Development of high performance nano-porous polyethersulfone ultrafiltration membranes with hydrophilic surface and superior antifouling properties

Hydrophilic nano-porous polyethersulfone ultrafiltration membranes were developed for milk concentration. The membranes were prepared from new dope solution containing polyethersulfone (PES)/polyvinylpirrolidone (PVP)/polyethyleneglycole (PEG)/cellulose acetate phthalate (CAP)/acrylic acid/Triton X-100 using phase inversion induced by immersion precipitation technique. This casting solution leads to formation of new hydrophilic membranes. The morphological studies were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the hydrophilicity and performance of membranes were examined by contact angel measurements and cross-flow filtration (pure water flux, milk water permeation, protein rejection and antifouling measurements). The contact angle measurements indicate that a surface with superior hydrophilicity was obtained for PES membranes. Two concentrations of PES (16 and 14.4 wt.%) and two different non-solvents (pure water and mixtures of water and IPA) were used for preparation of membranes. The morphological studies showed that the higher concentration of PES and the presence of IPA in the gelation media results in formation of a membrane with a dense top and sub-layer with small pores on the surface. The pure water flux of membranes was decreased when higher polymer concentration and mixtures of water and IPA were employed for membrane formation. On the other hand, the milk water permeation and protein rejection were increased using mixtures of water and IPA as non-solvent. Furthermore, the fouling analysis of the membranes demonstrated that the membrane surface with fewer tendencies for fouling was obtained.     

Preparation and characterization of asymmetric polyethersulfone and thin-film composite polyamide nanofiltration membranes for water softening

In this research, two types of nanofiltration membranes were prepared and evaluated for water softening. Their nanofiltration performance was evaluated by cross-flow filtration using NaCl (1 g/l) and MgSO₄ (1 g/l) solution at 5 and 10 bar, 25 °C and 10 l/min. The morphological studies were performed with SEM and AFM instruments. In addition, the hydrophilicity of membranes was examined by contact angle measurements. In the first type, asymmetric polyethersulfone (PES) nanofiltration membranes were prepared using phase inversion induced by immersion precipitation technique. Different components such as polyvinylpyrrolidone (PVP), polyethyleneglycole (PEG), acrylic acid and Triton X-100 were used as additive in the PES casting solution, which lead to the formation of new asymmetric nanofiltration membranes. Two concentrations of PES (20 and 25 wt%) and two different non-solvents (pure water and mixture of water (80 vol.%) and IPA (20 vol.%)) were used for preparing asymmetric nanofiltration membranes. The morphological studies showed that the membranes prepared with non-solvent containing 20 vol.% IPA have smoother surface and smaller pores in surface and sub-layer compared to membranes prepared with pure water as non-solvent. The flux was decreased when higher polymer concentration and mixture of water and IPA were employed for membrane formation. However, NaCl and MgSO₄ rejections were improved. In the second type, thin-film composite polyamide nanofiltration membrane was fabricated using interfacial polymerization of 1,3-phenylenediamine (PDA) with trimesoyl chloride (TMC). A rough and dense film was formed on the PES support membrane by interfacial polymerization. The water permeability of composite membrane was 7 and 21 kg m⁻² h⁻¹ at 5 and 10 bar, respectively. Moreover, the rejection to the MgSO₄ as divalent salt (85 and 90%) was high compared to the NaCl as monovalent salt (64 and 67%).     

The effect of non-contact heating (microwave irradiation) and contact heating (annealing process) on properties and performance of polyethersulfone nanofiltration membranes

In this work the effect of microwave irradiation on morphology and performance of polyethersulfone (PES) membranes was investigated. The membranes were prepared with 20 wt.% of PES by phase inversion method. N,N-dimethylformamide (DMF) and mixture of water and ethyl alcohol (90/10 vol.%) were employed as solvent and coagulant respectively. Polyvinylpirrolidone (PVP) with the concentration of 2 wt.% was selected as pore former. The effects of irradiation time (10, 30, 60, 90, 120 s) and microwave power (180, 360, 720 and 900 W) on structure and performance of membranes were studied. Increasing the irradiation time and power caused variation in permeate flux and ion rejection. Moreover, the effects of annealing processes (60, 70, 80 °C) were studied. Transmembrane pressure was selected around 1.5 MPa for all experiments. Scanning electron microscope (SEM) and atomic force microscope (AFM) were employed to describe the surface morphology of the prepared membranes. The effect of microwave irradiation time in different power revealed alterations in membrane surface morphology and AFM images represented that surface parameters (such as surface roughness) have been changed. The membrane exhibited moderate rejection (47%) and low permeate flux (4.5 kg/m² h) at 80 °C for NaCl solution. The SEM images indicate that the dense skin layer is formed at 80 °C annealing.     

