Dry-jet Wet Spinning Technique Research Articles

Coaxial Layered Fiber Spinning for Wind Turbine Blade Recycling.

Plastics' long degradation time and their role in adding millions of metric tons of plastic waste to our oceans annually present an acute environmental challenge. Handling end-of-life waste from wind turbine blades (WTBs) is equally pressing. Currently, WTB waste often finds its way into landfills, emphasizing the need for recycling and sustainable solutions. Mechanical recycling of composite WTB presents an avenue for the recovery of glass fibers (GF) for repurposing as fillers or reinforcements. The resulting composite materials exhibit improved properties compared to the pure PAN polymer. Through the employment of the dry-jet wet spinning technique, we have successfully manufactured PAN/GF coaxial-layered fibers with a 0.1 wt % GF content in the middle layer. These fibers demonstrate enhanced mechanical properties and a lightweight nature. Most notably, the composite fiber demonstrates a significant 24.4% increase in strength and a 17.7% increase in modulus. These fibers hold vast potential for various industrial applications, particularly in the production of structural components (e.g., electric vehicles), contributing to enhanced performance and energy efficiency.

Next-Generation Cellulosic Filaments from Hemp Pulp via Dry-Jet Wet Spinning Using HighPerCell® Technology

Fiber demand of cellulosic fibers is rapidly increasing; however, these fibers are mainly based on the use of wood pulp (WP), which often have long transport times and, consequently, a high CO2 footprint. So, alternative pulps based on non-wood, annual fast-growing plants are an option to cover the demand for raw materials and resources. Herein, we report on the use of a novel developed hemp pulp (HP) for man-made cellulosic fiber filament spinning. Commercial WP was used as a reference material. While HP could be used and directly spun as received without any further pretreatment, an additional step to adjust the degree of polymerization (DP) was needed to use the wood pulp. Continuous filaments were spun using a novel dry-jet wet spinning (HighPerCell® process) technique, which is based on the use of 1-ethyl-3-methylimidazolium octanoate ([C2C1im][Oc]) as a solvent. Via this approach, several thousand meters (12,000 m–15,000 m) of continuous multifilament filaments were spun. The HP pulps showed excellent spinning performance. The novel approach allows the preparation of cellulosic fibers for either technical—with high tensile strength—or textile—possessing a low fibrillation tendency—applications. Textile hemp-based filaments were used for first weaving trials, resulting in a flawless fabric.

Preparation and Structural Behavior of High-Performance PBO Fibers

To improve the dispersion ability of monomers in the high-viscosity PBO pre-polymerization system, a new large-capacity mixing paddle for PBO pre-polymerization reaction was designed. Through simulated calculation, it was found that the new mixing paddle has good dispersion effect and produced PBO polymer whose intrinsic viscosity was 37.5 dL/g, number-average molecular weight was 92700, and degree of polymerization was 396. Then the PBO fibers were prepared by the dry jet wet spinning technique. The morphology analysis showed that the PBO fibers were well formed, with a diameter of 14 µm. The infrared spectrum analysis verified the structure of PBO fibers. The mechanical test showed that the tensile strength of PBO fibers was 5.04-5.76 GPa and the elongation at break was 3.93% - 4.54%, which means they have good mechanical properties.

Effects of oxidized cellulose nanocrystals on the structure and mechanical properties of regenerated collagen fibers

The mechanical properties of regenerated collagen composite materials are of use in diverse applications. However, there are few efficient strategies to enhance the mechanical properties of regenerated collagen fibers. Herein, oxidized cellulose nanocrystals (oCNCs) were successfully prepared in aqueous media via oxidation of the hydroxyl groups on the surface of cellulose nanocrystals (CNCs) using ammonium persulfate (APS) as an oxidant. Collagen composite fibers were then prepared by introducing oCNCs into the collagen matrix via a dry-jet wet-spinning technique. The morphology, structures, and properties of prepared collagen composite fibers were carefully investigated. The results indicate that oCNCs and CNCs can induce collagen microfibril orientation during the formation process of fibers and protect the possibility of their interactions with collagen molecules. The oCNCs offered better enhancement efficiency than CNCs, and the as-prepared collagen/oCNC composite fibers exhibited extraordinary improvements in both tensile strength and toughness with only a 0.05 wt% oCNCs loading. The reason for this improvement is that the hydroxyl groups and carboxyl groups of oCNCs can form stronger hydrogen bonds and electrostatic interactions with collagen molecules, thus resulting in a synergistic enhancement of the tensile strength, toughness, and thermal stability of collagen composite fibers. This work provides an efficient and facile method to achieve collagen composite fibers with high mechanical properties for broad applications.

