Sorry, this one gets geekier than usual. There are a few physics lessons to be learned here.
There are two factors at play in an air filtration system: airflow and the sieve.
Inertial impaction: when the particulate matter is large enough to break off its airflow line and just run into the filter fiber. Helped along by a “tortuous path” mechanism (rather than aligned, oriented fibers).
Browning diffusion: small particles, when the particulate matter follows a somewhat random path and runs into the filter fiber,
Interception: a slightly larger radius of particulate matter that while staying on its airflow path will run into the filter fiber.
Electrostatic: If the filter fiber can be electrified (a permanent state, even when wet), a polarized particle will be ripped off of its airflow and attracted to the oppositely charged fiber. For instance, if the filter fibers are charged positive and the COVID-19 virus is negative, the fibers will attract the virus and the virus will stick. To learn more about positive/negative attraction and electrostatic charge, read up on the physical principal of Van der Waal's force.
How to Make Excellent Air Filters
If you decrease the diameter of the fiber towards the nano-scale, you get more surface area capture. Efficiency increases with smaller fiber diameter.
Notice in this graphic above that particulate matter at .3 microns is the most difficult to capture. The COVID-19 virus, at roughly .01 microns, is easier to capture due to electrostatic charge or Browning Diffusion (see first graphic above) than the larger particle. Air filtration (such as N95 and N99) is measured against the percentage to capture .3 microns. For instance, an N95 face mask is 95% effective in capturing .3 microns. Capturing this exact particle size is the gold standard of mask filtration. Larger than .3 and smaller than .3 microns are less worrisome as there is an even higher capacity to capture those sized microns (including a virus at .1 microns).
Electrospinning is the most reliable method for producing nano-scale fiber diameters, especially when compared to methods such as meltblown (like a 3M N95 mask). Electrospun can easily be cast (adhered) onto meltblown materials to increase their efficiency.
The main benefit of electrospun nano-fiber filtration is the high efficiency of filtration with low pressure drop (breathing resistance). The result is an effective product that is comfortable to wear.
There are environmentally friendly options with electrospinning, versus thermoplastic polymers as used in meltblowns. Please see the previous blog entry, Mask Are Bad for the Environment, about how masks have become trash and are not biodegradable. The forefront of environmentally friendly air filtration will be in electrospun materials.
Airveil Filter Technology stands behinds its name as the best products available and on the cutting edge of science.
Please protect yourself. Be well.
- July 2020
- May 2020