Polyethylene Hollow Fiber Membrane Research Articles

One‐Step Preparation of Hydrophilic and Reinforced Polyethylene Hollow Fiber Membranes via the Combination Technology of Braided Tube Reinforcement and TIPS Method

ABSTRACTIn this work, the hydrophilic and reinforced polyethylene (PE) hollow fiber membranes were prepared successfully via the combined technology of braided tube reinforcement and the thermally induced phase separation (TIPS) method. We selected PE as the membrane‐forming polymer, polyethylene glycol (PEG) and calcium chloride (CaCl2) as the composite pore‐forming agents, polyether alcohol compounds (HL560) and graphene oxide (GO) as the composite hydrophilic additives, white oil as the diluent, and polyester (PET) braided tube as the reinforcement. The effects of GO content on membrane structure and properties were analyzed and investigated in detail based on the FTIR, Raman, DSC, TG, SEM, pore size analyzer, and contact angle meter, and so forth. The results showed that the hydrophilicity, porosity, and permeability of the membranes improved obviously with the increase of GO content. When the GO content was 0.05 wt%, the water contact angle and the initial pure water flux was 72.5° and 912.5 L·m−2 h−1, respectively. In addition, the reinforced PE hollow fiber membranes exhibited excellent corrosion resistance and mechanical strength, which could meet the need for long‐term use.

Preparation of high-flux polyethylene hollow fiber microfiltration membranes with multiple pore structure through the combination technology of braided tube reinforcement and TIPS method

Our team proposed the continuous preparation of the reinforced polyethylene (PE) hollow fiber microfiltration (MF) membranes based on the combination technology of braided tube reinforcement and thermally induced phase separation (TIPS) method. In this work, to improve the permeability and reduce the flux attenuation, we selected PE as the membrane-forming polymer, polyethylene glycol (PEG) and sodium chloride (NaCl) as the composite pore-forming agents to optimize the membrane-forming composition. In particular, the effect of NaCl contents on the permeation of the reinforced PE hollow fiber membranes was studied in detail. The reinforced PE hollow fiber MF membranes obtained the multiple pore structure containing small pores, large pores and cavity structure. The small pores were formed by PEG and white oil. The large pores and the cavity structure were formed by the discreted and agglomerated NaCl, respectively. The cavity structure provided the connectivity gaps for the small pores and forming an internal highly connected pathways, which could reduce the transmembrane resistance. Thus, the flux improved obviously with the increasing NaCl contents. When the NaCl content was 30 wt%, the pure water flux of the reinforced PE hollow fiber MF membranes could reach 1606.0 L·m−2 h−1 after pre-pressuring for 30 min. In addition, the reinforced PE hollow fiber MF membranes exhibited excellent tensile strength with 170.0 MPa and good corrosion resistance, which showed a great application potential in harsh environments. In particular, this method provides a new idea for the continuous preparation of the reinforced PE hollow fiber MF membranes.

Preparation and characterization of fiber braided tube reinforced polyethylene hollow fiber membranes via thermally induced phase separation

In wastewater treatment applications, mechanical strength of the membranes often cannot meet practical requirements due to the disturbance of aeration flow or the damage of high-pressure cleaning. In this work, fiber braided tube reinforced polyethylene (BR PE) hollow fiber membranes with desirable filtration performance and high tensile strength were successfully prepared via fiber braided tube reinforcement (BR) and thermally induced phase separation (TIPS) methods. Especially, the effect of heat treatment temperature on structure and properties of the membranes was discussed. The results exhibited that tensile strength and interfacial bonding state between the surface separation layer and the fiber braided tube reinforcement were improved with the increase of heat treatment temperature. While the heat treatment temperature was 130 °C, BR PE hollow fiber membranes exhibited favorable interfacial bonding state, and tensile strength was up to 204.4 MPa, which was significantly higher than that of previously reported PE membranes. Moreover, the increase of heat treatment temperature could decrease the membrane pore size and improve filtration performance. Comprehensive consideration, the optimal heat treatment temperature of BR PE hollow fiber membranes was 110 °C. This work can provide scientific and practical basis for large-scale development of BR hollow fiber membranes with good comprehensive performance.

