Morphology and permeability of cellulose/chitin blend membranes

A series of biodegradable cellulose/chitin blend membranes were successfully prepared from blend solution of cellulose and chitin in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution coagulating with 5.0 wt% (NH₄)₂SO₄. The influence of chitin content on the morphology and structure of the membranes was studied by scanning electron microscopy, environmental scanning electron microscopy and wide-angle X-ray diffractometry, as well as Fourier transform infrared spectroscopy. Using double-cell method and solution depletion method, the permeability and partition coefficients of three model drugs (ceftazidine, cefazolin sodium, and thiourea) were determined in phosphate buffer solution to clarify the diffusion mechanism governing transport of solutes in these membranes. Diffusion coefficients were calculated from the permeability and partition coefficients in terms of Fick's law. The effects of the chitin content, pH, ionic strength, molecular size and temperature on the drug diffusion were also studied. Our results revealed that all of the membranes had a porous-like structure. The introduction of chitin exhibited great influence on the morphology and crystal structure of the blend membranes, resulting in a significant different permeability. For the first time, a dual diffusion mechanism with some hindrance of molecular diffusion via polymer obstruction was employed to explain the transport of drugs in the membranes.     

Thermodynamic model of gas permeability in polymer membranes

A new molecular thermodynamic model is developed of the gas permeability in polymer membranes on the basis of configurational entropy and Flory‐Huggins theory to predict permeability dependence on the concentration of penetrant. Three kinds of configurational entropy are taken into account by this model; that is, the disorientation entropy of polymer, the mixing entropy, and specific interaction entropy of polymer/gas. The validity of the mathematical model is examined against experimental gas permeability for polymer membranes. Agreement between experimental and predicted permeability is satisfactory. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 661–665, 2007     

Comparison of the accuracy of curve-fitting methods for the determination of gas permeability parameters of sheet polymer samples

Accuracy of the gas permeability parameters (GPPs), i.e. solubility, diffusivity and permeability deduced from permeation measurements, is investigated for the case of homogeneous polymer sheet samples. The widely used time-lag method (TLM) and the recently introduced full curve-fitting method (FCFM) are compared on simulated and on measured permeation curves artificially distorted in various ways in order to mimic potential deficiencies of permeation measurements. Accuracy of the methods is defined as the relative deviation of the calculated from the real GPPs, i.e. those which are deduced from the distorted and the original, non-distorted curves, respectively. The following distortions have been applied: temporal truncation of the permeation curves, increasing the noise level of the measurement and shifting the permeation curve either along the concentration or the time axis. (The latter two transformations correspond to an unnoticed background shift in the readings of the concentration detection unit and an uncertainty in the actual inception of the permeation process, respectively). While all these distortions mimic realistic deficiencies of permeation measurements, the last one is relevant only in case of fast permeation processes through highly permeable membranes. For all but the last transformation, FCFM has been found to yield more accurate GPPs than TLM.     

Evaluation of the permeability of modified cellulose acetate propionate membranes for use in biosensors based on hydrogen peroxide detection

Phase inversion cellulose acetate propionate membranes showed lowpermeability to hydrogen peroxide aqueous solutions. Their permeability wasincreased by alkaline hydrolysis of the ester linking units. However, thepermeability remained lower than that of an unsubstituted cellulose membrane.The inclusion of hydroxypropyl cellulose in the membrane formulation, followedby an alkaline hydrolysis step, increased permeability to hydrogen peroxideaqueous solutions to 29% of that of an unsubstituted cellulose membrane.     

The effect of polymer swelling and resistance to flow on solvent diffusion and permeability

The main purpose of this paper is to test the model of molecular sorption [Vesely D. Polymer 2001;42:4417-22] for Case II type diffusion by measuring the effect of sorption/swelling and resistance to flow through the swollen region on the mass transport of solvents in glassy amorphous polymer. The system of methanol and polymethylmethacrylate (PMMA) has been selected for easy comparison with the existing literature data.The weight loss of penetrant permeating through the polymer has been monitored using a permeability cell placed on a balance (gravimetry). The rate of diffusion and swelling has been measured using light microscopy on samples cut after different elapsed time exposure to the solvent.The contribution of polymer swelling and resistance to flow has been evaluated by comparing the mass transport during diffusion and permeation processes. It is shown that for thin films the thickness independent component of the mass transport process (swelling) makes a significant contribution to the diffusion rate. For thicker samples the thickness dependent component (the resistance to flow through the swollen polymer) dominates both, diffusion and permeation.     

