Modified Polypropylene Membrane Research Articles

FUNCTIONAL ION MEMBRANES SUPPORTED INSIDE MICROPOROUS POLYPROPYLENE MEMBRANES TO TRANSPORT CHROMIUM IONS: DETERMINATION OF MASS TRANSPORT COEFFICIENT

Polypropylene (PP) membranes incorporating interpenetrating polymer networks of poly[(ar-vinylbenzyl) trimethylammonium chloride](P(ClVBTA)) and poly[sodium (styrenesulfonate)] P(SSNa) were modified via an “ in-situ” radical polymerization synthesis inside the pores. The modified polypropylene membranes were characterized using SEM, ATR/FTIR, DRX, TGA, and Donnan dialysis for the transport of chromium ions. The modified membranes exhibited a percent modification between 2.5% and 4.0% in weight gain and a hydrophilic character with a water uptake capacity between 15% and 20%. The mass transport coefficient was determined using the non-linear fit of the experimental data to the exponential equation. Hexavalent chromium ions were efficiently transported by the modified membranes containing P(ClVBTA). At pH 3.0, the M4Cl.PEI (11.0 ×10-6 m s-1), and at pH 9.0, the M3Cl (14.4×10-6 m s-1) could transport hexavalent chromium ions efficiently using a 1 mol L -1 NaCl extraction agent. In the same way, the transport of trivalent chromium could be performed using membranes modified with P(SSNa). At pH 3.0 and 4.0×10 -2 mol L-1 trivalent chromium in the food chamber, the M9Na.PVA (16.3×10-6 m s-1) performed efficient transport using 1×10-3mol L-1 HNO 3 as the extraction agent.

Hydrophilic modification of polypropylene microporous membranes by grafting TiO2 nanoparticles with acrylic acid groups on the surface

Hydrophilic microporous membranes were prepared based on polypropylene (PP) cast films blended with a commercial acrylic acid grafted polypropylene (PP-g-AA) via melt extrusion followed by grafting titanium dioxide (TiO2) nanoparticles on its surface, annealing and stretching. ATR-FTIR, XPS and EDS analyses showed that the hydrophilic segments of an amphiphilic modifier (PP-g-AA) acted as surface functional groups on the film surface. The results indicated that the presence of the modifier was very important for grafting TiO2 nanoparticles on the film surface. Compared to PP and PP/PP-g-AA blend films, the water contact angle decreased by a factor of 2.5 after grafting TiO2 on the surface of the films, meanwhile the water vapor permeability of the microporous membranes prepared from those films increased by a factor of 1.5. All these results indicated that the hydrophilicity of the modified PP membranes was improved.

Remarkable pH-Responsive Polypropylene Microfiltration Membrane Through Surface Entrapment of Poly(2-(Diethylamino) Ethyl Methacrylate)-Containing Macromolecules by ATRP Method

Polypropylene (PP) microfiltration membrane were functionalized with an adsorption/surface entrapment process, using block copolymers with poly(n-butyl acrylate) (PBA) as anchor block being capable to tether the pH-responsive block poly(2-(diethylamino) ethyl methacrylate) (PDEA) to the surface, Homopolymer and Block copolymer synthesis was investigated by atom transfer radical polymerization (ATRP) using PMDETA, CuBr and ethyl acetate. These polymers were characterized by 1H NMR and GPC. Copolymer of PDEA with polybutylacrylate (PBA) was selected as best suitable modifier. Models related to the underlying deswelling/entrapment process which leads to fixation of the modifier were considered. Surface properties were analyzed by ATR-FTIR spectroscopy and water contact angle measurements, which confirmed the presence of modifier and a strong improvement of surface and pore wettability. The structure of membranes was evaluated using Polarized Optical Microscopy. Furthermore the pH-sensitive properties of modified PP membranes were verified by pH-dependence of water permeability which due to protonation/deprotonation and volume phase transition of PDEA around the pH 6-6.9.

