Acrylonitrile-based copolymer membranes containing reactive groups: effects of surface-immobilized poly(ethylene glycol)s on anti-fouling properties and blood compatibility

The anti-fouling properties and blood compatibility of poly(acrylonitrile-co-maleic acid) (PANCMA) membranes were improved by the immobilization of poly(ethylene glycol)s (PEG) on membrane surface. It was found that the reactive carboxyl groups on PANCMA membrane surface could be conveniently conversed into anhydride groups and then esterified with PEG. Chemical and morphological changes as well as biocompatibility on membrane surface were analyzed by Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy, water contact angle, protein adsorption, and platelet adhesion. Results revealed that, with the immobilization of PEG, the hydrophilicity and blood compatibility of the acrylonitrile-based copolymer membranes were improved obviously. The molecular weight of PEG had an obvious influence on the properties of the PEG-immobilized membranes. Permeation behaviors for the studied membranes were investigated by water and bovine serum albumin (BSA) filtration experiments. Compared with the original PANCMA membrane, the membrane immobilized with PEG 400 (M_w=400 g/mol) showed a three-fold increase in a BSA solution flux, a 40.4% reduction in total fouling, and a 57.9% decrease in BSA adsorption.     

Pore morphology control and hydrophilicity of polyacrylonitrile ultrafiltration membranes

The effects of different solvents (dimethyl formamide: DMF and dimethylsulfoxide: DMSO) on the solubility of polyacrylonitrile (PAN) were investigated by the phase diagrams of H₂O/DMF/PAN and H₂O/DMSO/PAN ternary systems through cloud‐point titration method at low polymer concentration. The influences of polymer concentrations and temperatures on the morphologies of PAN ultrafiltration membranes were elucidated. The morphologies of fabricated UF membranes were characterized by scanning electron microscopy (SEM) and atomic force microscope (AFM), and the basic performance of ultrafiltration including pure water flux and rejection of BSA were explored. At 25°C, the pure water flux of ultrafiltration membranes at the lower PAN content (16 wt % PAN in 84 wt % DMSO) reached 213.8 L/m/bar and the rejection of BSA was 100%. Interestingly, the water flux of UF membranes dramatically decreased to 20.6 L/m/bar (20 wt %) and 2.9 L/m/bar (24 wt %) when increasing PAN concentrations in DMSO. On the other hand, the hydrophilicity of membranes can be enhanced by increasing coagulation temperatures and polymer concentrations which were characterized by static contact angle, fitting well with the variation tendency of roughness. Although there are many works concerning on the effects of phase inversion conditions on the performance of PAN UF membranes, to our best knowledge, there is seldom works focusing on investigating the membrane hydrophilicity trend by adjusting phase inversion conditions. To disclose the reason of the enhanced hydrophilicity, the water and glycol contact angles of various membranes were measured and the surface tensions were presented. The results illustrated that the enhanced hydrophilicity of PAN UF membranes fabricated at higher temperatures or higher polymer concentrations was due to the higher polarity on membrane surface. Since the vast majority of ultrafiltration membranes in labs and in industrial scale have been fabricated by immersion phase inversion method, this work can provide a guidance to obtain hydrophilic PAN UF membranes by adjusting the process of phase inversion. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41991.     

Acrylonitrile-based copolymer membranes containing reactive groups: Surface modification by the immobilization of biomacromolecules

Asymmetric membranes fabricated from poly(acrylonitrile-co-maleic acid) (PANCMA) were immobilized with heparin and/or insulin to improve their surface properties. These biomacromolecule-immobilized PANCMA membranes were prepared by the amination of the membrane surface with ethylenediamine, followed by the reaction of the amino groups with heparin and/or insulin in the presence of 1-ethyl-3-(3-dimethyl amidopropyl) carbodiimide. The surface-modified membranes were analyzed by X-ray photoelectron spectroscopy to confirm the immobilization of the biomacromolecules. Morphological changes on the membrane surface and in the cross section were characterized by scanning electron microscopy. The surface hydrophilicity and hemocompatibility of the studied membranes were evaluated on the basis of water contact angle, platelets adhesion and cell attachment measurements. It was found that, after the immobilization of the biomacromolecules, the water contact angle and the amount of adhered platelets and macrophages on the membrane decreased significantly when compared with the nascent ones, indicating the improvement of surface hydrophilicity. Furthermore, the heparin immobilized membrane showed the best hemocompatibility among the corresponding membranes studied.     

