Hydrophilic Polyacrylonitrile Research Articles

Visualisierung aktiver Zentren in elektrogesponnenen photoaktiven Membranen mittels Fluoreszenz‐Lebensdauer‐Bildgebung

AbstractDas Interesse an antibakteriellen Nanomaterialien ist in den letzten Jahren aufgrund der zunehmenden Antibiotikaresistenz von Mikroben stark gestiegen. Ihre praktische Anwendung bleibt derzeit jedoch begrenzt, da viele essenzielle Eigenschaften noch eingehend untersucht werden müssen. In dieser Studie wurden neuartige Nanofasermembranen auf der Basis von hydrophilem Polyacrylnitril (PAN) sowie hydrophobem Polycaprolacton (PCL) mit eingebetteten hydrophilen oder hydrophoben Zink(II)phthalocyaninen (ZnPc) als Photosensibilisatoren entwickelt und ihre Wasserdesinfektionseigenschaften untersucht. Um einen Zusammenhang zwischen der Aktivität des Materials und der Zusammensetzung bzw. Struktur herzustellen, wurden mehrere Schlüsseleigenschaften untersucht. Die Ergebnisse der UV/Vis‐Reflexionsspektroskopie zeigen, dass der Aggregationszustand der Farbstoffe innerhalb des Polymerträgers erheblich variiert. Zur Visualisierung der „aktiven Zentren“ wurde die Fluoreszenzlebensdauer‐Mikroskopie (FLIM) verwendet und validiert. Die Ergebnisse dieser Studie liefern nützliche Erkenntnisse für die Entwicklung photoaktiver Nanomaterialien mit maßgeschneiderten Eigenschaften und verdeutlichen den entscheidenden Einfluss der Polymereigenschaften auf die Materialaktivität.

Preparation and characterization of pH-responsive Janus composite membranes with unidirectional moisture drainage and antioxidant resistance

Managing wound exudate, alleviating wound inflammation, and monitoring the healing process are the current focus of wound dressing research. However, the preparation of multifunctional dressings that simultaneously perform these functions remains a challenge. In this study, a pH-responsive Janus composite membrane with unidirectional moisture drainage and antioxidant properties is proposed for the wound healing process. This Janus composite membrane takes advantage of the difference in wettability between the hydrophilic polyacrylonitrile (PAN) layer and the hydrophobic polylactic acid (PLA) layer, which allows the fluid to be exported within 3 s and reduces the adhesion to the wound site. When the fibrous membrane was wetted, curcumin encapsulated in the fibers could be effectively released with a high antioxidant activity of 86.82 %. In response to pH changes during the wound healing process, the Janus composite membrane displays different colors under different conditions, which can be used to monitor wound healing. In addition, the biocompatibility of this Janus composite membrane increases the potential for its clinical use as a multifunctional wound dressing.

A brief review on systematic approach to polymer selection for development of capillary/hollow-fibre membrane for practical applications

Polymeric membranes are widely used for treatment of lean stream in chemical process industries. These membranes are used in different configurations such as tubular, plate & frame, disc-tube, spiral and capillary/hollow-fibre. Membrane modules with capillary/hollow-fibre configuration appears promising in ultrafiltration applications due to its relatively higher packing density, ease of backwashing, ease of cleaning and lower pressure drops since it can be operated at laminar flow regime with high cross-flow velocity. Hence, efforts are being made by researchers to make capillary/hollow-fibre membrane modules from various polymers, ranging from most hydrophilic polyacrylonitrile (PAN) to super-hydrophobic polypropylene (PP) and polytetrafluorethylene (PTFE). Here, we discuss the qualifying properties of the polymeric materials suitable to spin into capillary/hollow-fibre ultrafiltration membranes. Selection of polymers for making fibres requires in-depth knowledge of properties of base polymer and its processability/fabricability. The important properties to be considered for making capillary/hollow-fibre membrane are intrinsic structural properties of the base polymer like degree of crystallinity, tensile strength, tensile modulus, etc. The functional properties such as permeability, hydrophilicity/hydrophobicity etc. also plays role in selecting polymer for a given application. The polymer should also have appreciable dissolution in available solvents or should have degradation temperature higher than melting point so that it can be processed through appropriate membrane preparation process.

