Microporous Polypropylene Membrane Research Articles

Polyvinylidene fluoride‐co‐chlorotrifluoroethylene and polyvinylidene fluoride‐co‐hexafluoropropylene nanofiber‐coated polypropylene microporous battery separator membranes

AbstractNanofiber‐coated polypropylene (PP) separator membranes were prepared by coating a Celgard® microporous PP membrane with electrospun polyvinylidene fluoride‐co‐chlorotrifluoroethylene (PVDF‐co‐CTFE) and PVDF‐co‐CTFE/polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐co‐HFP) nanofibers. Three PVDF polymer solutions of varying compositions were used in the preparation of the nanofiber coatings. Two of the polymer solutions were PVDF‐co‐CTFE blends made using different types of PVDF‐co‐HFP copolymers. The PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP blend nanofiber coatings have been found to have comparable adhesion to the PP microporous membrane substrate. The electrolyte uptakes and separator–electrode adhesion properties of nanofiber‐coated membranes were evaluated. Both the electrolyte uptake and the separator–electrode adhesion were improved by the nanofiber coatings. The improvement in electrolyte update capacity is not only related to the gelation capability of the PVDF copolymer nanofibers, but also attributed to the increased porosity and capillary effect on nanofibrous structure of the electrospun nanofiber coatings. Enhancement of the separator–electrode adhesion was owing to the adhesion properties of the copolymer nanofiber coatings. Compared with the PVDF‐co‐CTFE/PVDF‐co‐HFP blend nanofiber coatings studied, the PVDF‐co‐CTFE coating was more effective in improving the electrolyte uptake and separator–electrode adhesion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

An absorbing microwave micro-solid-phase extraction device used in non-polar solvent microwave-assisted extraction for the determination of organophosphorus pesticides

A single-step extraction-cleanup method, including microwave-assisted extraction (MAE) and micro-solid-phase extraction (μ-SPE), was developed for the extraction of ten organophosphorus pesticides in vegetable and fruit samples. Without adding any polar solvent, only one kind of non-polar solvent (hexane) was used as extraction solvent in the whole extraction step. Absorbing microwave μ-SPE device, was prepared by packing activated carbon with microporous polypropylene membrane envelope, and used as not only the sorbent in μ-SPE, but also the microwave absorption medium. Some experimental parameters effecting on extraction efficiency was investigated and optimized. 1.0g of sample, 8mL of hexane and three absorbing microwave μ-SPE devices were added in the microwave extraction vessel, the extraction was carried out under 400W irradiation power at 60°C for 10min. The extracts obtained by MAE-μ-SPE were directly analyzed by GC–MS without any clean-up process. The recoveries were in the range of 93.5–104.6%, and the relative standard deviations were lower than 8.7%.

An Ion-Imprinted Microporous Polypropylene Membrane for the Selective Removal of Cu(II) from an Aqueous Solution

An ion-imprinted microporous polypropylene membrane for the selective removal of Cu(II) from an aqueous solution was successfully prepared by combining graft polymerization with chemical modification. The chemical and physical changes of the ion-imprinted membranes surface were characterized by Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (FESEM-EDX), and water contact angle (WCA). The adsorption behaviors of the ion-imprinted membranes towards Cu(II) were investigated in detail using batch experiments. The equilibrium was achieved in approximately 60 min, and the experimental kinetic data fitted the pseudo second-order model better. The maximum adsorption capacity was 183.49 µg/cm2, and the Langmuir equation fitted the adsorption isotherm data. The results of competitive adsorption experiments indicated that the ion-imprinted membranes had high selectivity towards Cu(II), and the selectivity coefficients with respect to Zn(II), Ni(II) and Pb(II) were 60.40, 68.80, and 70.64, respectively. Permeation experiments showed that the ion-imprinted membranes exhibited good permeability and permselectivity towards Cu(II). Furthermore, the ion-imprinted membranes could maintain almost the same adsorption capacity towards Cu(II) even after ten adsorption-desorption cycles.

