相转化法聚合物/溶剂/非溶剂铸膜体系的热力学计算

计算了相转化法铸膜体系中常见的典型三元相图,分析了聚合物与溶剂之间、聚合物与非溶剂之间、溶剂与非溶剂之间的相互作用参数对聚合物/溶剂/非溶剂铸膜液体系相图的影响,以及体系温度和聚合物摩尔体积对聚合物/溶剂/非溶剂铸膜液体系相图的影响。根据溶剂-非溶剂汽液平衡数据和溶解度参数得到了溶剂-非溶剂、溶剂与聚合物以及非溶剂与聚合物之间的Flory-Huggins相互作用参数,从而获得了几种常见铸膜液体系的相图。同时,利用聚合物/溶剂/非溶剂铸膜液体系的相图数据对热力学模型的参数进行了优化,取得了与实验结果较一致的计算结果。     

Analysis of nonsolvent–solvent–polymer phase diagrams and their relevance to membrane formation modeling

Calculations have been carried out, based on Flory–Huggins solution theory, to analyze the behavior of the ternary nonsolvent–solvent–polymer phase diagram for typical membrane-forming systems. Consideration is given to the behavior of the spinodal as well as binodal curves, tie-line slopes, and critical points as a function of various parameters, most especially those related to the concentration dependency of the interaction parameters. Implications regarding membrane structure formation are discussed, and the suitability of different functional forms for the interaction parameter concentration dependence is also analyzed. The net result of these calculations is to demonstrate the importance of the various parameters in controlling the phase-diagram behavior and particularly to show the critical role of the concentration dependence of the solvent–polymer interaction parameter in affecting the nature of the miscibility gap.     

Calculation of alcohol‐acetone‐cellulose acetate ternary phase diagram and their relevance to membrane formation

ABSTRACT Alcohol‐acetone‐cellulose acetate phase diagrams incorporated with methanol, ethanol, and isopropanol as nonsolvents are calculated according to a new form of the Flory–Huggins equation. Nonsolvent–cellulose acetate interaction parameters are measured by swelling experiments. Concentration‐dependent nonsolvent–solvent interaction parameters are obtained by vapor–liquid equilibrium and the Wilson equation. It is shown that alcohol is a week coagulant compared with water, and water > methanol > ethanol > isopropanol for cellulose acetate. The phase diagrams characteristic of acetone‐cellulose acetate combined with water, methanol, ethanol, and isopropanol as nonsolvents is different, which leads to the different morphological structure of a cellulose acetate membrane. The structure of a water coagulated membrane has large macrovoids from liquid–liquid phase separation. A methanol coagulated membrane has a honeycomb‐like structure from spinodal microphase separation. An ethanol or isopropanol coagulated membrane has a thicker, dense top layer from the delay time phase separation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1650–1657, 2001     

Solid-liquid phase relations of some normal long-chain fatty acids in N,N-dimethylacetamide and N,N-dimethylformamide

Solubility data are reported for capric, lauric, myristic, palmitic, stearic, and arachidic acids in N,N-dimethylacetamide (DMA) and N,N-dimethylformamide (DMF). Complete binary freezing-point diagrams were constructed for the capric, myristic, and stearic acid systems. A solid, incongruently melting 1:1 molecular compound formed in all except the stearic acid-DMF system. Calculated solubility data for lauric, palmitic, and arachidic acids in both solvents were in good agreement with experimental determinations on selected compositions.     

Permeation of H2, N2, CH4, C2H6, and C3H8 through asymmetric polyetherimide hollow‐fiber membranes

