Microporous Polypropylene Membrane Research Articles

Oxygen transfer characteristics of hydrophilic treated polypropylene hollow fiber membranes for bubbleless aeration

Bubbleless membrane aeration is a promising method for water oxygenation. In this work, the oxygen transfer characteristics of hydrophilic treated polypropylene (PP) microporous hollow fiber membranes were studied. Both cross flow and parallel flow modules were used for the bubbleless aeration of water with operating pressures up to 100 kPa. An intermittent degassing process was used in the aeration operation to maintain high oxygen transfer. A correlation was developed to evaluate the membrane resistance at different pressures. It was found that with an increase in operating pressure from 20 to 100 kPa, the membrane resistance decreased almost linearly from 8.8 × 10 4 to 4.6 × 10 4 s/m and from 4.0 × 10 4 to 2.1 × 10 4 s/m in cross flow and parallel flow, respectively. At appropriate operating pressures, the membrane resistance for hydrophilic treated PP membranes was similar to dense and composite membranes, while only one-third of the resistance of hydrophilic polysulfone membranes. Mass transfer was correlated with the Reynolds number over the range of operating pressures. The correlations obtained in this study are in agreement with previously reported correlations at a low Reynolds number.

High‐Density Glycosylation of Polymer Membrane Surfaces by Click Chemistry for Carbohydrate–Protein Recognition

To biologically mimic the carbohydrate-protein interactions in artificial systems, one of the challenges is to construct a glycosylated surface with a high glycosyl density to yield a notable 'glycoside cluster effect'. A novel strategy is presented for high density glycosylation of the surface of a microporous poly(propylene) membrane (MPPM) by click chemistry. It is promising that the surface glycosyl density can be well controlled over a wide range and the maximum value is over 10 µmol · cm(-2) . The recognition capability of these glycosylated MPPMs to lectins indicates the occurrence of the 'glycoside cluster effect' when the glycosyl density on the membrane surface exceeds 0.20 µmol · cm(-2) .

Surface hydrophilisation and antibacterial functionalisation for microporous polypropylene membranes

The surface properties of polymer membranes are crucial to their separation performances. For the microporous polypropylene membranes, the high hydrophobicity and lack of functionality easily cause protein adsorption and subsequent microorganism attachment and biofilm formation, i.e. biofouling. Thus, their applications in water treatment, bioseparation and biomedical fields are largely limited. Surface hydrophilisation and antibacterial functionalisation are, therefore, reasonably necessary. This review provides a concise summarisation of related studies according to the surface modification strategies. Especially, the interfacial crosslinking approach developed in our previous studies is presented in detail.

Grafting effect on the wetting and electrochemical performance of carbon cloth electrode and polypropylene separator in electric double layer capacitor

Activated carbon (AC) fiber cloths and hydrophobic microporous polypropylene (PP) membrane, both modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation, and filled with saturated lithium hydroxide solution were used as electrodes, a separator and electrolyte in electric double layer capacitors (EDLCs). The modification process changed the hydrophobic character of AC and PP materials to hydrophilic, made them wettable and serviceable as components of an electrochemical capacitor. The presence of poly(acrylic acid) on the AC and PP surface was confirmed by SEM and XPS methods. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy. At the 1000th cycle of potential cycling (1 A g −1) the specific capacitance of 110 F g −1 was obtained with a specific energy of 11 Wh kg −1 at power density of 1 kW kg −1. The above results provide valuable information which may be used when developing novel compositions of EDLCs.

