Electrokinetic and permeation characterization of hydrolyzed polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane

PAN membrane and hydrolyzed PAN membranes with the same pore size were used to investigate the relationship between the electrokinetic property and permeation performance by streaming potential measurement and ion exchange technology. SEM and FT-IR/ATR spectra were employed to analyze the reaction and the presence of the amide groups. The thickness of the polyacrylic acid (PAA) layer on the membrane surface measured by ion-exchange titration technology increased with the reaction time, and that on membrane hydrolyzed for 50 min could reach 10.8 nm. Streaming potential measurement was used to study the influence of the carboxylic and nitrile group on the membrane surface on their separation property. Zeta potential measured in pure water had close relationship with the permeation property. This measurement also proved that there was a maximum zeta potential between zero and the concentration tested. For the ionization or dissociation of the carboxylic group on the membrane surface, treated membranes had a more flexible zeta potential range than that of the untreated membrane in the pH range of 3–9. They were all negative in pure water and 1 g·L⁻¹ KCl solution, while the membranes hydrolyzed for 30 min and 50min had IEPs at pH 5.5 and 6.1 in 1 g·L⁻¹ MgCl₂ solution. Special inflection points of all the membranes were observed in AlCl₃ solution for the positive colloid structure of Al(OH)₃.     

Fractionation of casein hydrolysates using polysulfone ultrafiltration hollow fiber membranes

The objective of this study was to characterize the fractionation profile of casein hydrolysates obtained with polysulfone hollow fiber ultrafiltration membranes. The two-step ultrafiltration process developed by Turgeon and Gauthier [J. Food Sci., 55 (1990) 106] was used: a caseinate solution was submitted to proteolysis with chymotrypsin or trypsin, and the reaction mixture (RM) was subsequently ultrafiltered using a 30 kDa (MWCO) hollow-fiber polysulfone membrane. The total hydrolysate permeating from this first step was further fractionated using a 1 kDa (MWCO) membrane, producing the mixture of polypeptides (retentate) and the amino acid fraction (permeate). The effect of enzyme specificity and of membrane retentivitiy on the total composition (total nitrogen, fat, lactose, minerals) and amino acid profile of the fractions was studied. The overall composition of the fractions was not significantly affected by the nature of the enzyme but the degree of hydrolysis and the molecular weight distribution profile analyses showed a marked effect of the enzyme specificity, with trypsin giving a larger proportion of small peptides (< 200 Da) in the mixture of polypeptides. Amino acid profile analyses provided useful information on the phenomena governing the fractionation of amino acids with a polysulfone membrane: (1) the target amino acids of the enzyme are concentrated in the permeate as a result of their presence in all peptides produced by hydrolysis, (2) polar amino acids are retained by the membrane, (3) non-polar amino acids are not selectively rejected by the membrane. Our results suggest that the charge/hydrophobicity balance of the peptides produced is the predominant factor determining the fractionation of casein hydrolysates.     

Modification of polysulfone hollow fiber ultrafiltration membranes using hyperbranched polyesters with different molecular weights

A series of hyperbranched polyesters (HBPEs) using trimethylolpropane (TMP) as a core were synthesized via an esterification reaction, and the molecular weights of these HBPEs were 1600, 2260, 3370, and 5170 g/mol, respectively. Then, these HBPEs were added into dope solutions to prepare PSf hollow fiber membranes via a wet‐spinning method. When the HBPE molecule weight increased from 1600 to 5170 g/mol, the initial viscosities of the PSf–HBPE–PEG400–DMAc dope solutions increased, and the shear‐thinning phenomenon of these dope solutions became increasingly obvious. When these dope solutions were immersed into the deionized water, the demixing rate increased with an increase in the HBPE molecule weight at first and then decreased; this results in the increase of membrane porosity and the coexistence of finger‐like and sponge‐like structures. With the addition of HBPE, the start pure water contact angle and the mean effective pore size of the membranes decreased, and the J_w increased. For the mechanical properties of the membranes, the breaking strength and the elongation of the membranes also increased. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of polyacrylonitrile ultrafiltration membranes

Various methods have been used to characterize ultrafiltration membranes, such as gas flux measurements, (field emission) scanning electron microscopy, permporometry and liquid-liquid displacement. Significant differences in the pore size distributions determined from permporometry and liquid-liquid displacement were found.     

