Dry-jet Wet Spinning Process Research Articles

Dual-Charged Hollow Fiber Membranes for Low-Pressure Nanofiltration Based on Polyelectrolyte Complexes: One-Step Fabrication with Tailored Functionalities.

A new nanofiltration (NF) hollow fiber membrane is developed by using two oppositely charged polyelectrolytes coagulating into a polyelectrolyte complex (PEC) onto polyether sulfone base polymer. The particular membrane architecture emerges during a single-step procedure, allowing setting both the porous negatively charged support of the hollow fiber and the separation layer containing also the positive polyelectrolyte (PEI/PDADMAC) through a single layer dry-jet wet spinning process. The novelty is two-pronged: the composition of the hollow fiber membrane itself and its fabrication procedure (one-step fabrication of membranes employing polyelectrolytes). These result in highly permeable hollow fiber membranes with a stable separation layer and performance at par with the membranes reported in literature obtained by multistep processes. More importantly, the membranes are obtained through a simple, very fast (one-step), and less expensive procedure. The best performance among these newly obtained hollow-fiber membranes is achieved by PD5% hollow fiber (MWCO of 300 Da), which showed 7.6 L/m(2)·h·bar permeability and ∼90% rejection of MgCl2, MgSO4, and Na2SO4 at 2 bar pressure. Thus, the resulting membranes not only have the advantages of the hollow-fiber configuration, but perform very well at extremely low pressures (the lowest reported in the literature). The broad impact of the results presented in this Article lies in the potential to dramatically reduce both the fabrication (duration and complexity) and the price and desalination costs of highly performing NF hollow fiber membranes. These might result in interesting potential applications and open new directions toward designing efficient functional NF hollow fibers for water desalination.

Rheological behavior of poly(acrylonitrile) concentrated solutions: effect of Sb2O3 nanoparticles on shear and extensional flow

This study investigates the effect of antimony trioxide (Sb2O3) nanoparticles on shear and extensional flow properties of concentrated polyacrylonitrile (PAN) solutions. Through shear rheology, a wide variety of rheological observations, such as Payne effect, applicability of Cox–Merz rule, and range of linear viscoelastic behavior (critical strain) were assessed. The presence of Sb2O3 nanoparticles was found to promote the non-linear viscoelasticity of the solutions and give rise to enhanced heterogeneous domains of PAN in the solution. In elongational flow, thinning dynamics of the nanocomposites was tracked to reproduce the dynamics of deformation in the spinline of the dry-jet wet spinning process. Increasing amounts of Sb2O3 nanoparticles in the solution were shown to improve the lifetime of the filament. All solutions were ruptured through elastocapillary behavior, while strengthened strain-hardening behavior was observed after the addition of Sb2O3 nanoparticles to the polymer solution.

The formation of polysulfone hollow fiber membranes by the free fall spinning method

The basic principles of the spinning of polysulfone hollow fiber membranes by the dry-jet wet spinning process, where the polymer solution is extruded through an air gap between the spinneret and coagulation bath by the free fall spinning method, have been discussed. The main distinctive feature of the method is that the deformation of both the extruded polymer solution and the nascent hollow fiber (spinneret drawing) is due to the action of the gravity force alone without applying an external tensile force. Published data on the effect of the shear rate of the spinning solution at the spinneret outlet and nascent fiber drawing in the air gap on the structure and permeability of the hollow fiber membranes have been analyzed. The main factors affecting the spinneret drawing and dimensions of the hollow fiber membranes formed by free fall spinning have been experimentally revealed using polysulfones of different molecular weights. The factors are the dope composition, approaching ratio and viscosity, the air gap length, the temperature and the feed rate of the dope and the bore fluid, coagulation power of the bore fluid with respect to the dope. It has been found that as the spinneret draw value increases, the hydraulic permeability and the rejection coefficient of the resulting fiber generally change in a nonmonotonic manner: the pure water flux of the hollow fibers passes through a maximum and the rejection coefficient, through a maximum or minimum. The behavior is caused by the fact that the pore structure of the hollow fiber membranes is formed during uniaxial drawing and, in some cases (at increasing bore liquid flow rate), during biaxial deformation. When an external mechanical force is applied to the forming hollow fiber, an increase in the fraction of interconnected pores and the transition from cylindrical to slitlike pores are possible, which results in an increase in the hydraulic permeability of the fiber walls. A further increase in the spinneret draw ratio results in the reverse process, a decrease in the membrane matrix porosity due to the orientation and collapse of the pores, yielding a decrease in the flux and an increase in the rejection coefficient. By blocking the process of hollow fiber shrinkage through an increase in the bore fluid flow rate (increasing the internal diameter of the hollow fiber), it is possible to enhance the effective porosity of the fiber walls without substantial change in pore size, i.e., a transition from a system with isolated or partly isolated pores to a system of interconnected pores. A sharp increase in the hydraulic permeability of the hollow fiber membranes without a substantial change in their rejection is supposedly caused by this structural change.

