Polypropylene Membrane Surface Research Articles

Synthesis of hyperbranched polyethylene-graft-poly[3-ethyl-3-(methacryloyloxy)methyloxetane] via chain walking polymerization and ATRP for cationic photo-curing on membrane surface

Polyethylene is among the most widely-used coating materials due to the excellent physical and mechanical properties. However, the chemical inertness and poor solubility limit the application of polyethylene in coating. In this study, hyperbranched polyethylene-based graft copolymers containing functional oxetane groups (HBPE-g-POXMA) were synthesized via chain walking polymerization (CWP) and atom transfer radical polymerization (ATRP) in tandem. Macroinitiators were first synthesized via CWP of ethylene and trimethyl(undec-10-en-1-yloxy) silane following deprotection and esterification reaction. Subsequent ATRP of 3-ethyl-3-(methacryloyloxy) methyloxetane was performed to yield functional polyethylene with controlled molecular weight (MW), relatively narrow MW distribution, good solubility in organic solvents as well as pendant oxetane groups for photopolymerization. Finally, cationic photo-curing of HBPE-g-POXMA was conducted to build crosslinked polyethylene layers on polypropylene membrane surface. The composite membrane showed a narrow pore size distribution (0.03–0.63 μm) and an average pore size of merely 0.31 μm, which exhibited a retention ratio of over 90 % for different dyes. The strategy developed in this study could provide a synthetic route to hyperbranched polyethylene for functional coating via cationic photo-curing.

Surface modification of polypropylene hollow fiber membranes using fluorosilane for CO2 absorption in a gas-liquid membrane contactor

Conventional methods for improving the hydrophobicity of polypropylene (PP) membranes to prevent wetting phenomena require complex pretreatment procedures in order to activate the surface for enabling the reaction with fluorosilane (FS)-based materials. This study successfully prepared PP membrane contactors with enhanced hydrophobicity through a simple single-step dip-coating method using perfluoroether-grafted silanes for CO2 capture. The FS coating layer on the PP membrane surface was confirmed through ATR-FTIR spectroscopy, XPS, FE-SEM, and EDS. Furthermore, the evaluation of the CO2 absorption performance and long-term stability of the FS-coated PP membrane according to the variation of the gas flow rate (50, 100, 200, 400, and 800 mL/min) confirmed the superior chemical stability and durability of our membranes to those of previously reported hydrophobic membranes. The as-prepared FS-coated PP membrane expands the application scope of gas-liquid membrane contactors for CO2 capture from the flue gas of coal-fired power plants.

Advanced super-wetting biaxial polypropylene membrane with hierarchical rough surface for multipollutant removal from oily wastewater

The hazardous toxicity of oily wastewater creates a negative impact on the environment and ecosystem that has made water separation an open challenge on a global scale. A promising and workable tactic to prevent contaminations and effective water separation from oily wastewater has been proved using cutting-edge advanced polymeric membrane-based separation technology. Excessive hydrophobicity, contamination vulnerability, and membrane fouling are recurring and crippling problems for the treatment of oily wastewater. To overcome these difficulties, we design a facile, scalable, and highly efficient layer-by-layer modification technique using polyethylene imine and levo-3,4 dihydroxyphenylalanine cross-linked multi-layer assembled rough biaxial polypropylene membrane surface. The synergistic development of the rough surfaces causes the embeddedness of wetting properties of the modified membrane with excellent superhydrophilicity (0º) and underwater superoleophobicity (∼164.3º). Such great underwater superoleophobicity shows a superior oil-repulsive property that helps to achieve high separation efficiency (99.9 %) and permeate flux (2325.3 L m−2 h−1). Additionally, our modified membrane holds excellent anti-bacterial properties against S. aureus and E. coli bacteria with 92.8 % and 88.6 % viability, respectively. Notably, this highly efficient modified membrane is capable of removing multi pollutants (oil particles and bacteria) from oily wastewater in a more energy-efficient way.

Investigating the wetting behavior of polypropylene hydrophobic membrane using CF4 plasma treatment

Membrane wetting by liquid absorbents limits the performance of membrane contactor, which shows the necessity of using superhydrophobic membranes in these systems. In recent years, the use of plasma irradiation to modify polymer membranes has received much attention from researchers. In this experimental research, the polypropylene membrane surface was irradiated with CF4 plasma at different times to reduce the membrane wetting and create a superhydrophobic surface. The modified membranes were evaluated in terms of measurements of roughness and morphology, chemical properties, and hydrophilicity. In the results of the AFM * and SEM † tests, the structural difference caused by the surface modification and the resulting roughness can be well observed. The FTIR ‡ results showed the creation of new functional groups due to the surface modification process. The physicochemical changes of the modified surface led to an increase in the CA § to 166∘. Finally, the performance of modified membranes was evaluated for protein adsorption, and the results indicated a significant decrease in adsorption for modified superhydrophobic membranes compared to the control membrane. Achieving superhydrophobic PP membranes by plasma treatment without damaging the physical structure of these membranes is a significant result that is simply not achieved by other methods because it causes the membrane tissue to disintegrate. It has also been shown that the conditions of plasma application play a decisive role in the hydrophobicity of modified surfaces.

