DOI: 10.5061/dryad.ffbg79crq
title: Characterisation data for electrocharged facepiece respirator fabrics using common materials

description: Face masks in general, and N95 filtering facepiece respirators (FRs) that
 protect against SARS-Cov-2 virion in particular, have become scarce during
 the ongoing COVID-19 global pandemic. We developed a technique for
 fabrication of electrocharged filtration layers employed in N95 FRs using
 commonly available materials and easily replicable methods. Our input
 polymer was polypropylene or polystyrene, and could include discarded
 plastic containers of these materials, and the fabrication setup was based
 on the cotton candy (CC) principle.  We translate the primary
 parameters underlying the CC principle to simple design rules that allow
 anyone to construct their own fabrication system from common parts, or
 employ a commercial cotton candy machine with minimal modifications.
 Finally, we present basic characterization results for structural and
 filtration properties of electrocharged fabrics made using the CC
 principle. The data uploaded here belongs to our characterization studies
 for use by any interested party.
description: Density: The electrocharged fabric densities were measured by
 weighing electrocharged fabric samples of known dimensions and then
 dividing the mass by the volume. Scanning Electron
 Micrographs: Structural properties of the electrocharged filtration
 fabrics were studied using scanning electron microscopy (SEM). As a
 preparatory step, platinum-palladium sputter coating deposition was
 performed on the fabric sample surfaces for SEM visualization, followed by
 interrogation under a scanning electron microscope (Quanta 250 FEG,
 Manufacturer: FEI Thermo Fisher) at 2 kV acceleration voltage.
 Filtration Test: Setup: Filtration tests for
 face mask certification are usually performed on specialized equipment
 such as the Portacount Respirator Fit-Tester and MITA 8120, both from TSI
 Inc. or AccuFIT 9000 from Accutec-IHS Inc. We neither had access to such
 special testing system nor could we afford their price, and therefore
 designed our own filtration testing system in-house. We employed a manikin
 head used in retail store fronts and drilled a hole from its mouth to the
 back of its head. The face mask under test was then mounted onto the
 manikin head's face and placed in a confining box. An inexpensive
 piezeoelectric atomizer (APGTEK Aluminum Mist Maker) usually employed in
 home decoration was submerged in Sodium Chloride solution (5% by weight
 NaCl in de-ionized water) to generate aerosol particles. The generated
 mist was exposed to negative ion air purifier to charge the aerosol
 particles for some of the tests. The mist could pass through a pipe with a
 second connecting pipe open to ambient air and both pipes had valves to
 help control the total aerosol concentration in the air entering the
 confining box.   A portable PM2.5
 air quality monitor (Manufacturer: Dienmern) used normally for home and
 office air quality monitoring was placed in the confining box (Monitor A)
 to measure the particle concentration within the box. By reading this
 PM2.5 monitor, we were able to adjust the two values for aerosol mist and
 ambient air and control aerosol concentration in the confining box. The
 back of the manikin head was connected to a pipe which exited the
 confining box and terminated in a box containing a second PM2.5 air
 quality monitor (Monitor B). This monitor gave reading of particles that
 had passed through the fabric and manikin mouth and allowed measurement of
 filtration quality. This box containing the second PM2.5 monitor was, in
 turn connected to a vacuum pump. When the vacuum pump was turned on, a
 suction pressure was felt in the confining box and aerosol particles mixed
 with ambient air were sucked into the confining box and passed through the
 face mask to enter the drilled hole in the manikin head and exited the
 confining box. By controlling the vacuum pump valve, we were able to
 simulate flow rates for normal (30 liters per minute) and high (85 liters
 per minute) respiration rates. Design shortcomings: We
 emphasize that this filtration test setup does not conform to some of the
 stringent testing specifications employed in face piece respirator
 certification. For instance, NIOSH 42 CFR Part 84 standard for N95
 facepiece respirators (FRs) requires filter performance of greater than or
 equal to 95% with NaCl test agent at 85 liters per minute flow rate and
 inhalation resistance (maximum pressure drop across mask) of less than or
 equal to 343 Pa and exhalation resistance of less than or equal to 245 Pa.
 We had no means to measure the pressure drop nor could we simulate the
 oscillating respiratory air flow from inhalation and exhalation. Our
 scheme could only generate steady suction flow.
   An important quantity in face mask
 filtration quality testing is the Most Penetrating Particle Size (MPPS);
 MPPS for N95 FRs is 300 nm or 0.3 microns. An important shortcoming of our
 filtration test setup is we do not know the sizes of aerosol particles
 generated by our relatively inexpensive piezoelectric atomizer. Secondly,
 commercial respirator testing systems use laser-based particle counter
 sensors that are sensitive to detection of particles down to at least the
 MPPS value. The PM2.5 air quality monitors, as their name suggests, are
 rated for measuring particles as small as 2.5 microns. Be that as it may,
 PM2.5 monitors also employ the same laser-based particle counter sensors
 and do hold the capability to detect particles down to 0.3 microns. Though
 we were unable to verify, it is reasonable to assume the PM2.5 monitors
 could detect particles down to 0.3 micron diameter.
