Low-density Polyethylene Membrane Research Articles

Understanding the effects of operating conditions on the water management in anion exchange membrane fuel cells

While water management in Anion Exchange Membrane Fuel Cells (AEMFCs) is seen as crucial for performance and durability, measurements of water management within operating cells remain few. In this work, we measured the performance of an H2/O2 AEMFC based on a low-density polyethylene membrane AEM, PtRu/C anode and Fe–N–C cathode for various combinations of inlet relative humidities, gas pressures and flow rates. Simultaneously, the anode and cathode outlet relative humidities were measured using humidity sensors, from which the amount of water removed from the cell could be quantified for each side. The data shows that back-diffusion of water from anode to cathode results in increasing outlet relative humidity with increased current density, both at anode and cathode. Water produced in the AEMFC was thus removed from both sides. The maximum current density was found to be strongly connected to anode flooding, which is also the main cause for hysteresis during potentiodynamic scans. However, under atypical operating conditions, the cell performance may also be limited by low humidity at the cathode, with associated low ionomer conductivity. Overall, it is concluded that water management of AEMFC with thin AEMs can be achieved by playing with both the anode and cathode operating conditions.

The impact of temperature on the water isotope (2H/1H, 17O/16O, 18O/16O) fractionation upon transport through a low-density polyethylene membrane

ABSTRACT In the present study we investigated the isotope effects associated with water loss from closed low-density polyethylene (LDPE) bottles via diffusion at temperatures between 4 and 60 °C. While at low temperatures (4 and 10 °C) no substantial diffusional loss of water was observed within storage time, a pronounced loss was found for the experiments at room temperature and 60 °C. The latter was associated with a substantial increase in δ 18O, δ 17O, and δ 2Η values, and a decrease in the deuterium excess. The magnitude of the isotope effects essentially depended on the extent of water evaporation from the closed bottles through the LDPE membrane.

Passive sampling of toluene (and benzene) in indoor air using a semipermeable membrane device

The distribution and concentration of organic compounds in the environment have attracted great interest mainly due to their capability of bioaccumulation, dispersion, and danger to living organisms. Factors such as urbanization, population growth, and the emergence of new technologies contribute to the increase in pollutant emissions, especially volatile organic compounds (VOCs), such as benzene, toluene, ethylbenzene, and xylenes (BTEX). These compounds are emitted by several sources, becoming more common in work environments, influencing indoor air quality (IAQ), which can cause health damage, in addition to increasing the likelihood of cancer development. In this context, we developed a semipermeable membrane device (SPMD), consisting of low density polyethylene membrane (8 cm long × 3 cm wide), filled with 3 mL of acetonitrile, for passive sampling of toluene (and benzene) in gas phase. With this configuration, the SPMD needed 24 h exposure to the indoor air in order to achieve equilibrium. The target compounds were quantified in the acceptor phase by HPLC-DAD. The optimized SPMD was tested for the collection of toluene and benzene in six chemistry laboratories at Fluminense Federal University and in five nail salons in the city of Niterói, in the state of Rio de Janeiro, Brazil. The developed sampling method was able to identify the analytes in the indoor air of the studied environments, and was easy to operate, with no need to clean up the extracts, allowing their direct injection into the chromatographic system.

Membrane-assisted radiant cooling for expanding thermal comfort zones globally without air conditioning

We present results of a radiant cooling system that made the hot and humid tropical climate of Singapore feel cool and comfortable. Thermal radiation exchange between occupants and surfaces in the built environment can augment thermal comfort. The lack of widespread commercial adoption of radiant-cooling technologies is due to two widely held views: 1) The low temperature required for radiant cooling in humid environments will form condensation; and 2) cold surfaces will still cool adjacent air via convection, limiting overall radiant-cooling effectiveness. This work directly challenges these views and provides proof-of-concept solutions examined for a transient thermal-comfort scenario. We constructed a demonstrative outdoor radiant-cooling pavilion in Singapore that used an infrared-transparent, low-density polyethylene membrane to provide radiant cooling at temperatures below the dew point. Test subjects who experienced the pavilion (n = 37) reported a "satisfactory" thermal sensation 79% of the time, despite experiencing 29.6 ± 0.9 °C air at 66.5 ± 5% relative humidity and with low air movement of 0.26 ± 0.18 m⋅s-1 Comfort was achieved with a coincident mean radiant temperature of 23.9 ± 0.8 °C, requiring a chilled water-supply temperature of 17.0 ± 1.8 °C. The pavilion operated successfully without any observed condensation on exposed surfaces, despite an observed dew-point temperature of 23.7 ± 0.7 °C. The coldest conditions observed without condensation used a chilled water-supply temperature 12.7 °C below the dew point, which resulted in a mean radiant temperature 3.6 °C below the dew point.

