MIT Engineers Develop Recyclable Elastic Yarn as Alternative to Spandex Blends

Researchers at the Massachusetts Institute of Technology have designed a recyclable elastic yarn that could help address one of the textile industry’s most persistent circularity challenges: the difficulty of recycling clothing that contains spandex.

The experimental yarn is made from two forms of polyethylene, a widely used thermoplastic found in products such as packaging, bottles, bags and industrial materials. By selecting polyethylene-based resins with different mechanical properties, the researchers created a core-and-sheath yarn that combines elasticity with strength.

The material is intended to offer performance comparable to conventional elastic yarns made from spandex combined with polyester or nylon. Unlike those mixed-material yarns, however, the MIT design can be melted and processed without first separating its core from its outer layer.

The research was published in the journal ACS Materials Letters by a team including first author SeongHyeon Kim and MIT research scientist Svetlana Boriskina.

Why Spandex Makes Clothing Difficult to Recycle

Elastic yarns commonly use a polyurethane-based spandex core wrapped in a stronger polyester or nylon sheath. This structure provides the stretch, recovery and durability required for products ranging from sportswear and underwear to socks, jeans and medical textiles.

It also creates a recycling problem.

Polyurethane, polyester and nylon have different chemical and thermal properties. Recycling a conventional elastic yarn generally requires the materials to be separated before they can be processed. Chemical separation methods are possible in some cases, but they can increase costs, energy requirements and operational complexity while producing additional chemical waste.

MIT’s researchers estimate that around 80% of textiles sold in the United States contain some spandex. Even a relatively small quantity of the elastic fibre can interfere with conventional textile recycling processes, limiting the recovery of otherwise recyclable polyester or nylon.

The difficulty contributes to a broader textile waste problem. According to the latest material-specific figures published by the US Environmental Protection Agency, the United States generated approximately 17 million short tons of textiles in 2018. Around 11.3 million tons were landfilled, while only 2.5 million tons were recycled.

Europe faces similar constraints. The European Environment Agency estimates that the EU generated 6.95 million tonnes of textile waste in 2020, equivalent to about 16 kilograms per person. Only 4.4 kilograms per person were separately collected for reuse or recycling, while the majority entered mixed household waste.

A Yarn Made From Compatible Materials

To overcome the mixed-fibre problem, the MIT team produced both components of its yarn from the same broad polymer family.

For the core, the researchers selected a polyethylene-based resin capable of forming a relatively soft and elastic fibre. A second, stiffer polyethylene formulation was used for the surrounding sheath.

The resin pellets were heated to approximately 350 degrees Fahrenheit, or around 177 degrees Celsius, and pushed through small extruders to form hair-thin fibres. An industrial yarn spinner was then used to wind the sheath fibres around the elastic core.

Because both components are polyethylene-based, the completed yarn does not have to be chemically separated before recycling. It can be melted as a single material stream and converted into new fibres or moulded plastic products.

This compatibility is the central innovation. Designing products from materials that can be processed together may allow recyclers to avoid some of the expensive sorting and separation stages that currently undermine textile-to-textile recycling.

Material Retained Its Strength After Repeated Recycling

The researchers tested the material by melting and respinning the yarn through 10 recycling cycles. After each cycle, they measured its mechanical performance by stretching individual threads and recording the force required to break them.

The recycled sheath fibres retained strength comparable to the original material after the tenth cycle. The recovered fibres could then be wrapped around a newly produced elastic core to create another stretchable yarn.

The team says the material could eventually be knitted or woven into lightweight, stretchable garments. At the end of a product’s useful life, the fabric could potentially be melted and spun into new yarn or converted into items such as buttons, buckles and other accessories.

Previous research from the same MIT group found that polyethylene could also offer moisture-wicking, stain-resistant and cooling properties when used as a textile. Its relatively low moisture absorption may reduce the energy required for washing and drying, although the environmental performance of a commercial garment would need to be assessed across its full life cycle.

Potential Implications for Circular Textile Design

The research illustrates how material selection at the design stage can determine whether a garment is technically recyclable.

Many current recycling programmes receive clothing that contains several polymers, dyes, coatings, fasteners and finishing chemicals. Even where collection systems exist, these complex combinations can make fibre recovery uneconomic or technically impractical.

A yarn based on compatible polymers could help simplify future products, particularly where elasticity is required. Potential applications include activewear, uniforms, underwear and other garments that currently rely heavily on spandex blends.

The development is also relevant to emerging circular economy policies. EU countries have been required to establish separate collection systems for used textiles since 2025, but the EEA has warned that collection alone will not deliver circularity unless sorting and recycling capacity expands. Without sufficient processing infrastructure and demand for recovered fibres, more separately collected material could still be exported, incinerated or landfilled.

Designing garments around recyclable material families could make those collection systems more effective by creating cleaner and more predictable recycling streams.

Commercial and Environmental Questions Remain

The MIT material remains at the research stage. Although the team has used industrial spinning equipment and believes the process could be scaled to commercial-sized spools, the yarn has not yet been demonstrated in mass-produced garments.

Further testing will be needed to evaluate abrasion resistance, repeated washing, colour stability, comfort, long-term elasticity and compatibility with existing textile machinery. Manufacturers would also need reliable methods to identify, collect and sort polyethylene garments after use.

The yarn’s fossil-based feedstock is another consideration. Polyethylene is generally produced from oil or natural gas, and mechanical recyclability does not eliminate the emissions associated with primary polymer production. The greatest environmental benefit would therefore depend on keeping the material in circulation through multiple effective recycling cycles and reducing demand for virgin fibres.

As with other synthetic fabrics, potential microfibre release during manufacturing, washing and disposal will also require investigation.

The research does not solve the textile waste problem on its own. However, it provides a practical example of how products can be redesigned to avoid incompatible material combinations. If the yarn performs reliably at industrial scale, it could support a shift away from elastic garments that are effectively designed for disposal and towards textiles that can remain within a more circular material system.

Source: news.mit.edu