Preparation of Microporous Membranes by Swift Heavy Ion Irradiation and Impedance Characterization

Polypropylene (PP) microporous membranes were successfully prepared by swift heavy ion irradiation and track-etching. Polypropylene foils were irradiated with (197)Au ions of kinetic energy 11.4 MeV.u(-1) (total energy of 2245.8 MeV) and fluence 1x10(8) ions.cm(-2) at normal incidence. The damaged regions produced by the gold ions along the trajectories were etched in H(2)SO(4) and K(2)Cr(2)O(7) solutions leading to the formation of cylindrical pores in the membranes. The pore diameters of the PP microporous membranes increased from 380 to 1610 nm as the etching time increased from 5 to 30 min. The surface and cross-section morphologies of the porous membranes were characterized by scanning electron microscopy (SEM). The micropores in the membranes were found to be cylindrical in shape, homogeneous in distribution, and equal in size. Some mathematical relations of the porosity of the PP microporous membranes were established by analytic derivation. The microporous membranes were used in lithium-ion batteries to measure their properties as separators. The electrical conductivity of the porous membrane immersed in liquid electrolyte was found to be comparable to that of commercial separators by electrochemical impedance spectroscopy (EIS). The results showed that the porosity and electrical conductivity were dependent on the ion fluence and etching time. By adjusting these two factors, microporous membranes with good porosity and electrical conductivity were made that met the requirements for commercial use.

Development of a novel RAFT-UV grafting technique to modify polypropylene membrane used for NOM removal

Surface modification of polypropylene microporous membrane was conducted by reversible addition-fragmentation chain transfer (RAFT) polymerization under UV irradiation. Dibenzyltrithiocarbonate was used as a RAFT agent. Attenuated total reflection-Fourier transform infrared spectroscopy and filed emission scanning electron microscopy were used to characterize the structural and morphological changes on the membrane surface. The degree of grafting of poly(acrylic acid) (PAAc) on the membrane surface increased with the increase of UV irradiation time, and decreased with the increase of the concentration of chain transfer agent. Surface-initiated block graft copolymerization with acrylamide was carried out on the PAAc modified membrane surface in the presence of free radical initiator, 2,2′-azobisisobutyronitrile. The degree of grafting of polyacrylamide (PAAm) increased with the reaction time. These results demonstrated that block graft copolymer of PAAc and PAAm on the membrane surface was accomplished by the combination of UV irradiation and the surface-initiated RAFT method. The pure water flux through the PAAc grafted membranes increased with the degree of grafting up to 0.67 wt.%, and then it decreased. The membrane filtration of natural organic matter from the Yangtze River showed that the degree of grafting played a very important role. Reduction from pure water flux was lower, the flux recoveries after water and caustic cleaning and flux ratios after fouling were higher for the modified membrane than those of the unmodified membrane. The PAAc grafted PPMM with a degree of grafting of 2.51 wt.% possessed the best antifouling characteristics. The high hydrophilicity, high permeability, and low fouling character of the modified membranes make microporous polypropylene membranes desirable for water treatment.

Hollow fiber membrane supported thin liquid film extraction for determination of trace phenoxy acid herbicides and phenols in environmental water samples

Traces of phenoxy acid herbicides and phenols were determined in environmental water samples by high performance liquid chromatography (HPLC) coupled to thin liquid film extraction (TLFE). A TLFE sampling device was prepared by dipping pieces of a polypropylene microporous hollow fiber membrane into dihexyl ether (containing 10% tri-n-octylphosphine oxide as carrier) for a few minutes to impregnate the pores of the hollow fiber wall. Extraction of analytes takes place from the outer aqueous phase into the immobilized solvent. After extraction the removal of the organic solvent was accomplished with a few µl of methanol which was used for HPLC analysis. Enrichment factors as high as 446 were obtained for the target compounds. The method provided detection limits as low as 0.4–1.2 µg L−1, good repeatability (the RSD ranging from 2.1 to 6.3%, n = 5) and a linear range from 2 to 200 µg L−1 for the target compounds. Real sample analysis showed recoveries between 84.6% and 112% for all compounds investigated.

