Effects of bath temperature on the morphology and performance of EVOH membranes prepared by the cold‐solvent induced phase separation (CIPS) method

The development and characteristics of porous EVOH membranes by cold‐solvent induced phase separation (CIPS) process were investigated. Binary dopes of 1,3‐propandiol/EVOH prepared at 80 °C were immersed in 1,3‐propandiol at a lower temperature to engender polymer precipitation. The quench temperature affects phase separation modes, and hence structure and performance of resulting CIPS membranes. When the bath temperature was set below the crystallization line and above the binodal (e.g. 45 °C), the formed membrane was dominated by a packing of semicrystalline EVOH globules. When the bath was set at a temperature just below the spinodal (e.g. 20 °C), spinodal decomposition (SD) dominated the precipitation process to give a lacy‐like bicontinuous structure; yet there is also a clear imprint from polymer crystallization. When the bath temperature was set deeply within the spinodal dome (e.g. 5 °C), polymer crystallization affected only little the SD‐derived bicontinuous morphology. Water permeation flux, wettability, tensile strength, and ultra‐filtration experiments of the membranes were conducted. The results indicated that those properties were closely correlated with the porosity level, pore size, and membrane morphology. Moreover, X‐ray diffraction and DSC analyses indicated that the formed membranes had a crystallinity of 38 to 42%, consistent with the literature data. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44553.     

Development of polyethersulfone phase‐inversion membranes for membrane distillation using oleophobic coatings

Highly porous macrovoid‐free polyethersulfone membranes have been prepared using the phase‐inversion process with water as the non‐solvent. These membranes are of great interest for membrane distillation (MD) after application of a hydrophobic/oleophobic coating. The membrane structure was controlled by optimizing the process conditions and dope composition. Counter intuitively, increasing the polymer concentration favors the formation of larger surface pores under similar process conditions. A symmetric membrane is obtained when a sufficient amount of high‐molecular‐weight polyvinylpyrrolidone was added to the dope solution, which appears to play an important role in the structure formation process. The final membrane shows similar performance compared to commercial MD membranes. However, the membranes developed in this study show an oleophobic character, broadening the applications of MD. Moreover, the compressibility of these membranes is severely reduced compared to stretched membranes, which is expected to result in an improved MD performance at full scale. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45516.     

Effect of gas permeation temperature and annealing procedure on the performance of binary and ternary mixed matrix membranes of polyethersulfone,SAPO‐34, and 2‐hydroxy 5‐methyl aniline

This study investigated the effect of annealing time and temperature on gas separation performance of mixed matrix membranes (MMMs) prepared from polyethersulfone (PES), SAPO‐34, and 2‐hydroxy 5‐methyl aniline (HMA). A postannealing period at 120°C for a week extensively increased the reproducibility and stability of MMMs, but for pure PES membranes no post‐annealing was necessary for stable and reproducible performance. The effect of operation temperature was also investigated. The permeabilities of H₂, CO₂, and CH₄ increased with increasing permeation temperature from 35°C to 120°C, yet CO₂/CH₄ and H₂/CH₄ selectivities decreased. PES/SAPO‐34/HMA ternary and PES/SAPO‐34 binary MMMs exhibited the highest ideal selectivity and permeability values at all temperatures, respectively. For H₂/CO₂ pair, when temperature increased from 35°C to 120°C, selectivity increased from 3.2 to 4.6 and H₂ permeability increased from 8 to 26.5 Barrer for ternary MMM, demonstrating the advantage of using this membrane at high temperatures. The activation energies were in the order of CH₄ > H₂ > CO₂ for all membranes. PES/SAPO‐34/HMA membrane had activation energies higher than that of PES/SAPO‐34 membrane, suggesting that HMA acts as a compatibilizer between the two phases. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40679.     

Interfacial tuning and designer morphologies of microporous membranes based on polypropylene/natural rubber nanocomposites

Microporous polypropylene (PP) nanocomposite membranes are in great demand in various fields such as energy harvesting, water purification, and other industrial applications. Thin films of PP/natural rubber (NR) blend nanocomposite have been prepared by melt mixing and the membranes are made porous by extracting the NR phase from the blend. The present study gives a better insight into the nanoparticle shape and localization-tailored porous morphology of PP membrane. Thermodynamic prediction of nanofiller localization and its impact on morphology were studied. 2D clay platelets in PP matrix tune the morphology of the porous membrane into lamellar, whereas spherical nanofillers give elongated spherical pores. The localization of nanoparticles was observed using transmission electron microscope, which is also confirmed from theoretical prediction of localization of nanofillers with the help of interfacial energy and surface tension. Thermal studies reveal that nanofillers enhance the thermal stability of polymers. Mechanical studies reveal that nanoparticles improve the mechanical properties of the system. 2D platelet shaped-nanofillers enhance the mechanical strength of the polymer up to 39%, which is higher than that obtained for 3D spherical nanofillers. Nanofiller shape and localization have a great influence in deciding the properties and porosity of the membrane.     

