Polyether-type Polyurethane Foam Research Articles

Modelling PUF passive air samplers: Temperature dependence of polyurethane foam – Air partitioning of PAHs and their O-, N-, and S-derivatives computed by COSMO-RS

The response of polyether-type polyurethane foam (PUF) passive samplers used to estimate the gaseous concentration of organic chemicals has been modelled using the COSMO-RS methodology. Experimental data for equilibrium partitioning ratios were used to evaluate several different oligomers as surrogates for polyurethane foam over a temperature range of 15–95 °C. Models were built with varying mole ratios of mono- or di-isocyanates and ether-based linkers derived from glycerol, ethylene oxide, propylene oxide, styrene and oligomers of ethylene oxide. Several models were found to have comparable root-mean-square (RMS) error, and COSMO-RS results were generally consistent with the empirical data. A PUF model consisting of a 1:1 condensed pair of 2,4-toluene-diisocyanide and glycerol was found to have minimal RMS error for both aromatic organic molecules and a large set of organic molecules studied between 15 and 95 °C. This model was applied to a series of simple and heteroatom-substituted polycyclic aromatics, for which the temperature dependence of air-polymer partitioning was predicted between −5 and 40 °C. Log K(PUF-Air) is found to decrease by 1.5–2.5 log units over this range, reflecting the increased volatility of the compounds with temperature, demonstrating the need for accurate exposure temperatures for partitioning involving air. The model results support the application of the passive samplers for monitoring and research studies of polycyclic aromatic compounds (PACs) in air. The approach also illustrates an efficient strategy of selective acquisition of experimental data for COSMO-RS validation, coupled by theoretical prediction of a much larger number of chemicals at various temperatures.

Determination of gold in ore samples by energy dispersive X-ray fluorescence after separation and preconcentration on polyurethane foam

A sensitive and selective method to determine gold in ore samples was developed. It was based upon gold extraction from hydrochloric acid medium by unloaded polyether type polyurethane foam (PUF). After that direct measurement on the solid sorbent by energy dispersive X-ray fluorescence (EDXRF) was done. The main parameters that control the gold sorption on PUF were evaluated. HCl concentration, sorption kinetic, amount of PUF and influence of foreign ions are some examples of these parameters. No variation in the gold system sorption was observed in the concentration range of 10−2 to 1mol L−1 of HCl. A 0.3mol L−1 HCl concentration was selected. The sorption kinetics of Au (III) is rapid with a half-life of adsorption (t1/2) of 0.83min. The curve fitted by EDXRF measurement of gold Lα intensity signal on PUF was linear in the mass range of 0 to 25μg. The calibration sensitivity was 0.0860 CPS μg−1. The detection and quantification limits of gold in ore samples were 1.36 and 4.53μg .g−1, respectively. It was observed that Al, Cu (II), Fe (III), Mn (II) and Ni have no significant effect on gold sorption. The method was successfully applied to determine gold in ore reference materials. The results are in good agreement with the certified gold values at a 95% confidence level. The average relative standard deviation (RSD) was 6%.

Sorption Characteristics of Caffeine onto Untreated Polyurethane Foam: Application to Its Determination in Human Plasma

In the present paper, the sorption properties of caffeine (CAF) onto polyether type polyurethane foam (PUF) as solid phase sorbent were investigated with UV determination at 274.3 nm. Batch and column methods were used to optimize chemical, flow, kinetic and isothermal conditions for preconcentration of CAF. Results indicated quantitative sorption of CAF at pH 8 and 30 min shaking time. The maximum sorption capacity was found to be 4.1 mg g(-1). Column preconcentration was recommended at a flow rate of 1.5 mL min(-1) and desorption with 4 mL from 0.15 mol L(-1) hydrochloric acid. The procedure provided a linear analytical range of 0.05-30 mg L(-1). The detection and quantification limits are 0.016 and 0.047 mg L(-1), respectively. The procedure was applied to determination of CAF in spiked human plasma. The obtained recoveries were 98-101% and RSD values were from 0.05 to 9.5%.

