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41.
Yiming Zeng Zhigang Wang Lijun Wan Yanqiao Shi Guanwen Chen Chunli Bai 《应用聚合物科学杂志》2003,88(5):1328-1335
By the use of atomic force microscopy (AFM), formation mechanism of nodular structure in cellulose acetate membranes was systematically investigated. Elementary factors affecting the nodule formation were delineated on the basis of both kinetic and thermodynamic considerations. It was shown that (1) the exact nature of nodular structure is thermodynamic equilibrium glassy state; nodular structure will vanish in the rubbery state; (2) the thermodynamic factor affecting nodule formation is the membrane formation temperature; with the membrane formation temperature decreasing, more chain segments are able to form nodular structures; (3) nodule formation is dependent on the segment rearrangement; variation of the solvent environment is the major kinetic factor affecting the segment rearrangement and nodule formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1328–1335, 2003 相似文献
42.
The effect of thermal hysteresis on the polymer chain packing and permeation properties of two 6FDA‐based polyimide isomers was investigated. Thermal quenching resulted in a small increase in the fractional free volume of the polyimides with respect to the samples that had been annealed. Quenching from above the glass‐transition temperature also resulted in larger increases in the permeabilities for both 6FDA–6FmDA and 6FDA–6FpDA with respect to annealed samples. Meta‐connected 6FDA–6FmDA exhibited a larger increase in the permeability after quenching than the para‐connected isomer, 6FDA–6FpDA. This larger increase in the permeability for 6FDA–6FmDA may have been due to differences in the effects of the increases in the free volume on the intersegmental resistance to chain motions. Although physical aging over a 3‐month period resulted in a reduction in the permeability of quenched samples of 6FDA–6FpDA, the quenched samples maintained higher permeabilities than the annealed samples. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1174–1182, 2004 相似文献
43.
摘要:细胞固定化技术具有流程简单、生物相容、操作稳定等优点,可有效保证细胞活性,实现高效的细胞催化生产精细化学品。本文介绍了表面附着、凝胶包埋、聚电解质层层自组装膜等多细胞固定化方法,及其在二元醇、生物乙醇、乳酸、酯、多糖等精细化学品生产中的研究现状和进展,并分析讨论了各种方法存在的问题。同时,总结了近年来新发展的单细胞纳米涂层固定化方法的机理、趋势及应用于精细化学品生产的可能性。最后对细胞固定化催化生产精细化学品面临的技术挑战及研究方向做出展望,以期为精细化学品生产提供一定的技术支持。 相似文献
44.
New parameters, light transmission rate and minimum light transmissions, are proposed. These two parameters reflect the characteristics of the membrane‐forming system and the formation process of the membranes by phase inversion. The relationship between the light transmission and the porous structure of the membrane can be explained by the geometrical optics principles. Variation of the two parameters combining Reuvers's phase separation theory provided a convenient analytical method to predict effectively membrane morphologies. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 174–181, 2003 相似文献
45.
The impact that some membrane preparation steps had on ultrafiltration (UF) membrane characteristics and performance was studied. Polyethersulfone (PES) was employed as base polymer, while N‐methyl pyrrolidone (NMP) was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a nonsolvent pore‐forming additive. The manufacturing variables studied were solvent evaporation time and membrane surface modification, using a fluorine‐based copolymer referred to as surface‐modifying macromolecule (SMM). The flat sheet membranes, prepared via phase inversion, were characterized using solute transport data, X‐ray photoelectron spectroscopy (XPS), and contact angle measurements. Membrane performance was evaluated via filtration test protocol that included a 6‐day filtration of concentrated river water. The flux reduction with time was modeled using single and dual mechanisms of fouling. The pore blockage/cake filtration model described better the behavior of the permeation rate along the experiments. Increasing the solvent evaporation time decreased the size of the pores and the permeation rate. However, it did not significantly affect the removal of the organic compounds naturally present in the river water used as feed. XPS and contact angle measurements proved that the short evaporation periods did not allow enough SMM migration to the surface to provoke a significant effect on the membrane performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006 相似文献
46.
47.
