Effects Of Membrane Morphology Research Articles

Effect of membrane morphology on the thermo-physiological comfort of outdoor clothing

This article examines the effect of membrane type and its morphology on the chosen thermo-physiological properties of the middle layer of outdoor clothing. In total four different membranes were selected for the production and analysis of three-layer laminates, which could replace the second and third layers of layered clothing for sports/outdoor purposes. As an outer and lining material a polyester knitted fabric with fleece was chosen, whereas the lamination technology was used to join the individual layers. Chosen properties affecting the thermo-physiological comfort of the laminates were evaluated, to be able to select a membrane that, in combination with the outer and inner layer, enabled the use of laminate as an upper clothing layer – a jacket, thereby replacing the necessity of using a second clothing layer. The following properties were chosen as crucial: thermal resistance, air permeability, vapor permeability (water vapor penetration), and hydrostatic pressure resistance. The utility value methodology was used to evaluate individual fleece-based laminates. For the completeness of this study, two types of commercially available three-layer laminates containing soft-shell fabric as the top layer were incorporated for comparison.

Effect of membrane pore structure on fouling behavior of glycoconjugate vaccines

Sterile filtration can be difficult when processing large glycoconjugate vaccines. The objective of this work was to evaluate the performance of three commercial 0.2 μm nominal pore size sterilizing grade membranes with very different morphology: Millipore Durapore® (homogeneous), Millipore Express® (asymmetric), and Sartopore® Platinum (dual layer) during sterile filtration of a glycoconjugate vaccine provided by Pfizer. The location of deposited glycoconjugate within the filters was examined by confocal microscopy. The greatest capacity was obtained with the asymmetric membrane due to its high permeability, while the lowest capacity was found with the two-layer membrane in which the fouling occurred at the entrance to the 0.2 μm layer. The pressure profiles during constant flux filtration were analyzed using a modified intermediate pore blockage model accounting for the fouled and unfouled regions within the filter, providing additional insights into the effects of membrane morphology on the fouling characteristics.

Effects of membrane morphology on the rejection of oil droplets: Theoretical analysis based on network modeling

Membrane-based treatment is emerging as an effective way to remove the oil and reclaim fresh water from an oil-in-water emulsion. The mechanisms underlying the complex interactions between the oil droplets and the porous membrane substructures, however, are not fully understood, which may hinder our effort to design novel membranes. The objective of this study is to establish a correlation between the rejection of oil droplets and the membrane morphology via a theoretical approach based on network modeling. The porous membrane was numerically discretized into a system of cubic unit cells, whose coordinate directions were exploited to derive a bond-node structure. Numerical algorithms based on the finite element analysis and a ‘maze’ solver were developed to explore the network topology in a complementary way. It was established by the network modeling that the trans-droplet pressure (TDP) should be markedly less than the trans-membrane pressure (TMP) when the porous structure is highly connected; the surface coverage could have a significant impact on the distribution of the TDPs. Instead of assuming that the membrane be composed of straight-through cylindrical pores, a critical pressure model was integrated with the network modeling to predict the initial rejection of oil droplets as the membrane morphology was topologically varied. The modeling results were then exploited to reconcile the critical pressure model with the experimental data in the literature. To conclude, the network model would offer a powerful tool that could help understand mechanisms for the rejection of oil droplets and thus enhance the performance of membrane-based oily wastewater treatment.

Flow and fouling in membrane filters: effects of membrane morphology

Membrane filters are used extensively in microfiltration applications. The type of membrane used can vary widely depending on the particular application, but broadly speaking the requirements are to achieve fine control of separation, with low power consumption. The solution to this challenge might seem obvious: select the membrane with the largest pore size and void fraction consistent with the separation requirements. However, membrane fouling (an inevitable consequence of successful filtration) is a complicated process, which depends on many parameters other than membrane-pore size and void fraction; and which itself greatly affects the filtration process and membrane functionality. In this work we formulate mathematical models that can (i) account for the membrane internal morphology (internal structure, pore size and shape, etc.); (ii) describe fouling of membranes with specific morphology; and (iii) make some predictions as to what type of membrane morphology might offer optimum filtration performance.

