Effect of process parameters and composition on mechanical,thermal, and morphological properties of polypropylene/sawdust composites

Polypropylene/sawdust composites have been prepared according to a statistical experimental design, with varying sawdust and compatibilizer (maleic anhydride grafted PP) concentrations. To investigate process conditions, composites were first extruded in a twin screw extruder coupled to a Haake torque rheometer, without degassing, and then reextruded in a Werner Pfleiderer twin screw extruder, with two degassing zones. Process conditions were analyzed according to statistical techniques. Effect of the variables on mechanical properties was assessed through flexural modulus, tensile strength, and percent elongation at break and morphology was assessed by scanning electron microscopy. Comparison between the extruded and reextruded compounds indicated the need to reduce moisture, prior to and during processing, as well as the need of effective mixing of the compounds. Sawdust concentration showed to be the variable which affected most all properties assessed. Increase in sawdust concentration resulted in increased composite stiffness. The presence of the compatibilizer caused a slight increase in tensile strength and reduction in percent elongation at break, indicating improved adhesion at the PP/sawdust interface. The reprocessed compounds were also analyzed by differential scanning calorimetry. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Towards metal electrode interface scavenging of rare-earth scandates: A Sc2O3 and Gd2O3 study

Amorphous Gd₂O₃ and Sc₂O₃ thin films were deposited on Si by high-pressure sputtering (HPS). In order to reduce the uncontrolled interfacial SiO_x growth, firstly a metallic film of Gd or Sc was sputtered in pure Ar plasma. Subsequently, they were in situ plasma oxidized in an Ar/O₂ atmosphere. For post-processing interfacial SiO_x thickness reduction, three different top metal electrodes were studied: platinum, aluminum and titanium. For both dielectrics, it was found that Pt did not react with the films, while Al reacted with them forming an aluminate-like interface and, finally, Ti was effective in scavenging the SiO₂ interface thickness without severely compromising gate dielectric leakage.     

Inoculation of lactic acid bacteria on meat surfaces as a means of decontamination in semitropical conditions

Reduction of microbial populations on carcasses has been achieved and reported by some authors by spraying solutions of organic acids, mainly lactic acid, on the meat surface. However, in practice, lactic acid is very expensive. Production of lactic acid in situ by a controlled lactic fermentation seemed to be a feasible answer. The objective of the present study was to explore the viability of this concept at semitropical conditions, i.e. temperatures around 25°C. In a first experiment, seven starters were tested for their ability to produce lactic acid and reducing the growth rate of pseudomonads, taking these microorganisms as indicators of contamination by spoilage microorganisms. The lactic acid bacteria strains were isolated from native Mexican maize-based beverages, and inoculated on the meat surface. Addition of sucrose and wrapping the samples in PVC film in order to induce a microaerophilic environment encouraged the over-growth of L. bulgaricus and P. pentosaceous over pseudomonads. A second experiment was designed to test a mixture of these two strains and a commercial starter with respect to lactic acid production, overgrowth of lactic acid bacteria over pseudomonads, decolouration and oxidation of the meat samples. It was concluded that a commercial starter (L. plantarum + M. kristinae-varians) resulted in a reduction of pseudomonas growth rate, without notably affecting meat colour and degree of oxidation.     

Scale-up study of supercritical fluid extraction process for clove and sugarcane residue

Many scale-up criteria for supercritical fluid extraction (SFE) can be found in literature. However, the studies are often divergent and inconclusive; therefore, more studies on this field are needed. The objective of the present work was to study the scale-up of SFE process focusing application to Brazilian raw materials. A laboratory scale equipment (290 mL extraction vessel) and a pilot scale equipment (5.15 L extraction vessel) were used to study scale-up of SFE for clove and sugarcane residue. The scale-up criterion adopted consisted in maintaining solvent mass to feed mass ratio constant. The criterion was successfully used for a 15-fold scale-up of overall extraction curves for both raw materials studied; yields in pilot scale were slightly higher than in laboratory scale. The criterion studied allows a rapid and simple scale-up procedure, which can be very useful for the purpose of developing SFE technology at industrial scale in developing countries where such technology is still not available at industrial level.     

Phase Equilibrium Measurements of Sacha Inchi Oil (<Emphasis Type="Italic">Plukenetia volubilis</Emphasis>) and CO<Subscript>2</Subscript> at High Pressures

New data on phase equilibria for Sacha inchi seed oil in carbon dioxide have been measured using a variable volume cell phase equilibria system at temperatures of 303, 313 and 323 K and at pressures ranging from 4.3 to 27.7 MPa. The CO₂ mole fraction varied from 0.7488 to 0.9997. At the studied concentrations, phase transitions of vapor-liquid, liquid-liquid-vapor and liquid-liquid were observed. Sacha inchi oil contains 47% of omega-3 fatty acids, with a ratio of 0.76:1 for omega-6:omega-3, which is good for human health. The Peng-Robinson equation of state was used to describe the experimental data. A qualitative agreement was obtained between experimental and calculated data for the binary system CO₂ and Sacha inchi seed oil.     