 Test Results: FR filtration efficiency is usually measured in
 terms of the penetration percentage (P), defined as percentage of
 particles present in the environment that pass through the FRs and is
 quoted against the particle diameters. Since we could not measure particle
 sizes with our PM2.5 monitors, we define the penetration as:
 P(t) = C_B(t)/C_A(t) x 100% where C_A(t) and
 C_B(t) are the particle concentrations of PM2.5 monitors A and B
 respectively at time t. We followed the penetration as a function of time
 to study any deterioration in filtration properties. The PM2.5 monitors A
 and B were connected to a laptop and programmed to record concentration
 values at 15 minute intervals over a duration of 12 hours. The results we
 quote are for this 12 hour time series under various calibration and test
 conditions.
description: FabricDensity.txt: This file contains measured values for density
 of the electrocharged fabrics reported in Table 1 of the main manuscript.
 Reported here are measurements from a commercial N95 facepiece respirator
 (N95 FR), Surgical Mask (SM), Isotactic Polypropylene (PP), and
 Polypropylene-Polystyrene (PP-PS) blend material. The density measurements
 were obtained by dividing the measured weight (in grams) by the volume
 obtained from measured dimensions of the measured samples (in centimeter
 cubed). This is a tab-limited text file with the following
 format: Column 1: N95 FR -- there was only one N95
 facepiece respirator sample we could cut open to measure properties of its
 electrocharged filtration layer. Accordingly, only one measurement value
 is reported. Column 2: SM -- 10 independent
 measurements reported on various commercial surgical masks.
 Column 3: Isotactic PP -- 10 independent measurements reported
 for electrocharged filtration fabrics manufactured using the cotton candy
 method for isotactic polypropylene as the fabrication material.
 Column 4: PP-PS -- 10 independent measurements reported for
 electrocharged filtration fabrics manufactured using the cotton candy
 method for a blend of 80% polypropylene and 20% polystyrene as the base
 material. ---- Scanning Electron
 Micrographs: Full resolution Scanning Electron Micrographs (SEM) for
 fabrics from a commercial N95 facepiece respirator (N95 FR), Isotactic
 polypropylene (PP), Low Crystallinity polypropylene (PP), Polystyrene
 (PS), and polypropylene-polystyrene (PP-PS) blend. The specific SEM image
 files are: N95.tif: Scanning Electron Micrograph of the
 electrocharged filtration layer from a commercial N95 filtering facepiece
 respirator (N95 FR). This image is the full resolution SEM for figure 6a
 of the manuscript. IsotacticPP.tif: Scanning Electron
 Micrograph of the electrocharged filtration layer from a sample
 electrocharged filtration fabric manufactured using the cotton candy
 method with isotactic polypropylene as the fabrication material. This
 image is the full resolution SEM for figure 6b of the
 manuscript. PP-PS.tif: Scanning Electron Micrograph of
 the electrocharged filtration layer from a sample electrocharged
 filtration fabric manufactured using the cotton candy method with low
 crystallinity Polypropylene (80%) and polystyrene (20%) which we call
 PP-PS blend as the fabrication material. This image is the full resolution
 SEM for figure 6c of the manuscript.
 LowCrystallinePP.tif: Scanning Electron Micrograph of the
 electrocharged filtration layer from a sample electrocharged filtration
 fabric manufactured using the cotton candy method with low crystallinity
 polypropylene as the fabrication material. This image is the full
 resolution SEM for figure 7a of the manuscript. PS.tif:
 Scanning Electron Micrograph of the electrocharged filtration layer from a
 sample electrocharged filtration fabric manufactured using the cotton
 candy method with polystyrene as the fabrication material. This image is
 the full resolution SEM for figure 7b of the manuscript.
 ---- Mask Filtration Efficiency Test Data:
 These files provide the time series for particle penetration using the
 method described in the Methods section above and in the manuscript
 (Section 5b). The tests were performed using a filtration test setup
 constructed in-house as presented in figure 8 of the manuscript. The tests
 were conducted on a commercial N95 filtering facepiece respirator (N95 FR)
 and commercial Surgical Mask (SM) for calibration. These calibrations were
 followed by filtration tests on Isotactic PP and PP-PS fabrics tested on
 surgical mask as secondary layer and on Montana Mask 3D printed fabric
 holder. All data files are provided in tab-limited text format and their
 structure is described below: N95FR.txt: Penetration
 values as measured per Equation 5.1 of the manuscript, over a 12 hour
 period for a commercial N95 filtering facepiece respirator (N95 FR). This
 data is presented in Figure 9a of the manuscript.
