Mass transport of direct methanol fuel cell species in sulfonated poly(ether ether ketone) membranes

Homogeneous membranes based on sulfonated poly(ether ether ketone) (sPEEK) with different sulfonation degrees (SD) were prepared and characterized. In order to perform a critical analysis of the SD effect on the polymer barrier and mass transport properties towards direct methanol fuel cell species, proton conductivity, water/methanol pervaporation and nitrogen/oxygen/carbon dioxide pressure rise method experiments are proposed. This procedure allows the evaluation of the individual permeability coefficients in hydrated sPEEK membranes with different sulfonation degrees. Nafion^® 112 was used as reference material. DMFC tests were also performed at 50 °C. It was observed that the proton conductivity and the permeability towards water, methanol, oxygen and carbon dioxide increase with the sPEEK sulfonation degree. In contrast, the SD seems to not affect the nitrogen permeability coefficient. In terms of selectivity, it was observed that the carbon dioxide/oxygen selectivity increases with the sPEEK SD. In contrast, the nitrogen/oxygen selectivity decreases. In terms of barrier properties for preventing the DMFC reactants loss, the polymer electrolyte membrane based on the sulfonated poly(ether ether ketone) with SD lower or equal to 71%, although having slightly lower proton conductivity, presented much better characteristics for fuel cell applications compared with the well known Nafion^® 112. In terms of the DMFC tests of the studied membranes at low temperature, the sPEEK membrane with SD = 71% showed to have similar performance, or even better, as that of Nafion^® 112. However, the highest DMFC overall efficiency was achieved using sPEEK membrane with SD = 52%.     

Structural and mechanical characterization of poly(ether ether ketone) (PEEK) and sulfonated PEEK films: Effects of thermal history,sulfonation, and preparation conditions

In this work, virgin and sulfonated poly(ether ether ketone) films (PEEK and SPEEK, respectively) have been studied by dynamic mechanical analysis, modulated differential scanning calorimetry, wide‐angle X‐ray diffraction, birefringence, and optical microscopy. The properties of the unmodified polymer have been addressed to assess the original morphological characteristics and the changes induced by sulfonation. In general, the introduction of ionic groups in the polymer backbone alters dramatically the intrinsic properties of the parent material. The particular thermomechanical response exhibited by PEEK and SPEEK samples, characterized by a hysteresis loop, can be explained by the reversible and irreversible relaxation–orientation of the microstructure, even in the sub‐T_g region. The results showed that the preparation conditions largely determine the nonequilibrium morphological features of both compression‐molded PEEK films and solvent‐cast SPEEK membranes. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 756–774, 2006     

Sulfonated poly(ether ether ketone)‐induced porous poly(ether sulfone) blend membranes for the separation of proteins and metal ions

Asymmetric ultrafiltration (UF) membranes were prepared by the blending of poly(ether sulfone) (PES) and sulfonated poly(ether ether ketone) (SPEEK) polymers with N,N′‐dimethylformamide solvent by the phase‐inversion method. SPEEK was selected as the hydrophilic polymer in a blend with different composition of PES and SPEEK. The solution‐cast PES/SPEEK blend membranes were homogeneous for all of the studied compositions from 100/0 to 60/40 wt % in a total of 17.5 wt % polymer and 82.5 wt % solvent. The presence of SPEEK beyond 40 wt % in the casting solution did not form membranes. The prepared membranes were characterized for their UF performances, such as pure water flux, water content, porosity, and membrane hydraulic resistance, and morphology and melting temperature. We estimated that the pure water flux of the PES/SPEEK blend membranes increased from 17.3 to 85.6 L m^?2 h^?1 when the concentration of SPEEK increased from 0 to 40 wt % in the casting solution. The membranes were also characterized their separation performance with proteins and metal‐ion solutions. The results indicate significant improvement in the performance characteristics of the blend membranes with the addition of SPEEK. In particular, the rejection of proteins and metal ions was marginally decreased, whereas the permeate flux was radically improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization and application of composite membranes in DMFC