Versatile Molding Process for Tough Cellulose Hydrogel Materials.

Shape-persistent and tough cellulose hydrogels were fabricated by a stepwise solvent exchange from a homogeneous ionic liquid solution of cellulose exposure to methanol vapor. The cellulose hydrogels maintain their shapes under changing temperature, pH, and solvents. The micrometer-scale patterns on the mold were precisely transferred onto the surface of cellulose hydrogels. We also succeeded in the spinning of cellulose hydrogel fibers through a dry jet-wet spinning process. The mechanical property of regenerated cellulose fibers improved by the drawing of cellulose hydrogel fibers during the spinning process. This approach for the fabrication of tough cellulose hydrogels is a major advance in the fabrication of cellulose-based structures with defined shapes.

Morphology and performance changes of aromatic polysulphonamide fibres formed by dry-jet wet spinning process

Aromatic polysulphonamides fibre, as a high-performance polymer fibre, was prepared by dry-jet wet spinning. The morphology and properties of polysulphonamides fibre along spinning line during dry-jet wet spinning process were investigated. From the development of mechanical and thermal property, it is shown that the fibre showed an improved stress, modulus and density along spinning line and the remarkable improvement was observed only as the fibre was hot stretched above its glass transition temperature (Tg). The property development of the fibre on spinning line is coordinated with the morphology and structure. When the fibre was drawn at the temperature lower than Tg, only the amorphous orientation was observed whereas the crystalline structure was formed as the fibre drawing temperature higher than Tg. The further optimisation of dry-jet wet spinning technology of polysulphonamides fibre could be supported by our results.

Preparation and Performance Evaluation of Polyethersulfone Hollow Fiber Membranes for Ultrafiltration Processes

In this article, polyethersulfone hollow fiber membranes were prepared using dry–jet–wet spinning process via phase inversion method. Effects of polyethersulfone and polyethylene glycol concentrations and coagulation bath temperature, air–gap distance, and take-up speed on morphology of the prepared membranes were investigated. Based on L16 orthogonal array of Taguchi experimental design, 32 membranes were prepared. An experimental investigation on separation of the industrial oil from oily wastewater has been done. The results showed that synthesized polyethersulfone membranes was effective and suitable for the treatment of oily wastewater to achieve up to 66.6 and 95.0% removal of total organic carbon and oil–grease content, respectively, with a flux of 72.3 L/(m2h).

