By Paul
Ridden
March 16, 2021
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Researchers
have found a way to weave polyethylene fibers into fabric that allows for
passive cooling photo credit : MIT
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Due to its structure, fabric spun
from polyethylene could keep a wearer cool by allowing heat to escape, but it's
been largely dismissed by the scientific community as a fabric candidate due to
its less-than-desirable trait of tapping moisture in.
"Everyone we talked to said
polyethylene might keep you cool, but it wouldn’t absorb water and sweat because
it rejects water, and because of this, it wouldn’t work as a textile," said
Svetlana Boriskina from MIT's Department of Mechanical Engineering.
But the MIT engineering team has
found a way to make the material able to attract water molecules to its surface,
where it evaporates. The researchers started with raw polyethylene powder, then
made use of standard textile manufacturing equipment to produce thin fibers,
finding that the process resulted in mild oxidation that resulted in a weak
hydrophilic effect.
Suitably encouraged, the team
extruded multiple polyethylene fibers together in a weavable yarn, with the
spaces between the strands forming "capillaries through which water molecules
could be passively absorbed once attracted to a fiber’s surface."
After some modeling aimed at
maximizing the absorption and evaporation abilities, the engineers optimized the
arrangement and dimensions of the fiber before weaving the yarn into fabrics
using an industrial loom.
In a show down with cotton, nylon
and polyester fabrics, the polyethylene fabric was found to exhibit faster
wicking qualities, though repeated wetting did weaken its performance.
Fortunately, an easy fix was found.
"You can refresh the material by
rubbing it against itself, and that way it maintains its wicking ability,"
reported Boriskina. "It can continuously and passively pump away moisture."
As polyethylene doesn't play nice
with other molecules, traditional inks and dyes couldn't be used to add color.
Instead, colored particles were added to the raw powder before the yarn was
extruded.
The team says that coloring the
fabric in this way contributed to the material's "relatively small ecological
footprint." Using a life cycle assessment tool commonly employed by the textile
industry, the engineers determined that the material and the fabric production
method required less energy than polyester and cotton.
"Polyethylene has a lower melting
temperature so you don’t have to heat it up as much as other synthetic polymer
materials to make yarn, for example," explained Boriskina. "Synthesis of raw
polyethylene also releases less greenhouse gas and waste heat than synthesis of
more conventional textile materials such as polyester or nylon. Cotton also
takes a lot of land, fertilizer, and water to grow, and is treated with harsh
chemicals, which all comes with a huge ecological footprint."
The smaller environmental
footprint continues through to real-world use too, with Boriskina saying that a
10-minute cold cycle could be enough to keep clothing
clean and fresh.
It is hoped that the discovery
could lead to plastic bags, food wrapping, coffee cups and more being recycled
into clothing and footwear instead of adding to our huge waste problem. Indeed,
the team is currently looking at sportswear, military and space technology
applications.
A paper on the research has been
published in the journal Nature
Sustainability.
Source: MIT