Polyurethane Foam Samples Research Articles

DEPLETION OF 1-MCP BY 'NON-TARGET' MATERIALS DURING STORAGE

We tested the sorptive capacity of a number of non-target materials found in apple (Malus × domestica Borkh.) storage rooms on their capacity to remove 1-MCP from the storage atmosphere and thereby compete with the fruit for the active compound. Further, we evaluated the impact of temperature and moisture. Non-target materials included bin construction materials [high density polyethylene (HDPE), polypropylene (PP), weathered oak, non-weathered oak (Quercus sp.), plywood, and cardboard] and wall construction materials (polyurethane foam and cellulose-based fire retardant). Each piece had an external surface area of 76.9 cm 2 . We placed our 'non-target' materials in 1-L mason jars and added 1-MCP gas to the headspace at an initial concentration of approximately 30 μl·L -1 . Gas concentrations were measured after 2, 4, 6, 8, 10 and 24 h. The concentration of 1-MCP in empty jars was stable for the 24-h holding period. Little to no sorption was detected in jars containing dry samples of HDPE, PP, cardboard, polyurethane foam, or fire retardant. Inclusion of plywood, non-weathered oak, and weathered oak lead to a loss of 10, 55, and 75 percent of the 1-MCP after 24 hours. Using dampened materials, no sorption resulted from the inclusion of HDPE, PP, polyurethane foam, or the fire retardant. However, the rate of sorption of 1-MCP by dampened cardboard, plywood, weathered oak, and non-weathered oak increased markedly, resulting in a depletion of approximately 98, 70, 98 and 98 percent, respectively. For oak bin material, the rate of sorption was not impacted by temperature, and increasing the surface area by approximately 100% only marginally increased the rate of sorption. When dampened oak bin material was included with apple fruit in a proportion similar to that found in fruit storage, 80% depletion occurred in 5 hours compared to approximately 24 hours for fruit alone. The data suggest that in situations where 1-MCP levels can be compromised by wooden and cardboard bin and bin liner materials, but not by plastic bin materials or typical wall construction.

Effects of Starting Material and Reaction Temperature on the Morphology and Physical Properties of Polyurethane Foams

Polyurethane foams (PUFs) were prepared by mixing poly (ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and isocyanates in the ratio of 1:1.03 in the presence of additives such as catalyst, blowing agent and surfactant. The effects of types of starting material in PUF formulation on cell morphology and properties were investigated using scanning electron microscopy (SEM). The results indicated that starting material highly affected the morphology of PUF cells. Process parameters such as concentration of starting material and reaction temperature were investigated using SEM, foam density and capacity of water absorption. It was found that foam density depends on the cell size. While, the capacity of water absorption is depends on the percentage of the open cells and cell size. PUF samples have cell size between 200 to 600 μm, density in the range of 0.03 to 0.06 g cm-3, percentage of open cell at 25 to 60% and capacity of water absorption between 6 to 30%.

Comparison of conventional cervical cytological sampling (Ayre¿s spatula, endocervical brush) and the PapCone® as seen by scanning electron microscopy