Surface modification of polypropylene microporous membrane by atmospheric-pressure plasma induced N-vinyl-2-pyrrolidone graft polymerization

Membrane surfaces modified with poly(N-vinyl-2-pyrrolidone) (PNVP) can be endowed with hydrophilicity, biocompatibility and functionality. In this work, atmospheric pressure dielectric barrier discharge plasma graft polymerization of N-vinyl-2-pyrrolidone (NVP) onto polypropylene (PP) microporous membrane surface was studied. The experimental results reveal that plasma treatment conditions, such as discharge power, treatment time and adsorbed NVP amount, have remarkable effects on the grafting degree of NVP. Structural and morphological changes on the membrane surfaces were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR), X-ray photoelectron spectroscope (XPS) and field emission scanning electron microscopy (FE-SEM). Water contact angles of the membrane surfaces were also measured by the sessile drop method. Water contact angles on the membrane surfaces decrease with the increase of NVP grafting degree, which indicates an enhanced hydrophilicity for the modified membranes. The effects of grafting degrees on pure water fluxes were also measured. It is shown that pure water fluxes increase with grafting degree firstly and then decrease adversely. Finally, filtration of bovine serum albumin (BSA) solution and platelets adhesion of the PNVP modified membranes show good protein resistance and potential biocompatibility due to the enhancement of surface hydrophilicity.

Bio-inspired CaCO3 coating for superhydrophilic hybrid membranes with high water permeability

Surface hydrophilicity is a prerequisite of polymer membranes used for clean water regeneration, although commercial membranes are generally manufactured from hydrophobic polymers. Here, we report a promising approach to hydrophilize hydrophobic membranes using a CaCO3-based mineral coating inspired by biomineralization. Poly(acrylic acid) (PAA) brushes, which are negatively charged and can induce nucleation of CaCO3, were tethered on the pore surface of microporous polypropylene membranes (MPPMs) via photoinitiated graft polymerization. The CaCO3-based coating was then fabricated on the pore surface by an alternate soaking process. The resulting mineral coating is composed of CaCO3 nanoparticles which are much smaller than the pore diameter and distributed evenly on the pore surface throughout the membrane, ensuring the separation performance of membranes. Due to the intrinsic superhydrophilicity of CaCO3, the hybrid membranes are superhydrophilic, and show excellent water permeability with high water flux and ultralow operational pressure. As such, this work provides a generally applicable and cost-effective chemical route to improve the surface hydrophilicity of membranes or other porous materials which have potential in chemical separation, microfluidics, catalysis and other applications.

Surface modification of polypropylene membrane by acrylate epoxidized soybean oil to be used in water treatment

AbstractSurface modification of a microporous polypropylene (PP) membrane was performed by graft polymerization of acrylated epoxidized soybean oil (AESO) using UV radiation. This is a simple, environmentally friendly, and low cost method. The factors affecting the grafting degree such as monomer concentration and reaction time were studied. The morphological and microstructure changes of the membrane were characterized by scanning electron microscopy (SEM) and information regarding elemental composition was obtained by energy dispersive X‐ray spectroscopy (EDS). Surface functionalization was studied by X‐ray photoelectron spectroscopy (XPS). Thermal properties were analyzed by differential scanning calorimetry (DSC). The hydrophilicity increment was confirmed by pure water contact angle and swelling measurements. The filtration capability of the modified membrane was analyzed by determining color, turbidity, and chemical oxygen demand (COD) removal from a residual raw water. The results indicated that the contact angle of pure water on the grafted membrane decreased from 90° to 57°. The modified membrane shows filtration capability by removing color in 52% and reducing 95% of turbidity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Surface modification and characterization of an H2/O2 plasma‐treated polypropylene membrane

