Utilising new materials to combat flexible e-waste

Researchers at MIT, the University of Utah, and Meta have created a new type of flexible substrate material that offers a potential solution to this problem. This material not only facilitates the recycling of components and materials once a device reaches the end of its life but also allows for the scalable production of more intricate multilayered circuits than those currently available.

This innovative material is detailed in the journal RSC Applied Polymers, in a paper authored by MIT Professor Thomas J. Wallin, University of Utah Professor Chen Wang, and seven other researchers.

Wallin, an assistant professor in MIT’s Department of Materials Science and Engineering, commented on the broader issue:

“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.”

Historically, academic efforts have concentrated on developing alternatives to conventional flexible electronic substrates, which are typically made from a polymer known as Kapton—a trade name for polyimide.

While much research has focused on creating entirely new polymer materials, Wallin emphasised that this approach often overlooks the practical reasons for the original choice of materials:

“That really ignores the commercial side of it, as to why people chose the materials they did to begin with.” Kapton has been widely used due to its excellent thermal and insulating properties and the readily available source materials.

The global market for polyimide is projected to reach $4 billion by 2030. “It’s everywhere, in every electronic device basically,” Wang explained, referring to components like the flexible cables that connect different parts inside devices such as mobile phones or laptops. Its high heat tolerance also makes it popular in aerospace applications. Despite its widespread use, Wang noted: “It’s a classic material, but it has not been updated for three or four decades.”

However, Kapton’s resilience comes at a cost. Its resistance to melting or dissolving renders it difficult to reprocess, and its use in advanced architectures like multilayered electronics is hindered by the slow manufacturing process, which involves heating the material to between 200 and 300 degrees Celsius over several hours.

The alternative material developed by the research team, which is also a form of polyimide, offers compatibility with existing manufacturing infrastructure. This material is a light-cured polymer, similar to those used by dentists for durable fillings that harden within seconds under ultraviolet light. This new approach to hardening the substrate is not only faster but can also be done at room temperature.

This material could be used as the substrate for multilayered circuits, significantly increasing the number of components that can be integrated into small devices. Unlike Kapton, which requires layers to be glued together, adding time and cost, the new material's low-temperature, rapid-hardening process could enable the creation of new multilayer devices, according to Wang.

Regarding recyclability, the team incorporated subunits into the polymer backbone that can be quickly dissolved by an alcohol and catalyst solution. This process allows for the recovery of precious metals and entire microchips from the solution, which can then be reused in new devices.

Wang explained: “We designed the polymer with ester groups in the backbone,” unlike traditional Kapton. These ester groups can be easily broken apart by a mild solution that removes the substrate while leaving the rest of the device intact. The University of Utah team has already co-founded a company to commercialise this technology.

Wallin added: “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.”

The research team also included 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. The project received support from a startup fund at the Price College of Engineering at the University of Utah.