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.     

纺丝条件对PVDF/PVC中空纤维膜性能的影响

采用干-湿法纺丝工艺制备PVDF/PVC共混中空纤维膜,通过对水通量、孔径、截留率等的测试,研究了挤出速率、芯液流量、干纺程对PVDF/PVC中空纤维膜性能及结构的影响,并进行了详细的理论分析。试验结果表明挤出速率与膜通量存在最大值,芯液流量与膜通量及截留率呈线性关系,干纺程的影响效果跟挤出速率类似。可以通过改变纺丝条件来制备性能不同的中空纤维膜。     

Tailoring the morphology of self-assembled block copolymer hollow fiber membranes

Isoporous asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hollow fiber membranes were successfully made by a dry-jet wet spinning process. Well-defined nanometer-scale pores around 20–40 nm in diameter were tailored on the top surface of the fiber above a non-ordered macroporous layer by combining block copolymer self-assembly and non-solvent induced phase separation (SNIPS). Uniformity of the surface-assembled pores and fiber cross-section morphology was improved by adjusting the solution concentration, solvent composition as well as some important spinning parameters such as bore fluid flow rate, polymer solution flow rate and air gap distance between the spinneret and the precipitation bath. The formation of the well-organized self-assembled pores is a result of the interplay of fast relaxation of the shear-induced oriented block copolymer chains, the rapid evaporation of the solvent mixture on the outer surface and solvent extraction into the bore liquid on the lumen side, and gravity force during spinning. Structural features of the block copolymer solutions were investigated by small-angle X-ray scattering (SAXS) and rheological properties of the solutions were examined as well. The scattering patterns of the optimal solutions for membrane formation indicate a disordered phase which is very close to the disorder-order transition. The nanostructured surface and cross-section morphology of the membranes were characterized by scanning electron microscopy (SEM). The water flux of the membranes was measured and gas permeation was examined to test the pressure stability of the hollow fibers.     

Carbon dioxide absorption by monoethanolamine in hollow fiber membrane contactors: A parametric investigation

A mathematical and numerical investigations on the gas–liquid absorption of carbon dioxide in monoethanolamine solutions in a hollow fiber membrane contactor device is described. The reactive absorption mechanism was built based on momentum and mass transport conservation laws in all three compartments involved in the process, i.e., the gas phase, the membrane barrier, and the liquid phase. The liquid absorbing solution flows in the fiber bore in which the velocity is assumed to obey a fully developed laminar flow, and the gas mixture circulates counter‐currently to the liquid flow in the shell side where the velocity is characterized by the Navier‐Stokes momentum balance equations. The average outlet gas and liquid concentrations, the reactive absorption flux, and the gas removal efficiencies are parametrically simulated with operational parameters such as gas flow rate, fresh inlet amine concentrations, and fiber geometrical characteristics. The shell velocity was described by other flow hydrodynamics models besides Navier‐Stokes and their simulated results were favorably compared to experimental data. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Fundamental understanding of the effect of air‐gap distance on the fabrication of hollow fiber membranes

The objectives of this work are, fundamentally, to understand hollow fiber membrane formation from an engineering aspect, to develop the governing equations to describe the velocity profile of nascent hollow fiber during formation in the air gap region, and to predict fiber dimension as a function of air‐gap distance. We have derived the basic equations to relate the velocity profile of a nascent hollow fiber in the air‐gap region as a function of gravity, mass transfer, surface tension, drag forces, spinning stress, and rheological parameters of spinning solutions. Two simplified equations were also derived to predict the inner and outer diameters of hollow fibers. To prove our hypotheses, hollow fiber membranes were spun from 20 : 80 polybezimidazole/polyetherimide dopes with 25.6 wt % solid in N,N‐dimethylacetamide using water as the external and internal coagulants. We found that inner and outer diameters of as‐spun fibers are in agreement with our prediction. The effects of air‐gap distance or spin‐line stress on nascent fiber morphology, gas performance, and mechanical and thermal properties can be qualitatively explained by our mathematical equations. In short, the spin‐line stresses have positive or negative effects on membrane formation and separation performance. A high elongational stress may pull molecular chains or phase‐separated domains apart in the early stage of phase separation and create porosity, whereas a medium stress may induce molecular orientation and reduce membrane porosity or free volume. Scanning electron microscopic photographs, coefficient of thermal expansion, and gas selectivity data confirm these conclusions. T_g of dry‐jet wet‐spun fibers is lower than that of wet‐spun fibers, and T_g decreases with an increase in air‐gap distance possibly because of the reduction in free volume induced by gravity and elongational stress. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 379–395, 1999     