Preparation and characterization of PES/CA microporous membranes via reverse thermally induced phase separation process

The blend polyethersulfone (PES)/cellulose acetate (CA) flat‐sheet microporous membranes were prepared by reverse thermally induced phase separation (RTIPS) process. The effects of CA content and coagulation bath temperature on membrane structures and properties were investigated in terms of membrane morphology, water contact angle, permeation performance, and mechanical properties. The cloud point results indicated that the cloud point decreased with the increasing content of CA. When the coagulation bath temperature was lower than the cloud point, the membrane formation process underwent nonsolvent induced phase separation (NIPS) process and dense skin layer and finger‐like structure were formed in membranes. These membranes had lower pure water flux and poor mechanical properties. But when the coagulation bath temperature was higher than the cloud point, the membrane formation process underwent RTIPS process. The porous top surface as well as porous cross‐section of the membranes were formed. Therefore, high pure water flux and good mechanical properties were obtained. The contact angles results indicated that the hydrophilicity of the prepared membranes improved obviously with the addition of CA. When the content of CA was 0.5 wt% and the membrane formation temperature was 323K, the PES/CA microporous membrane which was prepared via the RTIPS process displayed a optimal permeability of the pure water flux of 816 L m^?2 h^?1 and the BSA rejection rate of 49.5%, which showed an increase of 48.9% and 23.6% than that of pure PES membrane, respectively. Moreover, the mechanical strengths of the membranes obtained by RTIPS process were better than those membranes prepared by NIPS process. POLYM. ENG. SCI., 58:180–191, 2018. © 2017 Society of Plastics Engineers     

Phase behavior and morphological studies of polyimide/PVP/solvent/water systems by phase inversion

The solubility gaps for poly(vinyl pyrrolidone) (PVP) in four polyimide solutions (NMP, DMF, GBL, DMSO) were determined by cloud point measurement and correlated with χ_PI/Solvent and Δδ_PVP/Solvent. Membranes prepared with NMP and DMF systems showed a tendency of suppressing fingerlike structure with addition of PVP. On the other hand, membranes prepared with GBL and DMSO systems showed an inclination toward inducing macrovoid formation. These effects of PVP on the membrane morphology were explained by means of miscibility gap, viscosity of the polymer solution, polymer–polymer phase separation, and overall porosity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3481–3488, 2001     

Preparation of porous hollow fiber membranes with a triple‐orifice spinneret

A triple‐orifice spinneret has been applied for the preparation of hollow fiber microfiltration membranes with a high surface porosity. Considering the general rules of diffusion induced phase separation, a low polymer concentration is required at the outer layer to obtain a highly interconnected open‐porous structure. Therefore, by using N‐methylpyrrolidone (NMP) as the external liquid at the outside orifice of the spinneret, a highly porous surface can be obtained. For a polymer solution containing a low molecular weight additive and with an initial concentration close to the cloud point, this technique shows slightly improvement on the pure water and gas fluxes since the major resistance of the membrane is located at the substructure and the inner skin. However, for a solution containing a high molecular weight additive and with an initial concentration far from the cloud point, a porous shell surface is obtained, resulting in a significant improvement in water flux. The effect of various external liquids on the morphology has been investigated as well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2151–2157, 2003     

Solvent effect and macrovoid formation in cellulose acetate phthalate (CAP)–polyacrylonitrile (PAN) blend hollow fiber membranes

