Dry-wet Spinning Process Research Articles

Swelling and dissolution behaviors of cellulose in phosphate-based ionic liquids-H2O binary systems: In-situ observation and molecular dynamics simulation

Swelling and dissolution of cellulose in ionic liquids (ILs) as the pretreatment processes are key steps for the high-value conversion and utilization of cellulose. However, the molar ratio of H2O to ILs has a significant effect on the swelling and dissolution of cellulose, and its molecular-scale mechanism is still unclear, which limits screening out the suitable ILs and recovery of ILs from coagulation bath in the spinning process. Herein, three phosphate-based ILs were chosen to couple with water as solvents for swelling and dissolution of cellulose by combining in-situ observation and molecular dynamics (MD) simulation. The results show that the redissolution time of swollen cellulose is greatly reduced, especially [Emim]DEP-H2O has the best swelling and dissolution performance for cellulose due to its high β value and low viscosity. Meanwhile, when the molar ratio of IL to H2O was more than 1: 1, the IL-H2O system still has the ability to dissolve cellulose. While with the molar ratio further decreased, cellulose was no longer dissolved and began to swell, and the fiber diameter obtained the maximum swelling rate with 40.1% at a molar ratio of 1: 3. Moreover, MD simulation was used to calculate the interaction between IL/water/cellulose, which further illustrated that the combination of IL with water molecular has a significant influence on the behavior of cellulose in IL-H2O systems at the molecular scale. Thus, the potential swelling and dissolution mechanism of cellulose in ILs-H2O binary systems was proposed based on experimental and simulation results. Furthermore, the characterization results of swollen cellulose indicate that the crystal structure and degree of polymerization (DP) were almost unchanged, but the specific surface area and pore size increased significantly, and the thermal stability and heat absorption were decreased, all the results prove that the swelling process increased the accessibility of cellulose and benefited to the subsequent dissolution. Consequently, preferable swelling and dissolving parameters of experiments and simulations will provide a new idea for the selection of suitable ILs and the recovery of ILs from a coagulation bath in the dry-wet spinning process.

A regenerated cellulose fiber with high mechanical properties for temperature-adaptive thermal management

The escalating global population has led to a surge in waste textiles, posing a significant challenge in landfill management worldwide. In this work, ionic liquid 1-butyl-3-methylimidazole acetate ([Bmim]OAc) and DMF (N, n-dimethylformamide) were used as solvents to dissolve waste denim fabric, then vanadium dioxide (VO2) nanoparticles were introduced into the spinning solution, and cellulose fibers were regenerated by dry-wet spinning process, to promote the recycling of waste cotton fabric. Finally, regenerated cellulose fibers with high added value were prepared by dry-wet spinning. Through this innovative strategy, on the one hand, because VO2 can form a large number of hydrogen bonds between the regenerated cellulose molecules, and realize the cross-networking structure of the molecular chains inside the fiber, the mechanical properties of the regenerated cellulose fibers are enhanced. On the other hand, due to the thermal phase transformation characteristics of VO2, it also endows the regenerated cellulose fiber unique intelligent temperature control function. Compared with the pristine regenerated fiber, the tensile stress of the regenerated fiber after adding VO2 nanoparticles (F-VO2) increased by 25.6 %, reaching 158.68 MPa. In addition, the F-VO2 fibric provides excellent intelligent temperature control, reducing temperatures by up to 6.7 °C.

Enhancing thin-film composite polyethersulfone hollow fiber membranes through alkali-induced interfacial polymerization modification for effective separation of monovalent/divalent salts

Amidst the escalating global water scarcity issues, finding better ways to sustainably treat brackish water and seawater while simultaneously recovering resources becomes increasingly important. In this work, we investigated the fabrication strategies to produce polyethersulfone hollow fiber membranes (PES HFMs) with robust characteristics and uniformly arranged shape. The presence of an air gap (AG) in the dry-wet spinning process facilitates the chain orientation due to the gravitational force and elongational stretch and moisture-induced early phase inversion, therefore preventing corrugations on the shell side. We extensively studied the correlation between HFM spinning parameters and the appearance and disappearance of buckling effects. Moreover, it was proven that the addition of N-methyl-2-pyrrolidone (NMP) to the bore fluid composition prolongs the demixing process, overcoming the HFMs' delamination issue. After optimizing the spinning conditions, a facile alkali-induced interfacial polymerization (IP) was employed to enhance the formation of a selective polyamide (PA) layer on PES HFM substrates. The final membrane made by this modification process, denoted as PES-IP-BOH, exhibits a Na2SO4 rejection higher than 96 %, while maintaining low rejections for other monovalent salts. Accordingly, it achieved a high ideal selectivity of >23 for the selective separation of monovalent and divalent salts.

