Wet Phase Inversion Process Research Articles

On the difference of composite membranes from polyvinyl alcohol- Butene dioic acid(cis/trans) onto polysulfone

While many composite membranes have been explored using phase inversion and coatings, few are there apart from the polyamide. In this present study, asymmetric polysulfone (PS) membranes were prepared by a wet phase inversion process and crosslinking mechanistic pathways to provide facile formation of coating materials suitable for filtration. Poly(vinyl alcohol) (PVA)-coated on polysulfone membranes were crosslinked using Butene dioic acid(cis/trans) (viz. maleic(MA) and fumaric(FA)acid). The membrane properties (viz. hydrophilicity, roughness, zeta potential) differed due to conformational differences between the two crosslinkers. PS-PVA(MA) membranes showed better salt separation abilities compared to PS-PVA(FA) membranes. The selective bivalent (SO42-) salt separation abilities were observed compared to monovalent (Cl-) ones. PS-PVA(FA) membranes showed a better separation ratio(2.77) of bivalent and monovalent ions (RSO42-/ RCl-) compared to PS-PVA(MA) membranes(2.7) for water matrix-1(TDS 5.4). The defluoridation capabilities were also experimented. PS-PVA(MA) membranes showed a 3% better rejection ability compared to PS-PVA(FA) membranes. PS- PVA(MA) membranes developed a low bacterial settlement tendency compared to PS- PVA(FA) membranes.

Membrane Unit for Integrated Gas Separation – Membrane Bioreactor (GS-MBR) System

One of the research directions of renewable energy sources is the production of biohydrogen from the dark fermentation of organic matter. During this fermentation process, since hydrogen is produced along with a complex mixture of other gases and vapors, hydrogen gas requires further purification. One relatively easy solution to this problem might be the utilization of gas separation membrane modules given their low energy consumption, simple operation and ease of upscaling. In this work, hollow fiber (HF) membranes based on polyetherimide (PEI) were developed and tested. HF membranes were spun from a polymer solution of PEI using the wet phase inversion process into a water bath using a pilot-scale spinning device. Gas transport measurements showed that membranes exhibited permeances of between 9.3 and 19.2 GPU with CO2/H2 selectivities within the range of 3.3 - 5.6. Morphology studies showed regular shapes resembling hollow fibers with outer diameters within the range of 250-320 microns, depending on various parameters of the spinning process. The best performing membranes were selected and a morphological analysis carried out. Selected fibers were incorporated into two types of membrane modules. One type was a laboratory-scale membrane mini-module used for preliminary tests, while the other membrane module was designed for the treatment of larger amounts of biohydrogen. Two types of laboratory-scale membrane separation units were constructed. For laboratory use, the low-pressure unit proved more accurate regulation to match the fermenters performance with the separation unit in comparison with the high-pressure one.

Low porosity, high areal-capacity Prussian blue analogue electrodes enhance salt removal and thermodynamic efficiency in symmetric Faradaic deionization with automated fluid control

Prussian blue analogues (PBAs) show great potential for low-energy Faradaic deionization (FDI) with reversible Na-ion capacity approaching 5 M in the solid-state. However, past continuous-flow demonstrations using PBAs in FDI were unable to desalinate brackish water to potable levels using single-pass architectures. Here, we show that recirculation of effluent from a symmetric cation intercalation desalination cell into brine/diluate reservoirs enables salt removal exceeding 80% at thermodynamic efficiency as high as 80% when cycled with 100 mM NaCl influent and when controlled by a low-volume, automated fluid circuit. This exceptional performance is achieved using a novel heated, alkaline wet phase inversion process that modulates colloidal forces to increase carbon black aggregation within electrode slurries to solidify crack-free, high areal-capacity PBA electrodes that are calendered to minimize cell impedance and electrode porosity. The results obtained demonstrate the need for co-design of auxiliary fluid-control systems together with electrode materials to advance FDI beyond brackish salinity.