Janus C-PAN/PH membrane for simulated shale gas wastewater (SGW) treatment in membrane distillation: Integrating surface property and catalytic degradation for anti-fouling

Membrane distillation (MD) is an effective method for treating shale gas wastewater (SGW), but membrane fouling remains a significant obstacle. To mitigate membrane fouling, we developed a dual-layer nanofibrous catalytic membrane (C-PAN/PH) that includes a hydrophilic polyacrylonitrile (PAN) layer with Co-TPML nano-catalysts and a hydrophobic poly(vinylidene fluoride-hexafluoropropylene) (PH) layer. This novel membrane can effectively treat feed solutions containing kerosene or aniline due to its surface hydration and peroxymonosulfate (PMS) activation. The water flux of the C-PAN/PH membrane was 38% higher than that of the PH membrane due to the higher thermal conductivity of hydrophilic layer. The C-PAN/PH membrane also exhibited stable flux for 10 h in treating 3,000 mg/L oil/water emulsion due to its hydration capability. Moreover, the C-PAN/PH membrane removed over 92% of the aniline within 2 min, and electron paramagnetic resonance (EPR) analysis indicated that reactive species (•OH and SO4•-) played a primary role in the degradation process. Density functional theory (DFT) simulations suggested that PMS was strongly adsorbed on Co with an adsorption energy of −3.77 eV. This study aimed to design a novel membrane specifically for MD in SGW treatment.

Multi-functional nanofiber membranes with asymmetric wettability and pine-needle-like structure for enhanced moisture-wicking

Developing air cleaning membranes that simultaneously meet the needs of efficient moisture transfer, particulate matter (PM) filtration, and bacterial inhibition still faces great challenges. Herein, a membrane with asymmetric wettability and pine-needle-like nanorods (NRs) was successfully prepared through hydrothermal treatment following sequential electrospinning. The zinc oxide (ZnO) nanorods, in-situ grown on the hydrophilic polyacrylonitrile (PAN) fibers, guide water transfer by extending to hydrophobic polyvinylidene fluoride (PVDF) channels, enhancing unidirectional water transport. Meanwhile, the ZnO nanorods also release antibacterial active ingredients and increase the contact between fibers and aerosols, so harmful microbes are deactivated after the aerosols are captured by the membrane. Consequently, the PVDF/(ZnO NRs@PAN) membrane exhibits an excellent water vapor transport rate (12.47 kg m−2 d−1), PM0.3 removal efficiency (99.83%), and bacteria inhibition rate (99.99%). Moreover, the membrane maintains high filtration performance after 10-cycle filtration and cleaning. Thus, the membrane shows extensive application prospects in the scenario that involves aerosol filtration, moisture management, and microbe inhibition, such as masks, protective clothing, and fresh air systems. This work paves the way for developing multi-functional air cleaning membranes with asymmetric wettability, based on interface design and microstructure regulation.

Synthesis of poly (vinylidene fluoride)/polyacrylonitrile electrospun substrate-based thin-film composite membranes for desalination by forward osmosis process

As a water treatment process that has the potential to require low energy inputs, forward osmosis (FO) has experienced a significant breakthrough in recent decades, particularly in membrane development. This paper focuses on blending poly (vinylidene fluoride) (PVDF) with hydrophilic polyacrylonitrile (PAN) to form PVDF/PAN substrates for thin film composite membranes (TFC). The membranes were characterized using a scanning electron microscopy, iS50 FTIR spectrometer, and contact angle system. With high porosity, low tortuosity, and interconnected hydrophilic pores of their substrates, the obtained TFC membranes showed high water fluxes. These membranes yielded superior water and reverse salt fluxes in FO tests compared to the commercial CTA membrane. The membranes also showed excellent mechanical performance under PRO test conditions.

A Multifunctional Janus Electrospun Nanofiber Dressing with Biofluid Draining, Monitoring, and Antibacterial Properties for Wound Healing.