Polymeric hollow fiber (HF) mixed matrix membranes (MMMs): Mutual effect of graphene oxide (GO) and polyvinylpyrrolidone (PVP) on nano-structuration

Hollow fiber (HF) membranes were fabricated using polysulfone (PSF) and 1.0 wt% graphene oxide (GO) synthesized through Hummer's method. The dry-wet spinning process was employed for their preparation. The structure and properties of both unmodified PSF HF membranes and those modified with GO were characterized. This encompassed analyses using scanning electron microscopy, attenuated total reflection Fourier Transform Infrared spectroscopy, thermo-gravimetric analysis, water contact angle (WCA) measurements, as well as evaluations of water permeability and mechanical attributes. The outcomes highlighted favorable mechanical and thermal characteristics. Moreover, the GO-modified PSF HF membranes exhibited larger surface pore sizes, along with an approximate 10% reduction in WCA and a fourfold increase in water permeability compared to the raw PSF HF membranes. Additionally, the influence of varying wt% of the pore-forming agent Polyvinylpyrrolidone (PVP) on the GO-modified PSF HF membranes was investigated. While no evidence suggests that GO can replace PVP, it is plausible to infer that this two-dimensional material complements the pore-forming agent's role by stabilizing the polymer-lean phase. This contributes to the creation of larger pores via phase separation mechanisms.

Sound absorption of woven fabrics produced from braid-reinforced polyvinylidene fluoride hollow fiber membranes

Noise pollution has become one of the four major pollutants in modern society, and the development of acoustical materials with superior noise reduction performance is urgent. In order to develop new and high-performance acoustic materials, braid-reinforced (BR) polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared via the dry–wet spinning process and were used to prepare woven fabrics with different basic textures. The effects of pump flux on the structure and performance of BR PVDF hollow fiber membranes was studied. The results showed that pump flux had an impact on the structural parameters, including the diameter, inner coating layer thickness and porosity, and the fabricated BR PVDF hollow fibers with a porous-resonant composite sound absorption structure had good interface bonding performance. Furthermore, the sound absorption of the woven fabrics was measured by using the impedance tube method in frequency range of 100–6300 Hz. The results demonstrated that plain fabric had a smaller thickness of 2.17 mm and better acoustical properties with a maximum sound absorption coefficient of 0.71. These woven fabrics may potentially be used as ideal materials for controlling noise in fields such as building and transportation.

Investigating the Effects of Nonsolvent Additive and Spinning Conditions on Morphology and Permeation of PAN Hollow Fiber Membranes

In this study, polyacrylonitrile hollow fiber (PAN HF) membranes were designed and fabricated with desired morphology and permeability for low pressure-driven applications via the dry-wet phase-inversion spinning process. The effects of multiple design and fabrication parameters on permeation, morphology, thickness, and pore size of membranes were investigated using various techniques. Moreover, the effects of water as the nonsolvent additive, chemical composition of the bore solution, dope solution flow rate, air gap, coagulation bath temperature, and tensile ratio (take-up speed) were investigated. The addition of 3% wt. water as the nonsolvent additive into the dope solution resulted in a seventeen-times increment in the water flux up to 495 L m-2 h-1 bar-1. It showed a significant improvement in membrane porosity compared with those prepared without water nonsolvent additive. Utilization of 90% wt. of the solvent in water solution as the bore solution instead of pure water showed the most significant effect on the water flux and membrane structure among the fabrication parameters. It resulted in a reduction in threshold permeation pressure by more than ten times. The results revealed that whichever variation, including increased dope solution flow rate or coagulation bath temperature, or reduced air gap or traction, leads to promotion of membrane water flux. Still, different effects on the structure and morphology of the membranes were observed. Based on the outcomes of this study and according to the SEM images, one can conclude that outer surface pore size reduction from about 300 nm resulted in decreased water flux from 448 to 226 L m-2 h-1 bar-1, so that no pores were observed in the outer surface until 50 K magnification of the SEM image. The findings in this study provide instructive guidelines for the design and fabrication of high-performance hydrophilic PAN-based hollow fiber membranes with the desired morphology and water flux. Best ranges of investigated parameters for relatively high permeate water flux and desired membrane morphology were reported.

