High Particle Counts Research Articles

In-line image analysis of particulate processes with deep learning: Optimizing training data generation via copy-paste augmentation

Monitoring particle properties directly in the process using in-situ microscopes can provide valuable input for control loops, improve process understanding, and facilitate process optimization. However, obtaining reliable information from these images is still challenging, particularly for higher solids concentrations or agglomerating systems. Recent studies have successfully applied deep learning models to extract particle characteristics from in-situ image data. Despite these advances, the problem of generating training data has not been properly addressed. Manual annotation is time-consuming and prone to bias due to high particle counts, particle overlap, and out-of-focus objects. This paper introduces a new approach to generating training data for segmentation models by combining conventional segmentation methods with copy-paste augmentation. A case study was conducted in which depth filtration experiments were performed using irregularly shaped alumina particles. An instance segmentation model trained on data created with the proposed approach successfully detected and characterized particles, even at high solids concentrations.

Particle analysis of surgical lung biopsies from deployed and non-deployed US service members during the Global War on Terrorism.

The role that inhaled particulate matter plays in the development of post-deployment lung disease among US service members deployed to Southwest Asia during the Global War on Terrorism has been difficult to define. There is a persistent gap in data addressing the relationship between relatively short-term (months to a few years) exposures to high levels of particulate matter during deployment and the subsequent development of adverse pulmonary outcomes. Surgical lung biopsies from deployed service members and veterans (DSMs) and non-deployed service members and veterans (NDSMs) who develop lung diseases can be analyzed to potentially identify residual deployment-specific particles and develop associations with pulmonary pathological diagnoses. We examined 52 surgical lung biopsies from 25 DSMs and 27 NDSMs using field emission scanning electron microscopy (FE-SEM) with energy dispersive x-ray spectroscopy (EDS) to identify any between-group differences in the number and composition of retained inorganic particles, then compared the particle analysis results with the original histopathologic diagnoses. We recorded a higher number of total particles in biopsies from DSMs than from NDSMs, and this difference was mainly accounted for by geologic clays (illite, kaolinite), feldspars, quartz/silica, and titanium-rich silicate mixtures. Biopsies from DSMs deployed to other Southwest Asia regions (SWA-Other) had higher particle counts than those from DSMs primarily deployed to Iraq or Afghanistan, due mainly to illite. Distinct deployment-specific particles were not identified. Particles did not qualitatively associate with country of deployment. The individual diagnoses of the DSMs and NDSMs were not associated with elevated levels of total particles, metals, cerium oxide, or titanium dioxide particles. These results support the examination of particle-related lung disease in DSMs in the context of comparison groups, such as NDSMs, to assist in determining the strength of associations between specific pulmonary pathology diagnoses and deployment-specific inorganic particulate matter exposure.

How many microplastics do you need to (sub)sample?

Analysis of microplastics in the environment requires polymer characterization as a confirmation step for suspected microplastic particles found in a sample. Material characterization is costly and can take a long time per particle. When microplastic particle counts are high, many researchers cannot characterize every particle in their sample due to time or monetary constraints. Moreover, characterizing every particle in samples with high plastic particle counts is unnecessary for describing the sample properties. We propose an a priori approach to determine the number of suspected microplastic particles in a sample that should be randomly subsampled for characterization to accurately assess the polymer distribution in the environmental sample. The proposed equation is well-founded in statistics literature and was validated using published microplastic data and simulations for typical microplastic subsampling routines. We report values from the whole equation but also derive a simple way to calculate the necessary particle count for samples or subsamples by taking the error to the power of negative two. Assuming an error of 0.05 (5 %) with a confidence interval of 95 %, an unknown expected proportion, and a sample with many particles (> 100k), the minimum number of particles in a subsample should be 386 particles to accurately characterize the polymer distribution of the sample, given the particles are randomly characterized from the full population of suspected particles. Extending this equation to simultaneously estimate polymer, color, size, and morphology distributions reveals more particles (620) would be needed in the subsample to achieve the same high absolute error threshold for all properties. The above proposal for minimum subsample size also applies to the minimum count that should be present in samples to accurately characterize particle type presence and diversity in a given environmental compartment.

