Sunday, April 05, 2020

Everything You Have Ever Wanted To Know About Masks by Sujoy D. Guha

Hi, my dear friends. Hope that you all are well. I worry about all my dear ones all over the globe. All I can do is share what I know, and if that little bit helps, I am happy.
Stay Safe, my loved ones.

Today I will discuss masks.

1) How do they work?
2) Materials used in mask manufacturing - Why are some materials better than others?
3) DIY masks - best choice of materials

Let’s start with realizations on the size of things.
Human hair size is 100 microns, while a virus size 0.14 microns. Give this some thought. The virus is nearly a 1000 times smaller.
How do you filter and block things that are so bloody small? You cannot make the masks non-air permeable or else you cannot breathe with a mask on. So, you make your filter smarter.

There are 3 simple rules on the filtration of removing particles from the airstream. A good mask starts with the following:
1) inertial impaction
2) diffusion
3) electrostatic attraction

Inertial Impaction:
Inertial impaction is effective for aerosol particles that are approximately 1 µm and larger. Such
particles have enough inertia that they cannot easily flow around the mask fibers. Instead of flowing
through the filter material, the large particles deviate from the air streamlines and collide with the
fibers and stick to or be caught in them.

Diffusion: (this is key)

For much smaller particles—those that are 0.1 µm and smaller
Diffusion is regarded as an effective filtration mechanism. Brownian motion—the process by which the constant motion of oxygen/nitrogen molecules causes
collisions between particles—results in a “wandering” pathway. The complex path that is followed by
the small particles increases the chance that they will collide with the filter fiber and remain there.

Electrostatic attraction:
In which electrically charged fibers affect the flow of the pollutants andd trap them in the fibers or repel them.

Part 1 was the science of how masks work. Now, let’s talk about masks available on the market.

Medical Masks: 3 layers (All Nonwoven material – think of the material used for making complimentary airplane or hotel slippers)

Layer#1, outside facing material that has been sprayed to ensure that it is waterproof

Layer#2, and this is KEY, a true filtration layer that has random orientation of fibers and have fibers that are a few microns in diameter with spacing that is random, between 1-10 microns spacing. It is this layer (typically melt blown nonwoven) that is the most effective barrier for viruses.

Layer#3, inside facing material, typically an absorbent layer to absorb moisture from breath.
All/Most Medical masks made of Nonwoven Polypropylene. During the manufacturing process the material gets electrically charged. This absolutely helps for the first few hours of use…unfortunately, the static reduces dramatically as it is exposed to moisture (your breath). So, I don’t have a definite answer here. I could not find a study of electrostatics on masks over time in general or over exposure to moisture over time. ( I am thinking of coming up with a test. If any of my friends know a good way to test static electricity for a mask over time over exposure to moisture, it would be extremely helpful).

Cotton Cloth Masks:

1) Structured pattern: If you look at cloth, you will see by the way it has been woven that it has a clear cut structured pattern (part of the weaving process). Thread, Space, Thread, Space…..structured. This is not good, because it does not give the virus a torturous path to your nose/mouth.

2) Cotton does not have the property of getting electrostatically charged.

3) Not waterproof

4) Spacing in general- large spaces between fibers

So, if you want to DIY this with cloth masks, you need to do this right, at best semi- helpful. Just using any material is not a good idea.

DIY Cloth Masks:

1. Use nonwoven cloth, I have seen results from blue shop towels – such as the kind car mechanics use. This is a good choice. Absorbent and not really a woven cloth. Really good!
2. Cotton is not the right choice. Material that generates more static is better. Silk, Wool, Nylon, Polypropylene ….
3. Layering is the right approach
4. A mask with a pocket, where the mask can be washed and the material in the central layer disposed every cycle.
5. Central layer being a nonwoven would be ideal
a. You have seen non-woven material at restaurants with fancy napkins that are not cloth but are disposable – they are cloth feel napkins. Bestchoice for DIY as central layer
b. Look for meltblown or spunlace nonwoven material that is being used for other purposes. These materials have many applications besides masks, so they be available, but are generally not known for their mask properties.
6. If you can find the correct non-toxic water-proof spray, spray it on the outer layer
7. Bottom line- structured textile (such as cotton or polyester cloth) is not a good idea.

All I can say is that your mask, at whatever level, provides some help. Your Humanistic Duty is to wear one, whether it is DIY or store bought…every little big helps. The bottom line is that wearing a mask protects others! You may unknowingly be a carrier or a potential carrier, or not at all, but wearing a mask ensures that you are not a SPREADER!

References: (worth checking out)

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