Every now and then, and
especially in distressed times such as these, it's good to spotlight an
engineer who has done the right thing, and keeps doing the right thing. Today I'm going to do that with Peter P. Tsai,
who is credited with inventing the electrostatic non-woven filter used in the
N95-type disposable masks that are such a hot topic nowadays.
In 1995, Prof. Tsai was a
materials scientist working at the University of Tennessee in the area of
non-woven filter materials. Air filters
have been used for many decades to separate undesirable particles from air. If the particles to filter out were large,
almost any finely woven material whose openings between the threads were
smaller than the particles could catch them.
But many of the most objectionable particles, such as tiny smoke
particles and virus particles, are smaller than one micron, which is one
millionth of a meter. Just to give you
an idea, a human hair is about 25 microns or more in diameter. So we are talking very, very small.
It's almost mechanically
impossible to weave cloth with fibers that are smaller than human hairs, so filter
designers looked around and discovered that a mat or mesh of non-woven fibers
was more effective than any woven fiber could be. The tortuous pathways a particle has to take
through the random labyrinth of a non-woven mat of fibers makes it more likely
that the particle will get caught somewhere before it makes its way through the
filter.
But even with non-woven
materials, there was a tradeoff between effectiveness and how hard it was to get
air to go through the filter. The
thicker a filter is, the more likely it is to catch particles, but the harder
it is to get air to go through it. This
problem can be fixed by making the area of the filter wider, and that is done
in stationary systems such as air conditioners.
But you can't attach a portable mask to a foot-square air conditioning
filter. So there was a quandary and it
looked like there weren't a lot of new ideas to make small filter masks more
effective for very small particles like viruses.
At this point Prof. Tsai,
and others preceding him, took a hint from the industrial filter technology
known as electrostatic precipitation.
Electrostatic precipitators use high electric fields to charge dust
particles and attract them to highly-charged wire grids, where they are trapped
and disposed of. They work well, but
they are huge structures attached to factory chimneys and require high-voltage
power supplies.
Prior to Prof. Tsai's work,
others had thought of the idea of making the plastic fibers in a non-woven
filter electrified through a process known as hot charging. When the fibers were still in a halfway-liquid
form right after they are spun from a melt, it is easy to put an electric field
on them that "freezes" into the plastic. But the charging-while-hot process was tricky
and probably expensive.
Prof. Tsai's innovation was
to find a way to take a cold pre-fabricated mat of non-woven material and
subject it to two electric discharges of opposite polarity, one after the
other. Under the right conditions, this
process embedded quasi-permanent electric charges into the plastic fibers and
made them very attractive to even sub-micron particles, like the 100-nanometer-diameter
SARS-CoV-2 virus that causes COVID-19.
The charge is durable and will persist even if the masks are sterilized
with steam, according to a new article that Prof. Tsai just put up on a
University of Tennessee website.
After a career in which he
obtained 12 patents and many commercial licensing agreements for his
university, Prof. Tsai retired recently, but he came out of retirement to write
the article I referred to, which tells health care workers how to reuse scarce
N95 masks and what methods will and won't work to sterilize them without
spoiling their electrostatic properties.
Another article about his work estimates that over a billion people have
benefited from using masks that employ his invention of cold-charging nonwoven
fibers.
Humility is not something
that today's culture looks upon favorably.
The media that get the most attention these days are constantly highlighting
people who use institutions as platforms to further their own fame and glory. Even some engineering and
science types (Elon Musk comes to mind) go this route and strive for public
recognition, fame, and the perks that go along with these things.
Peter Tsai is not a
limelight kind of guy. A brief biography
of him on the University of Tennessee website points out that he has had many
opportunities to take more prominent positions, but he has stuck to his
laboratory and continued to produce inventions right up to his retirement. I don't know this for a fact, but it's quite
possible that Prof. Tsai is an introvert—someone who is more comfortable
working alone or with a small group of carefully chosen colleagues than he is
speaking to a huge crowd at a conference, for example.
As Susan Cain points out in
a book of hers I've begun to read (Quiet:
The Power of Introverts in a World That Can't Stop Talking), much of
American society is set up to favor the talkative, sociable extrovert and to
view the introvert as weird or sad or even anti-social. But introverts can do things that other kinds
of people have trouble with—for instance, studying a dull materials-science
problem for years until insights and hard work pay off with an innovative
technique such as cold-charging nonwoven fibers.
For two or three decades
now, academia in general and engineering in particular has emphasized teamwork
almost to the exclusion of allowing people to do work on their own. I'm sure Prof. Tsai had help in doing what
he's done with filter-mask materials, but I hope he'll allow me to use him as an
example of what the non-attention-getter type of engineer can achieve. By and large, he has let his work speak for
itself, and now that is paying off in the lives saved, especially among medical
workers, who would otherwise have inferior filtering and higher risk for
contracting COVID-19. If you are one of
the lucky people these days with access to an N95 mask, take a moment to thank Prof.
Tsai and his colleagues for coming up with the ideas that make such things
possible.
Sources: An
article describing Prof. Tsai's work on cold-charged electrostatic non-woven filter
material is on the University of Tennessee website at https://utrf.tennessee.edu/ut-researchers-nonwoven-fabrics-protect-the-health-of-more-than-a-billion-people/. Prof. Tsai's own article describing effective
sterilization methods for the masks is at https://utrf.tennessee.edu/information-faqs-performance-protection-sterilization-of-face-mask-materials/. And the U. S. patent for cold-charging
non-woven materials that Prof. Tsai obtained in 1995 is No. 5401446, which can be viewed on Google or the U. S.
Patent Office site.
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