The interactions which govern the morphology of blend hollow fiber membranes is explored in detail in the present work. A hydrophilic (cellulose acetate phthalate) and a relatively hydrophobic polymer (polyacrylonitrile, critical surface tension 47.0 mJ/m²) blend in three solvents, viz., n ‐methylpyrrolidone (NMP), dimethyl formamide (DMF), and dimethylsulfoxide (DMSO), has been selected as an example to understand the polymeric blend—solvent and nonsolvent interactions. The deviation intrinsic parameter ( ) is estimated as well as cloud point, linearized cloud point (LCP), and Fourier transform‐infrared (FT‐IR) analysis have been performed for the blend membranes. The analysis yields that is negative for both DMF and NMP indicating miscibility, whereas for DMSO it is positive indicating immiscibility. Cloud point and LCP analysis too reveal DMSO to be the poorest solvent and liquid‐liquid demixing is the governing phenomenon for the phase inversion. In depth interaction is conducted with help of FT‐IR spectra. The higher red shift of >C==O (1747 to 1665 cm^?1) after complete phase inversion indicates stronger interaction in DMF and NMP, whereas, no shift in >C==O stretching in DMSO indicates weak or no interaction. This reveals that polymer blend‐solvent interaction is weak in case of DMSO than DMF or NMP. These observations manifest in DMSO membranes being most porous, with highest permeability and molecular weight cut off with poor tensile strength. On the other hand, NMP and DMF hollow fiber membranes yields denser structure with better mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133 , 44366.     

The formation of polyacrylonitrile nascent fibers in wet‐spinning process

The formation of polyacrylonitrile (PAN) nascent fibers in wet‐spinning process was studied by KMnO₄ back titration method and scanning electron microscopy (SEM). It has been found that the rate of DMSO diffusion was rapid at the beginning of coagulation then decreased and reached balance at 24 s. With coagulation time increase, the nascent fibers became denser and had fewer inner defects gradually, but transverse stripes appeared on the surface at 24 s, and got deeper. The main defects of nascent fibers included transverse stripes, impurity, fish tail, inner microvoids etc. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and performances of poly(phthalazinone ether sulfone ketone) hollow fiber membranes with excellent thermotolerance

The cloud points of PPESK/NMP/H₂O ternary system at different temperatures were measured by titrimetric method. The binodal lines in the ternary phase diagram of the poly(phthalazinone ether sulfone ketone (PPESK) dope system was determined, on the basis of the cloud point experimental data being linearly fitted with the semiempirical linear cloud point correlation. Furthermore, phase separation behavior during the phase inversion of PPESK membrane‐forming system was discussed in terms of the phase diagram. Then, dry–wet spinning technique was employed in manufacturing PPESK hollow fiber membranes by immersion precipitation method. The cross‐section morphologies of hollow fibers were observed by scanning electronic microscopy. Also, the effects of dope solution composition and spinning parameters, including the coagulant composition and the spinning temperature on the separation performances of fibers, were evaluated by permeability measurements. The thermotolerance of the PPESK hollow fiber membranes prepared in the work was examined for the permeation operation at different temperatures and pressure differences. The experimental results showed that pure water flux increases several fold along with the temperature increases from 20 to 80°C at different operation pressures, while the solute rejection only decreases slightly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 878–884, 2006     

Nanofiltration membranes based on PA6/EVOH with variable composition and morphology

Nanofiltration PA6/EVOH membranes were prepared through a nonsolvent induced phase separation technique. The effects of polymer concentration in the solution and solvent evaporation time on the performance and morphology of the resulting membranes were investigated by cloud point titration, permeation, and scanning electron microscopy (SEM). Experimental cloud point data for various prepared membranes suggested that polymer solutions with higher concentrations of PA6/EVOH need a less content of nonsolvent. SEM observations show that an increase in polymer concentration leads to formation of a thin dense layer on the surface of the membrane thanks to pore size reduction. However, dense top layer of membrane becomes thicker as polymer concentration increases from 15 wt% to 20 wt%. The performance of membranes reveals a decrease with polymer concentration in casting solution. By contrast, Polyamide/Poly(ethylene‐co‐vinyl alcohol) membranes show an optimal performance with various formic acid evaporation times. J. VINYL ADDIT. TECHNOL., 25:E28–E34, 2019. © 2018 Society of Plastics Engineers     

