High yield production of microcrystalline cellulose by a thermo-mechano-solvolytic treatment

By thermally treating a commercial cellulose in ethylene glycol, celluloses of controlled low degree of polymerization, DP_r = 1000 to 70, can be derived. Two general behaviors are observed in the range studied. At first, the depolymerization reaction is predominant down to a DP equal to 130. Beyond this level, the depolymerization process leads to extensive solubilization of the cellulose. The treated celluloses have been analyzed by X-ray diffraction, FTIR, TGA, elemental analysis and enzymatic hydrolysis. No chemical change of the cellulose could explain the two different behaviors. A physical modification in the form of depolymerization and destructuration is suspected.     

Evaluation of the effect of tracer pH on the sealing ability of glass ionomer cement and mineral trioxide aggregate

OBJECTIVES: The aim of this study was to evaluate the sealing ability and physical and chemical properties of glass ionomer cement (GIC) and mineral trioxide aggregate (MTA) using Rhodamine B at different pHs as tracer. METHODS: Chemical analysis, pH and micro-hardness of GIC and MTA were performed. In addition dye leakage was assessed by tracer leakage using Tandem Scanning Confocal Microscope (TSM) after immersion of premolar teeth in a stock and a buffered fluorescent Rhodamine B for 24 h. Ultra-structural changes within the materials were evaluated by viewing under the field emission scanning electron microscope (FESEM). RESULTS: GIC and MTA showed elemental peaks for silicon, aluminium and calcium while MTA also had bismuth. GIC was acidic (P = 0.001) and caused an increase in dye pH (P = 0). Immersion of MTA in any of the test solutions resulted in an increase in the pH of the solution (P < 0.05). Use of a dye solution of lower pH than the material under test increased the cement micro-hardness. GIC demonstrated marginal leakage on TSM and both increase in marginal leakage and material porosity on FESEM. MTA was not affected by the use of acidic dye but showed a tendency to take up dye within the material shown on TSM. CONCLUSIONS: Evaluation of marginal adaptation of dental materials was shown to be dependent on the technique used for viewing the material to tooth interface, the properties of the material under study and the pH of the dye used.     

Diffuse and point sources of silica in the Seine River watershed

Dissolved silica (DSi) is believed to enter aquatic ecosystems primarily through diffuse sources by weathering. Point sources have generally been considered negligible, although recent reports of DSi inputs from domestic and industrial sources suggest otherwise. In addition, particulate amorphous silica (ASi) inputs from terrestrial ecosystems during soil erosion and in vegetation can dissolve and also be a significant source of DSi. We quantify here both point and diffuse sources of DSi and particulate ASi to the Seine River watershed. The total per capita point source inputs of Si (DSi + ASi) were found to be 1.0 and 0.8 g Si inhabitant(-1) d(-1) in raw and treated waters of the Achères wastewater treatment plant, in agreement with calculations based on average food intake and silica-containing washing products consumption. A mass balance of Si inputs and outputs for the Seine drainage network was established for wet and dry hydrological conditions (2001 and 2003, respectively). Diffuse sources of Si are of 1775 kg Si km(-2) y(-1) in wet conditions and 762 kg Si km(-2) y(-1) in dry conditions, with the proportion of ASi around 6%. Point sources of Si from urban discharge can contribute to more than 8% of the total Si inputs at the basin scale in hydrologically dry years. An in-stream retention of 6% of total inputs in dry conditions and 12% in wet conditions is inferred from the budget.     

Interfacial Interactions Between W<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>N Substrates and a Gold-Tin Alloy

Au-Sn is an excellent material with superior attributes and is the solder of choice, with no obvious alternatives, in many microelectronic applications. Recently, this alloy has been chosen as a potential candidate for bonding in wafer level hermetic packaging at high temperature using WN as diffusion barrier. In this application, good wetting of WN by the liquid Au-Sn alloy is a key factor for the bonding process. To this end, wetting of W _x N (covered or not by a gold layer) by Au-Sn20 alloy was studied at 380 °C under high vacuum. Excellent wetting was observed when W _x N was protected from oxidation by a thin Au layer. The spreading process was found to be followed by a complete dissolution of a protection layer and slight receding of the triple line. Some preliminary bonding tests using Au-Sn alloy were also performed.     