Dynamic modeling of dry-jet wet spinning of cellulose/[BMIM]Cl solution: complete deformation in the air-gap region

During the dry-jet wet spinning process of cellulose solutions with 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as solvent, the special viscoelastic characteristics of the solution lead to a large air-gap distance where the extruded flow can extend completely before entering the coagulation bath. Therefore, online measurement of diameter and temperature can be carried out and the velocity on the spinning line determined reasonably. Therefore, a model of dry-jet wet spinning is proposed to simulate the extrusion and extending dynamics of cellulose/[BMIM]Cl solutions in the air-gap region with complete deformation. Material parameters such as the density and heat capacity were determined by experiment, and the heat transfer coefficient along the spin-line was evaluated by an inversion procedure involving online experimental data for temperature and diameter. A two-dimensional (2-D) approach in POLYFLOW was adopted to compute the dynamic parameters along both the axial and radial directions of the spinning line. The numerical results were verified by comparison with experimental data including temperature and diameter. It was found that the contraction flow in the spinneret orifice could not be neglected and use of a nonisothermal viscoelastic model in the constitutive equation gave better agreement between simulation and experiment.

A slow–fast phase separation (SFPS) process to fabricate dual-layer hollow fiber substrates for thin-film composite (TFC) organic solvent nanofiltration (OSN) membranes

A novel slow–fast phase separation (SFPS) process is proposed to fabricate the desirable ultrafiltration dual-layer hollow fiber substrate for effective interfacial polymerization. By controlling the ratios of non-solvents to volatile co-solvents in both the outer- and inner-layer dopes, the outer and inner layers undergo slow and fast coagulation, respectively, in the dry-jet wet-spinning co-extrusion process. The inner layer is highly porous for high solvent flux permeation, while the outer layer possesses a surface with nano-sized pores that have a sharp size distribution for effective thin film polymerization. The addition of polyvinylpyrrolidone in the outer dope further reduces the pore size, and enhances surface hydrophilicity as well as mechanical strength. The substrate was cross-linked and subjected to interfacial polymerization for fabricating thin-film composite (TFC) membranes. The effects of the substrate properties of various hollow fiber membranes from the SFPS process on the TFC membrane were systematically investigated in terms of morphology and organic solvent nanofiltration (OSN) performance. The membrane shows a 99.3% rejection of ramazol brilliant blue (MW: 626.54gmol−1) and a methanol flux of 14.4lm−2h−1 at 16bar.

Study on the chain entanglement of polyvinyl alcohol fiber during the dry-jet wet spinning process

The entanglement structure of polyvinyl alcohol (PVA) fiber during the dry-jet wet spinning process is studied in this article. The morphological changes of PVA fiber in swelling agent are observed under optical polarizing thermomicroscope, and the entanglement changes of PVA fiber during the spinning process are investigated using swelling DSC method. A specific mixture consisting of a good solvent (DMSO) and a poor solvent (EG) is used as the swelling agent for PVA. Results show that the entanglement structure of PVA fiber would disentangle after the crystalline phase is destroyed in the swelling agent during heating, and the entanglement structure of PVA fiber is greatly dependent on the spinning technological parameters such as spinning dope concentration, jet stretch ratio, extruding shear stress and draw ratio of the whole spinning process. When the spinning dope and spinning technological parameters are controlled properly, the entanglement structure in the PVA fiber can be greatly reduced and PVA fiber with a 17.5 cN/dtex tensile strength can be obtained.

Preparation and Characteristics of Novel Fibers Based on Cellulose Acetate and Soy Lecithin for Attracting and Binding POPs

Soy lecithin (SL)-modified cellulose acetate (L-CA) fibers for use as a novel biomimic material were prepared by a dry-jet wet spinning process from a solution of the polymer in dioxin. Characteristics of the L-CA fibers, such as structural properties, water absorbance, electrical conductivity and accumulation of trace persistent organic pollutants (POPs), were examined. Cross-sectional scanning electron microscopy (SEM) of L-CA unveiled a finger-like structure, along with a thin dense surface layer like that of CA. On the basis of X-ray photoelectron spectroscopic (XPS) observations, it was concluded that the enhancement of binding energy was optimum with 10% SL in the fiber, whereas superfluous SL led to self-assembly between the SL molecules, which weakened the binding between the SL and CA. Also, the L-CA fibers showed good water absorbance and a low charge conductivity in comparison to that of the non-modified CA fibers. Examination of the ability to accumulate POPs from water showed that L-CA is a effective candidate for the removal of micropollutants from aqueous solution.

