Nanoclay assisted strengthening of the fiber/matrix interface in functionally filled polyamide 6 composites

This study describes the contribution of a nano-filler, i.e. an organically modified layered silicate, in respect of the fiber/matrix interfacial shear strength (IFSS) of a short glass fiber reinforced and functionally filled polyamide 6, given an exfoliated nanocomposite morphology. Apparent IFSS values are determined using a continuum micromechanical method. Polymer chains in the nanoconfined environment of an exfoliated clay nanocomposite are found to crystallize preferentially in the form of a specific crystalline phase with increased degree of crystallinity. Strong dependence of IFSS on polymer crystallinity is found which is related to enhanced shrinkage stresses associated with increased degree of crystallinity.     

Measurements of Microhardness and Thermal and Electrical Properties of the Binary Zn-0.7wt.%Cu Hypoperitectic Alloy

Zn-0.7wt.%Cu hypoperitectic alloys were directionally solidified upwards with different temperature gradients (3.85 K/mm to 9.95 K/mm) at a constant growth rate (0.042 mm/s), and with different growth rates (0.0083 mm/s to 0.436 mm/s) at a constant temperature gradient (3.85 K/mm), using a Bridgman-type growth apparatus. Measurements of microhardness of the directionally solidified samples were carried out. The dependence of micro- hardness (HV) on growth rate (V) and temperature gradient (G) was analyzed. According to these results, it has been found that, for increasing values of G and V, the value of HV increases. Variations of electrical resistivity (ρ) and electrical conductivity (σ) for cast samples with temperature from 300 K to 670 K were also measured by using a standard direct-current (DC) four-point probe technique. The variation of the Lorenz coefficient with temperature for the Zn-0.7wt.%Cu hypoperitectic alloy was determined using the measured values of electrical conductivity and thermal conductivity. The enthalpy of fusion for the same alloy was determined by means of differential scanning calorimetry (DSC) from the heating trace during the transformation from liquid to solid.     

Technical note An assessment of the geometric accuracy of remotely-sensed images

Raw digital images cannot be used as maps because they contain geometric distortions which stem from the image acquisition process. To supply the same geometric integrity as a map, original raw images must be geometrically corrected and the distortions, such as variations in altitude, and earth curvature, must be compensated for. In this Technical Note, the geometric accuracy of a SPOT P image was evaluated by comparing a ground-based reference area, with areas calculated from the image. The areas were calculated using four different methods.     

Synthesis, characterization, and thermal degradation of new aromatic poly(azomethine-urethane)s and their polyphenol derivatives

A new polyurethane was synthesized by condensation reaction of 2,4-dihydroxy benzaldehyde (DHB) with methylene-di-p-phenyl-diisocyanate (MDI) under argon atmosphere. The synthesized polyurethane was converted to its poly(azomethine urethane) species (MP-2AP, MP-3AP, and MP-4AP) by graft copolymerization reactions with amino phenols (2-amino phenol, 3-amino phenol, and 4-amino phenol). Obtained poly(azomethine urethane)s (PAMUs) were converted to their polyphenol species (P-MP-2AP, P-MP-3AP, and P-MP-4AP) by oxidative polymerization reaction (OP) using NaOCl as the oxidant. The structures of the obtained compounds were confirmed by FT-IR, UV–vis, ¹H-NMR, and ¹³C-NMR techniques. The molecular weight distribution parameters of the synthesized compounds were determined by the size exclusion chromatography (SEC). The synthesized compounds were also characterized by solubility tests, TG-DTA, and DSC analyses. Thermal decomposition steps at various temperatures were clarified by FT-IR analyses of degraded products. Fluorescence measurements were carried out in various concentrated DMF solutions to determine the optimum concentrations to obtain the maximal PL intensities.     