Permeation properties of pure H₂, N₂, CH₄, C₂H₆, and C₃H₈ through asymmetric polyetherimide (PEI) hollow‐fiber membranes were studied as a function of pressure and temperature. The PEI asymmetric hollow‐fiber membrane was spun from a N‐methyl‐2‐pyrrolidone/ethanol solvent system via a dry‐wet phase‐inversion method, with water as the external coagulant and 50 wt % ethanol in water as the internal coagulant. The prepared asymmetric membrane exhibited sufficiently high selectivity (H₂/N₂ selectivity >50 at 25°C). H₂ permeation through the PEI hollow fiber was dominated by the solution‐diffusion mechanism in the nonporous part. For CH₄ and N₂, the transport mechanism for gas permeation was a combination of Knudsen flow and viscous flow in the porous part and solution diffusion in the nonporous part. In our analysis, operating pressure had little effect on the permeation of H₂, CH₄, and N₂. For C₂H₆ and C₃H₈, however, capillary condensation may have occurred at higher pressures, resulting in an increase in gas permeability. As far as the effect of operating temperature was concerned, H₂ permeability increased greatly with increasing temperature. Meanwhile, a slight permeability increment with increasing temperature was noted for N₂ and CH₄, whereas the permeability of C₂H₆ and C₃H₈ decreased with increasing temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 698–702, 2002     

Impact of recently discovered sodium calcium silicate solutions on the phase diagrams of relevance for glass-ceramics in the Na2O-CaO-SiO2 system

Although phase relations in the Na₂O-CaO-SiO₂ system are vital to melting and thermal treatments in glass and glass-ceramics industries, the available data for thermodynamic modeling are mostly based on reports published in 1920s and 1950s. The present investigation verifies the formation of solid solutions of Na₂CaSiO₄ and Na₂Ca₂Si₂O₇ which have previously assumed to be stoichiometric compounds. The impact of these solid solutions on the features of the phase diagram were investigated using the equilibration-quenching-EDS/EPMA technique. The data were reported as liquidus projections and in isothermal sections within the temperature range of 1000 and 1400 °C. Ten primary phase fields were identified, namely SiO₂, Na₂Ca₃Si₆O₁₆, combeite, Na₄CaSi₃O₉ss, CaSiO₃, Na₂CaSiO₄ss, Na₂Ca₂Si₂O₇ss, Na₂Ca₆Si₄O₁₅, Ca₃Si₂O₇ and Ca₂SiO₄. In addition, some novel liquidus data and invariants points were examined in more detail. The fundamental data obtained can be employed for the thermodynamic reassessment of the Na₂O-CaO-SiO₂ system. The present study also discusses the findings and their impact on melting and annealing processes during the manufacture of glass and glass-ceramics.     

Economic comparison of several membrane configurations for H2/N2 separation

Several one- and two-stage membrane systems were compared for use in separating H₂/N₂ mixtures from coal gasification processes. Computer models of cross flow membrane modules were used in the evaluations. The processing cost, determined by a discounted cash flow analysis of capital and operating expenses, was used as the basis for the comparison. Membrane properties were those of a poly[etherimide] composite membrane. Hydrogen mole fractions from 34% to 97% in the feed and from 80% to 99.9% in the product (permeate) were examined; in all cases it was required that 95% of the feed H₂ be recovered. Four configurations were evaluated: single module (SM), single module with recycle (SMR), two-module series (SER), and two-stage cascade (CAS). The results showed that for conditions where SM was capable of performing the separation the optimum recycle rate in SMR was zero, and thus SMR and SM were identical. In some conditions, SER also reduced to SM. In general, SM is best for easy separations (where the feed and product compositions are similar), CAS is best for difficult separations (where feed and product compositions are very different), and SER is best for separations of moderate difficulty; in this example, where the H₂ recovery is fixed, SMR is never the best configuration. In some circumstances, it is economically better to treat only a portion of the feed in the membrane system, but to a higher purity than is required, and then to mix the overconcentrated stream with the untreated feed to make a product stream of the desired purity.     

Characterization of N,N-dimethylacrylamide/2-methoxyethylacrylate copolymers and phase behaviour of their thermotropic aqueous solutions

Dimethylacrylamide (DMA) has been copolymerized with 2-methoxyethylacrylate (MOEA) and solutions of the products were analysed by FTIR to yield derived reactivity ratios r_DMA = 1.11 ± 0.13 and r_MOEA = 0.63 + 0.10. The measured glass transition temperatures T_g of PDMA and PMOEA were 395 K, and 242 K, respectively. These and the values of T_g for the copolymers accorded well with the Fox relationship. Cloud point curves for copolymers in water were established over a wide range of concentration, solubility decreasing with increase in temperature. For these reversibly thermotropic solutions, the lower critical solution temperature (LCST) increased from 9°C to 80°C with decrease in content of MOEA in the copolymer from 91.1 mol% to 38.6 mol%.     