Asymmetric polyethersulfone ultrafiltration membranes for oily wastewater treatment: Synthesis, characterization, ANFIS modeling, and performance

Oily wastewater in Tehran Oil Refining Company has become a big issue of water and environment pollution to be solved urgently. In this research, polyethersulfone ultrafiltration hollow fiber membranes were prepared via phase inversion induced by dry-jet wet spinning process. The membranes were characterized by water contact measurements, SEM analysis, filtration measurements (flux and fouling). In this work, the results of an experimental study on separation of oil from oily wastewaters are presented. To do these experiments, the outlet wastewater of the API unit of Tehran Refining was used as the feed. The results demonstrated that the prepared polyethersulfone hollow fiber membranes are effective in removing chemical oxygen demand (COD), total organic carbon (TOC), turbidity, total suspended solids (TSS), and oil and grease content (OGC). The results showed that the prepared polyethersulfone hollow fiber membranes exhibit COD, TOC, and OGC removals of about 83.1%, 96.3%, and 99.7%, and final flux and fouling of about 84.1L/(m2h) and 63.0%, respectively. Comparison of results of this method showed that quality of the finally treated outlet water is high and even better than standard water that are currently introduced to cooling towers. Moreover, this paper explores the application of the ANFIS as a model to predict permeation flux in UF process. The selected experimental data were trained by a hybrid learning algorithm combining the forward pass and the backward pass. The good agreement of the model with experimental data underscores the ease and accuracy of the ANFIS in modeling such a complex systems.

The effect of bore fluid type on performance of treated polysulfone hollow-fiber membrane

In this work, atomic force microscopy (AFM) analysis and application of the image processing technique on scanning electron microscope microphotographs were employed to investigate the performance of polysulfone (PSf) hollow-fiber membranes treated with hypochlorite and hot water in relation to composition of bore fluid used during spinning of hollow-fiber membranes. Fiber spinning dope containing PSf/poly vinyl pyrrolidone/ N-methyl-2-pyrrolidone (NMP) in a mass ratio of 15/5/80 were used for production of two types of hollow fibers via the dry-jet wet spinning process. A mixture of NMP and water in a 1/1 ratio, as well as distilled water alone, were used as bore fluids. The membranes were treated using 95℃ water and sodium hypochlorite 4% (w/v). Structurally superior membranes were produced with the mixed bore fluid. In addition, these membranes exhibited higher permeation in comparison to membranes made using other bore fluid. Hypochlorite treatment resulted in an increase in surface roughness of the membranes, and was found to be also responsible for the increase in the average membrane pore size and water flux. The hypochlorite-treated membrane produced using NMP/water as bore fluid exhibited a higher rate of flux than those produced using distilled water. It was also found that treatment with 95℃ water affected both type of membranes. However, the effect of this treatment on the membrane produced with mixed bore fluid was more pronounced. Linear regression was used to establish the correlations between mean surface roughness parameters and hydraulic permeability. AFM analysis strongly supported the consistency of the measured values of water flux.

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.

Novel method for treatment of hollow fiber membranes using hypochlorite

A novel hypochlorite treatment method that enhances hydraulic permeability of hollow fiber membranes used in ultra-filtration was successfully devised and tested. Dope containing polysulfone/poly vinyl pyrrolidon (PVP-K90)/N-methyl-2-pyrrolidone (NMP) in mass ratio of 15:5:80, respectively, were used to produce hollow fibers via dry-jet wet spinning process. NMP in 1:1 ratio and distilled water were used as bore fluid. Hollow fiber membrane samples were post-treated using the novel, 95°C water and traditional hypochlorite treatments. State of membranes before and after post-treatment were morphologically compared using SEM microphotographs of fiber cross-section in conjuncton with image proceesing techniques. It was observed that in general both the novel and the traditional methods results in elimination of PVP swelling alone with alteration of pore size and pore distribution. This was confirmed by an increase in water flux of the hollow fibers that were subjected to these two post-treatment methods. Atomic force microscopy analysis vividly pointed to an intense increase in the roughness of the inner and outer surfaces of the membranes. This was attributed to the effect of post-treatment methods. It was found that in general post-treatments involving hypochlorite, increases the surface roughness of the membranes. However, increase in rate of the roughness of inner surface of traditionally hypochlorite treated hollow fiber membrane was found to be much higher than those subjected to the novel treatment method. It was established that the developed novel hypochlorite treatment method can be successfully used for production of high permeable hollow fiber membranes which have vast potential in therapeutic applications.

