湿纺工艺纺制PAN中空纤维成形机理研究

利用C型喷丝板进行挤出凝固,采用湿法纺丝工艺制备聚丙烯腈(PAN)中空纤维,从PAN/二甲基亚砜(DMSO)纺丝原液的流变性能和凝固过程的相分离两个方面探讨了PAN中空纤维的成形机理。结果表明:纺丝液随剪切速率(γ)的增加逐渐发生由粘性向弹性的转变是挤出胀大的主要原因,其粘弹转变点随着温度的升高而向高γ移动,在60℃下的纺丝液弧片接触成孔的理论临界γ为212 s~(-1);纺丝液在凝固浴中表层成膜是PAN-DMSO-H_2O三元体系相分离的结果,纺丝液细流表面成膜速度是影响孔结构闭合的重要因素,可以通过凝固浴浓度和凝固浴调节剂来控制。     

Thermodynamic study of a water–dimethylformamide–polyacrylonitrile ternary system

Experimental cloud‐point data were obtained by cloud‐point titration. The phase diagram for a ternary system of water–dimethylformamide–polyacrylonitrile was determined by numerical calculation on the basis of the extended Flory–Huggins theory and was found to agree well with the cloud‐point data. To construct the theoretical phase diagram, three binary interaction parameters were obtained with different methods. The ternary phase diagram was used to investigate the mechanism of fiber formation. The skin–core structure and fingerlike pores in polyacrylonitrile fiber may be effectively eliminated if the composition of the spinning solution is properly chosen, and consequently, homogeneous polyacrylonitrile fiber with a bicontinuous structure and good mechanical properties can be obtained through the spinning process. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

PEEKWC ultrafiltration hollow‐fiber membranes: Preparation,morphology, and transport properties

A series of hollow‐fiber membranes was produced by the dry–wet spinning method from PEEKWC, a modified poly(ether ether ketone) with good mechanical, thermal, and chemical resistance. The fibers were prepared under different spinning conditions, varying the following spinning parameters: polymer concentration in the spinning solution, height of the air gap, and bore fluid composition. The effect of these parameters on the water permeability, the rejection of macromolecules (using dextrane with an average molecular weight of 68,800 g/mol), and the morphology of the membranes was studied. The results were also correlated to the viscosity of the spinning solution and to the ternary polymer/solvent/nonsolvent phase diagram. The morphology of the cross section and internal and external surfaces of the hollow fibers were analyzed using scanning electron microscopy (SEM). All membranes were shown to have a fingerlike void structure and a skin layer, depending on the spinning conditions, varying from (apparently) dense to porous. Pore size measurements by the bubble‐point method showed maximum pore sizes ranging from 0.3 to 2 μm. Permeability varied from 300 to 1000 L/(h^?1 m^?2 bar) and rejection to the dextrane from 10 to 78%. The viscosity of polymer solutions was in the range of 0.2 to 3.5 Pa s. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 841–853, 2004     

Simultaneously tuning dense skin and porous substrate of asymmetric hollow fiber membranes for efficient purification of aggressive natural gas

Highly permeable, selective, and stable asymmetric membranes are required to replace the traditional separation approaches for natural gas purification with higher energy efficiency and smaller footprints. Herein, we report on the design and engineering of defect-free asymmetric hollow fiber membranes with a thin dense skin and highly porous substrate to effectively deal with aggressive natural gas. A crosslinkable polymer with rigid molecular structure and high molecular weight was synthesized for developing spinning dope with desirable solution properties. Phase separation behavior of the polymer was carefully controlled by systematic formulation of the dope composition and optimizing spinning conditions, thereby realizing simultaneously tuning dense skins and porous substrates of the spun asymmetric hollow fiber membranes. The crosslinked hollow fiber membrane, with well-preserved delicate asymmetric nanostructures, exhibited unprecedentedly high and stable separation performance for long-term processing extremely aggressive CO₂/CH₄ mixtures (with pressure up to 820 psi containing C6⁺ hydrocarbons), thereby showing great potential for practical application of natural gas purification. This work offers a new platform to create hollow fiber membranes with both high permeance and plasticization resistance in natural gas service. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1269–1280, 2019     

Investigation on the effect of spinning conditions on the properties of hollow fiber membrane for hemodialysis application