Reduction by air purifier of particulate concentration during orthodontic procedures: a pilot study

BackgroundThe SARS-CoV-2 pandemic has raised awareness of the importance of air quality. This pilot study arose from the need to reduce the concentration of particulate matter in the dental office during orthodontic procedures. To evaluate the efficacy of using an air purifier during orthodontic care in the dental office to reduce the concentration of ambient particulate matter.ResultsSignificant reductions in particle numbers were obtained for all particle sizes except the largest particles counted (10 μm) through use of the air filter. A marked association between higher humidity levels and higher particle counts was also observed.ConclusionsUsing an air purifier during dental care achieves a significant reduction in the concentration of ambient particles in the dental office. There is a correlation between higher relative humidity and higher particle concentration. The probability of obtaining a maximum particulate concentration level of 0.3 and 0.5 μm is 1000 times lower when using an air purifier.

Differences in ultrasonic cavitation damage between new and used engine coolants with varying time in operation

This study investigates the cavitation erosion performance of heavy-duty engine coolants before and after operation in trucks using an ultrasonic test rig based on ASTM G32. Fresh coolants with 35% and 50% v/v glycol were compared with used coolants. One coolant was obtained from a gasoline-fueled vehicle with a mileage of 27000 km, and two from diesel-fueled vehicles with mileages of 16000 and 180 000 km, respectively. Surface tension and boiling point at atmospheric pressure were measured, a chemical analysis was carried out, and suspended particles were quantified by dynamic image analysis. The results showed that the used coolants caused a lower mass loss in ultrasonic cavitation testing than the fresh ones, and that they had higher boiling points, lower pH and a higher number of suspended particles, especially of those smaller than 30μm. Surface tension was higher for the used coolants from Diesel engines.The lower mass loss caused by all three used coolants can be attributed mainly to their high boiling point and high particle count. The presence of particles is believed to promote the heterogeneous nucleation of smaller, more stable bubbles, which may protect the exposed surface by shockwave absorption and microjet deflection. Some dissolved ions in the used coolants may help reduce their aggressivity by inhibiting bubble coalescence, reducing bubble collapse energy, despite increasing surface tension. Surface tension has complex interactions with the solutes, particles and bubble formation and cannot, in isolation, explain the differences in performance of the coolants.

Nano/microfluidic device for high-throughput passive trapping of nanoparticles.

We present a design and a fabrication method for devices designed for rapid collection of nanoparticles in a fluid. The design uses nanofluidic channels as a passive size-based barrier trap to isolate particles near a central point in the channel, which is also covered by a thin membrane. Particles that enter the collection region are trapped with 100% efficiency within a 6-12 m radius from a central point. Flow rates for particle-free fluid range from 1.88 to 3.69 nl/s for the pressure and geometries tested. Particle trapping tests show that high trapped particle counts significantly impact flow rates. For suspensions as dilute as 30-300 aM (20-200 particles/l), 8-80 particles are captured within 500 s.

CosmoGridV1: a simulated \U0001d5d0CDM theory prediction for map-level cosmological inference

We present CosmoGridV1: a large set of lightcone simulations for map-level cosmological inference with probes of large scale structure. It is designed for cosmological parameter measurement based on Stage-III photometric surveys with non-Gaussian statistics and machine learning. CosmoGridV1 spans the wCDM model by varying Ωm, σ 8, w 0, H 0, n s, Ω b , and assumes three degenerate neutrinos with fixed ∑ mν = 0.06 eV. This space is covered by 2500 grid points on a Sobol sequence. At each grid point, we run 7 simulations with PkdGrav3 and store 69 particle maps at nside = 2048 up to z = 3.5, as well as halo catalog snapshots. The fiducial cosmology has 200 independent simulations, along with their stencil derivatives. An important part of CosmoGridV1 is the benchmark set of 28 simulations, which include larger boxes, higher particle counts, and higher redshift resolution of shells. They allow for testing if new types of analyses are sensitive to choices made in CosmoGridV1. We add baryon feedback effects on the map level, using shell-based baryon correction model. The shells are used to create maps of weak gravitational lensing, intrinsic alignment, and galaxy clustering, using the UFalcon code. The main part of CosmoGridV1 are the raw particle count shells that can be used to create full-sky maps for a given n(z). We also release projected maps for a Stage-III forecast, as well as maps used previously in KiDS-1000 deep learning constraints with CosmoGridV1. The data is available at http://www.cosmogrid.ai/.

