Preparation Of Hollow Fiber Membranes Research Articles

Regulation of the microstructure for hollow fiber ultrafiltration membrane with “flocculation” effect and study on the mechanism of “adsorption flocculation-loose cake layer protection” against humic acid fouling

In this study, three types of hollow fiber ultrafiltration membranes with different hydrophilicity and flocculation capacity were fabricated by grafting polyethyleneimine (PEI), chitosan (CTS) and ε-polylysine (ε-PL) onto the membrane surface. The flocculation effects of the grafted chains on the adsorption of humic acid (HA) and the microstructure of the formed cake layer were investigated. The influences of the microstructure for the cake layer on the anti-fouling performance of the membrane were discussed. The results showed that the long grafted PEI-g-ε-PL chains could flocculate the contaminants to form loose contaminant flocs and in turn form cake layer. The low packing density (0.18 g·cm−3) of cake layer and specific cake resistance (1.81 %) enhanced the anti-fouling properties against HA (flux recovery rate (FRR) = 95.46 %) by delaying the formation of tight buildup contaminants on the membrane surface and maintaining long-term operational stability (The flux maintained around 83.23 % after 6 h of filtration). By analyzing the morphology variations of the cake layer and the size of HA agglomerates before and after membrane filtration, the anti-fouling mechanism of “adsorption flocculation-loose cake layer protection” was proposed. This work presents the application of flocculation mechanisms in enhancing the anti-fouling and provides a new strategy for the preparation of hollow fiber membranes with high anti-fouling for HA solution.

Preparation of Thermosensitive Lignocellulose Hollow Fiber Membrane Grafted With PNIPAAm and Its Application as a Cell Culture Carrier in a RSOC Dynamic Culture.

Currently, the cells, which are urgently required for large-scale application in biomedical-related fields, harvested by traditional trypsin digestion are usually subject to repeated digestion, leading to a reduction of cell activity. In this study, poly (N-isopropylacrylamide) (PNIPAAm) was grafted onto the lignocellulose hollow fiber membranes (HFMs) with cerium ammonium nitrate (CAN) as the initiator to prepare thermosensitive HFMs, which was combined with a rotation system of culture (RSOC) to achieve dynamic culture and non-destructive harvesting of cells from the HFMs. The results of ATR-FTIR, elemental analysis, and SEM confirmed the successful preparation of PNIPAAm-grafted-HFMs, which also showed good biocompatibility to apply for cell culture carriers. In cooling detachment, the HFMs-0.01 group could completely detach the cells within 1h with a cell separation efficiency of more than 90%. The laminin (LN) and fibronectin (FN) harvested by cooling detachment of P8 generation PC12 cells reached 0.0531±0.0032 and 2.5045±0.0001pg/cell, respectively, which were significantly higher than that by trypsin digestion. In addition, the cells on the thermosensitive HFMs proliferated fastest in RSOC at 30rpm with higher glucose consumption and lactate metabolism than in static conditions. Moreover, the cells that had dynamic detachment at 20rpm had the highest cell density and activity. Therefore, the thermosensitive HFMs could be applied as cell culture carriers in RSOC for cell culturing at 30rpm and harvesting at 20rpm, which would provide considerable potential for large-scale cell culture in vitro.

Effect of Viscosity and Air Gap within the Spinneret on the Morphology and Mechanical Properties of Hollow-Fiber Polymer Membranes for Separation Performance.

Hollow-fiber membranes for nanofiltration were prepared from the blending of Poly (ethylene glycol) (PEG) with Poly (vinyl chloride) (PVC) with different PEG molecular weights (400 and 4000 g/mol) and PVC via a dry/wet spinning process. In the spinning process, the effects of air gap, wind-up speed, dope extrusion rate, and bore extrusion rate were examined. In addition, the different lengths of the center tube, which acted as the inner-side fiber diameter during the preparation of hollow-fiber membranes, were studied. This research was investigated in order to observe the morphological, dielectric, and dynamic mechanical thermal properties to identify a suitable preparation of a hollow-fiber membrane for feasible applications. The morphology of the PVC-580 blended PEG-400 5 weight percent hollow-fiber membrane was seen to have a dense skin on both the inner and outer fiber surface, along with a suitable dope viscosity. Moreover, it offered finger-like substructures that could provide a high applicable feed-stream permeability and selectivity. Finger-like substructures were present on the near inner fiber surface at the controlled center-tube length of 0.3 cm, more so than at the center tube of 1 cm. This was because the solvent and non-solvent in the lumen tube exchanged more quickly than they did in the coagulant bath. The effect of the wind-up speed during the spinning process was significantly influenced by an affordable hollow fiber that can be indicated by the drawing ratio (λ). It was found that the drawing ratio of 3.3 showed a thickness thinner than 2.6 and 2.0, respectively. In summary, a controlled wind-up speed, an acceptable dope viscosity, and-most importantly-an agglomerated time resulted in membrane preparation.