Removal of Malachite Green from Aqueous Medium Employing Polyurethane Foam as Adsorbent and Sodium Dodecylsulfate as Carrier

The present work describes a detailed study about the adsorption of malachite green (MG) by a polyether-type polyurethane foam (PUF) using sodium dodecylsulfate (SDS) as a carrier. The adsorption process was based on the formation of a hydrophobic ionic-pair between the MG cationic dye and the dodecylsulfate anion, which presented high affinity for the PUF. The manifold employed in the study was built up by adjusting a cylinder of PUF with 200 mg in the arm of an overhead stirrer, which was soaked (and stirred) in the solution containing the dye and SDS. The adsorption process was characterized in relation to equilibrium and kinetic aspects. Langmuir (r 2 = 0.842) and Freundlich (r 2 = 0.996) isotherms were also employed for modeling the system as well as the Nernst partition law (r 2 = 0.999). A study about the recovery of MG and the PUF regeneration was conducted, and the acetonitrile was the most efficient solvent for the desorption of the adsorbed ionic pair. The obtained results showed that the concentration of SDS added to the medium plays an important role on the adsorption process, which can be better described by employing a second-order kinetic model.

Study of Rhodamine B Retention by Polyurethane Foam from Aqueous Medium in Presence of Sodium Dodecylsulfate

This work reports a study about the adsorption of Rhodamine B (RB) by unloaded polyether type polyurethane foam (PUF) in a medium containing sodium dodecylsulfate (SDS). The adsorption process was based on the formation of an ionic-pair between RB and SDS, which presented high affinity by PUF. Adsorption was characterized in relation to equilibrium, kinetic, and thermodynamic aspects and the results obtained showed that the ratio between the SDS and RB concentrations played an important role on the adsorption efficiency. A maximum adsorption capacity of 6.85 × 10−6 mol RB g−1 was observed at established experimental conditions. The adsorption process was spontaneous (negative ΔG) and presented an endothermic characteristic (positive ΔH). Also, its rate was regulated by an intraparticle diffusion process. Sequential extraction experiments were carried out by changing PUF plugs in 30 and 60 min time intervals, resulting in removal rates higher than 95%.

Estudo da sorção do corante catiônico violeta cristal por espuma de poliuretano em meio aquoso contendo dodecilsulfato de sódio

This work presents a detailed study about the sorption of crystal violet (CV) cationic dye onto polyether type polyurethane foam (PUF). The sorption process was based on the formation of an ionic-pair between cationic dye and dodecylsulfate anion (SDS), which presented high affinity by PUF. Set-up employed in the study was built up by adjusting a 200 mg cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium and kinetic aspects and it was modeled by employing Langmuir and Freundlich isotherms. Obtained results showed that the ratio between SDS and MB concentrations played an important role on the sorption process. According to results found it was possible to retain up to 3.4 mg of dye from 200 mL of a 5.0 x 10-5 mol L-1 CV solution containing 1.25 x 10-4 mol L-1 SDS, which represented a removal efficiency of around 92%.

Employment of polyurethane foam for the adsorption of Methylene Blue in aqueous medium

This work presents a detailed study about the adsorption of Methylene Blue (MB) onto polyether type polyurethane foam (PUF). The adsorption process is based on the formation of a hydrophobic ionic-pair between cationic dye MB and dodecylsulfate anion (SDS), which present high affinity by PUF. Set-up employed in the study was built up by adjusting a 200 mg cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium, kinetic and thermodynamic aspects and it was modeled by employing Langmuir and Freundlich isotherms. Obtained results showed that the ratio between SDS and MB concentrations plays an important role on the adsorption process. According to Langmuir isotherm, a maximum adsorption capacity of 7.20 × 10 −5 mol MB g −1 was achieved when optimized operational conditions were employed. The adsorption rate seems to be regulated by an intraparticle diffusion mechanism. Adsorption process was spontaneous (negative Δ G) at ambient temperature and presented an endothermic characteristic (positive Δ H). Sequential extraction experiments were carried out by changing PUF plugs in 30 min time intervals and around 96% of the MB present in solution could be removed through consecutive extractions with six 200 mg PUF cylinders.