Effect of draw ratio on the morphologies and properties of BPDA/PMDA/ODA polyimide fibers

3,3,4,4-Biphenyltetracarboxylic dianhydride/pyromellitic dianhydride/4,4-oxydianiline(BPDA/PMDA/ ODA) polyimide copolymer fibers with different draw ratios were prepared from the imidization of polyacrylic acid(PAA) fibers via a dry-jet wet-spinning process. Their morphologies, microcrystal orientations, thermal stabilities, and mechanical properties were investigated via scanning electron microscopy(SEM), wide angle X-ray diffraction( WAXD), thermogravimetric analysis(TGA), and tensile experiments. In order to acquire fibers with better mechanical performance, we aimed at obtaining the optimal draw ratio. Drawing during thermal imidization resulted in a decreased diameter of fiber from 25.8 μm to 16.9 μm corresponding to draw ratio from 1 to 3.5. WAXD results show that the degree of the orientation of the undrawn sample is 64.1%, whereas that of the drawn sample is up to 82%. The as-spun fiber and those with different draw ratios all exhibit high thermal stabilities, i.e., the temperature at a mass loss of 5% can reach as high as 570 °C. The tensile strengths and tensile modulus of the fibers increase with the draw ratios, and the maximum tensile strength and modulus are 0.90 and 12.61 GPa, respectively.

Properties, morphology and structure of BPDA/PPD/ODA polyimide fibres

A family of random co-poly(amic acid)s containing 4,4′-oxydianiline (ODA) moiety were synthesised in N,N′-dimethylacetamide. The co-poly(amic acid) solutions were used as spinning dope for dry jet wet spinning process into as spun poly(amic acid) (PAA) fibres. The polyimide (PI) fibres were obtained from PAA fibres after being imidised and drawn in furnace. The processability and mechanical properties of the fibres were notably improved by incorporating ODA into 3,3′,4,4′-biphenyltetracarboxylic dianhydride/p-phenylenediamine (BPDA/PPD) backbone. The best strength and modulus of BPDA/PPD/ODA PI fibre (diamine mole ratio of PPD/ODA = 85∶15) attained 2·25 and 96·5 GPa respectively, which were approximately three times the tenacity of the BPDA/PPD PI fibre. The SEM image showed that the cross-section of each stage fibres was round and void free. In addition, ‘skin–core’ and microfibrillar structure were not observed. The thermal properties of PI fibres were also investigated. The results showed that the PI fibres have excellent thermal stability; moreover, the dimensional stability and structural homogeneity of the fibres were significantly improved by heat drawn stage. Tg was found to be ∼290°C by thermomechanical and dynamic mechanical analyses. The X-ray (wide angle X-ray diffraction and small angle X-ray scattering) experiments indicated that the ordering degree of longitudinal and lateral stacks, as well as the molecular orientation of PI fibre, was improved in the preparation process of fibres. Furthermore, the mechanical properties of fibres are profoundly affected by the heat drawn conditions.