Construction of rough and porous surface of hydrophobic PTFE powder-embedded PVDF hollow fiber composite membrane for accelerated water mass transfer of membrane distillation

The construction of rough and porous hydrophobic membrane surface is expected to overcome the obstacles including low permeate water flux and membrane pore wetting which greatly restrict the development of membrane distillation (MD) technology. In this study, a rough and porous polytetrafluoroethylene (PTFE) powder-embedded polyvinylidene fluoride (PVDF) hydrophobic coating layer was compounded on the outer surface of PVDF hollow fiber support membrane by the dilute solution coating-phase inversion method. PVDF hollow fiber support membrane was fabricated by the dry-jet wet-spinning technique. PTFE powder was directly incorporated in PVDF dilute coating solution and embedded in the porous PVDF coating layer after the nonsolvent induced phase separation (NIPS). The variations of membrane morphology, surface chemical compositions, hydrophobicity and wetting resistance were investigated by scanning electron microscope (SEM), Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), dynamic water contact angle (WCA) and liquid entry pressure (LEP) analysis. Membrane separation performance including desalination and ionic dyes removal properties was evaluated by VMD experiment. Compared with PVDF hollow fiber support membrane, both the surface hydrophobicity and the water permeability of the PTFE powder-embedded PVDF hollow fiber composite membrane (HFC) had obvious improvement. The surface WCA and permeate water flux increased from 92.6° and 11.3 kg/m2.h for PVDF support membrane to 133.6° and 26.8 kg/m2.h for the PTFE powder-embedded HFC membrane meanwhile NaCl rejection can be maintained above 99.9% (3.5 wt% NaCl aqueous solution at 50 °C and permeate pressure at 31.3 kPa). The separation performance of HFC membrane can remain stable without obvious pore wetting during the continuous MD operation for 36 h. Different from the desalination, porous hollow fiber membrane would adsorb two different charged dyes, Congo red (CR) and methylene blue (MB) to a certain extent, resulting in the decrease of membrane flux and the change of permeate water quality. Finally, the MD separation mechanism of inorganic salt, anionic dye and cationic dye by PTFE powder-embedded HFC membrane was proposed.

An innovative hollow fiber vacuum membrane distillation-crystallization (VMDC) coupling process for dye house effluent separation to reclaim fresh water and salts

The discharge of dyeing wastewater has become one of the important restrictive factors for the green manufacturing and sustainable development of textile industry. Realizing the maximum reuse of dyeing wastewater resources is an efficient solution. Vacuum membrane distillation crystallization (VMDC) coupling process can separate and recover the components such as fresh water and salts (mordants) in dyeing wastewater as well as achieve the concentration of the valuable substances (dyes) simultaneously. In this study, hollow fiber VMDC coupling process was developed for the treatment of saline dye solution to recover the inorganic salt (mordant Al(NO3)3) and fresh water while realize the high-multiple concentration of dyes (Congo red, CR). High-performance hydrophobic PVDF hollow fiber porous membrane was prepared by the dry-jet wet-spinning technique and used in the VMDC process. The VMDC process in one cycle was optimized, including MD section, crystallization and membrane cleaning process. Variations of MD separation performance including permeate water flux and solute rejection of PVDF hollow fiber membrane for CR and Al(NO3)3 with operating time was determined by the vacuum membrane distillation (VMD) experiment. A three-cycle VMDC process was developed and the variations of MD separation performance and crystal yield in each VMDC cycle were investigated. In each VMDC process, the rejection of CR and Al (NO3) 3 by hollow fiber MD can be maintained above 99%. With the extension of VMDC operating time, the gradually decreased water flux can be recovered by around 90% through the combined cleaning method of NaOH and absolute ethanol (abs). In the three-cycle of VMDC process, 42.5, 32.5 and 9.8% of water were recovered from the feed solution with a total recovery ratio of 84.8%. In the second and third VMDC cycles, 48.0 and 21.5% of the salts in the saline dye solution were obtained with a total salt recovery ratio of 69.5%. An estimation of economic cost was also made to evaluate the economic feasibility of the proposed MDC process for its practical application. Hollow fiber VMDC coupling process was proved to be a simultaneously efficient separation method of saline dye solution.

