PVDF Hollow Fiber Membranes Research Articles

Influence of Air-Gap Length on CO2 Stripping from Diethanolamine Solution and Water Performance of Surface Modified PVDF Hollow Fiber Membrane Contactor

Surface Modifying Macromolecule (SMM) blended PVDF hollow fibers (HFs) were spun at different air-gaps (o to 20 cm) and used for CO2 stripping from aqueous DEA solution and water. The manufactured fibers were firstly subjected to various characterization tests such as contact angle and critical water entry pressure measurement to evaluate the HF hydrophobicity and wetting resistance, respectively. The pure helium permeation experiments were also conducted to obtain membrane pore size and effective porosity. Morphology of the HFs was investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The SEM images showed that both outer and inner diameters of HFs decreased significantly by increasing air-gap length which mainly because of elongation of HF caused by gravity while travelling through the air-gap. Also, the gradual decrease in roughness on the external surface of the produced HFs was observed from the AFM images. It was found that the increase of liquid velocity enhances the CO2 stripping flux. It was found that 10 cm air-gap gave maximum stripping flux of 3.34 x 10(-2) and 1.34 x 10(-3) (mol/m(2)s) for DEA solution and water, respectively. The increase in gas velocity, on the other hand, did not affect the stripping flux significantly. It was observed that the increase of temperature from 25 to 80 degrees C led to the marked enhancement of stripping flux from 6.30 x 10(-3) to 3.34 x 10(-2) (mol/m(2)s) and 6.5 x 10(-5) to 1.34 x 10(-3) (mol/m(2)s), for DEA solution and water, respectively. Furthermore, the increase in DEA concentration from 0.25 to 1 mol/L, led to the enhancement of the stripping flux from 6.84 x 10(-3) to 3.34 x 10(-2) (mol/m(2)s) at a liquid velocity of 0.7 m/s. It was concluded that the HF spun at 10 cm air-gap exhibited the best stripping performance among all fabricated HFs.

New insights in poly(vinylidene fluoride) (PVDF) membrane hemocompatibility: Synergistic effect of PVDF-g-(acryloyl morpholine) and PVDF-g-(poly(acrylic acid)-argatroban) copolymers

Hydrophilic and hemocompatible surface design is vital for poly(vinylidene fluoride) (PVDF) membranes in biological application especially for hemodialysis. In this work, the influence and synergistic effect of PVDF-g-(acryloyl morpholine) (PVDF-g-ACMO) and PVDF-g-(poly(acrylic acid)-argatroban) (PVDF-g-(PAA-AG)) copolymers blending modification on structure and properties of PVDF membrane were investigated. The membranes were prepared through immersion phase transition method. The copolymer structure was characterized by FT-IR and 1H NMR. Modified membrane surfaces obtained were characterized by XPS. The blending modified PVDF hollow fiber membranes were confirmed to have excellent hydrophilicity, good hemocompatibility properties (protein adsorption, platelets/ red blood cells adhesion, plasma coagulation), good permeability and anti-protein fouling performance. The hydrophilic and anti-hemolytic properties were significantly improved with the weight percentage of PVDF-g-ACMO copolymer, and PVDF-g-(PAA-AG) copolymer endow the anti-coagulation of modified membranes. And when the blend ratio was up to 1:3, the blend membranes show the longest clotting time (APTT 114.15 s and PT 25.65 s). This work provides a new modification method to improve the hemocompatibility for PVDF membranes in potential biological applications.

Preparation and characterization of polyvinylidenedifluoride-co-chlorotrifluoroethylene hollow fiber membranes with high alkaline resistance

In the present work, polyvinylidenedifluoride-co-chlorotrifluoroethylene (PVDF-co-CTFE) hollow fiber membranes were prepared via non-induced phase separation (NIPS) using 1-methyl-2-pyrrolidone (NMP) or triethyl phosphate (TEP) as the solvent. The thermodynamic characterization of both systems PVDF-co-CTFE/NMP/water and PVDF-co-CTFE/TEP/water) and the rheological properties of dope solutions were first investigated. Subsequently, the effect of dope concentration and spinning conditions such as air gap on the membrane permeability and mechanical strength was discussed in detail. The rejection of polystyrene with a size of 50 nm was 85, 100 and 100% for PVDF-co-CTFE hollow fiber membranes prepared with PVDF-co-CTFE concentrations of 14,17 and 20 wt%, while the permeability was 119, 39 and 2.5 L/m2 h bar, respectively. The morphologies of hollow fiber membranes were observed using scanning electron microscopy to evaluate the effect of solvent and spinning conditions on the membrane structure. The resultant PVDF and PVDF-co-CTFE hollow fiber membranes were immersed in a strong alkaline solution (NaOH (1 M)+NaClO (4000 ppm)) to evaluate the chemical resistance of PVDF-co-CTFE hollow fiber membranes in comparison with that of PVDF membranes. The mechanical properties of PVDF and PVDF-co-CTFE hollow fiber membranes immersed in the alkaline solution for 180 days were declined 90% and 10% as compared to the original ones, respectively. Moreover, the hollow fiber membranes were characterized using laser Raman spectra, Fourier-transform infrared spectra, differential scanning calorimetry, and X-ray photoelectron spectroscopy, before and after the immersion, to hypothesize the degradation mechanism of PVDF-co-CTFE and PVDF hollow fiber membranes in the alkaline solution.