Membrane Enhanced Bioaccessibility Extraction (MEBE) of hydrophobic soil pollutants – Using a semipermeable membrane for separating desorption medium and acceptor solvent

Bioaccessibility extractions are increasingly applied to measure the fraction of pollutants in soil, sediment and biochar, which can be released under environmentally or physiologically relevant conditions. However, the bioaccessibility of hydrophobic organic chemicals (HOCs) can be markedly underestimated when the sink capacity of the extraction medium is insufficient. Here, a novel method called “Membrane Enhanced Bioaccessibility Extraction” (MEBE) applies a semipermeable membrane to physically separate an aqueous desorption medium that sets the desorption conditions from an organic medium that serves as acceptor phase and infinite sink. The specific MEBE method combines HOC (1) desorption into a 2-hydroxypropyl-β-cyclodextrin solution, (2) transfer through a low-density polyethylene (LDPE) membrane and (3) release into ethanol, serving as analytical acceptor phase. The surface to volume ratio within the LDPE membrane is maximized for rapid depletion of desorbed molecules, and the capacity ratio between the acceptor phase and the environmental sample is maximized to achieve infinite sink conditions. Several experiments were conducted for developing, optimizing and pre-testing the method, which was then applied to four soils polluted with polycyclic aromatic hydrocarbons. MEBE minimized sample preparation and yielded a solvent extract readily analyzable by HPLC. This study focused on the proof-of-principle testing of the MEBE concept, which now can be extended and applied to other samples and desorption media.

Sorption kinetics of parent and substituted PAHs for low-density polyethylene (LDPE): Determining their partition coefficients between LDPE and water (KLDPE) for passive sampling

Low-density polyethylene (LDPE) has been widely used as a sorbent for passive sampling of hydrophobic organic contaminants (HOCs) in aquatic environments. However, it has seen only limited application in passive sampling for measurement of freely dissolved concentrations of parent and substituted PAHs (SPAHs), which are known to be toxic, mutagenic and carcinogenic. Here, the 16 priority PAHs and some typical PAHs were selected as target compounds and were simultaneously determined by gas chromatography–mass spectrometer (GC–MS). Some batch experiments were conducted in the laboratory to explore the adsorption kinetics of the target compounds in LDPE membranes. The results showed that both PAHs and SPAHs could reach equilibrium status within 19–38 days in sorption kinetic experiments. The coefficients of partitioning between LDPE film (50 μm thickness) and water (KLDPE) for the 16 priority PAHs were in good agreement with previously reported values, and the values of KLDPE for the 9 SPAHs are reported in this study for the first time. Significant linear relationships were observed, i.e., log KLDPE = 0.705 × log KOW + 1.534 for PAHs (R2 = 0.8361, p < 0.001) and log KLDPE = 0.458 × log KOW + 3.092 for SPAHs (R2 = 0.5609, p = 0.0077). The selected LDPE film was also proven to meet the condition of “zero sink” for the selected target compounds. These results could provide basic support for the configuration and in situ application of passive samplers.

Enhancement the properties of high and low-density polyethylene membranes by radiation grafting process

Enhancement the properties of high and low-density polyethylene membranes by radiation grafting process

Performance of passive sampling with low-density polyethylene membranes for the estimation of freely dissolved DDx concentrations in lake environments

Laboratory and field studies were used to evaluate the performance of low-density polyethylene (PE) passive samplers for assessing the freely dissolved concentrations of DDT and its degradates (DDD and DDE, together referred to as DDx) in an Italian lake environment. We tested commercially available 25 μm thick PE sheets as well as specially synthesized, 10 μm thick PE films which equilibrated with their surroundings more quickly. We measured PE-water partitioning coefficients (Kpew) of the 10 μm thick PE films, finding good correspondence with previously reported values for thicker PE. Use of the 10 μm PE for ex situ sampling of a lake sediment containing DDx in laboratory tumbling experiments showed repeatability of ±15% (= standard deviation/mean). Next, we deployed replicate 10 μm and 25 μm PE samplers (N = 4 for 10 d and for 30 d) in the water and sediment of a lake located in northern Italy; the results showed dissolved DDx concentrations in the picogram/L range in porewater and the bottom water. Values deduced from 10 μm thick PE films compared well (95% of all comparison pairs matched within a factor of 5) with those obtained using PE films of 25 μm thickness when dissolved DDx concentrations were estimated using performance reference compound (PRC) corrections, whether left at the bed-water interface for 10 or 30 days. These results demonstrated the potential of this sampling method to provide estimation of the truly dissolved DDx concentrations, and thereby the mobile and bio-available fractions in both surface waters and sediment beds.