Comparison of permeability coefficients of organic vapors through non-porous polymer membranes by two different experimental techniques

The permeability coefficients of saturated and non-saturated vapors of benzene, hexane and cyclohexane through flat polymer membranes (low density polyethylene BRALEN FB2-30 and polyether-block-amide PEBA 4033-PE) by two different experimental techniques at 298.15 K are reported. The permeation data have been obtained using the differential flow permeameter and sorption ones by glass sorption apparatus with McBain’s spiral balance. The so-called stationary (steady) diffusion theory has been applied for evaluating the permeability coefficients from sorption (equilibrium) data and obtained values have been compared with the permeability coefficients from permeation (steady-state) measurements. In the case of relative lower vapors sorption in polymers (hexane and cyclohexane) good agreement between permeability coefficients from sorption and permeation is obtained. Hence, this paper proves the possibility to estimate the permeability coefficients of organic vapors from sorption data without need of performing the permeation experiments.     

Turbulent flow technique for the estimation of oxygen diffusive permeability of membranes for the oxygenation of blood and other cell suspensions

When transport-efficient membrane modules (such as those where the liquid flows outside hollow fibre membranes) or membranes with prolonged resistance to wetting are used for the oxygenation of blood or other cell suspensions, membrane contribution to the overall oxygen transfer resistance into the liquid may become significant. Thus, estimation of membrane diffusive permeability towards relevant gases (e.g., oxygen) is important to develop new membranes and to ensure reproducible commercial membrane performance.

In this paper, we report on a turbulent flow technique for the estimation of the oxygen diffusive permeability of membranes used in outside-flow oxygenators. Water is re-circulated under turbulent flow conditions in a closed-loop from a reservoir to the shell of lab-scale membrane modules. The overall oxygen transfer to water coefficient is estimated at increasing water flow rates from the time the change of dissolved oxygen tension in the stream leaving the water reservoir occurs. Oxygen diffusive permeability is estimated as the reciprocal overall transfer resistance at infinitely high water flow rates, for negligible gas-side oxygen transport resistance. The technique was used to estimate oxygen diffusive permeability of commercial Oxyphan^® polypropylene membranes for blood oxygenation and of two laboratory polypropylene membranes, the one featuring a microporous wall structure with smaller-than-standard pore size, the other featuring an outer thin, dense layer supported by a thick spongy layer. The turbulent flow technique yields oxygen diffusive permeability estimates consistent both with membrane hydraulic permeability towards gaseous nitrogen, membrane wall structure, and with values in literature obtained using a liquid reactive with oxygen, but without the complications associated with reaction and physical transport kinetic characterisation. We conclude that the turbulent flow technique is a useful tool in the development and quality control of membranes for the oxygenation of blood and other cell suspensions.     

Tunable fiber laser and fiber amplifier based photoacoustic spectrometer for trace gas detection

A new wavelength modulated photoacoustic spectrometer based on a near-infrared tunable erbium doped fiber laser (TEDFL) and an erbium doped fiber amplifier (EDFA) is first developed for trace gas detection. This sensor has been applied to the detection of ammonia using a first longitudinal resonant photoacoustic cell with double absorption optical path (L = 20 cm) and lock-in harmonic detection technique. The minimum detectable limit of 3 parts-per-billion volume (signal-to-noise ratio = 1) and response time of approximately 1 min is achieved at room temperature and atmospheric pressure with 100 ms time constant and 500 mW optical power at the 1531.7 nm transition line.     

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25 mM detection limit and 0.25–2.5 mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.     

Research on permeability coefficient of a polyethylene controlled-release film coating for urea and relevant nutrient release pathways

The permeability coefficient is a key factor that reflects the nutrient release capability of polymer-coated fertilizers. To investigate the permeability coefficient of polyethylene (PE) controlled-release film and to determine the difference between the controlled-release film and a dense membrane, we designed a film permeation device to measure the permeability coefficient of a PE controlled-release film coating for urea, and a mathematical model was used to check the accuracy of these measurements. By measuring the permeation coefficient of a dense, PE membrane, the compactness of the PE controlled-release film was analyzed, and the nutrient release pathway of PE-coated fertilizer was discussed. Research indicated that urea was constantly released through PE controlled-release film and the permeability coefficient remained constant. The permeability coefficient for PE controlled-release film coating on urea with 1–4 months release time was in the range of 7.17–18.7E-15 m²/s with 2.6 times difference between the maximum and minimum. The permeability coefficient decreased as the release time increased, conforming to the inversely proportional relationship between permeation amount and time in the nutrient release model. It is investigated that the measured values are close to the theoretical values and can be used in model calculation. The urea permeability coefficient of PE dense membrane was 7.11E-18 m²/s, which is 1000–2600 times smaller than that of the PE controlled-release film. The contribution of permeability of polymer material itself is negligible. It can be concluded that PE controlled-release film is not a dense membrane but porous and that nutrient release is mainly determined by pore configuration of the film.     