An investigation of polymer dope and heating effects on hollow fiber membranes

Hollow fiber membranes were made from two different dope solutions by using a dry-jet wet spinning process. One dope solution contains cellulose acetate (CA)/N-methyl-2-pyrrolidone (NMP) with a mass ratio of 20/80 and the other contains polysulfone (PS)/NMP with a mass ratio of 15/85. The hollow fiber membranes were heated in a water bath to investigate the effect of heat treatment. It was found that for the CA membranes, the pore size shrank due to the heat treatment as there was a decrease in permeation and an increase in protein rejection. The most dramatic change for the CA membranes occurred after being heated to 95°C, which resulted in an increase in bovine serum albumin (BSA) rejection to 99% while the permeation decreased to 39 L h−1 m−2 bar−1. This is due to heating above the glass transition temperature (67–68°C) for CA. For the PS membranes, the pore size remained unchanged throughout the two heat treatments as the glass transition temperature is 185°C. The PS membranes did however have a smaller pore size to begin with as is evident by the ##xgt;99% rejection of BSA. The permeation declined more rapidly for the PS membranes compared to the CA membranes due to the more hydrophobic nature of the polymer.

Regenerated Bamboo Fiber from Green Solvent

Regenerated bamboo fiber was prepared with green solvent. The rheological behavior of the spinning solution was investigated and a dry-jet wet spinning process was applied for making bamboo fiber. The results showed that spinning solution belonged to the typical shear thinning fluid, and it is found that the content had influence on the apparent viscosity of solution. In addition, the regenerated bamboo fiber had cellulose II crystal structure. and the orientation and crystallinity of fiber increased with the increasing of draw ratio, thereby the mechanical properties of fiber improved.

Fabrication of catalytic membrane contactors based on polyoxometalates and polyvinylidene fluoride intended for degrading phenol in wastewater under mild conditions

A novel catalytic membrane contactor (CMC) has been designed and constructed by incorporating polyoxometalates (POMs) onto polymeric polyvinylidene fluoride (PVDF) micro-porous hollow fiber membranes which were fabricated by a dry–jet wet spinning process. A simple chemical deposition method was utilized to anchor the Keggin-type polyoxometalate H5[PV2Mo10O40] (PV2Mo10) on the outer surface of the PVDF hollow fiber, which was confirmed by the measurements of field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). The degradation of phenol in synthetic wastewater was carried out using air as green oxidant under room conditions using the CMC. A gas-catalyst-liquid interface was successfully built up to enhance the catalytic efficiency. It was observed that the pressure of the gas flow played an important role and a low pressure is preferable. The long-term stability of the CMC was also preliminarily studied. This novel and facile CMC with PV2Mo10 as catalyst potentially provides a feasible pathway for wastewater treatment under mild conditions.

The effects of substrate characteristics and pre-wetting agents on PAN–PDMS composite hollow fiber membranes for CO2/N2 and O2/N2 separation

In order to develop high performance poly(dimethylsiloxane)-polyacrylonitrile (PDMS/PAN) hollow fiber composite membranes for the separation of CO2/N2 and O2/N2 gas pairs, we have investigated: (1) the viscosity of PDMS solutions as a function of curing conditions; (2) pore size and pore size distribution of the PAN substrates as a function of spinning conditions and post-treatments and (3) the effects of pre-wetting agents, substrate morphology and PDMS concentration on the gas performance of the selective layer. Based on their complicated relationship, fundamental science and engineering have been elucidated to fabricate PDMS/PAN hollow fiber composite membranes with CO2, N2 and O2 permeances of 3700, 370 and 860GPU and selectivities of 10 and 2.2 for CO2/N2 and O2/N2 gas pairs at 25°C and 2atm, respectively. This O2/N2 separation performance is comparable with the best ever reported results for O2 enrichment. The PAN hollow fibers were prepared by a dry-jet wet spinning process and subsequently coated with PDMS by dip-coating. To increase gas permeance, experimental results show that, in addition to keeping substrate pores open, partially crosslinking PDMS and pre-wetting the PAN substrates by Fluorinert 72 (FC-72) or deionized water before dip coating in order to prevent intrusion are important. This study may provide insights and guidelines to fabricate highly permeable membranes in the industry for O2 enrichment, flue gas separation and CO2 capture.