Production of polymeric membranes made of polypropylene,poly(ethylene‐co‐vinyl acetate), and poly(vinyl alcohol)

In this study, we prepared and characterized membranes containing polypropylene, poly(ethylene‐co‐vinyl acetate) (EVA), and poly(vinyl alcohol) (PVA). The production process involved blend extrusion and calendering followed by solvent extraction by toluene and water of the EVA and PVA phases. Morphology studies involving scanning electron microscopy determined the pore size distribution at the surface and in the internal regions of the membrane. The resulting membrane properties were related to the processing variables (extension rate, process temperature, and solvent extraction methods) and blend composition. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3275–3286, 2004     

Preparation and characterization of poly(vinyl chloride)/polystyrene/poly(ethylene glycol) hollow‐fiber ultrafiltration membranes

Hollow‐fiber ultrafiltration (UF) membranes were prepared from blends of poly(vinyl chloride) (PVC) and polystyrene (PS) with a dry/wet phase inversion method. Poly(ethylene glycol) (PEG) and N,N‐dimethylacetamide were used as the additive and solvent, respectively. The effects of the PEG concentration in the dope solution as an additive on the cross sections and inner and outer surface morphologies, permeability, and separation performance of the hollow fibers were examined. The mean pore size, pore size distribution, and mean roughness of both the inner and outer surfaces of the produced hollow fibers were determined by atomic force microscopy. Also, the mechanical properties of the hollow‐fiber membranes were investigated. UF experiments were conducted with aqueous solutions of poly(vinyl pyrrolidone) (PVP; K‐90, M_w = 360 kDa). From the results, we found that the PVC/PS hollow‐fiber membranes had two layers with a fingerlike structure. These two layers were changed from a wide and long to a thin and short morphology with increasing PEG concentration. A novel and until now undescribed shape of the nodules in the outer surfaces, which was denoted as a sea‐waves shape, was observed. The outer and inner pore sizes both increased with increasing PEG concentration. The water permeation flux of the hollow fibers increased from 104 to 367 L m^?2 h^?1 bar^?1) at higher PEG concentrations. The PVP rejection reached the highest value at a PEG concentration of 4 wt %, whereas at higher values (from 4 to 9 wt %), the rejection decreased. The same trend was found also for the tensile stress at break, Young's modulus, and elongation at break of the hollow fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 989‐1004, 2013     

Preparation,structure, and transport properties of ultrafiltration membranes of poly(vinyl chloride) and poly(vinyl pyrrolidone) blends

Ultrafiltration (UF) membranes based on poly(vinyl chloride) and poly(vinyl pyrrolidone) blends were prepared by the phase inversion method, and the factors governing membrane properties were investigated. The membranes were characterized by scanning electron microscopy and atomic force microscopy. The fouling characteristics of the membranes were determined by UF of aqueous solutions of bovine serum albumin (BSA) over a pH range of 2–9 and varying salt concentrations. The maximum adsorption of the protein on the membrane surface occurred near the isoelectric point (pI 4.8) of BSA, and the presence of the salts increased the fouling of the membrane. The results can be explained in terms of the nature of the membrane polymer and the effect of different ionic environments on the permeability of the deposited protein layer. The net charge on the BSA molecules appears to be a dominant factor in determining the flux of water through the blend membranes. The UF flux is correlated by a model based on the membrane resistance, adsorbed protein resistance, and time dependent resistance of the concentration polarization layer near the membrane surface. The ζ potentials of the membranes were also determined before and after UF to characterize the surface potential of the membrane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2606–2620, 2000     

Effect of poly(vinyl pyrrolidone) concentration and coagulation bath temperature on the morphology,permeability, and thermal stability of asymmetric cellulose acetate membranes

Cellulose acetate (CA) is widely used in membrane processes. In this study, CA (weight‐average molecular weight = 52,000) was mixed with poly(vinyl pyrrolidone) (PVP; weight‐average molecular weight = 15,000) as an additive in 1‐methyl‐2‐pyrrolidone as a solvent. The phase‐inversion method was used for the preparation of flat‐sheet membranes. The effects of PVP concentration and coagulation bath temperature (CBT) on the morphology, pure water permeation flux, and thermal stability of the prepared membranes were studied and are discussed in this article. The solute rejection of the developed CA membranes was quantified with an insulin protein solution. The results showed that an increase in the CBT levels from 0 to 23°C along with an increase in the PVP concentration in the cast film from 0 to 1.5 wt % resulted in an increase in the macrovoid formation in the membrane sublayer, an increase in the pure water flux (PWF), and a decrease in insulin rejection. Further increases in the PVP concentration from 1.5 to 3, 6, and 9 wt % resulted in gradual suppression of the macrovoid formation, a decrease in PWF, and an increase in insulin rejection. Higher PVP concentrations and lower CBT levels also appeared to result in higher glass‐transition temperatures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Studies on cellulose acetate‐carboxylated polysulfone blend ultrafiltration membranes. III

