Woven-in labels made with inexpensive photonic fibres could eliminate the problem of garment sorting which results in 85% of the 92 million tonnes of clothing and other textiles discarded annually because they are so difficult to segregate.
- The research team, led by Prof Max Shtein of the University of Michigan, has applied for patent protection and is evaluating ways to move forward with the commercialisation of the technology.
- The findings have been published in Advanced Materials Technologies. Brian Iezzi, a postdoctoral researcher in Shtein’s lab, was the lead author of the study.
The Problem: Ordinary tags often don’t make it to the end of a garment’s life—they may be cut away or washed until illegible, and tagless information can wear off.
- Recycling could be more effective if a tag was woven into the fabric, invisible until it needs to be read.
- Recyclers already use near-infrared sorting systems that identify different materials according to their naturally occurring optical signatures.
- Different fabrics also have different optical signatures, but those signatures are of limited use to recyclers because of the prevalence of blended fabrics.
- For a truly circular recycling system to work, it’s important to know the precise composition of a fabric—a cotton recycler doesn’t want to pay for a garment that’s made of 70% polyester. Natural optical signatures can’t provide that level of precision, but the photonic fibres can.
The Solution: The researchers developed the technology by combining Iezzi and Shtein’s photonic expertise—usually applied to products like displays, solar cells and optical filters—with the advanced textile capabilities at MIT’s Lincoln Lab.
- The lab worked to incorporate the photonic properties into a process that would be compatible with large-scale production.
- They accomplished the task by starting with a preform—a plastic feedstock that comprises dozens of alternating layers. The team used acrylic and polycarbonate.
- While each individual layer is clear, the combination of two materials bends and refracts light to create optical effects that can look like colour. It’s the same basic phenomenon that gives butterfly wings their shimmer.
- The preform is heated and then mechanically pulled—a bit like taffy—into a hair-thin strand of fibre.
- While the manufacturing process method differs from the extrusion technique used to make conventional synthetic fibres like polyester, it can produce the same miles-long strands of fibre. Those strands can then be processed with the same equipment already used by textile makers.
- By adjusting the mix of materials and the speed at which the preform is pulled, the researchers tuned the fibre to create the desired optical properties and ensure recyclability.
- While the photonic fibre is more expensive than traditional textiles, it will only result in a small increase in the cost of finished goods.