Charge density dependence of elastic modulus of strong polyelectrolyte hydrogels

The mechanical behavior of a series of strong polyelectrolyte hydrogels based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid sodium salt (AMPS) was investigated. The hydrogels were prepared at a fixed crosslinker ratio and monomer concentration, but at various charge densities, i.e. AMPS contents between 0 and 100 mol%. The elastic modulus of the hydrogels after their preparation first increases with increasing charge density but then decreases continuously. Investigation of the swollen state properties of the hydrogels shows existence of a large number of ionic groups inside the gel that are ineffective in gel swelling. The results indicate two opposite effects of charged groups on the elastic modulus of the hydrogels: formation of multiplets acting as additional crosslinks in the gel increases the elastic modulus of ionic hydrogels, whereas the effect of the electrostatic interaction of charged groups on elastic free energy decreases the modulus.     

Inhomogeneities in poly(acrylamide) gels: position-dependent elastic modulus measurements

Summary The inhomogeneities in poly(acrylamide) (PAAm) gels and the formation mechanism of inhomogeneities were investigated using the results obtained by the mechanical measurements. The gels in the form of rods of 5.6 mm in diameter were prepared at various crosslinker (N,N'-methylene(bis)acrylamide) content. The initial monomer concentration was set to 5.1 w/v %. The results show that the elastic modulus of PAAm gels varies depending on the location, at which the mechanical measurements are carried out. The modulus increases with increasing distance from the bottom of the gel rod. The extent of modulus variation along the gel increases with increasing crosslinker content from 2.6 to 9 % BAAm. Received: 23 January 2001/Revised version: 17 May 2001/Accepted: 17 May 2001     

Roasting-Related Changes in Oxidative Stability and Antioxidant Capacity of Apricot Kernel Oil

Apricot kernels were roasted for various lengths of time (0–30 min) at 180 °C and changes in the oxidative stability, antioxidant capacity, color, as well as the level of tocopherols and fatty acids of the apricot kernel oil (AKO) were monitored. While the level of tocopherols decreased, the oxidative stability and antioxidant capacity of AKO increased with roasting, probably due to the formation of antioxidative Maillard reaction products (MRPs) during the roasting. Medium roasted samples (15–20 min) were found to be more resistant to oxidative deterioration. The oil from the 30-min roasted sample was more susceptible to oxidation compared to the oil from the 20-min roasted sample in most of the stability tests. Relatively shorter roasting periods (5–10 min) also led to a decrease in oxidative stability in comparison to the unroasted sample. Brownish color and antiradical activity increased with roasting and the highest values were measured in the 30 min roasted sample.     

Antifungal activity of organic and organometallic derivatives of benzimidazole and benzothiazole

Forty organic or organometallic derivatives of benzimidazole and benzothiazole and five rhodium(I) and ruthenium(II) complexes were evaluated for their in vitro antifungal activity against Candida albicans. Four of the tested compounds, the rhodium containing compounds 30, 31, 32 and 33, were found effective at the minimum inhibitory concentrations(MICs) between 400-600 micrograms/ml.     

Study of CdS/Cu(In, Ga)Se2 heterojunction interface using admittance and impedance spectroscopy

The interface properties of an unusual CdS/Cu(In, Ga)Se₂ solar cell have been studied by admittance and impedance spectroscopy. The current transport in this device has previously appeared to be dominated by tunnelling enhanced recombination at junction interface. The existence of this unexpected route was attributed to the presence of Cu-rich and indium depleted thin layer which might possibly be formed on the absorber surface. We have performed temperature dependent admittance and impedance measurements in order to clarify this phenomenon. An acceptor level with ionization energy of about 50 meV seems to be strongly correlated to the appearance of the CuGaSe₂ layer. The impedance spectra obtained at 100 K and 300 K exhibited single semi-circles. This indicates the dominance of the heterojunction interface without the effect of any other capacitive components. The equivalent circuit model consisting of a parallel resistor and capacitor in series with a resistor has been found to give a good fit to the experimental data.     