The separation performance of two different commercially available tubular inorganic membranes was studied for solvent dehydration. The separation layers consisted of A-type zeolite and microporous silica. The membrane characteristics were determined as function of operating conditions such as feed composition, temperature, and permeate pressure in pervaporation and vapor permeation. Among different membranes of the same batch, flux and selectivity were reproducible within 10%. The partial flux of water as the preferentially permeating component increases linearly with the water vapor pressure difference between feed and permeate and depends only marginally (viscosity influence) upon the properties of the organic component. The flux of the organic (retained) component is low and can best be described by assuming a substance and membrane specific permeance (flux over partial pressure difference) that is independent of composition. At very low water concentration in the feed one would expect a strong increase in permeability of the retained component through non-zeolite pores and larger silica pores as predicted by pure component measurements. However, this effect was not observed in mixtures within the concentration range studied here. A temperature rise improves flux rates exponentially while selectivity remains high. Thus, higher module cost in comparison to polymeric membranes can be compensated by reduced membrane area if a higher operating temperature can be chosen. Flux and selectivity decline as a function of permeate pressure with decreasing driving force. In vapor permeation with inorganic membranes superheating of the vaporous feed improves their performance while for polymeric materials a steep flux decline is observed. High flux and selectivity are obtained in the separation of water from alcohols. The normalized flux values of the A-type zeolite membrane are roughly 10 kg/m2 h bar with a mixture selectivity of 2000 for methanol, 4000 for ethanol and 8000 for n-butanol. The average permeance of the amorphous silica membrane lies above 12 kg/m2 h bar with mixture selectivity of 50 for methanol, 500 for ethanol and 2000 for n-butanol. The separation mechanism is mainly based on adsorption and diffusion enhanced by shape selectivity and size exclusion in some cases. The transport characteristics could be described with a simple transport model based on normalized permeate fluxes. With regard to the operation stability of the membranes, no deterioration of the performance was observed for the A-type zeolite in solvent dehydration or in separation of water from reaction mixtures. The silica membrane showed an initial conditioning effect involving a rearrangement of Si-OH groups with an increase in selectivity and decrease in flux of about 30%. After a few hours the performance stabilized and remained constant during further operation. 相似文献
48.
Ji‐Zhao Liang 《应用聚合物科学杂志》2007,104(3):1697-1701
The tensile properties of polypropylene (PP) filled with hollow glass beads have been measured at room temperature to identify the effects of the particle contents, size and its distribution on them in the present article. The mean diameters of the fillers were 11, 35, and 70 μm, and they were named as TK10, TK35, and TK70 respectively. The surface of these particles was pretreated with silane coupling agent. The results showed that the yield stress (σy) decreased gently for PP/TK70 systems, whereas decreased relatively obviously for PP/TK35 systems with increasing the volume fraction (?f) of the fillers. When ?f was less than 5%, the tensile strength at break (σb) of the composites increased with the increase of ?f. When ?f was more than 5%, σb was almost a constant for PP/TK70 systems, while σb decreased linearly for PP/TK35 systems. The tensile fracture strain (εb) of the composites decreased suddenly when ?f was less than 5%, and then decreased slightly with increasing ?f. When ?f was 10%, σy and σb increased while εb decreased with the increase of the bead diameter. Furthermore, the σy was predicted by means an equation proposed in the previous work, and good interfacial adhesion was shown between the hollow glass beads and the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1697–1701, 2007 相似文献
49.
Poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate) (VSA–SA)/polysulfone (PS) composite membranes were prepared for the separation of CO2. VSA–SA contained secondary amines and carboxylate ions that could act as carriers for CO2. At 20°C and 1.06 atm of feed pressure, a VSA–SA/PS composite membrane displayed a pure CO2 permeation rate of 6.12 × 10?6 cm3(STP)/cm2 s cmHg and a CO2/CH4 ideal selectivity of 524.5. In experiments with a mixed gas of 50 vol % CO2 and 50 vol % CH4, at 20°C and 1.04 atm of feed pressure, the CO2 permeation rate was 9.2 × 10?6 cm3 (STP)/cm2 s cmHg, and the selectivity of CO2/CH4 was 46.8. Crosslinkages with metal ions were effective for increasing the selectivity. Both the selectivity of CO2 over CH4 and the CO2 permeation rate had a maximum against the carrier concentration. The high CO2 permeation rate originated from the facilitated transport mechanism, which was confirmed by Fourier transform infrared with attenuated total reflectance techniques. The performance of the membranes prepared in this work had good stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 275–282, 2006 相似文献
50.
MACROPROCESS OF PARTICLE FORMATION IN SUSPENSION POLYMERIZATION OF STYRENE WITH INORGANIC STABILIZER SYSTEM 下载免费PDF全文
The macroprocess of particle formation from suspension droplets of styrene in a pdymerizationsystem was investigated.Inorganic hydroxyapatite or its mixture with polyvinyl alcohol as thepolymerization system was used.Those items such as the effects of the Weight fraction of dispersed-phase,the amount of the inorganic stabilizer and the agitation speed on the breakup and coalescence of thetransient dispersed drops etc.Were examined.Results showd that the dynamic behavior of the transi-ent polymer droplets changed in the presence of the suspension stabilizer during the reaction. 相似文献