Stable construction of superhydrophobic surface on polypropylene membrane via atomic layer deposition for high salt solution desalination

A facile and effective strategy, integrating atomic layer deposition (ALD) with photo-deposition, is developed to fabricate uniform a superhydrophobic surface on the membrane for high salt solution desalination. More specifically, a titanium interlayer was prepared by accurately controlled ALD on polypropylene (PP) microporous membrane, then a superhydrophobic modification was constructed on titanium interlayer by covalent silica deposition with nano silane emulsion (NMES). The ALD can uniformly coat an ultrathin TiO2 nanoparticle layer on the PP membrane surface by chemical adsorption, and photo-deposition assembles a stable composite layer reacting with TiO2 nanoparticles. It shows that the contact angle of the PP/TiO2-NMES composite membrane is higher than 150°, which exhibited an excellent anti-wetting capacity in high salt (15 wt%) vacuum membrane distillation. Moreover, the chemically stable bonding between the superhydrophobic layer and the PP membrane made the composite membrane to demonstrate its stability in long-term scaling experiments. Our work provides a viable bottom-up synthesis scheme to tailer and optimizes the inorganic layer on the inert polymeric surface.

In situ formation of tannic (TA)-aminopropyltriethoxysilane (APTES) nanospheres on inner and outer surface of polypropylene membrane toward enhanced dye removal capacity

Tannic acid (TA) − 3-aminopropyltriethoxysilane (APTES) coating (TA-APTES coating) composed of abundant nanospheres with secondary reaction sites has many distinct advantages for surface modification. Herein, an in-situ growth method is proposed to generate TA-APTES nanospheres on both the outer and inner surface of polypropylene (PP) membrane. Compared with previous reported TA-APTES nano spheres coating just on the outer surface of the membrane (named PP-Su-NPs), TA-APTES nano spheres on both outer and inner surfaces prepared with this method (named PP-En-NPs) exhibits much better functional performance after secondary reactions. As a proof of concept, the TA-APTES nanospheres is functionalized by tannic acid, polyethyleneimine (PEI) and Fe3+ to carry positive charges for absorbing anionic dyes, and the dye adsorption performance of the PP-En-NPs after the secondary reactions is 7–8 times higher than that of PP-Su-NPs. Interestingly, the functionalized coating can not only absorb anionic dyes, but also cationic dyes, and selective desorption is also realized for this functionalized coating. The possible mechanism is revealed in this study. This study will accelerate the development of the TA-APTES coating, and make it become a powerful tool for membrane modification.

Effects of Sanding Process on Adhesion of Waterborne Paint Film on a Polypropylene Membrane Surface

Abstract In this article, the surfaces of 2D and 3D polypropylene (PP) membranes were sanded with different brush-type sanding belts and a waterborne primer and topcoat were applied; the effect of the sanding process on the adhesion of the waterborne paint film on a PP decorative membrane surface was tested. A contact angle meter was used to determine the effect of the sanding process on the hydrophilicity of a PP decorative membrane surface. A scanning electron microscope and a roughness tester were used separately to observe the changes in the surface microfeatures and the roughness on PP decorative membranes before and after the sanding process. A 3D profilometer was used to test the changes in the surface roughness and 3D microtopography on PP decorative membranes before and after the sanding process, and a crosscut tester was used to test the changes in the surface adhesion of waterborne paint film on PP decorative membranes before and after the sanding process so as to research the effects of different sanding parameters on the adhesion of waterborne paint films on PP decorative membrane surfaces. The research results showed that the surface sanding process could be used to decrease the surface contact angle, increase the roughness, and improve the wettability of PP decorative membranes. In general, under experimental conditions, a 400-grit sanding belt and two sanding passes were the suitable parameters for 2D PP decorative membranes, and a 320-grit sanding belt and two sanding passes were suitable for 3D PP decorative membranes.

