The thread that could make stretchy clothes recyclable
A pair of leggings has lost its shape. The fabric is thin at the knees, a seam is coming apart, and nobody is likely to want it second-hand. The problem of what to do with it began years earlier, when its thread was chosen.
Elastic garments commonly combine spandex, also known as elastane, with polyester or nylon. Each fibre does a different job. Together they make clothing that fits closely, stretches and springs back. Once the garment is worn out, that combination is difficult to turn into new fibre.
Europe generates plenty of material to deal with. The EU produced an estimated 6.94 million tonnes of textile waste in 2022, about 16 kilograms per person. That total covers textiles of many kinds; there is no equivalent, reliable figure for waste from stretchy clothing alone. Globally, less than 1% of the material used to make clothing is recycled into new clothing, according to the Ellen MacArthur Foundation.
Researchers at the Massachusetts Institute of Technology (MIT) have made an elastic yarn with its eventual recovery in mind. Its stretchy centre and stronger outer wrapping are both made from forms of polyethylene, a plastic that can be melted and reshaped. In an experiment, the team recycled material from the yarn ten times. The old leggings cannot benefit from the discovery, but garments made with a thread like this might.
Why stretchy clothes are hard to recycle
A conventional elastic yarn has a springy spandex core wrapped in tougher polyester or nylon. The core supplies stretch; the wrapping supplies strength. Separating the materials after use requires additional processing. Melting the whole yarn does not neatly recover them.
Even a small amount of elastane can complicate sorting. A study of methods for detecting it notes that cotton or wool fabrics often contain 1–5% elastane by weight. The fibre can be hard for automated systems to identify when it is present in such small quantities and buried within a yarn. A garment that appears to be predominantly one material may therefore be less straightforward to recycle than its main fibre suggests.
MIT research scientist Svetlana Boriskina and her colleagues kept the useful core-and-wrapping structure but changed what went into it.
The researchers chose one polyethylene-based resin for the elastic core and another for a sturdier outer fibre. Both arrived as small pellets. The team heated them until they melted, pushed the material through narrow openings and drew it into hair-thin fibres. An industrial yarn spinner then wound the stronger fibres around the stretchy centre.
The two materials have different properties but belong to the same polyethylene family. That allows the researchers to melt the yarn without first separating its core from its wrapping.
Polyethylene is widely used in products including bags, containers and pipes. By choosing different forms of it, the MIT team could give one part of the thread stretch and another strength. Boriskina’s group had previously made polyethylene yarn and explored its properties in textiles. This research adds the elastic behaviour needed for clothing such as leggings and sportswear.
What the ten-cycle recycling test shows
The team made a spool of elastic yarn, melted it down and respun the recovered material into fibre. It repeated the process ten times, testing the fibre’s mechanical strength along the way.
The recovered fibre remained strong enough in those tests to serve as the outer wrapping of another elastic yarn, wound around a newly made core. That is the result the experiment establishes. It does not show a complete garment being recycled into another garment, or the same entire core-and-wrapping yarn being remade ten times.
The researchers’ next step is to knit or weave the yarn into fabric. That will bring questions the spool cannot answer. Will the fabric feel comfortable against skin and retain its shape after wear and washing? Can manufacturers produce kilometres of the yarn at a price clothing brands will accept? Those are practical tests of whether it can replace existing elastic blends.
Can a recyclable yarn become a recyclable garment?
A garment also has to reach a recycler. In 2022, 85% of textile waste from EU households was not collected separately and instead entered mixed household waste, according to the European Environment Agency. That figure includes all household textiles. It shows the collection challenge any new fibre would face.
Then comes sorting. A finished garment may include seams, labels, dyes and materials other than its main fabric. Collectors would need to identify clothing made with the new yarn, while recyclers would need a dependable supply of it and a process that works on finished garments.
MIT’s experiment addresses a specific obstacle within that larger chain: how to give an elastic thread strength without combining materials that must later be pulled apart. It shifts part of the recycling problem back to the moment the yarn is designed.
For now, it is a thread rather than a pair of leggings. But the laboratory result opens a worthwhile question for clothing makers: if stretch can be built from materials that can be processed together after use, how much easier could the next garment be to bring back?
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