Massachusetts Institute of Technology researchers described a method for producing a sustainable, fast-drying fabric by manipulating the mechanical properties of polyethylene, the most widely produced plastic, despite the fact that polyethylene is totally waterproof.

The study, published Monday in Nature Sustainability, offers a sustainable use of polyethylene plastic, which, despite its widespread use, frequently goes to waste because it is not always cost-effective to recycle it. The researchers are already working with the United States military on ways to incorporate the material into uniforms.

"As an engineer, I was originally interested in the performance of this material, but people on the business side pointed out that we should be focusing on the sustainable properties of this material as well," said Svetlana Boriskina, a research scientist in MIT's Department of Mechanical Engineering. "It's actually quite hard to combine these two things together."

Notably, there is no chemical manipulation involved in the process of making the material. It is an entirely physical transformation using standard equipment in the textile industry, meaning the material can be produced and recycled in a cost-effective manner.  

"There's no chemistry magic here," Boriskina said. "More like mechanical engineering magic."

This struggle between sustainability and functionality has been plaguing the fashion and textile industry for many years. The fashion industry is the third-most-polluting industry on Earth, behind only oil and gas. As reported in Nature Climate Change in 2018, about 60% of all produced garments are disposed of within a year of their production. The fashion industry also accounts for around 5% to 10% of global greenhouse gas emissions annually.

While plastic-based fabrics may not strike the average consumer as the most sustainable option, Boriskina explained in an interview with The Academic Times that the processes involved in producing more natural fibers such as cotton, silk and wool are frequently harmful to the environment in the long run. 

The chemicals involved in cotton production can run off into the environment, and the volume of water required for cotton irrigation can rapidly dry out natural bodies of water.

"I grew up in the former Soviet Union, and in the Kazakhstan region, the entire Aral Sea just disappeared because they were taking water from the sea for cotton irrigation, and now it's all gone," said Boriskina.

By some measures, wool and silk are not much better. Rearing the sheep for wool requires huge stretches of grass pastures that need water, and according to animal advocates, it takes around 3,000 silkworms to produce a single pound of silk, killing the worms in the process after they've eaten thousands of mulberry leaves. The relative inefficiency in the production of many natural fibers is part of the reason synthetic materials have taken over the market in the last century.

However, polyethylene is one form of plastic that until now has not seen great use as a textile. Polyethylene is the most produced plastic, at up to 80 million tons per year. And while polyethylene is easy to recycle, it is often not cost effective to do so because it is used in so many tiny, cheap products like plastic bags. 

To combat this effect, there is growing interest in researching new uses for recycled polyethylene in more valuable items, including textiles. Researchers have also developed sustainable plastic alternatives to high-density polyethylene that can be chemically recycled with near-perfect efficiency, although compared with the conventional material, their cost poses a disadvantage.

Boriskina and her colleagues first began investigating polyethylene as a potential textile for wearable garments because of its high transparency to infrared radiation, which would help the body keep cool while wearing garments made of polyethylene. But this particular plastic had not been considered a great material for textiles before because it usually can't absorb water.

"Because polyethylene is normally a hydrophobic material, it is something that you would use more for a raincoat or tarp," Boriskina said. "And that's not good for most wearable applications, because perspiration needs to be wicked away from the skin and evaporated, and that actually provides additional cooling functionality."

However, the team solved this problem by melting down the plastic and transforming it into a series of thin fibers.

"You melt down the polymer and put it through a device like a shower head or a sponge to make fibers, and when you do this in an oxygen-rich environment, it creates little defects on the surface where oxygen can attach, and this makes the material slightly hydrophilic," explained Boriskina.

Boriskina went on to explain that to make a moisture-wicking fabric, the material need only be slightly receptive to water. While something entirely hydrophobic will trap sweat in, like a rubber Halloween mask, if there is too much hydrophilicity the material just absorbs the water and takes even longer to dry, like a cotton shirt in a dryer full of polyester gym clothes.

In addition to the military collaboration, Boriskina also hopes that the fabric will soon work its way into clothing for the average consumer.

"The material also has a lot of easy-care properties. Because it's so easy to wash, it'll save water but also time for mothers and other people who need to wash clothes frequently," said Boriskina. "We think people will really appreciate that aspect immediately."

The study, "Sustainable polyethylene fabrics with engineered moisture transport for passive cooling," published March 15 in Nature Sustainability, was authored by Matteo Alberghini, Seongdon Hong, L. Marcelo Lozano, Volodymyr Korolovych, Yi Huang, Francesco Signorato, S. Hadi Zandavi, Corey Fucetola, Gang Chen and Svetlana V. Boriskina, Massachusetts Institute of Technology; Ihsan Uluturk and Richard M. Osgood III, United States Army Combat Capabilities Development Command Soldier Center; Michael Y. Tolstorukov, Dana-Farber Cancer Institute; and Pietro Asinari and Matteo Fasano, Politecnico di Torino.