Introduction Efforts to improve Pap smear performance have recently focused on reducing the number of false negative smears, i.e. cases in which premalignant or malignant cells have been misdiagnosed as normal. Considering that the basis for a good quality cervical smear is a correct sampling method, a variety of technologies or clinical strategies have been proposed to improve Pap testing including various devices for collecting cytological cervical samples, such as the PapCone® (Otto Bock, Duderstadt, Germany). The PapCone® is a cone-shaped polyurethane (foam) sampling device designed by the University Hospital Gottingen (Germany) to obtain simultaneously cells from the ectoand the endocervix. It has the properties of a soft brush and at the same time it acts as a soft spatula by being pressed to the ectocervix. Aim We evaluated the ultrastructure of human cervical cells by means of scanning electron microscopy (SEM), comparing the samples obtained with the Papcone® with the traditional wooden Ayre’s spatula (S) and the endocervical cytobrush (C). Materials and methods Twenty-two adult fertile (under 40 y), primiparous women were submitted to traditional Pap test (by S and/or C) and to PapCone® sampling 3 months after, with the related informed consent. Ultrastructural features of the 3 devices were analysed by SEM before and after sampling. Specimens were fixed in 2.5% glutaraldehyde in 0.1M PBS, stored at 4°C, postfixed in 1% osmium tetroxide, and dehydrated in increasing ethanol concentrations. Specimens were critical-point dried with carbon dioxide, mounted on aluminum stubs, coated with platinum, and observed with a Hitachi S-4000 FE-SEM (20 kV). Results SEM allowed to recognize large and flattened ectocervical cells with microplicae from cylindrical and smaller endocervical cells. However, S and C appeared less useful in case of abundant presence of mucus. The PapCone® surface was porous, partly occluded by membranes, and divided by trabecles lodging sampled cells. S showed a finely regular surface, sometimes showing wooden chips, and cells appearing clustered in usually overlapping groups. C often entrapped cells at or among the bristles, wherein red cells were usually noted. PapCone® showed lower bleeding and less overlapping cell layers in comparison with S and C. Conclusion PapCone® is a good and low traumatic method for sampling cervical cells, that can be useful especially in case of flogosis or cervical bleeding.

Mitigating Transverse Joint Faulting in Jointed Concrete Pavement with Polyurethane Foam

A case study was conducted to assess the effectiveness of reducing transverse faulting on jointed concrete pavement with polyurethane foam (PF) on a principal arterial roadway with an average daily traffic of 15,800 with 20% trucks. The PF fault correction process entailed reducing faults to approximately 0.25 in. by saw-cutting the full depth through the joints and lifting the slabs with PF. A sampling plan was established: the entire project was measured for faulting and roughness by a high-speed profiler before and after the PF fault correction process. Three test sections with 10 slabs each were assessed with a falling weight deflectometer, ARRB walking profiler, and manual fault measurements. Seventeen cores were taken at various locations to obtain in-place PF samples. Statistical hypothesis testing was conducted to compare the before-and-after treatment effect of the PF process. Approximately 18% improvement in ride quality and 79% improvement in fault reduction were realized by the PF fault correction process. Unfortunately, the PF process severely affected load transfer efficiency, with a 43% increase in joints having poor load transfer and a 27% increase in joints needing load transfer improvement. It is reasonable to assume that these problems were caused primarily by saw-cutting through the joints and not by PF itself. Void potentials were increased slightly (8%) by the process.

A study of gas/particle partitioning of SVOCs in the tropical atmosphere of Southeast Asia

Gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were collected at a tropical site in Southeast Asia over 12-h periods during November and December 2006 to determine their gas/particle distributions by analyzing integrated quartz filter and polyurethane foam samples. Gas/particle partitioning coefficients, K p, were calculated, and their relationship with the subcooled liquid vapor pressure p L o for both PAHs and PCBs was investigated. The regressions of log K p vs. log p L o for most of samples gave high correlations for both PAHs and PCBs and the slopes were statistically shallower than −1, but they were relatively steeper than those obtained in temperate zones of the Northern Hemisphere. By comparison, the particle-bound fraction of low molecular weight (LMW) PAHs was underestimated by both Junge-Pankow adsorption and K OA (octanol–air partition coefficient) absorption models, while the predicted values agree relatively better with those observed ones for high molecular weight (HMW) PAHs. In addition, the adsorption onto the soot phase (elemental carbon) predicted accurately the gas/particle partitioning of PAHs, especially for LMW compounds. On the other hand, the K OA absorption model using the measured organic matter fraction ( f OM) value fitted the PCB data much better than the adsorption model did, indicating the sorption of nonpolar compounds to aerosols might be dominated by absorption into organic matters in this area.

Influence of fireproof coatings on electrical properties of conducting materials and related constructions

The experimental results on the design of fireproof coatings based on paint and varnish silicate composites and starch solutions oxidized by oxygen are reported. The water glass modified by ethyl silicate is used as a silicate coating. These coatings on paper samples and the surface of other porous materials, such as fabrics and polyurethane foam samples, are foamed in contact with a flame and form a layer that prevents propagation of the burning front. It is revealed that the treatment of conducting materials with fireproof composites does not lead to a substantial change in their surface resistance in the microwave range.