The present work focuses on the characterization of membranes for direct methanol fuel cells (DMFC), prepared using composites of sulfonated poly(ether ether ketone) (sPEEK, with sulfonation degree, SD, of 42 and 68%) as polymer matrix. This polymer was inorganically modified incorporating different amounts of zirconium phosphate (ZrPh) pretreated with n-propylamine and polybenzimidazole (PBI). The investigated properties were: proton conductivity, water and aqueous methanol swelling, permeability coefficients for DMFC species and morphology. DMFC tests were performed at 110 °C with relative humidity (r.h.) in the cathode feed of 100 and 138%. The results obtained show that the inorganic modification of the polymer decreases the proton conductivity, water and aqueous methanol swelling and permeability towards DMFC species. In terms of morphology, it was found that the applied procedure enabled the preparation of membranes with good compatibility between inorganic and organic components. In terms of the DMFC tests of the composite membranes, working with the cathode feed at 100% r.h., the unmodified sPEEK membrane with SD = 42% proved to have the best performance, although with higher methanol crossover. In contrast, for r.h. of 138%, the best performance was achieved by the sPEEK composite membrane with SD = 68 and 20.0 wt.% of ZrPh and 11.2 wt.% of PBI.     

Double crosslinked polyetheretherketone-based polymer electrolyte membranes prepared by radiation and thermal crosslinking techniques

Novel one-step preparation of polymer electrolyte membranes without a membrane casting process is achieved by radiation crosslinking of a polyetheretherketone (PEEK) film to prevent dissolution and deformation of the original film in sulfonating solutions. The films crosslinked with doses more than 33 MGy can be effectively sulfonated in a chlorosulfonic solution, resulting in a crosslinked sulfonated PEEK (sPEEK) electrolyte membrane with high proton conductivity comparable to Nafion. Nevertheless, its water uptake was high for application in fuel cells. The thermal treatment was effective for further crosslinking of the membrane; as a result, the water uptake and methanol permeability of the double crosslinked sPEEK membranes drastically decreased, compensating for a slight decrease of proton conductivity. In addition, unlike the traditional cast sPEEK membrane showing the irreversible swelling in hot water, the double crosslinked sPEEK membranes exhibited excellent stability toward 100 °C hot water for more than 200 h without any decrease in proton conductivity, and had the mechanical and thermal properties superior to those of Nafion.     

Effects of polymer solvents on the performance of cellulose acetate membranes in methanol/methyl tertiary butyl ether separation

The performances of cellulose acetate membranes prepared with casting solutions, with acetone, dimethylformamide (DMF), and N‐methylpyrrolidone (NMP) as solvents, were studied in a series of methanol/methyl tertiary butyl ether separation experiments. The flux and selectivity of the membrane samples were affected by the type of solvent used to prepare the casting solution. The sample with DMF consistently gave the highest selectivity and lowest flux, followed by the samples with NMP and acetone. The differences in the performances were attributed to the effects of the volatility and evaporation rates of the solvents. Scanning electron microscopy and atomic force microscopy techniques were used for comparing the morphologies of the membranes. In addition, we used Raman spectroscopy as a novel technique to study the sorption selectivities of the membrane samples prepared with the three different solvents. In a parallel study, the relation between the polymer concentration in the casting solution and the morphology and performance of the membrane samples was studied. Under similar preparation conditions, the morphology of the membrane changed from being porous to being dense when the membrane was prepared with casting solutions with increasing polymer concentration. Also, the selectivity increased and the permeability decreased with increasing polymer concentration in the casting solution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2882–2895, 2001     

Behavior of sulfonated poly(ether ether ketone) in ethanol–water systems

The behavior of sulfonated poly(ether ether ketone) (sPEEK) membranes in ethanol–water systems was studied for possible application in direct ethanol fuel cells (DEFCs). Polymer membranes with different degrees of sulfonation were tested by means of uptake, swelling, and ethanol transport with dynamic measurements (liquid–liquid and liquid–gas systems). Ethanol permeability was determined in an liquid–liquid diffusion cell. For membranes with an ion‐exchange capacity (IEC) between 1.15 and 1.75 mmol/g, the ethanol permeability varied between 5 × 10^?8 and 1 × 10^?6 cm²/s, being dependent on the measuring temperature. Ethanol and water transport in liquid–gas systems was tested with pervaporation as a function of IEC and temperature. Higher IEC accounted for higher fluxes and lower water/ethanol selectivity. The temperature had a large effect on the fluxes, but the selectivity remained constant. Furthermore, the membranes were characterized with proton conductivity measurements. The proton diffusion coefficient was calculated, and a transition in the proton transfer mechanism was found at a water number of 12. Membranes with high IEC (>1.6 mmol/g) exhibited larger proton diffusion coefficients in ethanol–water systems than in water systems. The membrane with the lowest IEC exhibited the best proton transport to ethanol permeability selectivity. The use of sPEEK membranes in DEFC systems depends on possible modifications to stabilize the membranes in the higher conductive region rather than on modifications to increase the proton conductivity in the stable region. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Non-Fluorinated Membranes Thickness Effect on the DMFC Performance

