EFFECT OF POLYVINYLPYRROLIDONE ADDITIVE ON THE PORE SIZE AND THE PORE SIZE DISTRIBUTION OF POLYETHERSULFONE (VICTREX) MEMBRANES

Investigations were made on the effect of the presence of polyvinylpyrrolidone (PVP) additive in the casting solution on the performance of polyethersulfone (PES) ultrafiltration membranes in the range of PVP/PEs weight ratio below 0.5. It was further attempted to investigate the effect of PVP additive on the size of PES polymer in the casting solution and the pore size and the pore size distribution of PES membranes. It was found that the presence of PVP additive decreases both the polymer size and the membrane pore size. Discussions were made on the mechanism of the formation of the pore based on the correlation between the polymer size and the pore size.     

EFFECT OF POLYMER MOLECULAR WEIGHT, SOLVENT AND CASTING SOLUTION COMPOSITION ON THE PORE SIZE AND THE PORE SIZE DISTRIBUTION OF POLYETHERSULFONE (VICTREX) MEMBRANE

The effect of the molecular weight of polyethersulfone (Victrex) polymers, the nature of the solvent and the polymer concentration on the effective hydrodynamic radius of polymer in the membrane casting solution was investigated. The membranes were prepared from the casting solutions studied above and ultrafiltration experiments were performed with polyethylene glycol solutes. The average pore sizes and the pore size distributions on the membrane surfaces were further calculated from the ultrafiltration performance data obtained above. Strong correlations were found between the effective hydrodynamic radius of the polymer in the casting solution and the average pore size on the membrane surface. The mechanism of the pore formation was proposed on the basis of the polymer size—pore size correlation.     

EFFECT OF ISO- AND TERE-PHTHALOYL CONTENT ON THE PORE SIZE AND THE PORE SIZE DISTRIBUTION OF AROMATIC POLYAMIDE RO MEMBRANES

Poly-m-phenylene-iso(x)-co-tere(100-xc)-phthalamide copolymers with different x values were synthesized and viscoelastic properties of the polymer solution were studied in the presence of lithium chloride nonsolvent additive in order to determine the size of the polymer aggregate in the solution. Reverse osmosis membranes were also prepared using the polymers synthesized above. The membrane performance was then tested for the separation of sodium chloride solute and reference organic solutes, in order to obtain the average pore size and the pore size distribution of the membrane. The data for the pore size were further used to calculate the length of the polymer segment in the noncrystalline region. An interesting correlation was found between the above length and the isophythaloyl content, x, of the copolymer.     

Phase Inversion Technique-Based Polyamide Films and Their Applications: A Comprehensive Review

This is a comprehensive review regarding the particulars of phase inversion technique and its significance in polyamide films. Phase inversion is a versatile technique to form thin films of neat polyamide, composite, and blend system. Phase inversion can be induced by polymer solution immersion in nonsolvent, contact with nonsolvent vapor, thermal treatment, solvent evaporation, and quenching. Choice of solvent/nonsolvent system, polyamide, additive, coagulation bath, and film casting conditions are crucial. Only limitation of phase inversion is the requirement of polyamide solubility in suitable solvent. Promising applications of phase inversion polyamide are in fuel cell, gas separation, tissue engineering, and water filtration.     

小孔径PVDF超滤膜的研制

本文主要研究了高通量小孔径ＰＶＤＦ超滤膜。分析了溶剂体系，添加剂种类无机盐含量及第二组分ＰＭＭＡ等对膜性能的影响，实验结果表明，选择合适的溶剂体系和致孔剂，可制得高通量的致密小孔径ＰＶＤＦ超滤膜，同时，在ＰＶＤＦ膜中共混入少量与之相容的ＰＭＭＡ可显著改善该类膜的亲水性，进一步提高膜的水通量。     

Nanofiltration membranes based on PA6/EVOH with variable composition and morphology

Nanofiltration PA6/EVOH membranes were prepared through a nonsolvent induced phase separation technique. The effects of polymer concentration in the solution and solvent evaporation time on the performance and morphology of the resulting membranes were investigated by cloud point titration, permeation, and scanning electron microscopy (SEM). Experimental cloud point data for various prepared membranes suggested that polymer solutions with higher concentrations of PA6/EVOH need a less content of nonsolvent. SEM observations show that an increase in polymer concentration leads to formation of a thin dense layer on the surface of the membrane thanks to pore size reduction. However, dense top layer of membrane becomes thicker as polymer concentration increases from 15 wt% to 20 wt%. The performance of membranes reveals a decrease with polymer concentration in casting solution. By contrast, Polyamide/Poly(ethylene‐co‐vinyl alcohol) membranes show an optimal performance with various formic acid evaporation times. J. VINYL ADDIT. TECHNOL., 25:E28–E34, 2019. © 2018 Society of Plastics Engineers     

