Fiber Classification and the Influence of Average Air Humidity

The use of man-made vitreous fibers (MMVFs) as a substitute for asbestos in industrial and residential applications has raised the concerns of the potential hazards associated with inhalable aerosolized fibers. The complex movement of fiber makes it difficult to predict the pattern of fiber deposition in human airways from the behavior of spherical particles. Difficulties in producing monodisperse length fibers has been an obstacle to study fibrous particle deposition in the human respiratory system. To address this problem, a narrow length distribution of fibers was generated using dielectrophoretic classification. Dielectrophoresis is the motion of neutral matter in a nonuniform electric field due to an induced dipole moment. It is sensitive to the conductivity of the matter in the field. A fiber classifier has been used to study the influence of atmospheric humidity on the behavior of glass fibers. Glass fibers, as insulators, can not be classified by the dielectrophoretic classifier. However, our study shows that a humidity higher than 15% RH can change the conductivity of the glass fibers so as to permit their effective classification.     

A multi-channel electrical mobility spectrometer with wedge geometry—Design and first evaluation

This paper presents a new design for a multi-channel electrical mobility spectrometer which measures the lognormal size distribution and number concentration of aerosol particles in the size range 5–300 nm with a short response time. The spectrometer charges particles in the test sample by unipolar corona discharge, they are then classified into 16 channels by electrical mobility. Charged particles are detected in the channels by individual aerosol electrometers, giving an electrical mobility spectrum for the sample.The main aspect of the spectrometer design is a wedge-shaped classifier with flat electrodes. This allows a flow to be drawn from the classifier at 16 different levels/channels with minimal disturbance to the remaining flow, hence filter based aerosol electrometers can be used for detection. The varying field within the classifier caused by the wedge shape is advantageous to the classification and optimised through the selection of the wedge angle.Also presented is an alternative technique for inferring the lognormal size distribution of an aerosol from a measured electrical mobility spectrum. This involves using a theoretical model of the instrument to simulate the output mobility spectra for a large number of aerosol samples with lognormal size distributions. The resulting data library can be searched against a measured electrical mobility spectrum to find the corresponding size distribution.The experimental work presented in this paper is a first evaluation of this spectrometer and includes measurement of the classifier transfer functions, basic calibration of the charger, and finally testing the spectrometer's performance on some simple unimodal lognormal aerosol samples.     

Retrieving the ion mobility ratio and aerosol charge fractions for a neutralizer in real-world applications

Abstract

Electrical mobility size spectrometers (with a neutralizer, an electrical mobility classifier, and a detector as key components) are widely used to measure aerosol size distributions. The performance of a neutralizer is often evaluated separately from the spectrometer. In real-world applications of a neutralizer, i.e., typically with uncontrolled composition of the neutralizer carrier gas including trace constituents that can lead to variabilities in properties of positive and negative ions, charge fractions may differ from those predicted by widely used aerosol charging models with fixed ion properties and subsequently cause significant uncertainties in reported aerosol size distributions. In this study, we proposed an empirical method to retrieve the variations in neutralizer ion properties and aerosol charge fractions when measuring aerosol size distributions. Our approach requires measuring both positively and negatively charged particles using the electrical mobility size spectrometer to provide information on the performance of the neutralizer. Bipolar diffusion charging theories were applied to illustrate that aerosol charge fractions are governed by the mobility ratio of positive and negative ions. Positively and negatively charged particles measured by the spectrometer can be used to estimate the mobility ratio of positive and negative ions for the neutralizer. A modified Gunn and Woessner’s formula can then be used to calculate aerosol charge fractions from the retrieved ion mobility ratio. These charge fractions can be used for size distribution data inversion. Both simulated aerosols and experiments were used to evaluate the proposed method. We found that this new method can capture the variations in neutralizer ion properties and aerosol charge fractions under various conditions and help to achieve more accurate measurement of aerosol size distributions.

