Carbon fiber from natural biopolymer Bombyx mori silk fibroin with iodine treatment

Carbon fibers were prepared from silk fibers after an iodine treatment and the carbon yield, fiber morphology, structure and mechanical properties were investigated. A single or multi-step carbonization process was used for the preparation. In the single step process, silk fibroin (SF) fibers were heated from 25 to 800 °C with a heating rate of 5 °C min⁻¹ under Ar atmosphere. However, the carbon fiber obtained was partially melted and was too fragile to handle. For better performance, SF fibers were treated with iodine vapor at 100 °C for 12 h and untreated and iodinated SF fibers were heated from 25 to 800 °C by a multi-step carbonization process, which was defined based on the optimum thermal degradation rate of silk. In this multi-step process, the carbon fibers obtained from iodinated SF were structurally intact and stable in appearance, and the carbon yield achieved was ca. 36 wt.%, much higher than the value for untreated SF. X-ray diffraction, Raman spectroscopy and transmission electron microscopic observation revealed that the obtained carbon fibers from both untreated and iodinated SFs had a basically amorphous structure. The strength of carbon fibers prepared from iodinated SF using the multi-step carbonization was considerably increased compared to that of untreated SF. According to viscoelastic measurement, by heating above 280 °C the iodine introduced intermolecular cross-linking of the SF, and its melt flow was inhibited which produced a higher yield and better performance of the carbon fiber.     

Effect of medium-chain fatty acid positional distribution in dietary triacylglycerol on lymphatic lipid transport and chylomicron composition in rats

The present study was carried out to examine if the positional distribution of medium-chain fatty acid (MCF) in dietary synthetic fat influences lymphatic transport of dietary fat and the chemical composition of chylomicrons in rats with permanent cannulation of thoracic duct. Four types of synthetic triacylglycerol were prepared: (i) sn-1(3) MCF-sn 2 linoleic acid, (ii) interesterified sn-1(3) MCF-sn 2 linoleic acid, (iii) sn-2 MCF-sn-1(3) linoleic acid, and (iv) interesterified sn-2 MCF-sn-1(3) linoleic acid. A purified diet composed of equal amounts of the synthetic fat and cocoa butter was given to rats with permanent lymph duct cannulation. The positional distribution of MCF in the dietary fat had no significant effect on the lymph flow, triacylglycerol output, phospholipid output, lipid composition of chylomicrons, or the particle size. The positional distribution of MCF in the synthetic triacylglycerol was maintained in the chylomicron triacylglycerol. These results showed that MCF in the dietary triacylglycerol is transported into lymphatics and the positional distribution is well preserved in chylomicron triacylglycerol.     

Production of dihomo-γ-linolenic acid byMortierella alpina 1S-4

The mycelial dihomo-γ-linolenic acid content of an arachidonic acid-producing fungus,Mortierella alpina 1S-4, was found to increase, with an accompanying marked decrease in its arachidonic acid content, on cultivation with sesame oil. The resultant mycelia were found to be a rich source of dihomo-γ-linolenic acid. This unique phenomenon was suggested to be due to specific repression of the conversion of dihomo-γ-linolenic acid to arachidonic acid by the oil. After fractionation of the oil with acetone into oil and non-oil fractions, it was found that the effective factor(s) was present in the non-oil fraction. In a study on optimization of the culture conditions for the production of dihomo-γ-linolenic acid byM. alpina 1S-4, a medium containing glucose, yeast extract and the non-oil fraction was found to be suitable for the production. Under the optimal conditions in a 50-1 fermentor, the fungus produced 107 mg of dihomo-γ-linolenic acid/g dry mycelia (2.17 g/l of culture broth). This value accounted for 23.1% of the total fatty acids in the lipids extracted from the mycelia. The mycelia were also rich in arachidonic acid (53.5 mg/g dry mycelia, 11.2%). Other major fatty acids in the lipids were palmitic acid (24.1%), stearic acid (7.0), oleic acid (20.1), linoleic acid (6.6) and γ-linolenic acid (4.1). On leave from Suntory Ltd.     

Silica-supported cobalt catalysts for the selective reduction of nitrogen monoxide with propene

Catalytic behavior of silica-supported transition metals for NO reduction with propene in the presence of oxygen was investigated. While both silica and cobalt oxides did not show any activity for the selective NO reduction, impregnated CoO/SiO₂ prepared from cobalt acetate showed good activity although the preparation conditions had significant effect on the activity. It was suggested that highly dispersed surface Co²⁺ ions on silica are responsible for the catalytic activity.     

Synthesis and electrode performance of layered nickel dioxide containing alkaline ions

Several polymorphs of layered nickel dioxide were prepared by using the chemical insertion of alkaline ions into Li_0.10NiO₂. We used aqueous AOH (A = Li, Na, K) solutions as reducing agents. Sodium and potassium insertion resulted in hydrated layered compounds that can be classified as γ-NiOOH with high crystallinity, while lithium insertion occurred without hydration. We discuss the coordination environment around the A⁺ ions for these inserted compounds. The thermal behavior, analyzed using high temperature (HT) X-ray diffraction (XRD) and thermogravimetric (TG) measurements, indicated that heating the hydrate at 150 °C yielded its dehydrate. The electrode performance of the nickelate was studied in lithium cells. We discuss the effect of interlayer water on cell rechargeability and the similarity between these nickelate and hydrated manganese dioxide (birnessite).     