Effect of Casting Solution on Morphology and Performance of PVDF Microfiltration Membranes

The effects of preparation‐influencing parameters such as polymer concentration, thickness of casting solution, and type of solvent on morphology and performance of poly(vinylidene difluoride) (PVDF) microfiltration membranes for the treatment of emulsified oily wastewater were investigated. Flat‐sheet membranes were prepared from a casting solution of polymer and additive in various solvents by immersing the prepared films in nonsolvent‐containing mixtures of water and 2‐propanol. The membranes were characterized using scanning electron microscopy. Increasing the polymer concentration and membrane thickness significantly affected the pore size, leading to permeate flux decrease. An attempt was made to correlate the effect of the solvent on membrane morphology and performance employing solubility parameters between solvent and nonsolvent).     

Properties of asymmetric polyimide ultrafiltration membranes. I. Pore size and morphology characterization

Properties of asymmetric UF membranes made by solution casting of aromatic polyimides as a function of fabrication conditions are reported. The characteristic properties investigated include: the overall porosity, hydraulic permeability, the equivalent pore size of the skin layer (via a newly developed general diagram), and morphological features shown by the scanning electron microscope. It was found that as casting solution concentration and/or evaporation period was increased, the average pore size decreased while the skin thickness increased. At low casting solution concentrations the membranes were highly porous and the precipitated polymer phase had a granular structure consisting of aggregates of precipitated polymer micelles. While at high concentrations marcrovoid porosity was reduced but the precipitated polymer phase had a spongy structure. The interstitial openings of the granular skin structure of a membrane made from 15% polymer solution with no evaporation as revealed by SEM showed pore size values that were close to those calculated through pore models.     

合成条件对介孔氧化硅材料孔径尺寸的影响

分别在室温酸性、室温碱性、水热碱性条件下合成了介孔氧化硅材料MCM－41,通过XRD,HRTEM,氮气吸附等手段对介孔氧化硅材料进行了表征,并探讨了3种条件下材料介孔尺寸的变化。结果表明：室温酸性条件下合成的MCM－41材料具有最小的介孔尺寸,碱性条件则有利于合成较大孔径的样品。另外还发现无机盐离子的添加、反应温度的变化及煅烧过程均可以影响介孔尺寸,并提出了无机盐离子通过影响表面活性剂胶团的荷电性质和尺寸而改变材料孔径尺寸的模型。     

PVC/PAN共混超滤膜的研究 Ⅱ.铸膜液组成对膜结构与性能的影响

实验表明,铸膜液浓度、PVC 分子量及其分布主要是通过它们对膜孔大小的影响来影响膜的性能。铸膜液浓度提高,膜孔缩小,截留率提高而透水率下降。这种影响在铸膜液百分浓度低于15%时尤为明显。分子量的均一则有利于膜孔的均一。聚乙二醇因其具有较多的羟基,当被添加到PVC/PAN 共混铸膜液中时,既起交联剂的作用,又起溶胀剂的作用,前者有利三维聚合物网络的形成而提高截留率,后者有利提高开放形孔所占的比例而增大透水率。     

NH_4Cl水溶液在成膜过程中的致孔作用

本文以ＮＨ４Ｃｌ饱和水溶液做添加剂，对ＰＶＤＦ／ＮＭＰ体系在成膜过程中的致孔作用做了研究。铸膜液中随ＮＨ４Ｃｌ水溶液加入量的改变，膜孔径也发生变化，并出现最大值。通过Ｘ－射线衍射扫描发现制膜液中存在无机盐时膜中无定形态结构增加，表明无机盐的加入有助于膜孔形成     

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。     

Effects of Membrane-Making Conditions and Shrinkage Treatment on Morphology and Performance of Cellulose Acetate Butyrate Membranes

Abstract

The functions of additives in cellulose acetate butyrate (CAB) membrane casting solution, effect of thermal shrinkage treatment on porous CAB membranes, and the changes of CAB membrane surface morphology during the solvent evaporation step have been investigated. Additives (glycerol and lactic acid) in CAB membrane casting solution function only as pore number promoting agents when used at low concentration and function both as pore number and pore size promoting agents when used at higher concentrations. Triethyl phosphate in CAB membrane casting solution functions both as a pore number promoting agent and as a secondary solvent for CAB. Three distinct phases can be observed in the solvent evaporation step in making CAB membranes. With the increase in solvent evaporation time, the number of pores in the first pore size distribution increases in the initial small pore-forming phase and decreases in the large pore-forming phase, and the number of pores in the second pore size distribution always increases with solvent evaporation time. These changes in pore numbers, pore sizes, and pore number ratio in two pore size distributions as well as the membrane skin layer thickness together govern the ultimate membrane performance and result in a maximum solute separation which, in the case of CAB/ acetone membranes, falls at 60 seconds of solvent evaporation time. Significant improvement of the performance of a porous CAB membrane can be achieved by thermal shrinkage treatment. Equally high CAB membrane performance can also be achieved by using a lower concentration of additives in the membrane casting solution.     

