High Solids Content, Soap-Free, Film-Forming Latexes Stabilized by Laponite Clay Platelets

High solids content film-forming poly[styrene-co-(n-butyl acrylate)] [poly(Sty-co-BuA)] latexes armored with Laponite clay platelets have been synthesized by soap-free emulsion copolymerization of styrene and n-butyl acrylate. The polymerizations were performed in batch in the presence of Laponite and a methyl ether acrylateterminated poly(ethylene glycol) macromonomer in order to promote polymer/clay association. The overall polymerization kinetics showed a pronounced effect of clay on nucleation and stabilization of the latex particles. Cryo-transmission electron microscopy observation confirmed the armored morphology and indicated that the majority of Laponite platelets were located at the particle surface. The resulting nanostructured films displayed enhanced mechanical properties.

Anaerobic fluidized bed reactor with expanded clay as support for hydrogen production through dark fermentation of glucose

This study evaluated hydrogen production in an anaerobic fluidized bed reactor (AFBR) fed with glucose-based synthetic wastewater. Particles of expanded clay (2.8-3.35 mm) were used as a support material for biomass immobilization. The reactor was operated with hydraulic retention times (HRT) ranging from 8 to 1 h. The hydrogen yield production increased from 1.41 to 2.49 mol H(2) Mol(-1) glucose as HRT decreased from 8 to 2 h. However, when HRT was 1 h, there was a slight decrease to 2.41 mol H(2) Mol(-1) glucose. The biogas produced was composed of H(2) and CO(2), and the H(2) content increased from 8% to 35% as HRT decreased. The major soluble metabolites during H(2) fermentation were acetic acid (HAc) and butyric acid (HBu), accounting for 36.1-53.3% and 37.7-44.9% of total soluble metabolites, respectively. Overall, the results demonstrate the potential of using expanded clay as support material for hydrogen production in AFBRs. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Structural ceramics made with clay and steel dust pollutants

Electric arc furnace steel dust is a by-product of the steelmaking process and contains high amounts of the iron and zinc and significant amounts of lead, chromium, and cadmium. Metal recycling however, is not always economically feasible, especially due to the complex mineralogical composition of this material. In this study an application of this material is presented. Ceramics were produced with clay and variable amounts of steel dust. The bulk material was fired between 800 and 1100 degrees C. The influence of the composition and the processing temperature on the mechanical strength, linear shrinkage, water absorption, apparent density and bending strength and metal leaching of the ceramic samples was investigated. A blend of clay with up to 20% dust yielded ceramics with limited metal contamination risk and may thus be used for structural ceramics production. (C) 2011 Elsevier B.V. All rights reserved.

Quantification of Clay Dispersion in Nanocomposites of Styrenic Polymers

Polymer-clay nanocomposites are materials with many interesting structures, properties, and potential applications. Microstructural evaluation of a nanocomposite is not an easy task, as clay may form hierarchical structures which may look different when observed at various magnifications under a microscope, and also as the concepts of ""intercalation"" and ""exfoliation"" are not self-sufficient to describe its morphology. In this work polymer-clay nanocomposites of polystyrene and two styrene-containing block copolymers (styrene-butadiene-styrene and styrene-ethylene/butylene-styrene) were prepared using three different techniques. Clay dispersion was evaluated by a recently developed microscopy image analysis procedure, combining the analysis of optical and transmission electron micrographs, and the characterization was complemented by X-ray diffraction and rheological measurements. The results showed better clay dispersion for both block copolymers nanocomposites, mainly due to their molecular architectures. Moreover, the techniques which showed the best results involved mixing the materials in a solvent medium. POLYM. ENG. SCI., 50:257-267, 2010. (C) 2009 Society of Plastics Engineers

Linear viscoelasticity of styrenic block copolymers-clay nanocomposites

In this work, the rheological behavior of block copolymers with different morphologies (lamellar, cylindrical, spherical, and disordered) and their clay-containing nanocomposites was studied using small amplitude oscillatory shear. The copolymers studied were one asymmetric starblock styrene-butadiene-styrene copolymer and four styrene-ethylene/butylenes-styrene copolymers with different molecular architectures, one of them being modified with maleic anhydride. The nanocomposites of those copolymers were prepared by adding organophilic clay using three different preparation techniques: melt mixing, solution casting, and a hybrid melt mixing-solution technique. The nanocomposites were characterized by X-ray diffraction and transmission electron microscopy, and their viscoelastic properties were evaluated and compared to the ones of the pure copolymers. The influence of copolymer morphology and presence of clay on the storage modulus (G`) curves was studied by the evaluation of the changes in the low frequency slope of log G` x log omega (omega: frequency) curves upon variation of temperature and clay addition. This slope may be related to the degree of liquid- or solid-like behavior of a material. It was observed that at temperatures corresponding to the ordered state, the rheological behavior of the nanocomposites depended mainly on the viscoelasticity of each type of ordered phase and the variation of the slope due to the addition of clay was small. For temperatures corresponding to the disordered state, however, the rheological behavior of the copolymer nanocomposites was dictated mostly by the degree of clay dispersion: When the clay was well dispersed, a strong solid-like behavior corresponding to large G` slope variations was observed.

