Polypropylene Microfiltration Membranes Research Articles

Application of polypropylene microfiltration membranes for separation of wastewater from car wash

In the final stage of washing the car is waxed and rinsed with demineralized water, however, at an initial stage reusing treated effluents as process water is possible. In the current work, the application of microfiltration (MF) polypropylene (PP) membranes for treatment of carwash wastewater was investigated. To compare the transport properties, more hydrophobic PTFE capillary membranes were also used. The examined process is restricted by the fouling phenomenon, which has been thoroughly studied by filtering both the synthetic and real wastewaters. The use of different types of foaming agents and hydrowaxes, allowed to found that the membranes fouling was caused not only by the impurities removed from the car, but also by the mixtures of commercial washing agents. As a result, the permeate flux was quickly reduced, to a level of 100–200 LHM for PP membrane and to 50–150 LHM for PTFE membrane (TMP = 0.05 MPa). Regardless of the degree of feed contamination, the clean permeate with turbidity of 0.2–0.8 NTU was obtained. In the case PTFE membrane, the permeate turbidity was at a level of 2–3 NTU. The tested wastewaters (5–100 NTU) contained the particles with the size in the range of 0.1–400 μm. The removal of larger particles by prefiltration was found to increase the membranes fouling. It has been noted that rinsing the modules with water was not effective. Nevertheless, the membranes were cleaned using alkaline solutions (pH = 11.5–12.0) used at the car wash station to remove insects and to wash the wheel. This procedure was less effective for PTFE membranes, which experienced significantly greater irreversible fouling. It has been shown that the PP membranes used, in addition to removing turbidity, ensured the retention of Escherichia coli in almost 100%.

(TA-APTES)Plus: A rapid, green and universal coating for membrane modification toward oil-in-water emulsion separation

In our previous work, we have developed tannic acid (TA)-3-aminopropyltriethoxysilane (APTES) coating (TA-APTES coating) for membrane surface modification, which has several distinct advantages: suitable for various membranes, hierarchical structures, mild conditions, etc. In this work, we developed (TA-APTES)Plus coating, which exhibits much better performance than our previous TA-APTES coating: (1) Much faster: The membrane modification process based on our (TA-APTES)plus coating only needs 40 min, while our previous TA-APTES coating needs 12 h; (2) Much greener: The (TA-APTES)Plus coating is prepared in pure water system, without Tris-HCl buffer solution, without oxidants such as H2O2 or KIO4; (3) More stable: The (TA-APTES)Plus coating can remain superhydrophilic even after 30 days, which cannot be achieved by our previous TA-APTES coating. Moreover, the (TA-APTES)Plus coating reserves the advantages of our previous TA-APTES coating, such as universality and distinct hierarchical structures. Take polypropylene (PP) microfiltration membrane as an example, the PP membrane modified by (TA-APTES)Plus not only possesses ultra-high pure water flux (11,990 L m−2 h−1 bar−1) and high separation efficiency (>99.8%) of oil-in-water emulsion, but also exhibits excellent stability. Considering its much better performance, the (TA-APTES)Plus coating may become a more powerful tool for membrane modification toward oil/water separation.

Laccase‐Triggered Surface Co‐Deposition of Gentisic Acid and Chitosan for Multifunctional Polymer Membranes

AbstractCo‐deposition of phenols and amines inspired by mussel‐inspired chemistry has attracted much attention in the field of surface and interface science and technology. However, most deposition systems are still limited to phenols with at least one catechol group. In this work, a novel enzyme‐triggered co‐deposition system based on a natural phenol (gentisic acid, GA) and a kind of biomacromolecule (chitosan, CS) is reported. With the catalysis of laccase, GA can be oxidized and further react with CS to form effective surface coatings on various substrates such as polypropylene microfiltration membrane (PPMM). The co‐deposition process takes only 40 min at room temperature and endows the membrane with superhydrophilicity and underwater superoleophobicity. The modified membranes show excellent separation performance, reusability, and long‐term stability for the separation of oil‐in‐water emulsions. The modified membranes are highly charged (pI ≈7.2) and capable of efficient dye adsorption. In addition, the modified membranes possess better protein resistance properties compared with the nascent membranes. This work demonstrates a green, mild, and highly efficient surface modification process based on laccase catalysis. The co‐deposition system comes from natural sources and expands the phenol family for constructing multi‐functional surface coatings.