Enhanced permeability and antifouling performance of polyether sulfone (PES) membrane via elevating magnetic Ni@MXene nanoparticles to upper layer in phase inversion process

In this study, magnetic Ni@MXene nanoparticles were firstly developed and then elevated to the upper layer of polyether sulfone (PES) membrane by an external magnetic field during the wet phase inversion process. Flux of the prepared PES-Ni@MXene membrane was 2.5 times of that of the control PES membrane. Moreover, PES-Ni@MXene membranes showed a significant promotion of antifouling ability, evidenced by the flux recovery rates (FRR) of 64.6% and 99.8% for bovine serum albumin (BSA) and humic acid (HA) solutions, respectively. The antifouling performance of the PES-Ni@MXene membrane was comparable or better than those in the literature studies. Meanwhile, the optimal PES-Ni@MXene membrane possessed an efficient decoloration ability for Congo red (CR) solution and colored emulsion. To analyze the anti-fouling mechanism, the interaction energies between the membrane surface and pollutants (BSA and HA) were computed via the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The results showed that the total attraction energy between PES-Ni@MXene membrane and pollutant interface was smaller than that between the control PES membrane and pollutant interface. This study provided a new incentive to development of high-efficient Mxene-based membranes.

Hybrid Beads Bearing Immobilized Bacteria as Advanced Means for the Removal of Acid Blue 93 Dye

This paper describes the preparation of three- component hybrid copolymer beads, with water purification features. These newly developed hybrid beads were prepared starting from a mixture of poly(acrylonitrile- co- methacrylic acid) (PAN-co-PMAA), polyvinyl alcohol (PVA) and magnetite (Fe3O4), respectively. The preparation itself involved a Wet Phase Inversion (WPI) process. A Pseudomonas sp. strain was immobilized onto previously mentioned beads, before and after activation of the beads surface with glutardialdehyde, and afterwards used for the amendment of simulated water bearing an azo- blue dye, i.e. Acid Blue 93. In order to highlight the immobilization of Pseudomonas sp. strain, FTIR spectra and TGA results were recorded. CFU measurements as well as SEM images further provided evidence towards the occurrence of immobilization. The biodegradation studies of Acid Blue 93were carried out by means of UV spectroscopy at various contact times (24; 72 and 144 h) of the hybrid beads with the targeted dye.

An Experimental Study PVDF and PSF Hollow Fiber Membranes for Chemical Absorption Carbon Dioxide

Poly (vinylidene fluoride) (PVDF) and poly-sulfone (PSF) polymer solutions were made at a concentration of 18% by weight of the polymer as a non-soluble additive of polymer solution in 1-methyl-2-pyrrolidone (NMP) solvent. PVDF and PSF hollow fiber membranes were fabricated via the wet phase-inversion process. Fabricated membranes were characterized in terms of gas permeability, wetting resistance, water contact angle and overall porosity. In order to study the structure of the membranes made, the scanning electron microscopy images of the model (TM3000, HITACHI, Japan) were used. The morphology study indicates that the PSF membrane shows an open cross-section structure with smaller pore sizes. However, the PVDF membrane illustrates a thick sponge-like structure. The fabricated PVDF membrane shows higher wetting resistance, surface porosity, water contact angle, and N2 permeability. The performance of the produced membranes was examined for the Absorption of carbon dioxide in a gas-liquid contactor membrane through the solution of mono-ethanolamine (MEA). The results show that CO2 absorption flux of the PVDF hollow fiber membrane is higher than PSF hollow fiber membrane. The maximum CO2 absorption flux of 8.10 × 10-3 (mole/m2 s) at the liquid phase flow rate of 300 ml/min for PVDF hollow fiber membrane was achieved and also the maximum CO2 absorption flux of 6.50 × 10-3 (mole/m2 s) at the liquid phase flow rate of 300 ml/min for PSF hollow fiber membrane was obtained. It can be concluded that a porous hydrophobic hollow fiber membrane with high surface porosity and high gas permeability can be a productive alternative for CO2 absorption through gas-liquid membrane contactors.

Fabrication of Nanostructured Polyamic Acid Membranes for Antimicrobially Enhanced Water Purification