Controllable modification of polymer membranes by LDDLT plasma flow: Antibacterial layer onto PE hollow fiber membrane module

A high-density and uniform network-like antibacterial poly(methacryloxyethyl benzyl dimethyl ammonium chloride) (PDMAE-BC) layer was covalently constructed onto polyethylene (PE) hollow fiber membrane surface in a module scale via long-distance and dynamic low-temperature (LDDLT) plasma flow irradiation and subsequent graft polymerization. After the stepwise construction using this surface plasma chemical engineering method, the hydrophilicity of membrane surface was enhanced greatly due to implantation of numerous oxygen-containing groups. Meanwhile, the surface microstructures and chemical composition distributions were more uniform along with the axial distance from the module inlet and no significant damage/etching in membrane surface was observed. And even more prominent, the obtained PDMAE-BC membrane module can effectively destroy and/or inhibit bacteria by antibacterial layer, thereby preventing the formation of biofilms. It not only exhibited a high antibacterial activity against Gram-negative Escherichia coli, but also had an antifouling property, an increased water flux and an easy-cleanability. The antibacterial efficacy reached about 92.4% in the membrane module with only 10 PE–PDMAE-BC fibers and can be further improved by increasing the fiber packing density. In the long-term running, both original and PDMAE-BC membrane modules showed a 100% rejection ratio for E. coli. Moreover, the PE–PDMAE-BC membrane module can endure general water rinsing with little loss of antibacterial efficacy and exhibited an excellent antibacterial stability. This PE–PDMAE-BC membrane module should prove useful in actual water (mainly drinking water and wastewater) treatment.

Highly hydrophobic microporous low‐density polyethylene hollow fiber membranes by melt‐extrusion coupled with salt‐leaching technique

Microporous and highly hydrophobic low‐density polyethylene (LDPE) hollow fiber membranes were successfully prepared via a solvent‐free method, combining melt‐extrusion, and salt‐leaching techniques. NaCl particles with particle size of 5–10 µm were mixed with LDPE pellets to produce a blend of 35, 40, 50, 60, 65 and 68 wt% of salt. A microporous structure was produced by leaching the salt particles from the hollow fiber matrix via immersion in water at 60°C. The fabricated membranes were then characterized in terms of morphology, porosity and pore size distribution, surface roughness, and hydrophobicity, as well as mechanical properties. The remarkable increase in the water contact angles from 98° for LDPE hollow fibers fabricated without the addition of salt (blank sample) to 130° for membranes fabricated with initial salt content of 68 wt% is mainly attributed to the rough surface structure, comprising a large number of micropapillas produced by removing the imbedded salt crystals. The increase in surface roughness and porosity of hollow fiber membranes with increasing initial salt content was confirmed by scanning electron microscope and atomic force microscopy. Copyright © 2013 John Wiley & Sons, Ltd.

New Chiral Catalytic Membranes Created by Coupling UV-Photografting with Covalent Immobilization of Salen–Co(III) for Hydrolytic Kinetic Resolution of Racemic Epichlorohydrin

New chiral catalytic functional membranes (HFM-salens) were obtained successfully by covalent immobilizing aminated mono-CH2Cl–salen–Co(III) catalysts onto polyethylene (PE) hollow fiber membranes (HFMs) that had been, in advance, modified by UV-induced graft polymerization of acrylic acid. The catalytic properties of HFM-salens were investigated by carrying out hydrolytic kinetic resolution experiments of racemic epichlorohydrin. For homogeneous mono-CH2Cl–salen–Co(III) catalyst, the enantioselectivity (ee) and yield (Y) of S-epichlorohydrin were 86.67% and 57.26%, respectively. For the HFM-salens in type of segments, on which only about 2% of mono-CH2Cl–salen–Co(III) used in homogeneous catalysis was immobilized, an ee of 5.45% and a Y of 8.23% were achieved. Moreover, the ee and Y values reached 44.78% and 47.01%, respectively, using only eight HFM-salens packed in a catalytic membrane reactor (CMR), and the ee and Y values can be further improved by increasing packing density of fibers in the CMR. As an environment-friendly technology, immobilization of catalysts on membranes makes it easy to reuse the catalysts and reduce the amount of catalysts significantly. The results offer great potential for these modified membranes in the CMR for further research.