Janus membranes with asymmetric cellular adhesion behaviors for regenerating eardrum perforation.

The tympanic membrane plays an important role in the human hearing system, which is easily perforated under unfavorable conditions, leading to loss of hearing and otitis media. Many autologous materials and artificial materials have been used to repair a perforated tympanic membrane, but these materials sometimes can cause severe hearing loss because of their adhesion to the ossicle during the healing process and the postoperative process. Herein, we report Janus membranes with asymmetric cellular adhesion behaviors for regenerating the eardrum. These Janus membranes are constructed by co-depositing a tannic acid (TA)/3-aminopropyltriethoxysilane (APTES) coating on one surface of the polypropylene microfiltration membrane. Cellular experiments indicate that the Janus membranes have good biocompatibility and asymmetric cellular adhesion properties. The repair of the tympanic membrane perforation experiment and laser Doppler vibrometer (LDV) measurements prove that the hydrophilic surface of Janus membranes repairs perforated eardrums, and meanwhile the hydrophobic surface can avoid adhering to the inner ear tissue for reducing hearing loss. The Janus membranes have good prospects in the treatment of tympanic membrane perforation.

Biofouling 방지를 위한 항균성 멤브레인 필터의 제조 : GMA의 그라프트 중합과 아민화/술폰화에 의한 표면개질

Biofouling is a major problem of membrane processes in water and wastewater treatment. One of the anti-biofouling strategies is to construct an antimicrobial membrane surface. In this study, polypropylene(PP) microfiltration membranes with antimicrobial property were fabricated by grafting glycidyl methacrylate(GMA), followed by amination or sulfonation with ethylenediamine or sodium sulfite solution. GMA was facilely grafted onto PP membrane by UV-induced graft polymerization, and the graft chains were easily aminated or sulfonated by a simple chemical reaction. The modified PP membranes were characterized by FT-IR, SEM, water permeability and antimicrobial tests. The PP membranes modified by grafting GMA improved the water permeability due to the hydrophilization of the surface, but the antimicrobial activity was too low. In contrast, aminated or sulfonated PP membranes exhibited high antimicrobial activity against both E. coli and S. aureus without a significant reduction in the water permeability.

Rapid formation of metal−monophenolic networks on polymer membranes for oil/water separation and dye adsorption

Surface deposition based on metal-phenolic networks (MPNs) has received increasing interest in recent years. The catechol structure is generally considered to be essential to the formation of MPNs. Our most recent results have demonstrated that some kinds of monophenols can form MPNs on substrate surfaces. Herein, we report a fast and effective surface-coating system based on the coordination of 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid, a kind of monophenol, with Fe3+. Compared with other metal ions such as Cu2+ and Ni2+, Fe3+ with stronger electron acceptability can coordinate with the monophenol more strongly to form MPNs, and moreover, the deposition time significantly decreases to 40 min from generally 24 h. It is demonstrated that the deposition process is controlled by the coordination, Fe3+ hydrolysis, and deprotonation of the monophenol. The coatings endow substrates such as polypropylene microfiltration membrane with underwater superoleophobicity, which can be applied in oil/water separation with high separation efficiency and great long-term stability. In addition, the coated membranes are positively charged and thus are useful in selective adsorption of dyes. The present work not only provides a novel, fast, and one-step deposition method to fabricate MPNs, but also demonstrates that the fabrication efficiency of monophenol-based MPNs is comparable with that of polyphenol-based MPNs.

Surface Coatings via the Assembly of Metal-Monophenolic Networks.