Dye adsorption properties of poly(p-phenylene terephthalamide)-embedded hollow fiber composite membranes

Hollow fiber composite (HFC) membrane with improved dye adsorption properties was prepared by the embedding of poly(p-phenylene terephthalamide) (PPTA)/polysulphone (PSF) microparticles into the polyamide (PA) composite layer of PSF hollow fiber membrane. As the polymer raw material of Aramid-1414, high modulus and hydrophilic PPTA was polycondensated in situ in PSF system and PPTA/PSF microparticles were obtained by the cloud-point precipitation method. PSF hollow fiber membrane was fabricated by the dry-jet wet-spinning technique. The variations of membrane morphology, porosity, surface charge and hydrophilicity were evaluated by the scanning electron microscope (SEM) observation, dry-wet mass difference, Zeta potential and water contact angle (WCA) measurements. The adsorption thermodynamic and kinetic processes of different kinds of dyes including anionic dye (Congo red, CR) and cationic dye (methylene blue, MB) were thoroughly investigated by three typical typical sorption isotherm models and two classical kinetic models, respectively. Compared with the PSF hollow fiber membrane and the pristine HFC membrane, the surface roughness, hydrophilicity and electronegativity had an obvious enhancement. The PPTA-embedded HFC membrane presented an increased dye adsorption capacity. The adsorption isotherms for CR and MB of the PPTA-embedded HFC membrane could fit well with the Langmuir and Sips models. The adsorption kinetics for CR and MB are in good agreement with the pseudo-first-order model and pseudo-second-order model, respectively. The prepared PPTA-embedded hollow fiber composite membranes are expected to be a promising candidate for the treatment of textile dyeing wastewater.

Comparison between two Polyethersulfone concentrations in hollow fiber ultrafiltration membranes. Is it worth to use more polymer?

Polyethersulfone (PES) hollow fiber membranes were fabricated using dry-jet wet spinning technique, a phase inversion method, with 16 and 20% PES, N-methyl-2-pyrrolidone (NMP) as solvent and tap water as nonsolvent, in order to evaluate if the amount of polymer has a significant effect on its properties. They were characterized using SEM for a morphological analysis, a continuous system to measure pure water permeability (PWP) and molecular weight cutoff (MWCO), and a universal testing machine to tensile tests. The obtained results for PWP was an average of about 220 L m- ² h-1 bar-1 for the 16% PES membrane and 174 L m- ² h-1 bar-1 for the 20% PES membrane. The results of mechanical resistance and MWCO did not present statistical differences. Thus, it is confirmed that the 16% PES membrane can be as good as the 20%, despite using less polymer, a finding that can further motivate membrane modification studies and other related works.

Poly(ε-Caprolactone) Hollow Fiber Membranes for the Biofabrication of a Vascularized Human Liver Tissue.

The creation of a liver tissue that recapitulates the micro-architecture and functional complexity of a human organ is still one of the main challenges of liver tissue engineering. Here we report on the development of a 3D vascularized hepatic tissue based on biodegradable hollow fiber (HF) membranes of poly(ε-caprolactone) (PCL) that compartmentalize human hepatocytes on the external surface and between the fibers, and endothelial cells into the fiber lumen. To this purpose, PCL HF membranes were prepared by a dry-jet wet phase inversion spinning technique tailoring the operational parameters in order to obtain fibers with suitable properties. After characterization, the fibers were applied to generate a human vascularized hepatic unit by loading endothelial cells in their inner surface and hepatocytes on the external surface. The unit was connected to a perfusion system, and the morpho-functional behavior was evaluated. The results demonstrated the large integration of endothelial cells with the internal surface of individual PCL fibers forming vascular-like structures, and hepatocytes covered completely the external surface and the space between fibers. The perfused 3D hepatic unit retained its functional activity at high levels up to 18 days. This bottom-up tissue engineering approach represents a rational strategy to create relatively 3D vascularized tissues and organs.

Fabricating Fibers of a Porous-Polystyrene Shell and Particle-Loaded Core.