Wound healing greatly affects patients' health and produces medical burden. Therefore, we developed a multifunctional electrospun nanofiber dressing, which can inhibit methicillin-resistant Staphylococcus aureus (MRSA), drain excessive biofluid to promote wound healing, and simultaneously monitor wound pH level. The polyoxometalate (α-K6P2W18O62·14H2O, P2W18) and oxacillin (OXA) are encapsulated in hydrophobic polylactide (PLA) nanofiber to synergistically inhibit MRSA. The phenol red (PSP) is encapsulated in hydrophilic polyacrylonitrile (PAN) nanofiber to sensitively indicate wound pH in situ. The PSP/PAN nanofiber is directly electrospun on the patterning OXA/P2W18/PLA nanofiber layer to form a Janus dressing. By taking advantage of the wettability difference between the two layers, the excess biofluid can be drained away from the wound. In addition, the Janus dressing exhibits good biocompatibility and accelerates wound healing via its antimicrobial activity and skin repairing function. This multifunctional Janus electrospun nanofiber dressing would be beneficial for wound management and treatment.

Ultralight electrospun fiber foam with tunable lamellar macropores for efficient interfacial evaporation

Solar-driven interfacial evaporation is regarded as one of the most promising technologies to address the critical issue of global water scarcity. However, a great deal of energy is lost via conduction during the interfacial evaporation process. Herein, a self-floating Janus evaporator containing micron-sized isolated bubbles that can enhance heat localization is designed. The evaporator is synthesized by gas foaming polyacrylonitrile (PAN) nanofibers and subsequently depositing polypyrrole (PPy). The hydrophilic PAN nanofiber layer on the bottom of the evaporator with abundant macropores can continuously pump water upward through the capillary force. The hydrophobic PAN@PPy composite nanofiber layer on the top possesses a broadband solar absorption property, converting solar irradiation to heat efficiently. The low thermal conductivity of the isolated micron-sized bubbles enhances the thermal insulation of the obtained PAN foam@PPy Janus evaporator, while the stretching and expanding of the nanofibers induced by the bubbles contribute to its increased mechanical stability. This work offers a simple route to fabricate evaporators that can continuously produce drinking water from brine under sunlight, and provides a fresh idea to enhance the thermal insulation and mechanical properties of the conventional electrospinning-based fiber scaffold.

Hydrophilic/hydrophobic nanofibres intercalated multilayer membrane with hierarchical structure for efficient oil/water separation

Developing a membrane integrating high permeating flux and high separation efficiency for the purification of oil-in-water emulsions is significant but still challenging due to the perm-selectivity “trade-off”. Herein, we design a nanofibrous membrane with special hydrophilic/hydrophobic intercalated multilayer structure to efficiently separate oil-in-water emulsions. The multilayer membrane is composed of alternatively deposited hydrophilic polyacrylonitrile (PAN)/ZnO nanoneedles composite fibers layers and hydrophobic poly(vinylidene fluoride-co-hexa-fluoropropylene) (PVDF-HEP) fibers layers, where vertically grown ZnO nanoneedles pierce through PVDF-HEP fibers layer and connect the whole membrane up and down. The special multilayer structure can exert the synergistic effect between size sieving mechanism of hydrophilic layers and coalescence mechanism of hydrophobic layers during the separation of oil-in-water emulsion, which overcomes the size mismatch between large pore sizes of membrane and small droplets of emulsion. With the mean pore size of 1.1 μm for the multilayer composite membrane, a high permeating flux up to 32,100 L m-2h−1 bar−1 with the oil content in filtrate as low as 4 mg L−1 for treating toluene-in-water emulsion (a mean droplet size of 650 nm) was achieved. The separation performance is obviously superior to the hydrophilic membrane without hydrophobic layers intercalated structure. Our work provides a new strategy for developing hydrophilic-hydrophobic composite membranes to alleviate the trade-off between permeating flux and separation efficiency in oil/water emulsion separation through rationally designing the membrane structure.