Elaboración de membranas planas de polietileno por el método TIPS usando aceite de palma como solvente y su aplicación en destilación con membranas

Palm oil (PO) was used as new solvent for the elaboration of low density polyethylene (LDPE) flat sheet membranes via TIPS method. Phase diagram LDPE/PO was determined, and the effect of parameters such as polymer content (20, 30% w/w), temperature of coagulation bath (0, 25°C) and polymer size (#12, #6 mesh) on thickness, pore size, water vapor permeability and water intrusion pressure of the LDPE membranes was studied. The only parameter that significantly affects the membrane characteristics was polymer content (exempting thickness membrane). By an increase of polymer content, pore size and water vapor permeability decrease (2.7 and 1.2 times, respectively), while water intrusion pressure increases (>1.2 times). Membranes with a thickness of less than 400 μm and pore sizes between 2.3 and 0.8 μm were obtained. Membranes with 0.8 μm pore size were selected to concentrate ethanol-water and glucose solutions by vacuum membrane distillation. Membranes permeated 0.0667 and 0.0508 mol.m-2.s-1, respectively in 2 h of experimentation. Moreover, a 2.1 concentration factor was found using ethanol-water solutions.

Development and validation of a graphical sorption model: application to sorption of organic liquids into low density polyethylene polymeric membrane

AbstractIn this work, a model has been developed for the sorption process of pure liquids and liquid mixtures into polymeric membrane. The model is presented in terms of Gauss hypergeometric function and can be simply applied for system of interest using graphical form and step‐by‐step application procedure illustrated. The model includes both sorption and desorption mechanisms in equations, and consequently reaction orders and rate constants can be determined. Collected experimental data of the equilibrium sorption of various liquids including water, linear alcohols, linear alkanes, derivates of cyclohexane, aromates, 1‐chlorohexane, chlorobenzene, benzoyl chloride, and nitrobenzene into the low density polyethylene membrane at three temperatures (288.15, 298.15, and 308.15 K) were used for validation of model calculations and assessment of model reliability. Simply, the introduced apparent reaction order and reaction rate constant can be calculated, based on which one might readily access to the sorption and desorption individual reaction orders. The computational cost of proposed method is small, and much of calculations can be done following procedure provided in the form of graphical diagrams. The reliability of method was successfully examined and revealed potential for further uses. © 2017 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Use of low density polyethylene membranes for assessment of genotoxicity of PAHs in the Seine River.

The genotoxicity of river water dissolved contaminants is usually estimated after grab sampling of river water. Water contamination can now be obtained with passive samplers that allow a time-integrated sampling of contaminants. Since it was verified that low density polyethylene membranes (LDPE) accumulate labile hydrophobic compounds, their use was proposed as a passive sampler. This study was designed to test the applicability of passive sampling for combined chemical and genotoxicity measurements. The LDPE extracts were tested with the umu test (TA1535/pSK1002 ± S9) and the Ames assay (TA98, TA100 and YG1041 ± S9). We describe here this new protocol and its application in two field studies on four sites of the Seine River. Field LDPE extracts were negative with the YG1041 and TA100 and weakly positive with the TA98 + S9 and Umu test. Concentrations of labile mutagenic PAHs were higher upstream of Paris than downstream of Paris. Improvement of the method is needed to determine the genotoxicity of low concentrations of labile dissolved organic contaminants.

Extraction of Volatile Flavor Compounds From Tobacco Leaf Through a Low-Density Polyethylene Membrane.

A low-density polyethylene (LDPE) membrane pouch method was developed to extract volatile flavor compounds from tobacco leaf. Tobacco leaf suspended in water was enclosed in a pouch prepared from a LDPE membrane of specific gravity 0.92 g/cm3 and 0.03 mm thickness and then extracted with diethyl ether. In comparison with direct solvent extraction, LDPE membrane excluded larger and higher boiling point compounds which could contaminate a gas chromatograph inlet and damage a column. Whilst being more convenient than a reduced-pressure steam distillation, it could extract volatile flavor compounds of wide range of molecular weight and polarity. Repeatabilities in the extracted amounts were ranged from 0.38% of 2.3-bipyridyl to 26% of β-ionone, and average value of 39 compounds was 5.9%.

A one-step strategy for ultra-fast and low-cost mass production of plastic membrane microfluidic chips.