Preparation of thermo-responsive polypropylene membranes via surface entrapment of poly(N-isopropylacrylamide)-containing macromolecules

Thermo-responsive polypropylene (PP) microfiltration membranes have been fabricated via surface entrapment of poly(N-isopropylacrylamide) (PNIPAAm)-containing homopolymer and block copolymers. A previously developed approach based on using solutions of the polymeric modifier in a solvent which swells the base membrane polymer had been used, and conditions have been varied. One block copolymer of PNIPAAm with polybutylacrylate (PBA) had been selected as best suited modifier. Models related to the underlying deswelling/entrapment process which leads to fixation of the modifier have been considered. For PP membrane, characterization of pore size distribution in dry state revealed a significant decrease of pore size as a consequence of the entrapment modification. Surface properties have been analysed by ATR-FTIR spectroscopy and water contact angle measurements, which confirmed the presence of modifier and a strong improvement of surface and pore wettability. The thermo-sensitive properties of either outer surface and inner pore wall of modified PP membranes have been verified by temperature-dependence of captive bubble contact angle and water permeability, respectively, both due to hydratation/dehydratation and volume phase transition of PNIPAAm around the lower critical solution temperature (LCST) of the block copolymer PBA- b-PNIPAAm which was around 31–32 °C. The effects of protein desorption from the modified membrane where bovine serum albumin (BSA) had been previously adsorbed were studied by measuring water flux upon manipulating water temperature during water filtration cum washing. In addition, non-porous PP plates had been modified using the same procedure and all the surface characterization results showed similar modification efficiency and surface properties as for porous PP membranes, confirming the dominating role of entrapment of the amphiphilic functional macromolecules into the PP surface layer instead of simple deposition onto the surface.

Sulfonation Surface Treatment of Plasma Alkali Secondary Lithium Battery Separator

Modified membrane separators with lower cost using non-woven Polypropylene (PP) were widely used in the field of the secondary lithium batteries. Sulfonation is one of the most commonly modified methods for the surface modification of polymers. In order to make it effective in industry production, plasma surface treatment is applied to one, and it is an effective surface activation technology without changing its original properties. The characteristic properties of modified PP membrane separators have been studied by Alkali Absorption property Test, Tensile Strength Test, Fourier-Transform Infrared Measurements (FTIR), Scanning Electron Microscopy (SEM) and X-Ray Photoelectron Spectroscopy (XPS). Sulfonic acid groups in the polymer membranes were evidenced by the FTIR and the XPS spectroscopy. The results showed that the plasma sulfonation treatment reaction was very effective to improve the surface hydrophilicity of the non-woven membranes. The suitable sulfonation process could keep the lower cost in industry production.

Highly hydrophilic and low-protein-fouling polypropylene membrane prepared by surface modification with sulfobetaine-based zwitterionic polymer through a combined surface polymerization method

Poly(sulfobetaine methacrylate) [poly(SBMA)], a zwitterionic polymer, was successfully tethered in high density onto polypropylene (PP) membrane surface through a combined method consisting of UV-induced surface graft polymerization followed by surface-initiated atom transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first immobilized onto PP membrane surface by UV-induced graft polymerization, and then each of the grafted poly(HEMA) chains, after coupled with 2-bromopropionyl groups, provided multiple initiation sites for subsequent ATRP of SBMA. Images from scanning electron microscope (SEM) showed that the membrane surface was fully covered with small dot-like surface structures of poly(SBMA) after 6 h of ATRP. Both attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) and X-ray photoelectron spectroscopy (XPS) confirmed the grafted poly(HEMA) and poly(SBMA) on the membrane surface. Water contact angle measurements showed that the surface hydrophilicity of the PP membrane was improved significantly with the increase of the grafted poly(SBMA) content, and a water contact angle of as low as 17.4° was obtained in this study. Experimental results for protein solution filtration demonstrated that the extent of fouling was significantly reduced and most of the fouling on the modified PP membrane surface was reversible, suggesting good anti-protein-fouling performance.

Non-isothermal bioremediation of waters polluted by phenol and some of its derivatives by laccase covalently immobilized on polypropylene membranes

