VOLUME 38, NO3, JUNE-2014
123
 
The Nucleation Effect and Thermal Behavior of Poly(L-lactic acid) in the Presence of a Bisamides Compound

Yan-Hua Cai, Yin-Qing Fan and Yong-You Tian

The nucleation effect and thermal behavior of bisamides compound(N, N'-Bis(benzoyl) tridecanedioic acid dihydrazide (NA)) as organic nucleating agent for poly(L-lactic acid) (PLLA) was evaluated by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide angle X-ray diffraction (WAXD). Compared to neat PLLA, NA could increase the overall crystallization rate of PLLA. Upon the addition of 0.8% NA, the crystallization peak temperature increased from 96.28 ℃ to 113.58 ℃, and the crystallization enthalpy increased from 1.379 J•g-1 to 30.51 J•g-1. POM showed that the spherulite number of PLLA increased and the spherulite size significantly reduced in the presence of NA. The results of melting behavior at different conditions showed that the melting behavior of PLLA/NA samples was affected significantly by crystallization time, crystllization temperature and cooling rate. And there existed double-melting peaks resulting from melting-recrystallization at low crystallization temperature.
Pages(371)
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The Effects of Different Grain Brans Used as Substrates on Resistance to Catabolite Repression in Solid-State Fermentation Process

Bilal Balkan

Production of -amylase from Penicillium brevicompactum was investigated in solid-state fermentation (SSF) using as substrate wheat bran (WB), rye bran (RB) and barley bran (BB) enriched with different amount of glucose or not. Consumption of glucose by fungal cells in WB and RB cultures was more effective than BB cultures. Optimal moisture levels for maximal -amylase production in WB, RB and BB cultures without glucose were 55, 65 and 35 %, respectively. Water absorption capacities of substrates were WB>RB>BB. In SSF process, decrease in enzyme production was greater in high moisture level than optimal moisture level. According to the other two cultures, production of -amylase from P. brevicompactum was strongly inhibited in higher moisture levels than optimal moisture levels in BB cultures enriched with 500 mg/g glucose.
Pages(377)
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Effect of Experimental Variables on the Extraction of Silica from the Rice Husk Ash

Ikram Ul Haq, Khalida Akhtarand Abdul Malik

Silica was extracted from the locally obtained rice husk ash (RHA) by heating its dispersion in sodium hydroxide solution for various periods of time. Following this treatment, silica content of the dispersed RHA particles leached out into the liquid phase in the form of sodium silicate. On separation from the solid, the alkaline solution of sodium silicate was made acidified with sulfuric acid, which transformed the dissolved silicate into precipitated gelatinous silica. The yield of silica was dependent on the strength of the alkaline solution, aging time, etc. Optimum conditions were established under which maximum extraction could be made from the rice husk ash. The as-extracted silica maintained its gelatinous nature after washing with water; however, on washing with ethanol, it transformed into powder of discrete particles. On calcination at 750 oC, the water washed silica converted into powder form, comprised of ellipsoids, whereas the ethanol washed silica particles sintered together. Selected samples of the extracted materials were then subjected to characterization by various physical methods, such as SEM, EDX, XRD, and FT-IR.
Pages(382)
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Fabrication and Characterization of Potassium and Sodium Titanate via a Hydrothermal Method

Jiasheng Xu , He Zhang, Tongchao Liu and Jie Zhang

Various sized titanate nanofibers were prepared by hydrothermal reaction of aqueous solutions containing the respective alkali (KOH and NaOH) and anatase in stoichiometric amounts at 170-200 C for 96 h. Their morphological and structural properties were characterized by many methods, including the powder X-ray diffraction (XRD), the scanning electron microscopy (SEM), the fourier transform infrared spectroscopy (FTIR) and the UV/Vis spectrophotometer. Their morphologies depend on the experimental temperature and the solution conditions, in which the alkali metal plays an important role during the experimental process. When the size of titanate samples decrease, the UV-Vis spectra are blue-shift. This work provided an effective hydrothermal method to synthesize titanate nanofibers, which may be applicable to fabrication of other nanomaterials.
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A B3LYP Study Searching for B-B Triple Bond in XBBX System (X= CO, CS, N2, CNCH3, H2O, H2S, NH3, PH3, C5H5N, F-, CN-, NO2-)

Huimin Bi, Pengtao Xie, Xingquan Chai, Yan Liu, Qing li and Cuihong Sun

A DFT study using B3LYP/6-311+G(3df,2p) method, has been performed to investigate the total energies, equilibrium geometries, bonding energies, and the values of spin contamination of BX and XBBX molecules, where X=CO, CS, N2, CNCH3, H2O, H2S, NH3, PH3, C5H5N, F-, CN-, NO2-. NBO analysis calculations also obtain the natural charges and bond orders at B3LYP/6-311+G(3df,2p) level. The quadruplet is ground state for both CO and CS ligands, by dimer of which can form stable singlet of XBBX. But for the remaining ligands, the doublets are ground states, contrary to the BCO and BCS systems.
Pages(394)
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Analytical Data: Reliability and Presentation