An ultra-fast, extremely cost-effective, and environmentally friendly method was developed for fabricating flexible microfluidic chips with plastic membranes. With this method, we could fabricate plastic microfluidic chips rapidly (within 12 seconds per piece) at an extremely low cost (less than $0.02 per piece). We used a heated perfluoropolymer perfluoroalkoxy (often called Teflon PFA) solid stamp to press a pile of two pieces of plastic membranes, low density polyethylene (LDPE) and polyethylene terephthalate (PET) coated with an ethylene-vinyl acetate copolymer (EVA). During the short period of contact with the heated PFA stamp, the pressed area of the membranes permanently bonded, while the LDPE membrane spontaneously rose up at the area not pressed, forming microchannels automatically. These two regions were clearly distinguishable even at the micrometer scale so we were able to fabricate microchannels with widths down to 50 microns. This method combines the two steps in the conventional strategy for microchannel fabrication, generating microchannels and sealing channels, into a single step. The production is a green process without using any solvent or generating any waste. Also, the chips showed good resistance against the absorption of Rhodamine 6G, oligonucleotides, and green fluorescent protein (GFP). We demonstrated some typical microfluidic manipulations with the flexible plastic membrane chips, including droplet formation, on-chip capillary electrophoresis, and peristaltic pumping for quantitative injection of samples and reagents. In addition, we demonstrated convenient on-chip detection of lead ions in water samples by a peristaltic-pumping design, as an example of the application of the plastic membrane chips in a resource-limited environment. Due to the high speed and low cost of the fabrication process, this single-step method will facilitate the mass production of microfluidic chips and commercialization of microfluidic technologies.

Gas transport through nanocomposite membrane composed by polyethylene with dispersed graphite nanoplatelets

The gas separation and gas barrier properties of nanocomposite membrane made of low-density polyethylene (LDPE) with dispersed graphite nanoplatelets (GNPs) were studied by gas phase permeation technique. Structural and morphological analyses indicate that in nanocomposites prepared by film blowing technology: (i) the GNPs are iso-oriented with the platelet surface parallel to the membrane surface and (ii) the GNPs inclusion does not change the crystalline fraction of the polymeric matrix nor the size of the LDPE crystallites. The H2, N2, and CO2 transport through the nanocomposite membrane was investigated in samples with nominal GNPs content of 5wt%. The GNPs inclusion reduces the permeability by approximately a factor two compared to that of the pure LDPE membrane for all the examined gases without relevant changes in the gas selectivity properties. Gas transport through the nanocomposite membrane obeys to the solution–diffusion mechanism and shows, for the examined gases, the same value of activation energy for permeation as in the pure LDPE sample. The gas barrier properties of the nanocomposite were compared with those predicted by phenomenological models. The reduced permeability cannot be explained assuming that gas molecules have to cross a tortuous migration path in the polymeric matrix but was instead attributed to the formation of rigidified polymer layers around the GNPs filler particles.

Methodology for profiling anti-androgen mixtures in river water using multiple passive samplers and bioassay-directed analyses

The identification of endocrine disrupting chemicals in surface waters is challenging as they comprise a variety of structures which are often present at nanomolar concentrations and are temporally highly variable. Hence, a holistic passive sampling approach can be an efficient technique to overcome these limitations. In this study, a combination of 4 different passive samplers used for sampling polar (POCIS Apharm and POCIS Bpesticide) and apolar compounds (LDPE low density polyethylene membranes, and silicone strips) were used to profile anti-androgenic activity present in river water contaminated by a wastewater effluent. Extracts of passive samplers were analysed using HPLC fractionation in combination with an in vitro androgen receptor antagonist screen (YAS). Anti-androgenic activity was detected in extracts from silicone strips and POCIS A/B at (mean ± SD) 1.1 ± 0.1 and 0.55 ± 0.06 mg flutamide standard equivalents/sampler respectively, but was not detected in LDPE sampler extracts. POCIS samplers revealed higher selectivity for more polar anti-androgenic HPLC fractions compared with silicone strips. Over 31 contaminants were identified which showed inhibition of YAS activity and were potential anti-androgens, and these included fungicides, germicides, flame retardants and pharmaceuticals. This study reveals that passive sampling, using a combination of POCIS A and silicone samplers, is a promising tool for screening complex mixture of anti-androgenic contaminants present in surface waters, with the potential to identify new and emerging structures with endocrine disrupting activity.

