Electronic waste is piling up around the world at a rate that far outpaces recycling efforts , partly because it's so costly and time-consuming to recover useful materials from discarded gadgets. When processed improperly, spent electronics can expose workers and the environment to lead, mercury and other toxic chemicals. Without systemic changes, our global appetite for electronics could produce an annual 60 million tons of electronic waste by 2030 .
This conundrum inspired a team at the University of Washington to create an easily recyclable material that could one day replace many traditional circuit boards, the foundation of most electronics. The new material is flexible, self-healing and can be made conductive without additional components.
This suite of features could help produce a more sustainable generation of wearable electronics, soft robotics and more.
"We created a lot of functionality within one material," said senior author Mohammad Malakooti , a UW assistant professor of mechanical engineering. "Our goal is to build a widely useful platform for flexible, reusable devices."
The new research was published Sept. 12 in Advanced Functional Materials.
Conventional circuit boards pass electrical signals through conductive metal traces, which are bonded to a rigid board commonly made of fiberglass and resin. In contrast, the new material is a soft and stretchable composite made from a recyclable polymer infused with microscopic droplets of a liquid metal alloy based on gallium. A circuit can be created on this composite by lightly scoring a pattern into its surface, which connects adjacent embedded droplets and allows electricity to flow. The rest of the material remains electrically insulating.
Malakooti's research lab has been experimenting with liquid metal-infused polymers since 2019 — the team uses machine learning to explore different iterations of composites . It's proven to be a promising class of materials, but the rising cost of the liquid metal motivated the team to focus on reusability.
The new composite has a few tricks up its sleeve. The polymer holding the liquid metal droplets is still stretchy and strong, but it can be broken down through a simple chemical process, freeing the metal for reuse. In experiments, researchers recovered 94% of the metal from their samples.
The composite also has self-healing properties. Users can cut the material into pieces, rearrange them, and bond them back together using only heat and pressure. An electrical circuit chopped up in this manner will still function when reconnected in a new configuration.
Malakooti envisions a new wave of electronics built with composites like this one, but also a new paradigm for use and reuse. Instead of mass producing gadgets and then tossing them out, he argues, we could design devices and their components to be used, repaired, reconfigured and ultimately recycled.
"We're trying to make a difference now to shape the future of flexible and wearable electronics," Malakooti said. "We can't make all these devices and then go back and try to figure out how to recycle them. That's how we ended up with the electronic waste problem we face today. I want to tackle this problem from the very start."
Co-authors include Youngshang Han , a UW doctoral student of mechanical engineering; Shreya Paul , a UW undergraduate student of mechanical engineering; and Sargun Singh Rohewal , Sumit Gupta and Christopher C. Bowland at the Oak Ridge National Laboratory.
This research was funded by the National Science Foundation and the Department of Energy.