Evaluation of the Flux According to Membrane Distillation Module Structure and Operating Conditions Using PVDF Hollow Fiber Membrane

Evaluation of the Flux According to Membrane Distillation Module Structure and Operating Conditions Using PVDF Hollow Fiber Membrane

Enhancement of the crystallinity and surface hydrophilicity of a PVDF hollow fiber membrane on simultaneous stretching and coating method

A polyvinylidene fluoride hollow fiber membrane (PVDF membrane) was prepared by thermally induced phase separation (TIPS) and had low orientation and weak tensile strength. A hydrophobic PVDF membrane composed of a semi-crystalline structure was physically modified to improve the crystallinity degree and tensile strength values, and this was achieved by increasing the orientation of the PVDF polymer chains from the α-phase to the β-phase. PVDF membranes coating were simultaneously applied with the crosslinked poly (vinyl alcohol) (PVA) solution to increase water flux and fouling resistance using sonication during the stretching process.

Controlling the Morphology of PVDF Hollow Fiber Membranes by Promotion of Liquid–Liquid Phase Separation

In literature, liquid–liquid (L–L) phase separation has been widely adopted as the principle technique by which polymeric membranes are produced. However, the promotion of L–L phase separation as the means of controlling membrane morphology is still debatable. Thus, this work aims to introduce a facile and cost‐effective technique for controlling the morphology of poly(vinylidene fluoride) (PVDF) hollow fiber membranes (HFMs). The proposed technique is based on promotion of L–L phase separation which can be achieved through two different approaches: 1) reducing the distance between locations of dope and binodal curve through locating spinning dope on nonsolvent (water)/solvent (2‐pyrrolidone)/polymer (PVDF) ternary phase diagram by increasing of nonsolvent content and maintaining of polymer concentration at initial level; 2) simultaneous occurrence of thermally and nonsolvent induced phase separation (TNIPS). It is found that L–L phase separation promotion based on the above described approaches yields to PVDF HFM with partially double‐layered structure, enhanced mechanical properties, higher porosity, and smaller average pore radius with the potential to purify textile wastewater containing C.I. Disperse Violet 33. The proposed technique is advantageous due to lack of need for additives or post‐treatment process for HFM synthesis.

Hydrophilic PVDF Hollow Fiber Membrane for Water Treatment

Hydrophilic PVDF Hollow Fiber Membrane for Water Treatment

열유도 상분리/비용매유도 상분리 혼합 공정에 의한 PVDF 중공사막 제조에서 응고액의 영향

고분자/희석제/용매 시스템에서 열유도 상분리(TIPS)/비용매유도 상분리(NIPS) 혼합공정으로 poly(vinylidene fluoride)(PVDF) 막을 제조하였다. Water, glycerol, ethanol 등 다양한 비용매를 내부 응고액으로 사용하였다. 또한 비용매에 용매인 N-methyl-2-pyrrolidone(NMP)나 희석제인 dibutyl phthalate(DBP)를 첨가하여 상 분리 속도 및 dope 용액과의 친화도를 조절하였다. 내부 응고액에 따른 상분리 거동의 변화가 표면구조 및 물성에 영향을 미치는 것을 확인하였다. 광학현미경을 이용하여 계면에서의 상분리 거동을 실시간으로 확인하였고 그 결과를 실제 평막형태로 제조된 막의 구조와 비교하였다. 용융방사 장치를 사용하여 실제 중공사막을 제조하였고 내부 응고액의 변화에 따른 중공사막 내부 표면구조의 변화를 확인하였고 기계적 강도 및 제거율을 유지하면서 투과도가 향상됨을 확인하였다.

Polydopamine/cysteine surface modified hemocompatible poly(vinylidene fluoride) hollow fiber membranes for hemodialysis.

