Centers for Disease Control and Prevention around the world have recommended the use of cloth face masks when in public, reserving surgical masks and N95’s for healthcare workers. However, when it comes to filtering out airborne particles, not all fabrics were created equal.New research published in ACS Nano, a journal by the American Chemical Society, suggests a combination of cotton with natural silk or chiffon makes for the most effective mask.
When a person with a virus sneezes or coughs, they eject infected particles into the air. Saliva droplets are relatively large, ranging from one to five millimeters in size, and travel in a radius of around six feet from the source — this fact, of course, is the impetus behind our new social norm of retaining such distance from others in public. Coming into contact with virus-infected droplets on surfaces promotes the spread of disease, but the particles which dissolve into the air and remain suspended for long periods of time raise concerns of their own
These particles, called aerosols, can travel hundreds of meters through the air. Additionally, aerosols within 10 nanometers to 10 micrometers in size are respirable, which is to say they can be breathed into the lungs. So wearing a mask over the mouth and nose which prevents inhalation of particles containing the virus can be crucial to preventing infection.
For their research, the University of Chicago scientists tested a variety of fabrics including flannel, cotton, polyester, synthetic and natural silk, and chiffon. To test the filtration effectiveness of each fabric, the researchers used a fan to blow aerosol consisting of particles 10 nanometers to six micrometers in size at a resting respiration rate across the cloth samples. They then measured the size and number of particles remaining in the air after passing through the fabric as compared to before.
When each fabric was used in a single layer, high thread count cotton performed the best with a filtration efficiency of around 80% for particles larger than 300 nanometers. However, the fabric samples performed even better when layered, especially in hybrid combinations. One layer of cotton with two layers of silk was effective at filtering greater than 90% of particles larger than 300 nanometers. The results of combining one layer of cotton with two layers of chiffon or one layer of flannel were similar.
The scientists believe the high efficiency of hybrid fabrics is due to combined mechanical and electrostatic filtration. For example, while tightly woven cotton prevents particles from passing through gaps in the fibers, silk provides an electrostatic charge which traps particles.
Though fabric plays a role mask effectiveness, the most important thing to keep in mind when choosing or making a face mask is fit. Improperly fitting masks that left gaps for leakage decreased filtration efficiency over 60 percent.
In the end, the researchers concluded that a properly fitting mask made from a combination of these common fabrics can help provide significant protection against aerosol transmission of COVID-19.
Credit:- forbes.com
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