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.

Modification of porous polyetherimide hollow fiber membrane by dip-coating of Zonyl® BA for membrane distillation of dyeing wastewater.

Wetting and fouling have significantly affected the application of membrane distillation (MD). In this work, a dip-coating method was used for improving surface hydrophobicity of the polyetherimide (PEI) hollow fiber membrane. An air gap membrane distillation (AGMD) process was applied for treatment of the methylene blue (MB) solution. The porous PEI membrane was fabricated by a dry-wet spinning process and the hydrophobic 2-(Perfluoroalkyl) ethanol (Zonyl® BA) was used as the coating material. From FESEM, the modified PEI-Zonyl membrane showed an open structure with large finger-like cavities. The modified membrane displayed a narrow pore size distribution with mean pore size of 0.028 μm. The outer surface contact angle of the PEI-Zonyl membrane increased from 81.3° to 100.4° due to the formation of an ultra-thin coated layer. The pure water flux of the PEI-Zonyl membrane was slightly reduced compared to the pristine PEI membrane. A permeate flux of 6.5 kg/m2 h and MB rejection of 98% were found for the PEI-Zonyl membrane during 76 h of the AGMD operation. Adsorption of MB on the membrane surface was confirmed based on the Langmuir isotherm evaluation, AFM and FESEM analysis. The modified PEI-Zonyl membrane can be a favorable alternative for AGMD of dyeing wastewaters.

Effect of air gap distance of PSF/IONPs/ALG hollow fiber membrane on morphology and antifouling properties

The study conducted on polysulfone/iron oxide/alginate (PSF/IONPs/ALG) hollow fiber (HF) membranes were spun at various air gap distances (10, 30, 50 and 70 cm) for membrane morphology and anti-fouling properties in hemodialysis application. PSF/IONPs/ALG membranes were fabricated using dry-wet spinning process. Hollow fiber properties were investigated using scanning electron microscopy (SEM), contact angles, and ultrafiltration measurements. SEM results show that the cross-sectional morphology of the membranes was varies significantly over various air gap distances. The structure of the outer surface became more porous as the pore size and air gap distance increased. In addition, the hydrophilicity of the membrane increased by decreasing water contact angle from 78.56ο to 48.83ο at air gap distance of 10 to 50 cm. Moreover, the pure water permeability (PWP) was improved when air gap was increased up to 50 cm before showing a decreasing pattern. Similar trends were recorded in BSA rejection and antifouling test with the highest BSA rejection and Flux recovery ratio (FRR), 96.53% and 86.37%, respectively at 50 cm air gap.

Improving Mass Transport of Titanium Hollow Fibre Electrodes through Gas Flow Stimulated Hydrodynamics