Synthesis and characterization of graft copolymers of melamine: Thermal stability, electrical conductivity, and optical properties

In this study, novel three Schiff bases of melamine were synthesized via condensation reaction of melamine with salicylaldehyde, 3-hydroxybenzaldehyde, and 4-hydroxybenzaldehyde namely N,N′,N′′,-tris[(2-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (2-HPMTT), N,N′,N′′-tris[(3-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (3-HPMTT), N,N′,N′′-tris[(4-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (4-HPMTT), respectively. Then, oligo/polyphenol derivatives of these Schiff bases were obtained by grafting melamine onto oligosalicylaldehyde (OSA), oligo-3-hydroxybenzaldehyde, and oligo-4-hydroxybenzaldehyde that have generate names of poly-N,N′,N′′-tris[(2-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (P-2-HPMTT), poly-N, N′,N′′-tris[(3-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (P-3-HPMTT), and oligo-N,N′,N′′-tris[(4-hydroxyphenyl)methylene]-1,3,5-triazine-2,4,6-triamine (O-4-HPMTT), respectively. The structures of the synthesized compounds were confirmed by FT-IR, UV–vis, ¹H NMR, and ¹³C NMR techniques. The characterization was made by TG-DTA, DSC, size exclusion chromatography (SEC), and solubility tests. Electrical conductivities of the synthesized materials were measured by four-point probe technique using a Keithley 2400 electrometer showing that the synthesized oligo/polyphenols have higher electrical conductivities than the monomeric Schiff bases. Also considerable increases in the conductivities were observed when they were doped with iodine as a doping agent. The order of increase rates of the conductivities were found as follows: 2-HPMTT > P-2-HPMTT > P-3-HPMTT > 3-HPMTT > 4-HPMTT > P-4-HPMTT. Additionally, the optical band gaps (E_g) were calculated by using the absorption spectra and found to be 2.78, 2.17, 3.58, 3.30, 4.03, and 2.82 eV for 2-HPMTT, P-2-HPMTT, 3-HPMTT, P-3-HPMTT, 4-HPMTT, and O-4-HPMTT, respectively.     

Synthesis and characterization of aromatic and aliphatic ether bridged polymers containing carbazole moieties

In this study, the polymers were synthesized ether bridged containing carbazole moieties via HBr elimination. Also, these polymers include the aliphatic chains at the different lengths and aromatic groups in their structures. However, the polymers were characterized by FT-IR, NMR and UV–vis spectroscopy, and their thermal stabilities were determined via TGA measurements. Fluorescence measurements were performed using N,N′-dimethyl formamide solutions and also, the optimization of the concentrations to obtain maximal emission intensity was investigated in N,N′-dimethyl formamide. The morphologic properties of the polymers were investigated at different particle sizes by using Scanning Electron Microscopy (SEM). Additionally, the number average molecular weight (M_n), weight average molecular weight (M_w) and polydispersity index (PDI) values of the polymers were determined by size exclusion chromatography (SEC) technique. Resultantly, the remarkable properties related to the fluorescence and thermal measurements of the polymers were obtained. Therefore, these polymers could be used in various application fields because of the fluorescent and thermal properties.     

The effects of different levels of orange fiber and fat on microbiological, physical, chemical and sensorial properties of sucuk

The effects of orange fiber and fat levels on the physical, chemical and microbiological properties of sucuk (Turkish dry-fermented sausage) were investigated. Different levels of orange fiber (0, 2 and 4%) were added to sucuk batters with different levels of fat (10, 15 and 20%). Sucuk samples were analyzed during ripening. Lactic acid bacteria, Micrococcus/Staphylococcus and pH value were effected very significantly by orange fiber. Orange fiber caused a decrease in residual nitrite levels and an increase in the TBARS values. L^∗ and b^∗ values of sucuk samples increased with the use of fiber. Fiber use also decreased the cooking loss. No statistically significant difference was found between control and 2% fiber groups in terms of texture, color, odor taste and general acceptability scores. While fat levels had significant effects on cooking loss, taste and L^∗ values, ripening time effected all analyzed parameters.     

