A hydrodynamic study of the retention of polyethylene glycols by cellulose acetate membranes in the absence and presence of proteins

The ultrafiltration behaviour of polyethylene glycols has been investigated with respect to their partial retention by YM5 and YM10 membranes. Retention coefficients were found to follow a log-normal distribution except at low molecular weights, which exhibited higher than expected values. Increasing the applied pressure resulted in increased retention of PEG, although linear flux-pressure relationships were observed in all cases. Increasing hydrodynamic activity by applying higher stirrer speeds led to reduced permeate concentrations. The mean molecular weights of the permeates were higher under hydrodynamic conditions resulting in lower retention coefficients, which suggests increased permeabilities for the larger PEG component molecules.

The retention behaviour of solutions of PEG with varying concentration of bovine serum albumin (BSA) as the flux rate was altered paralleled the results for pure PEG solutions. However, when the flux rate was kept constant and the concentration varied, there was an initial increase of retention at a BSA concentration of 0.2% w/v and thereafter a reduction up to a tested bulk concentration of 10%. Various proposals were made to explain this behaviour.     

Preparation, characterization and effect of annealing on performance of cellulose acetate/sulfonated polysulfone and cellulose acetate/epoxy resin blend ultrafiltration membranes

Polymeric membranes based on cellulose acetate (CA)--sulfonated polysulfone blends at three different polymer compositions were prepared by solution blending and phase inversion technique, characterized and subjected to annealing at 70, 80 and 90 °C. The permeate water flux, separation of bovine serum albumin and its flux by the blend membranes before and after thermal treatment, have been compared and discussed. Similarly, CA and epoxy resin (diglycidyl ether of bisphenol-A) were blended in various compositions, in the presence and in the absence of polyethyleneglycol 600 as non-solvent additive, using N,N^′-dimethylformamide as solvent, and used for preparing ultraflltration membranes by phase inversion technique. The polymer blend composition, additive concentration, casting and gelation conditions were optimized. Blend membranes were characterized in terms of compaction, pure water flux, water content and membrane resistance. The effects of polymer blend composition and additive concentration on the above parameters were determined and the results are discussed.     

Orientation processes in cellulose acetate under the action of dimethyl sulfoxide vapor

Spontaneous variation of the linear size (elongation-contraction) of acetate fibers in a vapor of dimethyl sulfoxide, which is a mesophasogenic solvent, i.e., a solvent forming a liquid crystal phase with the polymer, is described. A mechanism of the interaction of the polymer with the solvent vapor is suggested.     

On the electrochemical characterization of ion-selective cellulose acetate membranes with and without stigmasterol liquid membranes

Stigmasterol, a plant product, has been used as a surfactant to generate liquid membranes supported on a cellulose acetate matrix. Electrochemical characterization of the membrane has been attempted with a view to simulating its behavior with natural membranes by measuring membrane potentials and membrane conductance. The selectivity of cellulose acetate membrane kept in contact with magnesium chloride solutions of different mean concentrations has been found to change from anion to cation. Transport numbers have been estimated from membrane potential data. Permselectivity and fixed charge density values for the cellulose acetate membrane with and without stigmasterol have been determined from transport numbers. The variation of these parameters with concentration and pH has also been examined.     

Development of an enantioselective membrane from cellulose acetate propionate/cellulose acetate,for the separation of trans-stilbene oxide

This paper reports the characterization of new synthesized chiral polymeric membranes, based on a cellulose acetate propionate polymer. The flux and permselective properties of the membrane were studied using 50 % ethanol solution of (R,S)-trans-stilbene oxide as feed solution. Scanning electron microscopy revealed the asymmetric structure of these membranes. The roughness of the surface was measured by atomic force microscopy. The resolution of over 97 % enantiomeric excess was achieved when the enantioselective membrane was prepared with 18 wt% cellulose acetate and 8 wt% cellulose acetate propionate in the casting solution of dimethyl formamide/N-methyl-2-pyrrolidone/acetone, at 20 °C and 55 % humidity, and a water bath at 10 °C for the gelation of the membrane. The operating pressure and the feed concentration of the trans-stilbene oxide were 275.57, 345.19, and 413.84 kPa and 2.6 mM, respectively.     