Modified poly(vinylidene fluoride) hollow fiber composite membranes reinforced by hydroxyapatite nanocrystal whiskers

The modified poly(vinylidene fluoride) (PVDF) hollow fiber composite membranes reinforced by hydroxyapatite (HAP) nanocrystal whiskers were fabricated with wet‐spinning method. The PVDF/HAP/N‐methyl‐2‐pyrrolidone dope solutions experienced delayed demixing mechanism, and the precipitation rate slightly increased as the HAP whisker content increased. The cross sections of PVDF‐HAP and neat PVDF hollow fiber composite membranes were composed of five distinct layers: two skin layers, two finger‐like sublayers, and a sponge‐like layer. The Young's modulus of and tensile strength of the PVDF‐HAP hollow fiber membranes gradually increased with the addition of nano‐HAP whiskers. The elongation ratio was also improved, which was different from the polymeric membranes modified by other inorganic nanofillers. The permeation flux of the PVDF‐HAP hollow fiber membranes slightly increased with the increase of HAP content in the composite membranes as its hydrophilicity was improved. The crystallization behaviors of PVDF in the composite membranes were also investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The Online Measurement of Lyocell Fibers and Investigation of Elongational Viscosity of Cellulose N‐methylmorpholine‐N‐oxide Monohydrate Solutions

In this paper, the development of diameter and surface temperature of Lyocell fibers was measured online. The diameter and tensile force on the spin line in the coagulation bath were traced. The velocity, velocity gradient and the tensile stress profiles development of the fibers in the air gap were studied. The apparent elongational viscosity of cellulose N‐methylmorpholine‐N‐oxide monohydrate (NMMO‐MH) solutions was studied by steady‐state melt spinning theory. The decrease of the fiber diameter was mainly taking place near the spinneret, and the decrease of the diameter became more dramatic with increasing taking‐up speed. The surface temperature of the fibers was also dropping faster with increasing taking‐up speed for the heat transfer coefficient increased. The diameter of the Lyocell fibers almost did not change before and after it entered the coagulation bath. The tensile force on the spin line increases with increasing taking‐up speed and coagulation bath length. The velocity and the tensile stress increase slowly near the spinneret, and then accelerate. The apparent elongational viscosity of cellulose NMMO‐MH solutions decreases with increasing temperature at the same elongation rate and decreases with increasing elongation rate at the same temperature. The fiber of the Lyocell process was not really solidified in the air gap and a gel or rubbery state was formed.     

Diverse morphologies of PVDF hollow fiber membranes and their performance analysis as gas/liquid contactors

A systematic investigation on the morphology development of polyvinylidene fluoride hollow fiber membrane made using various N‐methyl‐2‐pyrrolidone (NMP) aqueous solutions as an inner coagulant was carried out. The cross‐sectional and inner surface morphology were analyzed with scanning electronic microscopy (SEM). It is found that with increase on NMP concentration, the morphology of the resultant membranes gradually shifted from a double‐skin to a single‐skin structure. When 40.0 ～ 55.0 wt.% NMP solution was used, some unexpected macrovoids near the inner region were observed. This special morphology feature was attributed to the reduced solidification rate of the inner surface as a result of increase on NMP concentration, which sharply weakened the inner skin strength. While the existence of centralized stress formed in the phase inversion process, such as shrinkage stress from syneresis, resulted in fractured points in the nascent skin surface that finally made it difficult to maintain a uniform structure. Investigations on effects of the dope flow rate and the bore fluid velocity on the morphology of PVDF fiber membranes experimentally confirmed the suggestion. Three model membranes with double skins, single skin and single skin with macrovoids structures, respectively, were used to test their permeation performance in a CO₂ membrane contactor system. The experimental results show the membranes without an inner skin present higher permeability and lower mass transfer resistance than the membrane with a double skin structure. © 2010 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2010     

Hydrogen separation at elevated temperatures using metallic nickel hollow fiber membranes