MULTICOMPONENT ADSORPTION EQUILIBRIUM OF GASES IN ZEOLITE: EFFECT OF PORE SIZE DISTRIBUTION

The effect of pore size distribution of zeolite on the multicomponent adsorption equilibrium is studied. All species compete locally for a given pore and this can be described by the extended multicomponent Langmuir isotherm. The size exclusion effect is taken into account in the competition of different species for a given pore so large molecules have less degree of accessing available pores. The pore size is related to the adsorbate-adsorbent interaction energy by the Lennard-Jones potential. The isotherm parameters extracted from single-component data fitting are used to predict multicomponent adsorption equilibrium. When validated with binary experimental data of CO₂, H₂S and propane in H-mordenite, collected by Talu and Zwiebel (1986), this model provides better results than a previously proposed heterogeneous model based on a uniform energy distribution and a local IAST (Hu and Do, 1995).     

铸膜液结构对PVC/PMMA合金微滤膜性能的影响

通过高分子合金化,以L-S相转化法制备了PVC/PMMA非对称型合金微滤膜,考察了铸膜液结构对微滤膜结构与性能的影响.结果表明:随聚合物浓度、铸膜液温度升高合金膜水通量降低,平均孔径减小;增大PMMA含量,水通量上升,平均孔径增大;随添加剂量的增加,合金膜水通量上升,平均孔径减小.     

Controllable morphology and wettability of polymer microspheres prepared by nonsolvent assisted electrospraying

Polymethylmethacrylate (PMMA) microspheres with various morphologies are fabricated by nonsolvent assisted electrospraying. The morphology evolution is determined by nonsolvent properties including the solubility parameter, surface tension and viscosity, and nonsolvent induced phase separation is the main reason for the formation of the porous and/or hollow structures. It is found that nonsolvent possessing a high surface tension is beneficial to the formation of a hollow structure, while the large phase separation tendency between nonsolvent and the polymer can promote pore generation on the sphere surface. The nanosized pores, especially hierarchical pores, can enhance the hydrophobicity of the substrate surface coated with these microspheres. On the other hand, nonsolvent with a large viscosity could prevent the growth of the phase separated nuclei, leading to the presence of relatively small and discontinuous pores on the microsphere surface, which can finally cause the decrease of the contact angles. The surface pores of the electrosprayed microspheres are even eliminated if polymer additive, i.e., PVP, is incorporated into the polymer-solvent-nonsolvent solution. The addition of PVP renders the microsphere coated surface hydrophilic, which can be completely wetted by water droplets.     

孔隙率和孔径对反应烧结多孔氮化硅陶瓷介电性能的影响

研究添加成孔剂法制备的有球形宏观孔的多孔氮化硅陶瓷在不同孔隙率和孔径下的介电性能.通过控制成孔剂苯甲酸的加入量和调节成孔剂的粒径可达到烧结体的气孔率和孔径可控的目的.结果表明:随着成孔剂量的增加,样品气孔率变大,反应烧结后烧结体中的α-Si3N4相增多,样品的介电常数ε'和介电损耗tanδ降低.在成孔剂加入的质量分数为30%时,随着成孔剂的粒径变大,反应烧结后烧结体中气孔的直径变大而气孔率不变,样品的ε'和tan δ也相应降低.得到的样品中最低的ε'值为2.4297.     

炭化条件对分子筛型活性炭孔结构的影响

以木屑及宁夏太西煤混合物为原料,以木焦油为粘结剂,经压力成型,制备柱状分子筛型活性炭,考察了炭化条件对活性炭孔径分布及其性能的影响。结果表明,炭化温度是影响分子筛型活性炭性能的关键因素,制备的活性炭具有均匀的孔径分布, <0 9nm(9 A)的孔占活性炭总孔容的 80%以上。     

Sorption of poly(vinyl acetate) on cellulose. II. The role of the porous structure

The adsorption of poly(vinyl acetate) from benzene solution onto cellulosic materials having various porous structures was measured in an attempt to investigate the role of the pore size distribution in the sorption process. The variety of cellulose porous structures was obtained by combinations of different swelling agents—water, ethylenediamine, sodium hydroxide solution—with different subsequent drying treatments. The pore structure analysis was based on benzene desorption isotherms. The porosity of cellulose is responsible for selective adsorption of the smaller macromolecules from an unfractionated polymer solution. The amount of sorbed polymer increases when the polymer solution contains a greater fraction of lower molecular weight polymer. Only the pores above a certain size are accessible to the polymer. The amount of polymer sorbed is proportional to the area of such pores but is otherwise independent of the effects produced by swelling pretreatments.