Polymer nanocomposite membranes and their application for flow catalysis and photocatalytic degradation of organic pollutants

The modern world essentially needs a chemical industry that can operate with reduced production costs, and produce high-quality products with low environmental impact. The polymer nanocomposite-based flow catalytic membrane reactor where the reaction and separation can be amalgamated in one unit is considered as one of the new alternative solutions to solve these problems. In this review, we have discussed state-of-the-art flow-through catalytic reactors based on polymer nanocomposite membranes. The unique advantages of flow catalysis include uninterrupted operation, good recyclability, and reaction product without contamination that leads to simple purification. Various catalytic model reactions such as coupling, hydrogenation, esterification in the flow system are presented. We have also presented an overview of methods adopted for preparing such nanocomposite membranes. In the last section, a discussion has been made on the recent advances on polymer-based nanocomposite membranes for the degradation and separation of organic pollutants.     

Mass transfer characteristics for VOC permeation through flat sheet porous and composite membranes: The impact of the different membrane layers on the overall membrane resistance

In this paper, the mass transfer coefficients for trichloroethylene (TCE), toluene (TOL) and dimethyl sulfide (DMS) are experimentally determined for different porous and composite membranes. For polypropylene/polyvinylidenedifluoride porous layer/thin film polydimethylsiloxane dense layer composite membranes, membrane mass transfer coefficients are 2.55E−03, 2.82E−03 and 2.90E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. For polyester/polyacrylonitrile porous layer/thin film polydimethylsiloxane dense layer composite membranes, they are higher, namely 4.28E−03, 4.55E−03 and 4.81E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. Analysis of the contribution of the dense layer of both composite membranes to the total membrane resistance for mass transfer, showed that this contribution was small for both composite membranes. The higher mass transfer coefficients of the thin film polydimethylsiloxane composite membranes from this study in comparison to others from the literature are primarily due to improvement of the mass transfer characteristics of the porous layer. Analysis of the mass transfer characteristics of the different porous layers of which the total porous layer is composed, showed that the contribution of the porous “backing” layer for mechanical support can be substantial in comparison to the porous layer in contact with the dense layer.     

Correlation and prediction of gas permeability in glassy polymer membrane materials via a modified free volume based group contribution method

Over the past decade or more an extensive amount of data on the permeation of gases such as helium, hydrogen, oxygen, nitrogen, methane, and carbon dioxide in a wide array of glassy polymers has been published. Much of this work has been motivated by the search for materials with high permeability and high selectivity for potential use as gas separation membranes. This paper attempts to develop a method for correlating this data in a way that permits prediction of permselectivity behavior of other polymer structures. The method used involves an empirical modification of a free volume scheme that has been used in the past with some success. The previous method requires an experimental density of the polymer and an estimate of occupied volume from a group contribution method developed by Bondi. The present method actually predicts the density and uses a refined estimate of occupied volume specific to each gas. The parameters in the model were deduced from a database including over one hundred polymers. The new method significantly improves the accuracy of correlation and of prediction.     

Crosslinking and stabilization of nanoparticle filled PMP nanocomposite membranes for gas separations

Poly(4-methyl-2-pentyne) (PMP) has been crosslinked using 4,4′-(hexafluoroisopropylidene) diphenyl azide (HFBAA) to improve its chemical and physical stability over time. Crosslinking PMP renders it insoluble in good solvents for the uncrosslinked polymer. Gas permeability and fractional free volume (FFV) decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PMP was due to decrease in diffusion coefficient. Compared to the pure PMP membrane, the permeability of the crosslinked membrane is initially reduced for all gases tested due to the crosslinking. By adding nanoparticles (FS, TiO₂), the permeability is again increased; permeability reductions due to crosslinking could be offset by adding nanoparticles to the membranes. Increased selectivity is documented for the gas pairs O₂/N₂, H₂/N₂, CO₂/N₂, CO₂/CH₄ and H₂/CH₄ using crosslinking and addition of nanoparticles. Crosslinking is successful in maintaining the permeability and selectivity of PMP membranes and PMP/filler nanocomposites over time.     

β-Cyclodextrin polymer based fluorescence enhancement method for sensitive adenosine triphosphate detection

A sensitive and facile method for adenosine triphosphate detection has been developed that based on the prominent fluorescence enhancement capability of β-cyclodextrin polymer to pyrene through host-gest interaction.     