In view of the heath problems induced by the presence into the environment of endocrine disruptors, laccase from Trametes versicolor was covalently immobilized on a chemically modified polypropylene membrane in order to remove phenol and its derivatives from polluted waters. Using phenol as substrate model the optimal immobilization conditions were determined. The immobilized laccase exhibited maximal enzyme activity at pH 5.5 and optimal temperature at 55 °C. These operative parameters have been compared with those obtained with the soluble laccase in order to ascertain the immobilization effect. When employed in a bioreactor operating under isothermal conditions the immobilized laccase was able to oxidize a wide range of phenolic substrates. In particular it was found that some phenol derivatives (2-CP, 3-CP, 4-CP, NP and chlorophene) were oxidized at a similar rate than phenol, other derivatives (paracetamol, 3-MP and chloroxyphenol) at a smaller rate, while others (2,4-DCP and BPA) at higher rate. When the catalytic membrane was employed in a non-isothermal reactor the reaction rate increased with the increase of the applied temperature difference. Practically the increase of the laccase oxidative power under the non-isothermal conditions followed the same sequence observed under isothermal conditions. Interesting enough, the percentage increase of enzyme reaction rate under non-isothermal conditions resulted higher in the cases in which the isothermal reaction rate was smaller. When the reduction of the production times by the presence of a temperature gradient is considered, the measured values strongly candidate the technology of non-isothermal bioreactors as a useful tool in processes of detoxification of waste waters polluted by endocrine disruptors of phenolic origin.

Surface modification of polypropylene microfiltration membrane via entrapment of an amphiphilic alkyl oligoethyleneglycolether

For surface hydrophilic and antifouling modification of polypropylene (PP) microfiltration membrane, the novel method for entrapment of the amphiphilic modifier octaethyleneglycol monooctadecylether (C 18E 8) was investigated in detail. The effects of the modification conditions on PP membrane and polymer structure were characterized by gas flow/pore dewetting, nitrogen adsorption/BET analysis, scanning electron microscopy and X-ray diffraction; surface properties were evaluated by ATR-FTIR spectroscopy and static water contact angle; filtration performance as well as antifouling property were investigated by water flux measurement, trans-membrane zeta potential, static and dynamic protein adsorption experiments. Furthermore, a stability study of the modified membrane was performed to offer a comprehensive understanding of this physical entrapment strategy. It can be concluded that both outer surface and inner pore walls of PP membrane were covered with oligoethylene glycol after entrapment modification by C 18E 8, with only very slight changes of membrane pore and polymer structures. Correspondingly, PP membrane surface hydrophilicity and antifouling performance were evidently improved. It was also found that the entrapped modifier has a tendency to leach out of the PP membrane in water at room temperature. However, after 8 weeks changes became very small, and the modified PP membrane surface still exhibited significant hydrophilicity and antifouling properties.

Usefulness of microporous hydrophobic polypropylene membranes after plasma-induced graft polymerization of acrylic acid for high-power nickel–cadmium batteries

Commercial microporous polypropylene (PP) membranes were modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation. Under optimized conditions obtained membranes are hydrophilic and may be serviceable as separator in nickel–cadmium cell. Electrolytic resistance of modified membranes is evaluated and compared with that of commercial separators: conventional cellophane separation and hydrophilic polypropylene separation (Celgard 3501). This paper reports the maximum power test data for nickel–cadmium cells equipped with different separators. Cells with modified PP membrane show very good high-rate performance.

Studies on self-assembly phenomena of hydrophilization of microporous polypropylene membrane by acetone aldol condensation products: New separator for high-power alkaline batteries

Commercial hydrophobic polypropylene (PP) membranes were modified by a novel chemical method. This procedure consists of two steps. In the first step, the virgin hydrophobic PP membrane is saturated with acetone; in the second step, the filled membrane is dipped in aqueous KOH solution ( d = 1.28 g cm −3), i.e. in the electrolyte typical for the nickel–cadmium cell. This two-step procedure starts the aldol condensation process of acetone and its products accumulated and adsorbed onto walls of micropores make the membrane hydrophilic. The presented method provided the hydrophilic PP membrane, persistent and soaked with KOH solution with electrolytic resistance of 23–29 mΩ cm 2. This result was compared with the data obtained with commercial hydrophilic membranes: Celgard 3501 and Cellophane. The aldol condensation process of acetone was monitored using the HPLC-ES-MS technique, and modified PP membranes were evaluated by FT-IR and SEM measurements. With the above-mentioned membrane as a separator, nickel–cadmium cells showed good high-rate performance.

