In situ crystallization of bacterial cellulose II. Influences of different polymeric additives on the formation of celluloses Iα and Iβ at the early stage of incubation

Effects of polymeric additives with different degrees of polymerization (DP) or substitution (DS) on the crystallization of celluloses I and I have been examined at an early stage of the incubation of Acetobactor xylinum by using newly developed FT-IR spectroscopy. It was found that the mass fraction of cellulose I is greatly decreased with increasing concentrations of carboxymethyl cellulose sodium salt (CMC) or xyloglucan (XG) in the incubation medium. Such a decrease in the mass fraction of cellulose I, which corresponds to the enhanced crystallization of cellulose I, is more prominent for CMC or XG with lower DPs, but the additives with too low DPs are not so effective probably due to higher solubility and the lower adhesion on the surface of microfibrils. Moreover, the mass fractions of celluloses I and I are highly correlated with the crystallite size of microfibrils, indicating that I is crystallized in larger-size microfibrils while I is produced in smaller-size microfibrils. On the basis of these experimental results, the mechanism of the crystallization of celluloses I and I is discussed in the Acetobactor xylinum system.     

In Situ crystallization of bacterial cellulose I. Influences of polymeric additives,stirring and temperature on the formation celluloses I α and I β as revealed by cross polarization/magic angle spinning (CP/MAS)13C NMR spectroscopy

To obtain further information about the formation of cellulose I and I, cross polarization/magic angle spinning (CP/MAS)¹³C NMR spectroscopy was used to study the effects of polymeric additives, stirring and culture temperature on the I When xyloglucan (XG) or carboxymethyl cellulose sodium salt (CMC) was added to the incubation medium, the amount of cellulose I decreased markedly, from a normal level of 64% to as low as 30%, with the most additive giving the lowest levels of I. Moreover, stirring causes mixtures containing even small amounts of XG to have a large effect. These results suggest that CMC or XG interferes with the aggregation of fibrillar units into the normal ribbon assemblies. It may be that there is a strain associated with this aggregation that results in the higher-energy I form. Thus, cellulose I may grow preferentially when the strain caused by aggregation is not present. Lower temperatures (36–10 °C) gave an increase in I (from 56 to 72%).     

Pt(II) complexes in activation of saturated hydrocarbons

The rate constants of deuterium exchange for cyclohexane in CH₃COOD/D₂O have been measured in the presence of 12 complexes of Pt(II) with various ligands (Cl, H₂O, NH₃, Br, NO₂, py, DMSO, PPh₃, etc.). The change in the rate constant is shown to follow the reverse series of the trans-effect of Pt(II) ligands. The rate constant of the interaction of PtCl₂S_n (S is H₂O, CH₃COOH, n=1, 2) with cyclohexane in CH₃COOD/D₂O (11), k, equals 2.5×10⁸ exp (–18200/RT) 1 mol^–1 sec^–1 (at 354–385 K). The ratio of rate constants for PtCl₂S₂, PtCl₃S^– and PtCl ₄ ^2– is 10060.5 at 100°C.

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CH₃COOD–D₂O 12- Pt(II) (Cl, H₂O, NH₃, Br, NO₂, , DMCO, PPh₃ .). , Pt(II). PtCl₂S_n (S–H₂O, CH₃COOH, n=1,2) 11 CH₃COOD–D₂O k=2,5·10⁸ exp(–18200/RT). ^{–1 –1} (354–385°). 100°C PtCl₂S₂, PtCl₃S^– PtCl ₄ ^2– 10060,5.

     

In Situ Crystallization of Bacterial Cellulose III. Influences of Different Polymeric Additives on the Formation of Microfibrils as Revealed by Transmission Electron Microscopy

Effects of polymer additives on the formation of microfibrils of bacterial cellulose have been examined by transmission electron microscopy. Among additives with different degrees of polymerization (DP) or substitution (DS), carboxymethyl cellulose sodium salt (CMC) with DP = 80 and DS = 0.57 is the most effective in producing separate, smaller-size microfibrils. By increasing the concentration of this CMC from 0.1 to 1.5%, the percentage of microfibrils measuring 3–7 nm wide is increased and levels off at around 1.0%. Other polymer additives such as xyloglucan are less effective than CMC in producing microfibrils with smaller sizes and the resulting microfibrils still tend to aggregate. The number of charged substituents and the molecular weight seem to be important factors in the production of highly separate smaller-size microfibrils. The reduction in average microfibril size is well correlated to the decrease in mass fraction of cellulose I in bacterial cellulose crystals. On the basis of these results, the mechanism of the crystallization of celluloses I and I is discussed. The effect of colony types, smooth and rough, on the formation of microfibrils in the presence of CMC is also described.     