Abstract

In order to study the influence of the proton exchange membrane thickness on the direct methanol fuel cell (DMFC) performance, sulfonated poly (ether ether ketone) (sPEEK) membranes with a sulfonation degree (SD) of 42% and thicknesses of 25, 40, and 55 µm were prepared, characterized, and tested in a DMFC. These polymeric membranes were tested in a DMFC at several temperatures by evaluating the current-voltage polarization curve, the open circuit voltage (OCV) and the constant voltage current (CV, 35 mV). The CO₂ concentration at the cathode outlet was also measured. The thinnest sPEEK membrane proved to have the best DMFC performance, although having lower Faraday efficiency (lower ohmic losses but higher methanol permeation). In contrast, the thickest membrane presented improved properties in terms of methanol permeation (lower methanol crossover). DMFC tests results for this membrane showed 30% global efficiency, obtained with pure oxygen at the cathode feed.     

Preparation of novel semihomogeneous cation‐permeable membranes from blends of sulfonated poly(phenylene sulfide) and sulfonated phenolphthalein poly(ether ether ketone)

A series of semihomogeneous cation‐exchange membranes were prepared with binary blend systems, such as sulfonated phenolphthalein poly(ether ether ketone) (SPEEK‐C)/sulfonated poly(phenylene sulfide) (SPPS), or ternary blend systems, such as phenolphthalein poly(ether ether ketone) (PEEK‐C)/SPEEK‐C/SPPS, by solution blending and phase inversion, in which PEEK‐C and SPEEK‐C acted as binders and SPPS powder acted as a polyelectrolyte. Compared with homogeneous and heterogeneous membranes, the prepared semihomogeneous membranes had good electrochemical properties and mechanical strength as well as good dimensional stability. The fundamental properties of the membranes, such as the ion‐exchange capacity, water content, electrical resistance, transport number, diffusion coefficient of the electrolytes, and streaming potential, were largely dependent on both the loading of the SPPS resin and the sulfonation degree of PEEK‐C. Through the adjustment of these two important parameters, a series of semihomogeneous membranes with the desired conductivity and selectivity and the proper water content for different industrial purposes, such as electrodialysis, diffusional dialysis, and proton exchange, were achieved. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1478–1485, 2004     

Nanostructure and properties of proton‐conducting sulfonated poly(ether ether ketone) (SPEEK) and zirconia–SPEEK hybrid membranes for direct alcohol fuel cells: effect of the nature of swelling solvent and incorporation of heteropolyacid

The influence, on membrane nanostructure and properties, of water or ethanol as swelling solvent of sulfonated poly(ether ether ketone) (SPEEK) and zirconia–SPEEK hybrid membranes prepared using the sol–gel process has been investigated. Independent of the solvent, small‐angle X‐ray scattering measurements reveal the existence of a two‐level hierarchical structure in SPEEK of greater sulfonation level, consisting of solvent‐swelled spatially correlated primary SO₃H‐rich ionic clusters of around 15 Å in size, forming larger secondary aggregates well dispersed in the PEEK matrix. The size of the primary nanodomains and the connectivity between domains are determining parameters for protonic conductivity, solvent swelling ability and permeability of the membranes. For both SPEEK and zirconia–SPEEK membranes containing ethanol, the pronounced affinity of ethanol molecules with SPEEK leads to an increase in the size of ionic clusters and of the number of connecting channels between clusters compared to membranes containing water. This promotes solvent swelling and proton conductivity. The increase in permeability to water induced by incorporation of ethanol in place of water in both polymeric and hybrid membranes is less in the hybrid membranes. This result suggests that the potential use of zirconia–SPEEK hybrid membranes in direct alcohol fuel cells is more promising than that of pure SPEEK, due not only to the less probable alcohol and water penetration in the membranes associated with their lower permeability, but also to the fact that an eventual penetration of alcohol in hybrid membranes should reduce the risk of cathode flooding compared to zirconia‐free SPEEK membranes. Copyright © 2011 Society of Chemical Industry     

