MIT engineers have found a new use for a common plastic, managing to spin polyethylene into fabric that can passively cool the wearer by allowing heat through and moisture to evaporate. The discovery could see waste plastic bags being turned into sportswear.
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