Enhancement of the hydrophilicity in polymeric membrane materials results in membranes with higher flux and better membrane characteristics. Hence, polysulfone was carboxylated and ultrafiltration membranes were prepared from blends of cellulose acetate and carboxylated polysulfones having various degrees of carboxylation with a total polymer concentration of 20 wt % in casting solution and at different blend polymer compositions. The effects of degree of carboxylation on membrane characteristics such as compaction, pure water flux, and membrane hydraulic resistance (R_m) have been investigated. The influence of the polymer concentration in the blend solution on the performance of blend membranes at various blend polymer compositions has also been investigated and compared with that of blend membranes prepared from blends of cellulose acetate and polysulfone or carboxylated polysulfone with a total polymer concentration of 17.5 wt %. Further, the solute rejection performance of the membranes has also been investigated by subjecting the membranes to metal ion permeation studies using polyelectrolyte‐enhanced ultrafiltration. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 976–988, 2005     

Reactive compatibilization of polystyrene/poly(ethylene–co–vinyl acetate) (EVA) blends

A reactive compatibilizer, mercapto‐functionalized EVA (EVASH), in combination with styrene‐butadiene block copolymer (SBS), was used to compatibilize the blends of polystyrene (PS) and ethylene–vinyl acetate copolymer (EVA). The reactive compatibilization was confirmed by the presence of insoluble material and from dynamic‐mechanical analysis. In addition to a more uniform morphology with small phase size, the compatibilization also provided excellent stabilization of the morphology, with an almost complete suppression of coarsening during annealing. As a consequence, a substantial increase on the elongation at break without significant influence on ultimate tensile strength was achieved for compatibilized blends with different compositions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 14–22, 2006     

Foaming of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate‐co‐carbon monoxide) and their blends with carbon dioxide

Poly(ethylene‐co‐vinyl acetate) (EVA‐25) and poly(ethylene‐co‐vinyl acetate‐co‐carbon monoxide) (EVACO‐2410) and their blends with EVACO:EVA ratios of 80:20, 60:40, 40:60, and 20:80 were foamed using CO₂. These foams are of interest for applications ranging from footwear to medical devices. Foaming experiments were carried out using 1 mm thick melt‐extruded films in CO₂ at a range of pressures (100, 200, and 300 bar) and temperatures (30, 40, 50, and 60 °C). Foamability of the polymers was explored both under isothermal and gradient temperature conditions. Foams of EVACO‐2410 displayed high initial expansions followed by postfoaming relaxation and shrinkage while foams generated from EVA‐25 showed more dimensional stability. Blending EVACO‐2410 with EVA‐25 was explored as an approach to reduce postfoaming relaxation and shrinkage. The surfaces of the foamed samples displayed blistering that was linked to CO₂ bubble entrapment and coalescence at the surface. Scanning electron micrographs of the foams generated from blends displayed distinct morphologies reflecting whether the sections were representing the machine‐ or cross‐machine direction of extruded films. In going from EVACO‐2410 to EVA‐25, the cell densities ranged from about 10⁶ to 10¹⁰ cells/cm³. Foams with low bulk densities of about 0.11 g/cm³ could be generated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45841.     