Preparation and performance of polysulfone-sulfonated poly(ether ether ketone) blend ultrafiltration membranes. Part I

Ultrafiltration membranes were prepared from blends with polysulfone (PSf) and sulfonated poly(ether ether ketone) (SPEEK) by phase inversion technique. The blend membranes were prepared with polymer composition from 0 to15 wt%. Sulfonated poly(ether ether ketone) was used to improve the performance and permeability of blended membranes. The effects of polymer composition on compaction, pure water flux, water content, and membrane hydraulic resistance were studied. The membranes were also subjected to the determination of pore statistics and molecular weight cut-off (MWCO) determination studies by using different molecular weight of proteins. The porosity, pore size of the membranes increased with increasing concentrations of SPEEK in the casting solution. Similarly, the MWCOs of the blend membranes ranged from 20 to 45 kDa, depending on the various polymer blend compositions. The pure water flux of the PSf/SPEEK blend membranes increases from 16.7 to 61.5 l m⁻² h, when the concentration of SPEEK increased from 0 to 15 wt%. Scanning electron microscope (SEM) results qualitative evidence for the trends observed for the pore statistics and MWCO studies.     

Corona-induced graft polymerization for surface modification of porous polyethersulfone membranes

Graft polymerization of acrylic acid (AA) onto porous polyethersulfone (PES) membrane surfaces was developed using corona discharge in atmospheric ambience as an activation process followed by polymerization of AA in aqueous solution. The effects of the corona parameters and graft polymerization conditions on grafting yield (GY) of AA were investigated. The grafting of AA on the PES membranes was confirmed by ATR-FTIR and X-ray photoelectron spectroscopy (XPS) analysis. Porosimetry measurements indicate the average pore diameters and porosities of the modified membranes decrease with the increase of the GY. The hydrophilicity and surface wetting properties of the original and modified membranes were evaluated by observing the dynamic changes of water contact angles. It is found that the grafting of AA occurs not only on the membrane surfaces, but also on the pore walls of the cells inside the membrane. The permeability experiments of protein solution reveal that the grafting of PAA endows the modified membranes with enhanced fluxes and anti-fouling properties. The optimized GY of AA is in the range of 150-200 μg/cm². In addition, the tensile experiments show the corona discharge treatment with the power lower than 150 W yields little damage to the mechanical strength of the membranes.     

Hydrophilic modification of polyethersulfone porous membranes via a thermal-induced surface crosslinking approach

A thermal-induced surface crosslinking process was employed to perform a hydrophilic surface modification of PES porous membranes. Difunctional poly(ethylene glycol) diacrylate (PEGDA) was used as the main crosslinking modifier. The addition of trifunctional trimethylolpropane trimethylacrylate (TMPTMA) into the reaction solutions accelerated the crosslinking progress of PEGDA on PES membranes. The membrane surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and FTIR-ATR spectroscopy. The mass gains (MG) of the modified membranes could be conveniently modulated by varying the PEGDA concentration and crosslinking time. The measurements of water contact angle showed that the hydrophilicity of PES membranes was remarkably enhanced by the coating of crosslinked PEGDA layer. When a moderate mass gain of about 150 μg/cm² was reached, both the permeability and anti-fouling ability of PES membranes could be significantly improved. Excessive mass gain not only contributed little to the anti-fouling ability, but also brought a deteriorated permeability to PES membranes.     

