Preparation and characterization of LDPE and PP—Wood fiber composites

Natural fiber reinforced composites is an emerging area in polymer science. These natural fibers are low cost fibers with low density and high specific properties. These are biodegradable and nonabrasive. The natural fiber composites offer specific properties comparable to those of conventional fiber composites. However, in development of these composites, the incompatibility of the fibers and poor resistance to moisture often reduce the potential of natural fibers, and these draw backs become critical issue. Wood‐plastic composites (WPC) are a relatively new class of materials and one of the fastest growing sectors in the wood composites industry. Composites of wood in a thermoplastic matrix (wood–plastic composites) are considered a low maintenance solution to using wood in outdoor applications. WPCs are normally made from a mixture of wood fiber, thermoplastic, and small amounts of process and property modifiers through an extrusion process. In this study, Wood–plastic composites (WPC) are produce by adding a maleic anhydride modified low density polyethylene coupling agent to improve interfacial adhesion between the wood fiber and the plastic. Mixing is done with twin screw extruder. Subsequently, tensile strength, the modulus of elasticity, % elongation, hardness, Izod impact strength, melt flow index (MFI), and heat deflection temperature (HDT) are determined. Thermal transition temperatures and microstructure are determined with DSC and SEM, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Low Temperature Water–Gas Shift/Methanol Steam Reforming: Alkali Doping to Facilitate the Scission of Formate and Methoxy C–H Bonds over Pt/ceria Catalyst

Doping Pt/ceria catalysts with the Group 1 alkali metals was found to lead to an important weakening of the C–H bond of formate and methoxy species. This was demonstrated by a shift to lower wavenumbers of the formate and methoxy ν(CH) vibrational modes by DRIFTS spectroscopy. Li and Na-doped Pt/ceria catalysts were tested relative to the undoped catalyst for low temperature water–gas shift and methanol steam reforming using a fixed bed reactor and exhibited higher catalytic activity. Steaming of formate and methoxy species pre-adsorbed on the catalyst surface during in-situ DRIFTS spectroscopy suggested that the species were more reactive for dehydrogenation steps in the catalytic cycle for the Li and Na-doped catalysts relative to undoped Pt/ceria. However, with increasing atomic number over the series of alkali-doped catalysts, the stability of a fraction of the carbonate species was found to increase. This was observed during TPD-MS measurements of the adsorbed CO₂ probe molecule by a systematic increase of a high temperature peak for a fraction of the CO₂ desorbed. This result indicates that alkali-doping is an optimization problem—that is, while improving the dehydrogenation rates of methoxy and formate species, the carbonate intermediate stability increases, making it difficult to liberate the CO₂. Infrared spectroscopy results of CO adsorbed on Pt and ceria suggest that the alkali dopant is located on, and electronically modifies, both the Pt and ceria components. The results not only lend further support to the role that methoxy and formate species play as intermediates in the catalytic mechanisms, but also provide a path forward for improving rates by means other than resorting to higher noble metal loadings.     

Three-dimensional numerical study of heat and mass transfer in fluidized beds with spray nozzle

The numerical computations of temperature and concentration distributions inside a fluidized bed with spray injection in three-dimensions are presented. A continuum model, based on rigorous mass and energy balance equations developed from Nagaiah et al., is used for the three-dimensional simulations. The three-dimensional model equation for nozzle spray is reformulated in comparison to Heinrich. For solving the non-linear partial differential equations with boundary conditions a finite element method is used for space discretization and an implicit Euler method is used for time discretization.The time-dependent behavior of the air humidity, air temperature, degree of wetting, liquid film temperature and particle temperature is presented using two different sets of experimental data. The presented numerical results are validated with the experimental results. Finally, the parallel numerical results are presented using the domain decomposition methods.     

Depassivation and repassivation of stainless steels by stepwise pH change

Immersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5-day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium-rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.     

Validation of a Gas Chromatography-Mass Spectrometry Method for the Measurement of the Redox State Metabolic Ratios Lactate/Pyruvate and β-Hydroxybutyrate/Acetoacetate in Biological Samples

The metabolic ratios lactate/pyruvate and β-hydroxybutyrate/acetoacetate are considered valuable tools to evaluate the in vivo redox cellular state by estimating the free NAD+/NADH in cytoplasm and mitochondria, respectively. The aim of the current study was to validate a gas-chromatography mass spectrometry method for simultaneous determination of the four metabolites in plasma and liver tissue. The procedure included an o-phenylenediamine microwave-assisted derivatization, followed by liquid-liquid extraction with ethyl acetate and silylation with bis(trimethylsilyl)trifluoroacetamide:trimethylchlorosilane 99:1. The calibration curves presented acceptable linearity, with a limit of quantification of 0.001 mM for pyruvate, β-hydroxybutyrate and acetoacetate and of 0.01 mM for lactate. The intra-day and inter-day accuracy and precision were within the European Medicines Agency’s Guideline specifications. No significant differences were observed in the slope coefficient of three-point standard metabolite-spiked curves in plasma or liver and water, and acceptable recoveries were obtained in the metabolite-spiked samples. Applicability of the method was tested in precision-cut liver rat slices and also in HepG2 cells incubated under different experimental conditions challenging the redox state. In conclusion, the validated method presented good sensitivity, specificity and reproducibility in the quantification of lactate/pyruvate and β-hydroxybutyrate/acetate metabolites and may be useful in the evaluation of in vivo redox states.     

