MIT engineers design recyclable polyethylene elastic yarn to replace spandex blends

MIT engineers reported a recyclable elastic yarn made from polyethylene plastics commonly used in milk bottles and grocery bags, intended as an alternative to spandex-polyester or spandex-nylon blends that are hard to recycle together. The yarn combines a stretchy polyethylene-based core with a tougher polyethylene sheath so both layers share the same chemistry and can be melted and redrawn without chemical separation. In demonstrations, the team melted and respun yarn through multiple cycles and reported that after 10 cycles it remained as strong and flexible as conventional thread. Research scientist Svetlana Boriskina of MIT's Department of Mechanical Engineering said eighty percent of textiles on the U.S. market currently contain some amount of spandex, which makes them nonrecyclable, and that there is no widely adopted technology now that recycles textiles into textiles. The group published the work in ACS Materials Letters, with first author SeongHyeon Kim and other MIT co-authors. The researchers said spandex yarns normally pair a polyurethane core with a polyester or nylon sheath, requiring costly and often toxic chemical separation if any recycling is attempted. They extruded hair-thin fibers from two polyethylene resins at about 350 degrees Fahrenheit and wound sheath fibers around a core on an industrial spinner. Support included the DEVCOM Soldier Center through the U.S. Army Research Office, the Office of Naval Research Global via Tecnologico de Monterrey, and the MIT Portugal Program.