Exploring the influence of a XeCl laser treatment on biocompatibility of polyethersulfone film

The effect of XeCl laser irradiation on biocompatibility of polyethersulfone (PES) film surface was investigated. For this purpose, the surface of PES film was irradiated with different number of pulses at different fluences. The treated surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The platelet adhesion and cell culture measurements were done on the treated surface for investigation of the biocompatibility. It was shown that, irradiation of surface with 500 pulses at a fluence of 25 mJ/cm² is the most optimal condition for improving the platelet adhesion on the PES surface with a XeCl laser.     

Comparative performance study of four nanofiltration membranes in the separation of mercury and chromium

In this paper, four nanofiltration membranes, viz., (1) coating of N,O-carboxymethyl chitosan (NOCC) on polyethersulfone ultrafiltration (PES UF) substrate membrane; (2) chitosan and acrylonitrile butadiene styrene (ABS) in the blend ratio of 0:100 (ABS); (3) diethylenetriamine pentaacetic acid coating via casting method on PES UF substrate membrane (DC50); and (4) NOCC and cellulose acetate (CA) polymer blend solution (0.4?wt%) coated on a glass plate (NOCC?CCA), were selected from our previous work. By using these membranes, separation behaviour of mercury and chromium ions was studied at different operating conditions from their salt solutions. From the experimental data, it is evident that ABS membrane gave highest observed solute rejection (92.88 and 88.67?% for 10?ppm feed concentration of mercury sulphate?Cwater system and chromium sulphate?Cwater system, respectively) and NOCC?CCA membrane gave highest permeate volume flux. But from the rejection as well as permeate volume flux point of view, NOCC?CPES membrane is considered to be the best choice among all the membranes.     

Annealing effect on surface segregation behavior of hydroxypropylcellulose/polyethylenimine blend films

The surface properties of hydroxypropylcellulose (HPC) and polyethylenimine (PEI) blend films prepared by solution casting method before and after annealing were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and contact angle measurements. SEM and AFM analysis of the blends revealed that the PEI component segregated on the surface of the air-surface side of the blend films with increasing annealing temperature. The band intensity of PEI component at 1630 cm⁻¹ also increased depending on annealing temperature. The water contact angle decreased abruptly with increasing annealing temperature and reached almost 31° on the surface of the air-surface side of the blends at 150 °C. The results of these studies showed that the PEI chains with low surface energy segregated or enriched mainly on the surface of the air-surface side, and that, on the other hand, HPC chains with high surface energy oriented to the surface of the glass-surface side and inside of the films with increasing annealing temperature.     

Preparation and characterization of PES/TiO2 composite membranes

Polyethersulfone (PES)/TiO₂ composite membranes were prepared by phase inversion method with nano-TiO₂ as additive. The influence of TiO₂ on the morphologies and the performances of PES/TiO₂ membranes were investigated through the methods of SEM, XRD, TGA, contact angle goniometer, mechanical strength tests and filtration experiments. The results showed that the structure of membrane was not obviously affected by addition of TiO₂, and the performances such as hydrophilicity, thermal stability, mechanical strength and anti-fouling ability of membrane were enhanced through adding TiO₂ nanoparticles. At 0.5 wt.% TiO₂ content, the composite membrane has an excellent performance, however higher TiO₂ content (than 0.5 wt.%) resulted in defective pore structure of the membranes and decline of the performances, such as permeability and mechanical strength. TGA and mechanical strength analyses indicated good compatibility between polymers and TiO₂ nanoparticles.     

Effect of TiO2 nanoparticles on the surface morphology and performance of microporous PES membrane

PES-TiO₂ composite membranes were prepared via phase inversion by dispersing TiO₂ nanopaticles in PES casting solutions. The crystal structure, thermal stability, morphology, hydrophilicity, permeation performance, and mechanical properties of the composite membranes were characterized in detail. XRD, DSC and TGA results showed that the interaction existed between TiO₂ nanopaticles and PES and the thermal stability of the composite membrane had been improved by the addition of TiO₂ nanopaticles. As shown in the SEM images, the composite membrane had a top surface with high porosity at low loading amount of TiO₂, which was caused by the mass transfer acceleration in exposure time due to the addition of TiO₂ nanopaticles. At high loading amount of TiO₂, the skinlayer became much looser for a significant aggregation of TiO₂ nanopaticles, which could be observed in the composite membranes. EDX analysis also revealed that the nanoparticles distributed in membrane more uniformly at low loading amount. Dynamic contact angles indicated that the hydrophilicity of the composite membranes was enhanced by the addition of TiO₂ nanopaticles. The permeation properties of the composite membranes were significantly superior to the pure PES membrane and the mean pore size also increased with the addition amount of TiO₂ nanopaticles increased. When the TiO₂ content was 4%, the flux reached the maximum at 3711 L m⁻² h⁻¹, about 29.3% higher than that of the pure PES membrane. Mechanical test also revealed that the mechanical strength of composite membranes enhanced as the addition of TiO₂ nanopaticles.     

