Michigan researchers develop woven-in photonic fiber labels for enhanced textile recycling

Less than 15% of the 92 million tons of clothing and other textiles discarded annually are recycled—in part because they are so difficult to sort. Woven-in labels made with inexpensive photonic fibers, developed by a University of Michigan-led team, could change that. 

“It’s like a barcode that’s woven directly into the fabric of a garment,” Max Shtein, a University of Michigan professor of materials science and engineering and corresponding author of the study in Advanced Materials Technologies, said in a university release. “We 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.” 

The conventional tags found on garments often fail to last for the entire lifespan of the clothing item. They are prone to being cut away, washed until illegible, or can wear off. Recycling processes could become more effective if tags were woven directly into the fabric, invisible until they need to be read. This is what the new photonic fiber technology aims to achieve.

Recyclers currently employ near-infrared sorting systems that rely on naturally occurring optical signatures to identify different materials. For example, PET plastic in a water bottle appears differently under near-infrared light than the HDPE plastic in a milk jug. Similarly, different fabrics exhibit unique optical signatures. 

Brian Iezzi, a postdoctoral researcher in Shtein's lab and the lead author of the study, explained that the prevalence of blended fabrics limits the usefulness of these signatures to recyclers. 

“To establish a truly circular recycling system, it's crucial to know the precise composition of a fabric. A cotton recycler wouldn't want to pay for a garment that's 70% polyester," Iezzi said. "Natural optical signatures cannot provide that level of precision, but our photonic fibers can." 

The University of Michigan team successfully developed this groundbreaking technology by combining the photonic expertise of Iezzi and Shtein with the advanced textile capabilities of MIT's Lincoln Lab. The collaboration aimed to incorporate photonic properties into a large-scale production-compatible process. 

The process began with a preform—a plastic feedstock consisting of alternating layers of acrylic and polycarbonate, the university release said. Although each individual layer is transparent, the combination of the two materials bends and refracts light, creating optical effects that resemble color, similar to the shimmer found on butterfly wings.

The preform undergoes heating and is then mechanically pulled in a process resembling the stretching of taffy, resulting in a hair-thin strand of fiber. While this manufacturing method differs from the extrusion technique used for conventional synthetic fibers like polyester, it can produce strands of fiber that are miles long. These strands can be processed using existing equipment used by textile manufacturers. 

Through adjustments in the mix of materials and the speed at which the preform is pulled, the researchers fine-tuned the fiber to possess the desired optical properties and ensure recyclability. While the photonic fiber may be more expensive than traditional textiles, the researchers estimate that it will only marginally increase the cost of finished goods. 

"The photonic fibers only need to make up a small percentage—as little as 1%—of a finished garment," Iezzi said. "This would result in an increase in the cost of the finished product by approximately 25 cents, which is comparable to the cost of the use-and-care tags we are familiar with." 

Shtein said he believes that besides simplifying recycling processes, the photonic labeling has the potential to provide consumers with information about the origin and production methods of goods. Additionally, it could serve as a means to authenticate brand-name products, adding value and transparency to customer experiences. 

"As electronic devices like cell phones become more sophisticated, they could potentially have the ability to read this kind of photonic labeling," Shtein said. "So, I could imagine a future where woven-in labels are a useful feature for consumers as well as recyclers." 

The team has taken steps to protect their innovation by applying for patent protection and is currently evaluating pathways for the commercialization of this technology. The research received support from the National Science Foundation and the Under Secretary of Defense for Research and Engineering.