Effects of silicone surfactant on the cell size and thermal conductivity of rigid polyurethane foams by environmentally friendly blowing agents

Rigid polyurethane foams (PUF)s were synthesized with environmentally friendly blowing agents such as a cyclopentane/distilled water (10.0/1.0, pphp) mixture and distilled water only for four different silicone surfactants having different silicone/polyether ratios. An attempt was made to reduce the thermal conductivities of the PUF samples by varying the concentration and the silicone/polyether ratio of the various silicone surfactants. The scanning electron microscopy (SEM) results indicated an optimum concentration of the silicone surfactant of about 1.5 to 2.5 phpp for various surfactants to reduce the cell size and lower the thermal conductivity. The silicone surfactant having a higher silicone/polymer ratio showed a smaller cell size and, therefore, demonstrated the lower thermal conductivity of the PUF samples. From the relation between the thermal conductivity and the cell size of the PUF samples, the smaller cell size improved the thermal insulation property of the rigid PUF for both the PUF samples blown by the cyclopentane/distilled water (10.0/1.0, pphp) mixture and distilled water only. If the blowing agent is fixed, then the cell size is an important factor to decrease the thermal conductivity of the PUF samples. These results indicated that rigid PUF samples having lower thermal conductivity can be obtained by choosing a silicone surfactant containing a higher silicone/polyether ratio, as well as an optimum content of the surfactant.

Observations on persistent organic pollutants in indoor and outdoor air using passive polyurethane foam samplers

Air quality data of persistent organic pollutants (POPs) indoors and outdoors are sparse or lacking in several parts of the world, often hampered by the cost and inconvenience of active sampling techniques. Cheap and easy passive air sampling techniques are therefore helpful for reconnaissance surveys. As a part of the Megacity Initiative: Local and Global Research Observations (MILAGRO) project in Mexico City Metropolitan Area in 2006, a range of POPs (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs)) were analyzed in polyurethane foam (PUF) disks used as passive samplers in indoor and outdoor air. Results were compared to those from samplers deployed simultaneously in Gothenburg (Sweden) and Lancaster (United Kingdom). Using sampling rates suggested in the literature, the sums of 13 PAHs in the different sites were estimated to be 6.1–180 ng m −3, with phenanthrene as the predominant compound. Indoor PAH levels tended to be higher in Gothenburg and outdoor levels higher in Mexico City. The sum of PCBs ranged 59–2100 ng m −3, and seemed to be highest indoors in Gothenburg and Lancaster. PBDE levels (sum of seven) ranged 0.68–620 ng m −3, with the highest levels found in some indoor locations. OCPs (i.e. DDTs, HCHs, and chlordanes) were widely dispersed both outdoors and indoors at all three studied areas. In Gothenburg all POPs tended to be higher indoors than outdoors, while indoor and outdoor levels in Mexico City were similar. This could be due to the influence of indoor and outdoor sources, air exchange rates, and lifestyle factors. The study demonstrates how passive samplers can provide quick and cheap reconnaissance data simultaneously at many locations which can shed light on sources and other factors influencing POP levels in air, especially for the gaseous fractions.

Carbonyl Emissions from Gasoline and Diesel Motor Vehicles

Carbonyls from gasoline-powered light-duty vehicles (LDVs) and heavy-duty diesel-powered vehicles (HDDVs) operated on chassis dynamometers were measured by use of an annular denuder-quartz filter-polyurethane foam sampler with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine derivatization and chromatography-mass spectrometry analyses. Two internal standards were utilized based on carbonyl recovery: 4-fluorobenzaldehyde for < C8 carbonyls and 6-fluoro-4-chromanone for > or = C8 compounds. Gas- and particle-phase emissions for 39 aliphatic and 20 aromatic carbonyls ranged from 0.1 to 2000 microg/L of fuel for LDVs and from 1.8 to 27 000 microg/L of fuel for HDDVs. Gas-phase species accounted for 81-95% of the total carbonyls from LDVs and 86-88% from HDDVs. Particulate carbonyls emitted from a HDDV under realistic driving conditions were similar to concentrations measured in a diesel particulate matter (PM) standard reference material. Carbonyls accounted for 19% of particulate organic carbon (POC) emissions from low-emission LDVs and 37% of POC emissions from three-way catalyst-equipped LDVs. This identifies carbonyls as one of the largest classes of compounds in LDV PM emissions. The carbonyl fraction of HDDV POC was lower, 3.3-3.9% depending upon operational conditions. Partitioning analysis indicates the carbonyls had not achieved equilibrium between the gas and particle phases under the dilution factors of 126-584 used in the present study.