Nickel is a cheaper metallic material compared to palladium membranes for H₂ separation. In this work, metallic Ni hollow fiber membranes were fabricated by a combined phase inversion and atmospheric sintering method. The morphology and membrane thickness of the hollow fibers was tuned by varying the spinning parameters like bore liquid flow rate and air gap distance. H₂ permeation through the Ni hollow fibers with N₂ as the sweep gas was measured under various operating conditions. A rigorous model considering temperature profiles was developed to fit the experimental data. The results show that the hydrogen permeation flux can be well described by using the Sieverts’ equation, implying that the membrane bulk diffusion is still the rate‐limiting step. The hydrogen separation rate in the Ni hollow fiber module can be improved by 4–8% when switching the co‐current flow to the countercurrent flow operation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3026–3034, 2017     

The analysis and design of a both open ended hollow fiber type RO module

The use of seawater desalination plants using RO technology has spread and the scale of the plants has increased. In such a situation, a larger‐sized RO module has been strongly required. The conventional hollow fiber type RO element is a single open‐ended (SOE) structure. That is, one side of the hollow fibers in the modules is opened and the other side is closed. In this SOE structure, the increase in the flow pressure loss of the permeated water which flows in the bore side of the hollow fibers prevents development of a large‐sized (longer) RO element. In this work, a both open‐ended (BOE) element was devised which can reduce the flow pressure loss of the permeated water. It has been confirmed by analysis and experiment that the permeate flow rate of BOE is greater by about 30% than that of SOE. Furthermore, the large‐sized RO module with high volume efficiency was designed using the performance analysis method that was confirmed to be applicable to BOE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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     

Fabrication of 6FDA‐durene polyimide asymmetric hollow fibers for gas separation

We have developed defect‐free asymmetric hexafluoro propane diandydride (6FDA) durene polyimide (6FDA‐durene) hollow fibers with a selectivity of 4.2 for O₂/N₂ and a permeance of 33.1 ×10^?6 cm³ (STP)/cm²‐s‐cmHg for O_2. These fibers were spun from a high viscosity in situ imidization dope consisting of 14.7% 6FDA‐durene in a NMP solvent and the inherent viscosities (IV) of this 6FDA‐durene polymer was 0.84 dL/g. Low IV dopes cannot produce defect‐free hollow fibers, indicating a 6FDA‐durene spinning dope with a viscosity in the region of chain entanglement seems to be essential to yield hollow fibers with minimum defects. The effects of spinning parameters such as shear rates within a spinneret and bore fluids as well as air gap on gas separation performance were investigated. Experimental data demonstrate that hollow fibers spun with NMP/H₂O as the bore liquid have higher permeances and selectivities than those spun with glycerol as the bore liquid because the former has a relatively looser inner skin structure than the latter. In addition, the selectivity of hollow fibers spun with NMP/H₂O as the bore liquid changes moderately with shear rate, while the selectivity of hollow fibers spun with glycerol are less sensitive to the change of shear rate. These distinct behaviors are mainly attributed to the different morphologies generated by different bore fluids. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2166–2173, 2001     

Effect of polyethylene glycol molecular weights and concentrations on polyethersulfone hollow fiber ultrafiltration membranes

Polyethersulfone (PES) hollow‐fiber membranes were fabricated using poly(ethyleneglycol) (PEG) with different molecular weights (MW = PEG200, PEG600, PEG2000, PEG6000, and PEG10000) and poly(vinyl pyrrolidone) PVP40000 as additives and N‐methyl‐2‐pyrrolidone (NMP) as a solvent. Asymmetric hollow‐fiber membranes were spun by a wet phase‐inversion method from 25 wt % solids of 20 : 5 : 75 (weight ratio) PES/PEG/NMP or 18 : 7 : 75 of PES/(PEG600 + PVP40000)/NMP solutions, whereas both the bore fluid and the external coagulant were water. Effects of PEG molecular weights and PEG600 concentrations in the dope solution on separation properties, morphology, and mechanical properties of PES hollow‐fiber membranes were investigated. The membrane structures of PES hollow‐fiber membranes including cross section, external surface, and internal surface were characterized by scanning electron microscopy and the mechanical properties of PES hollow‐fiber membranes were discussed. Bovine serum albumin (BSA, MW 67,000), chicken egg albumin (CEA, MW 45,000), and lysozyme (MW 14,400) were used for the measurement of rejection. It was found that with an increase of PEG molecular weights from 200 to 10,000 in the dope solution, membrane structures were changed from double‐layer fingerlike structure to voids in the shape of spheres or ellipsoids; moreover, there were crack phenomena on the internal surfaces and external surfaces of PES hollow‐fiber membranes, pure water permeation fluxes increased from 22.0 to 64.0 L m^?2 h^?1 bar^?1, rejections of three protein for PES/PEG hollow‐fiber membranes were not significant, and changes in mechanical properties were decreased. Besides, with a decrease of PEG600 concentrations in the dope solution, permeation flux and elongation at break decreased, whereas the addition of PVP40000 in the dope solution resulted in more smooth surfaces (internal or external) of PES/(PEG600 + PVP40000) hollow‐fiber membranes than those of PES/PEG hollow‐fiber membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3398–3407, 2004     