The preparation of electrically-enhanced and hydrophilic CNTs-PVDF composite hollow fiber membranes for fouling resistance

The anaerobic membrane bioreactor has great potentials to treat the wastewater with high organic matter due to the efficient anaerobic digestion process and high biomass retention. However, the existence of membrane fouling significantly increases the maintenance cost, and always requires frequent and complex cleaning process to recover the membrane performance. Thus, it is significant to fabricate a membrane with excellent anti-fouling performance for the application in membrane bioreactors. Herein, we prepared the CNTs-PVDF hollow fiber membrane with fouling resistance via loading the conductive CNTs coating on the surface of commercial PVDF membrane by a simple cross-linking reaction with hydrophilic polyvinyl alcohol and succinic acid. “Dual defense” was constructed by the combination of the hydrophilic surface and conductive CNTs coating, which lifted the anti-fouling performance of this membrane. In the assistance of electrical effect, the permeance of the membrane with −1.2 V bias could be recovered to 95 % of original state by simple hydraulic cleaning, while that of the membrane without bias was only 58 % after filtrating the sludge of 2000 mg/L. Furthermore, this membrane also exhibited the superior stability and fouling resistance in the operation of anaerobic electrochemical membrane bioreactor, which was promising for the advanced water treatment.

Cellulose acetate/nanoclay composite membranes with enhanced mechanical properties and improved permeance in gas separation

AbstractDiethyl ether is a valuable chemical product in petrochemical industry used in different applications. In diethyl ether (DEE) production by the dehydration of ethanol (EtOH), the products from DEE production are commonly mixed with EtOH and the % yield of DEE generally has not exceeded 60%. This contribution describes the preparation and performance of hollow fiber membranes for the separation of gaseous product (DEE) and reactant (EtOH). Cellulose acetate (CA)/nanoclay (NC)‐based hollow fiber composite membranes were prepared using a wet spinning process of CA solution and the addition of hydrophilic NC particles to improve the mechanical properties and permeability. According to the findings, the 20 wt% CA/0.5 wt% NC hollow fiber showed the higher mechanical strength than the 20 wt% CA hollow fiber without NC. Moreover, the 20 wt% CA hollow fiber without NC provided EtOH and DEE permeances of 8.44 × 10−11 and 4.25 × 10−10 mol m−2 s−1 Pa−1, respectively, while the 20 wt% CA/0.5 wt% NC hollow fiber showed higher EtOH and DEE permeances of 6.50 × 10−10 and 8.49 × 10−9 mol m−2 s−1 Pa−1 plausibly because of the higher porosity based on the SEM images. Furthermore, both CA hollow fiber membranes were selective for DEE over EtOH and were more selective with the addition of NC.

Modified poly (4-methyl-1-pentene) membranes by surface segregation for blood oxygenation

Oxygenation membranes in extracorporeal membrane oxygenation (ECMO) with excellent gas permeability, good hemocompatibility and durable resistance to plasma leakage is the key to achieve long-term and efficient blood oxygenation. This study put forward surface segregation strategy in thermally induced phase separation (TIPS) of poly (4-methyl-1-pentene) (PMP) membranes to realize the in-situ surface modification. Heterostructured PMP membranes with hydrophilic hemocompatible surface and hydrophobic body were obtained by migration of hydrophilic segments of the amphiphilic block copolymer Pluronic F127 to the surface in their preparation process. The hydrophilic surface could effectively improve hemocompatibility of membranes through hydration layer effect and steric hindrance effect, also reduce platelet adhesion significantly, and prolong the coagulation time of the four coagulation items within the normal physiological range of human body. When adding 10 wt% F127, the membrane exhibited an optimum CO2 permeance of ∼11461 GPU and O2 permeance of ∼13335 GPU, respectively, and an optimized blood oxygenation performance in vitro with O2 flux of 122.9 ml min−1 m−2 and CO2 flux of 129.2 ml min−1 m−2, and the asymmetric structure ensures resistance to plasma leakage for more than two months, that showed great application potential. Besides, preparation of hollow fiber membranes based on surface segregation was also explored, aiming to realize the enhanced performance and large-scale preparation of PMP oxygenation membranes. The membranes prepared in this work exhibited an outstanding performance when applied in blood oxygenation, showing great application potentials.

