The researchers found a better way to test the fabrics that are used to make masks that slow the spread of the Corona virus, by testing those natural and synthetic fabrics under conditions that simulate the humidity of a person's breath, and the researchers obtained measurements that more accurately reflect how the fabrics perform when worn by a living person. breathes.
The results show that under wet conditions, filtration efficiency - a measure of how well the material captures particles - increased by 33% in cotton fabrics, synthetic fabrics performed poorly compared to cotton, their performance did not improve with humidity, and materials from medical procedure masks did not improve. With moisture, although it performs in roughly the same range as cottons.
The study, conducted by scientists at the National Institute of Standards and Technology (NIST) and the Smithsonian Institution Museum Conservation Institute of America, is published in the journal ACS Applied Nano Materials.
A previous study by the same research team showed that two-layer masks made of tightly-woven cotton fabrics with a raised piece, such as flannels, are particularly effective in filtering breathing, and that study was conducted in the laboratory under relatively dry conditions, and its main findings are still valid. .
Although cotton fabrics are still a great option preferred by some, this new study shows that cotton fabrics work better in masks than we thought. ”
The researchers also tested whether moisture makes the fabrics more difficult to breathe, and they found no change in breathability.
The Centers for Disease Control and Prevention (CDC) recommends that people wear masks to slow the spread of the Corona virus, and when worn correctly, these masks filter some of the droplets full of viruses that the infected person exhales, and they also provide some protection for the wearer by filtering the incoming air.
According to the researchers, the filtration efficiency of cotton fabrics increases in wet conditions because cotton is hydrophilic, and by absorbing small amounts of water in a person's breath, the cotton fibers create a moist environment inside the cloth, and when microscopic particles pass, they absorb some of this moisture and grow larger. This makes it more vulnerable to detention.
On the other hand, most synthetic fabrics are hydrophobic, which means that they do not like water. These fabrics do not absorb moisture and the filtration efficiency does not change in wet conditions.
In the study, the team tested fabric samples, not the actual masks. First, they prepared two-layer fabric masks by placing them inside a small box where the humidity of the air is maintained at 99% - roughly the same as the person's exhalation. For comparison, a second set of samples was prepared at 55% humidity.
After the fabrics had reached equilibrium with the humidified air, the researchers placed them in front of a tube that emits air at the same speed as an exhalation.This air carries salt particles in a range of typical sizes of droplets that a person exhales when breathing, speaking and coughing.
The researchers tested 9 different types of cotton fabrics, which under wet conditions increased the filtration efficiency from 12% to 45%, with an average increase of 33%. They also tested 6 types of synthetic fabrics, including nylon, polyester and rayon. All of them performed poorly compared to the cotton varieties regardless of humidity, while medical procedure masks and N95 respirators provided the same filtration efficiency under both high and low humidity conditions.
Comments
Post a Comment