Direktes Herstellungsverfahren von Komposit‐Hohlfasermembranen mit sinusförmiger Geometrie

Composite hollow fiber membranes are fabricated in a one‐step process by superimposing the phase inversion process with interfacial polymerization on the lumen side of the fiber. A pulsation module in the bore fluid channel pulsates the bore fluid flow and leads to hollow fiber membranes with sinusoidal geometry. The fabrication of composite hollow fiber membranes with sinusoidal geometry is focus of this work. The sinusoidal geometry leads to reduced concentration polarization effects in membrane applications.     

Effect of polyvinylpyrrolidone molecular weights on morphology,oil/water separation,mechanical and thermal properties of polyetherimide/polyvinylpyrrolidone hollow fiber membranes

We prepared polyetherimide (PEI) hollow fiber membranes using polyvinylpyrrolidones (PVP) with different molecular weights (PVP 10,000, PVP 40,000, and PVP 1,300,000) as additives for oil/water separation. Asymmetric hollow fiber membranes were fabricated by wet phase inversion technique from 25 wt % or 30 wt % solids of 20 : 5 : 75 or 20 : 10 : 70 (weight ratio) PEI/PVP/N‐metyl‐2‐pyrrolidone (NMP) solutions and a 95 : 5 NMP/water solution was used as bore fluid to eliminate resistance on the internal surface. Effects of PVP molecular weights on morphology, oil‐surfactant‐water separation characteristics, mechanical, and thermal properties of PEI/PVP hollow fiber membranes were investigated. It was found that an increase in PVP molecular weight and percentage in PEI/PVP dope solution resulted in the membrane morphology change from the finger‐like structure to the spongy structure. Without sodium hypochlorite posttreatment, hollow fiber membranes with higher PVP molecular weights had a higher rejection but with a lower water flux. For oil‐surfactant‐water emulsion systems (1600 ppm surfactant of sodium dodecylbenzenesulfonate and 2500 ppm oil of n‐decane), experimental results illustrated that the rejection rates for surfactant, total organic carbon, and oil were 76.1 ≈ 79.8%, 91.0 ≈ 93.0%, and more than 99%, respectively. Based on the glass transition temperature values, PVP existed in hollow fiber membranes and resulted in the hydrophilicity of membranes. In addition, using NaOCl as a posttreatment agent for membranes showed a significant improvement in membrane permeability for PVP with a molecular weight of 1300 K, whereas the elongation at break of the treated hollow fiber membranes decreased significantly. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2220–2233, 1999     

Studies on high‐speed melt spinning of noncircular cross‐section fibers. II. On‐line measurement of the spin line,including change in cross‐sectional shape

On‐line measurement was performed in the high‐speed spinning of flat, hollow, and circular fibers of poly(ethylene terephthalate), paying particular attention to the change in cross‐sectional shape along the spin line. The diameter profiles of hollow and circular fibers were essentially identical, whereas the deformation of flat fiber shifted to the region closer to the spinneret. The necklike deformation of hollow and circular fibers started at the takeup velocity of 5 km/min. In the case of flat fibers, presence of the necklike deformation was confirmed at 4 km/min, and extremely steep diameter attenuation was observed at 5 km/min. The spin‐line tension of the flat fiber was also larger than that of circular fibers. Combined measurements of fiber velocity and thickness enabled us to evaluate the aspect ratio of the flat fiber and hollow ratio of the hollow fiber in the spin line. These two factors were found to decrease steeply near the spinneret. Accordingly, the thinning of the spin line and the change in cross‐sectional shape appeared to proceed independently. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1582–1588, 2001     