Hollow fiber electrodes, also known as porous tube electrodes, creatively address common gas related challenges in electrochemistry. By purging gas through the electrode wall an intense three phase contact can be established along the entire electrode-electrolyte interface. The electrochemical behavior of the hollow fiber electrode has been hypothesized based on the CO2 reduction reaction on a copper hollow fiber electrode 1. It was however not studied to any significant extent. The electrochemical behavior of the hollow fiber electrode and it’s relevant parameters have now been clarified and studied in more detail.In this study highly conductive titanium hollow fiber electrodes are used, since it is an attractive base electrode material for a great variety of electrochemical applications 2. These titanium based hollow fibers have an electrical resistivity (4.1-9.6 μΩ·m) 3 that is orders of magnitude lower than those previously reported in literature 4. This results from utilization of the two-step thermal decomposition of the polymer, which is required for the construction of an inorganic hollow fiber in a dry-wet spinning process 3.The investigation of platinum electrodeposition onto titanium hollow fiber electrodes with different flow rates has proven exceptionally insightful with regard to understanding the electrochemical behavior of the hollow fiber electrodes. The effect of volumetric gas flow rate on the resulting platinum deposit is visualized through the platinum electrochemical surface area and SEM images (Figure 1). Looking beyond the volumetric gas flow rate it is found that the exerted pressure and the pore size distribution relate to the area depended flow rate and bubble frequency at a pore, which affect the platinum distribution. In order to deconvolute the mass transfer during the platinum electrodeposition process, the hydrogen evolution reaction and an Fe2+/3+-redox couple have been investigated. These experiments isolate mass transport as an electrical current response to flow rate in the cases of gas evolution and electron transfer in solution respectively. By drawing on analogues with the proven methods of porometry and rotating disk electrodes it was found that many aspects of the electrochemical behavior of hollow fiber electrodes can be explained. The Young-Laplace equation helps in matching pressure fluctuation to the chemical state of the electrode surface and following the principles of the Koutecký-Levich equation it is possible to describe the current changes resulting from gas flow rate. Kas, et al. (2016). Nat. Commun., 7. DOI: 10.1038/ncomms10748Devilliers & E. Mahé. (2007). Trends in Electrochemistry Research., 1. ISBN: 1-59454-457-3P. H. Jong, et al. (2020). To be submitted. David, et al. (2014). J. Membr. Sci., 139. DOI: 10.1016/j.memsci.2014.03.010 Figure 1

Polysulfone hemodialysis membrane incorporated with Fe2O3 for enhanced removal of middle molecular weight uremic toxin

Removing middle molecular weight uremic toxin remains as one of the most challenging tasks in hemodialysis. Hence, in this study a high performance polysulfone (PSf) hemodialysis membrane was developed by incorporating iron oxide (Fe2O3) nanoparticles. The PSf/Fe2O3 hemodialysis membrane and pristine PSf membrane were prepared via dry-wet spinning process. The membranes were characterized by scanning electron microscopy, water contact angle, average pore size, and porosity measurements. The biocompatibility profiles of the membranes were also evaluated in terms of protein adsorption and blood coagulation time. Next, the performance of the membranes was determined by measuring pure water permeability (PWP), bovine serum albumin rejection, and removal of various solutes such as urea and lysozyme. The incorporation of Fe2O3 resulted in significant increment of the PWP from 40.74 L/m2/h/bar to 58.6 L/m2/h/bar, mainly due to the improved water transport properties of the membrane. Moreover, the percent removal of urea and lysozyme was reported to be 75.1% and 35.6%, respectively. PSf/Fe2O3 hemodialysis membrane is proven to have a bright prospect for enhanced blood purification process.

Improving pressure durability and fractionation property via reinforced PES loose nanofiltration hollow fiber membranes for textile wastewater treatment

Abstract Loose nanofiltration (NF) hollow fiber membranes with excellent dye rejection and high inorganic salt transmission are promising for textile wastewater treatment. Herein, a novel kind of reinforced PES loose NF hollow fiber membranes with robust twisted fiber bundle was fabricated by a facile dry-wet spinning process. The SEM results indicate that the favorable interfacial bonding layer was formed between the separation and supporting layer for the sake of endowing the membranes with high longitudinal strength and lateral pressure resistance. For one thing, the tensile strength of the PST membranes was up to 185.7 MPa, a considerably higher than FEP hollow fiber membrane prepared by melt spinning process (18.5 MPa). Moreover, the PST-1 membranes show almost no deformation, compared to sever deformation of FEP hollow fiber membrane after 100 h at high pressure operation. For another, the prepared PST membranes display stable pure water flux of 52.3 L·m−2·h−1 under 0.6 MPa. Specifically, the PST membranes exhibit excellent fractionation efficiency of dye/salt mixtures, along with high dye rejection of 99.9% and low salt rejection (

Effects of air gap on membrane substrate properties and membrane performance for biomass processing

We studied a correlation between the membrane substrate properties and the final performance of hollow fiber thin film composite (TFC) membrane for xylose/glucose concentration and acetic acid removal. Polysulfone (PSf) hollow fiber membrane substrate was fabricated using 20 wt% PSf, 2 wt% polyvinylpyrrolidone and 78 wt% dimethylformamide via dry-wet spinning process. The air gap distance was manipulated from 6 cm to 15 cm during spinning to produce different substrate membrane properties. The molecular weight cut-off (MWCO) and porosity of the membrane substrate increased as the air gap distance increased. Membrane substrate that was spun at 6 cm air gap showed a rapid phase inversion without much chain relaxation, thus producing the smallest MWCO (8 kDa) and an average pore diameter (4.46 nm). The TFC membrane produced using this membrane substrate showed the best performance in terms of solute rejection and separation factor. The rejection for xylose, glucose and acetic acid was 91.66±0.09%, 67.28±13.97%, and 13.08±3.00%, respectively. This results in an ideal separation factor of 3.20±1.27 for acetic acid/glucose and 10.42±0.25 for acetic acid/xylose.