Polystyrene (PS) polymers have broad applications in protective packaging for food shipping, containers, lids, bottles, trays, tumblers, disposable cutlery and the making of models. Currently, most PS products, such as foams, are not accepted for recycling due to a low density in the porous structure. This poses a challenge for logistics as well as creating a lack of incentive to invest in high-value products. This study, however, demonstrated the use of a dry-jet wet-spinning technique to manufacture continuous PS fibers enabled by an in-house designed and developed spinning apparatus. The manufactured fibers showed porosity in the shell and the capability to load particles in their core, a structure with high potential use in environmentally relevant applications such as water treatment or CO2 collections. A two-phase liquid-state microstructure was first achieved via a co-axial spinneret. Following coagulation procedures and heat treatment, phase-separation-based selective dissolution successfully generated the porous-shell/particle-core fibers. The pore size and density were controlled by the porogen (i.e., PEG) concentrations and examined using scanning electron microscopy (SEM). Fiber formation dynamics were studied via rheology tests and gelation measurements. The shell components were characterized by tensile tests, thermogravimetric analysis, and differential scanning calorimetry for mechanical durability and thermal stability analyses.

The enhancement of mechanical properties of P84 hollow fiber membranes by thermally annealing below and above Tg

In this paper, BTDA-TDI/MDI (P84) co-polyimide hollow fiber membranes (HFMs) were prepared by dry-jet wet spinning technique. The P84 HFMs were thermally annealed below and above P84 Tg (321.5 °C) to investigate their mechanical and gas separation properties. Thermally annealing at different temperature below and above Tg influenced the tensile strength, Young's modulus and the elongation at break significantly. Compared with the pristine P84 HFMs, the tensile strength and Young's modulus of the thermally annealed P84 HFMs decreased slightly when the thermally annealing temperature was 180, 200 and 250 °C. However, the tensile strength of the thermally annealed P84 HFMs began to increase when the thermally annealing temperature approached to its Tg (such as 300 °C), which was induced by the increased molecular weight (Mw) and CTCs (charge transfer complexes) formation. Compared with the thermally annealed P84 HFMs below Tg, the HFMs' tensile strength, Young's modulus and the elongation at break increased greatly with thermally annealing above Tg, which was due to the obvious cross-linking reaction of P84. To further understand the effect of thermally annealing below and above Tg, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) with attenuated total reflection (ATR) mode, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), thermogravimetric-mass spectroscopy (TG-MS) measurements were explored.

Polysulfone mixed matrix hollow fiber membranes using zeolite templated carbon as a performance enhancement filler for gas separation

Zeolite-templated carbon (ZTC) was used as a new nanoporous filler to prepare mixed-matrix membranes (MMMs) with polysulfone as a continuous phase. The ZTC was prepared using a synthesized zeolite-Y template and sucrose carbon source via the impregnation method. The MMMs were fabricated through a dry-jet wet spinning technique, and the ZTC loadings were varied between 0.4–0.7wt%. The results showed that the integration of the ZTC did not change the microscopic structure of membranes. Additionally, the addition of filler did not affect the amorphous character of the polymer, while the polymer chain spacing slightly decreased. The thermal stability of MMMs improved with an increase in the glass transition temperature. The MMM at 0.4wt% loading exhibited the best separation performances as shown from the Robeson curve, with CH4, CO2, N2, O2, and H2 permeances of 5.9, 58.5, 5.0, 14.0, and 169.2 GPU, respectively. In addition, the improvements in CO2/CH4, O2/N2, H2/CH4, and CO2/N2 ideal selectivities were 290%, 117%, 272%, and 219%, respectively. On the other hand, the enhancement of the permeances and reduction in selectivities observed at 0.7wt% loading indicated that the existence of voids was a main factor in the permeation behavior of the MMMs.

An Important Factor Affecting the UV Aging Resistance of PBO Fiber Foped with Nano-TiO2: The Number of Amorphous Regions.

Modified nano-TiO2 was prepared by using triethanolamine and tetraisopropyl di (dioctylphosphate) titanate, respectively. Then the poly(p-phenylene benzobisoxazole) (PBO) fibers doped with different additions of modified nano-TiO2 particles were prepared by preparing PBO polymer solution and dry-jet wet spinning technique. Thermogravimetric and derivative thermogravimetry results showed that the addition of nano-TiO2 could improve the crystallinity and maximum thermal decomposition rate temperature of PBO fibers. Tensile strength results showed that nano-TiO2 addition did not affect the tensile properties of PBO fibers before ultraviolet (UV) aging began, and nano-TiO2 with addition values lower than 3% could improve the UV aging resistance performance of PBO fibers, while the aging resistance would be seriously reduced if values were over 5%. The size and quantity of the amorphous regions have a more important influence on the aging resistance of PBO fibers.