Note: Interfacial layer and phase inversion behavior in the blend of polyethersulfone and polycarbonate

A blend of polyethersulfone (PES) and polycarbonate (PC) with a ratio of 40/ 60 was studied by scanning electron microscopy (SEM), dynamic mechanical analysis, and transmission electron microscopy (TEM). It was found that the PES-PC blend is a partially miscible, two-phase system, and an interfacial layer exists between the phases of PES and PC. Specific interaction resulting from the n-complex between PES and PC provides the driving force for formation of the interfacial layer. In addition, phase inversion behavior was also observed for the 40/60 composition.     

Fabrication of superhydrophobic silica-based surfaces with high transmittance by using tetraethoxysilane precursor and different polymeric species

The preparation of superhydrophobic silica-based surfaces via the sol-gel process through the addition of different polymeric species into the precursor solution was done in this study. The surface roughness of the films was obtained by removing the organic polymer at a high temperature, and then the hydrophobic groups were bonded onto the films with a monolayer by chemical reaction with hexamethyldisilazane (HMDS). The characteristic properties of the as-prepared films were analyzed by contact angle measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption/desorption, and UV-vis scanning spectrophotometer. The experimental results revealed that the superhydrophobic thin films with high transmittance could easily be prepared using polypropylene (PPG), polyethylene (PEG), and poly(vinylpyrrolidone) (PVP). Surface roughness and pore size were enhanced using PPG polymeric species. The distribution of pore size was from the microporous to the mesoporous and marcoporous regions. In addition, the contact angles of the rough surfaces prepared at 500 °C without modification of HMDS were smaller than 5° but larger than 156° after modified by HMDS.     

Effect of hot pressing on the ionic conductivity of the PEO/LiCF3SO3 based electrolyte membranes

PEO/LiCF₃SO₃ (LiTFS) /Ethylene carbonate (EC) polymer electrolyte membranes were prepared with a solution casting method followed by a hot pressing process. The effect of the hot pressing process on the in-plane conductivity of the PEO electrolyte membranes was evaluated using a four-electrode AC impedance method. The composition, morphology, and microstructure of the composite polymer electrolyte were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The AC impedance measurement results indicate that the hot pressing process can increase the room temperature conductivity of the membranes 14 times to 1.7 × 10^− 3 S cm^− 1 depending upon the duration of the hot pressing process. The SEM, FTIR, XRD, and DSC results indicate that the hot pressing process could increase the amorphous part of the polymer electrolyte membrane or convert large spherulite crystals into nano-sized crystals.     

The influence of UV-irradiation and support type on surface properties of poly(methyl methacrylate) thin films

Thin poly(methyl methacrylate) (PMMA) films were prepared by a solution casting on different supports (glass and aluminium plates with different gloss). UV-irradiation (λ = 254 nm) was used for polymer modification. Surface properties of PMMA were studied by contact angle measurements, attenuated total reflection infrared spectroscopy and optical microscopy. It was found that support type has no influence on surface properties of virgin PMMA, however, the changes in these properties were observed during UV modification of polymer film. The most efficient photochemical reactions appeared in sample placed on the rough Al, whereas the smallest effect was observed in polymer on the glass.     