Influence of the coagulation medium on the performance of poly(ether sulfone) flat‐sheet membranes

Poly(ether sulfone) flat‐sheet membranes were fabricated via phase inversion with different nonsolvent mixtures. The effect of the nonsolvent water with the addition of various amounts of ethanol, acetone, or isopropyl alcohol on the membrane morphology (as measured with scanning electron microscopy and atomic force microscopy) and the filtration performance were investigated. For the statistical evaluation of the fabrication process, on average, six membranes were produced. The pure water flux (PWF) and macromolecule retention were determined via filtration experiments. The presence of coagulation additives resulted in modified precipitation kinetics and thermodynamics, yielded different membrane structures, and therefore, influenced the performance. The results show that the addition of ethanol, acetone, and isopropyl alcohol in low concentrations (up to 10%) to water led to an increasing PWF. Higher concentrations led to a decrease in PWF. For high concentrations (>30%), a change in the membrane morphology from fingerlike to spongelike structures was expected, and this was experimentally proven for the case of ethanol. One main finding was the similarity of the influence of the used additives on the membrane performance. This was to be expected from Flory–Huggins theory for additives with high water miscibility; hence, under these circumstances, entropic and not energetic reasoning dominated the phase‐inversion process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41645.     

Synergetic effects of organic and inorganic additives on improvement in hydrophilicity and performance of PVDF antifouling ultrafiltration membrane for removal of natural organic material from water

Surrounding vegetation, animal, human and microbiological decomposition are the strong source of humic acid (HA) falling into the surface water bodies through rain runoff in the monsoon. HA contains various functional groups, such as carboxylic, phenolic, hydroxyl, and quinine, which are the major foulant. Contact of HA may have an adversarial health issue to human beings namely goiter, black foot, and cancer disease. The maximum permissible limit of HA in drinking water should be less than 2 ppm as per the Environmental Protection Agency (EPA). The membrane technology has prevailed a prominent place worldwide in chemical, water and wastewater treatment technologies. The proposed work is focused on the blending of organic-water soluble polymer polyethylene glycol 6000 as a pore-forming agent and inorganic salt lithium bromide (LiBr) as membrane morphology modifier with polyvinylidene fluoride host polymer in the N,N-Dimethylacetamide solvent. All fabricated membranes were characterized for functional groups and morphology. The total number of pores per unit surface area of membrane for membranes M-LiBr-0, M-LiBr-1, M-LiBr-2, and M-LiBr-3 are 2 × 10¹³, 2.3 × 10¹⁴, 2.7 × 10¹⁴ and 2.82 × 10¹⁴, respectively. The static water contact angle was decreased from 68.2° to 50.6° with an increase in the content of LiBr from 0 to 3 wt%. The order of pure water flux and hydraulic permeability of the membrane was M-LiBr-0 < M-LiBr-1 < M-LiBr-2 < M-LiBr-3. The HA rejection of the membrane was also increased from 90.13% to 96.24% with LiBr content due to a decrease in pore size of the membrane with the addition of LiBr content.     

Sulfonated polyphenylsulfone asymmetric membranes: Effect of coagulation bath (acetic acid‐NaHCO3/isopropanol) on morphology and antifouling properties

Sulfonated polyphenylsulfone porous asymmetric membranes, S‐PPSU with different sulfonation degrees, 21, 33, 50 wt %, were prepared by phase inversion. Two different coagulation baths were explored for asymmetric membrane preparation: acetone/isopropanol and acetic acid (AA)‐NaHCO₃/isopropanol. The latter bath allows better morphology control for the nucleation and pore formation of the membrane. Scanning electron microscopy of membranes shows that pore interconnectivity is improved, when the mixture of AA‐NaHCO₃/isopropanol was used for asymmetric S‐PPSU ultrafiltration membranes preparation. S‐PPSU asymmetric membranes show an increasing hydrophilicity with increasing sulfonation degree. Asymmetric membrane antifouling properties improve as the concentration of sulfonic groups increases in the membrane showing twice the flux recovery ratio and lower BSA protein absorption in static and dynamic flux tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44502.     