AbstractLow‐pressure plasma treatments in a 13.56 MHz RF glow discharge of Hydrogen (H2)/Oxygen (O2) gas mixture were used to introduce polar functional groups onto microporous polypropylene (PP) membrane surfaces to improve the hydrophilicity and surface modification. The change in hydrophilicity and surface free energy was monitored by static contact angle measurement. Significant increased surface energy of polypropylene membranes from the H2/O2 mixture gas plasma treatments was observed. The PP membrane surfaces became highly hydrophilic when exposed for only 5 s to the H2/O2 mixture gas plasma. Optical emission spectroscopy (OES) was used to examine the various chemical species of low pressure plasma processing. The chemical structure and surface morphological changes on the membrane surface were characterized by X‐ray photoelectron spectroscopy (XPS) and confocal laser scanning microscopy (CLSM). XPS analysis showed significantly higher surface concentrations of oxygen functional groups for H2/O2 mixture gas plasma‐modified PP membrane surfaces than the originally unmodified PP membrane surfaces. The experimental results revealed low pressure H2/O2 plasma processing is an effective method to improve the surface hydrophilicity of microporous PP membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Changes in Morphology and Activity of Transglutaminase Following Cross-Linking and Immobilization on a Polypropylene Microporous Membrane

Transglutaminase (TGase) was cross-linked with glutaraldehyde, and cross-linked crystalline transglutaminase was immobilized on a polypropylene microporous membrane by UV-induced grafting. Immobilized enzyme activity were calculated to be 0.128 U/cm2 polypropylene microporous membrane. The microstructure and enzyme characteristics of free, cross-linked and immobilized transglutaminase were compared. The optimum temperature of free transglutaminase was determined to be approximately 40 °C, while cross-linking and immobilization resulted in an increase to approximately 45 °C and 50 °C. At 60 °C, immobilized, cross-linked and free transglutaminase retained 91.7 ± 1.20%, 63.2 ± 1.05% and 37.9 ± 0.98% maximum activity, respectively. The optimum pH was unaffected by the state of transglutaminase. However, the thermal and pH stabilities of cross-linked and immobilized transglutaminase were shown to increase.

Research of Immobilization of Transglutaminase on Polypropylene Microporous Membranes

Activated ozone as the carrier，crylic acid as the monomer and glutaraldehyde as the cross-linking agent were used to research the immobilization of transglutaminase on polypropylene microporous membranes. The effect of ozone activation time，grafting time，grafting temperature，monomer concentration and ammonium ferrous sulfate concentration on grafting degree were studied, the Immobilization conditions were also studied. We found the optimal reaction conditions as following: consistency of hexamethylendiamine was 15%，at 50°C for 120min and consistency，at 30°C for 45minites，consistency of enzyme was 15mg/mL at 4°C. So the immobilized amount of protein could come to 30.23mg/g membrane and the activity of immobilized MTG come to 16.9U/g membrane.

Surface Modification of Polypropylene Membrane by RF Methane/Oxygen Mixture Plasma Treatment

The hydrophilic surface modification of micro-porous polypropylene (PP) membranes is achieved by low-pressure 13.56 MHz RF methane (CH4)/oxygen (O2) gas mixture plasma treatment. The changes in surface wettability and surface free energy were examined by static contact angle analysis. The static water contact angle of the plasma modified membrane notably decreased with increases in treatment time and plasma power. The obvious increase in the surface energy of polypropylene membranes due to CH4/O2 mixture gas plasma treatments was also observed. Optical emission spectroscopy (OES) was used to analyze the chemical species of CH4/O2 mixture gas plasma treatment. The variations in the surface morphology and chemical structure of the micro-porous PP membranes were confirmed by confocal laser scanning microscopy (CLSM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) measurements. XPS analysis showed significantly higher surface concentrations of oxygen functional groups for CH4/O2 mixture gas plasma-modified polypropylene membrane surfaces than for the originally unmodified polypropylene membrane surface. The experimental results show the important role of chemical species in the interaction between a CH4/O2 mixture gas plasma and a membrane surface, which can be controlled by surface modification to tailor the hydrophilicity of the membrane to the requirements of various applications.