Morphological, chemical and thermal stability of microporous LDPE hollow fiber membranes in contact with single and mixed amine based CO2 absorbents

The gradual deterioration in the morphological and chemical stability of membranes in membrane contactors can extensively influence the membrane wettability, leading to reduction of CO2 absorption efficiency. In the present work, morphological, chemical and thermal stability of microporous low density polyethylene (LDPE) hollow fiber membranes, intended to be used in membrane contactors, was studied in contact with primary amine (monoethanolamine, MEA) and sterically hindered amine (2-amino-2-hydroxymethyl-1,3-propanediol, AHPD) solutions. The effect on membrane stabilization of a diamine (piperazine, PZ) having the operational advantages of fast CO2 absorption rate and capacity was also investigated.The surface properties of neat (before contact) and used (after contact with amine solutions) membranes were analyzed using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and contact angle measurements. For membranes immersed in amine solutions of commonly used concentrations (30wt.% MEA and 11wt.% AHPD), the results show morphological degradation of membranes, caused by the intrusion of the solution into the pores, as well as chemical degradation caused by the LDPE auto-oxidation. However, a less significant effect was found by the addition of PZ. A two-step mechanism was proposed to explain the stabilizing effect of PZ. PZ containing amine solutions are suggested as strong candidates for CO2 absorption in membrane contactors due to their efficient dual-function properties (high CO2 absorption efficiency and polyolefin membrane stabilization).

Study on Lamellar Structures and Parameters of Polyethylene Hollow Fiber Membranes Made by Melt-Spinning and Stretching Method

Lamellas important for micropores were well formed during extrusion and annealing process in melt-spinning and stretching method. This unusual crystalline structure and its changing during annealing and stretching process were well studied in term of lamellar size, lamellar crystallite orientation, degree of lamellar and observation of morphology. Lamellar and microfibril model was accepted as mechanism of making micropore for this process. Gas permeability and porosity testing experimental were used to characterize membrane properties.

Effect of transient sodium chloride shock loads on the performance of submerged membrane bioreactor

Membrane bioreactor (MBR) is a promising technological option to meet water reuse demands. Though MBR provides effluent quality of reusable standard, its versatility to shock loads remains unexplored. The present study investigates the robustness of MBR under sodium chloride shock load (5–60 g/L) conditions. A bench scale aerobic submerged MBR (6 L working volume) with polyethylene hollow fiber membrane module (pore size 0.4 μm) was operated with synthetic wastewater at steady state OLR of 3.6 gCOD/L/d and HRT of 8 h. This resulted in 99% TSS removal and 95% COD and TKN removal. The COD removal during the salt shock load was in the range of 84–64%. The TSS removal showed maximum disturbance (88%) with a corresponding decrease in biomass MLVSS by 8% at 60 g/L shock. TKN removal was reduced due to inhibition of nitrification with increasing shock loads. It took about 4–9 days for the MBR to regain its steady state performance.

Effect of stretching on structure and properties of polyethylene hollow fiber membranes made by melt‐spinning and stretching process

AbstractMicroporous polyethylene (PE) hollow fiber membrane was prepared by the melt‐spinning and stretching (MS‐S) method. The effect of stretching on the structure and properties of the membrane was investigated by water contact angle measurement, field emission scanning electron microscopy (FESEM), mercury porosimetry, and N2 permeation. The tensile experiment was used to study the hard elasticity and the mechanical properties of annealed PE fibers. During the stretching process, the stretching temperature, rate, and ratio have great effects on the morphology, crystal structure, pore structure, and N2 permeation of the membrane. Experimental results showed that N2 permeation and porosity of the membrane increased with the increase in stretching temperature, rate, and ratio. The pore size decreased with increase in the stretching rate and increased with the stretching ratio. The pore size distribution was also affected by the stretching process, and was investigated in detail. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of precursor properties on the preparation of polyethylene hollow fiber membranes by stretching