NMR of dissolved water in ultrathin and thick membranes of cellulose acetate

Wide-line proton magnetic resonance spectra of thick (100 μ) and ultrathin (0.25 μ) membranes of cellulose acetate have been obtained in the “bone-dry” state and in the wet state up to 2.5% water by weight. The NMR spectra were recorded with the membrane face aligned parallel and perpendicular to the magnetic field direction. The first derivative spectra of wet thick membrane (above 0.4% water) show a sharp center peak and at least one broad outer peak, both in the parallel and perpendicular orientations. The spectra of wet ultrathin membrane, on the other hand, show a pseudodoublet in the perpendicular orientation and a broad singlet in the parallel orientation. The differences in the spectra of the thick and ultrathin membranes are discussed in terms of “free” and restricted water believed to arise from the differences in the structure of thick and ultrathin membranes.     

Studies on the structural,kinetic and thermodynamic parameters of cellulose acetate membranes

Hydraulic permeability (L_p), osmotic permeability (Lπ) and tritium permeability (ω_THO) have been measured for cellulose acetate membranes of varying water contents (Ø_w). The porosity factor (g_p) has been calculated using the above parameters. Thermodynamic properties such as ΔG≠, ΔH≠, and ΔDwS≠ are estimated for the activated complex of the solute in the membrane phase using conductance measurements.     

Effect of whole blood and plasma on the permeability of glucose through different cellulose and cellulose acetate membranes

Model experiments were made with a flow-through dialysis cell to study how glucose in whole blood, plasma and aqueous standards is transferred through different membranes. Detection was via a glucose dehydrogenase reaction and NADH monitoring with a chemically modified electrode. The detector response was linear with the glucose concentration in all cases. The non-Newtonian properties of whole blood seem to be of great importance for the response. Theoretical models are proposed both for the effect of plasma viscosity and the red cell volume fraction (haematocrit) dependence on the glucose transfer rate. The models could only partially explain the differences between measurements in aqueous solutions and body fluids. Better agreement and less haematocrit dependence were obtained with low-permeability membranes.     

Synthesis and characterization of cellulose acetate from cellophane industry residues. Application as acetaminophen controlled-release membranes

Journal of Thermal Analysis and Calorimetry - Cellophane film production generates cellulosic residues from scraps, edges, and low-quality films. In this work, cellophane was used as a raw material...     

Structure and properties of the regenerated cellulose membranes prepared from cellulose carbamate in NaOH/ZnO aqueous solution

Regenerated cellulose (RC) membranes were prepared from cellulose carbamate—NaOH/ZnO aqueous solutions by coagulating with H₂SO₄ solution. Structure, morphology and properties of the membranes were investigated by using scanning electron micrograph (SEM), X-ray diffraction, Fourier transform infrared spectroscopy, flow rate method, and tensile testing. The results from SEM and water permeability revealed that the pore size and water permeability of the membranes in wet state changed drastically as a function of the concentration of H₂SO₄ and coagulation temperature, whereas they hardly changed with the coagulation time. RC membranes coagulated with the relatively dilute H₂SO₄ solution at relatively low temperature exhibited better mechanical properties. This work provided a promising way to prepare cellulose membranes with different pore sizes and good physical properties.     

Crystal growth of calcium carbonate on the cellulose acetate/pyrrolidon blend films in the presence of L-aspartic acid

The morphogenesis and growth process of calcium carbonate on the cellulose acetate/polyvinyl pyrrolidone (CA/PVP) blend films in the presence of L-aspartic acid was carefully investigated. The results showed that the concentration of L-aspartic acid, the initial pH value of reaction solution and temperature turned out to be important factors for the control of morphologies and polymorphs of calcium carbonate. Complex morphologies of CaCO₃ particles, such as cubes, rose-like spheres, twinborn-spheres, cone-like, bouquet-like, etc. could be obtained under the different experimental conditions. The dynamic process of formation of rose-like sphere crystals was analyzed by monitoring the continuous morphological and structural evolution and components of crystals in different crystal stages. This research may provide a promising method to prepare other inorganic materials with complex morphologies.     

The role of formamide in the preparation of cellulose acetate membranes by the phase inversion process

Summary By varying the concentration of formamide within the acetone solutions from which cellulose acetate membranes were fabricated, a series of membranes exhibiting a wide range of performance characteristics was prepared. The morphological, optical, swelling and water transport properties of these membrane gels have been interpreted with reference to a phase inversion in their sol precursors.

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Zusammenfassung Aus Acetonl?sung mit unterschiedlichem Gehalt an Formamid wurden Zellulosemembranen dargestellt. Die Eigenschaften der Membranen sind je nach den Konzentrationen des Formamids verschieden. Die Unterschiede werden durch Phasen?nderungen w?hrend des übergangs Sol-Gel erkl?rt.