XAS study of iron and arsenic speciation during Fe(II) oxidation in the presence of As(III)

The speciation of As and Fe was studied during the oxidation of Fe(II)-As(III) solutions by combining XAS analysis at both the Fe and As K-edges. Fe(II) and As(III) were first hydrolyzed to pH 7 under anoxic conditions; the precipitate was then allowed to oxidize in ambient air for 33 h under vigorous stirring. EXAFS analysis at the As K-edge shows clear evidence of formation of inner-sphere complexes between As(III) and Fe(II), i.e., before any oxidation. Inner-sphere complexes were also observed when Fe became sufficiently oxidized, in the form of edge-sharing and double-corner linkages between AsIIIO3 pyramids and FeIIIO6 octahedra. XAS analyses at the Fe K-edge reveal that the presence of As(III) in the solution limits the polymerization of Fe(II) and the formation of green rust and inhibits the formation of goethite and lepidocrocite. Indeed, As(III) accelerates the Fe(II) oxidation kinetics and leads to the formation of nanosized Fe-As subunits of amorphous aggregates. These observations, rather than a presumed weaker affinity of As(III) for iron oxyhydroxides, might explain why As(III) is more difficult to remove than As(V) by aerating reducing groundwater.     

Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on Spark Plasma Sintering of transparent alumina

A slurry of α-Al₂O₃ was doped with Mg, Zr and La nitrates or chlorides, in various amounts in the range 150-500 wt ppm and then freeze-dried to produce nanosized doped powder (∼150 nm). The powder was sintered by SPS to yield transparent polycrystalline alpha alumina. The influence of the nature of the doping element and the starting salt, the thermal treatment before sintering and the sintering temperature on the transparency of the ceramics were investigated. The transparency of the ceramics of nanosized Al₂O₃ was shown to depend mainly on the way the powder was prepared, the nature of the doping salt also had an effect. Finally, a high real inline transmittance, reaching 48.1% was achieved after optimization.     

Effect of interfacial oxidation occurring during the duplex process combining surface nanocrystallisation and co-rolling

This paper presents an investigation of the interface quality of nanocristallised 316 L stainless steel multilayer structures. They were produced by a duplex process, combining the Surface Mechanical Attrition Treatment (SMAT) and the co-rolling process at two different annealing temperatures (550 °C and 650 °C). Oxide layers were observed at the interfaces between the sheets and their morphology was characterised by optical microscopy. Their chemical composition was determined by Energy Dispersive X-ray spectrometry. The microstructure near the interfaces was analysed by Transmission Electron Microscopy (TEM). In the laminate co-rolled at 550 °C, the presence of ultrafine grains was demonstrated. Additional tensile tests have shown an influence of the annealing temperature on the yield strength, as well as on the resistance of the interfaces of the co-rolled multilayer structures.     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d _s and γ^d _l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d _s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^?2 K^?1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d _s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d _s and d(γ^d _s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

Self‐Defensive Biomaterial Coating Against Bacteria and Yeasts: Polysaccharide Multilayer Film with Embedded Antimicrobial Peptide

Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self‐defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host‐defensive antimicrobial peptide, and chitosan (HA‐CTL‐C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA‐CTL‐C/CHI films fully inhibit the development of Gram‐positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care‐associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA‐CTL‐C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.     

Integrated collector storage solar water heater: Temperature stratification

An analysis of the temperature stratification inside an Integrated Collector Storage Solar Water Heater (ICS-SWH) was carried out. The system takes the form of a rectangular-shaped box incorporating the solar collector and storage tank into a single unit and was optimised for simulation in Scottish weather conditions. A 3-month experimental study on the ICS-SWH was undertaken in order to provide empirical data for comparison with the computed results. Using a previously developed macro model; a number of improvements were made. The initial macro model was able to generate corresponding water bulk temperature in the collector with a given hourly incident solar radiation, ambient temperature and inlet water temperature and therefore able to predict ICS-SWH performance. The new model was able to compute the bulk water temperature variation in different SWH collectors for a given aspect ratio and the water temperature along the height of the collector (temperature stratification). Computed longitudinal temperature stratification results obtained were found to be in close agreement with the experimental data.