An Experimental Investigation into the Acoustic Characteristics of Fluid-filled Porous Structures—A Simplified Model of the Human Skull Cancellous Structure

In nature, shape and structure evolve from the struggle for better performance. Often, biological structures combine multiple beneficial properties, making research into mimicking them very complex. Presented here is a summary of observations from a series of experiments performed on a material that closely resembles the human skull bone’s cancellous structure under acoustic loads. Transmission loss through flat and curved open-cell polyurethane foam samples is observed using air and water as the two interstitial fluids. Reduction in strength and stiffness caused by porosity can be recovered partially by filling the interstitial pores with a fluid. The test findings demonstrate the influence of the interstitial fluid on the mechanical characteristics of a porous structure in a quantitative manner. It is also demonstrated that the transmission loss does not depend only on the mass per unit area of the structure as predicted by acoustic mass law. Current tests also demonstrate that the transmission loss is more sensitive to the interstitial fluid than the shape and support conditions of the structures. Test observations thus support the concepts of “moisture-sensitivity of biological design” and the “law of hierarchy in natural design”.

Simplification and validation of a large volume polyurethane foam sampler for the analysis of persistent hydrophobic compounds in drinking water

The use of a large volume polyurethane foam (PUF) sampler was validated for rapid extraction of persistent organic pollutants (POPs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), in raw water and treated water from drinking water plants. To validate the recovery of target compounds in the sampling process, a (37)Cl-labeled standard was spiked into the 1st PUF plug prior to filtration. An accelerated solvent extraction method, as a pressurized liquid extractor (PLE), was optimized to extract the PUF plug. For sample preparation, tandem column chromatography (TCC) clean-up was used for rapid analysis. The recoveries of labeled compounds in the analytical method were 80-110% (n = 9). The optimized PUF-PLE-TCC method was applied in the analysis of raw water and treated potable water from seven drinking water plants in South Korea. The sample volume used was between 18 and 102 L for raw water at a flow rate of 0.4-2 L min(-1), 95 and 107 L for treated water at a flow rate of 1.5-2.2 L min(-1). Limit of quantitation (LOQ) was a function of sample volume and it decreased with increasing sample volume. The LOQ of PCDD/Fs in raw waters analyzed by this method was 3-11 times lower than that described using large-size disk-type solid phase extraction (SPE) method. The LOQ of PCDD/F congeners in raw water and treated water were 0.022-3.9 ng L(-1) and 0.018-0.74 ng L(-1), respectively. Octachlorinated dibenzo-p-dioxin (OCDD) was found in some raw water samples, while their concentrations were well below the tentative criterion set by the Japanese Environmental Ministry for drinking water. OCDD was below the LOQ in the treated drinking water.

Atmospheric Polycyclic Aromatic Hydrocarbons in North China: A Winter-Time Study

The contamination and outflow of atmospheric polycyclic aromatic hydrocarbons (PAHs) in the Chinese Northern Plain, a region with a total area of 300 000 km2 and a high PAH emission density, were investigated. Polyurethane foam (PUF) and PM10 samples were collected at 46 sites located in urban, rural (towns or villages), and control (remote mountain) areas in the winter from November 2005 to February 2006. The observed concentrations of atmospheric PAHs were generally higher than those reported for developed countries and southern Chinese cities. It was found that there was no significant difference in air PAH concentrations between the urban and the rural areas (514 +/- 563 ng/m3 and 610 +/- 645 ng/ m3, respectively), while the PAH concentrations at the control sites (57.1 +/- 12.6 ng/m3) were 1 order of magnitude lower than those at the other sites. The primary reason for the similarity in PAH concentrations between urban and rural areas was the fact that the predominant sources of biomass and domestic coal combustion were widely spread over the study area. The partition constants (K(PM10)) of PAHs were significantly correlated to the corresponding values of subcooled liquid-vapor pressure (pL0). However, the regression slopes of log K(PM10) versus log pL0 were much steeper than -1, indicating adsorption dominated over absorption. Three distinct patterns of outflow from the study area were identified by forward trajectory and cluster analysis.