Characteristics of PVdF-HFP/TiO2 composite membrane electrolytes prepared by phase inversion and conventional casting methods

Porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP)-based polymer membranes filled with various contents of titania (TiO₂) nanocrystalline particles are prepared by phase inversion technique and, along with conventional casting method for comparison. N-methyl-2-pyrrolidone (NMP) as a solvent is used to dissolve the polymer and to make the slurry with TiO₂. Cast film is obtained by spreading the slurry and evaporating NMP in a dry oven, while phase inversion membrane by promptly immersing the spread slurry into flowing water as a non-solvent. Physical and electrochemical characterizations, such as morphology, thermal and crystalline behavior, and other transport properties of lithium ionic species, are carried out for the polymer films/membranes and the polymer electrolytes with absorbing an electrolyte solution. Phase inversion polymer electrolytes are proved to show superior behaviors in electrochemical properties, such as ionic conductivity, electrochemical and interfacial stability, than cast film electrolytes. This is greatly owed to highly porous structure of phase inversion membranes. Even including the feature of interfacial resistance with lithium electrode, phase inversion polymer electrolytes of PVdF-HFP/(5-20 wt.% TiO₂) can be optimized as the adequate ones in applying to the electrolyte medium of lithium rechargeable batteries.     

纤维素浆粕和Lyocell纤维在LiCl/DMAc中溶解差异的研究

为了研究Lyocell工艺中纤维素相对分子质量分布的变化,分析了纤维素浆粕和相应的由浆粕生产出的Lyocell纤维在LiCl/DMAc中的溶解情况,发现两者存在很大差异,分别从纤维素的晶型、取向和形态结构等方面分析原因。结果表明:由于Lyocell纤维(纤维素II)比纤维素浆粕(纤维素I)在热力学上更稳定,分子间的氢键更多,且Lyocell纤维的取向较纤维素浆粕高,纤维结构较致密,使得溶剂的渗透和氢键的破坏更加困难,因此Lyocell纤维在LiCl/DMAc中的溶解比纤维素浆粕差。     

PI/NMP/H_2O三元体系相行为与纤维成形研究

介绍了湿法纺丝中凝固剂/溶剂/聚合物三元体系热力学理论及三元相图双节线和旋节线的计算方法;在聚酰亚胺/N-甲基-2-吡咯烷酮/水(PI/NMP/H2O)三元体系中,采用黏度法计算了PI-NMP相互作用参数(χ23),平衡溶胀法测得PI-H2O相互作用参数(χ13),结合NMP-H2O相互作用参数,并根据FloryHuggins溶液理论绘制出不同温度下PI/NMP/H2O三元体系的理论相图,并研究了不同凝固浴温度下PI纤维纺制中的相分离及成形过程。结果表明:在25,40,60℃时,χ23分别为0.489 6,0.480 1,0.473 4,χ13分别为1.52,1.47,1.30;随着凝固浴温度升高至60℃时,纤维表面逐渐变得致密光滑,断面形态由肾形变为规则的圆形;凝固浴温度升高时,相图中亚稳态区域扩大,纤维成形过程更加缓和,有利于制备结构致密的PI纤维。     

Using dispersion/flocculation phase diagrams to visualize interactions of associative polymers, latexes, and surfactants

The colloidal interactions of associative polymers and latexes in the presence of surfactant are complex. This is because, in addition to good particle dispersion, both brid-ging and depletion flocculation can occur. Therefore, we have developed phase diagrams to help visualize these interactions. The various phases have a significant effect on coatings and applications properties. Examples of phase diagrams are presented for a model HEUR nonionic associative polymer and latexes in the presence of sodium dodecylsulfate. The major variables affecting phase behavior were found to be associative polymer concentration, latex particle size, latex surface hydrophobicity, and electrolyte, cosolvent, and surfactant concentrations. Presented at the PMSE Waterborne Coatings Symposium at the ACS Meeting, August 26–30, 2001, in Chicago IL. P.O. Box 904, Spring House, PA 19477-0904, E-mail: ekostansek@rohmhaas.com.     