Surface modified polypropylene membranes for treating hydraulic fracturing produced waters by membrane distillation

ABSTRACTMembrane distillation is an emerging technology for treating hydraulic fracturing flowback and produced waters (PW). Suppression of membrane fouling by inorganic and polar and non-polar organic compounds is a challenge. Here, polyhydroxyethyl methacrylate, polyacrylic acid, polvinylallyl imidazolium bromide and polyvinylhexyl imidazolium bromide chains have been grafted from the surface of polypropylene membranes. Fouling happens initially due to adsorption of organic compounds followed by scale formation. When challenged with PW, membranes modified with polvinylallyl imidazolium bromide chains provided the greatest resistance to fouling. For electrocoagulation pretreated PW and synthetic PW that contained mainly inorganic species, the flux decline was much less.

Grafting Branch Length and Density Dependent Performance of Zwitterionic Polymer Decorated Polypropylene Membrane

Branch length and density have critical effects on membrane performances; however, it is regarded to be traditionally difficult to investigate the relationship due to the uncontrolled membrane modification methods. In this study, zwitterionic polymer with controlled grafting branch chain length (degree of polymerization) and grafting density (grafting chains per membrane area) was tethered to the microporous polypropylene membrane surface based on the combination of reversible addition-fragmentation chain transfer (RAFT) polymerization technique with click reaction. The modified membranes were tested by filtrating protein dispersion to highlight the correlations of branch chain length and grafting density with the membrane permeation performances. The pure water flux, the flux recovery ratio are positively and significantly, and the irreversible fouling negatively and significantly correlated with grafting density. These results demonstrate that the larger the coverage of the membrane with poly{[2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl) ammonium hydroxide} (PMEDSAH), the higher the pure water flux and the higher the flux recover ratio, and the lower the irreversible fouling, which shows that high grafting density is favorable to fouling reducing.

Modification and Applications of Hydrophilic Polypropylene Membrane

Polypropylene (PP) is one of the most important polymers for microporous membrane due to its high void volume, well-controlled porosity, high thermal and chemical stability, and low cost. However, the hydrophobicity of PP becomes a limitation to broaden its applications. Furthermore, membrane fouling occurs more seriously on hydrophobic membranes than hydrophilic ones. To solve this problem, surface modifications have been developed to enhance PP membrane hydrophilicity without changing its bulk properties. Graft polymerization and plasma treatment are the most popular techniques for surface hydrophilization. Some studies showed that highly hydrophilic PP membranes with water contact angle less than 20° could be obtained by plasma treatment and graft polymerization. Furthermore, during plasma treatment, polar groups were formed on the PP membrane surface thus increased water uptake. To bring brief explanation on various research trends for PP modification, this paper provides a review of surface hydrophilization of microporous PP membrane, including plasma treatment and graft polymerization. The effects of surface modification on PP membrane performance such as porosity, water contact angle, and water flux are also discussed. In addition, the applications of modified PP membrane are presented as well.

The chemical modification and characterization of polypropylene membrane with environment response by in-situ chlorinating graft copolymerization

In this study, a novel chemical surface modification method of polyolefin membranes is applied following the in-situ chlorinating graft copolymerization (ISCGC). Polypropylene (PP)/methyl methacrylate (MMA) system was used as an example. A unique structure was formed by the modification process on the original membrane surface and the product exhibited an environmental response. Chlorine free radicals were generated using ultraviolet and heat and were used to capture the hydrogen in the polymer chains on the substrate surface. The formed macromolecular radicals could react with MMA over 2h to achieve a high coverage ratio polymer on the PP membrane surface. The graft copolymers were characterized using FTIR, 1H-NMR, DSC, and XPS, which all proved the feasibility of chemically modifying the PP membrane surface by ISCGC. The surface morphology of the grafted PP membrane was characterized using SEM and AFM. The results showed that the grafted product presents a uniform, neat, and dense mastoid structure with an average thickness of 4.44 μm, which was expected to be similar to the brush-like surface structure. The contact angle and AFM tests indicated that the product surface is responsive to solvent and pH. The experimental results showed that the PP membrane surface structure can be reconstructed using ISCGC, a method that can be used for environment-responsive polymer materials. Moreover, the product has the characteristics of polymer interfacial brush.

The functional aqueous slurry coated separator using polyvinylidene fluoride powder particles for Lithium-ion batteries

To improve the performance of lithium-ion batteries, the functional separators were developed by coating water-based polyvinylidene fluoride (PVDF) powder particles solution using polyvinyl alcohol as the binder on both sides of a conventional polypropylene (PP) microporous membrane by means of simple dipping. The electrochemical performance was tested and compared with that of pure PP membrane. It was found that the PVDF powder particles accumulated and scattered on the surface of PP membrane. Many voids existed among the powder particles. The thermal shrinkage percent tested at 130°C for 1h was decreased from 59.4% to 12.7%, whereas the electrolyte uptake was increased from 80% to 140%. The separator coated with 10% solid content of PVDF particles exhibited the best electrochemical performance, including the cycling performance and rate capability. The coated PVDF component not only decreased the interface resistance but also increased the ionic conductivity, owing to the high strong affinity of PVDF toward polar solvents and the voids among the PVDF particles to afford the passage for Li-ions.