Downstream processing of lactic acid-whey permeate fermentation broths by hollow fiber ultrafiltration

Membrane filtration is a suitable method for cell harvesting and clarification of fermentation broths. Hollow fiber ultrafilters gave essentially 100% rejection ofL. bulgaricus cells from a whey permeate fermentation broth. A combination of low pressures and high velocity generally gave the best permeate flux. Fermentation media components (in this case, from the whey permeate) contributed significantly to fouling. Considering the pressure limitations of the current generation of asymmetric hollow fiber modules and the changes in physical properties of the fermentation broths, a cell concentration of 100–150 g/L could be obtained with the flux still relatively high (above 20LMH), although the chemical compatibility of the membrane module itself under long-term exposure to high acid conditions should be considered.     

In vivo protein sampling using capillary ultrafiltration semi-permeable hollow fiber and protein identification via mass spectrometry-based proteomics

Here, we advanced a novel technique using capillary ultrafiltration (CUF) probes to collect in vivo secreted proteins in the subcutaneous tissue of mouse ear. We fabricated two kinds of CUF probe, one with and one without a semi-permeable membrane hollow fiber. Proteins collected by CUF probes were profiled and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MADLI-TOF-MS) and quadrupole time-of-flight tandem mass spectrometry (Q-TOF-MS/MS) without using two-dimensional gel electrophoresis (2-DE) separation. Five proteins including cofilin-1, futuin-A, complement C3, gelsolin, and apolipoprotein C-1 were identified from the sample collected by the CUF probe with a semi-permeable membrane hollow fiber. The presence of well documented secretory proteins supports the efficiency of CUF probes in sampling in vivo secreted proteins. We also found that hemoglobin collected by the CUF probe without a semi-permeable membrane hollow fiber completely masked protein identification by mass spectrometry. The presence of relatively large amounts of hemoglobin in this condition illustrates the necessity of the semi-permeable membrane hollow fiber to the technique of CUF probe in conjunction with mass spectrometry. Also, the technique represents a powerful method for the identification of in vivo secreted proteins and has potential application for in the detection of biomarkers for human diseases.     

Dead-end ultrafiltration in hollow fiber modules: Module design and process simulation

Ultrafiltration in a hollow-fiber module operating with outside-in and dead-end flow at a constant flow rate was simulated using a model that takes into account the longitudinal pressure drops inside the fibers and within the fiber bundle. The model considers both the filtration phase during which the membrane is fouled by the formation of a filter cake and the backwash phase in which it is cleaned, so as to predict the net rate of production of the module during an operating cycle.The results show that there is a combination of packing density and fiber diameter that gives a maximum net flow rate. Furthermore, this model allows the influence of operating conditions and feed properties on the module performance to be estimated. This can be used to determine how operating parameters must be modified when there is a change in the feed properties.     

Effect of nonsolvents on properties of spinning solutions and polyethersulfone hollow fiber ultrafiltration membranes

The relationship among the presence of nonsolvent additives, the rheological behavior of spinning solutions and properties of hollow fiber membranes was studied. The additives tested were water, polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), and the base mixture was polyethersulfone/N-methyl-2-pyrrolidone (PES–NMP). In addition the effect of combining water and PVP or PEG was also studied. Membranes were prepared using a spinneret having two concentric orifices. The internal coagulant used as well as the nonsolvent from the coagulation bath were both water at 28°C and 30°C, respectively. Rheological properties of polymer solutions were evaluated using a rheometer Haake RV 20. Changes on composition of spin-solutions were also evaluated in terms of membrane water permeability, solute rejection and membrane structure observed using scanning electron microscopy (SEM). Experimental results from this work showed that spinning solutions containing any of the three additives behave as Newtonian fluids in the range of shearing rates tested. The addition of water, PVP or PEG to the base PES–NMP solution increased its viscosity and this effect was independent of the type of additive used. A direct relation between viscosity of casting solutions and membrane thickness was found. However, rheological properties (viscosity and normal stress difference) could not be used to explain differences on membrane water flux (MWF) when using different additives at the same concentration. The addition of any of the three additives generally increased MWF. The extent of this increment seemed to be more related to changes on membrane porosity than changes on pore sizes induced by the nature and concentration of the additive used.     

Behaviors and mechanisms of copper adsorption on hydrolyzed polyacrylonitrile fibers

Polyacrylonitrile fiber (PANF) was hydrolyzed in a solution of sodium hydroxide and the hydrolyzed polyacrylonitrile fiber (HPANF) was used as an adsorbent to remove copper ions from aqueous solution. Scanning electron microscopy (SEM) showed that the hydrolysis process made the surface of HPANF rougher than that of PANF. Fourier transform infrared (FTIR) spectroscopy revealed that the HPANF contained conjugated imine (-Cz=Nz-) sequences. Batch adsorption results indicated that the HPANF was very effective in adsorbing copper, and the adsorption equilibrium could be reached within 10-20 min. Atomic force microscopy (AFM) showed that some aggregates formed on the surface of the HPANF after copper ion adsorption and the average surface roughness (R(a)) value of the HPANF changed from 0.363 to 3.763 nm due to copper adsorption. FTIR analysis indicated that copper adsorption caused a decrease of the light adsorption intensity of the imine (-Cz=Nz-) groups at 1573 and 1406 cm(-1) wavenumbers, and X-ray photoelectron spectroscopy (XPS) showed that the binding energy (BE) of some of the nitrogen atoms in the HPANF increased to a greater value due to copper adsorption. The FTIR and XPS results suggest that the adsorption of copper ions to the HPANF is attributed to the imine groups on the surface of the HPANF.     

