Disinfect your Nano mask
First of all, just to make one thing clear: I am blogging here about the sterilization of nano fiber respirators, not standard meltblown material masks. So if you need to sterilize your 3M N95, please also refer to our previous blog https://www.lungdragon.com/blog/reusablen95masks on the topic of meltblown material disinfection.
First to get some terminology out of the way; melt-blown fibers are commonly used in N95 standard masks. They function according to what is called the electrostatic principle. This is the same thing you get when you rub two balloons together; a static charge is created and that static charge is what catches the virus. It has been found in several reliable studies that using an ethanol, bleach or other alcohol type spray on this material, or immersion in ethanol, etc. technically will sterilize the material, but at the same time, will also greatly reduce the electrostatic capability. This means that your mask will be clean but it will only work half as well.
When we are talking about a nanofiber mask or nano fiber filters, we are talking about material produced by a process called electro-spinning. This process creates a membrane that is so thickly woven that it actually blocks the minuscule virus particles. It mechanically blocks them; ie, is so tightly-woven that it physically keeps the particles from coming through the membrane. So it makes perfect sense that we would use a different method of sterilization of this type of material than we would use for a meltblown fiber mask.
Japanese and South Korean researchers analyzed the filtration efficiency, air flow rate, and other properties of various masks after they underwent cleaning treatment. The focus of the research was a comparison of two methods; spraying ethanol on the materials versus total immersion of the materials in the ethanol solution for five minutes. They also did a comparison of nano-fibers to melt-blown materials. You can read their full research results here in Science Daily, or read below for my (shorter:-) summary.
Their study compared melt-blown filters of the type commonly used in N95 masks to nanofiber filters produced by electro-spinning. Prior to testing, the filtration efficiency of both materials was tested and found to be 95% or above. Both materials were then tested by spraying with ethanol 3-4 times and air-drying. This is where it got interesting. The filtration efficiency of the melt-blown filter decreased by up to 64% when cleaned with ethanol solution and reused. The nanofiber filters retained almost full filtering capability when reused, and continued to retain almost full efficacy when reused up to 10 times after ethanol spray cleaning.
It sounds kind of illogical, but it actually made a lot of sense. Basically, the ethanol was clogging up the pores in the meltblown material, and that meant that there was a significant decrease in static electricity in the filters after ethanol cleaning. And without that static charge, the meltblown was incapable of capturing the virus particles. Nanofibers do not rely on static electricity but instead filter mechanically, relying on the super-tiny pore size of the nano surface. The nanofiber filters in the test were not deformed at all by the ethanol and they were able to continue filtering at full capacity.
So what it all comes down to is that if you have a traditional N95 or FFP2 mask made of meltdown material, you are going to be sterilizing that meltblown material with slow dry heat or with steam. If you have a Nano fiber mask, or nano fiber filters, you'll be using 70-75% ethanol.
Handy to know, isn't it?
References:
Science Daily article re. Pohang University of Science & Technology (POSTECH) research
ACS Applied Nano Materials published by the American Chemical Society.
Journal of Nanofibers: Understanding Electrospinning
ACS Chemical Health and Safety: Can N95 Respirators Be Reused after Disinfection? How Many Times?