Multichannel mixed‐conducting hollow fiber membranes for oxygen separation

A multichannel mixed‐conducting hollow fiber (MMCHF) membrane, 0.5 wt % Nb₂O₅‐doped SrCo_0.8 Fe_0.2O_3‐δ (SCFNb), has been successfully prepared by phase inversion and sintering technique. The crystalline structure, morphology, sintering behavior, breaking load, and oxygen permeability of the MMCHF membrane were studied systematically. The MMCHF membrane with porous‐dense asymmetrical microstructure was obtained with the outer diameter of 2.46 mm and inner tetra‐bore diameter of 0.80 mm. The breaking load of the MMCHF membrane was 3–6 times that of conventional single‐channel mixed‐conducting hollow fiber membrane. The MMCHF membrane showed a high oxygen flux which was about two times that of symmetric capillary membrane at similar conditions as well as a good long‐term stability under low oxygen partial pressure atmosphere. This work proposed a new configuration for the mixed‐conducting membranes, combining advantages of multichannel tubular membrane technology and conventional hollow fibers. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1969–1976, 2014     

Studies on melt spinning process of hollow polyethylene terephthalate fibers

Dimensional change and profile development in the melt spinning process of polyethylene terephthalate hollow fibers were studied through the numerical simulations and experimental results. The simulation predicts the final dimensions and profiles development of the hollow fibers at various positions from the die. Experimental results show that the melt extruded from the spinneret coalesces initially to form a hollow inner core and the cross‐sectional shape holds for over the whole spinline with only variation in the hollow portion. Analysis of the effect of spinning parameters on hollow portion shows that the spinning temperature, mass throughput rate, and take‐up speed are the most critical variables in controlling the hollow portion followed by quench air velocity. The quench air temperature has relatively less effect than the other variables. As the mass throughput rate and quench air velocity increase and the take‐up speed and spinning temperature decrease, the hollow portion increases. To investigate the effect of die geometry, die having a different ratio of inner to outer diameter was used. The effect of change of process variables decreases as the die gap becomes narrow. POLYM. ENG. SCI. 46:609–616, 2006. © 2006 Society of Plastics Engineers     

Long‐term study of CO2 absorption by PVDF/ZSM‐5 hollow fiber mixed matrix membrane in gas–liquid contacting process

In order to fabricate hollow fiber mixed matrix membrane (HFMMM) for long‐term CO₂ absorption process, ZSM‐5 (Zeolite Socony Mobil–5) zeolite was modified using hexadecyltrichlorosilane for increasing hydrophobicity and then added to the polyvinylidene fluoride (PVDF) spinning dope. The in‐house made HFMMMs were characterized in terms of gas permeance, overall porosity, average pore size, effective surface porosity, surface roughness, mechanical stability, and wetting resistance. The morphology of the HFMMMs was studied using SEM. The cross‐sectional SEM images indicated that the membrane structure has changed from sponge‐like to finger‐like by ZSM‐5 loading. The surface roughness increased by increasing ZSM‐5 concentration in the spinning dope. The HFMMM spun from the spinning dope with 0.5 wt % of ZSM‐5 zeolite showed that the CO₂ absorption flux decreased 18.9% in the initial 115 h of the operation and then the absorption flux remained constant until the end of the operation. For plain PVDF HFM the absorption flux decreased 36% from the initial value in the first 15 h of the experiment. Thus it could be concluded that the long term stability of HFM was improved by the incorporation of ZSM‐5. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44606.     

Morphological and separation performance study of polysulfone/titanium dioxide (PSF/TiO2) ultrafiltration membranes for humic acid removal

In this study, polysulfone (PSF) hollow fiber membranes with enhanced performance for humic acid removal were prepared from a dope solution containing PSF/DMAc/PVP/TiO₂. The main reason for adding titanium oxide during dope solution preparation was to enhance the antifouling properties of membranes prepared. In the spinning process, air gap distance was varied in order to produce different properties of the hollow fiber membranes. Characterizations were conducted to determine membrane properties such as pure water flux, molecular weight cut off (MWCO), humic acid (HA) rejection and resistance to fouling tendency. The results indicated that the pure water flux and MWCO of membranes increased with an increase in air gap distance while HA retention decreased significantly with increasing air gap. Due to this, it is found that the PSF/TiO₂ membrane spun at zero air gap was the best amongst the membranes produced and demonstrated > 90% HA rejection. Analytical results from FESEM and AFM also provided supporting evidence to the experimental results obtained. Based on the anti-fouling performance investigation, it was found that membranes with the addition of TiO₂ were excellent in mitigating fouling particularly in reducing the fouling resistances due to concentration polarization, cake layer formation and absorption.