When combined with natural silk or chiffon, tightly woven cotton is the ideal material in the manufacture of protective masks against Covid-19. This is revealed by a study conducted in the United States.
The deconfinement is becoming clearer. In order to fight against the spread of Covid-19, the mask will become compulsory in public transport from May 11 in France, as announced by Christophe Castaner when he presented the bill extending the state of health emergency on May 2. An insufficient measure for certain institutions, such as the national academy of medicinewhich had published on April 22 a communicated asking for the systematic wearing of a mask in the public space.
Three weeks before deconfinement, the Academy was already calling on the French to mobilize by making washable and reusable fabric masks. A solution to which many families and businesses turned in April when faced with the difficulty of obtaining masks for the general public.
Aerosols, these droplets that slip easily between certain fabrics
Sheets, t-shirts, pillowcases… If we tend to opt for cotton to make our mask, researchers from the Argonne National Laboratoryin the United States, report that combining it with natural silk or chiffon more effectively filters out virus particles.
In study published by the journal ACS Nano, scientists became interested in the problem of homemade masks when they saw some questioning their reliability. In question: the main way in which SARS-CoV-2 is transmitted. Because, as a reminder, the virus is spread by the respiratory droplets emitted by an infected person when he coughs, sneezes, speaks, or even breathes. However, the smallest droplets, aerosols, can easily slip between the openings of certain fabric fibers.
Efficiency close to that of FFP2 masks
To carry out their work, the researchers created particles whose diameter ranged from 10 nanometers to 6 microns. They then used a fan to diffuse the aerosols through several common fabric samples. The experiment was carried out with two different airflows: a first equivalent to that of breathing at rest and a second similar to breathing during moderate effort.
Thus, the scientists were able to measure the number and size of the particles present in the air before and after they had passed through the tissues. Result: the combination of a layer of tightly woven cotton with two layers of polyester-spandex muslin — an extra-thin synthetic fabric — filtered the most aerosol particles, from 80 to 99 % according to their size. An efficiency that approached that of FFP2 protective masks.
The need to properly adjust your mask
The researchers came to the same conclusion by replacing the polyester-spandex chiffon with natural silk or chiffon. Indeed, the tight weave, as found in cotton, can act as a “mechanical barrier” against particles, while fabrics with static electricity, such as natural silk, can act as a “electrostatic barrier”.
Nevertheless, whatever the fabrics used, the researchers warn of the need to adjust your mask carefully: a difference of 1% reduces its effectiveness by half, or even more.
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