Partial Phase Behavior of HMX/DMSO Solutions

The phase diagram of HMX/DMSO and the solvated complex HMX·(DMSO)₂ has been investigated by visual observation, high performance liquid chromatography (HPLC), differential scanning calorimetry (DSC), and optical microscopy. Visual observations showed the solved complex exhibited an incongruent melting point, i.e., the melting point of the solvated crystal occurs within the region of the phase diagram where HMX itself precipitates. If the solvated crystal is removed from solution and heated, it reverts to solid HMX and DMSO at the peritectic temperature (∼70°C). Using HPLC the change in concentration of the liquid phase was monitored as a function of temperature to confirm the phase line of the DMSO/solvated complex based on visual observation. Polarized light microscopy of the dissolution of seeded solutions of different concentrations was also used to verify these results. It is possible that a 1:1 complex also exists, but no evidence for such a complex was found in these experiments.     

Cloud Point Extraction of Four Triphenylmethane Dyes by Triton X-114 as Nonionic Surfactant

A method for removing four triphenylmethane dyes from wastewater by cloud point extraction with the nonionic surfactant Triton X-114 (TX-114) was developed. The triphenylmethane dyes were crystal violet, ethyl violet, malachite green and brilliant green. The cloud point of TX-114 generally increased in the presence of any of the four dyes. In the cloud point system, these dyes were solubilized into a coacervate phase that left a color-free dilute phase. The extraction efficiency of the dyes increased with the temperature, TX-114 concentration, and salt (NaCl and CaCl₂) concentration. More than 97% TX-114 in the dilute phase was recovered by adjusting the volume ratio of dichloromethane to the dilute phase. The Langmuir-type adsorption isotherm was used to describe the dye solubilization. The Langmuir constants m and n were calculated as functions of temperature. The results showed that the solubilization of the triphenylmethane dyes in the cloud point system was related to the partition coefficient and their molecular structures.     

Solution properties of homogeneous polyglycerol dodecyl ether nonionic surfactants

The synthesis and solution properties of a homologous series of polyglycerol dodecyl ethers (R₁₂G_n) are described. The phase behavior, surface tension, cloud point and HLB value (hydrophile lipophile balance) of these surfactants in aqueous solutions and in mixed solutions of water/oil have been investigated and compared with values for polyoxyethylene dodecyl ether (R₁₂EO_n). The surface tension measurements showed that R₁₂G_n have sufficiently low values of surface tension and critical micellization concentration (cmc) to serve as useful nonionic surfactants. The mesophases appearing in the R₁₂G_n systems were more stable in a high temperature range than the mesophases of the R₁₂EO_n systems. The cloud point and HLB data indicated that addition of one glycerol group was equivalent to the addition of three oxyethylene units, as far as the hydrophilic property was concerned. The phase diagrams of the R₁₂G_n/dodecane/water systems showed that the solubilizing and emulsifying powers of R₁₂G_n were greater than those of R₁₂EO_n. It is concluded that the polyglycerol chain can be even more useful as the hydrophilic part of nonionic surfactants than the conventional oxyethylene chain.     

Cloud Point Extraction of Glycyrrhizic Acid from Licorice Root

Abstract

An attempt has been made to extract glycyrrhizic acid (GA) from licorice root by surfactant mediated cloud point extraction (CPE) using non‐ionic surfactant (Triton X‐100). Almost all of the GA molecules were concentrated in the surfactant‐rich phase (also called coacervate phase) after phase separation. The pH is the most critical factor regulating the distribution of GA in the micelle which related to the ionization form. The other effects of the concentration of GA and the surfactant, the temperature, and the salt concentration on the extraction efficiency of GA in the coacervate phase and aqueous phase have been studied. The mechanism of CPE of GA was explored with transmitting electron microscopy. It was deduced that aggregate GA molecules were adsorbed on micelles' outer poler mantle and inner cross‐linked micelles at high GA concentrations in coacervate phase.     