Mussel-inspired surface modification has received significant interest in recent years because of its simplicity and versatility. The deposition systems are still mainly limited to molecules with catechol chemical structures. In this paper, we report a novel deposition system based on a monophenol, vanillic acid (4-hydroxy-3-methoxybenzoic acid), to fabricate metal-phenolic network coatings on various substrates. The results of the water contact angle and zeta potential reveal that the modified polypropylene microfiltration membrane is underwater superhydrophobic and positively charged, showing applications in oil/water separation and dye removal. Furthermore, the single-face modified Janus membrane is promising in switchable oil/water separation. The results demonstrate a novel example of the metal-monophenolic deposition system, which expands the toolbox of surface coatings and facilitates the understanding of the deposition of phenols.

Mussel-inspired hydrophilic modification of polypropylene membrane for oil-in-water emulsion separation

During the water treatment process, the common polymer membranes with high interface energy are frequently contaminated by oily water. The wettability of the separation membrane surface greatly limits the application range of the membrane. Here, a facile method is reported to fabricate a hydrophilic and underwater superoleophobic coating on hydrophobic polypropylene (PP) microfiltration membrane via co-deposition of tannic acid (TA), polyethyleneimine (PEI), and dopamine (DA). After modification, the microfiltration membrane exhibits excellent hydrophilicity, outstanding acid, alkali and organic solvent resistance. In addition, they can be applied to separate n-hexane-in-water emulsions driven by self-gravity with excellent water flux (489 ± 24 Lm−2 h−1) and high separation efficiency (99.8%). The fabricated TA/DA/PEI coating with outstanding performances has great potential application in the field of oily water treatment.

Nitrate hydrogenation by microtubular CNT-made catalytic membrane contactor

Microtubular CNT-made catalytic membrane contactor is proposed for heterogeneous three-phase (i.e. solid-liquid-gas) catalytic processes aimed at hydrogenation and oxygenation of aqueous pollutants. The contactor comprises a mesoporous CNT-made microtube with an internal diameter of ≈ 1.5 mm, wall thickness of ≈ 0.2 mm, pore diameter of ≈30 nm, loaded with a nano-scale metal catalyst. In this study the concept of CNT-made contactors was proved for hydrogenation of nitrate ions. The CNT-made microtubes were fabricated by infiltration of CNT suspension through the polypropylene microfiltration membrane. The CNT-made microtubes were loaded with Pd-Cu catalysts using the wet-impregnation method followed by reduction by H2 gas or sodium borohydride. The catalytic contactors were investigated for nitrate reduction at varied pH (5–9) and H2 pressure (0.5–2.5 bar) in pure KNO3 solutions and groundwater. Lower pH and higher H2 promoted higher nitrate reduction rates but lower selectivity towards the nitrogen gas. The highest catalytic activity of 2.6 mgN/min/gPd was obtained at pH5.0 and H2 gauge pressure of 0.5 bar. The highest selectivity (79%) towards nitrogen gas was achieved at pH7.0 and H2 pressure of 0.1 bar. Hydrogen utilization efficiency of 93.4% (±7.6%) was obtained. Operation in groundwater resulted in lower selectivity to nitrogen than in experiments conducted on KNO3 solutions in deionized water.

Enhancing membrane surface antifouling by implanting amphiphilic polymer brushes using a swelling induced entrapment technique

In this work, a swelling induced entrapment technique was developed to enhance the hydrophilicity and antifouling performances of polypropylene (PP) microfiltration membranes. By this method, three amphiphilic polymers with different chemical structures (i.e., a homopolymer (polypropylene glycol), a di-block copolymer (oligoethylene glycol monooctadecylether), and a tri-block copolymer of ethylene glycol (EO) and propylene glycol) were successfully implanted onto membrane surfaces to be polymer brushes with high density, without having a significant effect on the membrane pore structure. The polymer brushes significantly enhanced the hydrophilicity and protein fouling resistance of the membrane. In particular, when using the di-block copolymer with a short hydrophilic EO chain, the modified membrane showed a low water contact angle, down to 20°, and low adsorption of bovine serum albumin of 1.1 μg cm−2. Furthermore, the implanted polymer brushes exhibited excellent durability. The hydrophobic segments of amphiphilic polymers played a leading role in the implantation and stability of the brushes on the PP membrane surface. This work provides a feasible strategy to achieve surface hydrophilicity and antifouling performances in a hydrophobic membrane for use in high-efficiency water treatment.