Membrane surface design is significant for the development and application of synthetic polymer hemodialysis membranes. In this study, the influence of zwitterionic cysteine on poly(vinylidene fluoride) (PVDF) hollow fiber membrane was investigated. The polydopamine layer was formed through dopamine self-polymerization on PVDF membrane surface, and then cysteine was covalent grafted onto the layer to improve the anti-biofouling property and hemocompatibility. The elementary composition of membrane surfaces was characterized by X-ray photoelectron spectroscopy. The influence of polydopamine and cysteine on modified membrane surface morphologies was studied by field emission scanning electron microscopy. The modified PVDF membranes were confirmed to have excellent hydrophilicity, stable mechanical properties and good hemocompatibility (dynamic and static anti-protein adsorption, hemolysis ratio, plasma coagulation). And these properties were increased with the incorporation of polydopamine and cysteine. The optimized modified membranes exhibited high pure water flux (∼ 195.5 L/m2 h at 0.1 MPa) and selectivity (clearance ratio of urea and lysozyme was 75.1 and 55.4%, and rejection rate of bovine serum albumin was 98.8%). This work provides a surface modification method of PVDF hollow fiber membranes and suggests a potential application of PVDF membranes in hemodialysis field. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2869-2877, 2018.

Tailoring the surface pore size of hollow fiber membranes in the TIPS process

A new method was used to tailor the surface pore size of PVDF hollow fiber membranes in the TIPS process by the co-extrusion of different solvents at the outer layer of the extruded polymeric solution.

Study on the evolution of reinforced PVDF hollow fiber membrane morphology and strong hydrophobicity

Study on the evolution of reinforced PVDF hollow fiber membrane morphology and strong hydrophobicity

Development of Submerged Type PVDF Hollow Fiber Membrane Module for Drinking Water Treatment

Development of Submerged Type PVDF Hollow Fiber Membrane Module for Drinking Water Treatment

Surface modification of poly(vinylidene fluoride) hollow fibre membranes for biogas purification in a gas-liquid membrane contactor system.

The wetting of hollow fibre membranes decreases the performance of the liquid–gas membrane contactor for CO2 capture in biogas upgrading. To solve this problem, in this work, a poly(vinylidene fluoride) (PVDF) hollow fibre membrane for a liquid–gas membrane contactor was coated with a superhydrophobic layer composed of a combination of hydrophobic SiO2 nanoparticles and polydimethylsiloxane (PDMS) by the method of spray deposition. A rough layer of SiO2 deposited on the PVDF membrane resulted in an enhanced surface hydrophobicity. The surface structure of the pristine PVDF significantly affected the homogeneity of the generated SiO2 layer. A uniform surface coating on the PVDF upper layer resulted from the presence of micrometre and nanometre-sized roughness on the surface of the PVDF membrane, which was achieved with a SiO2 concentration of 4.44 mg ml−1 (0.2 g/45 ml) in the coating solution. As a result, the water contact angle of the modified surface was recorded as 155 ± 3°, which is higher than that of the pristine surface. The high contact angle is advantageous for reducing the wetting of the membrane. Additional mass transfer resistance was introduced by the superhydrophobic layer. In addition, continuous CO2 absorption tests were carried out in original and modified PVDF hollow fibre membrane contactors, using monoethanolamine (MEA) solution as the absorbent. A long-term stability test revealed that the modified PVDF hollow fibre membrane contactor was able to outperform the original membrane contactor and demonstrated outstanding long-term stability, suggesting that spray deposition is a promising approach to obtain superhydrophobic PVDF membranes for liquid–gas membrane absorption.

Continuous dip coating of PVDF hollow fiber membranes with PVA for humidification

Composite hollow fiber membranes for gas-to-gas humidification were fabricated and their performance was tested for use in external humidifiers of polymer electrolyte fuel cells (PEMFC). Therefore porous poly(vinylidene fluoride) (PVDF) hollow fibers were manufactured by a wet spinning process, coated with thin layers of polyvinyl alcohols (PVA) via a continuous dip coating and crosslinked by glutaraldehyde. Coating parameters, such as surface tension and viscosity of the coating solution, were correlated with the layer thicknesses of the coatings. Influences of the layer thickness on crosslinking, water vapor transport and thermal stability of the membranes were studied.The layer thickness can be adjusted in the range of 0.3–4.29µm by controlling the coating parameters. It was found that thicker coatings have a higher water vapor permeability, which may be caused by a lower degree of crosslinking.A layer thickness of 1.75µm was formed when using, for example, a 5wt% PVA 67000g/mol aqueous solution. With this composite membrane, a water vapor permeability of 2890 Barrer and a selectivity over nitrogen of 289 was achieved at 25°C. The potential of the designed fabrication process was verified by thermal stability tests, which almost all membranes withstood.