SURFACE HEPARINIZATION OF POLYPROPYLENE MICROPOROUS MEMBRANES FOR SELECTIVE ADSORPTION OF LOW-DENSITY LIPOPROTEIN

To endow polypropylene microporous membrane(PPMM) with adsorption selectivity to low-density lipoprotein(LDL),a versatile method was developed to covalently immobilize heparin on the PPMM surface.This was achieved by grafting acrylic acid(AA) on the PPMM surface by UV irradiation,and subsequent chemical binding of heparin with ethylenediamine as a spacer.The membrane surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.The hydrophilicity and blood compatibility of the PPMM surface were improved obviously by the surface heparinization.Water contact angle of the membrane surface was decreased from(138±7.2)° for the nascent PPMM to(35.1±2.7)° for the heparinized PPMM with 7.39 μg/cm2 heparin.An enzyme-linked immunosorbent assay(ELISA) was employed to analyze the adsorption of the LDL on the nascent and heparinized PPMMs.It was found that the surface heparinization greatly enhanced the adsorption of LDL both from single protein solution and binary protein solution containing human serum albumin(HSA),and the heparinized PPMM could selectively adsorb LDL from binary protein solution.In addition,the adsorbed LDL could be desorbed from the heparinized PPMM with sodium chloride solution,which indicated the adsorption was of reversibility.

Effect of vessel type and growth regulators on micropropagation of Capsicum annuum

Leaves from 14-d-old Capsicum annuum L. cv. Anaheim seedlings were cultured on Murashige and Skoog (MS) medium containing different combinations of indole-3-acetic acid (IAA) and 6-benzyladenine (BA). After 3 months, cultures were transferred to new medium where BA was replaced with 9 μM isopentenyladenine (2iP) to enhance the growth of shoot buds. Developing shoots were elongated and rooted on MS medium enriched with 9 μM indole-3-butyric acid (IBA). All cultures were maintained in 250 cm3 baby jars covered with a clear polypropylene lid with or without microporous polypropylene membrane. Vessel type and plant growth regulators significantly affected callus morphogenic appearance, organogenesis and in vitro plantlet growth. Ventilated vessels supported photomixotrophic culture and improved regeneration and growth of plantlets. Higher plantlet dry mass and content of photosynthetic pigments, and lower stomatal density of plantlets grown in ventilated than in non-ventilated vessels facilitated ex vitro acclimation and growth.

Membrane surface with antibacterial property by grafting polycation

Biofouling is a major problem for membrane processes in biotechnologies for water treatment. One of the anti-biofouling strategies is to construct an antibacterial membrane surface. In this work, microporous polypropylene membrane (MPPM) was endowed with antibacterial property by grafting polycation and the action mechanism was studied from the viewpoint of the mobility of polycation chains. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) was tethered on the membrane surface by a sequential UV-induced graft polymerization, followed by quaternization with benzyl chloride or iodomethane. To explore the antibacterial mechanism, crosslinking structure was introduced by bifunctional alkylating reagents to modulate the chain mobility of quaternized PDMAEMA. Fluorescein (Na salt) staining, water contact angle measurement, FESEM observation and XPS analysis were used to characterize the grafting density, quaternization ratio, positive charge density, and crosslinking degree of PDMAEMA on the membrane surface. The antibacterial efficiencies of the studied membranes against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were compared with each other and related to the charge density and the chain mobility. These polycation-modified MPPMs exhibit high bactericidal efficiency against both E. coli and S. aureus. We found positive charge density higher than 3.50 μmol cm −2 and 2.50 μmol cm −2, respectively, is enough to obtain 100% antibacterial efficiency in 5 min contact with these two kinds of bacteria. However, once crosslinked the tethered PDMAEMA, the bactericidal activities are almost lost regardless of charge density and contact time. The mobility of grafted polycation is therefore considered to be the prerequisite of antibacterial action.

Cholic acids/salts as barriers to diffusing species: effect of pH.

Bile acids have been absorbed on a microporous polypropylene membrane and the diffusion of ionic and non-ionic compounds through the barriers obtained has been studied at different pH values. Results indicate that permeation rates are affected by environmental pH conditions and an explanation of this behaviour is proposed. This study represents an approach for a pH-controlled drug delivery system.

