Unloaded Polyurethane Foam Research Articles

Thermo‐mechanical property enhancement of rigid polyurethane foam using silica and alumina as hybrid fillers over single filler

AbstractSilica and alumina particles were loaded in the rigid polyurethane foam composite as hybrid fillers. After the successful addition of silica and alumina as fillers, various properties of the foam composite were enhanced up to a particular weight percentage (7.5 wt% of silica and alumina each) with respect to alumina loaded foams. Hard urea domains are well distributed in the urethane matrix which indicates the absence of the peak representing H‐bonded urea in the Fourier‐transform infrared spectroscopy results. The addition of hybrid fillers into the rigid polyurethane foam matrix improved the compressive strength of the foam composite by 14% in comparison to alumina loaded foams due to the synergistic effect of the hybrid fillers. The foam composite at 7.5 wt% loading of hybrid fillers was successful in decreasing the thermal conductivity by 9% with respect to the thermal conductivity of the unloaded foam. There was a reduction in the gross calorific value up to 7% in the hybrid filler loaded foam composite when compared with that of the alumina loaded composite. Hence, hybrid fillers should be added to enhance the composite's properties by a greater extent.Highlights From the compressive test results, an increase in the compressive strength up to 14% was observed in the samples loaded with hybrid fillers with respect to the samples loaded with alumina due to the synergistic effects of the two fillers. For the foam composite loaded with alumina, the gross calorific value decreased up to 6% when compared to the unloaded foam. The gross calorific value decreased by a further 7% when hybrid fillers were added to the polyurethane foam composite with respect to the alumina loaded foam composite. The foam composite loaded with 7.5 weight % of hybrid fillers had lower values of thermal conductivity when compared with that of the unloaded polyurethane foam. We propose the addition of both alumina and silica as hybrid filler particles as they enhanced the various properties of the polyurethane foam composite to a greater extent than the addition of alumina particles as a single filler and have potential to replace unloaded polyurethane foams in different applications.

Microwave-Assisted Digestion of Polyurethane Foam as an Alternative to Elution: Solid Phase Extraction of Cd(II) and Pb(II) for Their Determination in Swimming Pool Waters.

In this work, a separation/preconcentration method is proposed for the determination of Cd(II) and Pb(II) in swimming pool waters, using ammonium pyrrolidine dithiocarbamate (APDC) as a complexing agent and unloaded polyurethane foam (PUF) as a sorbent. The proposed method was optimized, and the defined optimal conditions were a pH of 7, 30 min of shaking time, 400 mg of PUF, and 0.5% (m/v) of the APDC solution. The release of Cd(II) and Pb(II) from the solid phase was achieved through the total digestion of PUF using a microwave-assisted acid approach with a 10.5 mol·L-1 HNO3 solution. The methodology was applied to four samples of swimming pool water for the determination of Cd(II) and Pb(II) using graphite furnace atomic absorption spectrometry (GF AAS). The limits of detection and quantification obtained were 0.02 and 0.06 μg·L-1 for Cd(II) and 0.5 e 1.8 μg·L-1 for Pb(II), respectively. We analyzed four samples of swimming pool waters, finding Cd concentrations between 0.22 and 1.37 μg·L-1. On the other hand, only one sample presented Pb concentration above the limit of quantification (11.4 μg·L-1). Recovery tests were performed by spiking the samples with known concentrations of the analytes, and recovery percentages between 82% and 105% were obtained.

Determination of Selenium in Biological Samples by Flame Atomic Absorption Spectrometry after Preconcentration on Modified Polyurethane Foam

An analytical method has been proposed based on the separation and determination of selenium(IV) ion using polyurethane foam as a solid sorbent coated with ammonium pyrrolidine dithiocarbamate (APDC). Different factors including the pH of sample solution, time of extraction, volume of sample, and amount of the loaded and unloaded polyurethane foam were examined and a preconcentration factor of 5 was obtained. The interference effects of some additional salts in the solution such as NaCl, FeCl3, BaCl2, CH3COONa and Na2SO4 have been investigated. The improved limit of detection (LOD) for the method is 0.064 mg/L. The improved LOD is much lower than the LOD of FAAS and approaching the LOD of GFAAS. The new developed procedure SPE-FAAS has been Found to be successful in separating the complex matrices (human hair, bovine liver, pork liver, bovine muscle) and pre-concentrating selenium ion from real blood sample. The developed method for solid-liquid extraction is convenient, simple, sensitive and of low costs.