Sulfonated graphene oxide‐doped proton conductive membranes based on polymer blends of highly sulfonated poly(ether ether ketone) and sulfonated polybenzimidazole

Simultaneously improving the proton conductivity and mechanical properties of a polymer electrolyte membrane is a considerable challenge in commercializing proton exchange membrane fuel cells. In response, we prepared a new series of miscible polymer blends and thus the corresponding crosslinked membranes based on highly sulfonated poly(ether ether ketone) and sulfonated polybenzimidazole. The blended membranes showed more compact structures, due to the acid‐base interactions between the two constituents, and improved mechanical and morphological properties. Further efforts by doping sulfonated graphene oxide (s‐GO) forming composite membranes led to not only significantly elevated proton conductivity and electrochemical performance, but also better mechanical properties. Notably, the composite membrane with the filler content of 15 wt % exhibited a proton conductivity of 0.217 S cm^?1 at 80 °C, and its maximum power density tested by the H₂/air single PEMFC cell at room temperature reached 171 mW cm^?2, almost two and half folds compared with that of the native membrane. As a result, these polymeric membranes provided new options as proton exchange membranes for fuel‐cell applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46547.     

Micro‐ and ultrafiltration film membranes from poly(ether ether ketone) (PEEK)

Film membranes from the thermoplastic poly(ether ether ketone) (PEEK) have been extruded and tested for their microfiltration and ultrafiltration performance. High‐performance asymmetric membranes have been obtained by extruding polymer blends of PEEK, polysulphone, and a small molecule solvent mixture, and then by removing the polysulphone and solvent in a subsequent extraction step. The process for making ultrafiltration membranes differs from microfiltration membranes only in the relative blend components, and the temperature of the film pick‐up rolls. Processing parameters with important effects on the membrane performance have been identified. Microfiltration membranes are characterized by their pore‐size distributions and SEM, and ultrafiltration membranes by their rejection of bovine serum albumin, bubble point, and SEM. Composite membrane for nanofiltration utilizing the PEEK ultrafiltration membrane as a substrate performed similarly to a commercial membrane for the same purpose. This work details the best method for making PEEK film membranes published to date. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1146–1155, 1999     

Composite Proton Exchange Membranes of Sulfonated Poly(ether ketone ether sulfone) (S-PEKES) and Molecular Sieve With High Mechanical Strength for Direct Methanol Fuel Cell

Composite proton exchange membranes are prepared by solvent casting via the incorporation of molecular sieves 3A, 4A, and 5A into the sulfonated poly(ether ketone ether sulfone) (S-PEKES) at the sulfonation degree of 0.66, with varying the ratio at of 3%, 6%, 9%, and 12% v/v. The influences of type and amount of the molecular sieves on the proton conductivity, methanol permeability, structural, thermal, and mechanical stabilities of the membranes are investigated. The composite membranes are characterized by FTIR, TGA, LCR meter, and GC techniques. All properties of the composite membrane are compared with the pristine S-PEKES and Nafion 117 membrane.     

Effect of thermal crosslinking on the properties of sulfonated poly(phenylene sulfone)s as proton conductive membranes

The synthesis and characterization of crosslinked aromatic polymer membranes with high ion exchange capacity (IEC) values are reported. Through aromatic nucleophilic substitution polycondensation and the subsequent sulfonation reaction, the highly sulfonated polymers SPPSU‐2S and SPPSU‐4S with high molecular weight (M_n = 138–145 kDa, M_w = 200–279 kDa) and well‐defined structures were synthesized. By solution casting and thermal annealing treatment, flexible crosslinked membranes with high solvent insolubility were obtained. The membranes exhibited mechanical and chemical stability as confirmed by dynamic mechanical analysis (DMA) and conductivity measurement. The crosslinked SPPSU‐4S membrane with IEC = 3.20 meq/g showed the highest proton conductivity of 0.163 S/cm at 120 °C, 90% RH, and improved thermal stability compared with its precursor (uncrosslinked) membrane. The results show that simple annealing method could improve significantly membranes properties of highly sulfonated aromatic polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44218.     

