The transient currents measured in discharge mode with cellulose acetate (CA): polyvinyl acetate (PVAc) blend films (≈ 20μm thick) as a function of charging field [(1.5–4.5)×104 V/cm], temperatures (323–373 K) and polymer weight ratio (90:10 and 75:25) have been found to follow Curie-von Schweidler
law, characterized with two slopes in short and long time regions. Isochronals characteristics (i.e. current/temperature plots
at constant times) constructed from these data seemed to reveal a broad peak observed at 363 K. Values of activation energy
increase with PAVc content and also with time of observation. Space charge due to trapping of injected charge carriers in
energetically distributed traps and induced dipoles created because of the piling up of charge carriers at the phase boundary
of heterogeneous structure of blend are considered to account for the observed currents. 相似文献
Ten promising microbial strains were screened for glucose fermentation over the temperature range of 37–47°C, and five temperature-tolerant
yeasts (Saccharomyces cerevisiae SERI strain (D5A),S. uvarum, andCandida generaacidothermophilium, brassicae, andlusitaniae), were chosen for SSF evaluation on Sigmacell-50 cellulose with Genencor 150 L cellulase enzyme.Brettanomyces clausenii (Y-1414) was included for comparison to previous studies both by itself and in mixed culture withS. cerevisiae (D5A). Good conversion rates were achieved at temperatures as high as 43°C withC. brassicae andS. uvarum; mixed cultures of either of these yeasts with the thermotolerant cellobiose fermenting yeastC. lusitaniae achieved higher rates and yields than any of the three yeasts alone. However, the mixed culture ofB. clausenii andS. cerevisiae at 37°C achieved as high conversion rates and higher yields than any of the other yeasts tested. 相似文献
To achieve rapid and highly efficient recovery of Li+ from seawater, a series of H2TiO3/cellulose aerogels (HTO/CA) with a porous network were prepared by a simple and effective method. The as-prepared HTO/CA were characterized and their Li+ adsorption performance was evaluated. The obtained results revealed that the maximum capacity of HTO/CA to adsorb Li+ was 28.58 ± 0.71 mg g−1. The dynamic k2 value indicated that the Li+ adsorption rate of HTO/CA was nearly five times that of HTO powder. Furthermore, the aerogel retained extremely high Li+ selectivity compared with Mg2+, Ca2+, K+, and Na+. After regeneration for five cycles, the HTO/CA retained a Li+ adsorption capacity of 22.95 mg g−1. Moreover, the HTO/CA showed an excellent adsorption efficiency of 69.93% ± 0.04% and high selectivity to Li+ in actual seawater. These findings confirm its potential as an adsorbent for recovering Li+ from seawater. 相似文献
Separation of veterinary drug alaptide ((S)-8-methyl-6,9-diazaspiro(4,5)decane-7,10-dione) from a chiral impurity (R-enantiomer) was developed. Five chiral columns (three amylose and two cellulose type) were evaluated in a reversed-phase system. Three of them offered satisfactory enantiomeric resolution. Finally, three methods were validated and proved to be applicable for the determination of a chiral impurity content below 0.1% (method A: 3-AmyCoat column, tris-[3,5-dimethylphenyl]carbamoyl amylose; mobile phase: water/methanol/propan-2-ol/butan-2-ol=75:20:3.5:1.5 v/v, flow rate: 0.40 mL/min; column temperature: 30 °C; method B: Chiralpak AS-3R, tris-[1-phenylethyl]carbamoyl amylose; water/acetonitrile=80:20 v/v, 0.40 mL/min; 40 °C; method C: Chiralcel OZ-3R, tris-[3-chloro-4-methylphenyl] carbamoyl cellulose; water/acetonitrile=80:20 v/v, 0.40 mL/min; 40 °C). Some decrease in efficiency with repeated sample injections was observed for the 3-AmyCoat column. The resistance to mass transfer in the stationary phase increased probably due to the change in chiral selector conformation. This effect was considerably suppressed by propan-2-ol or to a greater extent by butan-2-ol added to a mobile phase. Simple regeneration was also suggested to recover efficiency of the column. 相似文献
The present paper describes the synthesis of a new chemically modified cellulose microfiber through oxidation with sodium periodate and functionalization with N,N′-bis (2-aminoethyl)-1,2-ethanediamine for the fast and selective preconcentration of Cd(II) ions in flow system analysis. The new sorbentsorbent was characterized by FTIR, SEM, and surface area values. The uptake behavior of Cd(II) ions onto this sorbent was evaluated from kinetic data, pseudo-first-order and pseudo-second-order models, as well as from Langmuir, Freundlich and Langmuir-Freundlich adsorption isotherms. The maximum sorption capacity of 4.59 mg g−1 was estimated by the Langmuir-Freundlich model with fast kinetics for the sorption of Cd(II) described by the pseudo-second-order kinetic model. After characterization, the sorbent was packed in a mini-column, and a fast flow injection preconcentration system for Cd(II) determination by FAAS was developed. The best Cd(II) preconcentration condition, obtained by means of factorial design and response surface methodology, was achieved at pH 9.36 and a flow rate of 10 mL min−1 followed by elution with 1.0 mol L−1 nitric acid. By using 78 s preconcentration time, fast and highly sensitive determination of Cd(II) ions could be achieved with a limit of quantification of 0.20 μg L−1, preconcentration factor of 26, consumption index of 0.5 mL, concentration efficiency of 20 min−1, and sample throughput of 39 h−1. The repeatability for 10 replicate determinations was found to be 7.8 and 2.5% for Cd(II) ion concentrations of 5.0 and 100.0 μg L−1, respectively. The new sorbent efficiency for the interference-free preconcentration of Cd(II) ions was assessed by analysis of tap, mineral and lake waters, as well as synthetic seawater and normal saline waters. Furthermore, complex samples, such as biological samples, could be analysed by the proposed method in accordance with the accuracy attested by analysis of certified reference materials, TORT-2 (lobster hepatopancreas), and DOLT-4 (dogfish liver). 相似文献
Pure quaternary tetraalkylammonium chlorides with one long alkyl chain dissolved in various organic solvents constitute a new class of cellulose solvents. The electrolytes are prepared in high yields and purity by Menshutkin quaternization, an inexpensive and easy synthesis route. The pure molten tetraalkylammonium chlorides dissolve up to 15 wt% of cellulose. Cosolvents, including N,N‐dimethylacetamide (DMA), may be added in large excess, leading to a system of decreased viscosity. Contrary to the well‐established solvent DMA/LiCl, cellulose dissolves in DMA/quaternary ammonium chlorides without any pretreatment. Thus, the use of the new solvent avoids some disadvantages of DMA/LiCl and ionic liquids, the most extensively employed solvents for homogeneous cellulose chemistry.