Polyethersulfone (PES) hollow fiber membranes were fabricated via the dry‐wet phase inversion spinning technique, aiming to produce an asymmetric, micro porous ultrafiltration hollow‐fiber specifically for hemodialysis membrane. The objective of this study is to investigate the effect of spinning conditions on the morphological and permeation properties of the fabricated membrane. Among the parameters that were studied in this work are air gap distance, dope extrusion rate, bore fluid flow rate, and the take‐up speed. The contact angle was measured to determine the hydrophilicity of the fibers. Membrane with sufficient hydrophilicity properties is desired for hemodialysis application to avoid fouling and increase its biocompatibility. The influences of the hollow fiber's morphology (i.e., diameter and wall thickness) on the performance of the membranes were evaluated by pure water flux and BSA rejection. The experimental results showed that the dope extrusion rate to bore fluid flow rate ratio should be maintained at 1:1 ratio to produce a perfectly rounded asymmetric hollow fiber membrane. Moreover, the flux of the hollow fiber spun at higher air gap distance had better flux than the one spun at lower air gap distance. Furthermore, spinning asymmetric hollow fiber membranes at high air gap distance helps to produce a thin and porous skin layer, leading to a better flux but a relatively low percentage of rejection for BSA separation. Findings from this study would serve as primary data which will be a useful guide for fabricating a high performance hemodialysis hollow fiber membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43633.     

Yttria Stabilized Zirconia Hollow Fiber Membranes

Yttria-stabilized zirconia (YSZ) hollow fiber membranes have been developed by a combined phase inversion and sintering method. An organic binder solution (dope) containing suspended YSZ particles is spun to form a hollow fiber precursor, which is then sintered at elevated temperatures. The prepared hollow fibers have the asymmetric structure including the sponge-like structures at center, sandwiched by the long finger-like structures located at the outer and inner walls of the fibers. Experimental results indicate that by controlling the YSZ/polymer weight ratio at 9 or 10 and sintered at a temperature of 1590°C or 1550°C for 10 h, respectively, gas-tight asymmetric YSZ hollow fiber membranes with high mechanical strength can be obtained.     

The effects of spinning temperature on morphologies and properties of polyethersulfone hollow fiber membranes

Polyethersulfone (PES) hollow fiber membranes were prepared by traditional dry‐wet spinning technique. Scanning electronic microscopy (SEM) was used to characterize membrane morphologies, and the membrane properties were evaluated via bubble point measurements and ultrafiltration experiments. The effects of spinning temperature on the morphologies and properties of PES fibers were investigated in detail. At a high spinning temperature, the obtained membrane structure consisting of a thin skin‐layer and loose sponge‐like sublayer endows PES membrane with not only good permeability, but also high solute rejection. Based on the determination of ternary phase diagrams and light transmittance curves, the relationship of membrane morphologies with thermodynamics and precipitation kinetics of membrane‐forming system was discussed. It was concluded that the morphologies and properties of PES hollow fiber membrane could be conveniently tuned by the adjustment of the spinning temperature and air gap. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of diluent on poly(ethylene‐co‐vinyl alcohol) hollow‐fiber membrane formation via thermally induced phase separation

Poly(ethylene‐co‐vinyl alcohol) hollow‐fiber membranes with a 44 mol % ethylene content were prepared by thermally induced phase separation. A mixture of 1,3‐propanediol and glycerol was used as the diluent. The effects of the ratio of 1,3‐propanediol to glycerol in the diluent mixture on the phase diagram, membrane structure, and membrane performance were investigated. As the ratio increased, the cloud point shifted to lower temperatures, and the membrane structure changed from a cellular structure due to liquid–liquid phase separation to a particulate structure due to polymer crystallization. Better pore connectivity was obtained in the hollow‐fiber membrane when the ratio of 1,3‐propanediol to glycerol was 50:50, and the membrane showed about 100 times higher water permeability than the membrane prepared with pure glycerol. For the prepared hollow‐fiber membrane, the solute 20 nm in diameter was almost rejected. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 219–225, 2005     

聚砜中空纤维超滤膜制备条件的考察

考察了膜液温度，内外凝胶温度和膜液出喷丝头的剪切速度对聚砜中空纤维超滤膜性能的影响。结果表明，保持其它条件一定时，膜液温度升高或凝胶温度降低时，最终膜孔径变小，并用制膜体系三元相图进行了分析，当膜液出喷丝头的剪切速度达到某一极限值时（不同膜液体系，此极限值不同），获得了压密性能优良的聚砜中空纤维超滤膜。     