Development of an Analytical Method for Trace Gold in Aqueous Solution Using Polyurethane Foam Sorbents: Kinetic and Thermodynamic Characteristic of Gold(III) Sorption

The kinetic parameters of gold(III) sorption by unloaded polyurethane foams (PUFs) and PUFs impregnated with some onium cations e.g. tetramethylammonium perchlorate (TMA(+)ClO(4)(-)), tetrabutylammonium iodide (TBA(+)I(-)), and tetraheptylammonium bromide (THA(+)Br(-)), have been determined. The retention steps were found to be fast, reached equilibrium in a few minutes and followed a first-order rate equation with an overall rate constant, k, of 0.0076 and 0.007 min(-1), respectively. The thermodynamic characteristics of gold(III) retention by the unloaded PUFs and THA(+)Br(-) immobilized PUFs have been critically studied. The negative values of DeltaH and DeltaS are interpreted as the exothermic and spontaneous reaction of gold(III) sorption onto unloaded PUFs and foams impregnated with THA(+)Br(-). The cellular structure of the PUFs sorbent offer unique advantages over conventional bulk-type sorbents in the rapid, versatile effective separation and/or preconcentration of gold ions.

Sorption characteristics and chromatographic separation of gold (I and III) from silver and base metal ions using polyurethane foams

The influence of different parameters on the sorption profiles of trace and ultra traces of gold (I) species from the aqueous cyanide media onto the solid sorbents ion exchange polyurethane foams (IEPUFs) and commercial unloaded polyurethane foams (PUFs) based polyether type has been investigated. The retention of gold (I) species onto the investigated solid sorbents followed a first-order rate equation with an overall rate constant k in the range 2.2–2.8 ± 0.2 s −1. The sorption data of gold (I) followed Freundlich and Langmuir isotherm models. Thus, the a dual-mode of sorption mechanism involving absorption related to “weak base anion exchanger” and an added component for “surface adsorption” seems the most likely proposed dual mechanism for retention profile of gold (I) by the IEPUFs and PUFs solid sorbents. The capacity of the IEPUFs and PUFs towards gold (I) sorption calculated from the sorption isotherms was found to be 11.21 ± 1.8 and 5.29 ± 0.9 mg g −1, respectively. The chromatographic separation of the spiked inorganic gold (I) from de ionized water at concentrations 5–15 μg mL −1 onto the developed IEPUFs and PUFs packed columns at 10 mL min −1 flow rate was successfully achieved. The retained gold (I) species were then recovered quantitatively from the IEPUFs (98.4 ± 2.4%, n = 5) and PUFs (95.4 ± 3.4%, n = 5) packed columns using perchloric acid (60 mL, 1.0 mol L −1) as a proper eluating agent. Thiourea (1.0 mol L −1)–H 2SO 4 (0.1 mol L −1) system was also used as eluating agent for the recovery of gold (I) from IEPUFS (95.4 ± 5.4%, n = 3) and also PUFs (93.4 ± 4.4%, n = 3) packed columns. The performance of the IEPUFs and PUFs packed columns in terms of the height equivalent to the theoretical plates (HETP), number of plates ( N), and critical and breakthrough capacities towards gold (I) species were evaluated. The developed IEPUFs packed column was applied successfully for complete retention and recovery (98.5 ± 2.7) of gold (III) species spiked onto tap- and industrial wastewater samples at <10 μg Au mL −1 after reduction to gold (I). The IEPUFs packed column was applied satisfactorily for complete retention and recovery (98.5 ± 2.7) of total inorganic gold (I) and/or gold (III) species spiked to tap- and industrial wastewater samples at <10 μg mL −1 gold. Chromatographic separation of gold (I) from silver (I) and base metal ions (Fe, Ni, Cu and Zn) using IEPUFS packed columns was satisfactorily achieved. The proposed method was applied successfully for the pre-concentration and separation from anodic slime and subsequent FAAS determination of analyte with satisfactory results (recoveries >95%, relative standard deviations <4.0%).