A detachable sandwiched polybenzimidazole-based membrane for high-performance aqueous redox flow batteries

A cost-effective membrane is critical for commercialization of aqueous redox flow batteries (ARFBs). In this work, we design and fabricate a membrane composed of a thin polybenzimidazole (PBI) dense film physically sandwiched by two polyacrylonitrile (PAN) electrospun nanofiber layers. The thin PBI dense film (7 μm thick) simultaneously diminishes its area resistance and retains its innate ultrahigh ion selectivity, while the hydrophilic PAN porous layers (10 μm thick on each side) reinforce and protect the thin PBI dense film. As a result, the composite membrane enables a vanadium redox flow battery, one of the most promising ARFBs, to achieve a coulombic efficiency (CE) of 99.8% and an energy efficiency (EE) of 80.7% at the current density of 300 mA cm−2, surpassing the efficiencies using the commercial Nafion 211 membrane (CE∼97.7%, EE∼78.6%) and representing one of the best performances of the batteries using composite membranes in the open literature. More importantly, our detachable sandwiched design allows facile fabrication and wide choices of supporters, thereby providing more opportunities for the development of low-cost and high-efficiency membranes for ARFB applications.

Magnetic‐controllable Janus fibrous membranes with wind‐resistant floatability for airflow‐enhanced solar evaporation

AbstractInterfacial solar evaporation has been widely regarded as a promising pathway to desalinate seawater without secondary pollution and additional carbon emission. However, one of the challenges rarely considered is the floating stability and remote controllability of the evaporator in the face of wind and waves at the seawater surface. Herein, we demonstrate magnetic Janus membranes (MJMs) with remotely magnetic controllability and wind‐resistant floatation for enhanced interfacial solar evaporation in airflow condition. These membranes are fabricated by sequential electrospinning of a hydrophobic Fe3O4‐embedded polyvinylidene fluoride (PVDF) layer and a hydrophilic polyacrylonitrile (PAN) layer. Due to the superparamagnetism of Fe3O4, our MJMs can be remotely manipulated by a magnet and can float in situ with the aid of a magnetic field, even facing the blast of airflow with a speed of 1.75 m/s. Moreover, the MJMs realize an enhanced vapor diffusion under airflow (v = 0.5 m/s) and show a water evaporation rate of 1.39 ± 0.06 kg∙m−2∙h−1 under one sun, which is 40.4% higher than that in windless condition. This work provides a promising material solution with magnetic design for the practical offshore application of Janus membranes in interfacial solar evaporation.

Air nanobubbles (ANBs) incorporated sandwich-structured carbon nanotube membranes (CNM) for highly permeable and stable forward osmosis

The selective transport of water/ions through conventional forward osmosis (FO) membranes is largely impeded by solution-diffusion and internal concentration polarization (ICP). Herein, we report a novel air nanobubbles (ANBs) incorporated sandwich-structured carbon nanotube membrane (CNM) for highly permeable and stable FO desalination by taking advantage of the nanofluidic transport at the solid/liquid/vapor interface. Fluorinated multi-walled carbon nanotubes (F-MWCNTs) were assembled as the superhydrophobic interlayer between a hydrophilic cellulose acetate (CA) layer and a hydrophilic polyacrylonitrile (PAN) nanofibrous layer. The trapped ANBs in the superhydrophobic F-MWCNT layer crucially regulated the continuous water flow and effectively prevented salt diffusion. When tested with DI water as feed solution (FS) and 1 ​M NaCl as draw solution (DS), the ANBs incorporated sandwich-structured CNM achieved high water flux (158.0 ​L ​m−2 ​h−1) and ultralow reverse salt flux (0.4 ​g ​m−2 ​h−1) simultaneously, far beyond the state-of-the-art FO membranes. The PAN nanofibrous layer well protected the entrapped ANBs to allow a more durable FO performance. An ANBs-regulated nanofluidic flow model was proposed to elucidate selective water/salt transport mechanism. This work revealed the feasibility of ANBs incorporated membranes for osmosis-driven processes.