Gas Separation Hollow Fiber Membranes: Processing Conditions for Manipulating Morphology and Performance

Currently, membrane unit operations are widely applied at industrial level, replacing conventional separation systems. Membrane gas separation represents a successful case, with an increasing number of installed plants in chemical processes, petrochemical plants and refineries for the production of nitrogen from air, the hydrogen separation and recovery and the carbon dioxide separation from natural gas. Owing to the low space footprint and low energy consumption, membrane separation is an environmental friendly technique that meets the Process Intensification requirements.The present study concentrates on the hollow fiber (HF) configuration that is the most used in applications of industrial interest. HF modules, having a high membrane packing density, are compact devices with thousands of square meters of membrane area per unit of volume.The required membranes have an asymmetric structure, in which a thin dense layer performs the separation and a porous substructure provides the needed mechanical resistance. The manipulation of the HFs morphology, according to a dry-wet spinning process in a pilot plant apparatus, investigating the effect of the operating conditions adopted for the spinning on the membrane performance and microstructure, is experi-mentally examined. Commercially available glassy polymers are used to make a comparison of a conventional double orifice spinneret with a triple orifice spinneret. The prepared HF batches are characterized by means of a morphological characterization (SEM analysis) and gas permeation rate measurements.

Parameter Screening of PVDF/PVP Multi-Channel Capillary Membranes.

The increasing research in the field of polymeric multi-channel membranes has shown that their mechanical stability is beneficial for a wide range of applications. The more complex interplay of formation process parameters compared to a single-channel geometry makes an investigation using Design of Experiments (DoE) appealing. In this study, seven-channel capillary membranes were fabricated in a steam–dry–wet spinning process, while varying the composition of the polymer solution and the process temperatures in a three-level fractional factorial linear screening design. The polymers polyvinylidene flouride (PVDF) was the chemically resistant main polymer and polyvinylpyrrolidone (PVP) was added as hydrophilic co-polymer. Scanning electron microscopy and atomic force microscopy were applied to study the membrane morphology. Fabrication process conditions were established to yield PVDF/PVP multi-channel membranes, which reached from high flux (permeability P = ///bar, dextran 500 retention R = 18.3%) to high retention (P = ///bar, R = 80.0%). The concentration of the main polymer PVDF and the molecular weight of the co-polymer PVP showed linear relations with both P and R. The permeability could be increased using sodium hypochlorite post-treatment, although retention was slightly compromised. The obtained membranes may be suitable for micro- or ultra-filtration and, at the same time, demonstrate the merits and limitations of DoE for multi-channel membrane screening.

Preparation of cMWCNTs-incorporated Hollow Fiber Membrane with Improved Water Flux and Dye Adsorption Properties

Carboxylated multi-walled carbon nanotubes (cMWCNTs) were incorporated in membrane matrix during the drywet spinning process to improve membrane performance. Membrane surface composition and morphology were examined by means of FTIR and SEM. The effects of cMWCNTs content on membrane surface hydrophilicity, separation performance and dye adsorption properties were well investigated and characterized through WCA examination, the cross-flow filtration measurement and the adsorption experiment. The surface hydrophilicity, the water permeability, solute rejection and dye adsorption properties of the cMWNTs-incorporated hollow fiber membranes have been all improved. When cMWNTs content was 0.3 wt%, the cMWNTs-incorporated hollow fiber membrane obtained the obvious enhanced pure water flux (137.2 L·m-2·h-1, at 0.1 MPa) which was 1.5 times as high as that of the original PSF hollow fiber membrane. The prepared cMWCNTs-incorporated membranes are expected to be used in the treatment of textile dyeing wastewater or employed as the supports of the composite membranes.