The effect of microstructure on hydrogen permeability of high strength steels

Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size.     

Influence of the Cooling Temperature on the Mechanical Behavior of an Oxidized Self-Healing Ceramic Matrix Composite

Composites made of ceramic for both fibers and matrix are aimed at being used in aerospace applications, which means being submitted to mechanical stresses at high temperatures in oxidizing and corrosive environments for long durations. The oxidation/corrosion resistance of these materials is linked to their ability to self-heal by creating an oxide phase which can restrict the access of the oxygen into the bulk of the material. During thermomechanical cycles, the distribution of O₂ inside the material as well as the distribution and the state of the liquid oxides will undergo some modifications. A specific test has been conceived and performed in order to evidence the influence of the viscosity of this oxide on the mechanical properties of the material. Results have shown that the stiffening which is observed seems to be proportional to the increase in the viscosity of the sealing oxide, in conjunction with the decrease in the temperature.     

Plant-derived polyphenols attenuate lipopolysaccharide-induced nitric oxide and tumour necrosis factor production in murine microglia and macrophages

Lipopolysaccharides released during bacterial infections induce the expression of pro-inflammatory cytokines and lead to complications such as neuronal damage in the CNS and septic shock in the periphery. While the initial infection is treated by antibiotics, anti-inflammatory agents would be advantageous add-on medications. In order to identify such compounds, we have compared 29 commercially available polyphenol-containing plant extracts and pure compounds for their ability to prevent LPS-induced up-regulation of NO production. Among the botanical extracts, bearberry and grape seed were the most active preparations, exhibiting IC(50) values of around 20 mug/mL. Among the pure compounds, IC(50) values for apigenin, diosmetin and silybin were 15, 19 and 12 muM, in N-11 murine microglia, and 7, 16 and 25 muM, in RAW 264.7 murine macrophages, respectively. In addition, these flavonoids were also able to down-regulate LPS-induced tumour necrosis factor production. Structure-activity relationships of the flavonoids demonstrated three distinct principles: (i) flavonoid-aglycons are more potent than the corresponding glycosides, (ii) flavonoids with a 4'-OH substitution in the B-ring are more potent than those with a 3'-OH-4'-methoxy substitution, (iii) flavonoids of the flavone type (with a C2=C3 double bond) are more potent than those of the flavanone type (with a at C2-C3 single bond).     

Fly Ash Resistivity Profiling for South African Coal Fired Power Stations

Particulate emission is a major problem in industrial processes, mainly power plants that make use of coal as a primary source of energy. Stringent emissions limits, set by government organisations requires industries to conform to these limits to ensure that air quality is sustained and with minimum pollutant present. Electrostatic precipitators are typically used to filter and collect these particulate emissions. Fly ash resistivity is a primary parameter in the collection of particulate emissions, and there is a resistivity range at which electrostatic precipitator collection is most efficient and anything outside this range limits, their operation. High resistivity ash results in back-corona discharge, whilst low resistivity results in particle re-entrainment into the flue gas stream. The purpose of this paper is to investigate and obtain a fly ash resistivity profile for existing power plants in South Africa. Ash samples obtained from power plants are, tested making use of an ash-resistivity test oven, in accordance with IEEE Standard 548-1984. This paper discusses obtained experimental results, to determine the resistivity profile at which South African power plant electrostatic precipitators operate. The electrical efficiency of the electrostatic precipitator system is evaluated based on the obtained resistivity profiles.     

Effects of the mycotoxin deoxynivalenol on human primary hepatocytes

Toxic effects of the mycotoxin deoxynivalenol (DON) observed in animals range from diarrhea, vomiting, gastro-intestinal inflammation to necrosis of several tissues. In the last years, DON has been tested in hepatocytes of several animal species for its cytotoxicity. However, these tests are limited to the use of animal cells. No studies using human hepatocytes are available. Further investigations with the human hepatocellular liver carcinoma cell line HepG2 might be limited due to the disadvantages of cell lines (e. g. immortalization, tumor derivation, longtime cultivation) and do not necessarily reflect the response of normal human cells. In order to overcome this problem and to be closer to the human situation, we studied the effect of DON in human primary hepatocytes and compared these data to the effects in the HepG2 cell line. Cell viability, apoptotic and necrotic cell death, albumin secretion and metabolic activity were determined. It could be demonstrated that DON has a distinct cytotoxic effect on human primary hepatocytes. Viability, protein content and albumin secretion were reduced in a dose-dependent manner. The apoptotic key enzyme caspase-3 was activated, while LDH release occurred only after long incubation time due to a secondary necrosis. Furthermore, we studied the metabolism of DON using LC-MS/MS. DON was neither metabolized by primary hepatocytes cells nor by the HepG2 cell line.