Can plastic save us from fast fashion? (Photo: AnyLú Hinojosa-Peña Photography)
When considering materials that could become the fabrics of the future, scientists have largely ruled out one widely available option: polyethylene. However, a female-led team of scientists from the Massachusetts Institute of Technology (MIT) want to turn the page. Well, in this case, the plastic.
Polyethylene is used to make wrappers and grocery bags. It’s thin and light and could also keep you cooler than most textiles because it lets heat out, rather than trapping it in. But it also traps water and sweat, as moisture can’t escape and evaporate.
This anti-wrinkle property has been a major deterrent to adopting polyethylene as a wearable fabric.
MIT experts against ‘fast fashion’
Now, MIT engineers have spun polyethylene into fibers designed to remove moisture. They wove the threads and managed to make silky, lightweight fabrics that absorb and evaporate water faster than other common textiles, such as cotton, nylon, or polyester.
Spinning polyethylene at MIT. (Source: MIT)
They’ve also calculated the ecological footprint that polyethylene would have if it were produced and used as a textile.
Contrary to most assumptions, they estimate that polyethylene fabrics may have a lower environmental impact than cotton and nylon fabrics during their life cycle.
The researchers hope that fabrics made from polyethylene may provide an incentive to recycle plastic bags and other products into wearable textiles, increasing the material’s sustainability.
“Once someone throws a plastic bag into the ocean, that’s a problem. But those bags could easily be recycled, and if you can turn polyethylene into a sneaker or a sweatshirt, it would make economic sense to collect these bags and recycle them, ”says Svetlana Boriskina, a research scientist from the Department of Mechanical Engineering at MIT. Boriskina and her colleagues published their findings in Nature Sustainability.
Better than other materials
Polyethylene molecules have a backbone of carbon atoms, with a hydrogen atom on each side.
The simple structure, repeated over and over, forms a Teflon-like design that resists adhering to water and other molecules.
“Everyone we spoke to said that polyethylene could keep you cool but wouldn’t absorb water or sweat because it rejects water, so therefore it wouldn’t work as a textile,” says Boriskina.
However, she and her colleagues tried to make wearable fibers from polyethylene.
They started with polyethylene in its raw powder form, and they used standard textile manufacturing equipment to melt and extrude the polyethylene into thin fibers, similar to producing spaghetti strands.
Surprisingly, they found that this extrusion process slightly oxidized the material, changing the surface energy of the fiber so that the polyethylene became weakly hydrophilic and able to attract water molecules to its surface.
The team used a second standard extruder to put together several polyethylene fibers to make a wearable yarn. They discovered that, within a strand of yarn, the spaces between the fibers formed capillaries through which water molecules could be passively absorbed once attracted to the surface of a fiber.
To optimize this new absorbency, researchers modeled the properties of the fibers and found that fibers of a certain diameter, aligned in specific directions along the yarn, improved the fiber’s absorption capacity.
Based on their modeling, the researchers made polyethylene yarn with more optimized fiber arrangements and dimensions, then used an industrial loom to weave the yarn into fabrics.
They then tested the polyethylene fabric’s absorbency over cotton, nylon, and polyester by dipping strips of the fabrics in water and measuring the time it took for the liquid to be absorbed or to creep up each strip. They also placed each fabric on a scale over a single drop of water and measured its weight over time, as the water passed through the material and evaporated.
In each test, the polyethylene fabrics removed and evaporated water faster than other common fabrics. The researchers observed that polyethylene lost some of its ability to attract water after repeated wetting, but simply applying some friction, or exposing it to ultraviolet light, lead the material to become hydrophilic again.
“You can refresh the material by rubbing it against itself, and that way it maintains its absorption capacity,” says Boriskina. “You can pump out the moisture continuously and passively.”
The team also found a way to incorporate color into polyethylene fabrics, which has been challenging, due to the material’s resistance to bonding with other molecules, including traditional inks and dyes.
The researchers added color particles to powdered polyethylene before extruding the material into fiber form. This way, the particles were encapsulated within the fibers, successfully imparting color to them.
“We don’t need to go through the traditional process of dyeing textiles by dipping them in harsh chemical solutions,” says Boriskina.
“We can color the polyethylene fibers in a completely dry way, and at the end of their life cycle, we could melt, spin, and recover the particles in order to use them again.”
The team’s dry coloring process contributes to the relatively small ecological footprint that polyethylene would have if it were used to make textiles, say the researchers.
The team calculated this footprint using a life cycle assessment tool commonly used by the textile industry. Bearing in mind the physical properties of polyethylene, and the processes required to make and color the fabrics, researchers found that less energy would be required to produce polyethylene textiles, compared to polyester and cotton.
“Polyethylene has a lower melting temperature, so it’s not necessary to heat it as much as other synthetic polymeric materials in order to make yarn, for example,” explains Boriskina. “The synthesis of raw polyethylene also releases less greenhouse gases and residual heat than the synthesis of more conventional textile materials, such as polyester or nylon. Cotton also requires a lot of land, fertilizers, and water to grow, and it’s treated with harsh chemicals, which have a huge ecological footprint. ”
In its use phase, polyethylene fabric could also have a lower environmental impact, she says, as it would require less energy to wash and dry the material compared to cotton and other textiles.
“It doesn’t get dirty because nothing sticks to it,” says Boriskina. “I could wash polyethylene on a cold cycle for 10 minutes, instead of washing cotton on a hot cycle for an hour.”