Characterization of a micro spiral flow cell for chemiluminescence detection

A 5.5 μl spiral micro-flow cell, mounted in front of a photomultiplier, is made from Teflon capillary (75 cm×100 μm ID) with two inlets for the CL reagent and carrier buffer and a waste outlet. It allows the rapid mixing of CL reagent and analyte and simultaneous detection of the emitted light. Using a flow rate of 25 μl/min for a 0.4 mM luminol-8 μM hemin solution (pH 11.6) and 50 μl/min of carrier buffer (pH 11.6), the slight exponential calibration curve for the flow injection–chemiluminescence (FI–CL) determination of H₂O₂ is 2.5–10 μM and the detection limit is 1.5 μM. The detection limit achieved by using a spiral flow cell is 24 times lower than that obtained from a conventional FI system with a low dead volume tee mixer and a 12 μl flow cell in a HPLC fluorometer with the source lamp off. This luminol CL detection method is successfully applied to the enzymatic determination of -lactate by FI. The lactate sample is mixed with polyethylene glycol (PEG)-stabilized lactate oxidase (LO) enzyme and then injected into the buffered (pH 7.5) carrier stream for CL detection of the H₂O₂ product. Using the optimal conditions of reaction temperature set to 37.5 °C and flow rates of 45 μl/min for the CL reagent and 60 μl/min for the carrier buffer, the calibration range for lactate is 5–50 μM and the detection limit is 2.9 μM. This method is applied to the determination of -lactate in beer.     

Zirconium meta-sulfonphenyl phosphonic acid-incorporated Nafion membranes for reduction of methanol permeability

Zirconium meta-sulfonphenyl phosphonic acid (Zr-msPPA)/Nafion^® composite membranes were prepared to reduce methanol permeability of the Nafion^® 117 membrane in direct methanol fuel cell (DMFC) applications. Zr-msPPA crystalline nano proton conductors were synthesized inside the membranes via the reaction of zirconium chloride octahydrate and meta-sulfonphenyl phosphonic acid that had been soaked prior. Synthesis of the Zr-msPPA in the membranes was identified from a series of chemical and physical structure characterizations using FTIR, NMR, EDS, and XRD spectroscopy. The thermal stability of the composite membranes was enhanced by addition of the Zr-msPPA, with considerable reduction in methanol permeability with increasing Zr-msPPA content, as the Zr-msPPA nano conductors acted as crystalline barriers to methanol permeation. The ion conductivity also decreased with increasing Zr-msPPA content, but its effect was not as strong as with methanol permeation given the innate, high conductivity of Zr-msPPA.     

Performance evaluation of the different nano-enhanced polysulfone membranes via membrane distillation for produced water desalination in Sert Basin-Libya

A Polysulfone-Polyethylene glycol (PS/PEG) flat sheet membrane was prepared by phase inversion technique. Dimethyl Formamide (DMF) was utilized as a solvent and deionized water was utilized as the coagulant. Polyethylene glycol (PEG) of a various dose of PEG 2000 was utilized as the polymeric improvers and as a pore-forming agent in the casting mixture. The single-walled carbon nanotube (SWCNTs), multi-walled carbon nanotube (MWCNTs), aluminum oxide (Al₂O₃) and copper oxide (CuO) nanoparticles (NPs) were utilized to improve the PS/PEG membrane performances. The characterizations of the neat PS, PS/PEG, PS/PEG/Al2O3 (M1) PS-PEG/CuO (M2), PS-PEG/SWCNTs (M3) and PS/PEG/MWCNTs (M14) nanocomposite (NC) modified membranes were acquired via Fourier-transform infrared analysis (FTIR), water contact angle estimation (WCA), scanning electron microscope (SEM), dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA). Enhanced Direct contact membrane distillation (EDCMD) unit was used for estimating the efficiency of the performance of the synthesized NC membranes via 60 °C feed synthetic water and/or saline oil field produced water samples containing salinities 123,14 mg/L. Adjusting the operational procedures and water characteristics confirmed a high salt rejection of 99.99% by the synthesized NC membranes. The maximum permeate flux achieved in the order of SWCNTs (20.91) > Al₂O₃ (19.92) > CuO (18.92) > MWCNT (18.20) (L/m².h) with adjusted concentration of 0.5, 0.75, 0.75, 0.1 wt% compared with PS weight, i.e. 16%. The optimum operational circumstances comprised feed and permeate temperatures 60 °C and 20 °C, respectively. The achieved flux was 5.97 L/m².h, using brine oil field produced water, via PS/PEG/SWCNTs membrane with 0.5 wt% of SWCNTs. Moreover, the membrane indicated sustaining performance stability in the 480 min continuous desalination testing, showing that the synthesized PS/PEG/SWCNTs NC modified membrane may be of magnificent potential to be activated in EDCMD procedure for water desalination.     

Current-sensing atomic force microscopy for analyzing conformations and properties of polymer membranes for fuel cells

The three-dimensional structures of polymer membranes are different at surfaces and inside bulks, and thus, in general, physical/chemical properties are also different. Morphologies and properties of membrane surfaces are now visualized by current-sensing atomic force microscopy. The increase in performances of a single cell is discussed based on the three-dimensional structures of the polymer membrane, anion-exchange membrane as an example, used for fuel cells. Other reports on Nafion®, proton-exchange membrane, are also introduced to show the importance of this microscopic method.