Investigation of membrane preparation condition effect on the PSD and porosity of the membranes using a novel image processing technique

A totally computerized image processing program package is developed to analyze the SEM images of membrane surface and cross‐section. Pore size distribution and porosity of the fabricated membranes are determined using the proposed image processing procedure. Furthermore, effect of coagulation bath temperature on the morphology and mechanical properties (such as tensile strength, strain break, tensile energy absorbent, and tensile stiffness) of Polysulfone (PSf) membranes are investigated. The results reveal that the mechanical properties are higher when N‐methyl‐2‐pyrrolidone (NMP) is used as solvent. Also, an increase in the coagulation bath temperature caused a monotonous increase in the mean pore size value of Dimethylformamide (DMF)‐based membranes. However, mean pore size curve has a maximum when NMP is used as solvent. Also, porosity of the fabricated membranes increased when coagulation bath temperature increased. For the NMP‐base membranes, pore's diameter was in the range of 0–5 μm. However, DMF‐based membranes have pore size value of smaller than 1 μm when the precipitation medium is kept at 8°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39899.     

Effect of SiO2 content on performance of polypropylene separator for lithium‐ion batteries

Composite separators are prepared by introducing SiO₂ nanoparticles on both sides of polypropylene separator with various SiO₂ contents through a dip‐coating process, where polyvinylidene fluoride‐hexafluoropropylene is used as binder. Coated layers have highly porous structure, which is quantitatively analyzed by air permeability. Compared to pristine separator, composite separators show significant lower Gurley value, reduced thermal shrinkage, higher liquid electrolyte uptake, better mechanical properties, and better cell performance such as discharge C‐rate capability and cycle performance. The influence of SiO₂ content on these properties is also studied, and the best SiO₂ content is given. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41156.     

Preparation and characterization of cellulose triacetate membranes via thermally induced phase separation

A series of cellulose triacetate (CTA) membranes were prepared via thermally induced phase separation (TIPS) process with dimethyl sulfone (DMSO2) and polyethylene glycol (PEG400) as a crystallizable diluent and an additive, respectively. The phase separation behavior of CTA/DMSO2/PEG400 ternary system was investigated in detail by optical microscopy, differential scanning calorimetry and wide angle X‐ray diffraction. This ternary system dynamically undergoes solid‐solid phase separation and thus the CTA membranes possess cellular, lacy, plate‐, or even ellipse‐shaped pores. However, we can modulate the pore structure, porosity, water flux, and mechanical properties of the membranes by varying polymer concentration, composition of the mixed diluent, and cooling condition. Due to the intrinsic hydrophilicity, the prepared CTA membranes have better antifouling property than polysulfone membranes. These porous membranes were used as supports to fabricate thin‐film composite forward osmosis (FO) membranes, which show good water permeability and selectivity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44454.     

Synthesis of polydopamine‐mediated PP hollow fibrous membranes with good hydrophilicity and antifouling properties

Membrane fouling remains a major barrier to membrane separation, particularly obvious in polymer membranes. Dopamine (DA) is of great value as a precursor for conjugation hydrophilic molecules. In this study, PP hollow fibrous membranes were first modified by DA to form a layer of polydopamine (PDA) coating. Then taurine and glycidol were introduced respectively with assisted by PDA reactive layer, the prepared membranes corresponding to PP‐T and PP‐G membranes, respectively. PP and the modified PP membranes were confirmed by a thorough membrane characterization of ATR‐FTIR, XPS, and FESEM measurements. The hydrophilic properties and permeability were measured by water contact angle (WCA) and permeation flux test. BSA was used to as model protein to evaluate the antifouling properties of the membranes. The results showed that taurine and glycidol were successfully introduced onto the membrane surface. The WCA of PP‐T and PP‐G membranes can be reduced to 32° and 26°, and the flux recovery ratio increased around 90.6% and 89.8%, respectively. Based on the experimental results, taurine and glycidol effectively improved the hydrophilic and anti‐fouling performance of PP membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44430.     

Nanopaper membranes from chitin–protein composite nanofibers—structure and mechanical properties

Chitin nanofibers may be of interest as a component for nanocomposites. Composite nanofibers are therefore isolated from crab shells in order to characterize structure and analyze property potential. The mechanical properties of the porous nanopaper structures are much superior to regenerated chitin membranes. The nanofiber filtration‐processing route is much more environmentally friendly than for regenerated chitin. Minerals and extractives are removed using HCl and ethanol, respectively, followed by mild NaOH treatment and mechanical homogenization to maintain chitin–protein structure in the nanofibers produced. Atomic force microscope (AFM) and scanning transmission electron microscope (STEM) reveal the structure of chitin–protein composite nanofibers. The presence of protein is confirmed by colorimetric method. Porous nanopaper membranes are prepared by simple filtration in such a way that different nanofiber volume fractions are obtained: 43%, 52%, 68%, and 78%. Moisture sorption isotherms, structural properties, and mechanical properties of membranes are measured and analyzed. The current material is environmentally friendly, the techniques employed for both individualization and membrane preparation are simple and green, and the results are of interest for development of nanomaterials and biocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40121.     