Release of salicylic acid through poly(vinyl alcohol)/poly(vinyl pyrrolidone) and poly(vinyl alcohol‐g‐N‐vinyl‐2‐pyrrolidone) membranes

A controlled release profile of salicylic acid (SA) for transdermal administration has been developed. Poly (vinyl alcohol) (PVA) and Poly(vinyl alcohol)/Poly(vinyl pyrrolidone) (PVP) blended preparations were used to prepare the membranes by solvent‐casting technique. The release of the drug from the membranes was evaluated at in vitro conditions. The effects of PVA/PVP (v/v) ratio, pH, SA concentration and temperature were investigated. 60/40 (v/v) PVA/PVP ratio was found to be the best ratio for the SA release. Increase in pH and temperature was observed to increase the transport of SA. Instead of blending PVA with PVP, N‐Vinyl‐2‐pyrrolidone (VP) was grafted onto the PVA and the delivery performance for SA was compared with that of the blended PVA/PVP membranes. Grafted membranes gave higher transport percentages than the blended membranes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1244–1253, 2006     

Preparation and characterization of membranes obtained from blends of acrylonitrile copolymers with poly(vinyl alcohol)

New microfiltration and ultrafiltration membranes were obtained using acrylonitrile‐vinyl acetate copolymers in mixture with poly(vinyl alcohol) (PVA). Thus, a blend polymer solution was prepared in dimethylsulfoxide (DMSO) and used to obtain bicomponent polymer membranes by phase inversion. The rheological behavior of the DMSO polymer solutions was, mostly, dilatant at low shear gradients and pseudo plastic with quasi Newtonian tendency at higher gradients. Membranes were characterized by Fourier transform infrared spectrometry (FTIR), optical microscopy, atomic force microscopy, thermal gravimetric analysis‐differential thermal gravimetry, and pure water flux (PWF). FTIR spectra displayed the characteristic bands for acrylonitrile, vinyl acetate, and PVA. The morphology and the porosity can be tailored by the preparation conditions. PVA allows controlling the size of the pores and enables, in principle, to use the resulted membranes as supports for enzyme immobilization. PVA content influences the thermal stability. PWF values depend on the copolymer, on the content in PVA, but also on the coagulation bath composition. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41013.     

Solid‐state NMR and morphological studies of poly(ethylene‐co‐vinyl acetate)/poly(vinyl acetate) blends

To obtain a correlation among structure–morphology–mobility–compatibility properties of poly(ethylene‐co‐vinyl acetate) (EVA)/poly(vinyl acetate) (PVAc) blends, we have used scanning electron microscopy and solid‐state nuclear magnetic resonance in our investigations. The results are discussed in terms of blends, component dispersion, plasticization effect, and domain mobilities to acquire a response of the correlation between structural properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2990–2996, 1999     

pH‐ and temperature‐sensitive microfiltration membranes from blends of poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) and poly(N‐isopropylacrylamide)

The copolymer poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) (PVDF‐g‐P4VP) was prepared through the graft copolymerization of poly(vinylidene fluoride) with 4‐vinylpyridine. Through the blending of the PVDF‐g‐P4VP copolymer with poly(N‐isopropylacrylamide) (PNIPAm) in an N‐methyl‐2‐pyrrolidone solution, PVDF‐g‐P4VP/PNIPAm membranes were fabricated by phase inversion in aqueous media. Elemental analyses indicated that the blend concentration of PNIPAm in the blend membranes increased with an increase in the blend ratio used in the casting solution. Scanning electron microscopy revealed that the membrane surface tended to corrugate at a low PNIPAm concentration and transformed into a smooth morphology at a high PNIPAm concentration. The surface morphology and pore size distribution of the microfiltration membranes could be regulated by the blend concentration of the casting solution, temperature, pH, and ionic strength of the coagulation bath. X‐ray photoelectron spectroscopy revealed a significant enrichment of PNIPAm on the membrane surface. The flux of aqueous solutions through the blend membranes exhibited a pH‐ and temperature‐dependent behavior. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4089–4097, 2006     

Solution and solid‐state NMR investigation of poly(methyl methacrylate)/poly(vinyl pyrrolidone) blends

The development of polymer blends has become very important for the polymer industry because these blends have shown to be a successful and versatile alternative way to obtain a new polymer. In this study, binary blends formed by poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) were prepared by solution casting and evaluated by solution and solid‐state NMR. Variations in the microstructure of PMMA were analyzed by ¹³C solution NMR. Solid‐state NMR promotes responses on physical interaction, homogeneity, and compatibility to use these blends to understand the behavior of the ternary blends. The NMR results led‐us to acquire information on the polymer blend microstructure and molecular dynamic behavior. From the NMR solution, it was possible to evaluate the microstructure of both polymer blend components; they were atactic. From the solid state, good compatibility between both polymer components was characterized. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 372–377, 2004     

Compatibilization of poly(vinyl chloride) and polystyrene blends with poly(styrene‐co‐n‐methylolacrylamide)