Naila Siddique and Shahida Waheed

Chemical analysis whether it is used to determine the composition of a sample or to devise a procedure for testing or preparation of another sample requires systematic experiment design and implementation. In order to determine and verify the validity of results various methods are employed to evaluate the data obtained. This process enables the analyst not only to understand the results but to find possible reasons for differences and similarities between samples. A simple scheme for carrying out analysis in order to obtain valid and reliable results is outlined in this paper. Moreover the importance of using reference and quality control materials to obtain quantitative results is also highlighted. To evaluate the performance and capability of a laboratory or an analytical procedure, parameters such as relative bias, z-scores, u-test, tests for accuracy and precision etc can be used. The use and significance of these parameters is explained using examples in this manuscript. Uncertainties and errors in measurement as well as the limits of detection (LOD) of an experimental procedure can also provide vital information about the data obtained. Simple calculations are used to explain how these can be obtained and what their magnitudes imply.
Pages(399)
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Process Design Analyses of CO2 Capture from Natural Gas by Polymer Membrane

Arshad Hussain, Habib Nasir and Muhammad Ahsan

Membrane-based natural gas separation has become one of the promising technologies due to its compactness, energy efficiency, environment friendliness and economic advantages. In this work, a three stage membrane process for the separation of CO2/CH4 is proposed based on a novel fixed site carrier membrane which has the potential to meet the CO2/CH4 separation and durability requirement. A simulation analysis, which utilizes the Aspen Hysys capabilities to calculate and couple energy balances in the process model, has been conducted to investigate the effect of process parameters on the gas processing cost. Two different natural gas mixtures containing 9.5% and 2.9% CO2 have been simulated for various process conditions. This fixed site carrier membrane performs well when wetted with water. Therefore, natural gas feed streams are saturated with water. It is evident from the analysis that it is possible to maintain 2% CO2 in retentate and methane loss in permeate below 2% by optimizing the process conditions. The analysis shows that fixed site carrier membrane offers a viable solution for natural gas sweetening.
Pages(411)
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Protonation Reaction of Anion Radicals of some Dinitroaromatics in Hexamethylphosphortriamide (HMPA)

Farzana Hanif, Ghazala Yasmeen, Rashida Perveen and Muhammad Aamir

Cyclic voltammetric method has been employed to investigate the protonation of anion radicals of 1,2-, 1,3-, and 1,4- dinitrobenzenes in Hexamethylphosphortriamide (HMPA) in the temperature range 5°C, 15°C, 25°C and 35°C. Glassy carbon electrode and hanging mercury drop electrode are used as working electrodes. Benzoic acid and salicylic acid are used as protonating agents. Homogeneous rate constant is calculated by using Nicholson and Shain equation. The position of nucleophilic attack in dinitrobenzenes has been investigated by calculation of charge densities using MNDO and SCF-UHF molecular orbital methods. The heterogeneous rate constant ks,h for the first reduction process in dinitrobenzenes is determined by digital simulation of the cyclic voltammograms.
Pages(422)
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Hydrogen Absorption and Desorption Performance of Magnesium-Aluminium Alloys Produced by Powder Metallurgy

Muhammet Ali Nalbant and Özlem Korkut

The main scope of this study is investigating the hydrogen storage and desorption performance of Mg: Al (90:10), Mg17Al12 and Mg2Al3 alloys using a volumetric method. In the experiments, hydrogen pressure introduced into a reference volume was at approximately 20 Bar. Mg-Al alloys were prepared by a powder metallurgy technique. Pressing pressure levels of alloys were altered as 200, 400 and 600 MPa. Upon XRD patterns, after the pressing and sintering, β-Mg2Al3 and Mg:Al(90:10) phases decomposed into γ-Mg17Al12, Mg and Al compositions. γ-Mg17Al12 was the main phase in the hydrogen absorption/desorption process. The highest absorption of hydrogen was observed in the Mg:Al (90:10) alloys. The hydrogen desorption performance of the alloys decreased with the increase of absorption performance. Therefore the lowest desorption was observed in the Mg:Al (90:10) alloys.
Pages(439)
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Synthesis, Characterization and Antibacterial Activity of Halogenated Aryl Sulfonamides Derived from 2-Amino-4-chloroanisole

Aziz-ur-Rehman, Shahid Rasool, Muhammad Athar Abbasi, Khadija Nafeesa, Ambreen Fatima, Samreen Gul, Ghulam Hussain, Khalid Mohammed Khan, Irshad Ahmad and Saira Afzal

In the current work, a number of new N-(5-chloro-2-methoxyphenyl)aryl sulfonamides (3a-e) and N-ethyl/benzyl-N-(5-chloro-2-methoxyphenyl)aryl sulfonamides (6a-e and 7a-e) were synthesized and evaluated for their biological activities. The synthesis was carried out by coupling 2-amino-4-chloroanisole (1) with different aryl sulfonyl chlorides, 2a-e, under dynamic pH control in aqueous medium to form aryl sulfonamides, 3a-e. Further, N-ethyl/benzyl-N-(5-chloro-2-methoxyphenyl)aryl sulfonamides (6a-e and 7a-e) were synthesized by stirring 3a-e with the electrophiles, 4 and 5, in the presence of sodium hydride and N,N-dimethylformamide. The structures of the synthesized compounds were characterized from their spectral data. In addition, the in vitro antibacterial activity of all the target compounds was investigated against Gram-negative and Gram-positive bacteria using ciprofloxacin as a reference drug. Many of these compounds exhibited moderate to good activity and subtle structural changes in the substituents altered the inhibitory properties significantly.
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