In situ photo-thermal conversion nanofiber membrane consisting of hydrophilic PAN layer and hydrophobic PVDF-ATO layer for improving solar-thermal membrane distillation

Solar thermal membrane distillation is a promising technology for low-cost desalination and water purification. A novel photo-thermal conversion membrane composited by polyacrylonitrile (PAN) nanofiber layer and polyvinylidene fluoride (PVDF) with antimony tin oxide (ATO) as solar-thermal nanoparticles (PVDF-ATO/PAN nanofiber membrane) was fabricated by sequent electrospinning techniques. The dual-layer membrane with hydrophilic PAN and hydrophobic PVDF-ATO was examined by microscopic evaluation and contact angle measurement. In situ temperature increase on membrane superficial layer (PVDF-ATO) driven by solar light illumination was confirmed by thermal imaging system. PAN layer provides water transport channels for facilitating water flow of highly efficient membrane distillation and avoids the salting assembly during the vigorous evaporation. With the help of hydrophilic PAN layer, our PVDF-ATO/PAN nanofiber membrane can fulfill highly effective localized heating transfer with an evaporate rate of 0.93 kg m−2 h−1, showing great potential for low-cost water desalination and scalable water purification.

Simultaneous alkaline hydrolysis and non-solvent induced phase separation method for polyacrylonitrile (PAN) membrane with highly hydrophilic and enhanced anti-fouling performance

Microporous membranes are now favorably used as a separation tool for the purification of water and wastewater containing fine particles and macromolecular contaminants. However, organic fouling has often become one of the major problems hindering the wider applications of these membranes. In this study, a highly hydrophilic polyacrylonitrile (PAN) membrane with excellent anti-fouling performance was prepared from a method simultaneously combining alkaline hydrolysis and non-solvent induced phase separation (NIPS) processes together. The interplay of the PAN alkaline hydrolysis and NIPS was examined for its effects on both the structural and chemical properties of the prepared membranes. Morphological and porometric analyses confirmed that the new method produced PAN membranes with less macrovoids but highly ordered narrow flow channels in the cross-section structure, as well as a much denser selective surface layer with small and greatly uniform pore sizes. Characterizations in membrane surface wettability and chemical compositions revealed that the new preparation approach can endow the obtained membranes with significantly enhanced surface hydrophilicity as well as oleophobicity within a much shorter preparation time, in comparison with other conventional preparation methods, including the post alkaline hydrolysis of PAN membranes. Filtration experiments for oil (hexadecane)-in-water emulsion, NOM (humic acid) or protein (BSA) solutions have all confirmed that the developed membranes showed remarkably slow flux declining during filtration operation and high flux recovery by simple water flushing for membrane cleaning. Hence, it is anticipated that there is a great potential for the new approach to fabricate anti-fouling PAN membranes, especially for more challenging separation applications in water and wastewater treatment.

Fabricating Antibacterial and Antioxidant Electrospun Hydrophilic Polyacrylonitrile Nanofibers Loaded with AgNPs by Lignin-Induced In-Situ Method.

Concerning the environmental hazards owing to the chemical-based synthesis of silver nanoparticles (AgNPs), this study aimed to investigate the possibility of synthesizing AgNPs on the surface of polyacrylonitrile (PAN) nanofibers utilizing biomacromolecule lignin. SEM observations revealed that the average diameters of the produced nanofibers were slightly increased from ~512 nm to ~673 nm due to several factors like-swellings that happened during the salt treatment process, surface-bound lignin, and the presence of AgNPs. The presence of AgNPs was validated by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) analysis. The amount of synthesized AgNPs on PAN nanofibers was found to be dependent on both precursor silver salt and reductant lignin concentration. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectra confirm the presence of lignin on PAN nanofibers. Although the X-ray diffraction pattern did not show any AgNPs band, the reduced intensity of the stabilized PAN characteristics bands at 2θ = 17.28° and 29.38° demonstrated some misalignment of PAN polymeric chains. The water contact angle (WCA) of hydrophobic PAN nanofibers was reduced from 112.6 ± 4.16° to 21.4 ± 5.03° for the maximum AgNPs coated specimen. The prepared membranes exhibited low thermal stability and good swelling capacity up to 20.1 ± 0.92 g/g and 18.05 ± 0.68 g/g in distilled water and 0.9 wt% NaCl solution, respectively. Coated lignin imparts antioxidant activity up to 78.37 ± 0.12% at 12 h of incubation. The resultant nanofibrous membranes showed a proportional increase in antibacterial efficacy with the rise in AgNPs loading against both Gram-positive S. aureus and Gram-negative E. coli bacterial strains by disc diffusion test (AATCC 147-1998). Halos for maximum AgNPs loading was calculated to 18.89 ± 0.15 mm for S. aureus and 21.38 ± 0.17 mm for E. coli. An initial burst release of silver elements within 24 h was observed in the inductively coupled plasma-atomic emission spectrometry (ICP-AES) test, and the release amounts were proportionally expansive with the increase in Ag contents. Our results demonstrated that such types of composite nanofibers have a strong potential to be used in biomedicine.

