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Oak Ridge National Laboratory
When COVID-19 was declared a pandemic in March 2020, Parans Paranthaman of Oak Ridge National Laboratory suddenly found himself working from home like millions of other people.
As a corporate researcher in the Laboratory's Chemical Science Department, he quickly realized that his background in solid-state chemistry and materials could benefit healthcare communities that need equipment that can filter COVID-19 nano-particles.
“Merlin Theodore, who leads research at the carbon fiber technology facility, called me and said, “I need to know which material is best for making N95 mask filter media on our production line. I need to know this yesterday,” Paranthaman recalled. "She asked if we could use neutron and nanoscience facilities to prove this.
Theodore is part of a team led by ORNL researcher Lonnie Love, who is coordinating the COVID-19 manufacturing research response as part of the Department of Energy's National Virtual Biotechnology Laboratory. The team also consulted with Peter Tsai, a retired professor at the University of Tennessee, who invented the electrostatic charging process used to make N95 filter media to understand how to integrate this feature in CFTF.
"In this time frame, we have never tried something like this before," Paranthaman said. "We are stepping up research that should have taken a year or more until industrial use in the summer."
"But I haven't encountered a challenge. The purpose of my research is to find a solution."
Paranthaman's research results on N95 filter media were recently published in ACS Applied Polymer Materials, outlining the science behind ORNL's successful production of materials on the CFTF precursor production line. The technology was later transferred to two industry partners-Cummins and DemeTECH-for commercial use under user agreements, thereby supplying millions of masks in the United States and adding thousands of jobs.
As one of the first studies on COVID-19 polypropylene (also known as PP), Paranthaman's paper can be used as a guide to understanding how new viruses respond to polymer materials. PP has long been the industry standard material for filtration, but understanding which commercial compound or material precursor is most suitable for mass production usually requires time-consuming trial and error.
"We have a unique situation with COVID-19. First, it is a new type of virus that little is known about it. Second, it is very small, ranging from 60 to 140 nanometers, which means that the particles can penetrate the smallest Opening. And thirdly, we don’t have time to make mistakes,” Paranthaman explained. "We must have a material that can filter out more than 95% of sub-micron particles. It must be almost impermeable, but at the same time it must be breathable."
The N95 mask is made of two layers of PP, which is a non-woven material that is permanently electrostatically charged. Millions of microfibers are superimposed on each other to form a layer. CFTF's Theodore team used melt-blown technology to extrude polymer resin through a die at high air speed to make microfibers into fabrics, thereby producing three commercial-grade PP samples for Paranthaman's evaluation.
"We used several characterization methods at ORNL to better understand the filtration efficiency of PP, and called for the advantages of user facilities such as the Nanophase Materials Science Center and Spallation Neutron Source," Paranthaman said.
Characterization methods include differential scanning calorimetry to measure the energy transferred between meltblown fibers; X-ray diffraction to understand the crystal orientation or texture of the fibers; and neutron scattering to study molecular vibrations. Scanning electron microscopy is used to understand the arrangement and microstructure of meltblown fibers and to characterize their diameter.
"It's important to understand how many particles the filter prevents," Paranthaman said.
The team used sodium chloride aerosol particles that mimic the size of COVID-19 to penetrate the filter, and then measure the particles when they encounter PP. Two layers of meltblown fibers are stacked together and tested at an airflow rate of 50 liters per minute.
Paranthaman's research shows that although the composition of the raw materials is almost the same, their performance during charging is quite different. The most significant difference is crystallization, which is how the material solidifies atoms and molecules into a structured form.
"We compared charged and uncharged PP materials with and without additives," Paranthaman explains. "In each case, crystallization has a significant effect on the filtering ability of the material; more crystallites form a stronger charge, leading to more effective filtration."
The research results further confirm that materials with higher crystallization onset temperature, slower crystallization and a large number of smaller, microscopic crystallites are more effective in filtration. Paranthaman's research on PP samples showed which material might meet the filtration goals in terms of fabric weight, efficiency, resistance, fiber diameter size, and percentage of electrostatic charging.
By the end of April, materials produced by CFTF can filter 99% of viruses. By May, the technology had been transferred to industry.
The research team won ORNL’s Mission Support Director Award for the rapid development and technology transfer of N95 filter media. However, Paraanthaman said, scientific work on N95 filter media has just begun.
"This paper provides a three-dimensional view of the material, so we can see all the changes between charged and uncharged fibers," Paranthaman said. "For example, we know that charging will reduce the fiber diameter, but it will also change the porosity, which is critical to the performance of the material. Our follow-up paper will clearly outline the difference between charged and uncharged, and go deeper Learn about N95 filter media."
The title of the ACS Applied Polymer Materials article is "The Effect of Polymers, Additives and Processing on the Performance of N95 Filters." Further exploration of COVID-19 mask research found that stratification and material selection are important. More information: Gregory S. Larsen and others. The effect of polymers, additives and processing on the performance of N95 filters, ACS Applied Polymer Materials (2021). DOI: 10.1021/acsapm.0c01294 Citation provided by Oak Ridge National Laboratory: Research provides new insights into N95's COVID-19 filtration efficiency (2021, April 7), retrieved on December 13, 2021, from https://phys.org/news/2021-04-insights-n95-covid-filter-efficiency.html This document is protected by copyright. Except for any fair transaction for private learning or research purposes, no part may be copied without written permission. The content is for reference only.
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