Copyright © 2018 American Association for Aerosol Research     

A new miniature electrical aerosol spectrometer (MEAS): Experimental characterization

Design and theory of a new compact ultrafine particle sizing instrument, called the miniature electrical-mobility aerosol spectrometer (MEAS), was recently introduced [Ranjan, M., & Dhaniyala, S. (2007). A new miniature electrical spectrometer: Theory and design. Journal of Aerosol Science, 39, 950–963]. In the MEAS, electrostatic precipitation technique is used for both generation of sheath flow and classification of particles based on their electrical mobility. An electrometer-array, connected to the collection electrodes in the classifier section, is used to measure the number of particles collected in the different mobility channels, and these data are inverted using MEAS transfer functions to obtain particle number size distributions. Design of a prototype MEAS and the experimental approach to validate the performance of the individual components of the instrument are presented. Particle size distributions obtained from MEAS measurements compare well with those obtained using a scanning mobility particle sizer (SMPS; TSI 3936), validating theoretical calculations of instrument transfer functions. The operational limits of MEAS are determined from the calculation of error in the inverted size distribution as a function of total particle concentration. This analysis suggests that the designed MEAS can be used for applications such as personal and ambient monitoring under conditions of moderate to high particle concentrations.     

The Spider DMA: A miniature radial differential mobility analyzer

Abstract

The Spider differential mobility analyzer (DMA) is a novel, miniaturized radial DMA developed to provide size classification in the 10–500?nm range for applications requiring high portability and time resolution. Its external dimensions are ～12?cm in diameter by 6?cm in height (excluding tubing); it weighs ～350?g, and is designed to operate at 0.6–1.5?L/min sheath and 0.3?L/min sample flowrates. It features a new sample inlet geometry that is designed to produce a uniform azimuthal particle distribution at the entrance of the classifier, optimized sample/sheath flow streams introduction in the classifier to minimize particle delays, and extension of the electric field interaction volume for ～30% enhanced dynamic range. Based on three-dimensional finite element simulations of flows, electric fields, and particle trajectories, we demonstrate that the Spider DMA transfer functions can be predicted with high fidelity using a parameterized fit based on the Stolzenburg semi-analytical model. Experimental characterization of the instrument response with size-selected particles confirmed close agreement with model prediction; mobility size response is linear over three orders of magnitude in mobility span. Electrical ground shielding of the external surfaces of the DMA has been found to be necessary to avoid particle losses associated with field effects as the high voltage operating limit is approached. The mean deviation between the reference size of polystyrene latex spheres and the Spider DMA measurement is less than 2%, corroborating its high sizing precision and potential for high quality size distribution measurements.

Copyright © 2019 American Association for Aerosol Research     

Effects of particle dispersion and circulation systems on classification performance

To classify fine powders with particles smaller than 1 μm in diameter, air classifier design must take three factors into consideration: dispersion of feed powders, air flow uniformity in the classification zone, and recovery of fine particles adhering to the coarse fraction. The effects on the classification performance of a centrifugal air classifier using a dispersion nozzle for particle dispersion and a circulation mechanism using channel air jets for the recovery of fine particles are discussed.

By using a dispersion nozzle, the classification sharpness index was improved below 0.8 (D_p/D_p50) and the fine fraction yield was improved by 64% without changing size distribution. The circulation mechanism using channel air improved classification performance by 58% of the classification sharpness index and 65% of the fine fraction yield, although the particle size distribution of the fine fraction became 0.1 μm coarser than that without channel air.     

A novel miniature inverted-flame burner for the generation of soot nanoparticles

Lab-scale soot nanoparticle generators are used by the aerosol research community to study the properties of soot over a broad range of particle size distributions, and number and mass concentrations. In this study, a novel miniature inverted-flame burner is presented and its emitted soot particles were characterized. The burner consisted of two co-annular tubes for fuel and co-flow air and the flame was enclosed by the latter. The fuel used was ethylene. A scanning mobility particle sizer (SMPS) and an aerodynamic aerosol classifier (AAC) were used to measure mobility and aerodynamic size distribution of soot particles, respectively. Particle morphology was studied using transmission electron microscopy (TEM). The elemental carbon (EC) and organic carbon (OC) content of the soot were measured using thermal-optical analysis (TOA). The burner produced soot particles with mobility diameter range of 66–270?nm, aerodynamic diameter range of 56–140?nm, and total concentration range of 2?×?10⁵–1?×?10⁷?cm^?3. TEM images showed that most soot particles were sub-micron soot aggregates. Some soot superaggregates, typically larger than 2?µm in length, were observed and their abundance increased with ethylene flow rate. TOA showed that the concentration of EC in the generated soot increased with ethylene flow rate, and the soot was observed to have high EC fraction at high ethylene flow rates. The miniature inverted-flame burner was demonstrated to produce soot nanoparticles over a range of concentrations and sizes with high EC content, making it a practical device to study soot nanoparticle properties in different applications.