High-density polyethylene (HDPE) hollow fiber membranes were prepared by stretching the melt spun hollow fiber precursors. Slit-shaped pores were successfully developed by cold and hot stretching processes. Annealing before stretching had a great influence on the precursor properties such as orientation, crystallite size and crystallinity. These property changes directly affected the membrane structure, and stretching without annealing failed to make a microporous structure. Take-up speed affected the lamellar thickness and interlamellar amorphous domain size, which in turn determined the pore size. Installation of an air-cooling unit determined the cooling time for crystallization for various take-up speeds. A decrease of cooling time prohibited an increase in orientation, and caused the decrease of crystallite size and crystallinity of the precursor. Take-up speed and annealing conditions were optimized for proper structure formation by stretching.

Effect of polymer density on polyethylene hollow fiber membrane formation via thermally induced phase separation

AbstractMicroporous high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) hollow fiber membranes were prepared from polyethylene–diisodecyl phthalate solution via thermally induced phase separation. Effect of the polyethylene density on the membrane structure and performance was investigated. The HDPE membrane showed about five times higher water permeability than the LDPE membrane because it had the larger pore and the higher porosity at the outer membrane surface. The formation of the larger pore was owing to both the initial larger structure formed by spinodal decomposition and the suppression of the diluent evaporation from the outer membrane surface due to the higher solution viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 471–474, 2004

Preparation of polyethylene hollow fiber membrane via thermally induced phase separation

High-density polyethylene (HDPE) hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Two kinds of diluents such as diisodecyl phthalate (DIDP) and liquid paraffin (LP) were used in the preparation of membrane. In the case of DIDP, liquid–liquid phase separation occurred, while only the polymer crystallization occurred in the case of LP. In all cases, asymmetric structures with the smaller pores at the outer surface were obtained. Effects of polymer molecular weight, air gap distance, water bath temperature and kinds of diluents on the pore size and the water permeability were investigated. The use of the polymer with the higher molecular weight, the shorter air gap distance and the higher bath temperature were effective to obtain the higher water permeability. The membrane prepared with LP showed the lower water permeability than that with DIDP.

Ce(III) recovery by supported liquid membrane using polyethylene hollow fiber prepared via thermally induced phase separation

High-density polyethylene (HDPE) hollow fiber membranes were prepared via thermally induced phase separation (TIPS). The pore size at the outer surface was quite smaller than that at the inner surface and the membrane structure was asymmetric. A membrane module was prepared by the obtained hollow fiber membranes. Experiments on the carrier-mediated transport of Ce(III) through supported liquid membranes (SLMs) were performed using the membrane module. The SLMs consisted of organic solutions of octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) and tributyl phosphate (TBP) in dodecane absorbed into the microporous HDPE hollow fiber membrane. Effect of the aqueous strip solution flow rate on the membrane performance was investigated.

Evaluation of polyethylene hollow-fiber membranes for hydrogen delivery to support reductive dechlorination in a soil column

Engineered systems are often needed to supply an electron donor, such as hydrogen (H 2), to the subsurface to stimulate the biological dehalogenation of perchloroethene (PCE) to ethene. A column study was performed to evaluate the ability of gas permeable hollow-fiber membranes to supply H 2 directly to PCE-contaminated groundwater to facilitate bioremediation. Two glass columns were packed with soil obtained from a trichloroethene-contaminated site at Cape Canaveral, Florida, and were fed a minimal medium spiked with PCE (7 μM) for 391 days. The columns were operated in parallel, with one column receiving H 2 via polyethylene hollow-fiber membranes (lumen H 2 pressure of approximately 1 atm) and a control column receiving no H 2. PCE was initially dechlorinated at a similar rate and to a similar extent in both columns, likely due to the presence of soil organic matter that was able to support dechlorination. After 265 days of operation, dechlorination performance declined in the control column and the benefits of membrane-supplied H 2 became evident. Although the membrane-supplied H 2 effectively stimulated PCE dechlorination at the end of the experiment (days 359–391), the system was inefficient in that only 5% of the supplied H 2 was used for dechlorination. Most of the remainder was used to support methanogenesis (94%). Despite the dominance of methanogens, nearly complete dechlorination of PCE to ethene was observed in the H 2-fed column. In addition to the inefficient use of H 2, operational problems included excessive foulant accumulation on the outside of the membrane fibers and water condensation inside the fibers. Use of alternative membrane materials and changes to the operating approach (e.g. pulsing or supplying H 2 at low partial pressures) may help to overcome these problems so that this technology can provide effective and stable remediation of aquifers contaminated with chlorinated ethenes.