Dispersion and vulcanization characteristics of nitrile rubber reinforced with N,N-dimethylacetamide/lithium chloride treated silica

N,N-Dimethylacetamide/lithium chloride (DMAc/LiCl) treated silica is used as a reinforcing filler in nitrile rubber (NBR). Effect of the treatment on aggregate morphology and dispersion of silica in the matrix is investigated using XPS, SEM, and AFM. Binding energy levels of O1s and Si2p electrons in DMAc/LiCl treated silica have shifted significantly from 532.49 to 530.98 eV and 103.19 to 101.33 eV respectively. SEM observations have revealed a reduction in the agglomerate size of silica-a desirable feature for realizing better processing properties of silica filled rubber compounds. Data from AFM observations have also shown better dispersion of DMAc/LiCl treated silica. Mooney viscosity of masterbatches, measured at 100°C over a period of 7 days, has not exhibited any storage hardening which is an indication of easier processability. At 125°C, Mooney data exhibited a reduction in scorch time as a function of DMAc/LiCl concentration. However, MDR data at 160°C have not shown much changes in the scorch time while NBR with high nitrile content exhibited longer cure times. Higher crosslink density of vulcanizates indicate that DMAc/LiCl treatment of silica could effectively reduce filler-filler interactions and networking in silica filled rubber compounds thereby enabling mixing and processing operations energy efficient.     

Processing of biomorphic Si3N4 ceramics by CVI-R technique with SiCl4/H2/N2 system

Biomorphic porous silicon nitride Si₃N₄ ceramics have been produced by chemical vapor infiltration (CVI) of carbonized paper preforms with silicon, followed by gas–solid chemical reaction (R) of nitrogen with the infiltrated silicon. The paper was first carbonized in inert atmosphere to obtain a biocarbon (C_b) template. In a second step, silicon tetrachloride in excess of hydrogen was used to infiltrate silicon into the pores of the C_b template and to deposit silicon onto the C_b fibers. Finally, a gas–solid chemical reaction between nitrogen and infiltrated silicon in a temperature range of 1300–1450 °C took place in N₂ or N₂/H₂ atmosphere to form reaction bonded silicon nitride (RBSN) ceramics. After nitridation, the samples consist mainly of α-Si₃N₄ phase for thermal treatment below the melting point of silicon (1410 °C) or of β-Si₃N₄ phase and β-Si₃N₄/SiC-mixed ceramics for treatment at temperatures above.The crystalline phases α- and β-Si₃N₄ were identified by X-ray diffraction (XRD) analysis and the microstructure of these samples was investigated by scanning electron microscopy (SEM). Energy-dispersive X-ray analysis (EDX) was used to detect the presence of silicon, nitrogen, carbon and oxygen, whereas Raman spectroscopy was applied to identify the presence of Si and SiC. Using thermal gravimetric analysis (TGA), residual carbon was determined. It was found, that addition of 10% H₂ to the nitridation gas at temperatures near the melting point of silicon allows to increase the conversion of Si as well as to control the exothermic nitridation reaction obtaining the preferable needle-like microstructure.     

Hydrogen separation from the H2/N2 mixture by using a single and multi-stage inorganic membrane

The separation characteristics of hydrogen from a gas mixture were investigated by using a single and two-stage inorganic membrane. Three palladium impregnated membranes were prepared by using the sol-gel, hydrolysis, and soaking-and-vapor deposition (SVD) techniques. A two-stage gas separation system without a recycling stream was constructed to see how much the hydrogen separation factor would be increased. Numerical simulation for the separation system was conducted to predict the separation behavior for the multi-stage separation system and to determine the optimal operating conditions at which the highest separation factor is obtained. Gas separation through each prepared membrane was achieved mainly by Knudsen diffusion. The real separation factor for the H₂/ N₂ mixture was increased with the pressure difference and temperature for a single stage, respectively. For the twostage separation system, there was a maximum point at which the highest separation factor was obtained and the real hydrogen separation factor for H₂/N₂ mixture was increased about 40 % compared with a single stage separation. The numerical simulation for the single and two-stage separation system was in a good agreement with the experimental results. By numerical simulation for the three-stage separation system, which has a recycle stream and three membranes that have the same permeability and hydrogen selectivity near to the Knudsen value, it is clear that the hydrogen separation factors for H₂/N₂ mixture are increased from 1.8 to 3.65 and hydrogen can be concentrated up to about 80 %. The separation factors increased with increasing recycle ratio. Optimal operating conditions exist at which the maximum real separation factor for the gas mixture can be obtained for three-stage gas separation and they can be predicted successfully by numerical simulation.     