Copyright © 2019 American Association for Aerosol Research     

Transmission of charged nanoparticles through the DMA adverse axial electric field and its improvement

Abstract

Charged particles can be classified according to their electrical mobility using electrical methods. These particles are often transported against an adverse electric field from a region of high electric potential to a grounded region, e.g., in the aerosol sample outlet of a differential mobility analyzer (DMA). Electrostatic losses due to the adverse electric field can be reduced using a tube made of electrostatic dissipative (ESD) materials. The transmission of charged particles through an adverse axial electric field inside the ESD tube is studied considering particle losses due to electrostatic migration and Brownian motion. The electric field inside the ESD tube is solved analytically. Assuming Hagen-Poiseuille flow, plug flow, or turbulent flow, the transmission efficiency of the charged particles is evaluated using both a simplified analytical model and Monte-Carlo simulation. Transmission efficiencies of 1.48-nm ions are measured at various flow rates and for various tube lengths. The measured transmission efficiencies agree with the results from both the analytical model and Monte-Carlo simulation. The ideal tube length for relatively high transmission efficiencies is discussed. Both the analytical model and Monte-Carlo simulation show that the recommended tube length for the test DMA is longer than a threshold value corresponding to an adverse particle electrostatic migration velocity of less than ～20% of the average air flow velocity. Based on these findings, the sample outlet of a miniature cylindrical DMA is improved using an ESD tube. The measured penetration efficiency of 1.48-nm ions at a sheath flow rate of 25?L min^?1 and an aerosol flow rate of 1.5?L min^?1 is improved by 50%.

Copyright © 2019 American Association for Aerosol Research     

Properties of Hollow Fibers Used for Flow Field-Flow Fractionation

Abstract

An objective method for evaluating the suitability of different hollow fibers as separation channels in hollow-fiber flow-FFF is presented. The method is applied to evaluate four different fiber types and to compare several fibers of the same type. It is shown that the maximum plate number achievable with a certain fiber is governed by the homogeneity of the distribution of pores in the fiber wall. The method makes it possible to distinguish and measure the contribution to the peak width that originates from the inhomogeneity in pore distribution.     

Development of portable aerosol mobility spectrometer for personal and mobile aerosol measurement

We describe development of a portable aerosol mobility spectrometer (PAMS) for size distribution measurement of submicrometer aerosol. The spectrometer is designed for use in personal or mobile aerosol characterization studies and measures approximately 22.5×22.5×15 cm and weighs about 4.5 kg including the battery. PAMS uses electrical mobility technique to measure number-weighted particle size distribution of aerosol in the 10–855 nm range. Aerosol particles are electrically charged using a dual-corona bipolar corona charger, followed by classification in a cylindrical miniature differential mobility analyzer. A condensation particle counter is used to detect and count particles. The mobility classifier was operated at an aerosol flow rate of 0.05 L/min, and at two different user-selectable sheath flows of 0.2 L/min (for wider size range 15–855 nm) and 0.4 L/min (for higher size resolution over the size range of 10.6–436 nm). The instrument was operated in voltage stepping mode to retrieve the size distribution in approximately 1–2 min. Sizing accuracy and resolution were probed and found to be within the 25% limit of NIOSH criterion for direct-reading instruments. Comparison of size distribution measurements from PAMS and other commercial mobility spectrometers showed good agreement. The instrument offers unique measurement capability for on-person or mobile size distribution measurement of ultrafine and nanoparticle aerosol.     

