Electronic waste, or e-waste, is one of the fastest-growing solid waste streams worldwide. In 2022, the global population generated 62 million tonnes of e-waste, yet only 22.3% was recycled. In light of this, a group of students in the mechanical engineering department worked in professor Mohammad Malakooti’s research lab to create a sustainable alternative to non-recyclable composites used primarily in circuit boards.
E-waste also contains hazardous materials that become toxic when not disposed of properly. When such toxic wastes accumulate in the environment, it poses a health risk and exposes people to high levels of contaminants such as lead, mercury, and arsenic, which can lead to irreversible health effects like cancer and neurological damage.
“We’re trying to make a difference now to shape the future of flexible and wearable electronics,” Malakooti said in a UW News article. “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.”
The research, published Sept. 12, presented a composite design that utilizes a stretchable liquid metal-vitrimer with reconfigurable properties. Vitrimer is a recyclable thermoset, a polymer that, after curing, usually forms a rigid cross-linked structure that can’t be reshaped. However, the vitrimer’s unique network structure provides robustness and enables bond-exchange reactions, where chemical bonds are rearranged to form new ones, allowing reshaping and recycling for future use.
This composite can be recycled in two ways. The first method, thermomechanical reprocessing, involves using a high-temperature hot press to repair separated vitrimer pieces. However, this technique alters the composite’s original properties. Compressing liquid-metal fillers changes their shape, elongating them in the plane of the composite, thereby affecting its mechanical properties and thermal conductivity, two important attributes of a working composite.
The second way to recycle the composite is chemical recycling. Instead of using a hot press, the method involves separating the liquid metal particles from the vitrimer composite and reusing them in another composite. Using the same liquid metal ensures the new composite has the same properties as the original composite. However, lead author Youngshang Han said the downside of this method is that every time the liquid metal particles are extracted, they lose 5% of their weight, and so only about 95% of the liquid metal can be used in the new composite.
“Our current study opens a wider window for companies or manufacturers to recycle those composites to not only save costs from increasing precious metal prices, but to make their work more sustainable,” Han said. “The most promising applications of our composite would be flexible circuit boards and conductive adhesives to build parts for vehicles.”
Reach contributing writer Kaira Wullur at science@dailyuw.com. X: @kairawullurtd. Bluesky: @kairawullurtd.bsky.social.
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