Improving the Transport and Antifouling Properties of Poly(vinyl chloride) Hollow-Fiber Ultrafiltration Membranes by Incorporating Silica Nanoparticles

Poly(vinyl chloride) (PVC)/SiO2 nanocomposite hollow-fiber membranes with different nano-SiO2 particle loadings (0–5 wt %) were fabricated using the dry-jet wet-spinning technique. Effects of SiO2 nanoparticles on the morphology of the prepared hollow-fiber membranes were investigated using scanning electron microscopy. Transport and antifouling properties of the fabricated membranes were evaluated by conducting pure-water permeation, solute rejection, and fouling resistance experiments. These studies indicated that incorporating silica nanoparticles into the PVC matrix during phase inversion lowers the hydraulic resistance through the membrane and narrows the selective membrane pores. Moreover, the nanocomposite membranes showed better antifouling properties compared to the pristine membrane during the ultrafiltration of a milk solution because of improved hydrophilicity and uniform dispersion of the nanoparticles. This work indicates that embedding silica nanoparticles into the PVC matrix is a promising method for producing cost-effective hollow-fiber ultrafiltration membranes with superior transport and antifouling properties.

A Pathway to Fabricate Hollow Fiber Membranes with Isoporous Inner Surface

A novel inside isoporous hollow fiber membrane is prepared using the dry-jet wet spinning technique. Subsequently, the self-assembly of block copolymer in combination with nonsolvent-induced phase separation takes place in the lumen side of the spun hollow fibers with a diameter of less than 1 mm leading to technologically favored inside membranes for water purification.

PBI-HFA Hollow Fiber Membrane for Selective Hydrogen Separation

We demonstrated for the development of PBI-HFA based asymmetric hollow fiber membrane for hydrogen separation. High molecular weight PBI-HFA was synthesized in-house by a solution polycondensation method [1]. Hollow fiber membranes were fabricated by conventional dry-jet wet spinning technique. Defect free asymmetric PBI-HFA hollow fiber membranes were successfully produced, which influenced of PBI-HFA concentration and LiCl as shown in Fig. 1. The effect of bore fluid chemistry was found to have a significant effect on the morphology as well as gas performance of the hollow fiber membranes. Development of PBI-HFA hollow fiber membranes with improved gas permeation properties their known excellent thermal and chemical properties depicts their potential for gas separation applications at harsh environment. As shown in Fig. 2, PBI-HFA hollow fiber showed good gas flux and selectivities for industrially important gas pairs such as H2/CO, H2/N2 with the ideal selectivities of 35.7 and 43.4, respectively, while the permeation fluxes of H2, N2, CO2 and CO were at 664, 15.3, 263.37 and 18.6 GPU at 1bar as given in Table. 1. Mixed gas results as given in Table. 2 discussed above indicate that PBI-HFA hollow fiber is an excellent H2 selective membrane material for syngas separations. This improvement in gas selectivities was attributed to their increased closer chain packing by high solubility. Pressure P (H2) a P(N2) a P(CO2) a P(CO) a 1bar 664 15.3 263.37 18.6 43.4 2.52 35.70 17.21 2bar 1219 31.02 471.26 35.82 39.3 2.59 34.03 15.19 3bar 1783 46.61 691.78 54.13 38.25 2.58 32.94 14.84 4bar 2353 63.58 978.76 71.83 37.13 2.4 32.76 15.44 a Expressed as permeance in GPU (1 GPU = 1´10-6cm3(STP) cm-2s-1 cmHg-1). Table 1. Gas separation performance of PDMS coated PBI hollow fiber at normalized temperature. (H2)% (N2)% (CO2)% (CO)% Mixture gas composition 51.53 21.2 7.63 17.86 1 bar 89.6 0 3.05 0.33 2bar 84.19 0 2.49 7.99 3bar 65 3.7 6.49 23.5 Table 2. Mixture Gas separation performance of PDMS coated PBI hollow fiber membrane at 21℃, 100℃, and 200℃ temperature [1] S. Kumbharkar, M. N. Islam, R. Potrekar, and U. Kharul, "Variation in acid moiety of polybenzimidazoles: investigation of physico-chemical properties towards their applicability as proton exchange and gas separation membrane materials," Polymer, vol. 50, pp. 1403-1413, 2009. Figure 1