Facile modification of polysulfone hollow‐fiber membranes via the incorporation of well‐dispersed iron oxide nanoparticles for protein purification

ABSTRACTProtein existence in wastewater is an important issue in wastewater management because proteins are generally present as contaminants and foulants. Hence, in this study, we focused on designing a polysulfone (PSf) hollow‐fiber membrane embedded with hydrophilic iron oxide nanoparticles (IONPs) for protein purification by means of ultrafiltration. Before membrane fabrication, the dispersion stability of the IONPs was enhanced by the addition of a stabilizer, namely, citric acid (CA). Next, PSf–IONP–CA nanocomposite hollow‐fiber membranes were prepared via a dry–wet spinning process and then characterized in terms of their hydrophilicity and morphology. Ultrafiltration and adsorption experiments were then conducted with bovine serum albumin as a model protein. The results that an IONP/CA weight ratio of 1:20 contributed to the most stable IONP dispersion. It was also revealed that the membrane incorporated with IONP–CA at a weight ratio of 1:20 exhibited the highest pure water permeability (58.6 L m−2 h−1 bar−1) and protein rejection (98.5%) while maintaining a low protein adsorption (3.3 μg/cm2). The addition of well‐dispersed IONPs enhanced the separation features of the PSf hollow‐fiber membrane for protein purification. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47502.

Stretchable multi-luminescent fibers with AIEgens

Stretchable multicolor light-emitting fibers were realized by incorporating an ultralow content of AIEgens in polydimethylsiloxane fibers through a continuous dry–wet spinning process for applications in smart textiles.

Localization of antifouling surface additives in the pore structure of hollow fiber PVDF membranes

Industrial hollow fiber membranes for the purification of wastewater were manufactured by the phase inversion method in a dry-wet spinning process, adding an amphiphilic diblock copolymer to a standard PVDF/Polyvinylpyrrolidone (PVP) formulation. The copolymer designed to provide antifouling properties is composed of a PMMA block and a hydrophilic block bearing pendent hydroxy groups. As PMMA is miscible with PVDF, the copolymer is expected to anchor in the matrix more efficiently than the hydrophilic but water soluble PVP which is washed away overtime during repetitive cleaning procedures.Infrared experiments attest that both antifouling additives are well included in the fibers after the inversion process. Performances of the fibers were checked by permeability, burst pressure and tensile tests. The pore distribution observed by scanning electron microscopy goes from 10 to 30nm at the outer surface to 0.1–10µm inside the fiber. Observation of the pore structure by transmission electron microscopy, made possible by embedding the fibers into a resin that filled in the voids, and specific staining of the antifouling additives, shows that both PVP and the amphiphilic copolymer are located all around the pores. This study is the first direct proof at the microscopic scale of pore surface enrichment by antifouling agents.

The effect of air gap on the morphological properties of PSf/PVP90 membrane for hemodialysis application

Membrane morphology plays an important role in achieving high flux and excellent uremic toxin removal for efficient hemodialysis therapy. Hemodialysis membrane morphology correlates to spinning parameters applied during fabrication of membrane. The effect of air gap on the morphology and liquid separation performance of the polysulfone (PSf) hemodialysis membrane is investigated. PSf hollow fibre membranes were prepared via dry-wet spinning process from dope solution comprises of 18 wt% PSf and 4.8 wt% polyvinylpyrrolidone in Nmethyl- 2-pyrrolidone. The membrane morphology was characterised using a scanning electron microscope (SEM) before tested with the ultrafiltration system to measure the pure water flux (PWF) and protein rejection using bovine serum albumin (BSA). SEM analysis revealed that the air gap does change the structure of the membranes due to the elongation stress because of the gravitational pull on the PSf hollow fibres. At low air gap (3 cm), the lower average pore size on the outer surface reduced the PWF while at high air gap (50 cm), the larger average pore size of membranes permitted water molecules to pass through easier and faster. It was observed that the PWF of the membrane increased significantly with air gap due to the increasing pore size. Membrane fabricated at 50 cm air gap obtained better PWF (28.45 Lm-2h-1) and protein rejection (94.47 %) compared to the membranes fabricated at 3 and 30 cm air gap. The effect of air gap enhanced the morphology and the performance of PSf membrane for hemodialysis application.