Performance of the sulfonated poly ether ether ketone proton exchange membrane modified with sulfonated polystyrene and phosphotungstic acid for microbial fuel cell applications

In this research, the preparation of low cost proton exchange membranes (PEMs) based on sulfonated poly ether ether ketone (SPEEK) for application in the microbial fuel cells (MFCs) is studied. Sulfonated polystyrene (SPS) and phosphotungstic acid (PWA) were employed to improve the performance of PEM through the creation of more proton pathways. At first, the sulfonation of PEEK and polystyrene were performed through two modified methods to obtain uniform and high degree of sulfonation (DS) of the polymers and then, the PEMs were prepared through the solution casting method. Accordingly, the formation of uniform skin layer was confirmed by the SEM micrographs. Blending the aforementioned additives to the SPEEK polymer solution significantly enhanced the proton conductivity, water uptake and durability of the modified membranes. The proton conductivities of SPEEK/SPS and SPEEK/PWA membranes at additive/SPEEK weight ratio of 0.15 were 45.3% and 26.2% higher than that of the commercial Nafion117 membrane, respectively. Moreover, the degradation times for the abovementioned modified membranes were 140 and 350 min which indicated satisfactory oxidation stability. Besides, the aforementioned membranes exhibited two times more water uptake compared to the neat SPEEK membrane. Finally, SPEEK/SPS and SPEEK/PWA membranes produced 68% and 36% higher maximum power in the MFC, compared to the commercial Nafion117 membrane. Therefore, the fabricated PEMs are potentially suitable alternatives to be used in the fuel cell applications.     

Synthesis and characterization of sulfonated poly(ether sulfone ether ketone ketone) for proton exchange membranes

A series of sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) with different degree of sulfonation (DS) are prepared by the postsulfonation of PESEKK using chlorosulfonic acid as sulfonating agent and concentrated sulfuric acid as solvent. The chemical structures of the polymers are analyzed by the proton nuclear magnetic resonance. The thermal properties of the SPESEKK show that they are greatly influenced by the DS value and sulfonation time. The water uptake, proton conductivity, and Ion exchange capacity values increase as the sulfonation time increasing. The methanol permeability of the SPESEKK in the range of 7.02 × 10^?8 to 4.477 × 10^?7 cm² s^?1, is one or two orders of magnitude lower than that of Nafion 115. The morphology of the SPESEKK membranes is investigated by scanning electron microscope. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Proton exchange membrane bearing entangled structure: Sulfonated poly(ether ether ketone)/bismaleimide hyperbranch

Physical cross-linking of sulfonated poly(ether ether ketones) sPEEKs with hyper-branched bismaleimide oligomer (modified bismaleimide, mBMI) leads to densely packed polymer. Different curing conditions on the two sPEEK samples containing Bismaleimide (BMI) monomer and modified Bismaleimide oligomers (mBMI) mole ratios of 70:30 (mBMI(30)) and 2:98 (mBMI(98)) are present. As the amount of BMI monomer increases, the branched structure and their degree of entanglement with sPEEK polymer matrix also increase. More rigid and more compact membrane is found in the case of mBMI(30). In contrast, relatively loose entangled network is found for mBMI(98) sample where the mBMI unit remains far apart and mostly un-connected, until high concentration of mBMI(98) is present. The branched structure and their degree of entanglement with sPEEK polymer matrix increases with longer curing time. The results shows physical cross-linking with highly branched mBMI is effective in reducing water uptake, lower methanol permabiity with reduced sPEEK membrane swelling. Except for heavily entangled sample (sPEEK/mBMI(30)) annealed for 20 h, all membranes displayed fair proton conductivity above 10⁻² S/cm at room temperature. Methanol permeability is also substantially reduced to 1.39 × 10⁻⁷ cm²/s for sPEEK/15% mBMI(98). The DMFC single cell assembled by the sPEEK/20% mBMI(98) membrane (59 μm thickness) displayed the highest OCV of 839 mV with a power density reaching 30 mW/cm² at 60 °C. This value is higher than that using sPEEK membrane alone.     