Removal of bisphenol A by adsorption mechanism using PES–SiO2 composite membranes

ABSTRACTPolyethersulphone (PES) membranes blended with silicon dioxide (SiO2) nanoparticles were prepared via a dry-jet wet spinning technique for the removal of bisphenol A (BPA) by adsorption mechanism. The morphology of SiO2 nanoparticles was analysed using a transmission electron microscopy and particle size distribution was also analysed. The prepared membranes were characterized by several techniques including field emission scanning electron microscopy, Fourier transform infrared spectroscopy and water contact angle. The adsorption mechanism of membrane towards BPA was evaluated by batch experiments and kinetic model. The influence of natural organic matter (NOM) in feed water on membrane BPA removal was also studied by filtration experiments. Results showed that BPA adsorption capacity as high as 53 µg/g could be achieved by the PES membrane incorporated with 2 wt% SiO2 in which the adsorption mechanism was in accordance with the pseudo-second-order kinetic model. The intraparticles diffusion model suggested that the rate limiting factor of membrane adsorption mechanism is governed by the diffusion of BPA into the membrane pores. The presence of 10 ppm NOM has reported to negatively reduce BPA removal by 24%, as it tended to compete with BPA for membrane adsorption. This work has demonstrated that PES–SiO2 membrane has the potential to eliminate trace amount of BPA from water source containing NOM.

Simulation on contraction flow of concentrated cellulose/1-butyl-3-methylimidazolium chloride solution through spinneret orifice

Concentrated cellulose/1-butyl-3-methylimidazolium chloride ([bmim]Cl) solution which exhibits typical elasticity has been employed to prepare fibres by dry jet wet spinning technique. In order to design the spinneret, simulation on contraction flow of cellulose/[bmim]Cl solution through spinneret orifice was carried out. Geometry and mathematical models were established according to rheological behaviour and material parameters. The effects of geometry on variation of viscosity and flow pattern were simulated and discussed. The results show that an increase in aspect ratio decreased the apparent viscosity and a decrease in entrance angle reduced the size of ‘dead’ region. The aspect ratio and entrance angle of spinneret during dry jet wet spinning were optimised.

Enhancing antibacterial performances of PVDF hollow fibers by embedding Ag-loaded zeolites on the membrane outer layer via co-extruding technique

Ag-loaded zeolites were synthesized and embedded into the outer layer of poly(vinylidene fluoride) (PVDF) dual-layer hollow fiber membrane (D) using a dry-jet wet-spinning co-extruding technique. The distribution of the Ag-loaded zeolites in the outer layer was confirmed by field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX). It was found that the D contained only 54% of the amount of Ag-loaded zeolites that were distributed throughout the cross section of PVDF single-layer hollow fiber membrane (S), as calculated by thermogravimetric analysis (TGA). However, D showed excellent antibacterial efficiency and resistance to bacterial adhesion because of the higher concentration of Ag+ in the outer layer of the membrane. The surface morphologies, pure water flux, mean pore size, pore size distribution, and thermal stability of both PVDF membranes were also investigated. (C) 2014 Elsevier Ltd. All rights reserved.

Interfacial morphology between the two layers of the dual-layer asymmetric hollow fiber membranes fabricated by co-extrusion and dry-jet wet-spinning phase-inversion techniques

The dual-layer asymmetric hollow fiber membranes were fabricated with Matrimid® 5218 as the functional material by using co-extrusion and dry-jet wet-spinning phase-inversion techniques. Different polymers polysulfone (PSf), polyethersulfone (PES) and polyetherimide (PEI), were used as support materials. Different organic solvents N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and dimethylformamide (DMF) were used as solvents in the inner layer spinning dopes. The precipitation order of the two layers was estimated from the cloud point curves for the respective systems. The purpose of this paper was to give out a method to control the interface structure of the dual-layer asymmetric hollow fiber membranes. The experimental result shows that if the inner spinning dope demixes prior to the outer spinning dope, dense skin will form both on the outer surfaces of the two layers, while if the outer spinning dope demixes prior to the inner spinning dope, the dense skin on the outer surface of the outer layer will prevent the formation of the dense skin on the outer surface of the inner layer. The skin morphology investigated by scanning electron microscopy (SEM) proves this result. The double dense skin structure of membranes increases the mass transfer resistance and decreases the gas permeance.