纤维素LiCl/DMAc溶液流变性能研究

本文研究了9％LICI／DMAC纤维素溶液的流变性能。在该体系中纤维素溶液是非牛顿流体，属于假塑性流体，具有典型的幂律性。通过幂律方程拟合计算，其稠度系数为60～135，流动特性指数为0.62～0．70。随着浓度增大，稠度系数增大和流动特性指数降低；温度的变化对流动特性指数的影响不大，温度升高，流动特性指数略有减小，而稠度系数相对增大。溶液的粘度随着剪切速率的增大，开始时粘度迅速降低，后趋于稳定，这可能与纤维素分子在溶液中的取向有关。在不同剪切速率下，其流动活化能为23～30kJ．     

纳米氧化铝/环氧树脂/二氨基二苯砜复合体系性能研究

对纳米氧化铝(nano-Al2O3)/环氧树脂(EP)/二氨基二苯砜(DDS)体系的性能进行了研究,考察了nano-Al2O3用量及制备工艺对复合材料力学性能的影响,并通过扫描电镜(SEM)观察了nano-Al2O3/EP/DDS复合材料的断面形貌。结果表明:当w(nano-Al2O3)=5份时,复合材料的力学性能相对最高;经偶联剂和超声波分散处理后制取的nano-Al2O3/EP/DDS复合材料,其力学性能最好,高温剪切强度提高了4.01MPa,弯曲强度提高了7.63MPa,弯曲挠度提高了0.65mm,拉伸强度提高了9.30MPa,断裂伸长率提高了2.04%;SEM分析结果表明,一定量的nano-Al2O3可以明显提高EP的韧性。     

Conversions of fuel-N,volatile-N,and char-N to NO and N2O during combustion of a single coal particle in O2/N2 and O2/H2O at low temperature

Oxy-steam combustion is a promising next-generation combustion technology. Conversions of fuel-N, volatile-N, and char-N to NO and N₂O during combustion of a single coal particle in O₂/N₂ and O₂/H₂O were studied in a tube reactor at low temperature. In O₂/N₂, NO reaches the maximum value in the devolatilization stage and N₂O reaches the maximum value in the char combustion stage. In O₂/H₂O, both NO and N₂O reach the maximum values in the char combustion stage. The total conversion ratios of fuel-N to NO and N₂O in O₂/N₂ are obviously higher than those in O₂/H₂O, due to the reduction of H₂O on NO and N₂O. Temperature changes the trade-off between NO and N₂O. In O₂/N₂ and O₂/H₂O, the conversion ratios of fuel-N, volatile-N, and char-N to NO increase with increasing temperature, and those to N₂O show the opposite trends. The conversion ratios of fuel-N, volatile-N, and char-N to NO reach the maximum values at < O₂ > = 30 vol% in O₂/N₂. In O₂/H₂O, the conversion ratios of fuel-N and char-N to NO reach the maximum values at < O₂ > = 30 vol%, and the conversion ratio of volatile-N to NO shows a slightly increasing trend with increasing oxygen concentration. The conversion ratios of fuel-N, volatile-N, and char-N to N₂O decrease with increasing oxygen concentration in both atmospheres. A higher coal rank has higher conversion ratios of fuel-N to NO and N₂O. Anthracite coal exhibits the highest conversion ratios of fuel-N, volatile-N, and char-N to NO and N₂O in both atmospheres. This work is to develop efficient ways to understand and control NO and N₂O emissions for a clean and sustainable atmosphere.