Reviewed by Lexie CornerAug 7 2024
In a study published in RSC: Applied Polymers, Thomas J. Wallin of MIT, Chen Wang of the University of Utah, and seven other researchers introduced a novel flexible substrate material. This material has the potential to enable the scalable production of more complex multilayered circuits than current substrates, allowing and facilitating the recycling of materials and components when devices reach the end of their life cycle.
Electronic waste, or e-waste, is a rapidly growing global issue, predicted to increase with the advent of new flexible electronics for robots, wearable gadgets, health monitoring, and other applications, including single-use devices.
We recognize that electronic waste is an ongoing global crisis that’s only going to get worse as we continue to build more devices for the Internet of Things and as the rest of the world develops.
Thomas J. Wallin, Professor, Massachusetts Institute of Technology
Up to this point, a large portion of academic research has focused on developing alternative substrates for flexible electronics, which mainly employ polyimide under the brand name Kapton.
The majority of these studies have concentrated on entirely different polymer materials.
Wallin added, “That really ignores the commercial side of it, as to why people chose the materials they did to begin with.”
Kapton offers numerous benefits, including excellent thermal and insulating qualities and the ease of obtaining source materials. By 2030, the global polyimide market is expected to reach $4 billion.
According to Wang, “It is everywhere, in every electronic device basically,” including components like the flexible cables that link various sections inside the laptop or mobile.
It is also commonly utilized in aerospace applications due to its strong tolerance to heat.
It is a classic material, but it has not been updated for three or four decades.
Chen Wang, Professor, University of Utah
However, Kapton is almost impossible to melt or dissolve, making it non-recyclable. These same qualities also complicate the production of sophisticated structures like multilayered electronics. The traditional method of producing Kapton requires heating the material to temperatures between 200 and 300 degrees Celsius.
“It’s a rather slow process. It takes hours,” Wang added.
The team developed an alternative polyimide material that should be easily compatible with existing manufacturing infrastructure. This light-cured polymer, similar to those used by dentists for durable fillings, cures in seconds under ultraviolet light. This hardening process is not only rapid but can also be done at room temperature.
The novel material has the potential to serve as the foundation for multilayered circuits, significantly increasing the number of components that can be packed into a compact form factor. Previously, bonding layers together with Kapton substrates added steps and costs due to its resistance to melting.
According to Wang, the new material’s ability to harden rapidly on demand and process at low temperatures could enable the creation of novel multilayer devices. For recyclability, the researchers integrated subunits into the polymer backbone that can be easily removed with an alcohol and catalyst solution. This solution can then be used to recover valuable metals from circuits and microchips, which can be repurposed.
Wang added, “We designed the polymer with ester groups in the backbone,” unlike regular Kapton.
These ester groups are easily broken apart by a mild solution, removing the substrate while leaving the rest of the device intact. Wang notes that the University of Utah team has co-founded a company to commercialize this technology.
Wallin noted, “We break the polymer back into its original small molecules. Then, we can collect the expensive electronic components and reuse them. We all know about the supply chain shortage with chips and some materials. The rare earth minerals that are in those components are highly valuable. And so we think that there’s a huge economic incentive now, as well as an environmental one, to make these processes for the recapture of these components.”
Caleb Reese and Grant Musgrave from the University of Utah, along with Jenn Wong, Wenyang Pan, John Uehlin, Mason Zadan, and Omar Awartani from Meta's Reality Labs in Redmond, Washington, collaborated on the study. Funding for this research was provided by a startup fund from the University of Utah's Price College of Engineering.
Journal Reference:
Reese, C., et. al. (2024) Photopatternable, Degradable, and Performant Polyimide Network Substrates for E-Waste Mitigation. RSC: Applied Polymers. doi:10.1039/D4LP00182F