Assessment of personal exposure to PM for multiple transportation modes

• PM concentrations and inhalation doses in Guangzhou presented the following trend: shared bikes > buses > cars > subways. • The counts of particle size range of 0.25–0.5 µm were highest in all travel modes. • Travel by “cars CW” (i.e., with closed windows) effectively prevented PM infiltration from outside air. • PM concentrations on weekends with peaks usually observed in the morning, were higher than those on weekdays. Travelers are severely exposed to traffic-related particulate matter (PM). To assess the personal exposure to PM for multiple transportation modes, we conducted a study on particle concentrations, size fractions, and inhalation doses in Guangzhou, China. PM concentrations and inhalation doses showed the following trend: shared bikes > buses > cars > subways. PM 0.25-1 concentrations in subway accounted for 56%–63% of all size fractions, while PM 2.5-10 dominated PM 0.25-2.5 in other modes. The highest particle counts were observed in the size range of 0.25–0.5 µm. PM concentrations on weekends were higher than those on weekdays. Peak concentrations were usually recorded in the morning on weekends but in the evening during weekdays. Females had higher exposure risks than males for the same distance covered using shared bikes due to longer travel duration. These results can provide theoretical guides for travelers to reduce personal exposure and health risks associated with PM.

Visualization of Airborne Particles as a Risk for Microbial Contamination in Orthopedic Surgery.

Background: The operating theater is recognized to involve a high frequency of occupational blood and body fluid contacts.Objectives: This study aimed to visualize the production of blood and body fluid airborne particles by surgical procedures and to investigate risks of microbial contamination of the conjunctival membranes of surgical staff during orthopedic operations.Methods: Two physicians simulated total knee arthroplasty (TKA) and total hip arthroplasty (THA) in a bio-clean theater using model bones. The generation and behaviors of airborne particles were filmed using a fine particle visualization system, and numbers of airborne particles per 2.83 L of air were counted at the height of the operating and instrument tables. Each action was repeated five times, and particle counts were evaluated statistically.Results: Numerous airborne particles were dispersed to higher and wider areas while “cutting bones in TKA” and “striking and driving the cup component on the pelvic bone in THA” compared to other surgical procedures. The highest particle counts were detected while “cutting bones in TKA” under unidirectional laminar air flow.Discussion: These results provide a clearer image of the dispersion and distribution of airborne particles and identified higher-risk surgical procedures for microbial contamination of the conjunctival membranes. Surgical staff including surgeons, nurses, anesthesiologists, and visitors, should pay attention to and take measures against occupational infection particularly in high-risk surgical situations.

High particle counts in neonatal parenteral nutrition solutions with added cysteine: Relationship to crystal formation and effect of filtration on cysteine content.