     

Modified gas-permeable silicone rubber membranes for covalent immobilisation of enzymes and their use in biosensor development

Novel enzyme membranes are introduced. Modified polymeric gas-permeable layers were developed enabling biological components which have available reactive groups (-NH2, -OH, -SH, -COOH) to couple covalently on to their surfaces. Therefore, gas-permeable two component room temperature vulcanizing (2K-RTV) silicone rubber was modified using additional cross-linking agents. Triethoxysilanes with functional groups on their side chains such as epoxy or amino groups were used. A special attribute of the resulting gas-permeable membranes is that their formation and modification occur simultaneously during one reaction step. IR spectroscopy was used to observe the changes in the polymeric structure due to the reaction with the additional cross-linking agents. Sensors equipped with these layers are suitable to measure dissolved gases such as O2, CO2 and NH3 consumed or produced by enzymes converting their substrates. Determination of glucose, a well investigated enzymatic detection process, was chosen to demonstrate the applicability of the enzyme immobilisation. Glucose oxidase was immobilised on the membranes and glucose was detected by amperometric measurement of oxygen consumption. It is expected that this immobilisation method will also be useful for miniaturised planar biosensors.     

Kinetics of the desorption of surfactants and proteins from adsorption layers at the solution/air interface

It is shown by experiments that the DeSNa desorption kinetics is governed by a pure diffusion mechanism, while the desorption of more surface active surfactants such as C13DMPO and Triton X-100 obeys a mixed mechanism. The BLG desorption kinetics, as shown by experiments, is determined by a barrier mechanism. From the analysis of the temperature dependence of the BLG desorption kinetics it is possible to calculate the activation energy of this process, which is quite close to the free energy of BLG adsorption. The theoretical model of desorption kinetics predicts that these two energetic parameters are approximately equal to each other if the adsorption activation energy is low. This can explain the fact that the higher the adsorption activity of a substance is, the lower is its desorption rate.     

Impact of membrane immobilization on particle formation and trichloroethylene dechlorination for bimetallic Fe/Ni nanoparticles in cellulose acetate membranes

The use of membrane immobilization to carry out the batch dechlorination of trichloroethylene (TCE) using bimetallic Fe/Ni (4:1, Fe to Ni) nanoparticles in cellulose acetate membranes is examined using modeling of transport phenomenon based on experimental results. Membranes are synthesized using both gelation and solvent evaporation techniques for phase inversion. The reduction of metal ions within cellulose acetate phase-inversion membranes was accomplished using sodium borohydride reduction to obtain up to 2 wt % total metals. Characterization of the mixed-matrix structure reveals a bimodal particle distribution ranging between 18 and 80 nm within the membrane cross section. The distribution is the result of changes in the morphology of the cellulose acetate support. The diffusivity and linear partitioning coefficient for the chlorinated organic were measured and are 2.0 x 10(-8) cm2.s-1 and 3.5 x 10(-2) L.g-1, respectively. An unsteady-state model for diffusion through a membrane with reaction was developed to predict experimental results with an error of only 7.2%. The error can be attributed to the lack of the model to account for loss of reactivity through pH effects, alloy effects (bimetallic ratio), and oxidation of nanoparticles. Simulations were run to vary the major transport variables, partitioning and diffusivity, and determine their impact on reaction kinetics. Of the two, diffusivity was less significant because it really only influences the time required for maximum TCE partitioning to the membrane to be achieved and has no effect on the limiting capacity of the membrane for TCE. Therefore, selection of an appropriate support material is crucial for development of highly reactive mixed-matrix membrane systems.     

Sago/PVA blend membranes for the recovery of ethyl acetate from water

Sago starch is a relatively new polymeric material for development of a hydrophilic membrane for dehydration of alcohol/water. In this study sago based membranes were developed through casting technique for the dehydration of ethyl acetate at azeotropic conditions via pervaporation. Sago was blended with polyvinyl alcohol (PVA) to produce blended sago–PVA membranes with improved physical and chemical properties. The membranes were cross-linked using three different approaches; firstly, using glutaraldehyde, secondly using thermal treatment (80 °C) and thirdly by using both glutaraldehyde and thermal treatment. The effects of various cross-linking methods on the intrinsic properties of hydrophilic polymer membrane were investigated. The membranes were characterized using Fourier transform infrared (FTIR), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The effect of operating conditions such as feed temperature and concentration on the separation factor and flux was discussed. Sago starch polymer shows very high performance and very good stability after polymer blending and cross-linking, which is promising for use in industrial applications.     