Investigations on the adhesion and interfacial properties of polyurethane foam/thermoplastic materials

AbstractThe adhesion and interfacial properties of polyurethane (PU) foams with thermoplastic (TP) materials were investigated using different techniques. The adhesion performance of PU foam with TP materials was evaluated using the peel test method, and the adhesion durability was checked after different climate treatments. X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements were used to study the surface and interface morphology of PU foam and TP material system. Three types of PU foam samples which differ in their composition and also five commercially available TP blends systems, based on poly(carbonate), poly(styrene‐co‐maleic anhydride), poly(acrylonitrile‐butadiene‐styrene), and silicone acrylate rubber have been used. The slow reacting foam shows the best adhesion properties with all the TP materials. The climate treatments strongly effected the PU foam adhesion durability with poly(carbonate) containing TP materials (70–80% loss in adhesion), but nearly no effect with poly(styrene‐co‐maleic anhydride). The samples with lowered adhesion could be separated by peeling without visible foam residues on the TP surface. AFM, XPS, and surface tension studies have shown that the surface properties of the TP material are still governed by the PU foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 479–488, 2007

Determination of polycyclic aromatic hydrocarbons by gas chromatography — ion trap tandem mass spectrometry and source identifications by methods of diagnostic ratio in the ambient air of Campo Grande, Brazil

Polycyclic aromatic hydrocarbons (PAHs) were measured in samples collected from July to December of 2003, in Campo Grande — MS (Brazil), on three different sites: Ary Coelho Square (AC), Indigenous Nations' Park (NI) and Indubrasil (IB). Particle-bound PAHs were collected on quartz filters and gas-phase PAHs on glass cartridges using a polyurethane foam sampler, respectively. The substances of interest were extracted with a dichloromethane/methanol mixture (9:1 v/v) and subjected to gas chromatography — ion trap tandem mass spectrometry (GC-MS/MS). The concentration values of PAHs in AC varied from 0.03 to 26.28 μg m − 3 and the average value for the sum of 16 PAHs was 51.35 μg m − 3 (range: 2.98–79.91 μg m − 3 ). On the NI site were obtained values of PAHs with concentrations of between 0.02 and 13.84 μg m − 3 and an average value for the total of 16 PAHs was equal to 46.76 μg m − 3 (range: 21.20–85.32 μg m − 3 ). The PAH concentrations obtained in the IB sampling site varied from 0.02 to 16.74 μg m − 3 , with the obtained medium value, for the total of 16 PAHs, equal to 42.79 μg m − 3 (range: 26.53–58.49 μg m − 3 ). Strong positive correlations were found among samples ( r: 0.70 to 0.97, p < 0.005) in 39% of the associations and non-significant correlations were observed among PAHs, except for Flu–Acy, BaA–Phe, Chry–BaA, BkF–Naph, BaP–Phe and BghiP–Naph that were poorly correlated. The statistical analysis of the data showed high similarity among samples on the three sites. The diagnostic ratios indicated the vehicular traffic (diesel and gasoline engines) and the biomass combustion, as major PAH sources in the three sampling sites.