In this work, the compatibilization of blends of plasticized polyvinyl chloride (PVC) and polystyrene (PS) with poly(styrene‐co‐n‐methylolacrylamide) (PSnMA) was investigated. The PSnMA was synthesized by emulsion polymerization with different amounts of n‐methylolacrylamide (nMA). Particle size and phase behavior was determined by scanning electron microscopy, and mechanical properties were determined in an Universal Testing Machine. Micrographs revealed that an appreciable size reduction of the dispersed phase was achieved when small amounts of PSnMA were added to the blend, and as the amount of nMA was increased, particle size decreased. When the (PVC/PS/PSnMA) blend was subjected to solvent extraction to remove PS and unreacted PVC, the residue showed a single T_g. Tensile modulus and the ultimate strength of the blends increased with PSnMA content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Studies on dielectric relaxation and ac conductivity of cellulose acetate hydrogen phthalate–poly (vinyl pyrrolidone) blend

The dielectric constant, dielectric loss, and ac conductivity of polyblends of cellulose acetate hydrogen phthalate (CAP) and poly (vinyl pyrrolidone) (PVP) of different compositions were measured in the temperature range of 300–430 K and in the frequency range of 50 Hz–100 kHz. In the blends, the dielectric constant as well as the dielectric loss as a function of the temperature display a single peak corresponding to the glass transition temperature (T_g) in the region between the T_g values of the pure polymers. The T_g values observed agree well with those values obtained from DSC. Dielectric studies show that CAP forms a miscible blend with PVP. Ac conductivity values were calculated from the dielectric data and the conduction mechanism is discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1702–1708, 2002     

Preparation of novel heterogeneous cation‐permeable membranes from blends of sulfonated poly(phenylene sulfide) and poly(ether sulfone)

Novel heterogeneous cation‐exchange membranes using poly (ether sulfone)(PES) as binder and sulfonated poly(phenylene sulfide) (SPPS) powder as polyelectrolyte were prepared by the solution casting‐immersion method. Compared with a conventional route for heterogeneous membrane, the steps of milling resin into fine powders and the pressing at high temperature are avoided, and thus permits a simple technique for the preparation of such membrane. The effect of the particle size and loading of SPPS resin on the properties of the membranes such as ion‐exchange capacity, water content, electrical resistance, transport number, diffusion coefficient of electrolytes, etc., have been studied. It is shown that the membrane fundamental properties are largely dependent on both the resin loading and the particle size of SPPS resin. By adjusting these two important parameters, one can obtain heterogeneous membrane with both good conductivity, selectivity, and proper water content for different industrial purposes such as electrodialysis, diffusional dialysis, etc. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 167–174, 2004     

Protein separation by cellulose acetate/sulfonated poly(ether imide) blend ultrafiltration membranes

A process for purifying aqueous solutions containing macromolecular proteins such as bovine serum albumin (BSA), egg albumin (EA), pepsin, and trypsin has been investigated. Protein removal from food and biorelated industrial waste streams are gaining increased visibility due to environmental concern and saving precious materials. Ultrafiltration (UF) processes are largely being applied for protein separation from aqueous streams. In this work, an attempt has been made to separate the valuable proteins using cellulose acetate (CA)/sulfonated poly(ether imide) (SPEI) blend UF membranes prepared in the absence and presence of the additive, polyethyleneglycol (PEG600) in various compositions. The blend membranes were subjected to the determination of pore statistics and molecular weight cut‐off (MWCO). Porosity and pore size of the membranes increased with increasing concentrations of SPEI and PEG600 in the casting solution. Similarly, the MWCOs of the blend membranes ranged from 20 to greater than 69 kDa, depending on the various polymer blend compositions. Surface morphology of the blend membranes were analyzed using scanning electron microscopy. Studies were carried out to find the rejection and permeate flux of proteins. On increasing the concentration of SPEI and PEG600, the rejection of proteins is decreasing, whereas the permeate flux has an increasing trend. The effect of hydrophilicity of SPEI on fouling of protein for CA/SPEI blend membranes was also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of post‐treatments on the properties of porous poly(vinyl alcohol) membranes