Phase behavior and mechanism of formation of protofiber morphology of solution spun poly(acrylonitrile) copolymers in DMF‐water system

Phase diagrams of a series of copolymers of acrylonitrile (AN) and acrylic acid (AAc) were constructed using linearized cloud point correlation. The miscibility region in the phase diagram was found to increase with the increase in AAc content of the copolymers. For various compositions, χ₁₃ (polymer–water interaction parameter) values were estimated by sorption experiment. As the hydrophilic nature of the polymer increased with the increase in the content of acrylic acid, the χ₁₃ interaction parameter was found to decrease from poly(acrylonitrile) homopolymer to its copolymer with 50 mol % acrylic acid (AA50B). The polymer–solvent interaction parameters (χ₂₃) and composition at the critical points for all the polymers were determined by fitting the theoretical bimodal curves to the experimental cloud point curves using Kenji Kamide equations. The polymer composition at the critical point was found to increase by 400% with increasing AAc content. The polymers were solution spun in DMF‐water coagulation bath at 30°C and their protofiber structures were investigated under scanning electron microscopy. The observed morphological differences in protofibers were explained on the changes brought about in the phase separation behavior of the polymer–solvent–nonsolvent systems. The copolymers with higher acrylic acid content could be solution spun into void free homogeneous fibers even at conditions that produced void‐filled inhomogeneous fibers in poly(acrylonitrile) and its copolymers with lower AAc content. The experiments demonstrate the important role of thermodynamics in deciding the protofiber morphology during coagulation process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Permeability properties of isometrically temperature-responsive poly(acrylic acid)-graft- oligo(N-isopropylacrylamide) gel membranes

A series of temperature-responsive hydrogels were prepared by grafting oligo(N-isopropylacrylamide) (ONIPAAm) chains onto a crosslinked poly(acrylic acid) (PAAc) network, intending an application to drug delivery systems (DDS). Cloud points and swelling ratios of the obtained PAAc-graft-ONIPAAm gels were measured as a function of temperature under various pH conditions. At pH > 4.5, the clear cloud points were observed at 31–33°C, which were almost the same values as that of poly(N-isopropylacrylamide) (PNIPAAm), whereas swelling/shrinkage phenomenon was not observed in the temperature range 25–45°C. It seemed that grafted ONIPAAm chains underwent the coil-to-globule transition, while the crosslinked PAAc network remained unchanged, due to the anionic charges on the main chains. In the presence of NaCl in the buffer solution, the phase transition temperature was slightly lowered. To assess the applicability of these temperature-responsive PAAc-graft-ONIPAAm gels to DDS, permeability of theophylline through the gel membranes was measured as a function of temperature. At a temperature below the cloud point, the permeability of theophylline was low, whereas it was high at an elevated temperature above the cloud point. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1027–1034, 1998     

Demixing pressures of hydroxy-terminated poly(dimethylsiloxane)–carbon dioxide binary mixtures at 313.2 K, 323.2 K and 333.2 K

The phase behavior of PDMS(OH)–CO₂ binary mixtures was investigated. Two different molecular weight PDMS(OH) were utilized and the demixing pressures were determined at three temperatures for a wide composition range. Both of these polymers were found to form miscible mixtures with CO₂ at all compositions at pressures lower than 31 MPa in the temperature range 313.2–333.2 K. Depending on the composition of the binary mixtures, two types of phase separation was observed during depressurization; the bubble point and the cloud point. In addition, at specific weight fractions a color change was also observed which was attributed to the mixture critical point. The demixing pressures were observed to increase with temperature and decrease with increasing polymer weight fraction. In addition, higher demixing pressures were obtained for the higher molecular weight polymer mixtures. The bubble point data were modeled by using Sanchez–Lacombe equation of state (SLEoS) and the binary interaction parameters were regressed at the studied temperatures. It was observed that the binary interaction parameters decreased with increasing temperature.     