Experimental characterization of a short electrical mobility spectrometer for aerosol size classification

A prototype of a short column electrical mobility spectrometer (EMS) for size measurement of aerosol particle was design, constructed, and experimentally characterized. The short EMS consists of a particle charger, a size classifier column, and a multi-channel electrometer. Its particle size resolution is derived from a 10 channel electrometer detector. The short EMS is capable of size measurements in the range between 10 nm to 1,000 nm with a time response of about 50 s for full up and down scan. Particle number concentration in which the short EMS can measure ranges from 10¹¹ to 10¹³ particles/m³. The operating flow rate of the short EMS is set for the aerosol flow rate of 1.0–2.0 l/min and the sheath air flow rate fixed at 10.0 l/min. The inner electrode voltage of the classifier can be varied between 500–3,000 VDC. The short EMS operates at sub-atmospheric pressure, typically at 526 mbar. Validation of the short EMS performance was performed against a scanning electron microscope (SEM). Good agreements were obtained from comparison between sizes determined from the short EMS classifier and the SEM analysis. Signal current from the detector was also analyzed to give rise to number concentration of particles. Experimental results obtained appeared to agree well with the theoretical predictions.     

Adhesion Property of Functional Particle to Bagasse Pith for High Performance Composite Paper

Abstract

Natural fibers, such as baggase and bamboo were the focus of this work in producing a new high performance paper. In this work, bagasse pith with a porous structure, which is helpful for the attachment of a functional material, was used to produce a high performance composite paper. Powdered bamboo leaf particles were attached as the functional material to the bagasse pith using a variety of conditions involving treatment times, bamboo leaf concentrations and pith length. The smaller particles (less than 45 μm) which were classified by sieve showed a higher degree of attachment than the bamboo leaf particles which were of a size greater than 45 μm. It was found that a degassing process increased the amount of attached bamboo particles, by about 3 times. Moreover decreasing the volume of water necessary for particle flow resulted in a higher adhesion ratio of bamboo particles by about 50%. This was achieved without any chemical processing. Most bamboo particles around the inlet of the pith pores were easily removed on washing. Furthermore, cationization resulted in an improved adhesion ratio and a greater adhesion of the bamboo particles to the pith.     

Current distribution in a rectangular flow channel manufactured by 3‐D printing

The characterization and improvement of a rectangular channel electrolyte flow compartment used in an iron‐air flow battery was carried out by using an arrangement of copper electrodes to measure the current density distribution employing the limiting current technique. The present work addresses the hydrodynamics and mass transport distribution in the compartment and their improvement by an improved electrolyte compartment that results in a more uniform current distribution. The current distribution was evaluated as the ratio between the local and the averaged limiting current densities during the reduction of copper ions over a range of mean linear flow velocity across the electrode surface (2–30 cm s^?1). The initial compartment, showed larger differences between the minimum and maximum currents than the electrolyte compartment that resulted as part of the design process and showed a higher pressure drop at a given mean linear flow velocity. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1144–1151, 2017     

Reverse Direction Anion Capillary Electrophoresis: Theory and Application

Abstract

A new mode for operating capillary electrophoresis for separation of anions without using buffer modifiers has been demonstrated. Reverse direction anion capillary electrophoresis, as the new mode is designated, is performed on two anions, nitrate and nitrite, with similar electrophoretic mobilities at various buffer pH values. Since electroosmotic flow increases as buffer pH is increased, it is shown that resolution is poor at low pH and enhanced at neutral to high pH. Model equations are derived for predicting the resolution and number of theoretical plates for reverse direction anion capillary electrophoresis. From these equations, system efficiency (N) and resolution are plotted as a function of electroosmotic mobility to illustrate how performance can be improved by an increase in electroosmotic flow.     

Using the external magnetic field of composites to control fiber orientation and enhancement of electrical conductivity

The industrial developments have led to more applications of various composites. Since fiber orientation and distribution will influence product performance in composites, controlling said orientation and distribution is of critical importance. This study used external magnetic fields to control the fiber orientation and distribution in a polymer. The orientation of the actual fibers under magnetic field control during flowing was observed using a visualization system, which was made by PMMA and transparent epoxy as an upper cover and filling polymer. In order to clearly observe and calculate, 0.1 wt% fiber content was used, and 0.3 wt% fiber content was used to measure conductivity. Fiber distribution angles without a magnetic field concentrate parallel to the flow direction (0° ~ 30° and 151° ~ 180°) while distribution angles under magnetic field control were concentrated along the magnetic field direction, which was perpendicular to the flow direction (61° ~ 120°). The higher the magnetic flux density, the larger the torque of the electromagnetic field on the fibers and the higher the orientation of fibers was with the magnetic field. The electrical conductivity was 12.23 times higher for 1 mm fibers in an external magnetic field versus no magnetic field.     

Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

This article focuses on the effect of pulp bleaching and emerging commercial compatibilizers on physical performance of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. Industrially bleached and unbleached hardwood kraft pulp fibers are treated with several additive types, and compounded with PLA to fiber content of 30 wt %. After injection molding, the produced biocomposites are evaluated by their mechanical performance and fiber–matrix adhesion. For selected materials, fiber surface and fiber properties are reflected to composite performance by analyzing the compositions, dimensions, and lignin coverage of original fibers, as well as fiber dispersion and dimensions after melt processing. As a conclusion, unbleached kraft pulp fibers provide significant improvement in physical properties of PLA/pulp fiber composites. Of the screened compatibilizers, epoxidated linseed oil has a clear positive effect on performance when bleached kraft pulp fibers are used. The improvements correspond to enhanced fiber–matrix adhesion and differences in remaining fiber length distributions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47955.     

Zwitterions of 1-poly(oxyethylene)-2-imidazoline derivatives as anti-electrostatic agent for polyamide fiber

Summary This paper describes a group of anti-electrostatic agents 1 for polyamide fiber(Nylon 6). Agents 1 are calcium imidazolinium-carboxylates having poly(oxyethylene) chain and long alkyl group (C₁₁H₂₃ and C₁₇H₃₅). Eight derivatives of 1 were prepared by a four-step one-pot synthesis shown in Scheme 1. Nylon 6 fibers and films containing some of 1 (1.0 and 2.0 wt%) show improved anti-electrostatic property. The performance of 1 was increased by the increase of the length of poly(oxyethylene) chain.     

Particle Charge Distribution Measurement for Commonly Generated Laboratory Aerosols

ABSTRACT

An improved particle charge analyzer system has been developed to measure the absolute charge distribution of common generated laboratory aerosols. The charge analyzer system consists of an integral cylindrical mobility analyzer used in conjunction with an optical aerosol spectrometer, with computer assisted operation and data reduction. The charge analyzer collects aerosol particles over an absolute electrical mobility range from 4.2*10^?4 to 400 cm²/(stat · Volt second) and flow rates that can vary from 0.3 to 30 liters per minute. The charge analyzer has been used to investigate the nature of spray and contact electrification during aerosol generation by measuring the residual charge distribution on the liquid and solid generated particles. In addition, the neutralization of charged particles by bipolar ions also was studied using conventional neutralizers that use ionizing radiation from alpha and beta sources. Charge distribution measurements were performed on alumina dust (Al), Arizona road dust (ARD), potassium chloride (KCl), sodium chloride (NaCl) and di-octyl sebacate (DOS) liquid particles. Aerosol generation devices include a Collison atomizer, a condensation aerosol generator and a fluidized bed dust generator. Our work provides experimental charge distribution data for comparison with simple models of electrification theory. Experimental results showed that charge levels of atomized KCl and NaCl particles were high and decreased as the dissolved ion concentration increased. DOS particles generated by evaporation-condensation were both neutral and moderately charged. These conclusions support the existence of a dipole layer at the liquid-gas interface that interacts with dissolved particles and changes their charge state. Alumina and ARD generated by the fluidized bed disperser are highly charged due to strong contact electrification during dispersion. In most cases, the charge on generated aerosols could be reduced to Boltzmann charge equilibrium conditions by commonly used radioactive neutralizers.     

Continuous aligned poly(meta‐phenylene isophthalamide) fibers via stable jet electrospinning

Continuous aligned poly(meta‐phenylene isophthalamide) (PMIA) fibers are first fabricated by Stable Jet Electrospinning (SJES) with a collection distance of 15 cm. The unfolded length of every single fiber is calculated to be several hundred to several thousand meters. Morphology analysis by field emission scanning electron microscopy (FE‐SEM) shows that these fibers are well arranged and uniformly distributed and their average fiber diameters decrease gradually with increasing collection speed. The effects of ambient temperature and humidity on the duration of stable jet are also discussed. Moderate temperatures and humidity are preferred for fabricating PMIA fibers with ultra‐long size. Besides, the changes of the thermal and crystalline properties of PMIA fibers are also investigated. The significant decline in crystallinity should be responsible for its decreased thermal property. Further improvements to its thermal and crystalline performance must be given consideration in future applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43690.