Preparation and properties of phosphinic acid-functionalized polyacrylonitrile hollow fiber membrane for heavy metal adsorption.

In this study, phosphorylated polyacrylonitrile hollow fiber membrane was synthesized by reacting aminated polyacrylonitrile hollow fiber membrane with phosphinic acid in a Mannich reaction. The batch single-factor measurements revealed that the phosphorylated polyacrylonitrile (PPAN) membrane had an outstanding ability for Hg2+ adsorption. Thermodynamic investigations indicated that the adsorption process was homogenous, and the theoretical maximum adsorption capacity predicted by the Langmuir model was 371.75mg·g-1. The PPAN membrane was able to successfully chelate Hg2+ ions and attain saturation in 4h, demonstrating that the reaction was chemically controlled by the adsorption kinetics. Based on the FT-IR and XPS spectral characterization data, successful phosphinic acid group grafting was proven, and a plausible mechanism for Hg2+ adsorption by PPAN membranes was presented. Furthermore, the five adsorption-desorption cycle experiments revealed that PPAN hollow fiber membranes had outstanding reusability, indicating a possible use for removing heavy metal ions from wastewater.

A new superhydrophobic polypropylene hollow fiber membrane preparation method and its application in the treatment of brine with high salt concentration

A simple and effective strategy combining etching, electrostatic adsorption, and dip-coating methods was developed in this paper to prepare uniform and stable superhydrophobic surfaces on polypropylene hollow fiber membranes (PPHFM) for desalination of highly concentrated salt solutions (3.5 wt% − 15 wt%). A number of appropriate evaluation methods were used to characterize the membrane, and the results confirmed that the composite membrane was successfully modified. Compared with PPHFM, the water contact angle (WCA) was increased from 119° to 165°; the surface roughness was increased from 0.198 µm to 0.961 µm; the mean pore size was increased from 0.16 µm to 0.24 µm; the porosity was increased from 53% to 70%. The PPHFM and composite membranes were applied to a long-term (80 h) vacuum membrane distillation (VMD) with a salt concentration of 15 wt%. The average permeates flux of the composite membrane increased from 4.27 kg (m2 h)−1 to 12.33 kg (m2 h)−1 compared to the PPHFM, while the composite membrane had superior resistance to wetting and stability.

Green preparation of PVDF hollow fiber membranes with multiple pore structure via melt spinning method for oil/water separation

Poly(vinylidene fluoride) (PVDF) is one of the most widely used membrane forming polymers with good processability, outstanding mechanical properties, excellent thermal and chemical stability. In this work, PVDF hollow fiber membranes were prepared through the melt spinning method with CaCl2 and PEG as the composite pore forming agents. The influence of different contents of CaCl2 and PEG on the membrane’s structure and properties were studied based on the pore size distribution, porosity, permeation flux, and oil/water separation test etc. There was no obvious dense layer on the PVDF hollow fiber membrane surface, which exhibited multiple pore structure. With the increase of PEG contents, the pore size, the porosity and oil flux improved effectively, correspondingly, the water contact angle and liquid entry pressure decreased. The permeation fluxes of kerosene also increased obviously with the increase of PEG contents, and the maximum flux of M-3 reached as high as 398.4 L·m-2·h-1. Applied to oil/water separation test, M-3 exhibited good oil/water separation performance, and its separation efficiency for water-in-kerosene emulsion can still reach more than 95 % after ten cycles. In particular, there were not any solvents and diluents used in the preparation process, which was a relatively green preparation process.