Calibration of a Passive Sampler for Both Gaseous and Particulate Phase Polycyclic Aromatic Hydrocarbons

A novel passive air sampler was designed and tested that individually collects the gaseous and particulate phase polycyclic aromatic hydrocarbons (PAHs) in air. The sampler was calibrated against a conventional active sampler in an indoor environment. A PUF (polyurethane foam) disk and a piece of GFF (glass fiber filter) were installed in a sampling shelter for collecting gaseous and particulate phase PAHs, respectively. The passive samplers were deployed in seven indoor locations for 86 days. Six times during this period, 24-h conventional active sampling was conducted for calibration at an average interval of 17-days. Principle component analysis showed that the measured congener profile compositions were totally different between the gaseous and particulate phase PAHs, but similar between the passive and the active samples. This suggested that gaseous and particulate phase PAHs were primarily trapped by the PUF disk and GFF, respectively. Linear relationships between the passively and the actively measured and log-transformed concentrations were derived for calibration of both gaseous and particulate phase PAHs. The uptake rates of the sampler were 0.10 +/- 0.014 m3/d and 0.007 +/- 0.001 m3/d for gaseous and particulate phase PAHs, respectively. The rates were significantly lower than those reported in the literature using similar PUF samplers, mainly because of the special design with limited air circulation.

The influence of circumferential edge constraint on the acoustical properties of open-cell polyurethane foam samples

In this paper, a three-dimensional Laplace domain finite element model with four-node tetrahedral porous elements is developed and applied for the investigations. Without the incident acoustic field, the exact acoustical properties of a laterally infinite planar foam, which is backed with a rigid plane, are accurately predicted by assuming the circumferential edge constraints as rollers. It is found that the rigidity of the circumferential edge constraint has a profound effect on the predictions. If the circumferential edge constraints are all fixed, the amplitude of the first sound absorption peak is increased, and the peak is moved to a lower frequency as compared with the exact solutions. Measurements obtained by the two-microphone impedance tube method are bounded by the predictions of samples with roller as well as with fixed constraints. They are much closer to that predicted with fixed edge constraints. Upon increasing the diameter-to-thickness ratio of the sample, the influence of the fixed edge constraint is reduced. The measured acoustic results can be the representatives of the laterally infinite planar foam from which the sample was cut only if the roller edge constraint of the sample is managed or the diameter-to-thickness ratio of the sample is increased.

Use of a respirometer to measure oxidation rates of polymeric materials at ambient temperatures

The use of a respirometer is introduced as a novel technique for measuring the oxidation rates of thermally degrading polymers. A dual channel respirometer with fuel cell detectors demonstrates sufficient sensitivity to measure the oxidation rates of low-density polymeric samples at ambient temperatures in a relatively short period of time. Samples of low-density polyurethane foam were aged for various lengths of time in sealed chambers at temperatures ranging from 23 to 110 °C. The extent of oxygen depletion was measured by flushing the chamber with air and comparing the oxygen concentration in the chamber flow to that of a reference flow. Oxidation rates of the 0.1 g/cm 3 polyurethane foam could be measured in less than 600 h of aging time at 23 °C. This corresponds to approximately 2 ppm oxidation by weight. Oxidation rates of the foam were used to calculate acceleration factors over a wide temperature range, including ambient conditions. Acceleration factors for the compressive force of the polyurethane foam were determined at elevated temperatures. Assuming that the aging behavior of compressive force of the foam is correlated to its oxidation rate, it is possible to calculate acceleration factors for the compressive force and predict the performance of the foam at ambient temperatures.

Vapor-Phase and Fine Particulate Matter Concentrations of Polycyclic Aromatic Hydrocarbons Measured during the Winter Months in a Northern Rocky Mountain Urban Airshed