A physico-chemical study of iron-chromium-molybdenum catalysts

In the study of the Fe_1–xCr_xMo_1·5O₆ system by X-ray, IR and Mössbauer methods the formation of solid state substitution solutions has been detected, which possess similar catalytic properties in methanol oxidation.

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, , Fe_1–xMo_1·5O₆ , .

     

Thermal decomposition of Y,La and light lanthanide ferulates

The conditions of thermal decomposition of Y, La and light lanthanide ferulates have been studied. On heating, these complexes decomposed in various ways; lanthanum ferulate in four stages, Ce(III) ferulate in three stages, and the ferulates of Y, Pr(III), Nd, Sm, Eu(III) and Gd in two stages, the oxides finally being formed. The complexes lose crystallization water to form anhydrous or hydrated salts, and are then decomposed directly to oxides. Only lanthanum ferulate decomposes to the oxide with intermediate formation of La₂O₂CO₃. The temperatures of oxide formation change periodically with the decrease in the ionic potential in the lanthanide series.

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Zusammenfassung Es wurden die Bedingungen der Zersetzung der Y-, La- und leichten Lanthanidferulate untersucht. Die erhaltenen Komplexe werden beim Erhitzen auf verschiedene Weise zersetzt. Lanthanferulat wird über vier, Ce(III)-Ferulat über drei und die Ferulate von Y, Pr(III), Nd, Sm, Eu(III) und Gd über zwei Zwischenstufen in das entsprechende Oxid überführt. Aus den Komplexen entstehen zunächst unter Verlust von Kristallwasser wasserfreie oder hydratisierte Salze, die dann direkt zu den Oxiden abgebaut werden. Nur Lanthanferulat wird über eine intermediäre Verbindung des Typs M₂O₂CO₃ zum Oxid abgebaut. Die Bildungstemperaturen der Oxide ändern sich periodisch mit abnehmenden Ionenpotential in der Lanthanidenreihe.

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Y, La . . , — , Y, (III) Nd, Sm,Eu(III) Gd — . , , . L₂₂₃. .

     

Temperature-programmed reduction and oxidation of bimetallic catalysts Rh?Ag/Al2O3

Investigations of temperature-programmed reduction and oxidation of bimetallic catalysts Rh–Al₂O₃ seem to indicate that there are no strong interactions between rhodium and silver. Bimetallic catalysts rather show the additive properties of individual components, i. e. rhodium and silver.

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- Rh–Al/Al₂O₃ . , .

     

Thermochemical and kinetic studies on the effects of cobalt salicylate on the oxidative degradation of polystyrene

The effect of cobalt salicylate on the oxidative degradation and ignition of polystyrene has been studied. It was found that cobalt salicylate sensitizes both the degradation and ignition of polystyrene by facilitating electron-transfer processes in the propagation step. From thermochemical and kinetic studies it was found that the cobalt ion, owing to its ability to exist in variable valence states, promotes electron transfer in the propagation step of polymer degradation, increasing the rate of propagation and consequently the overall rate. Using solid-phase thermal ignition theory, an attempt has been made to explain the sensitization of ignition by the cobalt ion.

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Zusammenfassung Die Wirkung von Kobaltsalicylat auf den oxydativen Abbau und die Entzündung von Polystyrol wurde untersucht. Es wurde festgestellt, daß Kobaltsalicylat sowohl den Abbau als auch die Entzündung des Polystyrols durch Erleichterung von Elektrontransferprozessen im Kettenfortpflanzungsschritt begünstigt. Thermochemische und kinetische Untersuchungen ergeben, daß das Kobaltion infolge seiner Fähigkeit, in mehreren Valenzstufen aufzutreten, den Elektronentransfer im Kettenfortpflanzungsschritt erleichtert wodurch die Geschwindigkeit der Kettenfortpflanzung und damit die Geschwindigkeit des Gesamtprozesses erhöht wird. Basierend auf der Theorie der thermischen Festphasenentzündung wird ein Versuch unternommen, Erleichterung der Entzündung durch Kobaltionen zu erklären.

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. , , . , , , , . , .