A detailed study of sorption equilibria and kinetics of a model disperse dye in cellulose acetate

A detailed investigation of the sorption of 4-aminoazobenzene by cellulose acetate films from aqueous solution is reported. Sorption isotherms at 75 and 60°C were linear up to saturation, in agreement with previous findings that have led to the conclusion that cellulose acetate-disperse dye systems are thermodynamically ideal. Thermodynamic analysis of these data also gave results consistent with such previous findings. The isotherms for 45 and 25°C, on the other hand, exhibited increasing curvature, in line with similar recent findings for a variety of hydrophobic polymer-disperse dye systems, and consistent with the presence of some strong absorption sites. However, the situation appears to be more complex than envisaged by simple dual-mode sorption theory. Early time desorption kinetic data were found to be consistent with Fick's law, with no indication of any significant dependence of the diffusion coefficient D on concentration (in the medium- to high-concentration range) or on film thickness. On the other hand, D was affected significantly by the history of film formation, the method of introducing the dye or heat treatment of the film. The origin of these effects was traced by DSC to definite microstructural differences. Late time kinetic data deviated significantly from the theoretical predictions based on the corresponding early time data, indicating a progressive slowdown of the desorption process. The deviations in question were generally more marked at higher temperature or film thickness, or when dyeing had been effected from the vapor phase, and were attributed to slow release of strongly adsorbed dye molecules. © 1994 John Wiley & Sons, Inc.     

Water in polymer membranes. Part I : Water sorption and refractive index of cellulose acetate

The dependence of water absorption of 2 to 4 μm thick membranes of cellulose acetate on relative humidity was determined by measuring small changes in their asymmetric waveguide properties in the visible spectral region. Simultaneous measurements of changes in film thickness provide a direct method for obtaining the change in film volume as a function of water concentration and a new measure of polymer porosity. Data are presented for a typical film fabricated from cellulose acetate (CA398-30) which illustrate the usefulness of studying water absorption by integrated optics techniques.     

Determination of BHT in the presence of surfactants using a cellulose acetate coated electrode and square wave voltammetry

A direct voltammetric method for the rapid determination of butylated hydroxytoluene has been developed. The procedure utilizes a hydrolyzed cellulose acetate film in intimate contact with a glassy carbon electrode and square wave voltammetry. The coated electrode prevents passivation due to adsorption of polymeric oxidation products by way of a size exclusion principle. BHT solutions containing lipid-like surfactants can be analyzed without the need for frequent resurfacing of the electrode.     

Combined sorption/transport of sodium dodecyl sulfate and hydrochloric acid in a blend of cellulose acetate butyrate with cellulose acetate hydrogen phthalate

The transport of hydrochloric acid (0.001-0.1 M) and sodium dodecyl sulfate (0.001-0.1 M) has been measured through a membrane consisting of a blend of cellulose acetate butyrate and cellulose acetate hydrogen phthalate. The cellulose derivative blend is suggested to suffer an alteration in the degree of hydrophobicity when in equilibrium with sodium dodecyl sulfate (SDS) through hemimicelle formation. An increase in surface hydrophobicity of the blend when in equilibrium with SDS solution was observed by fluorescence measurements using the vibronic bands of the probe pyrene, as well as by water desorption kinetics; a decrease of the effective diffusion coefficients from 1.2 × 10⁻¹¹ m² s⁻¹ in the absence of SDS to approximately 2 × 10⁻¹³ m² s⁻¹ in its presence was found. The value obtained for the mutual diffusion coefficient of HCl in the concentration range 0.001-0.1 M (D=4.2×10⁻¹⁴ m² s⁻¹) shows also that the membrane presents hydrophobic features. The flux of SDS in the blend membrane at different pH values shows two distinct permeation rates depending on the cmc. However, from the calculation of permeability coefficients at SDS concentrations below the cmc a clear decrease in P is found, whilst, at concentrations above the cmc the permeability coefficients are nearly constant, only showing a slightly increase. The diffusion coefficients of SDS in the blend increase over the whole SDS concentration range analysed and show an effective diffusion coefficient 2-3 orders of magnitude below the diffusion coefficients of SDS in aqueous solutions. This fact suggests that the only diffusing species are SDS unimers. The presence of HCl in the SDS bulk solution has the effect of increasing the permeability and diffusion coefficients. Mutual analysis of permeation and diffusion coefficients and sorption isotherms shows that, on decreasing the pH, the interactions between SDS and the polymer network decrease. This is also reflected in a clear decrease of the hydrophobic interactions between the diffusing and polymeric species, provoked by a decrease in the unimer-unimer association.