixing the aqueous CNF dispersion and aqueous PEO solution at various weight ratios followed by casting and drying. The 20% CNF/PEO composite film was transparent, whereas the 100% PEO film was translucent. The addition of CNFs to the PEO matrix resulted in decreases of the crystallinity and crystal size of spherical PEO. The Young's modulus and tensile strength of the 100% PEO film were 0.2 GPa and 6.1 MPa, respectively, and remarkably increased to 2.4 GPa and 86 MPa, respectively, with the addition of 20% CNF. The CNF/PEO composite films had clear melting and crystallization temperatures in the heating and cooling processes, respectively. Nevertheless, the coefficients of thermal expansion at temperatures above the melting point of PEO significantly decreased with the CNF addition. The CNF/PEO composite films are therefore promising solid-solid phase-change materials for energy storage with high film dimensional stability.