Robust preparation of braid-reinforced hollow fiber membrane covered by PVDF nanofibers and PVDF/SiO2 micro/nanospheres for highly efficient emulsion separation

The PVDF nanofibers and the PVDF/silica (SiO2) micro/nanospheres were deposited simultaneously on the outer surface of a rotating PVDF braided tube by electrospinning and electrospraying to fabricate a new type of enhanced hollow fiber membrane. By adjusting the content of SiO2 in electrospraying solution, the micro/nanospheres with different morphology were obtained to optimize the performance of the prepared membranes. When 2 wt% SiO2 was added, the deposited micro/nanospheres mainly took loose porous PVDF aggregates as the skeleton and SiO2 particles as the filler to construct the micro/nano structure on the membrane surface like that on the lotus leaf surface. Therefore, the membrane surface exhibited superoleophilicity (θo = 0°) and underoil superhydrophobicity (θuow = 154°). In addition, the deposited micro/nanospheres can effectively weakened the stacking between the deposited nanofibers. The resultant membrane not only had the high permeability with pure oil flux of 8557 L·m−2·h−1, but also possessed the excellent oil-water separation performance with separation efficiency of 99.70%. Meanwhile, it also showed the outstanding tensile strength of 79.40 MPa. The preparation method was simple and easy to operate, which would provide more possibilities for the preparation of hollow fiber membranes with efficient separation performance to the water-in-oil emulsion.

Studying and Analyzing Operating Conditions of Hollow Fiber Membrane Preparation Process

Polymeric hollow fiber membrane is produced by a physical process called wet or dry/wet phase inversion; a technique includes many steps and depends on different factors (starting from selecting materials, end with post-treatment of hollow fiber membrane locally manufactured). This review highlights the most significant factors that affect and control the characterization and structure of ultrafiltration hollow fiber membranes used in different applications. Three different types of polymers (polysulfone PSF, polyethersulfone PES or polyvinyl chloride PVC) were considered to study morphology change and structure of hollow fiber membranes in this review. These hollow fiber membranes were manufactured with different process conditions and a reasonable starting point for factors remained constant to study the changing effect of specific factors.

Robust preparation and reinforcement mechanism study of PVDF hollow fiber membrane with homogeneous fibers

The homogeneous fiber-reinforced PVDF hollow fiber membrane was prepared successfully through dry-wet spinning process based on nonsolvent induced phase separation (NIPS) method. The three homogeneous fibers were evenly distributed in the separation layer (membrane matrix), and parallel to the axis of the membrane. The reinforcement mechanism was studied based on the change of structure and tensile properties of fibers before and after dry-wet spinning. The mechanical properties of the membrane reinforced by homogeneous fibers were improved significantly, which could meet the long-term use. Its breaking strength could reach 8.3 MPa, which was four times bigger than that of membrane without fiber reinforcement. And its pullout force could reach 4.48 N, which was sixteen times greater than that of polyester fiber-reinforced membrane. Meanwhile, its separation properties can still reach the level of the membrane without fiber reinforcement. In particular, the membranes properties could be adjusted by using the homogeneous fibers with different structures.

Preparation of defect-free hollow fiber membranes derived from PMDA-ODA polyimide for gas separation

Since PMDA-ODA polyimide is insoluble, its soluble precursor PMDA-ODA poly (amic acid) (PAA) is used to prepare hollow fiber membranes (HFMs). Due to the existence of –CO–NH– and –COOH groups, PAA is subject to form hydrogen bonds with water and consequently leads to a very slow phase inversion rate during the non-solvent induced phase inversion process. Therefore, the hollow fiber spinning has to be carried out with a low take-up speed that limits the productivity. In this paper, we increased the take-up speed of PAA hollow fiber to 60 m/min by simply adding LiCl into polymer dope. Moreover, an integrally skinned defect-free PMDA-ODA hollow fiber membrane was obtained at the high take-up speed where the gas permeances were 6.8 ± 0.7, 2.2 ± 0.2, 0.4 ± 0.04 and 0.07 ± 0.01 GPU for H2, CO2, O2 and N2, respectively, with an ideal selectivity of 3.1 ± 0.3, 31 ± 3.0 and 5.7 ± 0.6 for H2/CO2, CO2/N2 and O2/N2, respectively. These results indicated a dense PMDA-ODA layer of 1 μm. To our best knowledge, this is the first time that a defect-free hollow fiber membrane for gas separation is prepared based on PMDA-ODA.