Segmented polymer networks based on poly(N-isopropyl acrylamide) and poly(tetrahydrofuran) as polymer membranes with thermo-responsive permeability

Segmented polymer networks (SPNs) containing a polymer with a lower critical solution temperature were prepared by free radical copolymerization of poly(tetrahydrofuran) (PTHF) bis-macromonomers with N-isopropyl acrylamide (NIPAA). The PTHF bis-macromonomers, which were prepared by living cationic polymerization of tetrahydrofuran, were provided with acrylate or acrylamide end-groups by end-capping the living polymer chains with acrylic acid and 3-acrylaminopropanoic acid, respectively. Differential Scanning Calorimetry (DSC) experiments showed clearly that, for the same fractions of both network components, the phase morphology of the SPNs was highly influenced and adjustable by the nature of the end-groups of the bis-macromonomer as a result of their copolymerization behavior with NIPAA. For the same type of multi-component networks, the morphology changed from a heterogeneous up to a rather homogeneous nature by application of bis-macromonomers with, respectively, acrylate or acrylamide end-groups during their preparation. Swelling and DSC experiments on the swollen SPNs revealed, respectively, that the swelling properties and the cloud point temperature (T_cp) could be controlled by the network composition. The thermo-responsive water permeability and the possible application of the SPNs as pervaporation membranes for the separation of a water/isopropanol mixture were investigated as a function of temperature and network composition. The permeability and selectivity of the membranes decrease when the T_cp is reached. The permeability increases while the selectivity decreases with decreasing crosslink density or higher overall hydrophilicity of the SPNs.     

Diverse morphologies of PVDF hollow fiber membranes and their performance analysis as gas/liquid contactors

A systematic investigation on the morphology development of polyvinylidene fluoride hollow fiber membrane made using various N‐methyl‐2‐pyrrolidone (NMP) aqueous solutions as an inner coagulant was carried out. The cross‐sectional and inner surface morphology were analyzed with scanning electronic microscopy (SEM). It is found that with increase on NMP concentration, the morphology of the resultant membranes gradually shifted from a double‐skin to a single‐skin structure. When 40.0 ～ 55.0 wt.% NMP solution was used, some unexpected macrovoids near the inner region were observed. This special morphology feature was attributed to the reduced solidification rate of the inner surface as a result of increase on NMP concentration, which sharply weakened the inner skin strength. While the existence of centralized stress formed in the phase inversion process, such as shrinkage stress from syneresis, resulted in fractured points in the nascent skin surface that finally made it difficult to maintain a uniform structure. Investigations on effects of the dope flow rate and the bore fluid velocity on the morphology of PVDF fiber membranes experimentally confirmed the suggestion. Three model membranes with double skins, single skin and single skin with macrovoids structures, respectively, were used to test their permeation performance in a CO₂ membrane contactor system. The experimental results show the membranes without an inner skin present higher permeability and lower mass transfer resistance than the membrane with a double skin structure. © 2010 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2010     

Benzimidazole-based dendritic nanofiltration membranes

A dendritic-benzimidazole (D-BI) has been prepared using polyphosphoric acid (PPA) as a condensing medium with diaminobenzidine (DAB), 1,3,5-benzene tricarboxylic acid, and isophthalic acid as monomers. The structure of D-BI was ascertained by elemental analysis, FTIR, ¹H NMR, and solid-state ¹³C-NMR. The D-BI was incorporated into polysulphone (PSf) by blending with polyvinylpyrrolidone (PVP K-30) as a macromolecular additive. The membranes were cast by phase inversion technique. The physical properties such as surface morphology and the chemical properties such as contact angle and the performance attributes, such as NOM rejection, salt rejection, and pure water flux were studied. It is imperative that the infusibility of rigid polymeric backbone is overcome by the introduction of polar moieties with no compromise on thermal stability. The membranes displayed substantial increase in thermal stability with D-BI content. The marginal increase in flux has been attributed to the branching and steric effect of D-BI. This is because the introduction of polar group efficiently affords to stabilize the adjacent aromatic rings. The salt rejection shows the order of MgSO₄ ≈ Na₂SO₄ > MgCl₂ > NaCl, which follows that the divalent ions are rejected more than monovalent ions. The antifouling behaviour was also significant as the irreversible fouling (R_Ir 9%), which was found to be minimal for D-BI-incorporated membrane. The blended membranes exhibited good hydrophilicity, antifouling, and fairly good rejection of salts.