A study on LiBOB-based nanocomposite gel polymer electrolytes (NCGPE) for Lithium-ion batteries

Lithium bis(oxalato)borate (LiBOB) salt-based nanocomposite gel polymer blend electrolyte (PVdF/PVC) membranes have been prepared by solution casting technique for various concentrations of TiO₂. The effect of anatase structure of nanosized titanium dioxide in the plasticized PVC/PVdF + LiBOB matrix has been observed in the 2:1 salt filler ratio in the impedance measurements that the conductivity is increased one order of magnitude higher than the filler-free electrolyte (1:0 salt:filler ratio). The phase morphology of this electrolyte membrane represents the appearance of the free volume sites for ionic migration.     

Preparation of Symmetric Network PVDF Membranes for Protein Adsorption via Vapor-Induced Phase Separation

Symmetric network poly(vinylidene fluoride) (PVDF) membranes without a dense skin layer were prepared by vapor-induced phase separation from a PVDF/N,N-dimethylacetamide (DMAc)/water system. The effects of evaporation atmosphere, temperature, and humidity during the preparation of the membranes on their morphologies were investigated by scanning electron microscope (SEM). With low temperature and high humidity, the polymer crystallization mechanism dominated the membrane formation process, and the casting solution formed membranes with symmetric morphologies in the vapor phase containing 0.79% DMAc. The effect of additives on the membrane structure and performance was also investigated. The results of adsorption experiments showed that the binding capacity of bovine serum albumin (BSA) increased with the appearance of a circular network morphology and the decrease of mean pore size of the membrane. With the addition of LiCl to the casting solution, the obtained membrane can adsorb BSA up to 150 μg/cm². Proteins on sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis gels were successfully electro-blotted onto these PVDF membranes. Compared with commercial membranes, the PVDF membranes prepared in this work were more suitable for protein blotting.     

Investigations on the effect of complexation of NaF salt with polymer blend (PEO/PVP) electrolytes on ionic conductivity and optical energy band gaps

Sodium ion conducting polymer blend electrolyte films, based on polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) complexed with NaF salt, were prepared using solution casting technique. The complexation of the salt with the polymer blend was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-vis spectroscopy. Electrical conductivity of the films was measured with impedance analyzer in the frequency range of 1 Hz to 1 MHz and in the temperature range of 303-348 K. It was observed that the magnitude of conductivity increased with the increase in the salt concentration as well as the temperature. UV-vis absorption spectra in wavelength region of 200-800 nm were used to evaluate the optical properties like direct and indirect optical energy band gaps, optical absorption edge. The optical band gaps decreased with the increase in Na⁺ ion concentration. This suggests that NaF, as a dopant, is a good choice to improve the electrical properties of PEO/PVP polymer blend electrolytes.     

PVA nano composite membrane for DMFC application

A new PEM composite membrane comprising of polyvinyl alcohol (PVA), sulfonic acid functionalized CNT and fluorinated MMT has been fabricated. Composite polymer membrane has been prepared by simple solution casting method. Composite properties have been evaluated by using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and FTIR techniques. The proton conductivity, methanol crossover and water uptake properties of newly fabricated membrane have been studied. The polymer membrane shows good thermal properties. The water content is in the range of 35-45%. Especially, it has been found that the fluorinated MMT used in this study plays a decisive role in water uptake and acts as a hydrophobic surface for controlling the swelling. The proton conductivities and the methanol permeabilities of all the membranes are in the range of 10^− 3 to 10^− 2 S/cm and 2.08 × 10^− 6 cm²/s at room temperature, respectively.     

Preparation and characterizations of PVAc/P(VdF-HFP)-based polymer blend electrolytes

A novel group of polymer blend electrolytes based on the mixture of poly(vinyl acetate) (PVAc), poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), and the lithium salt (LiClO₄) are prepared by solvent casting technique. Ionic conductivity of the polymer blend electrolytes has been investigated by varying the PVAc and PVdF-HFP content in the polymer matrix. The maximum ionic conductivity has been obtained as 0.527 × 10⁻⁴ Scm⁻¹ at 303 K for PVAc/PVdF-HFP ((25/75) wt.%)/LiClO₄ (8 wt.%). The complex formations ascertained from XRD and FTIR spectroscopic techniques and the thermal behavior of the prepared samples has been performed by DSC analysis. The surface morphology and the surface roughness are studied using SEM and AFM scanning techniques respectively.