     

Characterization of chiral building blocks for vitamin D metabolites by DSC

The enantiometric purity of a vitamin D₃ metabolite was determined more exactly by means of DSC than by¹ H-NMR. The melting curve was analysed by the partial area method based on the Schröder-van Laar equation. In order to find a suitable method for separation(R)-2,3-dihydroxy-3-methylbutylp-toluenesulfonate from the racemate, the phase diagram of the enantiomers was evaluated from DSC results. The occurrence of a racemic compound was confirmed by an X-ray diffraction investigation of the racemate and the enantiomers. The conclusions are discussed in comparison with the results of previous investigations.

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Zusammenfassung Die Enantiomeren-Reinheit des Vitamin D3-Metaboliten (R)-2,3-Dihydroxy-3-methylbutyl-p-toluensulfonat (R-I) lässt sich durch DSC genauer als mittels¹ H-NMR ermitteln. Dazu wird die Schmelzkurve nach der Partialflächenmethode ausgewertet, die auf der Schröder-van Laar'schen Gleichung beruht.Zum Auffinden einer geeigneten Methode für die Abtrennung des R-Enantiomeren aus dem Racemat wurde das Phasendiagramm der Enantiomeren aus DSC-Messungen konstruiert. Das Vorliegen einer racemischen Verbindung wurde durch Röntgenbeugungsuntersuchungen von Racemat und reinen Enantiomeren bestätigt. Die Ergebnisse werden mit denen früherer Untersuchungen verglichen.

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D₃ , . , -. (R) -2,3--- -- , . . .

     

Activity of some crystal faces of supported palladium catalysts for benzene hydrogenation

Using known coverages of preadsorbed carbon monoxide as a specific poison on supported polycrystalline Pd, the degree of benzene conversion into cyclohexane was measured and compared with the conversion over a CO-free catalyst surface. Palladium crystal faces adsorbing carbon monoxide in various manners are uniformly active for benzene hydrogenation, which appears to be a structure insensitive reaction.

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. . , , . , .

     

A new differential thermal analysis method

A new differential thermal analysis method has been developed which allows fast and accurate determinations of phase equilibria in condensed systems between 400 and 1100°. In this method the temperature is increased stepwise, heat effects being determined by analysis of the transient thermoelectric effects after each step. Between steps the temperature is kept constant until equilibrium is attained. The method has been tested in measurements of displacive solid-state transformations and melting points.

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Zusammenfassung Eine neue Methode der Differentialthermoanalyse wurde entwickelt, welche rasche und genaue Bestimmungen von Phasengleichgewichten in kondensierten Systemen zwischen 400° und 1100° ermöglicht. Bei dieser Methode wird die Temperatur stufenweise erhöht und die Wärmeeffekte durch Analyse der thermoelektischen Übergangseffekte nach jeder Stufe bestimmt. Zwischen den Stufen wird die Temperatur bis zum Erreichen des Gleichgewichts konstant gehalten. Die Methode wurde bei Messungen von Verschiebungsumsetzungen in festem Zustand und von Schmelzpunkten erprobt.

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Résumé Une nouvelle méthode d'analyse thermique différentielle a été mise au point. Elle permet de déterminer de façon rapide et exacte les équilibres de phases dans des systèmes condensés, entre 400 et 1100°. Selon cette méthode, on augmente graduellement la température en déterminant les effets thermiques par analyse des effets thermoélectriques intermédiaires après chaque palier. A chaque palier, on maintient la température constante jusqu'à ce que l'équilibre soit atteint. On a contrôlé la méthode par l'étude de changements de phases displacifs dans l'état solide et par mesure de points de fusion.

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, 400° 1100°. , . . .

     

Influence of ammonia on propylene oxidation on tin-antimony and bismuth-antimony catalysts

The influence of ammonia on the direction of the oxidative transformations of propylene has been studied. Ammonia has been shown to block the surface oxygen of antimony catalysts. As a result, an increase in the selectivity with respect to the products of partial oxidation is observed.

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. , , .

     

Characterization of tension and normally lignified wood cellulose inPopulus maximowiczii

We have investigated unlignified tension wood and normally lignified wood celluloses inPopulus maximowiczii with particular reference to the composition of two crystalline phases I/I (triclinic/ monoclinic). Four independent techniques, which enable us to detect the two phases, CP/MAS¹³C NMR, Fourier transform infrared microscopy, selected-area electron diffraction, and X-ray diffraction were applied. Because of the low crystallinity of wood celluloses, particularly in the case of celluloses in the lignified cell wall, no single method was decisive enough to be able to determine the composition of the two phases as one can with highly crystalline materials. The I dominant structure (monoclinic crystal type) was, however, preferred for both tension and normal wood celluloses.     