Toluene and naphthalene sorption by iron oxide/clay composites

Commercial bentonite (BFN) and organoclay (WS35), as well as iron oxide/clay composite (Mag_BFN) and iron/oxide organoclay composite (Mag_S35) were prepared for toluene and naphthalene sorption. Mag_BFN and Mag_S35 were obtained, respectively, by the precipitation of iron oxide hydrates onto sodium BFN and S35 clay particles. The materials were characterized by powder X-ray diffraction (XRD), X-ray Fluorescence (XRF), and TG and DTA. From XRF results and TG data on calcined mass basis, a quantitative method was developed to estimate the iron compound contents of the composites, as well as the organic matter content present in WS35 and Mag_S35.

MACRONUTRIENTS UPTAKE BY POTATO (Solanum tuberosum L.) IN SEED-TUBER PRODUCTION

In greenhouse potato cultivation, mineral nutrition is one of the main factors contributing to high yields and better product quality. Knowledge about the amount of nutrients accumulated in the plants at each growing phase provides important information that helps the establishment of a more balanced fertilizer application. The objective of this research was to determine the time course of macronutrients uptake and accumulation in potato plants for seed-tuber production, grown in nutrient solution. The experiment was carried out in a greenhouse, using in vitro material from the pre-basic category of the `Atlantic` variety. The plants were collected weekly from 14 days after transplanting (DAT) until 70 DAT The experimental design was a completely randomized block with 9 treatments to sampling times and four replicates. The highest nutrient requirement in the plant shoot occurred at the periods between 28 and 56 DAT while in the tubers it was after 49 DAT The maximum accumulation sequence of macronutrients was K > N > S > Ca > P > Mg.

The Genome Sequence of Taurine Cattle: A Window to Ruminant Biology and Evolution

To understand the biology and evolution of ruminants, the cattle genome was sequenced to about sevenfold coverage. The cattle genome contains a minimum of 22,000 genes, with a core set of 14,345 orthologs shared among seven mammalian species of which 1217 are absent or undetected in noneutherian (marsupial or monotreme) genomes. Cattle-specific evolutionary breakpoint regions in chromosomes have a higher density of segmental duplications, enrichment of repetitive elements, and species-specific variations in genes associated with lactation and immune responsiveness. Genes involved in metabolism are generally highly conserved, although five metabolic genes are deleted or extensively diverged from their human orthologs. The cattle genome sequence thus provides a resource for understanding mammalian evolution and accelerating livestock genetic improvement for milk and meat production.

Redescription of Amblyomma varium Koch, 1844 (Acari : Ixodidae) based on light and scanning electron microscopy

Amblyomma varium Koch, 1844 is a Neotropical tick, known as the `sloth`s giant tick`, with records from southern Central America to Argentina. It is found almost exclusively on mammals of the families Bradypodidae and Magalonychidae (Xenarthra). Differences exist in discussions with regard to the dentition of the female hypostome being either 3/3 or 4/4. The male was also originally described as having a short spur on coxa IV, but some specimens recently collected from different Brazilian localities have this spur three times longer. These differences beg the question of whether there is more than one species included under this taxon. In order to answer this question and to clarify the taxonomic characters of this species, 258 adult specimens were examined, and a redescription of male and female based on light and scanning electron microscopy is provided. In addition, DNA was extracted from males with either a long or a short spur on coxa IV to help settle this question for future investigations on their taxonomy. The morphological study showed that the dental formula pattern for males and females is 3/3 and 4/4, respectively. When sequenced, the 12 S rDNA genes of both A. varium males with long and short spurs on coxa IV were found to be identical, indicating that the length of the spurs on coxa IV is likely to be an intraspecifically polymorphic character of this species.

Comments on the validity of Haemaphysalis cinnabarina Koch, 1844 (Acari : Ixodidae), a taxon known solely by the type specimens from northern Brazil

The types of Haemaphysalis cinnabarina Koch and its junior synonym H. sanguinolenta Koch, both from State of Para, Brazil, have been studied. Although H. cinnabarina has been considered a synonym of H. punctata Canestrini and Fanzago (a Palearctic species), they were compared to another closely related species H. chordedis (Packard) (a Nearctic species). Based on the morphology and geographical distance among of H. cinnabarina, H. chordedis and H. punctata, we are reasonably sure that all are valid taxa. The lack of additional reports of H. cinnabarina is more related to few investigations in South America, mainly in Northern Brazil, rather than suggesting that it does not exist.