State of the water in crosslinked sulfonated poly(ether ether ketone)

We investigated the material properties of different crosslinked sulfonated poly(aryl ether ketone) membranes, focusing on the effect of the degree of sulfonation and crosslinking density on the water uptake, the physical state of the water, and the pore size distribution within the membranes. We observed that the degree of sulfonation and, in particular, the ion‐exchange capacity (IEC) had less effect on the control of the extent of water absorbed than the crosslinking density of the membranes. Crosslinking also enabled the membranes to reach a higher water contents without losing mechanical integrity. Moreover, increasing the crosslinking density resulted in the presence of more bound water, without dissolution of the membrane. The crosslinked membranes had lower methanol permeability and electroosmotic drag values. Only at low IEC values and low water uptake in partially crystalline sulphonated poly(ether ether ketone), SPEEK could the presence of nanometer pores in the water‐equilibrated crosslinked membranes be confirmed by thermoporometry and the pore size distributions were then comparable to those reported for Nafion membranes. At higher IEC values, the water uptake was extremely high, up to 300%, and then the structure of the swollen membranes was more analogous to that of a dilute aqueous solution of the sulfonated polymer, and no nanopores were present. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Pore structure and properties of poly(ether ether ketone) hollow fiber membranes: influence of solvent‐induced crystallization during extraction

Poly(ether ether ketone) (PEEK) hollow fiber membranes were prepared by a thermally induced phase separation method with polyetherimide as diluent, and N‐methyl pyrrolidone (NMP), dichloromethane and a composite extractant composed of NMP, ethanolamine and water as extractant. The effects of the different solvents induced crystallization on the pore structure during extraction and the properties of the PEEK hollow fiber membranes were investigated in detail. The crystallization behaviors of the membranes were characterized by DSC and XRD. The effect of the extractants on the microscopic morphologies, pore structures, water fluxes and mechanical properties of the membranes were investigated. The results showed that the extraction ability of the composite extractant was the most significant, followed by NMP and dichloromethane. The crystallinity of the hollow fiber was 39.0% before extraction and was elevated to 39.2% after the extraction with NMP, 46.6% with dichloromethane and 46.7% with the composite extractant, which shows that dichloromethane and the composite extractant have strong ability to induce the crystallization of PEEK. The inner and outer surfaces of the membranes obtained after extraction by the composite extractant had the largest pore size and the highest surface porosity. The most probable pore diameter of the membranes obtained after extraction by NMP, dichloromethane and the composite extractant was 23.26 nm, 24.43 nm and 24.43 nm, respectively, which indicated that solvent‐induced crystallization was beneficial for the formation of larger pores. The pure water flux of the PEEK membrane prepared by the composite extractant was the largest, but the tensile strength was the lowest. © 2019 Society of Chemical Industry     

Novel polymer electrolyte membranes based on semi‐interpenetrating blends of poly(vinyl alcohol) and sulfonated poly(ether ether ketone)

In this work, the properties of novel ionic polymer blends of crosslinked and sulfonated poly(vinyl alcohol) (PVA) and sulfonated poly(ether ether ketone) (SPEEK) are investigated. Crosslinking and sulfonation of PVA were carried out using sulfosuccinic acid (SSA) in the presence of dispersed SPEEK to obtain semi‐interpenetrating network blends. PVA–SSA/SPEEK blend membranes of different compositions were studied for their ion‐exchange capacity, proton conductivity, water uptake, and thermal and mechanical properties. The hydrated blend membranes show good proton conductivities in the range of 10^?3 to 10^?2 S/cm. When compared with pure component membranes, the PVA–SSA/SPEEK blend membranes also exhibit improvement in tensile strength, tensile modulus, and delay in the onset of thermal and chemical degradation. Semi‐interpenetrating nature of the blends is established from morphology and dynamic mechanical analysis. Morphology of the membranes was studied using scanning electron microscopy after selective chemical treatment. The dynamic mechanical properties of the membranes are examined to understand the miscibility characteristics of the blends. The relative proportions of PVA and SPEEK and the degree of crosslinking of PVA–SSA are important factors in determining the optimum properties for the blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013