Hydrothermal Gelation of Pure Cellulose Nanofiber Dispersions

The gelation of cellulose nanofibers (CNFs) through conventional cross-linking or reprecipitation requires the use of additives. Here, for the first time the gelation of pure CNF dispersions has been achieved solely by mechanical disintegration and a hydrothermal process without chemical modification. Different concentrations of cellulose powder were dispersed in water, following which these CNF dispersions were subjected to hydrothermal treatment at 160 degrees C for different lengths of time in a sealed reactor. Self-sustaining hydrogels with no discoloration were obtained. The chemical properties and crystal structures of the CNFs were essentially unchanged following hydrothermal treatment. Although the molecular mass of the cellulose was slightly reduced, the polymer density of cellulose at the same hydrodynamic radius was unchanged by hydrothermal treatment. Hence, chemically cross-linked structures did not form during the hydrothermal process. Instead, physical network structures developed within the CNF hydrogels, which increased the mechanical strength. Moreover, this network structure and therefore the strength of the hydrogel could be improved by increasing the mechanical disintegration time or the cellulose concentration of the CNF dispersion. To ensure sufficient hydrothermal gelation, it was important that the CNF dispersion had a storage modulus greater than 20 Pa.ArticleACS Applied Polymer Materials. 1: 1045-1053. (2019)journal articl

Systematic dynamic viscoelasticity measurements for chitin nanofibers prepared with various concentrations, disintegration times, acidities, and crystalline structures

Epub 2018 Apr 16Dynamic viscoelasticities were measured for chitin nanofiber (ChNF) dispersions prepared with various concentrations, disintegration times, acidities, and crystalline structures. The 0.05 w/v% dispersions of pH neutral ChNFs continuously exhibited elastic behavior. The 0.05 w/v% dispersions of acidified ChNFs, on the other hand, transitioned from a colloidal dispersion to a critical gel and then exhibited elastic behavior with increasing ChNF concentration. A double-logarithmic chart of the concentration vs. the storage modulus was prepared and indicated the fractal dimension and the nanostructure in the dispersion. The results determined that the neutral alpha- and beta-ChNFs were dispersed but showed some remaining aggregations and that the acidified beta-ChNFs were completely individualized. In addition, the alpha-chitin steadily disintegrated with increasing disintegration time, and the aspect ratio of the beta-chitin decreased as a result of the exscessive disintegration. The storage moduli of the ChNFs were greater than those of chitin solutions, nanorods, and nanowhiskers with the same solids concentrations.ArticleINTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES. 115:431-437 (2018)journal articl

Self-Sustaining Cellulose Nanofiber Hydrogel Produced by Hydrothermal Gelation without Additives

We prepared a self-sustaining hydrogel from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs) via hydrothermal treatment at 160 °C. The self-sustaining hydrogels could be obtained at less than 1 wt% TOCNs without any additives. Brownish hydrogels obtained after the hydrothermal treatment could be rendered transparent by immersing them in distilled water at 5 °C. The compressive modulus of the hydrogel increased with increasing heating time. X-ray diffraction studies reveal that the crystal structure of the internal layers of the TOCNs remained intact after the hydrothermal treatment and depigmentation. The hydrothermal treatment caused the hydrolysis of molecules, especially the glucuronate units, from the external layer of TOCN. The elimination of the glucuronate units decreased the net negative surface charge of the TOCNs, resulting in their aggregation into a three-dimensional network structure owing to the predominance of attractive forces. Such additive-free hydrogels which can be shaped into diverse forms are promising for medical applications.ArticleACS Biomaterials Science & Engineering. 4: 1536-1545. (2018)journal articl

Effect of the degree of acetylation on the physicochemical properties of α-chitin nanofibers

Available online 27 March 2020.The effective utilization of abundant α-chitin resources for materials engineering applications requires methods for controlling the physicochemical properties of α-chitin nanofiber (NF) dispersions. Herein, the relationship between the degree of acetylation (DA) of α-chitin and the physicochemical properties of α-chitin nanofibers (α-ChNFs) was investigated. α-Chitin with different DAs was prepared by varying the deacetylation treatment time. These α-chitin samples were disintegrated into NFs using wet pulverization. The average width of the α-ChNFs decreased with decreasing DA. Furthermore, the transmittance and viscosity of the α-ChNF dispersions increased with decreasing DA. We successfully developed a simple model for estimating the average width of α-ChNFs with different DAs. These results indicate that the DA is an effective parameter for defining and controlling the physicochemical properties of α-ChNFs.ArticleInternational Journal of Biological Macromolecules.155:350-357(2020)journal articl

Conversion of N-acetyl-d-glucosamine to nitrogen-containing chemicals in high-temperature water