Gas sparging to enhance permeate flux in ultrafiltration using hollow fibre membranes

This study focuses on the use of gas-liquid two-phase crossflow to overcome concentration polarisation in the ultrafiltration of macromolecular solutions as applied to hollow fibre membrane systems. The experimental work was conducted on a purpose built pilot-plant scale rig with albumin and dextran as the test media. The effect of gas injection on the permeate flux and membrane sieving coefficient was examined experimentally at different transmembrane pressures, feed concentrations and gas to liquid flow ratios.The results were encouraging, with flux enhancements of 20–50% obtained for dextrans and 10–60% for albumin, when air was injected into the system over the range of process variables examined. The sieving coefficient of albumin was considerably reduced when gas-liquid two-phase cross-flow was used. These results were compared to those obtained with tubular membrane systems, and an additional mechanism, based on physical displacement of the concentration polarisation boundary layer is proposed. The operational difficulty related to protein foaming is also discussed.     

Effect of crystallization and annealing on polyacrylonitrile membranes for ultrafiltration

Polyacrylonitrile (PAN) membrane is known as one of the hydrophilic membranes for ultrafiltration. However, the membrane has been preventing from the versatile applications, because the semi-crystalline PAN membranes are so brittle that cannot reuse once the membrane has been dried. The effect of crystalline domains in asymmetric polyacrylonitrile membranes is investigated, when the membranes are annealed in hot water and when the membranes are dried. Asymmetric polyacrylonitrile membranes were prepared via phase inversion process in a water bath and the effect of additive, PVP to the casting solution on the morphology and the water flux and the rejection were investigated. When the membranes were annealed in hot water (80 °C), the size of pores have been reduced and the water flux also decreased. Using wide angle X-ray scattering (WAXS), the effect of absorbed water on PAN membranes was studied. The absorption of water in PAN membranes mainly occurred through amorphous phase like a plasticizer, and induced the change of crystalline structure. The size of crystallite and the degree of crystallinity have changed when the membrane were annealed in the hot water. When the asymmetric PAN membranes were dried, the moisture also plays a crucial role in transforming the crystalline structures. The kinetics of drying strongly influences the size of crystallite as well as the crystallinity.     

Voltage-controlled separation of proteins by electromobility focusing in a dialysis hollow fiber

Electromobility focusing (EMF) is a relatively new protein separation technique that utilizes an electric field gradient and a hydrodynamic flow. Proteins are focused in order of electrophoretic mobility at points where their electrophoretic migration velocities balance the hydrodynamic flow velocity. Steady state bands are formed along the separation channel when equilibrium is reached. Further separation and detection can be easily achieved by changing the electric field profile. In this paper. we describe an EMF system with on-line UV absorption detection in which the electric field gradient was formed using a dialysis hollow fiber. Protein focusing and preconcentration were performed with this system. Voltage-controlled separation was demonstrated using bovine serum albumin and myoglobin as model proteins. The limitations of the current method are discussed, and possible solutions are proposed.     

Surface glycosylation of polyacrylonitrile ultrafiltration membrane to improve its anti-fouling performance

Surface glycosylation is one of the most promising strategies to fabricate biomimetic surface for membrane. Previous studies confirmed that cyclic sugars provide recognition sites for specific proteins, while ring-opening sugars offer better hydrophilicity and anti-adsorption ability to proteins. To improve the anti-fouling property of polyacrylonitrile (PAN) ultrafiltration membrane, a ring-opening glycomonomer d-gluconamidoethyl methacrylate (GAMA) was grafted onto the surface of the membrane by ultraviolet (UV)-initiated grafting polymerization. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and field emission scanning electron microscopy (FESEM) were used to characterize the chemical and morphological changes of the membrane surface. Water contact angle, protein adsorption and protein filtration were employed to evaluate the anti-fouling performance of the membrane. The protein adsorption experiment was carried out with fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA), and the adsorption quantity was measured locally by laser confocal scanning microscope (LCSM). This method supplied a simple and direct manner to evaluate the protein adsorption performance of membrane, and the interference of the support was also avoided. The results revealed that by the surface glycosylation procedure, the hydrophilicity was enhanced and the adsorption of FITC-BSA was inhibited significantly. The flux recovery ratio was also increased after modification, indicating that the anti-fouling performance of PAN membrane was improved by the glycosylation strategy.     

