Labels made with inexpensive photonic fibers could improve clothing recycling, researchers report.
Less than 15% of the 92 million tons of clothing and other textiles discarded annually are recycledโin part because they are so difficult to sort.
โItโs like a barcode thatโs woven directly into the fabric of a garment,โ says Max Shtein, a professor of materials science and engineering at the University of Michigan and corresponding author of the study in Advanced Materials Technologies.
โWe can customize the photonic properties of the fibers to make them visible to the naked eye, readable only under near-infrared light or any combination.โ
Ordinary tags often donโt make it to the end of a garmentโs lifeโthey 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. This is what the new fiber could do.
Recyclers already use near-infrared sorting systems that identify different materials according to their naturally occurring optical signaturesโthe PET plastic in a water bottle, for example, looks different under near-infrared light than the HDPE plastic in a milk jug.
Different fabrics also have different optical signatures, but those signatures are of limited use to recyclers because of the prevalence of blended fabrics, explains lead author Brian Iezzi, a postdoctoral researcher in Shteinโs lab.
โFor a truly circular recycling system to work, itโs important to know the precise composition of a fabricโa cotton recycler doesnโt want to pay for a garment thatโs made of 70% polyester,โ Iezzi says. โNatural optical signatures canโt provide that level of precision, but our photonic fibers can.โ
To develop the technology, the team combined Iezzi and Shteinโs photonic expertiseโusually applied to products like displays, solar cells, and optical filtersโwith the advanced textile capabilities at MITโs 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 preformโa plastic feedstock that comprises dozens of alternating layers. In this case, they 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 color. Itโs the same basic phenomenon that gives butterfly wings their shimmer.
The preform is heated and then mechanically pulledโa bit like taffyโinto a hair-thin strand of fiber. While the manufacturing process method differs from the extrusion technique used to make conventional synthetic fibers like polyester, it can produce the same miles-long strands of fiber. 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 fiber to create the desired optical properties and ensure recyclability. While the photonic fiber is more expensive than traditional textiles, the researchers estimate that it will only result in a small increase in the cost of finished goods.
โThe photonic fibers only need to make up a small percentageโas little as 1% of a finished garment,โ Iezzi says. โThat might increase the cost of the finished product by around 25 centsโsimilar to the cost of those use-and-care tags weโre all familiar with.โ
In addition to making recycling easier, the photonic labeling could be used to tell consumers where and how goods are made, and even to verify the authenticity of brand-name products, Shtein says. It could be a way to add important value for customers.
โAs electronic devices like cell phones become more sophisticated, they could potentially have the ability to read this kind of photonic labeling,โ Shtein says. โSo I could imagine a future where woven-in labels are a useful feature for consumers as well as recyclers.โ
The team has applied for patent protection and is evaluating ways to move forward with the commercialization of the technology.
The National Science Foundation and the Under Secretary of Defense for Research and Engineering funded the work.
Source: University of Michigan
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