Characterization of solid-phase extraction of Fe(III) by unloaded polyurethane foam as thiocyanate complex

This work presents a detailed study about the adsorption of iron(III)–thiocyanate complexes onto unloaded polyether-type polyurethane foam (PUF). A novel strategy was employed for this purpose, utilizing the adjustment of the plug cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium and kinetic aspects and it was modeled by applying Langmuir and Freundlich isotherms. The results obtained showed that adsorption occurs on a monolayer and that external transport of the solute from solution to adsorbent was the rate-determining mechanism. A maximum adsorption capacity of 2.06 × 10 −4 mol Fe g −1 was obtained under established experimental conditions (0.5 mol L −1 SCN − and 0.005 mol L −1 HCl). Sequential extraction experiments were carried out by changing PUF in time intervals previously defined (5, 20, and 40 min), and the obtained results showed that it is possible to remove around 95% of the Fe(III) in solution through five consecutive extractions of 5 min with five 200 mg PUF cylinders.

Gallium trace on-line preconcentration/separation and determination using a polyurethane foam mini-column and flame atomic absorption spectrometry.: Application in aluminum alloys, natural waters and urine

A sensitive and selective flow injection time-based method for on-line preconcentration/separation and determination of gallium by flame atomic absorption spectrometry at trace levels was developed. The on-line formed gallium chloride complex is sorbed onto a polyether-type polyurethane foam mini-column, followed by on-line quantitative elution with isobutyl methyl ketone and direct introduction into the flame pneumatic nebulizer of the atomic absorption spectrometer. All chemical and flow variables of the system as well as the possible interferences were studied. The manner of strong HCl solutions propulsion was investigated and established using a combination of two displacement bottles. For 90 s preconcentration time, a sample frequency of 28 h −1, an enhancement factor of 40, a detection limit of 6 μg l −1 and a precision expressed as relative standard deviation ( s r) of 3.3% (at 1.00 mg l −1) were achieved. The calibration curve is linear over the concentration range 0.02–3.00 mg l −1. The accuracy of the developed method was sufficient and evaluated by the analysis of a silicon–aluminum alloy standard reference material. Finally, it was successfully applied to gallium determination in commercial aluminum alloys, natural waters and urine.

On-line solid phase extraction with polyurethane foam: trace level spectrophotometric determination of iron in natural waters and biological materials.

This paper reports the development of a simple and accurate on-line procedure for preconcentration and determination of dissolved iron in waters and biological materials using unloaded polyether-type polyurethane foam as solid extractor. In the developed flow injection system, the analyte was preconcentrated from acidic aqueous medium as iron-thiocyanate complex with post-elution with ascorbic acid solution and spectrophotometric measurement with 1,10-phenanthroline as colorimetric reagent. In order to improve the performance of the system several chemical and flow variables were investigated as well as the effect caused by the presence of possible interferents. The method was validated by the analysis of two certified reference materials. Application of the methodology was carried out by the determination of dissolved iron content in eight natural water samples with different characteristics. The results were compared with those obtained by electrothermal atomic absorption spectrometry (ETAAS) and no statistical difference was observed. The detection limit was 0.75 microgram l-1 and the RSD was 1.2% for 2 min preconcentration time. At this condition, a productivity of 20 samples h-1 was achieved. Increasing the preconcentration time up to 3 min, a detection limit of 0.45 microgram l-1, an RSD of 1.5% and an analytical throughput of 15 h-1 were verified.