Hollow Fiber Ultrafiltration Membranes from Poly(Vinyl Chloride): Preparation,Morphologies, and Properties

Hollow fiber poly(vinyl chloride) membranes were prepared by using the dry/wet spinning method. Cross-section, internal, and external surfaces of the hollow fibers structure were studied by SEM. The pore size and pore size distribution of the hollow fibers were measured by a PMI capillary flow porometer. UF experiments of pure water and aqueous solution of PVP K-90 were carried out. The effect of the PVC concentration on the hollow fibers mechanical properties was also investigated. It was found that the PVC fibers cross-sectional structure was affected by the polymer concentration in the dope solution. In particular, reduction of macrovoids size was observed when increasing PVC concentration from 15 to 19 wt%. The pore size distribution of the PVC hollow fibers was controlled by adjusting the PVC concentration. Indeed, an increase of PVC concentration up to 19 wt% leads to fibers with sharp pore size distribution (the 99% of pores is about 0.15 µm).The pure water permeation flux decreased from 162 to 128 (l/m² · h · bar), while the solute separation performance increased from 82 to 97.5%, when increasing the PVC concentration. The elongation at break, the tensile strength, and the Young's modulus of the PVC hollow fibers were improved with PVC concentration in dope solution.     

Preparation of polysulfone hollow fiber affinity membrane modified with mercapto and its recovery properties. I. Synthesis and preparation of hollow fiber matrix membrane

Several kinds of chloromethyl polysulfones (CMPSF) with different chlorinity and reactive groups were synthesized by Friedel‐Crafts reaction, which could be utilized as reactively matrix membrane materials. The CMPSF hollow matrix membranes were prepared with phase inversion by utilization of the CMPSF/additive/DMAC casting solution and CMPSF as membrane materials. The rheological behavior of CMPSF/additives/DMAC spinning casting solution was studied. The experimental results showed that the spinning casting solution was a pseudoplastic fluid, the apparent viscosity of the spinning casting solution decreased with the increase of shearing rate, and the viscous flow activity energy of the spinning casting solution was inclined to unchange at high shearing rate. The effects of composition of spinning casting solution and process parameters of dry–wet spinning on the structure of CMPSF hollow fiber matrix membrane were investigated. The pore size, porosity, and water flux of membrane decreased with the increase of additive content, bore liquid, and dry spinning distance. With the increase of extrusion volume outflow, the external diameter, wall thickness, and porosity of the hollow fiber matrix membrane increased, but the pore size and water flux of the membrane decreased. It was also found that the effects of internal coagulant composition and external coagulant composition on the structure of CMPSF hollow fiber matrix membrane were different. The experimental results showed that thermal drawing could increase the mechanical properties of CMPSF hollow fiber matrix membrane and decrease the pore size, porosity, and water flux of the CMPSF hollow fiber matrix membrane, and the thermal treatment could increase the homogeneity and stability of the structure of the CMPSF hollow fiber matrix membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 758–771, 2006     

Integrally skinned polysulfone hollow fiber membranes for pervaporation

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 μm have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent. © 1994 John Wiley & Sons, Inc.     

Preparation of poly(phthalazinone ether sulfone ketone) hollow fiber membrane for gas separation

Poly(phthalazinone ether sulfone ketone) (PPESK) asymmetric hollow fiber membranes for gas separation were prepared by dry/wet phase inversion technique. The effects of various preparation conditions such as solvent, nonsolvent-additives(NSA), PPESK concentration, and air gap on the membrane performance were studied. The heat resistance of the PPESK hollow fiber membrane was also examined. The hollow fiber membrane prepared from solvent with stronger solubility showed low gas permeation and high O₂/N₂ selectivity due to the denser skin layer. Hollow fiber membrane made from PPESK/DMAc/EtOH/THF system had thicker skin layer than that made from PPESK/DMAc/GBL system with the same ratio of near-to-cloud-point of NSA, which resulted in the higher O₂/N₂ selectivity. Along with the increase of NSA content, the gas permeation increased and the O₂/N₂ selectivity decreased. The O₂/N₂ selectivity of hollow fiber membranes made from PPESK/DMAc/GBL and PPESK/DMAc/EtOH/THF systems were 4.9 and 4.8 respectively, when the membrane forming systems contained appropriate content of NSA. The high polymer concentration resulted in low gas permeation and high O₂/N₂ selectivity. When the air gap was excessively long, the membrane performance dropped because of the damage to the dense skin layer. There was no significant drop on the membrane performance when the operation temperature was elevated to 90°C. The average O₂/N₂ selectivity was higher than 3.0 at 70°C during a long period of 55 days' test time. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Two‐dimensional simulation of hollow fiber membrane fabricated by phase inversion method