Alumina coated with oxazolone derivative for extraction of trace amounts of cadmium and copper from water and plant samples

A solid phase extraction procedure is proposed for simultaneous separation and preconcentration trace amounts of Cu(II) and Cd(II) using alumina coated with N'-{4-[4-{1-[4-(dimethylamino)phenyl]methylidene}-5-(4-H)oxazolone]phenyle}acetamide and determination by flame atomic absorption spectrometry. Using 0.1g of the sorbent, the metal ions were sorbed at pH 7 and recovered with 5.0 mL of 0.5 mol L(-1) HNO(3). It was found that extraction can be performed from the sample volumes of 2000 and 800 mL for Cu and Cd, respectively (preconcentration factors of 400 for Cu and 160 for Cd). Obtained sorption capacities for 1g sorbent were 8 mg Cu and 14 mg Cd. The linearity was maintained in the concentration range of 0.1 ng mL(-1) to 7.0 μg mL(-1) for Cu and 0.13 ng mL(-1) to 2.0 μg mL(-1) for Cd in the original solution. Eight replicate determinations of a mixture containing 1.0 μg mL(-1) each of the elements in the final solution gave relative standard deviation ±1.6 and ±1.3% for Cu and Cd, respectively. The detection limit was calculated as 0.06 and 0.05 ng mL(-1) for Cu and Cd, respectively. The proposed method was successfully applied to the determination trace amounts of Cu and Cd in the water and plant samples.     

Separation of IPA/water mixtures by pervaporation: sorption and pervaporation results

Homogeneous membranes were prepared by blending polyvinyl alcohol (PVA) with polyacrylic acid (PAA) and furthermore the blend membrane is cross-linked covalently through an ester linkage formation between a hydroxyl group of PVA and carboxyl group of PAA. These membranes were evaluated for separation of azeotropic isopropyl alcohol (IPA)/water mixtures by pervaporation, that is, a vacuum applying membrane process. The overall and preferential sorption of IPA/water mixtures in cross-linked membranes were determined to investigate the influence of PVA/PAA ratio and of liquid mixture composition. Pervaporation characteristics were also determined as a function of PVA/PAA ratio and of the feed mixture composition. With increasing PAA content in the membranes, solubilities and fluxes decreased and selectivities increased. Because of polarity, water permeated preferentially through the membranes. Sorption results showed the same tendency as pervaporation results.     

Development and characterization of poly(vinyl alcohol) and casein blend films

Blends of plasticized casein (CA) and poly(vinyl alcohol) (PVA) at various ratios were prepared using the solution‐casting method. The prepared blend solutions were cast onto polystyrene petri plates and bend films were obtained. The characterization of films was performed using Fourier transform infrared spectroscopy, tensile testing, thermogravimetric analysis, contact angle measurements and water vapour permeability. According to spectroscopic analysis, there were interactions between the CA and PVA molecules. The tensile test results showed that the tensile strength of CA increased with increasing PVA content. The flexibility of plasticized CA film increased with the incorporation of PVA. The thermal stability and water vapour barrier properties of plasticized CA improved on blending with PVA. As a result, it was seen that blend films were successfully produced using plasticized CA and PVA with potential for use in biodegradable packaging applications. © 2019 Society of Chemical Industry     

Olive cake combustion in a circulating fluidized bed

In this study, a circulating fluidized bed of 125 mm diameter and 1800 mm height was used to find the combustion characteristics of olive cake (OC) produced in Turkey. A lignite coal that is most widely used in Turkey was also burned in the same combustor. The combustion experiments were carried out with various excess air ratios. The excess air ratio, λ, has been changed between 1.1 and 2.16. Temperature distribution along the bed was measured with thermocouples. On-line concentrations of O₂, SO₂, CO₂, CO, NO_x and total hydrocarbons were measured in the flue gas. Combustion efficiencies of OC and lignite coal are calculated, and the optimum conditions for operating parameters are discussed. The combustion efficiency of OC changes between 82.25 and 98.66% depending on the excess air ratio. There is a sharp decrease observed in the combustion losses due to hydrocarbons and CO as the excess air ratio increases. The minimum emissions are observed at λ=1.35. Combustion losses due to unburned carbon in the bed material do not exceed 1.4 wt% for OC and 1.85 wt% for coal. The combustion efficiency for coal changes between 82.25 and 98.66% for various excess air ratios used in the study. The ash analysis for OC is carried out to find the suitability of OC ash to be used as fertilizer. The ash does not contain any hazardous metal.