Polyethylene passive samplers to determine sediment–pore water distribution coefficients of persistent organic pollutants in five heavily contaminated dredged sediments

Pore concentration and partition coefficients of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were determined in sediments from five distinct contaminated sites in France (marine harbour, rivers canals and highway sedimentation tank). The assessment of the risk caused by such micropollutants requires, in most cases, the measurement of their availability. To assess this availability, low density polyethylene (LDPE) membrane samplers were exposed to these sediments under constant and low-level agitation over a period of 46days. Freely dissolved pore water contaminant concentrations were estimated from the concentration at equilibrium in the LDPE membrane. The depletion of contaminants in the sediments was monitored by the use of performance reference compounds (PRCs). Marked differences in freely dissolved PAH and PCB concentrations and resulting sediment–pore water partition coefficients between these five sediments were observed. Data set was tested onto different empirical and mechanistic models. As final findings, triple domain sorption (a total organic carbon, black carbon and oil phase model) could model PCB data successfully whereas the best fitting for PAH partitioning was obtained by Raoult's Law model.

Novel instrument and method for the investigation of small permeation fluxes of gases through different membranes

In this study a new permeation measurement equipment is presented which is shown to be capable of measuring low and high gas fluxes through different membranes. The new membrane support system which is introduced here is suitable for thin membranes (>10μm) and is expected to provide more accurate results than the design used in earlier permeation measurements.In order to provide a glimpse of the possibilities of the new equipment, hydrogen permeation measurements through a low-density polyethylene (LDPE) and a nickel membrane are presented. The pressure difference dependence of the hydrogen fluxes measured agreed well with the behaviour expected according to Sieverts’ law. In case of the LDPE membrane our results can be explained with the molecular diffusion of hydrogen, which agrees with literature data. As for the nickel membrane the results suggest that under our experimental conditions the speed determining step of the permeation is the atomic diffusion.

Study of passive sampling of polycyclic aromatic hydrocarbons in gas phase using Amberlite XAD resins as filling materials of semipermeable membranes

Abstract In this work, a study was performed to evaluate the use of Amberlite XAD resins (XAD-2, XAD-4 and XAD-16), for the first time, as filling materials for low-density polyethylene membranes, which will be inserted as passive samplers for polycyclic aromatic hydrocarbons (PAHs) in gas phase. The use of samplers deployed for 48 h evidenced a relative capability to retain the compounds under study. A detailed study was performed to evaluate the recovery of analytes from the sampler through microwave-assisted extraction by using acetonitrile. A clean-up step using alumina-C18 cartridges was necessary before determination of the PAHs by high performance liquid chromatography with fluorescence detection. The limits of detection were of the order of μg L− 1 with relative standard deviation values that varied from 1 to 16% as a function of the compound and the XAD resin employed. Amberlite XAD resins can be considered an excellent alternative as filling material of semipermeable membrane devices for passive sampling of PAHs in air due to their low cost, ease of manipulation and suitable chemical and mechanical characteristics.

Derivation of the permeation equation for diffusion of gases and vapors in flat membrane by using Laplace transform

Generally, the model of forced diffusion of a penetrant through nonporous polymer membranes can be quantitatively described by a partial differential equation of parabolic type, which is known as Fick’s second law. In this article, the detailed explanation of application of the integral transform method (especially Laplace transform) for the solution of Fick’s second law at given initial and boundary conditions is presented. Obtained final expression for the concentration profile inside a flat membrane and the diffusion flux through a membrane were verified on permeability data of carbon dioxide and cyclohexane through low-density polyethylene membrane. While CO2 permeation data can be successfully fitted by obtained model, in the case of cyclohexane vapors, when the diffusion coefficient cannot be supposed to be constant due to strong polymer–penetrant interactions (swelling), the agreement between model and experimental data is lower.

Semi-empirical model of toluene transport in polyethylene membranes based on the data using a new type of apparatus for determining gas permeability, diffusivity and solubility

Solubility, diffusivity and permeability of toluene vapors in low-density polyethylene (LDPE) membranes of various thicknesses (approximately 48, 93, 138 and 187 μm) at different temperatures 30, 40 and 50 °C in the range of relative vapor pressure p/ p 0=(0.05; 0.95) were measured using new type of permeation apparatus. Moreover, special construction of the new cell enables determination of the permeant amount sorbed in the membrane in the steady state operation of vapor permeation. The simple semi-empirical model of toluene transport in a polyethylene membrane based on relation between experimentally obtained effective diffusion coefficients and concentration dependent diffusion coefficients evaluated from experiments on a new permeation apparatus was proposed. The model enables estimation of toluene fluxes, sorption in the steady state of vapor permeation and concentration profiles in a polyethylene membrane from equilibrium sorption isotherms and effective diffusion coefficients. Very good agreement between experimental and calculated values from the proposed model was obtained.