Showing papers by "Jun-ichi Kadokawa published in 2015"

Fabrication and characterization of polysaccharide ion gels with ionic liquids and their further conversion into value-added sustainable materials.

Abstract: A review of the fabrication of polysaccharide ion gels with ionic liquids is presented. From various polysaccharides, the corresponding ion gels were fabricated through the dissolution with ionic liquids. As ionic liquids, in the most cases, 1-butyl-3-methylimidazolium chloride has been used, whereas 1-allyl-3methylimidazolium acetate was specifically used for chitin. The resulting ion gels have been characterized by suitable analytical measurements. Characterization of a pregel state by viscoelastic measurement provided the molecular weight information. Furthermore, the polysaccharide ion gels have been converted into value-added sustainable materials by appropriate procedures, such as exchange with other disperse media and regeneration.

Fabrication of nanostructured and microstructured chitin materials through gelation with suitable dispersion media

Abstract: Recent developments in the fabrication of nano- and microstructured chitin materials are reviewed, specifically focusing on approaches through gelation with suitable dispersion media. Although chitin is one of the most abundant natural polysaccharides, it is under-used as a result of its poor solubility and difficulties in processing. The dissolution of chitin in different solvent systems, including ionic liquids, has been investigated for the production of various materials. For example, the ionic liquid 1-allyl-3-methylimidazolium bromide dissolved chitin at concentrations up to 5% w/w and formed ion gels at higher concentrations of chitin. A highly concentrated solution of CaBr2·2H2O/methanol also induced the gelation of chitin. As one of the most efficient methods of production of nanomaterials from chitin, self-assembled nanofibers have been fabricated by regeneration from solutions or gels of chitin with the appropriate solvents and dispersion media using a bottom-up approach. For example, a chitin ion gel with 1-allyl-3-methylimidazolium bromide was regenerated using methanol to produce a chitin nanofiber dispersion, which was then used to construct a film with a highly entangled nanofiber morphology by filtration. Physical and chemical approaches have been investigated for the fabrication of composite materials of self-assembled chitin nanofibers with other polymeric components. Poly(vinyl alcohol) and carboxymethyl cellulose were made compatible with chitin nanofibers by co-regeneration and electrostatic interaction procedures, respectively. Surface-initiated graft polymerization of some monomers from chitin nanofiber films with the appropriate initiating groups have been conducted using the latter approach to obtain composite films covalently linked to graft chains on the nanofibers. Regeneration from gels with CaBr2·2H2O/methanol resulted in the efficient production of microporous materials.

Synthesis of chitin and chitosan stereoisomers by thermostable α-glucan phosphorylase-catalyzed enzymatic polymerization of α-D-glucosamine 1-phosphate

Abstract: The relationship between two aminopolysaccharide stereoisomers, namely α-(1→4)- and β-(1→4)-linked (N-acetyl)-D-glucosamine polymers, is of significant interest within the field of polysaccharide science, as they correspond to amino analogs of the representative abundant natural polysaccharides, viz. amylose and cellulose. While the latter glucosamine polymer is the basis of well-known natural polysaccharides, chitin and chitosan (linear polysaccharides composed of β-(1→4)-linked N-acetyl-D-glucosamine and D-glucosamine), to the best of our knowledge, the former (α-(1→4)-linked) has not been observed in nature. For the purpose of these studies, the synthesis of such non-natural aminopolysaccharides was performed by the thermostable α-glucan phosphorylase (from Aquifex aeolicus VF5)-catalyzed enzymatic polymerization of α-D-glucosamine 1-phosphate (GlcN-1-P), via successive α-glucosaminylations, in ammonia buffer containing Mg2+ ions, resulting in the production of the α-(1→4)-linked D-glucosamine polymers, corresponding to the structure of the chitosan stereoisomer. Subsequent N-acetylation of the products gave the aminopolysaccharides, corresponding to the chitin stereoisomer.