Porous poly(vinyl alcohol) (PVA) membranes were prepared by a phase‐inversion method. The influence of chemical crosslinking and heat treatments on the swelling degree, resistance to compaction, mechanical strength, and morphology of porous PVA membranes was extensively studied. The crosslinking degree and crystallinity of the membranes, calculated from IR spectra, increased with the treatment time. The porosity, calculated on the basis of swelling experiments, showed a decreasing trend for heat‐treated membranes but remained almost at a constant value for crosslinked membranes. Such a change was further proved with scanning electron microscopy pictures. The behavior was explained by the rearrangement of PVA chains during the heat‐treatment process, which led to morphological changes in the membranes. The mechanical properties of the porous membranes in dry and wet states were measured, and a great difference was observed between crosslinked and heat‐treated membranes in the dry and wet states. The crosslinked membranes showed good mechanical properties in the dry state but became fragile in the wet state. On the contrary, the heat‐treated membranes were more flexible in the wet state than in the dry state. This change was explained by the turnaround of inner stress in the systems during the swelling process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High‐resolution solid‐state NMR and SEM study of the interaction behavior of poly(ethylene‐co‐vinyl acetate)/poly(vinyl acetate) blends

Binary blends formed by two types of ethylene‐co‐vinyl acetate (EVA), which have different vinyl acetate contents, and poly(vinyl acetate) (PVAc) were prepared in a Haake Rheocord 9000 plastograph. A series of samples were obtained varying the PVAc amount up to 50%. The studies were carried out employing solid‐state nuclear magnetic resonance spectroscopy (NMR) and scanning electronic microscopy (SEM). The xenon‐129 (¹²⁹Xe) and carbon‐13 (¹³C) NMR response together with the microscopy results showed that the systems are heterogeneous. Therefore, EVA with a higher vinyl acetate content presented some interaction between the polymer blend components. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 116–124, 2002     

Rheology of poly(N‐vinyl pyrrolidone)–poly(ethylene glycol) adhesive blends under shear flow

The rheological properties of adhesive miscible blends of high‐molecular‐weight poly(N‐vinyl pyrrolidone) (PVP) with short‐chain poly(ethylene glycol) (PEG) under oscillatory and steady‐state shear flow have been examined with dynamic mechanical and squeezing‐flow analysis. The latter allows the rheological characterization of adhesive blends under conditions modeling adhesive‐bond formation as a fixed compressive force is applied to an adhesive film. The most adhesive PVP blend with 36 wt % PEG has been established to flow like a viscoplastic (yield stress) liquid with a power‐law index of about 0.12. The study of the apparent yield stress as a function of the PVP–PEG composition, content of sorbed water, molecular weight of PVP, and temperature shows that the occurrence of a yield stress in the blends results most likely from a noncovalent crosslinking of PVP macromolecules through short PEG chains by means of hydrogen bonding of both terminal OH groups of PEG to the complementary functional groups in PVP monomer units. A molecular mechanism of PVP–PEG interaction was established earlier by direct and independent methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 522–537, 2006     

Performances of poly(vinylidene fluoride‐co‐hexafluoropropylene) ultrafiltration membranes modified with poly(vinyl pyrrolidone)

The structure and performance of modified poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVdF‐co‐HFP) ultra‐filtration membranes prepared from casting solutions with different concentrations of poly(vinyl pyrrolidone) (PVP) were investigated in this study. Membrane properties were studied in terms of membrane compaction, pure water flux (PWF), water content (WC), membrane hydraulic resistance ( R _m), protein rejection, molecular weight cut‐off (MWCO), average pore size, and porosity. PWF, WC, and thermal stability of the blend membranes increased whereas the crystalline nature and mechanical strength of the blend membranes decreased when PVP additive concentration was increased. The contact angle (CA) decreased as the PVP concentration increased in the casting solution, which indicates that the hydro‐philicity of the surface increased upon addition of PVP. The average pore size and porosity of the PVdF‐co‐HFP membrane increased to 42.82 Å and 25.12%, respectively, when 7.5 wt% PVP was blended in the casting solution. The MWCO increased from 20 to 45 kDa with an increase in PVP concentration from 0 to 7.5 wt%. The protein separation study revealed that the rejection increased as the protein molecular weight increased. The PVdF‐co‐HFP/PVP blended membrane prepared from a 7.5 wt% PVP solution had a maximum flux recovery ratio of 74.3%, which explains its better antifouling properties as compared to the neat PVdF‐co‐HFP membrane. POLYM. ENG. SCI., 55:2482–2492, 2015. © 2015 Society of Plastics Engineers