Localization of Iα and Iβ phases in algal cellulose revealed by acid treatments

Highly crystalline I-rich type Cladophora cellulose, which had been kept in never-dried condition, was treated in 60wt% sulfuric acid at 100°C, for 1–48h. The cellulose microcrystals thus obtained were analysed by X-ray diffractometry, FT-IR, and transmission electron microscopy. The I component was found to be more degraded than the I component. The cellulose I/I ratios of the samples acid-treated for 0, 24, and 48 h were about 8:2, 6:4, and 4:6, respectively. After the acid treatment, the microcrystals became narrower in width, and very sharp at their ends. These results indicate that the I phase is mostly located at the surface of the microcrystals, which is morphologically more susceptible to the acid treatment.     

Studies of crystalline native celluloses using potential energy calculations

Energies for various trial packing arrangements of unit cells for the I and I phases of native cellulose discovered by Sugiyamaet al. were evaluated. Both a rigid-ring method, PLMR, and the full-optimization, molecular mechanics program, MM3(90), were used. For both phases the models that had the lowest PLMR energy also had the lowest MM3 energy. Both calculated models have the chains packed up, O6s intg positions, and the same sheets of hydrogen-bonded chains. The I structure model is essentially identical to that proposed previously for ramie cellulose by Woodcock and Sarko. It is also the same as the best parallel model previously proposed that was based on the X-ray data of Mann, Gonzalez and Wellard, once the various unit cell conventions are considered. Also, the energies from both methods for all three celluloses, I, I and II, are in the order that rationalizes their relative stabilites.     

Crystalline transformation of native cellulose from cellulose I to cellulose ID polymorph by a ball-milling method with a specific amount of water

We have demonstrated for the first time that a mechano-chemical treatment of native cellulose with a specific amount of water (30 wt%) present ID the cellulose solid state caused the crystalline transformation from cellulose I into cellulose ID polymorph. X-ray diffractometry was used to show that the extent of transformation into cellulose ID increased with milling time. This specific phenomenon can be explained by considering the chain mobility ID the cellulose–water system, because ₁ ^1H measurement shows that cellulose molecules are most mobile when the water content ID around 30 wt%, and thus are favorable for molecular rearrangement under external forces.     

[3]Ferrocenophanes with a tetramethyldisiloxane bridge: Synthesis and molecular structure

Summary 6,6,8,8-Tetramethyl-7-oxa-6,8-disila[3]ferrocenophane2 was obtained from the di(alkoxysilyl) ferrocene (H₄C₅SiMe₂OR)₂Fe (R=CH₂CH₂OCH₂CH₂OCH₂CH₂OMe) by hydrolysis and subsequent intramolecular disiloxane formation. 2,2,3,3,4,4,5,5,6,6,8,8-Dodecamethyl-7-oxa-6,8-disila-[3]ferrocenophane3 was formed by air oxidation of 2,23,3,4,4,5,5,6,6,7,7-dodecamethyl-6,7-disila[2]ferrocenophane. The crystal structures of both compounds were determined by single-crystal X-ray diffraction (2:a=8.5330(10),b=15.610(3),c=18.774(5)Å, =70.68(2), =77.94(2), =75.150(10)°,V=2259.8(8)ų,Z=6, space group P ,R=0.045,R _w =0.044;3:a=12.388(3),b=9.924(3),c=19.136(10)Å, =105.11(3)°,V=2271.2(15)ų,Z=4, space group P2₁/c,R=0.076,R _w =0.060). Owing to the flexibility of the disiloxane bridge,2 and3 are unstrained molecules.

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[3]Ferrocenophane mit Tetramethyldisiloxan-Brücke: Synthese und Molekülstruktur

Zusammenfassung 6,6,8,8-Tetramethyl-7-oxa-6,8-disila[3]-ferrocenophan2 entsteht aus dem Di(alkoxysilyl)ferrocen (H₄C₅SiMe₂OR)₂Fe (R=CH₂CH₂OCH₂CH₂OCH₂CH₂OMe) durch Hydrolyse und anschließende intramolekulare Disiloxan-Bildung. 2,2,3,3,4,4,5,5,6,6,8,8-Dodecamethyl-7-oxa-6,8-disila[3]ferrocenophan3 wurde durch Luftoxidation von 2,2,3,3,4,4,5,5,6,6,7,7-Dodecamethyl-6,7-disila[2]ferrocenophan erhaeten. Die Kristallstrukturen beider Verbindungen wurden durch Einkristall-Röntgenstrukturanalyse bestimmt (2:a=8.5330(10),b=15.610(3),c=18.774(5)Å, =70.68(2), =77.94(2), =75.150(10)°,V=2259.8(8)ų,Z=6, Raumgruppe P ,R=0.045,R _w =0.044;3:a=12.388(3),b=9.924(3),c=19.136(10)Å, =105.11(3)°,V=2271.2(15)ų,Z=4, Raumgruppe P2₁/c,R=0.076,R _w =0.060). Wegen der Flexibilität der Disiloxan-Brücke sind2 und3 ungespannte Moleküle.