Preparation of Chitin Nanofiber-Reinforced Cellulose Films Through Stepwise Regenerations from Individually Prepared Ion Gels

Abstract: In this study, we investigated the preparation of chitin nanofiber (CNF)-reinforced cellulose films through stepwise regeneration procedures from the respective ion gels with ionic liquids. Self-assembled CNF dispersions were prepared by regeneration from the chitin ion gel with the ionic liquid, 1-allyl-3-methylimidazolium bromide, using methanol, followed by dilution with adjusted amounts of methanol. Cellulose ion gels with the ionic liquid, 1-butyl-3-methylimidazolium chloride, were then prepared, soaked in the CNF dispersions, and centrifuged to simultaneously occur regeneration of cellulose and compatibilization with the CNFs. Soxhlet extraction with methanol and subsequent drying of the resulting materials gave the CNF/cellulose composite films. The IR and SEM results of the films indicated the presence of CNFs not only on the surfaces of the films but also inside the films. Powder X-ray diffraction patterns showed the amorphous structure of the cellulose in the film. Tensile testing of the films suggested the reinforcing effect of the CNFs on the mechanical properties of the films.

Surface-Initiated Graft Atom Transfer Radical Polymerization of Methyl Methacrylate from Chitin Nanofiber Macroinitiator under Dispersion Conditions

Abstract: Surface-initiated graft atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) from self-assembled chitin nanofibers (CNFs) was performed under dispersion conditions. Self-assembled CNFs were initially prepared by regeneration from a chitin ion gel with 1-allyl-3-methylimidazolium bromide using methanol; the product was then converted into the chitin nanofiber macroinitiator by reaction with α-bromoisobutyryl bromide in a dispersion containing N,N-dimethylformamide. Surface-initiated graft ATRP of MMA from the initiating sites on the CNFs was subsequently carried out under dispersion conditions, followed by filtration to obtain the CNF-graft-polyMMA film. Analysis of the product confirmed the occurrence of the graft ATRP on the surface of the CNFs.

Synthesis of Amylose-Polyether Inclusion Supramolecular Polymers by Vine-twining Polymerization Using Maltoheptaose-functionalized Poly(tetrahydrofuran) as a Primer-guest Conjugate

Abstract: We achieved to synthesize a novel inclusion supramolecular polymer composed of continuum of amylose-poly(tetrahydrofuran) (PTHF) inclusion complexes by phosphorylase-catalyzed enzymatic polymerization using a maltoheptaose-PTHF conjugate according vine-twining polymerization manner. The 1H NMR and X-ray diffraction measurements indicated the presence of the inclusion complex structure in the product. The GPC peak of the amylose segment, which was dissociated by heating the vine-twining polymerization product, shifted to the lower molecular weight region, compared with that of the product, supporting the structure of the inclusion supramolecular polymer. The product by the G-1-P/G7-PTHF feed ratio = 100 was the supramolecular polymer composed of continuum of the amylose-PTHF inclusion complexes, whereas both inclusion complexes and amylose double helixes were present in the product by the G-1-P/G7-PTHF feed ratio over 200.

Acetylation of Xanthan Gum in Ionic Liquid

Abstract: In this paper, we report acetylation of xanthan gum using acetic anhydride in an ionic liquid solvent, 1-butyl-3-methylimidazolium chloride (BMIMCl). Xanthan gum was dissolved with BMIMCl [2 % (w/w)] and the reaction was carried out in the presence of acetic anhydride (five equiv. for hydroxy groups in a repeating unit) with stirring the solution at elevated temperatures. The structures of xanthan gum acetates were confirmed by the 1H NMR and IR spectra. The degree of acetylation (DA) values determined by the 1H NMR analysis increased with the higher reaction temperatures. The thermal gravimetric analysis (TGA) indicated the enhancement of thermal stability by acetylation. Furthermore, the TGA as well as differential scanning calorimetric (DSC) analysis of the products suggested the presence of the highly and less acetylated segments in a xanthan gum chain. The DSC profile of the product with the high DA value also exhibited a small endothermic peak, which might potentially be ascribed to the melting temperature.