Water scarcity and quality challenges facing the world can be alleviated by Point-of-Use filtration devices (POU). The use of filtration membranes in POU devices has been limited largely because of membrane fouling, which occurs when suspended solids, microbes, and organic materials are deposited on the surface of filtration membranes significantly decreasing the membrane lifespan, thereby increasing operation costs. There is need therefore to develop filtration membranes that are devoid of these challenges. In this work, nanotechnology was used to fabricate nanostructured polyamic acid (nPAA) membranes, which can be used for microbial decontamination of water. The PAA was used as support and reducing agent to introduce silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) with antimicrobial properties. The nPAA membranes were fabricated via thermal and wet phase inversion technique and then tested against Escherichia coli and Staphylococcus aureus following standard tests. The resulting nanoparticles exhibited excellent dispersibility and stability as indicated by the color change of the solution and increments of optical density at 415 nm for AgNPs and 520 nm for AuNPs. The wet phase inversion process used produced highly porous, strong, and flexible nPAA membranes, which showed well-dispersed spherical AuNPs and AgNPs whose rough average size was found to be 35 nm and 25 nm, respectively. The AgNPs demonstrated inhibition for both gram positive E. coli and gram negative S. aureus, with a better inhibitory activity against S. aureus. A synergistic enhancement of AgNPs antimicrobial activity upon AuNPs addition was demonstrated. The nPAA membranes can thus be used to remove microbials from water and can hence be used in water purification.

Polyurethane Synthetic Papers Based on Different Inorganic Fillers with Water and Fire Resistance

AbstractPolyurethane synthetic papers based on different inorganic fillers are prepared via wet phase inversion process and inorganic mineral filling modification technique. The surface and cross‐section morphology, tensile strength and elongation at break, fire resistance, water and oil adsorption, ink contact angle, writing and printing effects, and water resistance of synthetic paper are investigated, respectively. A large number of pores are present on the surface and in the interior of the synthetic papers and provide huge space for ink molecules. The synthetic paper with transparent powder filled exhibits the optimal performance in tensile strength and elongation at break. Moreover, the fire resistance of polyurethane is improved by inorganic particles, and the highest limit oxygen index value of synthetic paper reaches up to 31.8%, which meets the standard of flame retardant. Meanwhile, filled synthetic papers exhibit high water and oil adsorption capacity, good ink‐affinity, excellent writing and printing effects. In addition, filled synthetic papers perform well in water resistance when written and printed synthetic papers are immersed in water. This work may provide a new idea to design a novel, greener, and multifunctional synthetic paper for its broad applications.

Electrochemical Properties of Chemically Treated Polyvinylchloride‐Based Heterogeneous Cation‐Exchange Membrane

Chemical treatment is a facile method for improving electrochemical properties of a heterogeneous ion‐exchange membrane. In this work, polyvinylchloride (PVC)‐based heterogeneous cation‐exchange membrane is prepared by a dry–wet phase inversion process. The membrane is treated with a sulfuric acid solution in a room and a high temperature (80 °C). Effects of the treatment procedure and hydrophilic additive on membrane electrochemical properties are investigated. Chemically treated PVC and PVC/additive heterogeneous cation‐exchange membranes show a change in membrane electrochemical properties in terms of water uptake (Wu), conductivity, ion‐exchange capacity (IEC), and permselectivity (Ps). In general, Wu and conductivity increase after the chemical treatment. Significant improvement is observed when a high temperature is used. Meanwhile, the conductivity is more pronounced for PVC/additive membranes. The improvement may be associated with an increase in hydrophilicity. A significant increase in IEC is also observed for modified PVC/additive membrane. This may be associated with the removal or leaching of the additive during the treatment which in turn increases the portion of ion‐exchange resins in the membrane. Most of the modified membranes show a decrease in Ps. It may be due to a decrease in the effectiveness of Donnan effect indicated by Donnan equilibrium constant (K+). POLYM. ENG. SCI., 59:E219–E226, 2019. © 2018 Society of Plastics Engineers

Potential of Polysulfone/Polydimethyl Siloxane Thin Film Composite (PSf-PDMS-TFC) Membrane for CO2/N2 Gas Separation

The capture and storage of carbon dioxide has been identified as one potential solution to greenhouse gas driven climate change. Efficient separation technologies are required for removal of carbon dioxide from flue gas streams to allow this solution to be widely implemented. This study is mainly focusing on the effect of different concentration of polydimethyl siloxane (PDMS) in dip-coating solution on the membrane’s performance. The asymmetric thin flat sheet membrane was prepared by dry / wet phase inversion process consisting 20 %w/v of polysulfone (PSf) as the support layer polymer and 80 %w/v of N-methyl-2-pyrrolidone (NMP) as the solvent. PDMS was coated on the support PSf membrane with the composition of 10, 15 and 20 wt% of PSf in n-hexane respectively. The characterization of morphology of TFC membrane will be conducted by using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR). The membrane’s performance and the selectivity of CO2/N2 separation will be determined by conducting gas permeation test. The result obtained, show that membrane with highest concentration of PDMS in dip-coating solution give a highest performance in selectivity and unfortunately it contributes to lower permeability. It is vice versa from the membrane without PDMS in the top layer which gives highest value of permeability but lowest in selectivity. From the characterization and permeation test of the membrane, hereby the membrane with highest percentage of PDMS should be selected for the future development of membrane due to its highest value of selectivity which contributes to highest efficiency in separating the gas.

