A newly engineered elastic yarn made entirely from polyethylene can be melted down and respun into fresh thread, offering a recyclable alternative to the spandex blends found in most stretchy clothing. The yarn matches the strength and flexibility of conventional elastic fibres, yet because it is built from a single plastic family, it needs no chemical separation before recycling.
- The yarn combines a stretchy polyethylene core with a stiffer sheath of the same material, mimicking the tough, springy behaviour of spandex while remaining suited to lightweight, wearable clothing.
- At the end of a garment's life, the material can be melted and redrawn into new yarn or cast into plastic accessories such as buttons and belt buckles, reducing textile waste.
- Polyethylene is a thermoplastic commonly used in milk bottles and grocery bags, meaning it can be reheated and reformed repeatedly into new products without the chemical separation that conventional elastic yarns require.
- The findings have been published in ACS Materials Letters, by SeongHyeon Kim and colleagues at MIT.
THE RECYCLING TRAP: Conventional elastic yarns are nearly impossible to recycle because of how they are constructed. Each thread pairs a springy spandex core, made from polyurethane, a synthetic polymer, with a tougher polyester or nylon sheath, and separating these two materials demands chemical treatment before either can be reused. Most stretchy clothing, as a result, ends up discarded.
- Spandex delivers springiness but little strength, so it is wrapped in a sturdier polyester or nylon sheath that together produces the familiar stretch of elastic garments.
- Recovering the sheath means chemically stripping it from the core first before the polyester material can be melted down and reused.
- These separation processes add cost and complexity and typically rely on toxic chemicals that harm the environment, discouraging recycling of stretchy garments altogether.
- Without an affordable way to split the fibres, most elastic clothing bypasses recycling entirely and heads straight for disposal.
INSIDE THE LAB: To build the yarn, the team selected two polyethylene resins, one yielding a stretchier fibre for the core and a stiffer one for the sheath. Pellets of each were heated to about 350 degrees Fahrenheit, past melting point, then drawn through small extruders into hair-thin fibres. An industrial spinner wound the sheath fibres around a core fibre to form the finished elastic yarn.
- Because both core and sheath belong to the same polyethylene family, the finished yarn can be melted and reformed as a whole, with no chemical separation step required beforehand.
- To test recyclability, the researchers twisted an elastic yarn, melted it down, and respun it 10 times over, checking its performance after each cycle.
- Each round was assessed by stretching a thread precisely and measuring the pulling force at which it finally broke, producing a quantified measure of the yarn's mechanical strength.
- The recycled sheath yarn proved just as strong as the original, and can be twisted around a freshly spun elastic core to make new stretchy yarn.
- The research was supported by the DEVCOM Soldier Center, the US Army Research Office, the Office of Naval Research Global, and the MIT Portugal Program.
WHAT THEY SAID
Even though chemical separation technologies exist, they add extra cost and complexity, and usually require toxic chemicals that are harmful to the environment. That's why most stretchy garments go to the dump.
— Svetlana Boriskina
Research Scientist, Department of Mechanical Engineering
MIT
Polyethylene can give us a wide range of properties, depending on how you make it… You just melt it in a barrel with a heater, and then you extrude and spin it into fibers. It's like a spaghetti machine.
— SeongHyeon Kim
First Author, Department of Mechanical Engineering
MIT