Preparation and characterization of microporous polyethylene hollow fiber membranes

AbstractMicroporous polyethylene (PE) hollow fiber membrane with a porosity of 43% and N2 permeation of 4.96 cm3 (STP)/cm2 s cmHg was prepared by melt‐spinning and cold‐stretching method. It was found that PE with a density higher than 0.96 g/cm3 should be used for the preparation of microporous PE hollow fiber membranes. By increasing the spin–draw ratio, both the porosity and the N2 permeation of the hollow fiber membranes increased. Annealing the nascent hollow fiber at 115°C for 2 h was suitable for attaining membranes with good performance. By straining the hollow fiber to higher extensions, the amount and size of the micropores in the hollow fiber wall increased, and the N2 permeation of the membranes increased accordingly. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 203–210, 2002; DOI 10.1002/app.10305

The swelling behavior and wet morphology of water-absorbable polymer materials.

In this research work, a low-temperature examination method for scanning electron microscopy (SEM) is introduced. A water-absorbable polymer material, the sulfonated polyethylene (SPE) ion-exchange hollow fiber membrane, was used for the experiments. With this low-temperature technique, the wet morphology of the water-absorbable sulfonated polyethylene hollow fiber membrane was revealed. The results obtained from this investigation offer some important information to explain the behavior of the SPE hollow fiber membranes when they are applied in pervaporation separation of water/organic solvent mixtures, such as water/ethylene glycol, water/ethanol, and so forth.

Polyethylene Hollow Fiber Membranes and Micro-filtration of Tap Water.

Polyethylene Hollow Fiber Membranes and Micro-filtration of Tap Water.

High‐density polyethylene (HDPE) hollow fiber membrane via thermally induced phase separation. I. Phase separation behaviors of HDPE–liquid paraffin (LP) blends and its influence on the morphology of the membrane

Phase separation behaviors of the blends that consist of high-density polyethylene (HDPE) and LP was investigated by means of thermal analysis. The miscibility of the two components was evaluated in terms of the Flory–Huggins interaction parameter, determined from the Hoffman–Weeks plot, gave a value of 0.36. This leads us to a conclusion that this blend system is applicable to the preparation of microporous hollow fiber membrane by melt spinning of the blend. The homogeneous blends in the molten state become heterogeneous systems to yield microporous HDPE membranes in the course of cooling due to thermally induced phase separation. The influence of the phase separation on the membrane morphology was also discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2135–2142, 1999

High-density polyethylene (HDPE) hollow fiber membrane via thermally induced phase separation. I. Phase separation behaviors of HDPE-liquid paraffin (LP) blends and its influence on the morphology of the membrane

Phase separation behaviors of the blends that consist of high-density polyethylene (HDPE) and LP was investigated by means of thermal analysis. The miscibility of the two components was evaluated in terms of the Flory–Huggins interaction parameter, determined from the Hoffman–Weeks plot, gave a value of 0.36. This leads us to a conclusion that this blend system is applicable to the preparation of microporous hollow fiber membrane by melt spinning of the blend. The homogeneous blends in the molten state become heterogeneous systems to yield microporous HDPE membranes in the course of cooling due to thermally induced phase separation. The influence of the phase separation on the membrane morphology was also discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2135–2142, 1999