CO2 Absorption with NaOH Solution through the Porous PVDF Hollow Fibre Membrane Contactor

In this study, porous hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated via a wet phase inversion process. In order to improve the phase inversion rate and provide porous membranes, 4 wt.% lithium chloride (LiCl) was used in the spinning dope. The prepared membrane morphology was studied using field emission scanning electron microscopy (FESEM). Chemical CO2absorption by NaOH solution (1M) was conducted through the PVDF hollow fiber membrane contactor. The effect of the main operating condition such as absorbent temperature, CO2 pressure and absorbent flow rate on the performance of CO2 absorption was investigated. From FESEM examination, the membrane possesses an almost sponge–like structure with ultra thin skin layer. Results of CO2absorption test showed that by increasing the absorbent flow rate the CO2 flux increased which confirmed the existence of liquid side mass transfer resistance. It was found that by increasing the absorbent temperature the CO2 flux considerably improved. Meanwhile, the effect of CO2 pressure on the absorption rate was insignificant. Therefore, it can be concluded that by applying a porous hydrophobic membrane with improved structure and optimizing the operating conditions, high CO2 removal efficiency can be achieved through gas–liquid membrane contactors

Effect of hydrophobically modified PVA on the temperature-responsive structure and permeation of PAN-based composite ultrafiltration membranes

Temperature-responsive flat composite ultrafiltration membranes were prepared by dry–wet phase inversion process from casting solution of polyacrylonitrile and hydrophobically modified polyvinyl alcohol (HMPVA) in dimethylsulfoxide solvent. HMPVA is characterized by multiple reversible temperature-stimulated change of its physicochemical properties with the temperature of transformation (T tr) being dependent on the degree of acetalization. Based on the dynamic viscosity, the limit of the polymer concentration in the solution was established to be from 0.6 to 3.5 wt% for HMPVA at constant concentration of 16 wt% PAN. HMPVA remained homogeneously scattered within the membrane structure which was proved by Fourier transform infrared spectroscopy (FTIR). The studies on membrane morphology by scanning electron microscopy and on permeability (J, l/m2 h) and rejection (R, %) for water and albumin showed an asymmetry of the porous structure with pores having capillary macroporosity—on the surface and inner walls of the pores. The optimal for membrane parameters is a concentration of 1.2 wt% HMPVA. The permeability to water at 0.3 MPa changes from 58 to 80 l/m2 h and permeability to albumin—from 30 to 56 l/m2 h, when changing the temperature relative to T tr = 29.5 °C. Adjusting the temperature, it allows us to control the amount of flow passing through the membrane and widens the possibilities for self-cleaning and regenerations of the membrane.

Anti-fouling and high water permeable forward osmosis membrane fabricated via layer by layer assembly of chitosan/graphene oxide

To date, forward osmosis (FO) has received considerable attention due to its potential application in seawater desalination. FO does not require external hydraulic pressure and consequently is believed to have a low fouling propensity. Despite the numerous privileges of FO process, a major challenge ahead for its development is the lack of high performance membranes. In this study, we fabricated a novel highly-efficient FO membrane using layer-by-layer (LbL) assembly of positive chitosan (CS) and negative graphene oxide (GO) nanosheets via electrostatic interaction on a porous support layer. The support layer was prepared by blending hydrophilic sulfonated polyethersulfone (SPES) into polyethersulfone (PES) matrix using wet phase inversion process. Various characterization techniques were used to confirm successful fabrication of LbL membrane. The number of layers formed on the SPES-PES support layer was easily adjusted by repeating the CS and GO deposition cycles. Thin film composite (TFC) membrane was also prepared by the same SPES-PES support layer and polyamide (PA) active layer to compare membranes performances. The water permeability and salt rejection of the fabricated membranes were obtained by two kinds of draw solutions (including Na2SO4 and sucrose) under two different membrane orientations. The results showed that membrane coated by a CS/GO bilayers had water flux of 2–4 orders of magnitude higher than the TFC one. By increasing the number of CS/GO bilayers, the selectivity of the LbL membrane was improved. The novel fabricated LbL membrane showed better fouling resistance than the TFC one in the feed solution containing 200ppm of sodium alginate as a foulant model.