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.

Kinetics and retention characteristics of some nitrophenols onto polyurethane foams

The kinetics of sorption of the nitrophenols by the unloaded polyurethane foams (PUFs) were found fast, reached equilibrium in few minutes and followed a first-order rate equation with an overall rate constant k in the range (0.16–0.21)±0.01 min −1. The retention of the tested nitrophenols by the unloaded foams is consistent with the “solvent extraction” mechanism. However, the sorption also followed Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms. The mean free sorption energy of the nitrophenols onto the PUF was found equal to 7.5±0.4 kJ/mol, which reflects physical sorption. Thus, a dual-mode involves both absorption related to solvent extraction and an added component for surface adsorption seems a more likely sorption mechanism model. While a dual-mode sorption model explains the observed retention behavior, the data suggest that, solvent extraction plays a much larger role than the added component for surface adsorption. The sorption and recovery percentages of the nitrophenols from fresh, natural and industrial wastewater by the proposed unloaded foam columns were quantitatively achieved. The height equivalent to theoretical plates (HETP), N, the breakthrough capacity and the critical capacity for the unloaded foam columns were found in the range of (0.8–1.1)±0.6 mm, (94–132)±3, 3.2–4.02 and 1.5–2.67 mg/g, respectively. The method was successfully applied for the retention and recovery of the tested nitrophenols spiked to fresh and industrial wastewaters.

On-line preconcentration and determination of copper, lead and chromium(VI) using unloaded polyurethane foam packed column by flame atomic absorption spectrometry in natural waters and biological samples

A simple, sensitive and low cost, flow injection time-based method was developed for on-line preconcentration and determination of copper, lead and chromium(VI) at sub μg l −1 levels in natural waters and biological samples. At the optimum pH, the on-line formed metal–ammonium pyrrolidine dithiocarbamate (APDC) complexes were sorbed on the unloaded commercial polyurethane foam (PUF), and subsequent eluted quantitatively by isobutylmethylketone and determined by flame atomic absorption spectrometry (FAAS). All chemical, and flow injection variables were optimized for the quantitative preconcentration of each metal and a study of interference level of various ions was also carried out. The system offered improved flexibility, low backpressure and applicability to all the studied metals. At a sample frequency of 36 h −1 and a 60 s preconcentration time, the enhancement factor was 170, 131 and 28, the detection limit was 0.2, 1.8 and 2.0 μg l −1, and the precision, expressed as relative standard deviation ( s r), was 2.8 (at 10 μg l −1), 3.4 (at 50 μg l −1) and 3.6% (at 50 μg l −1) for Cu(II), Pb(II) and Cr(VI), respectively. The accuracy of the developed method was sufficient and evaluated by the analysis of certified reference materials and spiked water samples. Finally, the method was applied to the analysis of environmental samples.

On-line preconcentration system for flame atomic absorption spectrometry using unloaded polyurethane foam: determination of zinc in waters and biological materials

An on-line procedure for the preconcentration and determination of zinc in waters and biological materials was developed. Zinc is preconcentrated from acidic medium (pH 3.0) as its thiocyanate complex onto a polyurethane foam mini-column placed in the loop of a four-way valve. The elution step is performed with a stream of 30% acetone in 2% HNO3 and the zinc displaced is introduced directly into the nebuliser of a flame atomic absorption spectrometer. The system was operated under two different preconcentration times since the concentration of zinc in the two types of samples was different. For biological samples, 1 min was used and a detection limit of 3.0 µg L–1 was achieved with a throughput of 40 samples per hour. At a concentration of 20 µg L–1, an RSD of 2.5% was obtained. For the determination of zinc in natural water, a preconcentration time of 3 min was employed and a detection limit of 0.85 µg L–1 was obtained. In this case, the system was slower with a throughput of 17 samples per hour. The RSD at 10 µg L–1 was 6.0%. The continuous flow system was applied to the analysis of several biological reference materials and natural water samples.