One-pot mussel-inspiration and silication: A platform for constructing oil-repellent surfaces toward crude oil/water separation

Superhydrophilic filters with excellent subaqueous oil-repellent surfaces are of great significance in the field of crude oil/water separation. Their pore size should be matched with the separation target (smaller than the oil droplets) based on the “size sieving” principle. However, it is a tricky task to facilely and flexibly tune the pore size of filters to effectively separate oily wastewater containing crude oil droplets with different sizes in practice. Herein, a universal platform based on the one-pot mussel-inspiration and silication has been verified to prepare free-standing nanofilms at the air/water interface and deposited coatings on the polypropylene microfiltration membrane or the copper mesh simultaneously. The evolution of chemistries and morphologies of the free-standing films and the deposited coatings is in real-time monitored to deeply understand the formation of the surfaces. We suggest the mussel-inspiration and the silication is asynchronous, being responsible for the formation of the nanofilm and coating surfaces with tunable hydrophilic moieties and micro-nano composite structures. These structure characteristics endow the surfaces with a superhydrophilicity/superoleophobicity underwater and with a low crude oil adhesion especially in basic aqueous environment or salty water regardless of the salt type. The free-standing nanofilms with nano-sized intervals are able to reject nano-droplets from the crude oil-in-water nanoemulsions. The coated polypropylene microfiltration membrane and copper mesh can be applied in oil-in-water microemulsions and oil/water mixtures separation, respectively. All filters show a highly efficient oil repellence of crude oil (>99%) during the separation. This work contributes a promising concept of a one-pot fabrication methodology for fulfilling task-specific requirements of crude oil/water separation.

Fouling resistant sericin‐coated polymeric microfiltration membrane

AbstractBACKGROUNDGreywater and produced water are undoubtedly valuable resources for reclaimed water, which can lessen the burden on use of freshwater. However, most often the membrane technology used for treatment of greywater and produced water suffers massively from fouling‐related issues. In the present study, a novel and facile method is successfully developed for modification of polypropylene (PP) microfiltration (MF) membrane via surface coating with sericin for imparting better antifouling properties.RESULTThe membrane hydrophilicity significantly improved after sericin coating and exhibited high water content (64.87%) and low water contact angle (38°). In a comparative study with synthetic greywater, the sericin‐coated membrane removed <90% turbidity and produced a greater volume of purified water with 15% less fouling compared to the uncoated membrane. The fouling experiment concludes that the sericin‐coated membrane can reduce reversible and irreversible fouling by ≈30% and ≈83.00%, respectively, relative to the uncoated membrane using pure water backwash operation. In the second case, the sericin‐coated membrane was able to provide consistent permeate quality with produced water: chemical oxygen demand <43 ppm, biological oxygen demand <6.8 ppm, suspended solids completely removed, total dissolved solids <112 ppm, turbidity <5 NTU and oil content <0.044 ppm, together with 10.5% less fouling than uncoated membrane.CONCLUSIONThis study reveals that sericin coating enhanced membrane hydrophilicity and hence exhibited better antifouling properties. The sericin‐coated MF membrane effectively treated greywater as well as produced water with less fouling and within limits of national standards for reusability. © 2019 Society of Chemical Industry

Facile preparation of N-rich functional polymer with porous framework as QCM sensing material for rapid humidity detection

Although many humidity sensing materials have satisfactory properties based on quartz crystal microbalance (QCM) transducer, their synthesis processes are complex. Herein, we report an effective and facile method to modify porous polypropylene microfiltration membrane (PPMM) evenly via the deposition of N-rich functional polymer (PDA-PEI), which was easily synthesized by crosslinking polydopamine (PDA) and polyethyleneimine (PEI). The PDA-PEI modified PPMM well retained the pore structure and was first employed to detect relative humidity based on QCM featured with rapid response, satisfactory repeatability and stability. Compared with PDA modified PPMM, the humidity sensing performance of PDA-PEI modified PPMM is improved considerably. Furthermore, the sensing mechanism study based on Gaussian 09 software reveals that the interaction between PDA-PEI and water molecules belongs to weak chemical adsorption. Such a comprehensive research foresees the potential application of PDA-PEI modified PPMM for fast detection of humidity indoor and outdoor.

