Direct Measurement of Energy Barriers on Rough and Heterogeneous Solid Surfaces

The “three-liquid” contact angle approach to the surface free energy components of solids was applied to poly (vinyl fluoride), rough and flattened, with and without flame treatment. Lifshitz-van der Waals (LW), γ ^LW _SL , and acid-base (AB), γ ^LW _SL , components were determined and used to calculate ?δG _SL (W ^adhesion _SL ) for the formation of interfaces of five liquids with polymer. The automated goniometer allowed the determination of the energy barriers, ?δ G? _SL as the advancing liquid moved from pinned configuration to a metastable one. The acid-base component of the barriers was much greater than the LW, and the magnitude of the barriers was only slightly reduced by flattening.     

Development of a Portable Aerosol Collector and Spectrometer (PACS)

This article presents the development of a Portable Aerosol Collector and Spectrometer (PACS), an instrument designed to measure particle number, surface area, and mass concentrations continuously and time-weighted mass concentration by composition from 10?nm to 10?µm. The PACS consists of a six-stage particle size selector, a valve system, a water condensation particle counter to detect number concentrations, and a photometer to detect mass concentrations. The stages of the selector include three impactor and two diffusion stages, which resolve particles by size and collect particles for later chemical analysis. Particle penetration by size was measured through each stage to determine actual collection performance and account for particle losses. The data inversion algorithm uses an adaptive grid-search process with a constrained linear least-square solver to fit a tri-modal (ultrafine, fine, and coarse), log-normal distribution to the input data (number and mass concentration exiting each stage). The measured 50% cutoff diameter of each stage was similar to the design. The pressure drop of each stage was sufficiently low to permit its operation with portable air pumps. Sensitivity studies were conducted to explore the influence of unknown particle density (range from 500 to 3,000?kg/m³) and shape factor (range from 1.0 to 3.0) on algorithm output. Assuming standard density spheres, the aerosol size distributions fit well with a normalized mean bias of ?4.9% to 3.5%, normalized mean error of 3.3% to 27.6%, and R² values of 0.90 to 1.00. The fitted number and mass concentration biases were within ±10% regardless of uncertainties in density and shape. However, fitted surface area concentrations were more likely to be underestimated/overestimated due to the variation in particle density and shape. The PACS represents a novel way to simultaneously assess airborne aerosol composition and concentration by number, surface area, and mass over a wide size range.

Copyright © 2018 American Association for Aerosol Research     

Field Comparison of P-Trak and Condensation Particle Counters

The P-trak ultrafine particle counter is a portable version of a condensation particle counter (CPC). Both instruments detect particle number concentrations in real time but have different detection limits. The P-trak has been widely used for indoor air quality evaluation and aerosol research. However, there is very limited information about the reliability and precision of this instrument and its comparability with other similar instruments. The purpose of this study was to compare a P-trak ultrafine particle counter with a standard CPC and evaluate its applicability to ambient air monitoring.

This study was carried out near the Interstate 405 freeway (I-405) in Los Angeles. Measurements were made at increasing distances from the freeway on both sides at night as well as inside and outside of two 2-bedroom apartments located near the freeway. A CPC and a Scanning Mobility Particle Sizer (SMPS) were collocated with two P-traks and measurement results compared.

In general, higher correlations were observed between P-trak and CPC data for indoor measurements than outdoor. The highest P-trak and CPC correlation ( r ² = 0.9385) was detected inside Apartment 2, which is located farther away from the freeway than Apartment 1. The poorest correlation occurred at 30 m downwind from the freeway. In that case, the P-trak reported about 25% of ultrafine particle concentration that CPC did. A sigmoid (S-shape) function was fitted to observed P-trak to CPC ratios and geometric mean diameters of the corresponding ultrafine particle size distributions. Overall, we concluded the P-trak worked reasonably well when sampled indoor air. However, it has significant limitations in detecting freshly emitted ultrafine particles from vehicles. The P-trak underestimated ultrafine particles especially for particles smaller than its activation size which was found to be approximately 25–30 nm. Caution must be given in interpreting data collected by P-trak monitors near combustion sources.     

A Shelter to Protect a Passive Sampler for Coarse Particulate Matter,PM10 − 2.5

This work designed and tested a shelter to protect a passive sampler for measuring coarse particulate matter, PM _{10 ? 2.5} . The shelter protects the sampler from precipitation and reduces the effects of wind on the deposition of particles to its collection surface. Six shelters were tested in a wind tunnel at three wind speeds: 2, 8, and 24 km hr ^?1 . Shelter performance was expressed as the ratio of PM _{10 ? 2.5} measured with the passive samplers to that measured with a filter-based dichotomous sampler. For most shelters, the PM _{10 ? 2.5} ratio averaged across wind speeds was well above one (2.4 to 8.5) and was generally dependent on wind speed. However, the PM _{10 ? 2.5} ratio for one shelter, the Flat Plates shelter, was 1.04 with substantially less effect on particle deposition from wind speed. Eight week-long field tests were conducted to compare PM _{10 ? 2.5} measured with a passive sampler installed in a Flat Plates shelter to that measured with a collocated filter-based dichotomous sampler. In these tests, the mean PM _{10 ? 2.5} ratio was 1.29. The linear relationship between PM _{10 ? 2.5} measured passively to that measured with the filter-based sampler had a Pearson correlation coefficient of 0.97 and was not significantly affected by the addition of weekly mean wind speed (p = 0.35). Although temperature was significant in this regression model (p = 0.02), it only improved the relationship marginally. The passive sampler in a Flat Plates shelter offers an inexpensive means to assess ambient PM _{10 ? 2.5} without on-site measurement of wind speed.     