Multienzyme‐immobilized modified polypropylene membrane for an amperometric creatinine biosensor

AbstractCreatinine has become an important clinical analyte that is used for the determination of renal and muscular dysfunction. It is essential to determine its concentration in the serum of patients suffering from renal insufficiency. Therefore, an amperometric creatinine biosensor fabricated from a covered platinum/silver electrode with a thin layer of an immobilized multienzyme membrane was studied. Poly(acrylic acid) was introduced onto an argon‐plasma‐treated porous polypropylene membrane surface by graft copolymerization. Subsequently, three different enzymes (sarcosine oxidase, creatinase, and creatininase) were immobilized onto this novel grafted membrane simultaneously via a carbodiimine agent to form a thin layer. The sensor performance was evaluated with a biochemistry analyzer. Moreover, attenuated total reflection/Fourier transform infrared, electron spectroscopy for chemical analysis, and scanning electron microscopy were used to confirm the progression of these reactions. The developed sensor showed a linear detection range of 3.2–320 μM for creatinine in a pH 7.4 buffered solution with 0.1M phosphate. The immobilized multienzyme membrane could be used for at least 3 weeks. The results obtained in our study will hopefully lead to the successful application of modified polypropylene for the development of a creatinine sensor. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3126–3134, 2004

Application of Surface Modified Polypropylene Membranes to an Anaerobic Membrane Bioreactor

In order to increase hydrophilicity and thereby to reduce membrane fouling caused by hydrophobic adsorption, the surface of a hydrophobic 0.2 µm polypropylene (PP) membrane was modified by ozone treatment followed by graft polymerization with 2-hydroxy-ethyl methacrylate (HEMA). The modified PP (MPP) membranes were characterized in terms of contact angle, morphology and degree of grafting (DG). The contact angle was reduced from 112° for a PP membrane to nearly 0° for MPP membranes by introducing functional groups such as hydroxyl (-OH) and carbonyl groups (C=O) on the membrane surface. As the DG increased, the O/C ratio and membrane resistance of the MPP membrane increased. Using the MPP membrane in the crossflow operation of an anaerobic membrane bioreactor (MBR), the membrane permeability was enhanced although it was largely dependent on the DG of MPP.

MEMBRANE SURFACE MODIFICATION AND BACKPULSING FOR WASTEWATER TREATMENT

Using a novel photoinduced grafting method, hydrophobic polypropylene (PP) membranes were rendered hydrophilic by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), to produce a neutral, positive, or negative charge, respectively, on the membrane surface. Using both unmodified and modified PP membranes, as well as a hydrophilic cellulose acetate (CA) membrane, the effects of backpulsing and surface chemistries on membrane fouling were investigated for crossflow microfiltration of bentonite clay suspensions and crude oil emulsions. Without backpulsing, the permeate volumes collected over 60 min were not strongly dependent on membrane surface chemistry and morphology for the filtration of either clay or oil. With backpulsing, however, 5-fold and 6-fold permeate enhancements were obtained by backpulsing alone and by a combination of backpulsing and surface modification, respectively, for clay filtration. The recovered water fluxes after backwashing the PP membranes fouled without backpulsing were approximately 80% of the initial water flux, showing that bentonite fouling is primarily nonadhesive. However, the recovered fluxes with backpulsing were slightly less than those without backpulsing, due to internal fouling after each backpulse. For the filtration of crude oil, 1.3-fold and 2.7-fold permeate volume enhancements were obtained by backpulsing alone and by a combination of backpulsing and surface modification, respectively. More than a 3-fold permeate volume enhancement was obtained upon adding an anionic or cationic surfactant to the oil mixture when the modified membrane was similarly charged. The recovered flux after backwashing the unmodified PP membrane fouled without backpulsing or surfactant was only about 30% of the initial water flux, indicating adhesive primarily fouled by oil, but the recovered flux doubled when the membranes were rendered hydrophilic by surface modification.