Available online 19 July 2019To demonstrate the conversion of renewable biomass to platform chemicals, we previously reported the non catalytic conversion of N-acetyl-D-glucosamine (GlcNAc), which is obtained from chitin, to nitrogen-containing chemicals; however, various aspects of this process were not clarified. Herein, we reported updated and expanded results for the synthesis of nitrogen-containing chemicals from GlcNAc in high-temperature water at 180-280 degrees C and 25 MPa with a reaction time of 5-34 s. The main products were 2-acetamido-2,3-dideoxy-D-erythro-hex-2-enofuranose (Chromogen I) and 3-acetamido-5-(1',2'-dihydroxyethyl)furan (Chromogen III) with the maximum yields of 37.0% and 34.5%, respectively. Although 3-acetamido-5-acetylfuran was expected to form by the dehydration of Chromogen III, a yield of only < 1% was obtained, likely because the dehydration of Chromogen III is difficult in the absence of a catalyst. The evaluation of the effects of acid and base catalysts on the dehydration of GlcNAc revealed that the acid catalyst suppressed the transformation of GlcNAc to Chromogen I and promoted the transformation of Chromogen I to Chromogen III, whereas the base catalyst had the opposite effects on these processes. The synthesis of nitrogen-containing chemicals from GlcNAc in high temperature water is an environmentally benign method for utilizing renewable chitin biomass.ArticleFUEL PROCESSING TECHNOLOGY. 195:106154 (2019)journal articl

Non-catalytic conversion of chitin into Chromogen I in high-temperature water

Epub 2019 June 21The non-catalytic conversion of chitin into N-acetyl-ᴅ-glucosamine (GlcNAc) derivatives such as 2-acetamido-2,3-dideoxy-ᴅ-erythro-hex-2-enofuranose (Chromogen I) was investigated in high-temperature water at 290–390 °C and 25 MPa with a reaction time of 0–180 min. High-temperature water treatment is a promising method for chitin conversion as it does not require the use of any additional organic solvents or ionic liquids. A semi-batch reactor was developed to control the reaction temperature and time. It was found that the chitin powder could be converted into a water-soluble fraction in ~90% yield, with Chromogen I being obtained in a maximum yield of 2.6%. Furthermore, a kinetic model was developed to estimate the reaction rate for the conversion of the chitin powder to the water-soluble fraction.ArticleINTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES. 136:994-999 (2019)journal articl

Control-Data Separation and Logical Condition Propagation for Efficient Inference on Probabilistic Programs

We introduce a novel sampling algorithm for Bayesian inference on imperative probabilistic programs. It features a hierarchical architecture that separates control flows from data: the top-level samples a control flow, and the bottom level samples data values along the control flow picked by the top level. This separation allows us to plug various language-based analysis techniques in probabilistic program sampling; specifically, we use logical backward propagation of observations for sampling efficiency. We implemented our algorithm on top of Anglican. The experimental results demonstrate our algorithm's efficiency, especially for programs with while loops and rare observations.Comment: 11 pages with appendice

Effect of purification method of β-chitin from squid pen on the properties of β-chitin nanofibers

Published online 20 June 2016The relationship between purification methods of β-chitin from squid pen and the physicochemical properties of β-chitin nanofibers (NFs) were investigated. Two types of β-chitin were prepared, with β-chitin (a → b) subjected to acid treatment for decalcification and then base treatment for deproteinization, while β-chitin (b → a) was treated in the opposite order. These β-chitins were disintegrated into NFs using wet pulverization. The β-chitin (b → a) NF dispersion has higher transmittance and viscosity than the β-chitin (a → b) NF dispersion. For the first time, we succeeded in obtaining 3D images of the β-chitin NF dispersion in water by using quick-freeze deep-etch replication with high-angle annular dark field scanning transmission electron microscopy. The β-chitin (b → a) NF dispersion has a denser and more uniform 3D network structure than the β-chitin (a → b) NF dispersion. Widths of the β-chitin (a → b) and (b → a) NFs were approximately 8–25 and 3–10 nm, respectively.ArticleINTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES. 91:987-993 (2016)journal articl

Effect of acidity on the physicochemical properties of α- and β-chitin nanofibers

Published online 11 Apr 2017We have investigated whether acidity can be used to control the physicochemical properties of chitin nanofibers (ChNFs). In this study, we define acidity as the molar ratio of dissociated protons from the acid to the amino groups in the raw chitin powder. The effect of acidity on the physicochemical properties of α- and β-ChNFs was compared. The transmittance and viscosity of the β-ChNFs drastically and continuously increased with increasing acidity, while those of the α-ChNFs were not affected by acidity. These differences are because of the higher ability for cationization based on the more flexible crystal structure of β-chitin than α-chitin. In addition, the effect of the acid species on the transmittance of β-ChNFs was investigated. The transmittance of β-ChNFs can be expressed by the acidity regardless of the acid species, such as hydrochloric acid, phosphoric acid, and acetic acid. These results indicate that the acidity defined in this work is an effective parameter to define and control the physicochemical properties of ChNFs.ArticleINTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES. 102:358-366 (2017)journal articl

Identification, cloning and heterologous expression of biosynthetic gene cluster for desertomycin

From our in-house microbial genome database of secondary metabolite producers, we identified a candidate biosynthetic gene cluster for desertomycin from Streptomyces nobilis JCM4274. We report herein the cloning of the 127-kb entire gene cluster for desertomycin biosynthesis using bacterial artificial chromosome vector. The entire biosynthetic gene cluster for desertomycin was introduced in the heterologous host, Streptomyces lividans TK23, with an average yield of more than 130 mg l(-1)