Flow injection determination of cobalt after its sorption onto polyurethane foam loaded with 2-(2-thiazolylazo)- p-cresol (TAC)

This paper reports the development of a new methodology for determination of cobalt in water samples by using a flow injection system with loaded PUF as solid phase to preconcentrate analytes. Procedure is based on on-line retention of Co(III) ions (generated in alkaline medium by Co(II) oxidation) in a minicolumn packed with a polyether type polyurethane foam loaded with TAC (2-(2-thiazolylazo)- p-cresol) and elution with 2 mol l −1 HCl directly to the flame atomic absorption spectrometer nebulizer. Several chemical and flow variables that could affect the performance of this system were investigated as well as the possible interferents. For 2 min of preconcentration time (10.0 ml of sample volume) the system achieved a detection limit 3.2 μg l −1, a R.S.D. 5% at 20 μg l −1 and an analytical throughput 24 h −1. Whereas for 3 min of preconcentration time (15.0 ml of sample volume) a detection limit 2.4 μg l −1, a R.S.D. under 8% at 10 μg l −1 and a sampling frequency 17 h −1 were reported.

Spectrophotometric determination of carbaryl by on-line elution after its preconcentration onto polyurethane foam

An analytical methodology has been developed for the UV-spectrophotometric determination of carbaryl in waters after its preconcentration onto a polyether type polyurethane foam followed by on-line elution. The aforementioned strategy offers an easy way for in-field sampling and to improve the analytical sensitivity. Several chemical and flow variables (mass of sorbent, sample flow rate, sample volume and carrier flow rate) were studied to ensure the best performance of the system. Recovery studies, carried out on natural water samples spiked with known amounts of carbaryl at concentration levels between 250 and 500 μg l −1, provided recovery percentages between 94 and 105%. A detection limit of 12 μg l −1 was achieved and a variation coefficient of 3.4% was obtained at 0.50 μg ml −1.

Retention of carbaryl by polyether type polyurethane foam: a critical study

This paper reports the retention of carbaryl by polyether type polyurethane foam in a dynamic mode. Several parameters that can influence the extraction of carbaryl from water samples were investigated such as concentration of carbaryl, mass of sorbent in the column, sample pH, saline concentration, solvent washing and sample flow rate. Results show that it is possible to achieve quantitative extractions when the sample flow rate is maintained up to 2.4 mL min−1, a mass of foam of 300 mg and a sample volume of 30 mL in 0.5 NaCl are employed. They also indicate that there is an ether-like solvent extraction mechanism controlling the sorption of the substance by the foam. Some recovery tests were performed in spiked water samples and recoveries between 93 and 102% were obtained.

Recovery of Gallium from Aluminum Industry Residues

A procedure is proposed to recover gallium from flue dust aluminum residues produced in plants by using solid-phase extraction with a commercial polyether-type polyurethane foam (PUF). Gallium can be separated from high concentrations of aluminum, iron, nickel, titanium, vanadium, copper, zinc, sulfate, fluoride, and chloride by extraction with PUF from 3 M sulfuric acid and 3 M sodium chloride concentration medium with at least a 92% efficiency. Gallium backextraction was fast and quantitative with ethanol solution. In all recovery steps commercial-grade reagents could be used, including tap water. The recovered gallium was precipitated with sodium hydroxide solution, purified by dissolution and precipitation, calcinated, and the final oxide was 98.6% pure.

Simple and rapid extraction of polycyclic aromatic hydrocarbons collected on polyurethane foam adsorbent