In the steady fabricating process, two‐dimensional hollow fiber membrane near the spinneret was numerically simulated using the finite element method (FEM). The unknown positions of free surface and moving interface were calculated simultaneously by the velocity and pressure fields. The effects of seven relevant parameters, i.e., inertia term, gravity term, dope flow rate, bore flow rate, dope viscosity, tensile force, end velocity and non‐Newtonian on the velocity and diameter profile were studied. On the basis of the simulated results, the inertia term in hollow fiber‐spinning process was safely neglected in low speed, while the effect of gravity was not be neglected. Besides, the outer diameter of the fibers increased with an increase of dope flow rate and bore flow rate; Large tensile force or large end velocity could cause large deformation in the air gap; larger viscous dope solution tended to make less deformation in the air gap. It was found that an increase of the dope flow rate at small dope flow rate resulted in an increase of the inner diameter, while at large dope flow rate, it decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2067–2074, 2006     

Effect of the preparation conditions on the morphology and performance of poly(imide) hollow fiber membranes

Poly(imide) (PI) hollow fiber membranes were prepared by using classical phase inversion process. Effects of different external coagulation bath temperatures (ECBT) and various bore flow rates (BFR) on the morphology and separation performance of the membranes were studied. Cross‐section, inner and outer structures were characterized by using scanning electron microscope and atomic force microscopy (AFM). Mean pore size, pore size distribution, and mean roughness of the PI hollow fibers surfaces were estimated by AFM. It was found that the hollow fibers morphology composed of sponge‐like and finger‐like structures with different ECBT and BFR. A circular shape of the nodules with different sizes was observed in the outer surface of the PI hollow fibers. Mean pore size of the outer surface increases with increasing ECBT and BFR. The important result observed in this study is that the ECBT clearly has the largest effect on hollow fiber PI membrane roughness compared with the BFR. Pure water permeability of the PI hollow fibers was improved with increase of ECBT and BFR. The solute rejection (R%) was reduced when the ECBT and BFR was increased. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40428.     

Effect of stretching on continuous oil/water separation performance of polypropylene hollow fiber membrane

In this work, polypropylene (PP) hollow fiber membranes were fabricated by thermal-induced phase separation method. The influence of cold-stretched and hot-stretched treatment on the morphology and permeability of the PP hollow fiber membranes was investigated. The results showed that there were cracks and crystalline particulate structures on the outer and inner surfaces of the stretched PP hollow fiber membranes, which were not isolated but linked together through fiber-like connections. Compared to the original PP hollow fiber membrane, the mean pore sizes, the porosities, the hydrophobicity and water entry pressure of the stretched PP hollow fiber membranes improved significantly. When applied in conjunction with a vacuum system, the PP hollow fiber membranes could continuously remove oils from water surface, and separate surfactant-free and surfactant-stabilized water-in-oil emulsions, as well. The initial kerosene fluxes of the hot-stretched PP hollow fiber membrane were higher than that of the membranes prepared from original PP hollow fibers or cold-stretched PP hollow fibers. The permeate fluxes of the hot-stretched PP hollow fiber membrane for all different emulsion separations were higher than those of the original PP hollow fiber membrane. There could be seen no emulsion droplet in the optical micrographs after separation, indicating that the water-in-oil emulsions were effectively separated in one-step method.     

The effects of air gap length on the internal and external morphology of hollow fiber membranes

