Education Hour

Every day I have an education hour.

I choose a topic and delve into it.  Yesterday it was N95 respirator masks.  What are they made of, how are they made, why are they so different than cloth masks.

In brief, I learned they are mostly made of nonwoven polypropylene, a recycled plastics material, and consist of at least three layers.  The outer layer is spunbond PP.  The middle layer is an electret PP, whose charge along with the dense chaotic fibers of the nonwoven PP both attract and trap the bacterial and fiber particles.  The inner layer is usually a softer paperlike material that won't irritate the face.  The FE (filtration efficiency) of the mask is entirely determined by the filtration middle layer.  The outer layer needs to be slightly water attractive, which most PP is not, hence the use of spunbond PP on the outer layer.

Ok, so what else is made of nonwoven PP?

Like something I might have around the house, now that face masks are recommended for public use.

Ok, that was easy to find.  Reusable grocery bags often are made of PP, both woven and nonwoven.

Your standard grocery bag

Look at the tag info at the top, not the bottom.  People on facebook notice the bottom, but the fold covers the part that says "does not" then the "contain lead, etc", and thought it must contain all those heavy metals.  

The part of the bag that is red on the outside and white on the inside, bottom of the second photo, is woven polypropylene while the black part, above the tag in second photo, is nonwoven PP.  Its fiber density is of course not that of a regular N95 respirator mask, but oh well.  A few layers of it might be effective.  Whether it carries the charge needed to help attract particles---probably not.  But you can buy electret nonwoven PP online in bulk many places.  And other woven and nonwoven electret materials, like hepa cotton.

Attract and trap, those are the key words in creating the effectiveness of the filter layer of an N95 mask.

Then there is this article about N95 masks.

I found it fascinating.  I've heard about health care providers soaking their masks in cleansing solutions held in plastic bags in their pockets between patients so they can reuse them.  That's a no no.  Cleansing solutions that contain alcohol or bleach will destroy the filtration layers' charge, reducing drastically their ability to attract viral particles.  The best way to clean an N95 mask is with heat or with steam (think autoclave).  You can also boil for three minutes but don't stir.  But don't be soaking them in antiseptic.

I wondered why the Chinese and now other countries are so adament homemade, non surgical grade and cloth masks should be worn by the general public when outside, to prevent spread of the virus.  The virus is less than a half a micron in size.  Meaning it can easily penetrate cloth masks, especially around the edges.

Then I thought to myself, "oh, ok."  Those teensy viral particles aren't out there flying out of the nose or mouth even when we just talk or breath by themselves.  They would still be attached to something I would think, like a teensy micron bit of water or dust or anything else.  So maybe those homemade masks are pretty decent at stopping a good share of it from coming in or going out.

I had posted about the grocery bags being made of the same material as N95 masks yesterday on facebook.  Coincidentally, today I find a video on making a mask using grocery bags and pipe cleaners for the fittable nose bridge.