self cooling fabric

Plastic bag material turned into water-repellent fabric

Image credit: MIT

Engineers have developed self-cooling fabrics from polyethylene, a material commonly used in plastic bags.

The thin, lightweight material could keep the wearer cooler than most textiles because it lets heat through rather than trapping it, the MIT engineers said. However, it also locks in water and sweat, a major deterrent to polyethylene’s adoption as a wearable textile.

The team has now managed to spin polyethylene into fibres and yarns designed to wick away moisture. They wove the yarns into silky, lightweight fabrics that absorb and evaporate water more quickly than common textiles such as cotton, nylon, and polyester.

They have also calculated the ecological footprint that polyethylene would have if it were produced and used as a textile, and estimate that it may have a smaller environmental impact over their life cycle than cotton and nylon textiles.

The researchers hope that fabrics made from polyethylene could provide an incentive to recycle plastic bags and other polyethylene products into wearable textiles, adding to the material’s sustainability.

“Once someone throws a plastic bag in the ocean, that’s a problem. But those bags could easily be recycled, and if you can make polyethylene into a sneaker or a hoodie, it would make economic sense to pick up these bags and recycle them,” said researcher Svetlana Boriskina.

A molecule of polyethylene has a backbone of carbon atoms, each with a hydrogen atom attached. The simple structure, repeated many times over, forms a Teflon-like architecture that resists sticking to water and other molecules.

The team started with polyethylene in its raw powder form and used standard textile manufacturing equipment to melt and extrude polyethylene into thin fibres, similar to turning out strands of spaghetti. Surprisingly, they found that this extrusion process slightly oxidised the material, changing the fibre’s surface energy so that polyethylene became weakly hydrophilic, and able to attract water molecules to its surface.

The team used a second standard extruder to bunch multiple polyethylene fibres together to make a weavable yarn. They found that, within a strand of yarn, the spaces between fibres formed capillaries through which water molecules could be passively absorbed once attracted to a fibre’s surface.

In every test, polyethylene fabrics wicked away and evaporated the water faster than other common textiles.

The researchers did observe that polyethylene lost some of its water-attracting ability with repeated wetting, but by simply applying some friction, or exposing it to ultraviolet light, they induced the material to become hydrophilic again.

“You can refresh the material by rubbing it against itself, and that way it maintains its wicking ability,” Boriskina said. “It can continuously and passively pump away moisture.”

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