Novel PVDF membranes comprising n-butylamine functionalized graphene oxide for direct contact membrane distillation

To enhance the mechanical properties and wetting resistance of poly(vinylidene fluoride) (PVDF) membranes for membrane distillation (MD) of seawater, we have added n-butylamine modified graphene oxide (GO-NBA) in PVDF flat-sheet and hollow fiber membranes. For the first time, it is found that the addition of GO-NBA leads to PVDF flat sheet membranes with greater mechanical properties than that of conventional GO because of better compatibility, dispersity and crystalline structure. The addition of the GO-NBA also improves the mechanical properties of PVDF hollow fiber membranes in both tensile and hoop directions. With a small loading of 0.5wt% GO-NBA in PVDF hollow fiber membranes, the maximum tensile stress, maximum tensile stain and Young's modulus increase by 32%, 63% and 71%, respectively, while the liquid entry pressure (LEP) and burst pressure jump by 67% and 15%, respectively. Under direct contact membrane distillation (DCMD), the 0.5wt% GO-NBA incorporated membrane shows a flux of 61.9kgm-2h-1 and a salt rejection of 99.9% using a model seawater as the feed at 80°C. This work might provide useful insights to fabricate robust MD membranes for seawater desalination.

PVDF hollow fibers with novel sandwich structure and superior wetting resistance for vacuum membrane distillation

PVDF hollow fiber membranes with a unique sandwich structure and superior wetting resistance have been designed for vacuum membrane distillation (VMD) of seawater desalination in this study. The sandwich structure consists of two sponge-like inner and outer porous layers and a thin middle layer full of small-size macrovoids. The sponge-like structure in the two porous layers is specially designed because it enhances the mechanical strength of hollow fibers with high wetting resistance. This structure is derived from the spinodal liquid-liquid decomposition during phase inversion. Meanwhile, the middle layer of macrovoids is beneficial for VMD flux because they perform as highways for water transport. Comparing to the large size macrovoids, the small-size macrovoids in PVDF hollow fibers are preferred for VMD applications because they would not significantly reduce the membrane mechanical strength. As a result, the newly developed membranes possess impressively high liquid entry pressures (LEPs) of >3bar. This study may provide valuable guidelines in designing next generation PVDF hollow fiber membranes for practical VMD applications.

Preparation of PVDF hollow fiber membranes with high adsorption performance by one-step physical coating and chemical cross-linking

ABSTRACTIn this paper, PVDF hollow fiber membrane with high adsorption performance was prepared by coating polyvinyl alcohol on the surface of commercial PVDF hollow fiber ultrafiltration membrane and initiating partial hydroxyl acetalization. The modification effect was studied by scanning electron microscopy, infrared spectroscopy, contact angle test and organic dye adsorption capacity test. The results show that the polyvinyl alcohol is effectively fixed on the surface of PVDF hollow fiber membrane with polyvinyl alcohol used as coating agent to initiate partial acetalization reaction in the presence of glutaraldehyde and acid catalyst. The pure water contact angle of PVDF hollow fiber membrane decreases from 76.20° to 57.56°, which greatly improves the of PVDF hollow fiber membrane. The incorporation of the coating and cross-linked structure results in a decrease in the micro-porous permeability of the modified PVDF hollow fiber membrane. The adsorption performance of PVDF hollow fiber membrane modified by hydrophilic coating and cross-linked for organic dye Rhodamine B is significantly improved.

Wetting mechanism of a PVDF hollow fiber membrane in immersed membrane contactors for CO2 capture in the presence of monoethanolamine

As an emerging technology, membrane gas absorption (MGA) contactors for carbon dioxide (CO2) capture exhibit great advantages compared to conventional chemical CO2 absorption processes.

Study the Effect of Addition Silver Nanoparticle on Structure and Morphological Properties for PVDF Hollow Fiber

In this research was the study of the impact of silver nanoparticles solution on the structure and properties of the morphological membrane fibrous hollow PVDF through a dip PVDF Hollow fiber membrane in silver nanoparticle solution preparation via using laser ablation method. The characteristics of membrane and silver Nano particle solution and was examined using X-ray diffraction (XRD)and Scanning Electron Microscopy (SEM) also using laser particle size analyzer for Silver nanoparticles (AgNPs ) to measurement particle size to AgNPs.

PVDF/PVDF-g-PACMO blend hollow fiber membranes for hemodialysis: preparation, characterization, and performance

A novel approach to improve the biocompatibility of PVDF hollow fiber membrane by blending PVDF-g-PACMO copolymer for hemodialysis is provided.