Layered silicate nanocomposites based on various high‐functionality epoxy resins. Part II: The influence of an organoclay on the rheological behavior of epoxy prepolymers

The effect of an organically surface modified layered silicate on the viscosity of various epoxy resins of different structures and different functionalities was investigated. Steady and dynamic shear viscosities of the epoxy resins containing 0–10 Wt% of the organoclay were determined using parallel plate rheology. Viscosity results were compared with those achieved through addition of a commonly used micronsized CaCO₃ filler. It was found that changes in viscosities due to the different fillers were of the same order, since the layered silicate was only dispersed on a micron‐sized scale in the monomer (prior to reaction), as indicated by X‐ray diffraction measurements. Flow activation energies at a low frequency were determined and did not show any significant changes due to the addition of organoclay or CaCO₃. Comparison between dynamic and steady shear experiments showed good agreement for low layered silicate concentrations below 7.5 wt%, i.e. the Cox‐Merz rule can be applied. Deviations from the Cox‐Merz rule appeared at and above 10 wt%, although such deviations were only slightly above experimental error. Most resin organoclay blends were well predicted by the Power Law model, only concentrations of 10 wt% and above requiring the Herschel‐Buckley (yield stress) model to achieve better fits. Wide‐angle X‐ray measurements have shown that the epoxy resin swells the layered silicate with an increase in the interlayer distance of approximately 15 Å, and that the rheology behavior is due to the lateral, micron‐size of these swollen tactoids.     

Effect of Adding Transition Metals to Copper on the Dehydrogenation Reaction of Ethanol

The present work aims to investigate the effect adding Ag, Co, Ni, Cd and Pt to copper on ethanol dehydrogenation. The catalysts synthesized by deposition–precipitation method were characterized using various physicochemical methods such as N₂ adsorption–desorption, TPR, SEM–EDX, XRD, XPS and TGA–DSC-MS. Catalytic evaluation results revealed that the predominant product of the reaction was acetaldehyde. Monometallic copper or mixed with Cd, Ag or Co show good catalytic performances. Adding nickel to copper improves the process conversion but reduces acetaldehyde selectivity, giving rise to methane in produced hydrogen. Pt-Cu/SiO₂ catalyst guides the reaction towards diethyl ether. Time on stream tests performed during 12 h at 260 °C, showed that adding Cd to Cu enhances its stability by over 30% of conversion, this is explained by the reduction of copper crystallites sintering, which makes Cd-Cu/SiO₂ a promising catalyst for the production of acetaldehyde by ethanol dehydrogenation.

Graphic Abstract

     

The Strength of Liquid Bridges Between Dissimilar Materials

The strength of the liquid bridge between a sphere and a plate of dissimilar materials was studied. An equation was derived using the surface energy approach. For small amounts of liquid, the force of adhesion f was f=2πRy(cosθ₁ + cosθ₂ where R is the sphere radius, y is the surface tension, and θ₂, θ₂ the contact angles. In the derivationn, major simplications about the meniscus shape were possible.

The equation was experimentally tested with water, ethyl alcohol, aniline and iodobenzene using factorial combinations with different solids. Force of adhesion measurements were carried out using a tensile testing machine at controlled loading rates. Excellent agreement was obtained in the experimental and predicted adhesion values. The McFarlane-Tabor equation was identified as correct only for small amounts of liquids and similarly wet solids.     

The effect of carbon black filling and cross-linking in stretched SBR networks: a 2H-NMR study

Summary The line splitting v in ²H-NMR spectra of deuterated benzene in stretched crosslinked SBR depended linearly on the classical stretch term ² – 1/ for samples with and without carbon black filling. The ratio LS = v/(² – 1/) was measured in dependence on the solvent fraction . The extrapolated value L of this ratio at =0 gave a linear dependence on the inverse molecular mass 1/M_c of inter-crosslink chains. This was expected according to a simple model of chain dynamics and offers a further NMR-method for M_c-determination even in filled networks. However, the slope of the L(1/M_c)-line increases with an addition of carbon black which indicates a higher molecular order. Three reasons for this could be discussed. However, one of them is preferable.     

LIGA micro-openings for coherence characterization of X-rays

Infinitely thin opaque screens serving for diaphragms as defined in the visible-light optics are not feasible for operation with X-ray beams due to their high penetrability. Micro-openings of predicted sidewall shape in a gold layer up to 140 μm thick which would provide low transparency, are proposed. The proposed micro-openings were made using the LIGA technique and tested successfully at photon energies of up to 25 keV. The micro-openings can be used as targets for coherence X-ray pattern or, if long interference tails are avoided by means of the advanced sidewall shape, as X-ray beam collimators.     