Low-level gate current injections in flash memories initiated byminority carrier collection action of floating terminals

An unintentional channel hot carrier injection phenomenon is reported for flash memory cells. The injection occurs near the source metallurgical junction during electrical erase and is caused by subthreshold leakage current between source and floating drains. This mechanism is initiated by a minority carrier population (electrons) which is generated by impact ionization around the source junction and later collected by the floating drains. Subsequently, when the floating gate potential approaches threshold voltage, these collected electrons drift from the drain toward the source. When they reach the source junction depletion region, they experience carrier multiplications and some hot carriers are injected onto the floating gate. The injected carriers can be either hot holes or hot electrons depending on the magnitude of the floating gate potential. This mechanism affects the final threshold voltage distribution of flash memories, especially when the electric field across the tunnel oxide is low     

Stress intensity factors and COD in an orthotropic strip

The elasticity problem for an orthotropic strip or a beam with an internal or an edge crack under general loading conditions is considered. The numerical results are given for four basic loading conditions, namely, uniform tension, pure bending, three point bending, and concentrated surface shear loading. For the strip with an edge crack additional results regarding the crack opening displacements are obtained by using the plastic strip model. A critical quantity which is tabulated is the maximum compressive stress in the plane of the crack. It is shown that this stress may easily exceed the yield limit in compression and hence may severely limit the range of application of the plasticity results.

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Résumé On considère le problème d'élasticité dans une bande orthotrope ou dans une poutre présentant une fissure interne ou une fissure de bord soumise à des conditions générales de mise en charge. Des résultats numériques sont fournis dans le cas de 4 conditions de charge déterminées, à savoir la tension uniforme, la flexion pure, la flexion sur 3 points, et le cisaillement concentré en surface. Pour la bande présentant une fissure de bord, des résultats supplémentaires relatifs au COD sont obtenus en utilisant un modèle de bande plastique. On détermine une quantité critique, qui est présentée sous forme de tableau, et qui représente la contrainte de compression maximale dans le plan de la fissure. On montre que cette contrainte peut aisément dépasser la limite d'écoulement en compression et dès lors peut constituer une limitation sévère dans le domaine d'application des résultats de plasticité. Le papier inclue aussi des résultats complets pour une bande isotropique avec une fissure de bord.

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This work was supported by NASA-Langley under the Grant NGR 39-007-011 and by NSF under the Grant ENG 78-09737.

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This work was supported by NASA-Langley under the Grant NGR 39-007-011 and by NSF under the Grant ENG 78-09737.     

Microfiltration of whey proteins adsorbed on yeast cells

Soluble whey proteins (WPs), adsorbed on yeast cells, were recovered by a crossflow microfiltration (MF) technique using a cellulose nitrate membrane with a pore size of 0.45 μm. The crossflow velocity was 1.5 m s^?1 with a transmembrane pressure of 200 kPa at 25 °C. A series of protein rejections occured at various pH values ranging from 2 to 8. WPs adsorbed more on to yeast cells at low pH (pH < 4) than at high pH values, probably because they were positively charged at low pH. It was also shown that permeate flux increased and Modified Membrane Fouling Index values decreased at low pH levels. When the yeast concentration was 50 g L^?1, the flux decreased five times compared with that in the absence of yeast. Protein recovery increased with increasing yeast concentrations. The highest protein recovery was found to be 85% at a yeast concentration of 50 g L^?1 at a steady state flux rate of 10^?6 m s^?1 at 25 °C. When diluted solutions of whey were used, the same rejection of protein, adsorbed on yeast cells, was achieved at ten times lower amounts of yeast cells. This technique not only provides for the recovery of protein but also may give rise to the direct use of yeast cells, which are rich in protein, in the baking industry. WPs absorbed by yeast cells can be used to produce nutritionally rich products in areas where yeasts have been already used.