Parenteral nutrition(PN) solutions containing calcium gluconate and cysteine have elevated particle counts when analyzed using laser light obscuration (LO) as recommended by the United States Pharmacopeia. It is unclear whether increased particle formation in these solutions results in decreased availability of cysteine to neonatal patients due to filtration. The purpose of this study was to measure cysteine concentrations in neonatal PN solutions before and after filtration as well as analyze precipitates on filters. Solutions of PN containing amino acids with and without cysteine that were compounded with calcium chloride or calcium gluconate plus potassium phosphate were analyzed using LO. Concentrations of cysteine were measured before and after filtration. The effect on particle formation of magnesium sulfate (MgSO4 ) and D70 was also evaluated. Multiple additives including the specific calcium or D70 additive, cysteine, and MgSO4 influenced particle formation of particles detected using LO. There was no significant decrease in cysteine concentration because of filtering and there was no difference in the amount of calcium on filters of various solutions after filtration regardless of LO particle counts. Scanning electron micrographic (SEM) analysis found no significant differences in crystal composition. Light microscopic and SEM examination did not show evidence of high particle counts on filters. The increased particle counts detected in neonatal PN solutions containing cysteine added at the time of compounding does not appear to result in increased precipitate or crystal formation. It is not associated witha decrease in cysteine delivery to patients.

Particulate generation with different oxygen delivery devices

BackgroundThe Coronavirus pandemic has a high mortality rate in patients that are mechanically ventilated, which has led to an ever increasing interest in noninvasive forms of oxygenation. The use of these devices has the theoretical risk of increased exposure risk because of possible particulate generation. This study aimed to quantify the particulate generation associated with different oxygen devices. MethodsThis was a prospective single center study conducted during September 2020 using ten healthy adult volunteers. Testing was conducted in a negative pressure hospital room using a light scattering particle counter. The oxygen devices used were a nasal cannula, an OxyMask™, a non-rebreathing mask, and a high flow system. Particle measurements were obtained at baseline in the room and then with each oxygen delivery device and pre-specified oxygen flow rates. These measurements were obtained different distances from the volunteer with their mouth open. A Wilcoxon/Kruskal-Wallis test was performed on each separate oxygen modality with all flow rates as one model. ResultsThe particle concentrations were slightly non-significantly increased with the OxyMask™ and non-rebreathing mask at the closest distance measured. As the distance increased, these counts decreased closer to ambient levels. The nasal cannula and high flow nasal cannula particle counts were not significantly different from ambient measurements at either distance. ConclusionNasal cannula, OxyMask™, non-rebreathing mask, and high flow oxygen did not generate any additional aerosols or droplets above a baseline room measurement, but further studies are necessary to determine infectious risk.

PARTICULATE MATTER FROM SYRINGES USED FOR INTRAVITREAL INJECTIONS.

Syringes containing anti-vascular endothelial growth factor drugs to treat retinal diseases are prepared in different ways by various parties with syringe selection, preparation, and storage conditions affecting the risk of injecting particles into the vitreous. This study examines particle loads from various syringes over time. Four syringes were studied: two plastic transfer syringes lubricated with silicone oil or oleamide, a glass syringe with baked-on silicone, and a lubricant-free polymer syringe. Syringes were rinsed with water or filled with buffer and analyzed over time; particles were quantified by flow imaging. Particle formation in a bevacizumab formulation was also characterized. Insulin syringes consistently showed very high particle counts. Oleamide-lubricated syringes had substantially fewer particles, but showed appreciable increases over time (leading to visible particles). Baked-on silicone glass syringes and lubricant-free polymer syringes both showed low particle levels ≥10 μm. Lubricant-free syringes showed the lowest particle levels ≥1 μm and the lowest particle levels with bevacizumab agitation. Syringes have different intrinsic particle loads which can contribute to particle loads in the delivered drug. Oleamide-lubricated transfer syringes, commonly used for bevacizumab repackaging, have time-dependent particle loads and are associated with the formation of visible particles beyond 30 days of storage.