Preparation and Characterization of High Flux Polypropylene Microfiltration Membrane via Non-Solvent Induced Phase Separation

Abstract High flux polypropylene (PP) membranes were prepared by using non solvent induced phase separation method. Polyethylene glycol (PEG) was used as an additive. The highest flux was obtains by PP membrane prepared with 5 % wt. PEG, i.e. 1230 Lm-2h-1, while the PP membrane without addition of PEG was 813 Lm-2h-1. The IR Spectra confirmed the presence of PEG in PP membranes. Visualization of membrane morphology demonstrated uniform structure for the PP membrane prepared using addition of PEG 5 %wt. with the pore size within the range 0.3-0.4 µm.

Microfiltration membrane characterization by gas-liquid displacement porometry: Matching experimental pore number distribution with liquid permeability and bulk porosity

The variable viscosity Poiseuille model (VVPM), developed recently to treat gas-liquid displacement (GLD) porometry data for track-etched polyethylene terephthalate (PET) membranes, is applied to polyethersulfone (PES) and polypropylene (PP) microfiltration membranes prepared by phase inversion. It is found that in general aspects the pore size distribution as estimated by the model, with the intrinsic assumption of isolated capillary pores, perfectly reproduces wet and dry fluxes during porometry measurements, but the estimated porosity appeared to be much higher than unity. To eliminate the discrepancy, two additional parameters, namely non-uniformity and tortuosity coefficient, have been introduced in the flux and porosity estimating equations. The apparent viscosity of the gas in porometry analysis is found to be several fold higher than that available in literature, and also the viscosity range appeared to be membrane type dependent. The pore size distribution curve shifts along the diameter axis depending on the gas flow direction applied in porometry data acquisition. However, because the membranes had narrow pore size disribution, the estimated parameters had been averaged within acceptable confidence range. With the inclusion of non-uniformity and tortuosity of the capillaries, the revised version of the VVPM made an advancement in porometry data analysis of membranes with both isolated and interconnected pore structure; it characterizes the assumed model capillaries in terms of Young-Laplace pore diameter, but also non-uniformity and tortuosity of pores. The procedure for data treatment has been illustrated in detail and the method could easily be adapted to gas-liquid displacement porometer software system for regular data treatment. Based on a set of readily available experimental data, including the typical output from standard GLD porometry, the here established extended version of the VVPM allows the step-by-step determination of all the parameters which characterize the pore structure of the membranes. Also the absolute pore number density distributions can be obtained, including estimates of additional pore characteristics such as non-uniformity and tortuosity.

Codeposition of Polydopamine and Zwitterionic Polymer on Membrane Surface with Enhanced Stability and Antibiofouling Property.

Although abundant works have been developed in mussel-inspired antifouling coatings, most of them suffer from poor chemical stability, especially in a strongly alkaline environment. Herein, we report a robust one-step mussel-inspired method to construct a highly chemical stable and excellent antibiofouling membrane surface coating with a highly efficient codeposition of polydopamine (PDA) with zwitterionic polymer. In the study, PDA and polyethylenimine-quaternized derivative (PEI-S) are codeposited on the surface of poly(ether sulfone) (PES) ultrafiltration membrane in water at room temperature. In contrast to individual PDA coating, the obtained PDA/PEI-S coating exhibits excellent chemical stability even in a strongly alkaline environment owing to the cross-linking and unexpected cation-π interaction between the PEI-S and PDA. Thanks to the introduction of PEI-S, systematic protein adsorption tests and bacteria adhesion experiments demonstrated that the surfaces could prevent bovine serum fibrinogen and lysozyme adsorption and could reduce Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli adhesion. Benefiting from the versatile functionality of PDA, the proposed strategy is not limited to PES membrane surface but also others such as poly(ethylene terephthalate) sheets and commercial polypropylene microfiltration membranes. Overall, this work enriches the exploration of a remarkable coating with enhanced stability and excellent antifouling property via a facile, robust, and material-independent approach to modifying the membrane surface.