Effect of membrane morphology on rising properties of filtration resistance in microfiltration of dilute colloids

The effect of membrane morphology on the flux decline behaviors in dead‐end unstirred microfiltration of very dilute colloids of polystyrene latex was examined using mixed cellulose ester and cellulose acetate membranes with interconnected tortuous pores and track‐etched polycarbonate membranes with uniform straight cylindrical pores. The plots of reciprocal filtration rate against the filtrate volume per unit membrane area for the former two membranes exhibit concave downward curves in the initial period when the membrane pore blocking is significant, whereas the plot for the latter shows a concave upward curve in that period. The former results were described by a serial resistance model consisting of the initial membrane pore blocking followed by filter cake growth, and the latter was represented by a parallel resistance model in which the pore blocking and cake growth develop simultaneously from the beginning of filtration. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3511–3522, 2017

Effects of membrane morphology and operating conditions on microfiltration particle fouling

The effects of membrane morphology and operating conditions on the particle fouling in dead-end microfiltration are studied to verify the criteria for membrane selection. Three kinds of membranes, Isopore, Durapore and MF-Millipore membranes, with similar mean pore sizes around 0.45 μm are used for filtering 0.15 μm PMMA particles. The blocking index and resistance coefficient used for membrane blocking models are analyzed during microfiltration. The membrane pore blocking is dominant and the blocking index decreases gradually in the early filtration period. The blocking index drops suddenly to zero when a critical condition reaches; and the filtration follows up the cake filtration model thereafter. A membrane blocking chart is established for relating the blocking index and operating conditions for the used membranes. Comparing the results under a fixed filtration pressures, the blocking occurred in Isopore membrane is the most serious. The use of MF-Millipore membrane causes a filter cake to more easily form on the membrane surface. While the use of Durapore membrane results in the highest filtration flux due to its antifouling behavior. To analyze the critical filtration flux and particle accumulation at the changing point of blocking models, the sequence of difficulty in transforming to cake filtration is Isopore > Durapore > MF-Millipore membrane. The force analysis on depositing particles shows that a power relationship exists between the overall filtration resistance and filtration pressure at the critical condition. The critical overall filtration resistance has a sequence of Isopore > Durapore > MF-Millipore membrane under a fixed filtration pressure.

Enhanced forward osmosis from chemically modified polybenzimidazole (PBI) nanofiltration hollow fiber membranes with a thin wall

To develop high-flux and high-rejection forward osmosis (FO) membranes for water reuses and seawater desalination, we have fabricated polybenzimidazole (PBI) nanofiltration (NF) hollow fiber membranes with a thin wall and a desired pore size via non-solvent induced phase inversion and chemically cross-linking modification. The cross-linking by p-xylylene dichloride can finely tune the mean pore size and enhance the salt selectivity. High water permeation flux and improved salt selectivity for water reuses were achieved by using the 2-h modified PBI NF membrane which has a narrow pore size distribution. Cross-linking at a longer time produces even a lower salt permeation flux potentially suitable for desalination but at the expense of permeation flux due to tightened pore sizes. It is found that draw solution concentration and membrane orientations are main factors determining the water permeation flux. In addition, effects of membrane morphology and operation conditions on water and salt transport through membrane have been investigated.

Polybenzimidazole (PBI) nanofiltration hollow fiber membranes applied in forward osmosis process

For the first time, the potential of polybenzimidazole (PBI) nanofiltration membrane as a forward osmosis membrane has been investigated. PBI was chosen mainly because of its unique nanofiltration characteristics, robust mechanical strength and excellent chemical stability. The MgCl 2 solutions with different concentrations and other different salt solutions were employed as draw solutions to test the water permeation flux through the PBI membrane during forward osmosis. High water permeation flux and excellent salt selectivity were achieved by using the PBI nanofiltration membrane which has a narrow pore size distribution. Effects of membrane morphology, operation conditions and flowing patterns of two feed streams within the membrane module on water transport performance have been investigated. It may conclude that PBI nanofiltration membrane is a promising candidate as a forward osmosis (FO) membrane.

Effect of membrane morphology in pervaporative separation of isopropyl alcohol–aromatic mixtures— a thermodynamic approach to membrane selection

AbstractIsopropyl alcohol (IPA)–benzene and IPA–toluene, which forms azeotropic mixtures, are commonly encountered in pharmaceutical industries. The present study deals with the use of pervaporation to separate these mixtures. For this purpose, several polymeric hydrophilic membranes with variation in solubility parameters such as regenerated cellulose or cellophane, poly(vinyl alcohol) (PVA), cellulose acetate (CA), cellulose diacetate (CDA), and cellulose triacetate (CTA) were studied. Some of these membranes gave a gradual shift of azeotropic point according to the variation of solubility parameter and interaction parameter values between solute and polymer matrix. Regenerated cellulose film gave the best pervaporation performance in terms of IPA selectivity and durability. PVA showed high selectivity with reasonable flux. Poly(dimethylsiloxane), which is hydrophobic, was also studied as an aromatic selective membrane. The experiments were carried out over the entire range of 0–100% at 30°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3912–3921, 2003

Effect of morphology of polymeric membrane on the performance of cross-flow microfiltration

