Low-density Polyethylene Membrane Research Articles

Development of an integrative passive sampler for the monitoring of organic water pollutants.

The development of convenient and competitive devices and methods for monitoring of organic pollutants in the aquatic environment is of increasing interest. An integrative passive sampling system has been developed which consists of a solid poly(dimethylsiloxane) (PDMS) material (tube or rod), acting as hydrophobic organic receiving phase, enclosed in a water-filled or an air-filled low-density polyethylene (LDPE) membrane tubing. These samplers enable the direct analysis of the pollutants accumulated during exposure in the receiving phase by thermodesorption-GC/MS, avoiding expensive sample preparation and cleanups. The capabilities of these sampling devices were studied for the sampling of 20 persistent organic pollutants (chlorobenzenes, hexachlorocyclohexanes, p,p'-DDE, PAHs, and PCBs) in laboratory exposure experiments. For the three sampler designs investigated the uptake of all target analytes was integrative over exposure periods up to 9 days (except PCB 101). The determined sampling rates range from 4 to 1340 microl h(-1) for the water-filled samplers and from 20 to 6360 microl h(-1) for the air-filled ones, respectively. The sampling rate of the analytes is dependent on their molecular weight, partition between water and sampler media (PDMS, polyethylene, water, air) and also of the sampler design. The passive samplers enable the estimation of time-weighted average (TWA) concentration of water pollutants in the lower ng l(-1) to pg l(-1) range.

Pervaporation of Toluene/Alcohol Mixtures through a Coextruded Linear Low-Density Polyethylene Membrane

Pervaporation of Toluene/Alcohol Mixtures through a Coextruded Linear Low-Density Polyethylene Membrane

Temperature-dependent uptake rates of nonpolar organic compounds by semipermeable membrane devices and low-density polyethylene membranes.

The effect of temperature on sampling rates and sampler-water partition coefficients of semipermeable membrane devices (SPMDs) and low-density polyethylene (LDPE) strips was studied in an experimental setup under controlled flow conditions. Aqueous concentrations of chlorobenzenes, polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs) were maintained by continuous circulation of the water over a generator column. Sampling rates for standard design SPMDs (460 cm2) were in the range of 20-200 L d(-1). No significant differences were observed between sampling rates of SPMDs and LDPE strips, but the latter samplers reached equilibrium faster because of their smaller sorption capacity. Sampling rates at 30 degrees C were higher than at 2 degrees C by a factor of about 3. Sampling rate modeling indicated boundary layer-controlled uptake for compounds with log octanol-water partition coefficients smaller than 4.4 and aqueous boundary-layer controlled uptake for more hydrophobic compounds. SPMD-water partition coefficients did not significantly change with temperature, but LDPE-water partition coefficients were larger at 2 degrees C than at 30 degrees C by a factor of 2. For field application of SPMDs, the results imply that temperature is not a key factor that controls uptake rates unless large geographical and temporal scales are involved. The results confirm that water flow velocity has a profound effect on sampling rates.

Trimethylpentane‐containing passive samplers for predicting time‐integrated concentrations of pesticides in water: Laboratory and field studies

A laboratory continuous-flow system delivering known aqueous concentrations of pesticides to passive samplers was used to examine the kinetics of pesticide uptake and release. The passive samplers were constructed of low-density polyethylene membrane bags containing 2.2.4-trimethylpentane solvent (TRIMPS). Both uptake and release experiments were run in triplicate. Each experiment involved four treatments, including a control and three fivefold dilutions of a pesticide mixture that included the usual range of these pesticides as measured in the riverine environment of cotton-growing regions of Australia. The results indicated that for nonpolar pesticides with a log K(ow) > 3.5. uptake was linear over the 42-d exposure time and was independent of the treatment concentration. The half-lives for release of these pesticides from the TRIMPS varied from 26 to 130 d in clean water. The relatively polar pesticides with a log K(ow) < 3.5 had lower uptake rates into the TRIMPS because of their affinity for water. Release of trimethylpentane from the TRIMPS placed in 0.85-mm mesh nylon bags in river water was used as an indicator for chemical diffusion across the aqueous boundary to examine the effect of environmental factors. Most variability in solvent release in the field-deployed TRIMPS across all sites was explained by time of deployment and was not significantly influenced by river flow or water temperature. This suggests that river flow and water temperature may not be important in influencing uptake rates of pesticides into TRIMPS when employed in the field.

Novel integrative passive samplers for the long-term monitoring of semivolatile organic air pollutants.

Two types of passive sampler were developed for the long-term monitoring of semivolatile organic compounds (SOCs) in air. They consist of poly(dimethylsiloxane) (PDMS)-coated stir bars (type A) or silicone tubing (type B), acting as a solid receiving medium, enclosed in a heat-sealed low-density polyethylene (LDPE) membrane. These samplers combine the advantages of integrative passive sampling with those of analysing accumulated analytes by thermodesorption-GC-MS, whilst avoiding the use of solvents and expensive sample preparation and cleanup steps. The performance of these samplers was investigated for the integrative sampling of SOCs, including alpha- and gamma-hexachlorocyclohexanes, hexachlorobenzene, 2,4,4'-trichlorobiphenyl, 2,2',5,5'-tetrachlorobiphenyl and fluoranthene, in laboratory exposure experiments under controlled conditions. For both types of sampler, the uptake of all the analytes investigated was linear over an exposure period of 15 days. The sampling rates calculated ranged from 70 to 320 ml h(-1) (sampler A) and 630 to 4300 ml h(-1) (sampler B). The passive samplers are able to detect low time-weighted average air concentrations in the pg m(-3) range. The small, robust and inexpensive sampling devices were tested successfully for the long-term air monitoring of semivolatile organic pollutants in a polluted area over an exposure period of up to 28 days.