DIN-Norm-orientierte Standard-Spezifikationen für Rührwerke

DIN Standard-Oriented Specifications for Stirring Systems. Stirring as a unit operation is characterised by universal application possibilities for material and energy transmission in process industries. DIN standards provide an overview of the wide variety of equipment in technical use and define the conditions for low-cost, exchangeable standard stirring systems. In many cases important process parameters are fixed only for a limited time. Possible operation time should be long, therefore performance reserves are justified; they will be useful for later tasks as well as for improving safety of existing processes. Engineering of such stirring systems requires definition of standard stirring tasks. This article deals with economic aspects, defines standard stirring tasks as well as design conditions and shows the principal engineering data of standard stirring systems for stainless steel vessels up to 20 m³ by means of pictures, tables and nomograms. In conclusion, adequate processing of construction materials as well as surface finishing and practical work with standard specifications for stirring systems are discussed.     

Effects of estrogen-induced hyperlipidemia on the erythrocyte membrane in chicks

The effects of estrogen-induced hyperlipidemia on plasma lipid peroxidation, fatty acid composition and osmotic fragility of erythrocytes in chickens were studied. Young male chickens implanted with estrogen for three wk developed a marked hyperlipidemia. Plasma levels of triglyceride, cholesterol and phospholipid were elevated 68-, four- and 24-fold, respectively, over controls. There was also a two-fold increase in plasma lipid peroxidation measured by the thiobarbituric acid test. Vitamin E supplement (1,000 IU/kg diet) reduced the plasma lipid peroxidation to the control level, but had no effect on the plasma lipid content. Estrogen-induced hyperlipidemia resulted in changes in the fatty acid composition of membrane lipids of erythrocytes. The major changes were an increase in oleic acid from 10.0% to 14.2% and a decrease in linoleic acid from 31.3% to 26.0%. The erytrocytes with an altered membrane fatty acid composition were found to have an increased osmotic fragility. It was apparent that there was a direct correlation between the oleic acid content and the osmotic fragility of erythrocytes.     

Constructing and applying higher order textons: Estimating breast cancer risk

Texture analysis based on textons is extended by introducing a method for computing textons of arbitrary order. First-, second- and third-order textons are applied to classify screening mammograms as to indicate a low or high risk of breast cancer. First-order textons are found to provide better estimates of breast cancer risk than other orders on their own but the combination of first- and second-order textons outperforms first-order textons alone and other combinations of two orders. Combining all three orders of textons does not improve classification. This example indicates that including higher-order textons has the potential to improve classification performance.     

Length preferences and periodicity in {beta}-strands. Antiparallel edge {beta}-sheets are more likely to finish in non-hydrogen bonded rings

We analysed the length distributions of different types of ß-strandin a high resolution, non-homologous set of 500 protein structures,finding differences in their mean lengths. Antiparallel edgestrands in strand–turn–strand motifs show a preferencefor an even number of residues. This propensity is enhancedif the length is corrected for ß-bulges, which insertan extra residue into the strand. Residues in antiparallel edgeß-strands alternate between being in hydrogen bondedand non-hydrogen bonded rings. Antiparallel edges with an evennumber of residues are more likely to have their final ßresidue in a non-hydrogen bonded ring. This suggests that non-hydrogenbonded rings are intrinsically more stable than hydrogen bondedrings, perhaps because its side chain packing is closer. Therefore,we suggest that a simple way to increase ß-hairpinstability, or the stability of an antiparallel edge strand,is to have a non-hydrogen bonded ring at the end of the strand. Received June 19, 2003; revised October 25, 2003; accepted November 7, 2003     

Friction of linerboard based on recycled fiber

The purpose of this investigation was to study the origin of the differences in paper‐to‐paper friction of linerboards based on old corrugated containers (OCC). The sheets were subjected to two extraction stages and analyzed with respect to, surface roughness, and their content of low‐molecular‐mass lipophilic compounds (LLC). Friction was measured using a friction tester based on the horizontal plane principle. The surface roughness was measured using a Perthometer profiler and the low molecular mass lipophilic constituent of the paper sheets was determined by gas chromatography‐mass spectroscopy. The sheets were imaged using environmental scanning electron microscopy (ESEM), and the relative compositions of inorganic ions on the paper surfaces were determined by energy dispersive X‐ray spectroscopy (EDS). The results showed that a high amount of LLC in the sheets lead to low friction, due to lubrication. It was also observed that large CaCO₃ particles on the surface had a friction‐increasing effect, and that there was no relationship between the surface roughness and the friction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1511–1520, 2002