 Column 1: Time (Hours) Column 2: Penetration
 values (%) for charged aerosol particles at 30 liters per minute flow
 rate. Column 3: Penetration values (%) for neutrally
 charged aerosol particles at 30 liters per minute flow rate.
 Column 4: Penetration values (%) for charged aerosol particles at
 85 liters per minute flow rate. Column 5: Penetration
 values (%) for neutrally charged aerosol particles at 85 liters per minute
 flow rate. -- SM.txt: Penetration
 values over a 12 hour period for a commercial surgical mask (SM). All
 measurements in this test were performed using only neutrally charged
 aerosols. This data is presented in figure 9b of the manuscript.
 Column 1: Time (Hours) Column 2: Penetration
 values (%) without tape on the surgical mask at 30 liters per minute flow
 rate. Column 3: Penetration values (%) with tape on the
 surgical mask at 30 liters per minute flow rate. Column
 4: Penetration values (%) without tape on the surgical mask at 85 liters
 per minute flow rate. Column 5: Penetration values (%)
 with tape on the surgical mask at 85 liters per minute flow
 rate. -- IsotacticPP.txt:
 Penetration values as measured per Equation 5.1 of the manuscript, over a
 12 hour period for an isotactic polypropylene fabric made using the cotton
 candy method. This data is presented in Figure 9a (columns 1-5 below) and
 b (columns 1 and 6-9 below) of the manuscript. Column
 1: Time (Hours) Column 2: Penetration values (%) for
 non-electrocharged filtration fabric mounted onto a taped surgical mask at
 30 liters per minute flow rate with neutrally charged aerosols.
 Column 3: Penetration values (%) for non-electrocharged
 filtration fabric mounted onto a taped surgical mask at 85 liters per
 minute flow rate with neutrally charged aerosols.
 Column 4: Penetration values (%) for electrocharged filtration
 fabric mounted onto a taped surgical mask at 30 liters per minute flow
 rate with neutrally charged aerosols. Column 5:
 Penetration values (%) for electrocharged filtration fabric mounted onto a
 taped surgical mask at 85 liters per minute flow rate with neutrally
 charged aerosol particles. Column 6: Penetration values
 (%) for electrocharged filtration fabric mounted on a 3D printed Montana
 Mask holder exposed to charged aerosols at 30 liters per minute flow
 rate. Column 7: Penetration values (%) for
 electrocharged filtration fabric mounted on a 3D printed Montana Mask
 holder exposed to neutrally charged aerosols at 30 liters per minute flow
 rate. Column 8: Penetration values (%) for
 electrocharged filtration fabric mounted on a 3D printed Montana Mask
 holder exposed to charged aerosols at 85 liters per minute flow
 rate. Column 9: Penetration values (%) for
 electrocharged filtration fabric mounted on a 3D printed Montana Mask
 holder exposed to neutrally charged aerosols at 85 liters per minute flow
 rate. -- PP-PS.txt: Penetration
 values as measured per Equation 5.1 of the manuscript, over a 12 hour
 period for a polypropylene-polystyrene blend (PP-PS)  fabric made using
 the cotton candy method. This data is presented in Figure 9c (columns 1-5
 below) and c (columns 1 and 6-9 below) of the manuscript.
 Column 1: Time (Hours) Column 2: Penetration
 values (%) for non-electrocharged filtration fabric mounted onto a taped
 surgical mask at 30 liters per minute flow rate with neutrally charged
 aerosols. Column 3: Penetration values (%) for
 non-electrocharged filtration fabric mounted onto a taped surgical mask at
 85 liters per minute flow rate with neutrally charged aerosols.
 Column 4: Penetration values (%) for electrocharged filtration
 fabric mounted onto a taped surgical mask at 30 liters per minute flow
 rate with neutrally charged aerosols. Column 5:
 Penetration values (%) for electrocharged filtration fabric mounted onto a
 taped surgical mask at 85 liters per minute flow rate with neutrally
 charged aerosol particles. Column 6: Penetration values
 (%) for electrocharged filtration fabric mounted on a 3D printed Montana
 Mask holder exposed to charged aerosols at 30 liters per minute flow
 rate. Column 7: Penetration values (%) for
 electrocharged filtration fabric mounted on a 3D printed Montana Mask
 holder exposed to neutrally charged aerosols at 30 liters per minute flow
 rate. Column 8: Penetration values (%) for
 electrocharged filtration fabric mounted on a 3D printed Montana Mask
 holder exposed to charged aerosols at 85 liters per minute flow
 rate. Column 9: Penetration values (%) for
 electrocharged filtration fabric mounted on a 3D printed Montana Mask
 holder exposed to neutrally charged aerosols at 85 liters per minute flow
 rate. --