Preparation and assessment of polyvinylidene fluoride hollow fiber membrane for desalination by membrane distillation

Preparation and assessment of polyvinylidene fluoride hollow fiber membrane for desalination by membrane distillation

Preparation of Hollow Fiber Membranes Based On Poly(4-methyl-1-pentene) for Gas Separation

New hollow fiber gas separation membranes with a non-porous selective layer based on poly(4-methyl-1-pentene) (PMP) granules have been obtained using the solution-free melt spinning process. The influence of the preparation conditions on the geometry of the obtained samples was studied. It was found that a spin head temperature of 280 °C and a specific mass throughput of 103 g mm−2 h−1 are optimal to obtain defect-free, thin-walled hollow fibers in a stable melt spinning process, using the given spinneret geometry and a winding speed of 25 m/min. The gas permeability and separation properties of new fibers were studied using CO2/N2 and CO2/CH4 mixtures, and it was found that the level of gas selectivity characteristic of homogeneous polymer films can be achieved. The features of the gas mixture components permeability below and above the PMP glass transition temperature have been experimentally studied in the range of CO2 concentrations from 10 to 90% vol. The temperature dependences of the permeability of the CO2/CH4/N2 mixture through the obtained HF based on PMP have been investigated, and the values of the apparent activation energies of the permeability have been calculated, which make it possible to predict the properties of membrane modules based on the obtained membranes in a wide temperature range.

Polyether-block-amide thin-film composite hollow fiber membranes for the recovery of butanol from ABE process by pervaporation

• PEBA thin-film composite hollow fiber were fabricated by coating. • Pervaporation tests were carried out with membranes of different active layer thicknesses. • Good performance of membranes for recovery of butanol from ABE mixtures. • Membrane support has a relevant contribution to mass transfer resistance. This work reports the continuation of previous efforts to recover butanol from the ABE (acetone-butanol-ethanol) fermentation process by pervaporation (PV). A key aspect to improve the efficiency of the technology is the membrane used to perform the selective butanol separation; hence, this study focuses on the implementation of hollow fiber (HF) membrane configuration for the ABE separation by PV as opposed to flat sheet membrane configuration. The HF membrane preparation was done by dip coating, a frequently used process for the production of HF membranes, which involves the deposition of a thin film of a coating solution. Different thicknesses of the active layer were obtained by modifying the polymer content in the coating solution, allowing later to evaluate the influence of the thickness on the separation performance. This study includes a description of the procedure to prepare selective membranes, its characterization and an analysis of the influence of operating conditions on membrane separation performance. SEM and water contact angle were used to characterize the produced membranes. The mass transport phenomena in the pervaporation process were characterized using a resistances-in-series model. The results allow to adopt a criterion to select the most suitable thickness for the membrane active layer, which allows to achieve an adequate separation performance, and reveal the importance in the choice of the membrane support material. Finally, a comparative analysis of the self-made hollow fiber membranes performance in terms of flux, separation factor and PSI with respect to those found in the literature is presented.

Preparation of Hollow Fiber Membrane Containing ZnO Nanoparticles to Remove Natural Organic Matter

Polyethersulfone/zinc oxide mixed matrix hollow fiber membrane was fabricated using dry/wet phase inversion method. Zinc oxide nanoparticles (2 wt.%) were dispersed in N,N-dimethylacetamide (DMAc) solvent in the present of polyvinylepyrrolidene. The dope solution speed and take up speed was similar with performing the spinning process at room temperature. The produced membranes were characterized using scanning electron microscope (SEM), atomic force microscope (AFM), and Fourier transform infrared (FTIR) analysis. Membrane performance was evaluated using pure water flux (PWF), relative flux ration (RFR), and total organic carbon (TOC) removal efficiency. From SEM analysis, it was found that the nanoparticles were well dispersed in the polymeric matrix. From AFM results, it was observed that the modified membrane has higher surface roughness. The PWF of the modified membrane was enhanced, while the RFR showed to increase due to rougher membrane surface. The NOM remaoval of PES/ZnO membrane was higher than that of PES membrane and reached to 27% compared to only 16.9 % for pristine PES.