Glycopolymer-filled microporous polypropylene membranes for pervaporation dehydration

Natural polysaccharides such as chitosan have been widely used to prepare polymer membranes for pervaporation dehydration. As their synthetic analogues, glycopolymers are also promising materials for the same purpose due to their high affinity interactions with water. In this work, glycopolymer-filled composite membranes were prepared by a pore-filling strategy from microporous polypropylene membrane using ultraviolet-initiated in situ copolymerization of acrylic acid (AA) and d-gluconamidoethyl methacrylate (GAMA). The morphologies and chemical structures of the fabricated membranes were characterized and the dense pore-filled structure was evaluated. Swelling experiments in water, isopropanol and their mixture revealed that the sorption selectivity of the GAMA units in the glycopolymer with water was higher than that of the AA units. Pervaporation on isopropanol/water mixture containing 10 wt% water was carried out and the membranes showed separation selectivity on water with high normalized flux. Investigation on sorption selectivity and diffusion selectivity indicated that the sorption selectivity of the GAMA units on water was the determining factor for the separation property of the glycopolymer-filled composite membranes. These membranes showed fine structural and performance stability during a ten-day operation.

New design of electric double layer capacitors with aqueous LiOH electrolyte as alternative to capacitor with KOH solution

Activated carbon (AC) fiber cloths and a hydrophobic microporous polypropylene (PP) membrane, both modified with lithiated acetone oligomers, were used as electrodes and a separator in electric double layer capacitors (EDLCs) with aqueous lithium hydroxide (LiOH) as the electrolyte. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge cycle tests and impedance spectroscopy (EIS), compared with a case of the capacitor with aqueous potassium hydroxide (KOH) as an electrolyte. As a result, the capacitor with LiOH aqueous solution and a modified separator and electrodes was found to exhibit higher specific capacitance, maximum energy stored and maximum power than that with KOH aqueous solution.

Simultaneous liquid–liquid microextraction and polypropylene microporous membrane solid-phase extraction of organochlorine pesticides in water, tomato and strawberry samples

A procedure involving the simultaneous performance of liquid–liquid microextraction and polypropylene microporous membrane solid-phase extraction was carried out. The applicability of the proposed procedure was evaluated through extraction of several organochlorine pesticides from river water, tomato and strawberry samples. The parameters affecting the extraction efficiency were optimized by multivariable designs, and the analytical features were estimated. Under optimized conditions, analytes were concentrated onto 1.5 cm long microporous membranes placed directly into the sample containing 15 mL of water with 20 μL of 1-octanol. The best extraction conditions were achieved at 59 °C, with 60 min of extraction time and 2.91 g of sodium chloride. The desorption of the analytes was carried out using 30 μL of a mixture of toluene and hexane in the proportion of 60:40% (v/v) for 10 min. Detection limits in the range of 2.7–20.0 ng L −1, 0.50–1.15 μg kg −1, and 1.53–12.77 μg kg −1 were obtained for river water, strawberry and tomato samples, respectively. Good repeatability was obtained for all three sample types. The results suggest that the proposed procedure represents a very simple and low-cost microextraction alternative rendering adequate limits of quantification for the determination of organochlorine pesticides in environmental and food samples.

Influence of ventilation and sucrose on growth and leaf anatomy of micropropagated potato plantlets

Potato single nodes were cultured in vessels containing MS medium supplemented with 10, 20 and 30 g/l of sucrose. Vessels were closed with a clear polypropylene lid with or without 10 mm microporous polypropylene membrane. Sucrose concentration significantly increased plantlet height, shoot fresh weight and chlorophyll a content. Plantlets grown in ventilated vessels were significantly shorter, had lower shoot fresh weight and higher shoot dry weight than those in non-ventilated vessels. The highest leaf chlorophyll a content (21.83 mg/g fresh weight) was found in plantlets grown in ventilated vessels using MS medium with 20 g/l of sucrose, whereas those grown on medium with 10 g/l of sucrose had the highest chlorophyll b content (24.00 mg/g fresh weight). Total chlorophyll content was significantly higher when plantlets were grown in ventilated vessels containing medium with 10 or 30 g/l sucrose than in non-ventilated vessels. There was no significant difference in total chlorophyll content among plantlets grown in ventilated vessels with different concentrations of sucrose. Stomatal density was significantly lower when plants were grown under ventilated conditions. Leaf replica examination showed that stomata under non-ventilated condition were spherical with wide openings whereas, those in ventilated vessels were elliptical with narrow openings. Plantlets grown in non-ventilated vessels had thinner leaves and failed to build up a distinct defined upper epidermis, palisade parenchyma layer and spongy cells. On the other hand, leaves under ventilated conditions showed comparatively well organized layers with small intercellular space. The vascular system of leaves under the ventilated conditions demonstrated very well developed xylem unlike leaves under non-ventilated conditions. Thus, ventilated vessels with the 20 g/l of sucrose under ambient CO 2 in the growth room could successfully promote photomixotrophic culture and produce healthy plantlets.

