More accurate product labeling and traceability are required in circular supply networks. Product life cycle management in the apparel sector needs to be improved in part by imprecise, difficult to read and removable standard care labels. This study aims to enable an intrinsically recyclable, low-cost labeling method to encode information and quickly read it out after years of normal use.
In the US, an estimated 15 million tons of textiles are incinerated or end up in landfills each year. This waste, which represents 85% of the substances produced in a given year, is a major environmental problem. Massachusetts was the first state to pass laws banning textile dumping in the trash by 2022 to increase recycling rates.
Recycling textiles is sometimes easy. Those cannot be resold because they are shipped to facilities where they are categorized by fabric type. Manual sorting is time consuming and challenging due to worn or missing labels. More modern approaches that study the chemistry of a garment need to be reviewed to identify components in fabric mixes, which make up most clothing.
A team from MIT Lincoln Laboratory and the University of Michigan offers an innovative fabric labeling technique to improve this sorting process: weaving fibers with engineered reflectivity. This fiber only reflects under specific infrared light wavelengths, allowing recyclers to determine what type of substance the fiber represents.
To identify a product, the fiber acts as an optical barcode, and a way to quickly identify fabric types and sort them as they come in could help recycling systems scale up.
Erin Doran, a co-author of the team’s study, said: “If we have a way to easily identify dust types and sort them as they come in, we can scale up the recycling processes. We want to find ways to identify materials for another use after the life cycle of the garment.”
Erin Doran, a textile specialist at Lincoln Laboratory’s Defense Fabric Development Center (DFDC), is working with researchers from the Advanced Materials and Microsystems Group to create “future fabrics” by fusing fibers with tiny electronics and sensors.
Brian Iezzi, the study’s lead author, is exploring ways to improve the recyclability of textiles. His work at U-Michigan’s Shtein Lab focuses on applying photonics to fiber-based devices, such as a fiber with structural colors developed at MIT by Professor Yoel Fink. It is an area of expertise of the DFDC.
He evaluates marketing alternatives after the team filed for patent protection for their technology. The fibers generated in this study are still significantly thicker than clothing fibers. Therefore, further dilution while maintaining reflectivity at the required wavelengths is an ongoing area of research.
DFDC researcher Bradford Perkins, a study co-author, said: “It is a fiber that works like a perfect mirror. By layering certain materials, you can design this mirror to reflect specific wavelengths.
In this case, you want reflections at wavelengths distinct from the optical signatures of the other materials in your fabric, which tend to be dark because ordinary fabrics absorb infrared radiation.
Perkins says, “Unlike the striking designs of butterfly wings, the fibers are not meant to stand out. They would make up less than a few percent of the fabric. No one could say they’re there until they had an infrared detector.”
The fiber starts out as a block of a polymer called a preform. The team carefully constructed the preform to contain more than 50 alternating layers of acrylic and polycarbonate. It is heated and drawn like fudge to produce a fiber the same size as a conventional fabric yarn.
The combination of the two materials reflects and absorbs light to create an optical effect that can look like color, similar to butterfly wings.
Tairan Wang, also from Lincoln Laboratory, said: “Butterfly wings are an example of structural color in nature. If you look at them very closely, they are actually a shell of material with nanostructured patterns that scatter light, similar to what we do with the fibres.”
Researchers can “tune” the fibers to reflect and absorb specific, periodic ranges of wavelengths by controlling the rate at which the fibers are pulled, resulting in an individual optical barcode in each fiber.
The associated fabric types can then be assigned to this barcode, where one symbol stands for cotton, for example, and the other for polyester.
According to the researchers, a detector similar to the one used to classify plastics in the recycling industry could be adapted. Such sensors also use infrared sensing to identify the unique optical characteristics of different polymers.
The researchers are also studying how structural dye fibers could help solve other environmental problems in the textile industry, such as toxic waste from dyes.
Doran said, “It is important for us to consider recyclability now that the market for electronic textiles is also growing. This idea could open avenues for the recovery of chips and metals during the textile recycling process. Sustainability is a big part of the future and it has been exciting to work on this vision together.”
- Brian Iezzi, Erin Doran, et al. Polymeric photonic crystal fibers for textile tracing and sorting. Advanced material technologies. DOI: https://doi.org/10.1002/admt.202201099