Growth of ZnO nanowires on polypropylene membrane surface—Characterization and reactivity

Need for a new membrane is clearly visible in recent studies, mostly due to the fouling phenomenon. Authors, focused on problem of biofouling caused by microorganisms that are present in water environment. An attempt to form a new membrane with zinc oxide (ZnO) nanowires was made; where plasma treatment was used as a first step of modification followed by chemical bath deposition. Such membrane will exhibit additional reactive properties. ZnO, because of its antibacterial and photocatalytic properties, is more and more often used in commercial applications. The authors used SEM imaging, measurement of the contact angle, XRD and the FT–IR analysis for membrane characterization. Amount of ZnO deposited on membrane surface was also investigated by dithizone method. Photocatalytic properties of such membranes were examined through methylene blue and humic acid degradation in laboratory scale modules with LEDs as either: wide range white or UV light source. Antibacterial and antifouling properties of polypropylene membranes modified with ZnO nanowires were examined through a series of tests involving microorganisms: model gram-positive and −negative bacteria. The obtained results showed that it is possible to modify the membrane surface in such a way, that additional reactive properties will be given. Thus, not only did the membrane become a physical barrier, but also turned out to be a reactive one.

Enhancing the hydrophilicity and water permeability of polypropylene membranes by nitric acid activation and metal oxide deposition

Activation by nitric acid oxidation has been combined with atomic layer deposition (ALD) to modify microporous polypropylene (PP) membranes. Nitric acid oxidation with prewetting of t-butanol generates active groups on the inert surface of PP membranes. Metal oxides including Al2O3 and TiO2 are subsequently ALD-deposited on the activated membrane. Nitric acid oxidation is a mild approach to activate PP membranes. A short immersion in nitric acid for 10min is able to generate oxygen/nitrogen-containing active species on the membrane surface, which leads to an evident increase (38%) in the membrane permeability. The mechanical stability and the integrity of the porous structure are well preserved after activation. Surface elemental analyses and microscopy observations confirm the successful deposition of metal oxides thin layers onto the activated membranes. In the deposition of either Al2O3 or TiO2, the hydrophilicity of the deposited membranes is continuously improved with increasing ALD cycles, resulting in further increase in water flux. After 100 ALD cycles, the flux is doubled compared to that of the bare membrane. Al2O3 is more efficient in enhancing the hydrophilicity and permeation than TiO2 under identical deposition conditions because of the faster growth of Al2O3 on the activated PP surface.

Integration of RAFT polymerization and click chemistry to fabricate PAMPS modified macroporous polypropylene membrane for protein fouling mitigation

A copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) grafting-to method was used to tether alkyne-terminated poly(2-acrylamido-2-methyl propane sulfonic acid) (alkyne-PAMPS) to the azide functionalized macroporous polypropylene membrane (MPPM-N3). Alkyne-PAMPS was synthesized by the reversible addition-fragmentation chain transfer polymerization (RAFT) of AMPS with an alkyne-terminated trithiocarbonate served as a chain transfer agent. The combination of RAFT polymerization with click chemistry to graft polymer to the surface of polypropylene membrane produced relatively high grafting density and controllable grafting chain length.The structure and composition of the modified and unmodified MPPM surfaces were analyzed by attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FT-IR), X-ray photoelectron spectroscopy (XPS); field emission scanning electron microscopy (FE-SEM) was employed to observe the morphological changes on the membrane surface.The permeation performances were tested by the filtration of protein dispersion. The experimental results show that with the grafting degree going up, the relative flux reduction decreases, while the relative flux recovery ratio increases, and the protein fouling is obviously mitigated by tethering PAMPS to the membrane surface. The modified membranes can be potentially applied for fouling reduction during the filtration of proteins.