Stabilized liquid membrane device (SLMD) for the passive, integrative sampling of labile metals in water

A stabilized liquid membrane device (SLMD) is described forpotential use as an in situ, passive, integrative samplerfor cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead(Pb), and zinc (Zn) in natural waters. The SLMD (patent pending)consists of a 2.5-cm-wide by 15-cm-long strip of low-density polyethylene (LDPE) layflat tubing containing 1 mL of an equalmixture (v/v) of oleic acid (cis-9-octadecenoic acid) and EMO-8Q (7-[4-ethyl-1-methyloctyl]-8-quinolinol). The reagentmixture continuously diffuses to the exterior surface of the LDPE membrane, and provides for sequestration of several divalent metals for up to several weeks. Depending on samplerconfiguration, concentration factors of several thousand canbe realized for these metal ions after just a few days. In addition to in situ deployment, the SLMD may be useful for laboratory determination of labile metal species in grab samples. Methods for minimizing the effects of water flow onthe sampling rate are currently under investigation.

Experimental estimation of gas‐transport properties of linear low‐density polyethylene membranes by an integral permeation method

In recent years, we have investigated gas-transport phenomena in coextruded linear low-density polyethylene (LLDPE) membranes. For the most part, coextruded LLDPE membranes were investigated because of their excellent mechanical properties, which explain their extensive use in the packaging industry. Because of the small thickness of coextruded LLDPE membranes, significant errors can be involved in the determination of the diffusion coefficient of gases in the membranes by the time-lag method. To obtain more precise transport parameters for LLDPE membranes, we determined the permeability and diffusion coefficients for O2, CO2, He, and N2 from 298 to 348 K by employing an alternative method recently developed. The results indicate that the procedure used in this study for determining the diffusivity of gases in membranes was precise and more efficient than a method based on the evaluation of the time-lag parameter. With respect to permeability, the coefficients obtained in this work agree satisfactorily with those obtained by the time-lag method. In general, the permeability and diffusivity results are in satisfactory agreement with the literature values reported for semicrystalline polyethylene membranes. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3013–3021, 2001

Percutaneous Absorption of Sunscreen Agents from Liquid Paraffin: Self-Association of Octyl Salicylate and Effects on Skin Flux

This study provides an investigation of the availability of octyl salicylate (OS), a common sunscreen agent, from liquid paraffin and the effect of OS on skin permeability. A model membrane system to isolate the vehicle effect from membrane permeability has been developed. Partitioning of OS between liquid paraffin and aqueous receptor phases was conducted. Partition coefficients increased with increase in OS concentration. A range of OS concentrations in liquid paraffin was diffused across human epidermis and synthetic membranes into 4% bovine serum albumin in phosphate-buffered saline and 50% ethanol. Absorption profiles of OS obtained from silicone and low-density polyethylene (LDPE) membranes were similar to each other but higher than for the high-density polyethylene [HDPE (3 times)] membrane and human epidermis (15 times). The steady state fluxes and apparent permeability coefficients (Kp′) obtained from the diffusion studies showed the same trends with all membranes, except for the HDPE membrane which showed greater increase in flux and Kp′ at concentrations above 30%. IR spectra showed that several bands of OS were shifted with concentrations, and the molecular models further suggested that the main contribution to the self-association is from non-1,4 van der Waals interactions.

Development of a membrane respirometer

The respirometric technique relies upon reoxygenation of a wastewater sample through a quality controlled polyethylene membrane. The fluid sample is surrounded by a low density polyethylene membrane permeable to oxygen and the sample is stirred in the respirometer. In studies the DO saturation concentration of the sample in the respirometer was experimentally determined. The respirometer was initially standardized and the rate of oxygen transfer was estimated. The experimental data was fitted to Fick's linear law of diffusion, using a quality controlled polyethylene membrane, the rate of oxygen transfer was found to be reproducible. In oxygen uptake studies, DO vs time recorder plots were obtained. The course of oxygen uptake is depicted and a complete fingerprint of the course of oxidation of the organic contents in the wastewater may be obtained.

Liquid permeation of organic mixture by surface-modified polyethylene membrane

Linear low-density polyethylene membranes were prepared by a casting method. IN order to modify the surface, the membrane was irradiated with UV light. In an atmosphere of carbon disulfide vapor, multiple internal reflection spectra observations showed that the surface of membrane had a carbonyl group. The casted membrane is an asymmetric membrane. When the flat surfce of membrane faces the upstream side, the flux of the membrane is twice as that of the other surface of membrane. From the comparision of the pervaporation characteristics of casted membrane and blown film, the crystallinity of membrane affects the separation factor and flux of the membrane. The higher the crystallinity of the membrane, the better the selectivity, and the poorer the flux.