Personal exposures to PM during short distance highway travel in India

Traffic is the largest contributor (37%) to urban air pollution in India. During commuting, passengers are significantly exposed to pollutants. We carried out a study on a National Highway (NH) in India to measure personal exposure to Particulate Matter (PM) in five travel modes. PM2.5 concentrations showed the following trend: Bus > Car FA (fresh air mode of air condition) > Bus AC > Car > Car RC (re-circulation mode of air condition). Highest and lowest concentrations of PM10 were observed in Bus (134 ± 47 µg m−3) and Car RC (20 ± 5 µg m−3), respectively. The exposures were highest at the rear seats during the Bus AC journeys. In Car FA, the contribution of PM1 to total concentrations was dominant (61%). Travel modes explained highest variabilities in PM10, PM2.5 and PM1 concentrations. In all travel modes, the highest particle counts were observed for PM0.3–0.5. PM>0.5–5.0 counts during Bus journeys were comparatively higher than remaining modes. Deposition doses of passengers were as high as 3.22 µg of PM10 (in Bus), 0.66 µg of PM2.5 (in Bus) and 0.06 µg of PM1 (in Bus AC) during the ~1 h journey. Our study revealed that Car RC is the safest mode of travel, both in terms of personal exposures and PM depositions in respiratory system. The results from this study can be used to target efforts to reduce personal exposure of highway commuters.

Comparison between manta trawl and in situ pump filtration methods, and guidance for visual identification of microplastics in surface waters

Owing to the development and adoption of a variety of methods for sampling and identifying microplastics, there is now data showing the presence of microplastics in surface waters from all over the world. The difference between the methods, however, hampers comparisons, and to date, most studies are qualitative rather than quantitative. In order to allow for a quantitative comparison of microplastics abundance, it is crucial to understand the differences between sampling methods. Therefore, a manta trawl and an in situ filtering pump were compared during realistic, but controlled, field tests. Identical microplastic analyses of all replicates allowed the differences between the methods with respect to (1) precision, (2) concentrations, and (3) composition to be assessed. The results show that the pump gave higher accuracy with respect to volume than the trawl. The trawl, however, sampled higher concentrations, which appeared to be due to a more efficient sampling of particles on the sea surface microlayer, such as expanded polystyrene and air-filled microspheres. The trawl also sampled a higher volume, which decreased statistical counting uncertainties. A key finding in this study was that, regardless of sampling method, it is critical that a sufficiently high volume is sampled to provide enough particles for statistical evaluation. Due to the patchiness of this type of contaminant, our data indicate that a minimum of 26 particles per sample should be recorded to allow for concentration comparisons and to avoid false null values. The necessary amount of replicates to detect temporal or spatial differences is also discussed. For compositional differences and size distributions, even higher particle counts would be necessary. Quantitative measurements and comparisons would also require an unbiased approach towards both visual and spectroscopic identification. To facilitate the development of such methods, a visual protocol that can be further developed to fit different needs is introduced and discussed. Some of the challenges encountered while using FTIR microspectroscopic particle identification are also critically discussed in relation to specific compositions found.

Impact of improved low-density lipoprotein cholesterol assessment on guideline classification in the modern treatment era—Results from a racially diverse Brazilian cross-sectional study

The Martin/Hopkins low-density lipoprotein cholesterol equation (LDL-CN) was previously demonstrated as more accurate than Friedewald LDL-C estimation (LDL-CF) in a North American database not able to take race into account. We hypothesized that LDL-CN would be more accurate than LDL-CF and correlate better with LDL particle number (LDL-P) in a racially diverse Brazilian cohort. We performed a cross-sectional analysis of 4897 participants in the Brazilian Longitudinal Study of Adult Health, assessing LDL-CF and LDL-CN accuracy via overlap with ultracentrifugation-based measurement among clinical guideline LDL-C categories as well as mg/dL and percent error differences. We analyzed by triglyceride categories and correlated LDL-C estimation with LDL-P. LDL-CN demonstrated improved accuracy at 70 to <100 and <70mg/dL (P<.001), with large errors ≥20mg/dL about 9 times more frequent in LDL-CF at LDL-C <70mg/dL, mainly due to underestimation. Among individuals with LDL-C <70mg/dL and triglycerides ≥150mg/dL, 65% vs 100% of ultracentrifugation-based low-density lipoprotein cholesterol calculation fell within appropriate categories of estimated LDL-CF and LDL-CN, respectively (P<.001). Similar results were observed when analyzed for age, sex, and race. Participants at LDL-C <70 and 70 to <100mg/dL with discordantly elevated LDL-CN vs LDL-CF had a 58.5% and 41.5% higher LDL-P than those with concordance (P<.0001), respectively. In a diverse Brazilian cohort, LDL-CN was more accurate than LDL-CF at low LDL-C and high triglycerides. LDL-CN may avoid underestimation of LDL-C and better reflect atherogenic lipid burden in low particle size, high particle count states.