A single-pass flow through extraction (FTE) method for polycyclic aromatic hydrocarbons (PAHs) that have been collected on poly-ether type polyurethane foam (PUF) is described and demonstrated. The method is based on the principles of trace enrichment and solid-phase extraction where the analyte of interest is collected or concentrated on the expanded PUF matrix. Following collection, the PUF is compressed to reduce the solvent requirement and a single-pass gravity fed mobile-phase extraction is used to remove the analyte. Two extraction mobile phases were tested (dichloromethane, DCM and a 10% (V:V) mixture of acetone in hexane, AH). We obtained quantitative recoveries of 18 PAHs from 115 cm 3 PUF plugs with less than 4 ml of DCM or 6 ml of AH. Average standard recoveries of 18 spiked PAHs were 97% and 104% for the DCM and the AH extractions, respectively. The semi-volatile fraction of PAHs in an environmental sample of a complex mixture (diesel exhaust) were also quantitatively extracted using the FTE method. Finally, the FTE method was used to extract samples collected from an exposure chamber that was designed to measure the transfer of semi-volatile atmospheric pollutants into vegetation. Total variance reported as percent relative standard deviation in the measured steady-state atmospheric concentrations of pyrene, fluoranthene, anthracene and phenanthrene were 3.4, 10.5, 8.5 and 4.4%, respectively, thus demonstrating the excellent precision of the method. The FTE method is simple, fast and effective for extracting PAH that has been collected on PUF adsorbent.

Extraction of azo dyes by polyurethane foam

The extraction of 12 closely related mono-azo dyes by polyester and polyether-type polyurethane foams was studied to gain more information regarding the mechanism of the extraction of organic compounds. The effects on extraction of solution pH, dye concentration and salt concentration were investigated. It was found that the extraction of the dyes involved a neutral zwitterionic species and is highly dependent on the parameters studied. The dependency of the extraction on these parameters can be explained in a manner consistent with solvent extraction; however, the dual-mode sorption mechanism seems a more likely model. This mechanism involves both absorption related to solvent extraction, and an added component for surface adsorption. While the dual-mode sorption model explains the observed extraction behaviour, the data suggest that surface adsorption plays a much larger role than previously considered.

Direct determination of gallium on polyurethane foam by X-ray fluorescence

Gallium chloride is easily extracted from 6 M HCl by comminuted polyether-type polyurethane foam. After the extraction step, the gallium absorbed by the PU foam can be quantitatively determined by X-ray fluorescence. A procedure for the direct determination of gallium absorbed by PU foam by XRFS is thus described. Gallium is determined at levels as low as 60 ng/ml ( C L), with a calibration sensitivity of 424 cps ml/μg, within a linear range 0.1–2.30 μg/ml. The procedure investigated was successfully applied to determination of gallium in aluminum alloys, bauxite and industrial residue samples.

Unloaded polyether type polyurethane foams as solid extractants for trace elements

Polyether type polyurethane foams (PU) are regular stacks of solid quasi-spherical membranes produced by the reaction of polyisocyanates with polyols of polyether nature in the presence of a catalyst and a blowing agent. Contrary to conventional membrane separations, where a solid membrane is merely a differentially separating agent, or a transport medium, PU foams, apart from separation and preconcentration, also retain, i.e., sorb the species on, or in the membranes. Therefore, PU foam membranes can be considered to act as true sorbents. The membrane properties of PU foam sorbents offer unique advantages over conventional bulk type granular sorbents in rapid, versatile and effective separations and preconcentrations of different compounds from fluid samples. Unloaded PU foam sorbents have received considerable attention in the separation of different trace inorganic species.

Sorption of organic dyes by polyurethane foam

The sorption of fifty-nine organic dyes, indicators and stains by polyester and polyether-type polyurethane foams was investigated by use of aqueous solutions and powdered foam material. Comparisons were made with sorption from 50% methanol solutions for some dyes and also with solvent extractions done with diethyl ether or ethyl acetate for several dyes. The R f values for the dyes run on cellulose TLC plates in water or a mixed solvent mobile phase were compared to the distribution coefficients with polyurethane foam. The relationship between the structure of the test substances and their sorption is discussed.

Extraction of zirconium and hafnium thiocyanate with polyurethane foam

Conditions for the extraction of zirconium and hafnium thiocyanate by polyether-type polyurethane foam were studied in detail. The composition of the extractable species was found to be dependent on both the thiocyanate and metal-ion concentrations. The extraction efficiency for zirconium and hafnium depended on the size of the counter-cation as well as on the type of anion.