Mixed-matrix membranes for efficient ammonium removal from wastewaters

Novel mixed matrix membranes and fibers were fabricated to investigate ammonium removal for the first time from wastewaters especially aquaculture wastewaters. Several approaches were adopted to fabricate these mixed-matrix membranes including a wet phase inversion process as well as pore filling of commercially available membranes. Natural zeolite particles were effectively incorporated into polysulfone polymer matrices. These composite materials are found to be efficient for ammonium removal with high capacity and high stability. No leaching of zeolite materials was detected. These mixed-matrix membranes demonstrate high water flux and are easy to regenerate. Over 90% of total ammonia nitrogen (TAN) can be removed from relatively low TAN concentration aquaculture wastewaters. These novel adsorptive membranes are reusable and exhibit high viability for large scale industrial applications.

A novel asymmetric membrane osmotic pump capsule with in situ formed delivery orifices for controlled release of gliclazide solid dispersion system

In this study, a novel asymmetric membrane osmotic pump capsule of gliclazide (GLC) solid dispersion was developed to achieve a controlled drug release. The capsule shells were obtained by wet phase inversion process using cellulose acetate as semi-permeable membrane, glycerol and kolliphor P188 as pore formers, then filled with the mixture of GLC solid dispersion and pH modifiers. Differentiate from the conventional formulations, sodium carbonate was chosen as the osmotic agent and effervescent agent simultaneously to control the drug release, instead of the polymer materials. The ternary solid dispersion of GLC, with polyethylene glycol 6000 and kolliphor P188 as carriers, was prepared by solvent-evaporation method, realizing a 2.09-fold increment in solubility and dissolution rate in comparison with unprocessed GLC. Influence of the composition of the coating solution and pH modifiers on the drug release from the asymmetric membrane capsule (AMC) was investigated. The ultimate cumulative release of the optimal formulation reached 91.32% in an approximately zero-order manner. The osmotic pressure test and dye test were conducted to validate the drug release mechanism from the AMC. The in vivo pharmacokinetic study of the AMC indicated a 102.66±10.95% relative bioavailability compared with the commercial tablet, suggesting the bioequivalence between the two formulations. Consequently, the novel controlled delivery system with combination of solid dispersion and AMC system is capable of providing a satisfactory alternative to release the water-insoluble drugs in a controlled manner.

Synthesis, characterization and performance studies of polysulfone and polysulfone/polymer-grafted bentonite based ultrafiltration membranes for the efficient separation of oil field oily wastewater

In this study, polysulfone based mixed-matrix ultrafiltration membranes were prepared by blending polysulfone with different polymer-grafted bentonite additives. Formation of polymer-grafted bentonite was confirmed by Fourier transformed infra-red spectroscopy, energy-dispersive X-ray and thermal gravimetric analysis. Membranes were fabricated via wet phase inversion process with varying additive concentration. Hydrophilicity and structural changes of grafted polysulfone membranes were investigated by scanning electron microscope, water contact angle, molecular weight cut-off and pure water flux measurement. Prepared polysulfone/polymer grafted bentonite membrane was used for the separation of oil from oil-field oily wastewater and the membrane performance was evaluated in terms of permeate flux, oil rejection and fouling characteristics. Finally, results were compared with plain polysulfone and polysulfone/bentonite ultrafiltration membranes.

Microfiltration/ultrafiltration polyamide-6 membranes for copper removal from aqueous solutions

Microfiltration/ultrafiltration (MF/UF) Adsorptive polyamide-6 (PA-6) membranes were prepared using wet phase inversion process. The prepared PA-6 membranes are characterized by scanning electron microscopy (SEM), porosity and swelling degree. In this study, the membranes performance has examined by adsorptive removal of copper ions from aqueous solutions in a batch adsorption mode. The PA-6/H2O membranes display sponge like and highly porous structures, with porosities of 41-73%. Under the conditions examined, the adsorption experiments have showed that the PA-6/H2O membranes had a good adsorption capacity (up to 120-280 mg/g at the initial copper ion concentration (C0) = 680 mg/L, pH7), fast adsorption rates and short adsorption equilibrium times (less than 1.5-2 hrs) for copper ions. The fast adsorption in this study may be attributed to the high porosities and large pore sizes of the PA-6/H2O membranes, which have facilitated the transport of copper ions to the adsorption. The results obtained from the study illustrated that the copper ions which have adsorbed on the polyamide membranes can be effectively desorbed in an Ethylene dinitrilotetra acetic acid Di sodium salt (Na2 EDTA) solution from initial concentration (up to 92% desorption efficiency) and the PA-6 membranes can be reused almost without loss of the adsorption capacity for copper ions. The results obtained from the study suggested that the PA-6/H2O membranes can be effectively applied for the adsorptive removal of copper ions from aqueous solutions.