Different particle flow patterns from the airways after recruitment manoeuvres using volume-controlled or pressure-controlled ventilation

ObjectivesNoninvasive online monitoring of different particle flows from the airways may serve as an additional tool to assess mechanical ventilation. In the present study, we used a customised PExA, an optical particle counter for monitoring particle flow and size distribution in exhaled air, to analyse airway particle flow for three subsequent days. We compared volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) and performed recruitment manoeuvres (RM).MethodsSix animals were randomised into two groups: half received VCV before PCV and the other half received PCV before VCV. Measurements were taken daily for 1 h in each mode during three subsequent days in six fully anaesthetised domestic pigs. A RM was performed twice daily for 60 s at positive end-expiratory pressure (PEEP) of 10, 4 breaths/min and inspiratory-expiratory ratio (I:E) of 2:1. Measurements were taken for 3 min before the RM, 1 min during the RM and for 3 min after the RM. The particle sizes measured were between 0.48 and 3.37 μm.ResultsA significant stepwise decrease was observed in total particle count from day 1 to day 3, and at the same time, an increase in fluid levels was seen. Comparing VCV to PCV, a significant increase in total particle count was observed on day 2, with the highest particle count occurring during VCV. A significant increase was observed comparing before and after RM on day 1 and 2 but not on day 3. One animal developed ARDS and showed a different particle pattern compared to the other animals.ConclusionsThis study shows the safety and useability of the PExA technique used in conjunction with mechanical ventilation. We detected differences between the ventilation modes VCV and PCV in total particle count without any significant changes in ventilator pressure levels, FiO2 levels or the animals’ vital parameters. The findings during RM indicate an opening of the small airways, but the effect is short lived. We have also showed that VCV and PCV may affect the lung physiology differently during recruitment manoeuvres. These findings might indicate that this technique may provide more refined information on the impact of mechanical ventilation.

Silicone Oil-Free Polymer Syringes for the Storage of Therapeutic Proteins

Prefilled syringes are a popular choice for the delivery of biopharmaceuticals. However, glass syringes might not be the optimal primary packaging material for all biopharmaceuticals. There is evidence that the necessary lubricant silicone oil in glass syringes can interact with proteins and can be shed from the surface into the product solution. In recent years, silicone oil-free polymer syringes were developed. Despite several advantages, however, a major shortcoming of these polymer systems is their relatively high gas permeability, which might be a limitation for the storage of oxygen sensitive biopharmaceuticals. So far, no long-term protein stability studies regarding such polymer systems have been published. In this study, 2 therapeutic proteins were stored in glass syringes and in silicone oil-free polymer syringes. In addition, polymer syringes stored in nitrogen-filled aluminum pouches or covered with oxygen-tight labels were included. Similar chemical protein stability was achieved at 4°C for all syringes. However, in contrast to the polymer syringes, high particle counts were observed in the glass syringes. Polymer syringes stored in nitrogen-filled aluminum pouches presented a promising alternative for the storage of biopharmaceuticals as they do not expose patients to silicone oil and silicone oil-protein aggregates.