A systematic study of the air gap effects on both the internal and the external morphology, permeability and separation performance of polyvinylidene fluoride (PVDF) hollow fiber membranes has been carried out. The hollow fibers were prepared using the dry-jet wet spinning process using a dope solution containing PVDF/ethylene glycol/N, N-dimethylacetamide with a weight ratio of 23/4/73. Ethanol aqueous solution, 50% by volume, was used as internal and external coagulants. The inner and the outer surfaces of the prepared hollow fibers were analyzed by atomic force microscopy (AFM), while their cross-sectional structure was studied by scanning electron microscopy (SEM). Ultrafiltration experiments were conducted using non-ionic solutes of different molecular weights. The results show that both the pore sizes and nodule sizes have a log-normal distribution. The pore size, nodule size and roughness parameters of the inner and outer surfaces of the hollow fibers were affected by the air gap distance. Alignment of nodules to the spinning direction was observed. Experimental results indicate that an increase in air gap distance, from 1 to , results in a hollow fiber with a lower permeation flux and a higher solute separation performance due to the decrease of the pore size. AFM analysis reveals that the air gap introduces an elongational stress because of gravity on the internal or external surfaces of the PVDF hollow fibers. At low air gap distance, the inner surface controls the ultrafiltration performance of the PVDF hollow fiber membranes because of its lower pore size, while at high air gap lengths the inner pore size becomes larger than the outer pore size. The turning point was observed at an air gap distance of .     

Thermodynamic-based predictions of membrane morphology in water/dimethylsulfoxide/polyethersulfone systems

In this paper, ternary phase diagram was used to predict morphology of the membranes prepared via phase inversion process. Theoretical ternary phase diagrams were calculated based on a compressible regular solution (CRS) model for water/dimethylsulfoxide/polyethersulfone membrane forming system. The CRS model is an alternative for the traditional Flory–Huggins theory. The experimental cloud point data were determined using titration method. The constructed theoretical ternary phase diagrams were consistent with the experimental results. The precipitation rate of the polymeric solution in the non-solvent was obtained by light transmission experiments. The membrane morphology was predicted using the theoretical phase diagram and the phase separation kinetics. To verify this prediction, the light scattering experiments were performed.     

Nanometric thin skinned dual‐layer hollow fiber membranes for dehydration of isopropanol

A novel sulfonated polyphenylsulfone (sPPSU)/polyphenylsulfone (PPSU)‐based dual‐layer hollow fiber membrane with a nanometric thin skin layer has been designed for biofuel dehydration via pervaporation. The thickness of skin selective layer is in the range of 15–90 nm under different spinning conditions measured by positron annihilation spectroscopy (PAS) coupled with a mono‐energetic positron beam. The effects of outer‐layer dope properties, coagulation temperature, and dope flow rate during spinning were systematically investigated. By tuning these spinning parameters, a high performance sPPSU/PPSU‐based dual‐layer hollow fiber membrane with desirable morphology was successfully obtained. Particularly owing to its nanometric thin skin layer, a high flux of 3.47 kg/m²h with a separation factor of 156 was achieved for dehydration of an 85 wt % isopropanol aqueous solution at 50°C. After post thermal treatment at 150°C for 2 h, the separation factor was dramatically improved to 687 while flux dropped to 2.30 kg/m²h, which make it comparable to the inorganic membranes. In addition, excellent correlations were found among the results from field emission scanning electron microscopy, PAS spectra, and separation performance. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2943–2956, 2013     

Engineering design of outer‐selective tribore hollow fiber membranes for forward osmosis and oil‐water separation

Outer‐selective thin‐film composite (TFC) hollow fiber membranes offer advantages like less fiber blockage in the feed stream and high packing density for industrial applications. However, outer‐selective TFC hollow fiber membranes are rarely commercially available due to the lack of effective ways to remove residual reactants from fiber's outer surface during interfacial polymerization and form a defect‐free polyamide film. A new simplified method to fabricate outer‐selective TFC membranes on tribore hollow fiber substrates is reported. Mechanically robust tribore hollow fiber substrates containing three circular‐sector channels were first prepared by spinning a P84/ethylene glycol mixed dope solution with delayed demixing at the fiber lumen. The thin wall tribore hollow fibers have a large pure water permeability up to 300 L m^?2 h^?1 bar^?1. Outer‐selective TFC tribore hollow fiber membranes were then fabricated by interfacial polymerization with the aid of vacuum sucking to ensure the TFC layer well‐attached to the substrate. Under forward osmosis studies, the TFC tribore hollow fiber membrane exhibits a good water flux and a small flux difference between active‐to‐draw (i.e., the active layer facing the draw solution) and active‐to‐feed (i.e., the active layer facing the feed solution) modes due to the small internal concentration polarization. A hyperbranched polyglycerol was further grafted on top of the newly developed TFC tribore hollow fiber membranes for oily wastewater treatment. The membrane displays low fouling propensity and can fully recover its water flux after a simple 20‐min water wash at 0.5 bar from its lumen side, which makes the membrane preferentially suitable for oil‐water separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4491–4501, 2015