Hollow-fiber liquid–liquid–solid micro-extraction of lead in soft drinks and determination by graphite furnace atomic absorption spectrometry

A novel hollow-fiber liquid–liquid–solid micro-extraction technique based on simultaneous liquid–liquid micro-extraction and solid phase micro-extraction using a polypropylene microporous membrane has been developed. The applicability of the proposed procedure was evaluated by extraction of Pb(II) from aqueous solutions and soft drinks. The parameters affecting the extraction efficiency were optimized using multivariate methodology, and the analytical features were established. Under optimized conditions, Pb(II) was concentrated for 20 min on three microporous membrane hollow fibers of 6 mm of length each, placed into 20 mL of sample containing 60 μL of toluene and ammonium O,O-diethyl dithiophosphate. The fibers were introduced directly into the graphite furnace as a solid sample, and the analyte was thermally desorbed from the fiber and atomized using ruthenium as a permanent modifier. A detection limit of 7 ng L −1 Pb was obtained for soft drink samples and good repeatability was found for all samples. The enrichment factor varied between 22 and 66, depending if only one or all three hollow fibers were used for the determination of lead. The results suggest that the proposed procedure represents a simple and low-cost micro-extraction alternative rendering adequate limits of quantification for the determination of Pb(II) in soft drink samples.

Surface Engineering of Microporous Polypropylene Membrane for Antifouling: A Mini-Review

The surface properties of polymer membranes are very important to their separation performance. It is generally accepted that a hydrophilic membrane surface is favorable for applications in water treatment and bioseparation, because the hydrophilic surface can enhance water permeate flux and mitigate membrane fouling. Microporous polypropylene membrane (MPPM) is a promising membrane material for membrane distillation and membrane gas–liquid contactor, due to the intrinsically high hydrophobicity of polypropylene. However, it is the hydrophobicity that severely limits the wider application of MPPM in aqueous solutions and biomedical fields. Surface hydrophilization is, therefore, logically necessary. Surface engineering of polymer membranes encompasses those processes which modify the membrane surfaces to confer different properties to those of the bulk and thus improve their in-service performance. This review provides a concise summary and discussion of the surface engineering strategies developed in our laboratory and reported in scientific literature, which aim at enhancing the surface hydrophilicity and antifouling property of MPPM.

Electrochemical characteristics of a new electric double layer capacitor with acidic polymer hydrogel electrolyte

The article presents the results of a study on activated carbon fiber cloth (AC) and a hydrophobic microporous polypropylene (PP) membrane, both chemically modified with acidic acetone aldol condensation products, and on testing their use as an electrode material and separator in electric double layer capacitors (EDLCs). Polymer hydrogel used was based on poly(acrylamide) (PAAM), H2SO4 and water. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy. As a result, the capacitor with polymer hydrogel was found to exhibit similar capacitance as that with the H2SO4 aqueous solution and an excellent high-rate dischargeability. At the 4000th cycle of potential cycling (0.5Ag−1) the specific capacitance of 132Fg−1 was obtained with a energy density of 3.45Whkg−1 at a power density of 56Wkg−1. The above results provide valuable information to explore the novel composition of EDLCs.

Carbohydrate decoration of microporous polypropylene membranes for lectin affinity adsorption: comparison of mono- and disaccharides