Plasma activation and atomic layer deposition of TiO2 on polypropylene membranes for improved performances of lithium-ion batteries

Atomic layer deposition (ALD) of TiO2 was applied on porous polypropylene (PP) membranes which were used as separators in lithium-ion batteries (LIBs) composed of Li4Ti5O12 (LTO) anode/Li cathode. Without plasma activation on the bare PP membrane, the initial deposition of TiO2 was based on the subsurface nucleation mechanism, which prevented the formation of a conformal hydrophilic TiO2 layer at low ALD cycles. The improvement of wettability of the PP membrane to the electrolyte could only be achieved at high ALD cycles up to 500. However, the severe narrowing of membrane pores counterbalanced the wetting enhancement, which hardly improved the performance of the LIBs. Plasma pretreatment was efficient to generate active groups on the highly chemically inert surface of polypropylene membranes, thus ultrathin TiO2 films could be conformally deposited by ALD on the membrane surface based on the layer-by-layer mechanism at cycles as low as 20. Such a conformal ultrathin layer of TiO2 was confirmed to concurrently overcome both the thermal shrinkage and poor wettability of the PP membranes. Beneficial from the improved wettability at no expense of pore size, the electrochemical performances of LIBs such as specific discharge capacities at different discharge rates were upgraded.

Interfacially polymerized thin-film composite membrane on UV-induced surface hydrophilic-modified polypropylene support for nanofiltration

A novel thin-film composite (TFC) nanofiltration membrane was prepared through interfacial polymerization on surface hydrophilic-modified polypropylene (PP) membrane. Firstly, PP membranes were hydrophilized to ensure the formation of separation layer on it by interfacial polymerization. In this work, the UV-induced grafting of acrylic acid (AAc) was applied to modify the surface of PP membranes. Secondly, the TFC membranes were fabricated on PP membranes with different grafting degrees of AAc via interfacial polymerization. Effects of the UV-induced graft polymerization conditions, such as benzophenone concentration, monomer concentration and UV irradiation time, were systematically investigated. The surface-modified PP membranes and the TFC membranes were characterized with water contact angle measurement, attenuated total reflectance infrared and scanning electron microscopy. Furthermore, the permeation experiments were employed to evaluate the membranes’ nanofiltration performance.

Glycosylation of the polypropylene membrane surface via thiol–yne click chemistry for lectin adsorption

Glycosylated membrane, as one of the most important affinity membranes, permits affinity separation/purification of proteins based on carbohydrate–protein interactions. It is an important scientific issue to screen facile method for fabricating the glycosylated membrane surface with high glycosyl density. Such a surface can be fabricated by the direct covalent immobilization of carbohydrate ligands on the surfaces of microporous polypropylene membrane (MPPM). First, alkyne-functionalized membrane surface was fabricated by plasma pretreatment combined with UV-induced graft polymerization of 3-(trimethylsilyl) propargyl methacrylate. Then, the glycosylated membrane surface was directly fabricated with the thiol–yne click reaction to ensure rapid process, improved efficiency, and high glycosyl density. Chemical and physical properties of the membrane surface were characterized by ATR/FT-IR, XPS, FESEM and water contact angle measurement. Static lectin adsorption indicates that the glycosylated membrane can specifically adsorb lectin concanavalin A (Con A) other than peanut agglutinin (PNA). Break through curves from dynamic Con A adsorption show the membrane has unique properties such as strong specificity, high adsorption capacity, and reversible binding capability. We suggest that the prepared glycosylated membrane is of great potentials in affinity membrane chromatography for rapid and high-resolution separation/purification of lectins.

Hemocompatible Control of Sulfobetaine-Grafted Polypropylene Fibrous Membranes in Human Whole Blood via Plasma-Induced Surface Zwitterionization

In this work, the hemocompatibility of zwitterionic polypropylene (PP) fibrous membranes with varying grafting coverage of poly(sulfobetaine methacrylate) (PSBMA) via plasma-induced surface polymerization was studied. Charge neutrality of PSBMA-grafted layers on PP membrane surfaces was controlled by the low-pressure and atmospheric plasma treatment in this study. The effects of grafting composition, surface hydrophilicity, and hydration capability on blood compatibility of the membranes were determined. Protein adsorption onto the different PSBMA-grafted PP membranes from human fibrinogen solutions was measured by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. Blood platelet adhesion and plasma clotting time measurements from a recalcified platelet-rich plasma solution were used to determine if platelet activation depends on the charge bias of the grafted PSBMA layer. The charge bias of PSBMA layer deviated from the electrical balance of positively and negatively charged moieties can be well-controlled via atmospheric plasma-induced interfacial zwitterionization and was further tested with human whole blood. The optimized PSBMA surface graft layer in overall charge neutrality has a high hydration capability and keeps its original blood-inert property of antifouling, anticoagulant, and antithrmbogenic activities when it comes into contact with human blood. This work suggests that the hemocompatible nature of grafted PSBMA polymers by controlling grafting quality via atmospheric plasma treatment gives a great potential in the surface zwitterionization of hydrophobic membranes for use in human whole blood.

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