Multi-scaled, hierarchical nanofibrous membrane for oil/water separation and photocatalysis: Preparation, characterization and properties evaluation

Increasing oily wastewater is produced by various industrial, various oil-water separation technologies and materials have been developed to solve this issue. A facile method is proposed to build multi-scaled and hierarchical membranes with efficiently oil/water separation and photocatalysis. The multi-scaled, hierarchical membrane is fabricated by a hydrophilic polyacrylonitrile (PAN) electrospinning nanofibrous and PAN/TiO2 electrospraying spheres, then the polydopamine (PDA) decorated membrane via in-situ growth. This multi-scaled, hierarchical structure endows the membrane with superhydrophilicity (water contact angle ∼ 0°), and underwater superoleophobicity (oil contact angle ∼152°). And the multi-scaled, hierarchical membrane shows superior water permeation and hydrophilic properties than pure PAN membranes. In addition, the membrane indicates an excellent photocatalytic ability for organic pollutant (∼98 %). And after 5 cycles, the water flux still maintains a high level showing good recyclability. This multi-scaled, hierarchical nanofibrous membrane shows very promising application potentials in oil-water separation and photocatalysis.

Polyacrylonitrile Nanofiber Membrane Modified with Ag/GO Composite for Water Purification System.

Silver nanoparticle-modified graphene oxide (Ag/GO) was reliably prepared by using sodium borohydride (NaBH4) in the presence of citric acid capping agent via a simple wet chemistry method. This rapidly formed Ag/GO composite exhibited good dispersity in a solution containing hydrophilic polyacrylonitrile (PAN). Subsequent electrospinning of this precursor solution resulted in the successful formation of nanofibers without any notable defects. The Ag/GO-incorporated PAN nanofibers showed thinner fiber strands (544 ± 82 nm) compared to those of GO-PAN (688 ± 177 nm) and bare-PAN (656 ± 59 nm). Subsequent thermal treatment of nanofibers resulted in the preparation of thin membranes to possess the desired pore property and outstanding wettability. The Ag/GO-PAN nanofiber membrane also showed 30% higher water flux value (390 LMH) than that of bare-PAN (300 LMH) for possible microfiltration (MF) application. In addition, the resulting Ag/GO-PAN nanofiber membrane exhibited antibacterial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive). Furthermore, this composite membrane exhibited outstanding anti-fouling property compared to the GO-PAN nanofiber membrane in the wastewater treatment. Therefore, the simple modification strategy allows for the effective formation of Ag/GO composite as a filler that can be reliably incorporated into polymer nanofiber membranes to possess improved overall properties for wastewater treatment applications.

Vein-supported porous membranes with enhanced superhydrophilicity and mechanical strength for oil-water separation

Oil fouling is a major obstacle for the efficient and reliable oil-water separation of mesh-based membrane processes. Innovations in membrane materials and preparation processes are therefore needed to develop anti-oil-adhesion strategies. This study reports a series of vein-supported porous membranes (VPMs) fabricated by casting polyacrylonitrile (PAN) on veins through non-solvent induced phase separation, confirmed by FTIR, SEM and XRD characterizations, and applied as an effective oil-water separation membrane. Benefiting from the combination of tubular-like vein and hydrophilic PAN, the resultant VPM demonstrates a fine-tunable morphology and superhydrophilicity, extremely boosting underwater superoleophobicty, mechanical strength and superior performance for oil/water separation to various oily mixtures/emulsions, showing underwater oil contact angles over 157° and nearly zero underwater oil adhesion. In oil-water mixture separation process, a separation efficiency of > 99% and ultrahigh permeation flux of 9592 LMH can be achieved under gravity conditions using VPM-2 (casting with 2 wt% PAN). For oil-water emulsion separation, a highest flux of 3011 LMH and trace oil concentration <10 ppm in the filtrate was generated using VPM-9 (casting with 9 wt% PAN) under a low external pressure of 3 kPa. The VPM-2 membrane is further carried out a 40-h cycling separation, showing a constantly stable water flux of ~6000 LMH. The developed VPMs open a bright path to use biomaterials for design and fabrication of novel oil-water separation membrane.

