Recyclable Polymers Offer Light-Emitting Efficiency and Sustainability

Luminescent polymers, a class of flexible materials known for their light-emitting capability, are ubiquitous across diverse industries, from bioimaging to security signage and computer displays. When these organic polymers reach their end of life, they are usually relegated to landfills or buried underground.

Recycling electronic waste is expensive and complex. Although there is an economic incentive to recycle the semiconducting materials in electronics, existing strategies for the depolymerization and recycling of luminescent polymers often compromise the light-emitting efficiency of the material.

Researchers at the U.S. Department of Energy’s Argonne National Laboratory worked with colleagues at the University of Chicago, Purdue University, and Yale University to design a sustainable luminescent polymer. “We were able to make this material biodegradable and recyclable without sacrificing the functionality,” said researcher and project leader Jie Xu.

To enable recyclability of the material while maintaining high light-emitting efficiency, the researchers developed thermally activated delayed fluorescence (TADF) polymers with cleavable moieties. They incorporated tert-butyl ester, a chemical that breaks down when exposed to heat or mild acid, into the polymers to make them biodegradable.

A method born out of a collaboration between Argonne National Laboratory, the University of Chicago, Purdue University, and Yale University enables the design of light-emitting semiconductors that are both biodegradable and recyclable. Courtesy of Argonne National Laboratory/Jie Xu and Yukun Wu.

When the researchers tested electroluminescent devices based on the TADF polymers, they found that the devices achieved a high external quantum efficiency of up to 15.1%. According to the team, this is a tenfold increase from the existing degradable luminescent polymers.

At the end of life, the TADF polymers can be degraded under mild acidic conditions or with relatively low-heat treatments, while precise control of the kinetics is maintained. The pure monomers obtained from depolymerization can be isolated and remade into new materials for future applications.

The polymers developed by the Argonne-led team enable circularity of luminescent materials, preparing the way to more sustainable optoelectronics applications. “This work serves as an important benchmark in addressing the urgent need for sustainability in the design of future electronics,” Xu said.

In addition to making future electronics easier to degrade or recycle, the researchers believe that the new polymer’s capabilities could be expanded for use in other fields. They anticipate that the degradable, recyclable polymer will be applied to existing technologies such as displays, medical imaging and diagnosis, biostimulation, and security, as well as new applications.

“Design is still compatible with processibility and in the end, you have to use this in real applications,” said materials scientist Yuepeng Zhang.

The team plans to move its depolymerization technology from the lab onto cell phones, computer screens, and other electronics with continued testing.

“This is a $46 billion-a-year industry, and it is only growing,” she said. “By 2032, the industry is estimated to grow to $260 billion. With this method, we can eliminate this type of electronic waste that would otherwise be piling up in landfills.”

The research was published in Nature Sustainability (www.doi.org/10.1038/s41893-024-01373-z).