Membrane fouling reduction by backpulsing and surface modification

A combined method of backpulsing and membrane surface modification was employed for the reduction of membrane fouling. A novel photoinduced grafting method was used to render polypropylene (PP) membranes hydrophilic with neutral or positively or negatively charged surfaces by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), respectively. Both unmodified and modified PP membranes, as well as commercial cellulose acetate (CA) membranes, were evaluated in a crossflow microfiltration system with and without backpulsing in the presence of Escherichia coli bacterial suspensions. Without backpulsing, the resulting permeate volume is nearly the same for the different membranes. With backpulsing, however, considerable improvement was obtained by surface modification, especially for low feed concentrations and for short filtration times. For example, the permeate volume for backpulsed filtration of 0.14 g/l E. coli for 1 h using the unmodified PP membrane is 1.7 times that without backpulsing, and it is even higher for the other membranes. The permeate volume with backpulsing is highest for the neutral, hydrophilically modified PP membrane and for the commercial CA membrane, approximately 2.6 times that of the unmodified PP membrane without backpulsing. Moreover, the recovered pure buffer flux after backwashing the fouled membranes for an extended period is approximately twice as high for these neutral hydrophilic membranes as it is for the unmodified hydrophobic PP membrane. However, the recovered flux after a long backwash of the membranes fouled with backpulsing is 20–40% lower than that of the membrane fouled without backpulsing, apparently due to greater adhesive internal fouling when the membrane surface is frequently exposed by rapid backpulsing.

Low fluorescence background electroblotting membrane for DNA sequencing.

A low fluorescence background polypropylene (PP) membrane has been developed for ultimate use as an electroblotting membrane in DNA sequencing based on fluorescence detection. The DNA binding capacity of this membrane is improved by a surface modification using radio frequency plasma discharge (RFPD) in ammonia gas. The RFPD operational parameters are evaluated both in terms of membrane nitrogen content and in terms of the product's capacity for binding radioisotope-labeled DNA fragments. The surface morphologies of the derivatized membranes are examined by scanning electron microscopy; their mechanical and electrical properties, which are important for the subsequent sequencing procedures, are likewise established. Due to the goal of developing a membrane suitable for multiplex processing, in which the electroblotted DNA must withstand dozens of hybridization/stripping cycles, special attention is given the covalent attachment of DNA to the membrane. The modified PP membrane is evaluated in a multiplex sequencing application using radioisotope-labeled DNA probes, and found to yield somewhat better binding of a given amount of electroblotted DNA than the commonly used GeneScreen membrane. A tenfold repetition of the probing indicates little loss of signal; the membrane-bound DNA is stable upon storage and shows no detectable loss in probing efficiency after one month.

A one-side hydrophilic polypropylene membrane prepared by plasma treatment

The surface on one side of a hydrophobic polypropylene (PP) membrane was modified with a gaseous plasma of 60 W discharge power in the presence of ammonia gas at 0.9 Torr pressure. Results of contact angle measurements indicate that one side of the hydrophobic membrane was modified; it became hydrophilic while the other side remained hydrophobic. Data from ESCA (electron spectroscopy for chemical analysis; X-ray photoelectron spectroscopy) and ATR-IR (attenuated total reflectance infrared) spectral analysis showed that the hydrophilicity was mainly derived from the amino groups on the modified surface. The modified PP membrane was coupled to urease and used to construct a urea sensor, which gave electrode response time only half that of the conventional urea sensor. The enzyme electrode gave a potential change of 30 mV per decade of increase in analyte concentration. The response of this electrode remained stable during continuous use for up to 12 days.

Structure–property relationships for liquid transport in modified polypropylene membranes

AbstractIn view of the intensifying interest in the application of polymeric membranes in mixture separation processes, the permeation and permselective properties of polypropylene films toward several candidate organic liquids and vapors were investigated. Polymer films were subjected to solvent and thermal treatments, and the effects of these treatments on film morphology and transport properties were studied. Structure–property relationships for membrane permeation were then developed. Polypropylene films were found to be selective toward toluene, relative to isooctane, and p‐xylene relative to o‐xylene. Liquid flux rates were found to depend primarily upon the solubility of the permeants in the films and the absolute difference in the solubility parameters of the polymer–liquid pair provided a good basis for correlation of this effect. Considering liquids of closely similar solubility parameters, fluxes were found to be dependent upon the apparent molecular cross sections of the permeants. Films annealed in various organic solvents at temperatures of 60–100°C exhibited enhanced permeability, with up to fifteenfold increase relative to untreated membranes, but with reduced selectivity towards the permeants. A mechanism to account for these effects through consideration of the influence of treating solvent type on polymer morphology is proposed. It postulates the formation of more open or coarser spherulitic structures as a result of recrystallization in the presence of solvent during annealing. The enhanced flux rates in the treated films are attributed to the changes in the spherulite textures and to diminished intercrystalline tie chain constrainment within the spherulitic substructure.