Adsorption syntax of Au(III) on unloaded polyurethane foam

The nature of adsorption behavior of Au(III) on polyurethane (PUR) foam was studied in 0.2M HCl aqueous solution. The effect of shaking time and amount of adsorbent were optimized for 3.16·10−5M solution of Au(III) in 0.2M HCl. The classical Freundlich and Langmuir adsorption isotherms have been employed successfully. The Freundlich parameters 1/n and adsorption capacityK are 0.488±0.016 and (1.40±0.22)·10−2 mol·g−1, respectively. The Langmuir constants of saturation capacityM and binding energyb are (1.66±0.08)·10−4mol·g−1 and 40294±2947 l·g−1, respectively, indicating the monolayer chemical sorption. The mean free energy (E) of adsorption of Au(III) on PUR foam has been evaluated using D-R isotherm and found to be 11.5±0.16 kJ·mol−1 reflecting the ion exchange type of chemical adsorption. The effect of temperature on the adsorption has also been studied. the isosteric heat of adsorption was found to be 44.03±1.66 kJ·mol−1. The thermodynamic parameters of ΔG, ΔH, ΔS and equilibrium constantKc have been calculated. The negative values of ΔG, ΔH and ΔS support that the adsorption of Au(III) on PUR foam is spontaneous, exothermic and of ion exchange chemisorption. The nature of the Au(III) species sorbed on PUR foam have been discussed.

Preconcentration of strontium on polyurethane foams

A method for the preconcenration of strontium on loaded and unloaded polyurethane foams is described. Parameters affecting the extraction of metal ion, such as pH, reagent concentration and background medium have been investigated. The method can be applied to preconcentrate strontium from aqueous samples.

Removal of organic pollutants from aqueous solution : V. Comparative study of the extraction, recovery and chromatographic separation of some organic insectisides using unloaded polyurethane foam columns

The concentration of dissolved insecticides in aqueous media was determined by chromatographic separation on polyurethane foam columns. The results of preliminary screening tests on the removal of insecticides by the unloaded polyurethane foam indicated that a reasonable percentage of the insecticides was retained on the foam. Therefore attempts were made to extract these compounds from aqueous media using foam columns. Various parameters affecting the retention and separation of these compounds were studied, including temperature, flow-rate, pH, insecticide concentration, shaking time, sample volume and eluting solvent. The complete separation and quantitative recovery of these compounds from the foam with acetone in a Soxhlet extractor were achieved. The method can be used to preconcentrate insecticides in tap water and modified to determine dissolved insecticides in industrial and natural waters. Polyurethane foam has a good capacity for use when large volume samples need to be handled and is an inexpensive sorbent compared to other known solid sorbents.

Unloaded polyurethane foams as solid extractants for some metal thiocyanate complexes from aqueous solution

Zinc, mercury, and indium are quantitatively extracted with unloaded polyurethane foams from aqueous thiocyanate solution. The unloaded polyester type foam will extract the thiocyanate complexes of the three metals as well as the polyether type. The extraction is strongly dependent on the thiocyanate concentration and is quantitative over a wide pH range.

Reagent-loaded and unloaded polyurethane foam as preconcentration matrix in neutron activation analysis

Loaded and unloaded polyurethane foams were examined as a preconcentration matrix in combination with neutron activation analysis. The structure of the foamed polymer is not damaged by short irradiation periods. However the foam skeleton degraded after irradiations for one hour or longer in a neutron flux of 3·1013 n ·cm−2·s−1. The presence of tin as a major impurity in the polyether-type foam has been detected. This may affect the sensitivity of determination of the relatively short lived isotopes of the elements collected on the foam. On the other hand the polyester-type foam was found to contain only very low amounts of tin. Antimony, indium, gold and mercury collected on the foams were determined with reasonable accuracy.

The recovery of gold from thiourea solutions with open-cell polyurethane foams

The recovery of the gold-thiourea complex from aqueous solutions with TBP-loaded and unloaded polyurethane foams was investigated in batch experiments. The rates of adsorption of the gold complex on various types of loaded and unloaded foams were studied in detail and compared with the rate of adsorption on active carbon. Loaded and unloaded polyurethane foams of the polyether or polyester type behaved similarly to active carbon. The adsorption capacity of the foams was lower than that of active carbon but the use of foam simplifies the procedure by eliminating the filtration process which is necessary with carbon.