Fouling control in a submerged membrane‐bioreactor by the membrane surface modification

AbstractTo improve the antifouling characteristics, polypropylene microporous membranes (PPHFMMs) were surface‐modified by the sequential photoinduced graft polymerization of acrylic acid and acrylamide. The grafting density and the grafting chain length, which played important roles in the antifouling characteristics, were controlled in the first and the second step, respectively. The ATR/FTIR results clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously with the increase of the grafting chain length. The contact angle of the acrylic acid modified membranes was lower than that of the acrylamide modified membrane with similar grafting chain length. The grafting chain length increased with the increase of UV irradiation time and monomer concentration. The grafting chain length of poly(acrylic acid) (PAAc) was lower than that of the polyacrylamide (PAAm) under the same polymerization conditions. Pure water flux for the modified membranes increased with the increase of grafting chain length, and had maximums. The antifouling characteristics of the modified membranes in a submerged membrane‐bioreactor (SMBR) were evaluated. The modified membranes showed better filtration performances in the SMBR than the unmodified membrane, and the acrylic acid grafted membrane presented better antifouling characteristics than acrylamide modified membranes. The results demonstrated that the surface carboxyl‐containing membranes were better than the surface amido‐containing membranes. The results of Pearson correlations demonstrated that the PAAc modified membranes with longer grafting chain length had higher flux recoveries, while the PAAm modified membranes with longer grafting chain length had lower flux recoveries. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Membrane distillation operated at high seawater concentration factors: Role of the membrane on CaCO3 scaling in presence of humic acid

Abstract This study aims at investigating the kinetics of calcium carbonate precipitation (scaling), that occurs in the form of vaterite, when treating seawater by direct contact membrane distillation (DCMD) operated at high concentration factors (from 4 to 6). Induction time measurements carried out by dynamic light scattering (DLS) allowed to identify the shifting between homogeneous and heterogeneous nucleation mechanisms as a function of supersaturation. CaCO 3 interfacial energy, evaluated for concentrated seawater solutions as 45 mJ/m 2 , increased by 7% as a consequence of the inhibition effect of humic acid, and it was reduced to 32 mJ/m 2 in correspondence of heterogeneous nucleation occurring on microporous polypropylene membranes. Gibbs free energy barrier to the formation of critical nuclei was predicted with good accuracy as a function of physico-chemical properties of the membrane (porosity: 0.70, contact angle: 115 ± 2°). DCMD tests, carried out under a temperature gradient of ∼20 °C (feed temperature: 40 °C), showed a progressive deterioration of the system performance, and the initial distillate flux (2.05 ± 0.05 l/m 2 h) was reduced by 45% after 35 h of uninterrupted operation. Two-step cleaning with citric acid aqueous solution (20 min)/NaOH aqueous solution (20 min) allowed to completely restore the transmembrane flux and the hydrophobicity of the membrane.

Electric double layer capacitors with polymer hydrogel electrolyte based on poly(acrylamide) and modified electrode and separator materials

Activated carbon fiber cloths (AC) and hydrophobic microporous polypropylene (PP) membrane, both modified by acetone aldol condensation products, and filled with polymer hydrogel were used as electrodes, separator and electrolyte in electric double layer capacitors (EDLCs). Polymer hydrogel used was based on poly(acrylamide) (PAAM), KOH and water. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy, compared with a case of the capacitor with only a KOH aqueous solution used as an electrolyte. As a result, the capacitor with polymer hydrogel was found to exhibit higher capacitance than that with the KOH aqueous solution and an excellent high-rate dischargeability. The above results provide valuable information to explore novel composition of EDLCs.