Asymmetric hydrolysis of a meso-diester using pig liver esterase immobilised in hollow fibre ultrafiltration membrane

Pig liver esterase (PLE) was physically immobilised in a polysulphone ultrafiltration hollow fibre membrane reactor and used for the repetitive batch two-phase hydrolysis and separation, on a multigram scale, of the meso-diester dimethyl cis-cycloxex-4-ene-1,2-dicarboxylate 1 to enantiomerically pure (1S,2R)-cyclohex-4-ene-1,2-dicarboxylic acid monomethyl ester 2. After 25 days, the enzyme still retained its initial activity, which corresponds to 62% of its activity in the free form, and the enantiomeric purity of monoester 2 was still higher than 97%. Simple experimental conditions were established for the large laboratory scale preparation of substrate 1 and isolation of product 2 from the aqueous phase.     

Analysis of constant permeate flow filtration using dead-end hollow fiber membranes

Dead-end filtration of colloids using hollow fibers has been analysed theoretically and experimentally. A mathematical model for constant flux filtration using dead-end hollow fiber membranes has been developed by combining the Hagen–Poiseuille equation, the (standard) filtration equation, and cake filtration theory of Petsev et al. [D.N. Petsev, V.M. Starov, I.B. Ivanov, Concentrated dispersions of charged colloidal particles: sedimentation, ultrafiltration and diffusion, Colloid Surf. A: Physicochem. Eng. Aspects, 81 (1993) 65–81.] to describe the time dependence of the filtration behavior of hollow fiber membranes experiencing particle deposition on their surface. Instead of using traditional constitutive equations, the resistance of the cake layer formed by the deposited colloids has been directly correlated to the cake structure. This structure is determined by application of a force balance on a particle in the cake layer combined with the assumption that an electrostatically stable cake layer of mono-sized particles would be ordered in a regular packing geometry of minimum energy. The developed model has been used to identify the relationship between the filtration behavior of the hollow fiber membrane and the particle properties, fiber size, and imposed average flux. Filtration experiments using polystyrene latex particles of relatively narrow size distribution with a single dead-end hollow fiber membrane demonstrate good consistency between experimental results and model prediction. The developed model has been used to simulate the distribution of the cake resistance, transmembrane pressure, and flux along the hollow fiber membrane and used to assess the effect of fiber size, particle size, zeta potential, and the average imposed flux on the suction pressure-time profiles, flux, and cake resistance distributions. These results provide new insights into the filtration behavior of the hollow fiber membrane under constant flux conditions.     

Thermal‐crosslinked polyacrylonitrile fiber compacts

Polyacrylonitrile (PAN) textile fibers, in the form of fabrics or threads, were compacted in a heat‐pressure cycle and crosslinked by nitrile polymerization to form a thermoset composite article, whose mechanical properties were found to surpass those of commercially available polypropylene (PP) fiber counterparts. Additional advantages of the PAN compacts included their significant thermal stability (>300°C, i.e., twice that of PP) in addition to their flame retardancy, thereby rendering them as the structural material of choice for applications where heat protection and fire resistance are essential. Copyright © 2009 John Wiley & Sons, Ltd.     

Cutoff performance of Escherichia coli by charged and noncharged polyacrylonitrile ultrafiltration membranes

Cutoff performance of Escherichia coli (E. coli) was studied by three types of polyacrylonitrile (PAN) ultrafiltration (UF) membranes without and with charge groups of sulfonate sodium salt (SSS) and trimethylammonium chloride (TMA). These UF membranes were prepared by phase inversion method in water coagulation bath with various concentrations of dimethylsulfoxide (DMSO) and used for the E. coli cutoff experiments under 2.5 kPa applied pressure. With the increase of the polymer concentration in the DMSO cast solution, the pore size of the molecular size exclusion effect of the resultant UF membrane decreased. For UF experiments of E. coli suspension solution with 10⁷ colony forming unit/unit volume (cfu/ml), the permeability of the bacteria through the membrane was in the range of about 10⁻³% in PAN homopolymer membranes. It was found that E. coli permeation through copolymer UF membranes with SSS and TMA groups was completely restricted. Difference of the E. coli cutoff performance in these UF membranes was discussed in comparison with membrane filtration properties such as molecular sieve effect, permeation rate of solute and membrane morphology.