     

Some perspectives on the modeling of plasma jets

A mathematical representation is developed describing the temperature and the velocity profiles and mixing in a plasma jet discharging into ambient air. In the model, realistic allowance is made for turbulent behavior, the temperature-dependent property values, and also for the boundary conditions, including entrainment. The more precise definition of the boundary conditions, mixing, and entrainment are thought to be important novel features of this work. The theoretical predictions were found to be in good agreement with measurements reported by Vardelle regarding the behavior of a nitrogen plasma, but the agreement was less satisfactory for an argon plasma jet. Possible reasons for the discrepancy are discussed.Notation C ₁,C ₂,C _D constants inK- turbulence model - h enthalpy - H ₁ length of integration region - H ₂ width of integration region - K turbulent kinetic energy per unit mass - m mass concentration of plasma - Q _f mass flow rate of plasma gas for flat inlet profiles - Q _P mass flow rate of plasma gas for parabolic inlet profiles - P _w torch power - r radial coordinate - R ₀ internal radius of torch exit - S source term for dependent variable - S _R radiation loss per unit volume of plasma - T _a ambient temperature - T _m maximum temperature - T _t torch tip temperature - u velocity inz-direction - u _{C 1} velocity at and in the direction of the symmetry axis of the flow - u _m velocity of plasma atr=0 andz=0 (maximum velocity) - u axial direction velocity difference across the width of the mixing region - v velocity in r direction - Y radial width of the mixing region - z axial coordinate - density - , _e, _t molecular, effective, and turbulent viscosities, respectively - dissipation rate of turbulence energy - thermal efficiency of plasma torch - Prandtl/Schmidt number forh, K, , andm Visiting Fulbright Scholar and Associate Professor of Chemical Engineering, on leave from the Institute of Chemical Engineering and Technology, Punjab University, Lahore-20, Pakistan.     

Some aspects of lateral chain order in cellulosics from X-ray scattering

This paper gives an overview of our recent research activities on the lateral supramolecular order of a variety of native and man-made cellulosics considering respective results from the literature. Wide-angle X-ray scattering (WAXS) was the main investigation technique used. Lateral root mean squared lattice strains between 2 and 3% were determined for the materials investigated. Crystallite sizes obtained without considering lattice distortions usually do not deviate by much more than –10% from the real, i.e. fully corrected values. This means that it is sufficient to use the simple Scherrer equation for determining lateral crystallite sizes for most routine investigations of cellulosic materials. The possible superposition of WAXS peaks of the triclinic I and monoclinic I lattice types, however, has to be considered in crystallite size determinations for Valonia cellulose. It could be shown that neglecting this fact can lead to crystallite sizes being about 20% below the true ones. Lateral crystallite dimaensions for native celluloses vary between 4nm (dissolving pulps) and 10-15 nm (Valonia). Except for bacterial cellulose, the WAXS crystallite sizes are distinctly smaller than the microfibril dimensions obtained from electron microscopy. The man-made fibres investigated showed lateral crystallite dimensions between 3 and 5nm. The importance of lateral crystallite dimensions for the properties of man-made fibres and for the alkalization process of native cellulose id demonstrated.     

Structure and morphology of cellulose in wheat straw

The structure and morphology of cellulose extracted from wheat were studied. It was found that the extraction process is effective and hemicelluloses and lignin can be extracted completely. Cellulose in wheat straw was identified as cellulose I allomorph with low crystallinity and the crystallinity of cellulose from different parts of the wheat straw has little difference. There was no metastable cellulose I crystalline modification found in wheat straw; only the more stable cellulose I crystalline modification existed. Cellulose chains in the epidermis of wheat straw were observed with their orientation along the growth direction of wheat straw, while those in parenchyma were observed with almost no preferred orientation. There are two kinds of morphologies on the surface of wheat straw. One is the fiber structure with fibrils of about 5 m diameter, and the other is the fiber structure with serration morphology at the edge of the fiber, with which the fibers are connected together. The diameter of the latter one is about 10 m. The vascular bundles consist of circular rings while spiral structure cellulose backbones covered with thin cellulose film were also observed.