Thermo- and pH-responsive polypropylene microporous membrane prepared by the photoinduced RAFT-mediated graft copolymerization

Thermo- and pH-responsive polypropylene microporous membrane prepared by photoinduced reversible addition–fragmentation chain transfer (RAFT) graft copolymerization of acrylic acid and N-isopropyl acrylamide by using dibenzyltrithiocarbonate as a RAFT agent. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FT-IR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM) were used to characterize the structural and morphological changes on the membrane surface. Results of ATR/FT-IR and XPS clearly indicated that poly(acrylic acid) (PAAc) and poly(N-isopropyl acrylamide) (PNIPAAm) were successfully grafted onto the membrane surface. The grafting chain length of PAAc on the membrane surface increased with the increase of UV irradiation time, and decreased with the increase of the concentration of chain transfer agent. The PAAc grafted membranes containing macro-chain transfer agents, or the living membrane surfaces were further functionalized via surface-initiated block copolymerization with N-isopropyl acrylamide in the presence of free radical initiator, 2,2′-azobisisobutyronitrile. It was found that PNIPAAm can be grafted onto the PAAc grafted membrane surface. The results demonstrated that polymerization of AAc and NIPAAm by the RAFT method could be accomplished under UV irradiation and the process possessing the living character. The PPMMs with PAAc and PNIPAAm grafting chains exhibited both pH- and temperature-dependent permeability to aqueous media.

Novel polypropylene microporous membranes via spherulitic deformation – Processing perspectives

Abstract The processing boundaries for initiating intra-/inter-spherulitic deformation to create microporous polypropylene membranes by lamellar separation are delineated. The processing parameters are: annealing temperature, extension ratio, stretching rate, and stretching temperature. A fixed set of extrusion conditions was chosen for producing precursor films having similar spherulitic morphologies. The morphological changes indicating the occurrence of intra-/inter-spherulitic transition on a spherulitic scale can also be detected on a lamellar scale by WAXS examination via analysis of the α-form orientation index. Membrane porosity measurements showed a consistent correlation with the observed values of the α-form orientation index. Increasing the extension ratio did not change the microstructure in the non-annealed sample; however, the lamellae can be further oriented in the annealed samples. Inter-spherulitic deformation became obvious at slow stretching rates; intra-spherulitic deformation was favored at fast stretching rates. The DSC thermal analysis of the precursor films showed two significant endothermic discontinuities ( T 1 at 0 °C and T 2 at 40 °C) in both non-annealed and annealed precursor films; T 1 is believed to be the conventional T g of polypropylene whereas T 2 appears to originate from the rigid-amorphous fraction trapped within the lamellar “wells” where the amorphous phase is surrounded by the R-lamellae and the T-lamellae. The lamellae could break down or slip from the lamellar knots as stretching temperatures are high enough to minimize the influence of the rigid-amorphous fraction, and the annealed lamellae can still be oriented without a catastrophic cold-drawn deformation.

Reducing protein fouling of a polypropylene microporous membrane by CO 2 plasma surface modification

CO 2 plasma was used to modify hydrophobic polypropylene microporous membranes to create hydrophilic surfaces. Structural and morphological changes on the membrane surface were characterized by X-ray photoelectron spectroscopy and scanning electron microscope. Membrane performance was tested with water flux measurements as well as protein fouling studies. The relative pure water flux of the modified membranes had a maximal value for the plasma treatment time of 2 min. It was found that the surface modified membranes showed better regeneration behavior. Flux recoveries after water and caustic cleaning were 33.1 and 27.5% higher, while reduction of pure water flux was 9.2% lower for the 30 s CO 2 plasma treated polypropylene microporous membranes than those of the virgin membranes. Moreover, the amount of protein adsorption decreased by over 50% for the treated membranes compared to the unmodified membranes. The results demonstrated that the bovine serum albumin fouling was suppressed significantly by plasma surface modification.