A fine particulate matter (PM2.5) sampling program was conducted in Missoula, MT, to investigate both the particle and vapor phases of PM2.5-associated polycyclic aromatic hydrocarbons (PAHs) found in a northern Rocky Mountain urban airshed. Twenty-four-hour samples were collected during the cold winter months of January through April 2002, when many of the more volatile organic components of PM2.5 were expected to be found in the condensed particle form. To meet analytical detection limits, each of the 12 individual sample days were aggregated into four total filter and polyurethane foam (PUF) samples, respectively, with each aggregate containing 3 sample days. Quartz filter (particle-phase PAHs) and PUF (vapor-phase PAHs) aggregates were analyzed separately for 18 individual PAHs and phenolics by gas chromatography/mass spectrometry. Results showed that 87% of the PM2.5-associated phenolics and PAHs measured in this study were found in the vapor phase. PM2.5-associated gas/particle partition coefficients (Kp,2.5) ranged from 0 for the lighter phenolics and PAHs to ~0.1 for some of the heavier PAHs, such as fluoranthene and pyrene. Calculating Kp,2.5 for the heaviest measured PAHs was not feasible because of low or undetectable concentrations in the vapor phases of these compounds. Phenolics and two-ringed and three-ringed PAHs were found almost exclusively in the vapor phase. Four-ringed PAHs were distributed between the particle and vapor phases, with more mass measured in the vapor phase. Very little five-ringed and higher PAHs were measured from either the filter or PUF sampling medium. These results provide information on both the concentrations and different phases of PM2.5-associated PAHs measured during the winter months in a northern Rocky Mountain urban airshed, when concentrations of PM2.5 are generally at their highest compared with the rest of the year.

Absorption of 1-MCP by Nontarget Materials during Storage

We tested the sorptive capacity of a number of nontarget materials found in apple storage rooms on their capacity to remove 1-MCP from the storage atmosphere and thereby compete with the fruit for the active compound. Furthermore, we evaluated the impact of temperature and moisture. Nontarget materials included bin construction materials [high density polyethylene (HDPE), polypropylene (PP), weathered oak, nonweathered oak, plywood, and cardboard] and wall construction materials (polyurethane foam and cellulose-based fire retardant). Each piece had an external surface area of 76.9 cm2. We placed our “nontarget” materials in 1-L mason jars and added 1-MCP gas to the headspace at an initial concentration of ≈30 μL·L-1. Gas concentrations were measured after 2, 4, 6, 8, 10, and 24 hours. The concentration of 1-MCP in empty jars was stable for the 24-hour holding period. Little to no sorption was detected in jars containing dry samples of HDPE, PP, cardboard, polyurethane foam, or fire retardant. Inclusion of plywood, nonweathered oak, and weathered oak lead to a loss of 10%, 55%, and 75% of the 1-MCP after 24 hours, respectively. Using dampened materials, no sorption resulted from the inclusion of HDPE, PP, polyurethane foam, or the fire retardant. However, the rate of sorption of 1-MCP by dampened cardboard, plywood, weathered oak, and nonweathered oak increased markedly, resulting in a depletion of ≈98%, 70%, 98%, and 98%, respectively. The data suggest that there are situations where 1-MCP levels can be compromised by wooden and cardboard bin and bin liner materials, but not by plastic bin materials or typical wall construction materials.

Transition from forward smoldering to flaming in small polyurethane foam samples

Experimental observations are presented of the effect of flow velocity, oxygen concentration, and a thermal radiant flux on the transition from smoldering to flaming in forward smoldering of small samples of polyurethane foam with a gas/solid interface. The experiments are part of a project studying the transition from smoldering to flaming under conditions encountered in spacecraft facilities, i.e., microgravity, low velocity variable oxygen concentration flows. Because the microgravity experiments are planned for the International Space Station, the foam samples had to be limited in size for safety and launch mass reasons. The feasible sample size is too small for smolder to self-propagate because of heat losses to the surroundings. Thus, the smolder propagation and the transition to flaming had to be assisted by reducing heat losses to the surroundings and increasing the oxygen concentration. The experiments are conducted with small parallelepiped samples vertically placed in a wind tunnel. Three of the sample lateral-sides are maintained at elevated temperature, and the fourth side is exposed to an upward flow and a radiant flux. It is found that decreasing the flow velocity and increasing its oxygen concentration, and/or increasing the radiant flux enhances the transition to flaming and reduces the time delay to transition. Limiting external conditions for the transition to flaming are reported for this experimental configuration. The results show that smolder propagation and transition to flaming can occur in relatively small fuel samples if the external conditions are appropriate. The results also indicate that transition to flaming occurs in the char region left behind by the smolder reaction, and it has the characteristics of a gas-phase ignition induced by the smolder reaction, which acts as the source of both gaseous fuel and heat. A simplified energy balance analysis is able to predict the boundaries between the transition/no transition regions.