Crack-Healing Behavior of Si3N4/SiC Ceramics under Cyclic Stress and Resultant Fatigue Strength at the Healing Temperature

Si₃N₄/SiC composite ceramics were sintered and subjected to three-point bending. A semi-elliptical surface crack of 100 μm surface length was made on each specimen. The crack-healing behavior under cyclic stress of 5 Hz, and resultant cyclic fatigue strengths at healing temperatures of 1100° and 1200°C, were systematically investigated. The main conclusions are as follows: (1) Si₃N₄/SiC composite ceramics have an excellent ability to heal a crack at 1100° and 1200°C. (2) This sample could heal a crack even under cyclic stress at a frequency of 5 Hz. (3) The crack-healed sample exhibited quite high cyclic fatigue strength at each crack-healing temperature, 1100° and 1200°C.     

Bromine addition and successive amine substitution of mesoporous ethylenesilica: Reaction, characterizations and arsenate adsorption

Bromination and subsequent ethylenediamine substitution of the CC double bond in mesoporous ethylenesilica were carried out to explore the characteristics of this periodic mesoporous organosilica. The structures of the products (BrPMO and EDA–BrPMO, respectively) were analysed by IR, Br K-edge EXAFS and NMR spectroscopies, as well as X-ray diffraction and nitrogen adsorption. We showed (1) that the formulae of the two products that formed were [CHBrSiO_1.5]_0.45[CHSiO_1.5]_0.55 and [NH₂CH₂CH₂NHCHSiO_1.5]_0.05 [CHBrSiO_1.5]_0.40[CHSiO_1.5]_0.55, respectively, (2) that the addition of Br₂ at room temperature occurred on the CC double bonds with disturbing the framework structure, (3) that IR absorption band of CC bonds that reacted with Br₂ is significantly different from that of inactive CC bond, (4) that the length of the C–Br bond was considerably longer than in conventional alkyl bromides, and (5) that a large proportion of the ν(C–Br) band remained at the same position in the IR absorption spectrum after the ethylenediamine (EDA) substitution, while a new ν(C–Br) absorption also appeared. The mechanisms of these reactions are discussed at both the micro and mesoscopic levels.

Arsenate adsorption on EDA–BrPMO, in which the EDA is directly bound to the “surface” of the mesopores, was compared with adsorption on EDA–Pr–PMO, which was prepared by the direct synthesis of 3-chloropropyl-functionalized mesoporous ethanesilica followed by the substitution of Cl with EDA. The strength of the adsorption, as measured with the distribution coefficient, was greater for the former adsorbent than the latter. The origin of this difference was attributed to the distance between amino group and the surface.     

Radical-induced ionic polymerization in the presence of maleic anhydride. I. Mechanism of polymerization of maleic anhydride by radical initiators

Three kinds of trapped radicals are observed in poly(maleic anhydride) (Poly-MAH) which were prepared by the use of radical initiators such as AIBN or BPO. It was found that these radicals were transformed to the active species so as to initiate the cationic polymerization. The structure of these radicals was studied by the ESR and the kinetic analysis of MAH polymerization in the presence of various additives.     

Control of molecular weight distribution of isotactic polypropylene obtained by a MgCl2-supported TiCl4 catalyst

It is of great importance in propene polymerization to control molecular weight and molecular weight distribution as well as isotacticity. Propene polymerization was carried out with an isospecific MgCl₂/TiCl₄-Cp₂TiMe₂ catalyst in the presence of various kinds of external Lewis bases. It was found that the molecular weight distribution of the isotactic polymer could be controlled while retaining high activity, high isospecificity and high molecular weight only by changing the kind and/or amount of the Lewis bases. © 1997 Elsevier Science Ltd.     

Anodic oxidation effects on pyrolytic graphite surfaces in acid

Anodic oxidation effects on the basal and edge surfaces of pyrolytic graphite in acid were studied by laser Raman spectroscopy, and by a gas-phase chemical modification method coupled with X-ray photoelectron spectroscopy. Surface covering fractions were also studied by -epichlorohydrin monolayer formation. It was found that the species of surface chemical groups added by anodic oxidation was closely related to the structure of the oxidized surface. In the case of the basal surface, carboxyl groups were added by anodic oxidation, being always accompanied by the destruction of its surface structure. On the other hand, in the case of the edge surface, hydroxyl groups were added without the destruction of its structure with a mild treatment. With more severe treatment, carboxyl groups were added and this addition was also accompanied by destruction of the surface structure. There was a range of treatment in which hydroxyl groups could be added without destroying the structure. Finally it was confirmed that both carboxyl and hydroxyl groups could make covalent bonds with epoxy groups of -epichlorohydrin.