Correlation between membrane surface properties, polymer nature and fouling in skim milk ultrafiltration

The fouling of the membranes in skim milk ultrafiltration with the nominal molecular weight cut-off (MWCO) of 100 kDa fabricated from different polymers (polysulfone (PSF), polysulfonamide (PSA), aromatic polyamide (PA), polyacrylonitrile (PAN), cellulose acetate (CA) and regenerated cellulose (RC)) was studied. The membrane structure and physical-chemical properties of the selective layer were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (θ, °) measurements, free surface energy measurements and bovine serum albumin (BSA) adsorption. Additionally, the flux of the skim milk at the constant product concentration, protein adsorption, resistance of the gel layer of the membranes were determined. It was found that according to the decrease in water contact angle of the membrane selective layers membranes can be arranged in the series as follows: PSF > PSA > PA > PAN > CA > RC. It was revealed that there was no direct correlation between the membrane hydrophilicity and the protein adsorption. It was noted, that the studied membranes featured significantly different hydraulic resistances of the protein gel-layer, which can be considered as a secondary dynamic membrane. Comparison of the parameters – water contact angle and polar component of the free surface energy of the membrane selective layer, and normalized dipole moment of the membrane polymers - with the adsorption values of the proteins during ultrafiltration proves that the protein adsorption to the membrane surface increases with an increase in hydrophobicity and polarity of the membrane. The high protein adsorption by the moderately hydrophilic PAN membrane is due to the contribution of the high normalized dipole moment of the polymer. In the case of the polar RC-100 membrane, the influence of the membrane polarity was shown to be counter-balanced by its high hydrophilicity. The study highlights the impact of the physical-chemical properties and structure of the membrane on the protein gel-layer and thus their importance in membrane fouling control in dairy applications.

Surface PEGylation of polyacrylonitrile membrane via thiol-ene click chemistry for efficient separation of oil-in-water emulsions

Because of their low hydrophilic properties, the polymeric membranes are always subjected to fouling problems, which have become a major obstruction in the path of the practical application of membrane technology in oil–water separation. The present work describes a highly hydrophilic polyacrylonitrile (PAN) membrane successfully developed via thiol-ene click chemistry. To fabricate the membrane, the pristine PAN membrane was first hydrolyzed and then reacted with cysteamine hydrochloride to create a thiolated surface. Afterward, poly(ethylene glycol) methyl ether methacrylate (PEGMA) was covalently grafted onto the thiolated surface to obtain the PEGylated membrane. The effects of the number-average molecular weight (Mn) of PEGMA monomers on the structure, surface wettability, anti-fouling abilities and separation performances of the PEGylated membrane were investigated systematically. The grafting density of PEGMA chains increases with the increase in PEGMA concentration in the reaction solution, whereas it diminishes with the increasing Mn of PEGMA monomers as a result of the steric hindrance. The PEGylated PAN membrane has the superhydrophilic and underwater superoleophobic characteristics when it is grafted with the low-Mn PEGMA monomers. It is observed that the surface grafting of PEGMA chains results in the reduction of membrane pore size, which endows the PEGylated PAN membrane with a low flux. The separation efficiency of PEGylated membrane for several kinds of oil-in-water emulsions is as high as 99.9%, indicative of an excellent separation performance. The cycle filtrations of oil-in-water emulsions demonstrate that the flux decline of PEGylated membrane caused by both the irreversible and reversible fouling is suppressed effectively, as compared with the pure PAN membrane. Even after the three-cycle filtration of the oil-in-water emulsion, the recovery ratio of pure water flux of PEGylated membrane remains greater than 95%, suggesting a high fouling-resistant ability in the permeation process of emulsions.