Effects of membrane morphology and operating conditions on the performance of cross-flow microfiltration are studied. Three kinds of membranes with the same mean pore size of 0.1 μm are selected for filtration experiments. They are MF-Millipore, Durapore and Isopore membrane. The variations of cake and membrane resistance during filtration using these membranes are measured and used for blocking analysis. Although complete pore blocking occurs, Isopore membrane results in the highest filtration rate due to less cake formation. The filtration rate of Durapore membrane is lower than that of Isopore membrane. It is because, more particles deposit on the surface of Durapore membrane to form filter cake. MF-Millipore membrane results in the lowest filtration rate due to the most cake formation and a serious pore blocking. The pore structures of each membrane are modeled in order to understand the mechanisms of pore blocking. At the initial stage of filtration, a standard blocking occurs in MF-Millipore membrane, an intermediate blocking in Durapore membrane, and a complete blocking in Isopore membrane. These blocking models are transferred to cake filtration after 10 min for all kinds of membranes. The pore blocking in each membrane is also observed and demonstrated by scanning electronic microscopy. Furthermore, filtration rate increases with either increasing cross-flow velocity or increasing filtration pressure.

Theoretical Analysis of the Effect of Membrane Morphology on Fouling during Microfiltration

Previous studies of membrane fouling have often employed one of the classical blocking laws to describe the variation of filtrate flux with time. However, these models implicitly assume that the membrane has straight-through noninterconnected pores, even though most commercial microfiltration and ultrafiltration membranes have a highly interconnected pore structure. We have developed a theoretical model for the effects of pore blockage on the fluid velocity and pressure profiles within membranes having different interconnected pore structures assuming Darcy flow in the porous membrane. Model calculations are in good agreement with filtrate flux data obtained during protein microfiltration using membranes with very different pore morphologies. The results clearly demonstrate that the membrane pore connectivity has a significant influence on the flux decline due to the possibility for fluid to flow around the pore blockage, an effect which has been ignored in previous studies.

Effect of membrane morphology and operation on protein deposition in ultrafiltration membranes

Membrane morphology is compared to protein depostion under passive adsorption and ultrafiltration conditions. Solute resistance of protein deposits for membranes of varying roughness, structure, and permeability can vary dramatically with operating conditions. Using Brunauer-Emmett-Teller adsorption isotherm (BET), study of the internal area and accessibility of several uttrafiltration membranes to protein deposition allows better understanding of the fouling mechanisms and interpretation of adsorbed protein quantities. (c) 1995 John Wiley & Sons, Inc.

Microfiltration of biomass and biofluids: Effects of membrane morphology and operating conditions

Fundamental studies carried out at the Centre for Membrane and Separation Technology (Australia) considered the effect of membrane surface properties and ionic strength using biomass microfiltration on controlled suspensions of Escherichia Coli. Anopore, Nuclepore and Millipore (hydrophilic and hydrophobic) membranes of similar pore size (0.2 μm) were characterised and subjected to flux tests with E.Coli suspension at different ionic strengths and transmembrane pressures. Membrane recovery after shear was also monitored and analysis using Scanning Electron Microscopy was performed on the cake formation. It was found that both ionic strength and membrane surface properties affected flux significantly and influenced recovery. The more porous and smooth hydrophilic Anopore membrane returned higher fluxes than the less porous Nuclepore and the rough Millipore membranes. High ionic strength solutions resulted in lower fluxes which can be explained using the colloid double-layer theory. Membrane recovery was easier for low pressure operation and low ionic strength suspensions.

Cooperativity of the phase transition in single- and multibilayer lipid vesicles

The effect of membrane morphology on the cooperativity of the ordered-fluid, lipid phase transition has been investigated by comparing the transition widths in extended, multibilayer dispersions of dimyristoyl phosphatidylcholine, and also of dipalmitoyl phosphatidylcholine, with those in the small, single-bilayer vesicles obtained by sonication. The electron spin resonance spectra of three different spin-labelled probes, 2,2,6,6- tetramethylpiperdine-N- oxyl , phosphatidylcholine and stearic acid, and also 90° light scattering and optical turbidity measurements were used as indicators of the phase transition. In all cases the transition was broader in the single-bilayer vesicles than in the multibilayer dispersions, corresponding to a decreased cooperativity on going to the small vesicles. Comparison of the light scattering properties of centrifuged and uncentrifuged, sonicated vesicles suggests that these are particularly sensitive to the presence of intermediate-size particles, and thus the spin label measurements are likely to give a more reliable measure of the degree of cooperativity of the small, single-bilayer vesicles. Application of the Zimm and Bragg theory ((1959) J. Chem. Phys. 31, 526–535) of cooperative transitions to the two-dimensional bilayer system shows that the size of the cooperative unit, 1/✓σ, is a measure of the mean number of molecules, per perimeter molecule, in a given region of ordered or fluid lipid at the centre of the transition. From this result it is found that it is the vesicle size which limits the cooperativity of the transition in the small, single-bilayer vesicles. The implications for the effect of membrane structure and morphology on the cooperativity of phase transitions in biological membranes, and for the possibility of achieving lateral communication in the plane of the membrane, are discussed.