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Science offers recipes for homemade coronavirus masks | Science News for Students

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Many people wear homemade masks to limit the spread of the new coronavirus. The effectiveness of these masks depends on the materials they are made of and the degree of suitability.

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In supermarkets, hardware stores, workplaces, etc. The goal is to slow the spread of the virus that causes COVID-19. Now, two new studies provide data on which fabrics are used. They also show an important point: a close fit.

To understand why, it can help you understand how the virus spreads through the air. People infected with COVID-19 will spit out some very small saliva, nasal mucus or virus particles in water vapor droplets. There is nothing to stop them, and the larger droplets will fall within a few feet. That's why

It is important between people. However, the smallest droplets (called aerosols) can stay high for several hours before falling onto the surface. This is also the reason for frequent hand washing, surface cleaning and other disinfection steps.

Masks can help limit the spread of aerosols. However, medical-grade masks are in short supply. Hospitals and health practices need them most. Therefore, in the public, many people have begun to make masks at home. It is not yet clear which material may work best.

Supratik Guha pointed out that the range of aerosols ranges from approximately 6 microns (or microns) to 10 nanometers. In contrast, materials scientists explain: "A human hair is about 7,500 microns." (A micron is one millionth of a meter; a nanometer is one billionth of a meter.) Guha is in

In Lemont, Illinois and the nearby University of Chicago.

In order to understand which fabric is the most effective at blocking aerosols, Guha and his colleagues conducted tests. They built a chamber to produce salt aerosols within the droplet size range that can carry the COVID-19 virus. The fan blows these aerosols to the duct. A piece of fabric-sometimes a layer of one or more types of fabric-covers the proximal end of each tube. The research team then measured the share of aerosols passing through the fabric.

In general, mixed fabrics have the best effect. Not only any fabric. The best performer paired it with two layers of silk or tulle and woven 600 needle count cotton (meaning 600 yarns per square inch of fabric). On average, each type will block at least 90% of the particles.

What does it mean if you make your own masks? Guha said: "Use tighter fabrics and tighter weaves." Tighter weaves have smaller holes that allow particles to sneak. He added: "Try to use a combination of multiple materials, they filter particles in different ways."

For example, tightly woven cotton acts as a mechanical filter. Just like a sieve, it prevents too big onboard drill bits from passing through the holes between its threads. Chiffon or silk can also use the second method. Guha explained that the molecular structure that makes up these fabrics makes them attract electrons or discard them. In this way, they can attract charged aerosols. This electrostatic property allows threads and aerosols to bond with each other.

However, if you don't have the right type of high-count cotton, silk or chiffon, don't be nervous. The quilt samples drawn from the quilt also performed very well in the test, as did the four-layer silk. Guha found that an important lesson is "there are some simple materials that work well." (and as

, It is not very difficult to make a mask with them. )

However, if the mask does not fit well, even the best fabrics will not work well. The purpose is to limit leakage.

Any air that can leak through the sides, top or bottom of the mask may carry viral carrier gas. To test the importance of this leak, Guha's team drilled a small hole in the side of the fabric support. These generated gaps may account for 1% of the fabric filtration area. However, such a small amount of filtration efficiency is reduced by at least 50%!

"What we are doing is not rocket science," Guha pointed out. He said that none of the things his team learned was "really surprising. But we want good, reliable data." In other words, the team has an assumption. But before the test, researchers could not determine its affordability.


  April 24


Raina MacIntyre said the team’s work is “an excellent study that has enriched our understanding of cloth masks.” She leads biosafety research at the University of New South Wales in Sydney, Australia. She said: "The results first confirmed that it is important to be suitable." "Even if it is not appropriate, the efficiency of the N95 mask will be greatly reduced." (In high-risk situations, medical staff wear N95 masks).

Loretta Fernandez and Amy Mueller are environmental scientists at Northeastern University in Boston, Massachusetts. They usually do not learn masks. But talking about masks during the current pandemic makes them curious. Therefore, they used science to compare 10 types of homemade fabric masks with N95 masks and less protective surgical masks. Quern Fernandez said: "We really feel like we are working on a science fair project."

They also built a particle generator to crush salt particles. But one of the researchers did not test the masks on a sturdy shelf, but instead wore each mask. A separate counter measures the concentration of particles inside and inside the mask. The sewn mask filters out about 30% to 70% of particles.

Then, the team tested the effect of fitting the mask on the performance of the mask. For this, they used a part of women's stockings. They passed through the legs of the stockings to form an elastic nylon mesh tube. The researchers then slid the test tube over the top of the head until it covered the mask they were wearing. This greatly improves the filtering effect of each mask.

For example, a cotton mask with a cotton filter initially filtered out about 33% of salt particles. After being tightly fixed with a nylon sleeve, it can now prevent more than 80% of objects from passing through the mask. The findings of Fernandez and Mueller appeared on the medRxiv website. (Their research has not been peer reviewed.)

McIntyre said that water resistance is also the key, but new research has not solved this problem. Moisture in the breath or internal sweat can make the mask uncomfortable. She pointed out that the bigger problem is: "Masks that become damp or let liquids flow through will not be very protective, no matter how well they filter the [dry] air."

Some people insert filters made of various materials into homemade masks. Fernandez recommends considering the respiratory safety of any particles inhaled from these filters. Something is safe for a certain type of use, such as a fabric softener sheet or a vacuum cleaner bag, does not always mean that it is safe to breathe.

Another important point: You need to be able to breathe easily through a mask. Guha pointed out that fabrics like silk can be "very breathable." It can be very thin, but tightly woven. Although some high-risk people may try to wear stockings to get tight, Fernandez said she just wore a mask when she went out. Otherwise, it may feel too tight and too hot.