Carbohydrates (saccharides) are ubiquitous on the extracellular surface of living cells and mediate a myriad of biological recognition and signaling processes. Carbohydrate decoration of polymer surfaces with covalent attachment of saccharides offers a new realm of opportunities to mimic cellular events such as protein recognition and binding. We describe the carbohydrate decoration (surface glycosylation) of poly(2-hydroxyethyl methacrylate)-grafted microporous polypropylene membranes (poly(HEMA)-g-MPPMs) with mono- and disaccharides. Galactose, lactose, glucose, and maltose were covalently attached on the surfaces of poly(HEMA)-g-MPPMs and were compared in detail. The process was verified by solid state (13)C NMR spectra. Membranes with high binding degree (BD) of saccharide ligands on the surfaces were facilely prepared from poly(HEMA)-g-MPPMs with high grafting degree (GD) of poly(HEMA). For poly(HEMA)-g-MPPM with the same GD of poly(HEMA), the BD of disaccharides is lower than that of monosaccharides and the disaccharide-decorated MPPMs are more hydrophilic than the monosaccharide-decorated ones. The carbohydrate-decorated MPPMs prepared from galactose, lactose, glucose, and maltose (denoted as MPPM-Gal, MPPM-Lac, MPPM-Glc and MPPM-Mal, respectively) recognize and adsorb specifically one of the two lectins, concanavalin A (Con A) and peanut agglutinin (PNA). As the BD of saccharide increases, the "glycoside cluster effect" plays a primary role in lectin adsorption. MPPM-Lac has enhanced affinity to PNA as compared with MPPM-Gal having similar BD of saccharide., on the other hand, MPPM-Mal shows no enhanced affinity to Con A in comparison with MPPM-Glc as the BD of saccharide is above 0.9 μmol/cm(2), where the "glycoside cluster effect" occurs.

Surface Modification of Polypropylene Microporous Membrane by Atmospheric-Pressure Plasma Immobilization of N,N-dimethylamino Ethyl Methacrylate

Surface modification of polypropylene microporous membrane (PPMM) was performed by atmospheric pressure dielectric barrier discharge plasma immobilization of N,N-dimethylamino ethyl methacrylate (DMAEMA). Structural and morphological changes on the membrane surface were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR), X-ray photoelectron spectroscope (XPS) and field emission scanning electron microscopy (FE-SEM). Water contact angles of the membrane surfaces were also measured by the sessile drop method. Results reveal that both the plasma-treating conditions and the adsorbed DMAEMA amount have remarkable effects on the immobilization degree of DMAEMA. Peroxide determination by 1,1-diphenyl-2-picrvlhydrazyl (DPPH) method verifies the exsistence of radicals induced by plasma, which activize the immobilization reaction. Pure water contact angle on the membrane surface decreased with the increase of DMAEMA immobilization degree, which indicates an enhanced hydrophilicity for the modified membranes. The effects of immobilization degrees on pure water fluxes were also measured. It is shown that pure water fluxes first increased with immobilization degree and then decreased. Finally, permeation of bovine serum albumin (BSA) and lysozyme solution were measured to evaluate the antifouling property of the DMAEMA-modified membranes, from which it is shown that both hydrophilicity and electrostatic repulsion are beneficial for membrane antifouling.

Surface hydrophilization of microporous polypropylene membrane by grafting zwitterionic polymer for anti-biofouling

The anti-biofouling properties, i.e. the resistance to protein adsorption and the inhibition of bacterial adhesion (biofilm formation) are of vital importance to separation membranes. Surface hydrophilization is thought to be the most common approach to improve these performances for hydrophobic polymer membranes, such as microporous polypropylene membrane (MPPM). In this work, MPPM was highly hydrophilized by the UV-induced grafting of polysulfobetaine methacrylate (polySBMA), an outstanding representative of zwitterionic anti-/non-fouling polymers. A sequential grafting strategy was improved by combining the conventional benzophenone entrapment and covalent immobilization methods. FT-IR/ATR, XPS and FESEM were used to characterize the detailed surface structures of MPPM. The hydrophilization effect was evaluated by water contact angle (WCA) and pure water flux measurements. Besides, both protein filtration and initial adhesion of bacteria were performed to investigate the anti-biofouling properties of the modified MPPM. The surface hydrophobicity of the bacteria was also measured and correlated with the adhesion results. It is found that the improved strategy allows the grafting to take place on the external surface and the grafting density to be well controlled by modulating the SBMA concentration. The surface hydrophilicity of MPPM is significantly enhanced, characterized by a decrease of WCA from 145 to ∼15° and an increase of flux by 4 times. These hydrophilized MPPM has strong resistance to protein fouling, having a flux recovery ratio higher than 95% under optimized conditions. The initial adhesion of bacteria on the MPPM can be completely suppressed when the grafting density reaches 560 μg/cm 2, regardless of the bacterial surface hydrophobicity.