Particle count and black carbon measurements at schools in Las Vegas, NV and in the greater Salt Lake City, UT area

ABSTRACTAs part of two separate studies aimed to characterize ambient pollutant concentrations at schools in urban areas, we compare black carbon and particle count measurements at Adcock Elementary in Las Vegas, NV (April–June 2013), and Hunter High School in the West Valley City area of greater Salt Lake City, UT (February 2012). Both schools are in urban environments, but Adcock Elementary is next to the U.S. 95 freeway. Black carbon (BC) concentrations were 13% higher at Adcock compared to Hunter, while particle count concentrations were 60% higher. When wind speeds were low—less than 2 m/sec—both BC and particle count concentrations were significantly higher at Adcock, while concentrations at Hunter did not have as strong a variation with wind speed. When wind speeds were less than 2 m/sec, emissions from the adjacent freeway greatly affected concentrations at Adcock, regardless of wind direction. At both sites, BC and particle count concentrations peaked in the morning during commute hours. At Adcock, particle count also peaked during midday or early afternoon, when BC was low and conditions were conducive to new particle formation. While this midday peak occurred at Adcock on roughly 45% of the measured days, it occurred on only about 25% of the days at Hunter, since conditions for particle formation (higher solar radiation, lower wind speeds, lower relative humidity) were more conducive at Adcock. Thus, children attending these schools are likely to be exposed to pollution peaks during school drop-off in the morning, when BC and particle count concentrations peak, and often again during lunchtime recess when particle count peaks again.Implications: Particle count concentrations at two schools were shown to typically be independent of BC or other pollutants. At a school in close proximity to a major freeway, particle count concentrations were high during the midday and when wind speeds were low, regardless of wind direction, showing a large area of effect from roadway emissions even when the school was not downwind of the roadway. At the second school, which sits in an urban neighborhood away from freeways, high particle counts occurred even though solar radiation was low during wintertime conditions, meaning that exposure to high particle counts can occur throughout the year.

Nano-object Release During Machining of Polymer-Based Nanocomposites Depends on Process Factors and the Type of Nanofiller.

We tested the nanomaterial release from composites during two different mechanical treatment processes, automated drilling and manual sawing. Polyurethane (PU) polymer discs (1-cm thickness and 11-cm diameter) were created using different nanomaterial fillers: multiwall carbon nanotubes (MWCNT), carbon black (CB), silicon dioxide (SiO2), and an unfilled PU control. Drilling generated far more submicron range particles than sawing. In the drilling experiments, none of the tested nanofillers showed a significant influence on particle number concentrations or sizes, except for the PU/MWCNT samples, from which larger particles were released than from control samples. Higher drilling speed and larger drill bit size were associated with higher particle counts. Differences between composites were observed during sawing: PU/CB released higher number concentrations of micro-sized particles compared to reference samples. When sawing PU/SiO2 more nanoparticle agglomerates were observed. Furthermore, polymer fumes were released during sawing experiments, which was attributed to the process heat. For both drilling and sawing, the majority of the aerosolized particles were polymer matrix materials containing nanofillers (or protruding from their surface), as evidenced by electron microscopic analysis. Results suggest that: (i) processes associated with higher energy inputs are more likely to result in higher particle release in terms of number concentration; (ii) nanofillers may alter release processes; and (iii) other types of released particles, in particular polymer fumes from high-temperature processes, must also be considered in occupational exposure and risk assessments.

A Problem of Particulate Contamination in an Automated Assembly Machine Successfully Solved by CFD and Simple Experiments

Assembly of hard disk drives (HDDs) needs to be done in an automated assembly machine (AAM) virtually free of particulate contamination that can cause them to malfunction. Fan filter units (FFUs) are installed above the AAM to reduce the number of suspended particles in the recirculating air flowing over and around them. At one time, several HDDs were found to be defective. To find out the root cause of this problem, computational fluid dynamics (CFD) was used to investigate the airflow over and around the AAM. It was found that the cause of the high particle counts was improper air speed from the FFUs. The optimal FFUs air speed needed to be in the range of 0.35–0.65 m/s in which the airflow would block out nearby airborne particles and purge away particles generated by the AAM effectively which would, in effect, reduce the particle counts down below the threshold level of class 100 clean room. A few available measurement tools at the factory were then used to perform validating measurements against the simulation results, and the validation was positive. This optimal speed range was implemented at the factory after which the level of contamination was reduced to an acceptable level.