Surface hydrophilization of microporous polypropylene membrane by the interfacial crosslinking of polyethylenimine

To endow microporous polypropylene membrane (MPPM) with durable surface hydrophilicity, a facile interfacial crosslinking approach was developed, combined with a pretreatment by dielectric barrier discharge (DBD) plasma at atmospheric pressure. The commercially available polyethylenimine (PEI) was coated on MPPM firstly and was sequentially crosslinked with p-xylylene dichloride and quaternized with iodomethane to form a permanently positively charged layer. The physical and chemical changes of the membrane surface were characterized by tensile test, FT-IR/ATR, XPS, and FESEM. The surface hydrophilicity of the modified MPPMs was evaluated by water contact angle and pure water flux measurements. Besides, the influence of surface charge on protein filtration involving flux decline and protein transmission was also investigated in detail. It is found that the optimal time of DBD plasma treatment is ∼30 s. Mass gain for the MPPMs during the interfacial crosslinking can be controlled conveniently by adjusting the PEI concentration from 1.0 to 15 g/L. The surface hydrophilicity can be significantly enhanced and is durable, characterized by the sharp decrease of water contact angle, the double increase of pure water flux and the stability test. The results of protein filtration suggest that the obtained highly hydrophilic and charged membrane surface is resistant to protein fouling. Furthermore, almost 100% of protein transmission indicates that the microfiltration characteristic of MPPMs is unchanged.

Multilayer adsorption of lectins on glycosylated microporous polypropylene membranes

Affinity membranes are fast growing for bioseparation techniques. Using membrane as the chromatography media can overcome some disadvantages of the column chromatography. The products of affinity membrane chromatography possess extremely high purity due to the highly specific binding between the ligands immobilized on the membranes and the targets in the solution. The glycosylated microporous polypropylene membranes (MPPMs) can be used as affinity membranes for proteins separation on the basis of the specific interactions between saccharide ligands and lectins. These glycosylated membranes can be facilely prepared by the immobilization of saccharide ligands on the poly(2-hydroxyethyl methacrylate) (poly(HEMA))-grafted MPPMs through the reaction between hydroxyl groups and acetylated saccharides. The tentacle-like poly(HEMA) chains on the membrane with pendent saccharide ligands not only increase the specific area of membrane but also are benefit to adsorb multilayer proteins, which can enhance the binding capacity of protein on the affinity membrane. The glucose modified MPPMs can specifically adsorb one kind of lectin, Concanavalin A (Con A). Binding degree of glucose residues on the affinity membrane plays a positive role on the binding capacity of Con A. The protein molecules adsorbed on the outer layer of flexible polymer chains can be transferred into the inner layer through the reversible binding between Con A and glucose residues. Therefore, multilayer of Con A is adsorbed on the affinity membrane. Compared with the competitive eluants, such as glucose and methyl α-mannopyranoside, 1 M HAc solution is more effective to elute the adsorbed Con A from the glucose modified MPPMs. Besides, the results of CLSM directly demonstrate the specific adsorption of proteins on the glycosylated MPPMs.

Surface modification of polypropylene microporous membrane by grafting acrylic acid using physisorbed initiators method

AbstractSurface modification of microporous polypropylene (PP) membrane was performed by graft polymerization of acrylic acid using physisorbed initiators method. The factors effecting on the grafting degree such as monomer concentration, reaction temperature and initiator density were determined. The morphological and microstructure changes of the membrane were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). The pure water contact angle, protein adsorbed amount, water flux, and antifouling property of the grafted membrane were investigated. The results indicated that the pore size and porosity of the grafted membrane were reduced and the static contact angle of pure water on the grafted membrane decreased from 108° to 40° with the increase of grafting degree. The amount of protein adsorbed on the grafted membrane decreased about 30% compared to the virgin polypropylene membrane when the grafting degree was 18.71%. Though the water flux reduced, the flux recovery of the grafted membrane increased 82.66% with the grafting degree 16.0%. The hydrophilic and antifouling property of the grafted membrane also were improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009