Wet‐phase‐separation membranes from the polysulfone/N,N‐dimethylacetamide/water ternary system: The formation and elements of their structure and properties

Asymmetric and porous polysulfone (PSf) membranes were prepared by wet phase separation. Binary (PSf)/N,N‐dimethylacetamide (DMA) solutions with polymer concentrations of 12.5–30 wt % were cast in thicknesses of 80–700 μm and immersed in a coagulation bath of pure water. The morphology of the formed membranes' cross sections consisted of a cellular structure and macrovoids; the cellular structure density was highest when the cast solution contained about 21 wt % PSf, regardless of the cast thickness. The membranes' pure water permeability decreased as the cast thickness increased. The instantaneous onset of the turbidity, regardless of the PSf content and cast thickness, its steep growth, and relatively high end value were the main characteristics of the turbidity phenomena taking place during the formation of the protomembranes. Again, the membrane‐forming system with a PSf/DMA solution with about 21 wt % polymer, regardless of the cast thickness, had the highest turbidity end value. The shrinkage of the cast solutions into the corresponding protomembrane was also examined quantitatively. Inverse experiments showed that the direction of the gravitation field had no influence on the shrinkage of the membrane‐forming ternary system or the membranes' morphology and its water permeability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1667–1674, 2005     

Mixed‐matrix membranes based on polyurethane containing nanohydroxyapatite and its potential applications

In this study, new asymmetric polyurethane (PU) mixed‐matrix membranes with different nanohydroxyapatite loadings were prepared via a dry–wet phase inversion method by the dispersion of hydroxyapatite (HA) nanoparticles in the PU matrix. The HA nanopowder was obtained by a wet chemical precipitation method; it showed an average crystallite size of 58.3 nm, a specific surface area of 261 m²/g, and a pore size of about 1.6 nm. The effects of the HA loading (10–50 wt %) on the PU membrane characteristics were studied. The scanning electron microscopy images revealed that the HA nanoparticles were well dispersed enough in the PU matrix. The average pore size in the top layer and porosity of the membranes slowly decreased, whereas the hydrophilicity and water permeability increased with increasing content of HA. The evaluation of the nanofiltration performance was performed by investigation of the NaCl rejection. The composite membranes had a higher salt‐removal capacity than the unfilled PU membrane. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41813.     

Morphological control of porous membranes based on aromatic polyether/water soluble polymers

This work describes the development of porous membranes based on blends of an aromatic polyether bearing main and side chain pyridine units (AP) with hydrophilic ionic polymers, like poly(sodium 4‐styrenesulfonate) (PSSNa) and its acid form (PSSH), or non‐ionic like polyvinylpyrrolidone and polyethylene glycol. Porous membranes were obtained after the removal of the water soluble polymers from the respective blend. The effect of various parameters such as water soluble polymer used (pore former), blend composition, casting solvent, and solvent evaporation level on porous structure formation was studied thoroughly. Specifically, SEM examination for the aforementioned systems indicated various porous morphologies depending on experimental conditions as well as thermodynamic and kinetic parameters occurring during their formation. The thermal properties of the membranes were influenced by the kind of the pore former, as revealed by thermogravimetric analysis. Special attention was paid to the systems AP/PSSNa and AP/PSSH to evaluate their miscibility via dynamic mechanical analysis and ATR‐FTIR spectroscopy. AP/PSSNa membranes have been preliminary used to test the water permeability for water purification. The tests revealed high water flux values at increased PSSNa concentrations. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44539.     

Coagulation bath composition and desiccation environment as tuning parameters to prepare skinless membranes via diffusion induced phase separation

Diffusion Induced Phase Separation (DIPS) is a currently used technique to produce porous membranes for a large variety of applications. A strong limitation is represented by the occurrence of a dense skin, which is formed during the process, highly reducing the membrane permeability. To overcome this issue, two modifications of the standard DIPS protocol were investigated: the use of coagulation baths composed by a solvent/nonsolvent mixture and the desiccation in a controlled environment, by modulating the partial pressure of nonsolvent vapor. An appropriate choice of coagulation bath composition, together with an appropriate desiccation protocol (i.e., the use of a nonsolvent vapor), will produce a skinless membrane, and offers the chance to control the morphology of both membrane surfaces. These results underline the importance of post‐treatment stage in membrane preparation via phase separation, thus suggesting that membrane washing/drying stage will affect the final morphology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42151.     