Improved antibacterial activity of nanofiltration polysulfone membranes modified with silver nanoparticles

Polysulfone membranes (PSf) containing silver nanoparticles were prepared by the wet phase-inversion process. Silver nanoparticles (AgNP) were dispersed into the polymer matrix using two different methodologies. In the first one, the AgNP were synthesized and further dispersed into the polymer solution (ex situ process). In the second method, the formation of the AgNP was performed in situ. The AgNP crystalline structure in the PSf membranes was confirmed by X-ray diffraction. Field emission scanning electron microscopy images showed that the addition of AgNP in PSf membranes caused no significant changes to the finger-like morphology. When the ex situ methodology was applied, 45 nm average size AgNP were uniformly distributed in the internal pores of the membranes. However, when the AgNP were formed through the in situ process, the AgNP were uniformly and preferentially distributed on the top and bottom surfaces of the membrane. In the last case, the AgNP showed cubic morphology when present in the bottom and top surfaces, however, when inside the membrane their morphology was spherical. The cubic-like nanoparticles displayed a 38 nm average edge length. The silver ion released from the membrane during water filtration was measured using inductively coupled plasma mass spectrometry, which showed a silver leaching of approximately 2 μg L−1. The nanocomposite membranes prepared by the in situ method exhibited a better antibacterial activity, in comparison to those prepared by ex situ, and also a decrease in 90% Escherichia coli adhered cells compared to the pristine PSf membranes. In conclusion, the in situ procedure can be considered a feasible, simple, and reproducible methodology to prepare anti-biofouling polysulfone membranes containing AgNP.

Influence of Hydrophilic Polymer on Proteins Separation, Molecular Weight Cut-off (MWCO) and Average Pore Size of Polysulfone Blend Membrane

The aim of this study is to investigate the influence of different composition of cellulose acetate phtalate (CAP) on the membrane structural properties of polysulfone (PSf) membrane which in turn affect the separation performance of PSf/CAP blend membrane. The PSf/CAP blend membranes were prepared by using casting solutions contain 17 wt% of polymer via wet phase inversion process. The results showed that increasing the composition of CAP in PSf/CAP blend membranes increased molecular weight cut-off (MWCO), average pore size and pore density which then increased protein solution permeate fluxes but reduced proteins rejection of PSf/CAP blend membranes. Pure PSf membranehas the lowest membrane structural properties compared to blend membranes. This characteristic contributed to decrease in protein permeation flux and increase proteins rejection.

Preparation and characterization of PVDF flat-sheet membranes for direct contact membrane distillation

The polyvinylidene fluoride (PVDF) flat-sheet membranes for direct contact membrane distillation (DCMD) were prepared through coating and wet phase inversion process. The effects of solvent, polymer concentration, non-solvent additive and nonwoven fabric on membrane morphology, porosity, pore size, pore size distribution, hydrophobicity and permeability were investigated. It was found that the membrane using N,N-dimethylacetamide as solvent obtained good permeability, and the polymer dope containing 20wt.% PVDF was the most suitable for hydrophobic flat-sheet membrane preparation. The PVDF flat-sheet membranes with different non-solvent additive such as acetone, phosphoric acid, glycerine, LiCl and PEG 400 were prepared and the membrane using 5wt.% acetone and 3wt.% H3PO4 as mixed additive had the highest permeate flux. The nonwoven fabric could prevent membrane shrinkage, while both pore size and permeate flux of the PVDF/nonwoven fabric composite membrane were enhanced. Although the nonwoven fabric caused the membrane surface roughness decline, the contact angle only decreased slightly. The PVDF/nonwoven fabric composite membrane exhibited satisfying performance stability during the 240h continuous desalination experiments, indicating that the resultant flat-sheet membrane may be of great potential to be utilized in DCMD process for desalination.