The hydrophilic polypropylene/poly(ethylene-co-vinyl alcohol) hollow fiber membrane with bimodal microporous structure prepared by melt-spinning and stretching

Green and sustainable preparation of high-performance polymeric hollow fiber membranes will be more competitive in the context of advocating green manufacturing. Herein, hydrophilic polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes (PMEVOH-HFMs) with PP grafted maleic anhydride (PP-g-MAH) as compatibilizer were prepared by melt-spinning and stretching. Due to the bimodal microporous structure of PMEVOH-HFMs, compared with PPHFM, the porosity (>80%) and pure water flux (>300% L/(m2·h)) of PMEVOH-HFMs were significantly improved, and PMEVOH-HFMs exhibted good rejection performance (>99.5%). The regulation of bimodal microporous structure was correlated with crystallization behavior of PMEVOH blends. EVOH played an important role in heterogeneous nucleation for PP phase, which could increase nucleation density of PP phase and reduce the PP spherulite size. The pore sizes of small micropores in bimodal microporous structure of PMEVOH-HFMs were lower than PPHFM, and was similar to the variation tendency of lamellae in PMEVOH hollow fibers. The pore sizes of large micropores in bimodal microporous structure was increased due to the deterioration of system compatibility. Moreover, the rejection model and antifouling model of PMEVOH-HFMs were also established in order to better understand the characteristics of bimodal microporous structure. This work provided a new idea for green and controllable fabrication of high-performance polymeric hollow fiber membranes.

Preparation and vacuum membrane distillation performance of a superhydrophobic polypropylene hollow fiber membrane modified via ATRP

Superhydrophobic polypropylene hollow fiber membranes were fabricated using single- and multi-step atom transfer radical polymerization methods. The degree of grafting was improved by intermittently adding equal doses of monomers. Membrane morphology and anti-wetting properties of the membranes produced using the two methods were thoroughly investigated to understand the influence of structure on vacuum membrane distillation (VMD) performance. Initial monomer dosages of 20% and 30% facilitated the production of superhydrophobic modified membranes with water contact angles of 167.9° and 179.0°, respectively. The samples with the highest liquid entry pressure were produced using an initial monomer dosage of 20%, and were selected for the VMD experiments. Testing was conducted for 21 h and indicated that the modification method significantly affected VMD performance. This was attributed to the prominent differences in morphology and pore distribution. The average flux of the membrane produced with 20% monomer using the single-step method was 11.01 kg/m2h, which was 4.53 kg/m2h higher than that of the unmodified membrane; the long-term stability was superior. Although the membrane produced using the multi-step method exhibited an excellent average flux of 12.71 kg/m2h, the performance was highly unstable, and flux suddenly dropped after 6 h. Furthermore, the rejection performance was unsatisfactory. Overall, the two new membranes showed pronounced distinctions in VMD performances, which agrees well with our hypotheses.

Hollow-fiber membranes of block copolymers by melt spinning and selective swelling

Selective swelling of block copolymers has emerged as an efficient strategy to prepare ultrafiltration membranes with well-defined porosities. However, the application of this strategy is only limited to the preparation of flat-sheet membranes so far. Herein, we extend this selective swelling strategy, for the first time, to the preparation of hollow-fiber membranes (HFMs). A mechanically strong copolymer available at large scale, polysulfone-block-poly(ethylene glycol) (PSF-b-PEG), is employed as the membrane-forming polymer. The PSF-b-PEG melt without any diluters or additives exhibits good fluidity, enabling stable and continuous melt spinning of primary hollow fibers with dense fiber walls. Subsequent selective swelling in the mixture of n-propyl alcohol and acetone produces interconnected nanoporosities throughout the fiber walls, thus forming HFMs with PEG chains enriched on the membrane surface. The wall thicknesses as well as pore sizes, and thus the separation performances of the HFMs are tunable by changing the spinning and swelling parameters. In contrast to the strong hydrophobicity of HFMs prepared by cold stretching of polyolfins, our HFMs possess water-wettable surfaces due to the presence of PEG chains, and can be directly used in aqueous milieu. Because of the PSF-based skeleton and homogenous distribution of nanopores, the HFMs exhibit excellent tensile strengths up to 12.5 MPa, much higher than that of HFMs prepared by the commonly used phase inversion processes. Furthermore, the BSA rejection and water permeance of the HFMs currently can be tuned in the range of 29.9–88.2% and 13.7–119.3 L m-2·h-1·bar-1, respectively, by changing the spinning and/or swelling parameters. Their performances are expected to enhance by optimizing the hollow fiber geometries and pore structures. This strategy neither uses any solvents to fluidize the polymer nor produces wastewater, and therefore is a “cleaner” process. This work not only extends the usages of selective swelling, but also establishes a new process to manufacture HFMs.