Tannin-inspired superhydrophilic and underwater superoleophobic polypropylene membrane for effective oil/water emulsions separation

In this work, a novel two-pot coating process that facilely transform polypropylene (PP) microfiltration membrane hydrophobicity into superhydrophilicity and underwater superoleophobicity was reported. Tannic acid (TA) and ferric ions (FeIII) were selected as organic ligand and inorganic cross-linker, respectively. Compared with the membrane modified by the one-pot method, the two-pot treated substrate has uniformly distributed coatings, better wettability, higher water permeability (7092Lm−2h−1bar−1, which is 4.5 times higher than that of the one-pot modified membrane), and excellent oil/water emulsions separation performance. This treatment only took about 15min and the underwater superoleophobicity was well maintained even after rigorous long-term washing operation. More importantly, both the remaining solutions of TA and FeIII could be recycled and reused easily in the next two-pot coating process. Such a rapid, green, and cost-effective modification method highlights its potential for practical application in oil/water emulsions separation.

Fabrication of submicrosized imprinted spheres attached polypropylene membrane using “two-dimensional” molecular imprinting method for targeted separation

The submicrosized imprinted polypropylene microfiltration membrane (SIPM) for salicylic acid (SA) was prepared by water-in-oil emulsion polymerization method and two-dimensional imprinting method based on polypropylene microfiltration membrane with salicylic acid as template molecule, 4-vinyl pyridine as functional monomer, Span 80 as emulsifier, toluene as the oil phase, ethyleneglycol dimethacrylate as cross-linking agent, and 2,2′-azobis (2-methylpropionitrile) as initiator. The structure, morphology, and surface wettability of SIPM were characterized by Raman spectra, contact angle, and scanning electron microscopy. Flux test shows that the submicrosized imprinted spheres on the membrane is beneficial for increasing the membrane flux. Static adsorption experiment indicates that SIPM has a selective rebinding for salicylic acid. Moreover, the adsorption amount of salicylic acid over SIPM increased with properly increasing the amount of imprinted spheres on the SIPM. Permeation experiment shows that transport mechanism for permeation of the salicylic acid and acetylsalicylic acid toward SIPM is accordance with the facilitated mechanism.

Effects of polyethyleneimine molecular weight and proportion on the membrane hydrophilization by codepositing with dopamine

ABSTRACTMussel‐inspired chemistry has attracted widespread interest in the surface modification of polymer membranes. We have previously demonstrated a dopamine (DA) assisted codeposition process of polyethyleneimine onto polypropylene microfiltration membranes (PPMMs) for surface hydrophilization. In this work, we further investigate the effects of PEI molecular weight and DA/PEI mass ratio on the codeposition process and membrane performance. The results indicate that only low‐molecular‐weight PEI bring a distinct promotion in both surface wettability and water permeation flux for PPMMs. On the other hand, either excess DA or PEI is detrimental to the surface hydrophilicity of the studied membranes. The optimized PEI molecular weight is 600 Da and the corresponding mass ratio is 1:1 for the surface hydrophilization of PPMMs. These results are beneficial to understand those codeposition processes of dopamine with other polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43792.

Polypropylene microfiltration membranes modified with TiO2 nanoparticles for surface wettability and antifouling property

TiO2 nanoparticles have attracted much attention in the surface modification of polymer membranes for antifouling purpose due to their excellent hydrophilicity. In this work, a polydopamine/polyethyleneimine (PDA/PEI) intermediate layer was fabricated on the polypropylene microfiltration membrane via a co-deposition method and then TiO2 nanoparticles (NPs) were modified on the membrane surfaces through a sol–gel process. TiO2-modified membranes with various Ti/C ratios were prepared and their surface structures and properties are compared with those of the nascent and PDA/PEI-deposited ones. Results indicate that the TiO2 NPs modification increases both the surface wettability and the water permeation flux of the membranes remarkably. TiO2 NPs also endow the membranes with promoted protein resistance properties. The relative flux reduction and flux recovery ratio are 31±3% and 82±5% for bovine serum albumin solution, while 26±4% and 86±3% for lysozyme solution. The TiO2 NPs are also stable on the membrane surfaces under a wide range of pH value.