She pointed out that, after all, a mask cannot protect you or others unless you wear a mask.

: A group of tiny particles suspended in air or gas. Aerosols can be natural, such as mist or gas from volcanic eruptions, or man-made, such as smoke from burning fossil fuels.

: A federal laboratory owned by the U.S. Department of Energy outside of Chicago, Illinois. The laboratory was formally established on July 1, 1946. Today, its approximately 1,400 scientists and engineers (and 1,000 students) conduct research in various fields, from biology and physics to materials science, energy development, and climate research.

: (Scientific) term for arithmetic mean, it is the sum of a group of numbers, then divided by the size of the group.

: (In textiles) a fluffy material, usually non-woven, such as the filling between quilt layers.

: A person who works with another person; a colleague or team member.

: (Chemically) a measure of the dissolution of a substance into another substance.

: Beginning in December 2019, the name of the coronavirus has caused a huge outbreak of potentially fatal diseases. Symptoms include pneumonia, fever, headache and difficulty breathing.

: Negatively charged particles, usually in the outer region of the atom; also, the carrier of electricity in the solid.

: Refers to the condition that exists around the area of ​​electronic imbalance compared with the surrounding environment. When a surface has fewer electrons than the surrounding area, there will be a positive charge. When there are too many electrons, a negative electrostatic field is generated.

: Any woven, braided or flexible material that can be fused into a sheet by heating.

: (In the fields of chemistry and environmental sciences) a device or system that allows certain materials to pass based on their size or certain other characteristics, while other materials cannot pass. (In physics) A screen, panel, or layer of material that absorbs light or other radiation or selectively prevents transmission of some of its components.

: The process of using fabrics, screens or some other type of material (called filters) to prevent certain objects from passing through. Curtains can restrict the filtering of sunlight into the room. The wire mesh can filter out large particles in water or air. Sand or soil can provide filtration to prevent certain water-based chemicals or bacteria from entering the groundwater.

: (Relative to hypothesis) a suggested explanation of the phenomenon. In science, a hypothesis is an idea that must be accepted or rejected, and must undergo rigorous testing.

: Researchers who study the relationship between the atomic and molecular structure of materials and the overall properties of materials. Materials scientists can design new materials or analyze existing materials. Their analysis of the material's overall properties (such as density, strength, and melting point) can help engineers and other researchers choose the most suitable material for a new application.

: Something that occupies space and has quality. Anything related to matter on the earth will have the nature of "weight".

: Related to mobile equipment, including tools, engines and other machines (maybe even living machines); or things caused by the physical movement of other things.

: (Sometimes called micron): One thousandth of a millimeter or one millionth of a meter. It is also equal to a few tenths of an inch.

: There is a small amount of water in the air in the form of vapor. It can also exist in liquid form, such as water droplets condensing on the inside of windows or moisture in clothing or soil.

: The neutral group of atoms, representing as few compounds as possible. Molecules can be made of a single type of atoms or different types of atoms. For example, oxygen in the air is composed of two oxygen atoms (

), but water is composed of two hydrogen atoms and one oxygen atom (H


: A prefix representing one-billionth. In the metric measurement system, it is often used as an abbreviation to refer to objects that are one billionth of a meter in length or diameter.

: One of the eastern states that make up Australia. It is the oldest, largest, and most urban city in these states, with approximately 8 million people living in it. Most residents of Sydney are located in the central, eastern and southeastern parts of the country, living in or near the state capital, Sydney.

: A silky material made of long, manufactured molecules (called polymers). These are long chains of atoms that are connected together.

: An epidemic that affects a large proportion of the entire country or the world’s population.

: A small amount of things.

: (In science) a process in which scientists in a certain field carefully read and criticize the work of their peers before publishing their work in a scientific journal. Peer review helps prevent sloppy science and serious errors from being published.

: (Adjustment) A term that refers to things that exist in the real world, rather than things in memory or imagination. It can also refer to material properties due to its size and non-chemical interactions (for example, when one block hits another block hard and hard).

: The full range or distribution of something. For example, the range of plants or animals is an area that naturally exists.

: (In physics) something that prevents a physical substance (such as a piece of wood, water, or a stream of air) from moving freely, usually because it provides friction that hinders its movement.

: The chance or mathematical possibility that something bad may happen. For example, exposure to radiation brings the risk of cancer. Or the hazard (or danger) itself. (E.g:


: A compound made by mixing an acid and a base (in a reaction that also produces water). The ocean contains many different salts-collectively referred to as "sea salt". Ordinary table salt is made of sodium and chlorine.

: The shape is firm and stable; it is not liquid or gas.

: (In biology) factors that affect the health of a species or ecosystem, such as abnormal temperature, movement, humidity, or pollution. (In psychology) the mental, physical, emotional, or behavioral response to an event or situation (stressor) that disrupts the normal living conditions of people or animals or places higher demands on people or animals ; Psychological pressure can be positive or negative. (In physics) the pressure or tension exerted on matter.

: Tiny infectious particles, composed of RNA or DNA surrounded by protein. Viruses can only reproduce by injecting their genetic material into the cells of living organisms. Although scientists often refer to viruses as live viruses or dead viruses, no virus is actually alive. It does not eat like animals, nor does it make its own food like plants. It must hijack the cellular machinery of living cells to survive.

 A. Konda et al.


. April 24, 2020. doi: 10.1021 / acsnano.0c03252.

 A. Mueller and L. Fernandez.

. April 2020. doi: 10.1011/2020.04.17.20069567.

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