Two Genera of Aulacoscelinae Beetles Reflexively Bleed Azoxyglycosides Found in Their Host Cycads

Aulacoscelinae beetles have an ancient relationship with cycads (Cycadophyta: Zamiaceae), which contain highly toxic azoxyglycoside (AZG) compounds. How these “primitive” leaf beetles deal with such host-derived compounds remains largely unknown. Collections were made of adult Aulacoscelis appendiculata from Zamia cf. elegantissima in Panama, A. vogti from Dioon edule in Mexico, and Janbechynea paradoxa from Zamia boliviana in Bolivia. Total AZG levels were quantified in both cycad leaves and adult beetles by high performance liquid chromatography (HPLC). On average, cycad leaves contained between 0.5–0.8% AZG (frozen weight, FW), while adult beetles feeding on the same leaves contained even higher levels of the compounds (average 0.9–1.5% FW). High AZG levels were isolated from reflex bleeding secreted at the leg joints when beetles were disturbed. Nuclear magnetic resonance and mass spectroscopy identified two AZGs, cycasin and macrozamin, in the reflex bleeding; this is the first account of potentially plant-derived compounds in secretions of the Aulacoscelinae. These data as well as the basal phylogenetic position of the Aulacoscelinae suggest that sequestration of plant secondary metabolites appeared early in leaf beetle evolution.     

Synthesis, Characterization and Cold Workability of Cast Copper-Magnesium-Tin Alloys

The use of Mg as an alloying element in copper alloys has largely been overlooked in scientific literature and technological applications. Its supposed tribological compatibility with iron makes it an interesting option to replace Pb in tribological alloys. This work describes the casting process of high-quality thin slabs of Cu-Mg-Sn alloys with different compositions by means of conventional methods. The resulting phases were analyzed using X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray spectroscopy techniques. Typical dendritic α-Cu, eutectic Cu₂Mg(Sn) and eutectoid non-equilibrium microstructures were found. Tensile tests and Vickers microhardness show the excellent hardening capability of Mg as compared to other copper alloys in the as-cast condition. For some of the slabs and compositions, cold rolling reductions of over 95 pct have been easily achieved. Other compositions and slabs have failed during the deformation process. Failure analysis after cold rolling reveals that one cause for brittleness is the presence of casting defects such as microshrinkage and inclusions, which can be eliminated. However, for high Mg contents, a high volume fraction of the intermetallic phase provides a contiguous path for crack propagation through the connected interdendritic regions.     

Effect of in‐office bleaching agents on the surface roughness and morphology of different dental composites: An AFM study

The aim of this study was to evaluate, using atomic force microscopy, the effect of two different bleaching agents on the modification of dental composites materials. This modification will be judged by analyzing the variation of surface roughness and surface morphology of two different composites: one containing nanoparticles and other consisting of microhybrid resin. The bleaching was performed by using two different concentrations of hydrogen peroxide: HP Blue (20% hydrogen peroxide) and Whiteness HP Maxx (35% hydrogen peroxide). Disks of Esthet X and Filtek? Z350 composites were used. Atomic force microscopy was used for analyses of the same place of the sample before and after treatment. A total of 12 analyses were performed per group (n = 12). The samples were analyzed qualitatively by evaluating morphological changes in the images and quantitatively by using roughness parameters (Ra). Data were analyzed statistically using Kruskal–Wallis, Mann–Whitney, and Friedman tests (P < 0.05). Changes were observed both qualitatively and quantitatively only in the groups where Esthet X resin was used. The use of hydrogen peroxide bleaching agents caused changes only in the surface of microhybrid composites, with no changes being observed in the composite containing nanoparticles. Despite being even significant, these alterations are clinically slight and can be eliminated by polishing them. Microsc. Res. Tech. 76:481–485, 2013. © 2013 Wiley Periodicals, Inc.     

INVESTIGATION OF THE EXISTENCE OF COAL MATRIX EFFECTS ON THE HYDROLIQUEFACTION OF VITRINITES DERIVED FROM LOW RANK SPANISH COALS

Two lignites (Mequinenza, Spain) and two subbituminous coals (Teruel, Spain), their demineralized derivatives (HCl/HF + HCl) and their corresponding derived vitrinite concentrates were submitted to hydroliquefaction in tetralin in fixed conditions to study a possible synergism of vitrinite concentrates in the original coal matrix.

Sufficiently pure amounts of vitrinite concentrates were isolated by a method based on differential centrifugation in CsCl. The coals were characterized by densimetric and petrographic analyses including reflectance-frequency distributions.

A synergism for vitrinite concentrates related to the demineralized coals has not been found here because all the vitrinite concentrates, once separated, have similar or higher reactivity than in the corresponding original coal matrix. On the other hand, the studied lignite-derived vitrinite concentrates have proved to be much more reactive than the subbituminous-derived ones. Displacements of Absorbance-Density curves and maxima toward higher densities (densimetric analyses data) and appearance of V-4 vitrinite type structures (coal reflectograms) in the case of the subbituminous coals imply differences in chemical structures for the lignite and the subbituminous derived vitrinite concentrates which could explain the differences in reactivity.     

Drying of Seeds and Gels

In an attempt to contribute to the integration of research that deals with the drying of seeds and gels, the aim of the present study is to analyze the drying of porous particles covered with a gel layer, whether natural or artificial. Two case studies are presented. In the first case, the emphasis is to study the combined effect of heat and mass transfer and the shrinkage in the drying of mucilaginous seeds. The focus of the second case study is the development of an experimental methodology for coating seeds with a gel-based polymer.