Comparison of Predicted and Experimentally Measured Aerosol Deposition Efficiency in BALB/C Mice in a New Nose-Only Exposure System

The use of respiratory tract dosimetry predictions to estimate the desired aerosol exposure concentration required for a specific target deposited dose in animal inhalation studies has been hindered by: (1) a lack of species/strain specific quantitative respiratory tract anatomy; and (2) verification by comparison of calculated and experimentally measured deposited doses. Using recent literature on tracheobronchial and pulmonary respiratory tract anatomy, dosimetry predictions for the Balb/c mouse were compared with deposited doses for 0.5, 1.0, and 2.0 micrometer diameter aerosols in a newly available nose-only exposure system. Spatial and temporal aerosol port to port uniformity of this nose-only exposure system was within ± 10% of the mean. Dosimetry predictions were in agreement with the measured mean deposited doses for the aerosols tested.     

Mathematical Description of Experimentally Determined Charge Distributions of a Unipolar Diffusion Charger

The charge distributions of an improved opposed flow unipolar diffusion charger were measured using a tandem differential mobility analyzer (DMA) set up in a size range of approximately 20–400 nm. The charger is intended to be used in a portable aerosol sizer to measure particle size distributions. The determined charge distributions were represented by lognormal distributions, and a set of equations and coefficients was developed to calculate the charge distributions. These equations can be easily implemented in software for size distribution measurements. The agreement between the mathematically derived and measured charge distributions is very good, with regression coefficients R ² > 0.96. The investigations showed that approximately 55% of 20-nm particles remain uncharged, while up to 25 elementary charges need to be considered for multiple charge correction of 400-nm particles. Comparison with the Fuchs theory delivered satisfying agreement with the measured average charge levels, but charge distributions cannot be described by the Fuchs theory, likely caused by the charger geometry.

Copyright 2012 American Association for Aerosol Research     

A Novel Method for Enhanced Recovery of Lignin from Aqueous Process Streams

Abstract

This study demonstrates that acid precipitation of lignin in the presence of magnetite followed by an applied magnetic field provides a simple method for enhanced lignin recovery from an aqueous stream. The extraction procedure was shown to be sensitive to the relative charge of magnetite and solution pH. Under optimized conditions, 93 wt.% of the softwood lignin from a kraft cooking liquor could be recovered employing this novel separation approach.     

Evaluating The Extent of Bio-Polyester Polymerization in Solid Wood by Thermogravimetric Analysis

In this study, the thermogravimetric analysis (TGA) technique has been applied to determine the extent of in situ polymerization achievable in solid wood on treating with bio-polyester oligomers. Low-molecular-weight oligomers of poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(butylene succinate) (PBS), and poly(butylene adipate) (PBA) were impregnated and then thermally polymerized within solid wood to enhance the physical properties of wood. TGA revealed a similar degree of oligomer polymerization was achieved either with pure oligomers or within the wood structure. The influence of relatively acidic treatments, such as low-molecular-weight PGA oligomers, was observed to lead to degradation of the hemicellulose wood component. Polymerization of PLA and PGA oligomer treatments which penetrate the wood cell wall gave relatively lower wood thermal stability. Treatment and polymerization of lumen filling PBS and PBA oligomers contributed to increased wood thermal stability.     

Particleboard from Cashew Nut Shell Liquid

Cashew nut shell liquid (CNSL) is a cheap agro by-product and a renewable resource, which consists mainly of substituted phenols. A CNSL-based reactive resin was used in this study as binder for particleboards. The resin was prepared by heating a mixture of CNSL, phenol, and hexamethylenetetramine. Properties of the board, viz. water absorption, tensile strength parallel to the surface, tensile strength perpendicular to the surface, and compressibility are determined. The effect of the resin content, P:F ratio of resin, and CNSL:P ratio of resin on the properties of particleboard are also studied. It is found that about 15% resin in the molding formulation is essential to give a board of acceptable quality. It is possible to include up to 20% CNSL without any deterioration in the properties of the board. This is significant from the conservation viewpoint.     

Effect of Casting Solvents and Compatibilizer Loading on the Morphology and Properties of Natural Rubber/Polystyrene Blends

Thermoplastic elastomers from blends of natural rubber (NR) and polystyrene (PS) have been prepared by the solution-casting technique. The blend of NR and PS is an incompatible one and can be made compatible by the addition of NR-g-PS. The compatibilizing action of NR-g-PS in NR/PS blends has been studied with special reference to the effect of the nature of the casting solvents and compatibilizer loading. Chloroform and carbon tetrachloride were selected as the casting solvents. The nature of the casting solvent has a profound influence on the compatibilizing action of the graft copolymer. This has been explained based on the preferential interaction of the solvent with one of the components in the mixture. The domain size of the dispersed polystyrene phase was decreased by the addition of a few percent of the compatibilizer, followed by a leveling off at higher concentrations. The leveling off is an indication of interfacial saturation. The mechanical properties of the blends were improved by the addition of the compatibilizer.