Study of the characteristics and the performance of self-made nanoporous polyethersulfone membranes

Polyethersulfone (PES) membranes were prepared in this study by using the DIPS technique (diffusion induced phase separation) in view of a better insight into the performance of commercial polyethersulfone membranes and a verification for the limited information given by the manufacturer. During this process, a lot of conditions influence the final membrane structure. Beside the choice of the solvent (dimethylformamide (DMF) or N-methyl-pyrrolidone (NMP)), it was shown that the concentration of the polymer and the relative air humidity are the most crucial ones. Optimizing these factors led to reproducible membranes, which were characterized for hydrophobicity, roughness, surface charge and molecular weight cut-off (MWCO). The performance was studied by doing cross-flow filtration experiments with aqueous solutions of uncharged and charged component. Although the self-made membranes were characterized by a larger MWCO in comparison with commercial polyethersulfone nanofiltration membranes, the retention for the self-made membranes was almost equal to or even higher than the commercial membranes in the case of filtrating negatively, respectively, positively charged component. The high retention of the self-made membranes for positively charged component can be explained by adsorption experiments or by surface charge measurements before and after filtration.     

Influence of annealing treatment on the structure and properties of poly(4‐methyl‐1‐pentene)‐based films and membranes

The poly(4‐methyl‐1‐pentene) casting films were prepared by melt extrusion and annealed below the melting temperature. The effect of annealing conditions on the structure and properties of casting films and stretched membranes was discussed. In this work, a new peak around annealing temperature, as shown in melting curves, revealed the increase in thickness of lamellar structure. Annealing treatment led to improvements of amorphous thickness and crystal orientation. And the thickness of crystal phase correlated with the logarithm of annealing time. The increase in annealing temperature or time led to the improvements of the hard elasticity of samples. Additionally, the larger porosity of stretched membranes was observed as the annealing time and temperature increased. An optimum annealing condition to prepare microporous membranes was 30 min, 200 °C. This work also discussed the importance of annealing treatment in the preparation of microporous membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46491.     

Effect of solvents on morphology and polymorphism of polyvinylidene fluoride membrane via supercritical CO2 induced phase separation

Poly vinylidene fluoride (PVDF) membranes were prepared via supercritical CO₂ induced phase separation. The effects of solvent power on PVDF membrane morphology and polymorphism were investigated using N‐N‐dimethylformamide (DMF), triethyl phosphate (TEP), and their mixture respectively. The morphology evolution including cross‐section and surfaces were thoroughly studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). The differences of solubility parameters between the solvent and PVDF affected the phase separation and the resultant morphology. The various crystalline phases of the membranes were mainly investigated by Fourier transform infrared spectroscopy (FTIR) and X‐ray diffractometer (XRD). Solvent with larger dipole moment tended to form polar β phase. Decreasing the difference of solubility parameters favored the formation of α phase. Furthermore, the effects of salt additive on PVDF membrane morphology and crystalline form were studied as well. Results turned out that lithium chloride (LiCl) induced a porous top surface and boosted the formation of β phase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41065.     

The influence of solvent properties on the performance of polysulfone/β‐cyclodextrin polyurethane mixed‐matrix membranes

This study investigates the effect of solvent properties on the structural morphology and permeation properties of polysulfone/β‐cyclodextrin polyurethane (PSf/β‐CDPU) mixed‐matrix membranes (MMMs). The membranes were prepared by a modified phase‐inversion route using four different casting solvents [dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), dimethyl acetamide (DMA), and N‐methyl‐2‐pyrrolidone (NMP)]. While DMSO‐based membranes demonstrated particularly high permeability (ca 147 L/m²h.bar), their crystallinity was low compared to MMMs prepared using DMA, DMF and NMP due to the formation of thin active layers on their surfaces. Cross‐sectional morphology revealed that the MMMs have a dense top skin with finger‐like inner pore structures. Membranes prepared using NMP displayed the highest hydrophilicity, porosity, and crystallinity due to the low volatility of NMP; DMF membranes exhibited superior mechanical and thermal stability due to its (DMF) high hydrogen bonding (δH) values. Thus, the morphological parameters, bulk porosity, and flux performance of MMMs have a significant inter‐relationship with the solubility properties of each solvent (i.e., δH, density, volatility, solubility parameter). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2005–2014, 2013