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Engineers create dissolving circuit boards that can be recycled over and over again

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Engineers create dissolving circuit boards that can be recycled over and over again

Electronic waste is the fastest growing waste problem in the world. Instead of burning it to recover gold and copper, this new method separates the components for reuse.
May 2, 2024

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Inside the phone or computer you are reading this story on is a fiberglass board bearing all the circuit chips, wires and other electronic components that make the device work. And every year, hundreds of thousands of tons of these printed circuit boards (PCBs) get dumped in landfills as electronics become obsolete.

There has been a lot of research on finding ways to extract valuable metals from electronic waste. But recycling the PCBs themselves, which are made of a type of tough plastic, is challenging.

Researchers at the University of Washington now report a possible solution. “We have created a new formulation for circuit boards that has performance on par with the industry standard material and can be recycled repeatedly without degradation,” says Vikram Iyer, a professor of computer science and engineering and co-author of a paper appearing in Nature Sustainability.

PCBs are made of sheets of glass fibers laminated in a epoxy plastic similar to the epoxy glues found in hardware store. This composite material gives PCBs the heat and chemical resistance they need for electronics. But the plastic and glass are hard to separate so the material is typically burned to recover valuable metals like gold and copper used in electronics. This creates waste that contaminates the air, soil, and water.

Also, much of the world’s e-waste is sent to poor countries, “where people try to extract small amounts of valuable minerals from the waste in unsafe conditions that release toxic fumes,” Iyer says.

 

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So he, mechanical engineer Aniruddh Vashisth and their colleagues replaced the epoxy in PCBs with a type of plastic known as a vitrimer. “Vitrimers flow and form new, strong chemical bonds when they are heated past a certain temperature,” he says, “allowing them to be recycled over and over, unlike the plastic in water bottles that degrade with each recycling cycle.”

To separate the vitrimer from the glass fibers, the researchers dip the board in a solvent and heat it to a mild temperature. The vitrimer softens and swells, and the researchers can separate the raw materials and use them to make a new PCB. In experiments, the team was able to reuse 98 percent of the vitrimer and 91 percent of the solvent. They were able to recycle the material multiple times without losing its properties.

What is most exciting about the approach, Iyer adds, is that the new PCBs give performance comparable to conventional materials, and are compatible with standard processing used to make circuits so the costs of manufacturing PCBs should be similar. While the team has not done a detailed cost analysis, he says, “we use off-the-shelf chemicals that are produced at industrial scale, and the processing steps here are largely the same as industrially produced materials like epoxy, suggesting it has potential to be cost competitive in larger volumes.”

Source: Zhihan Zhang et al. Recyclable vitrimer-based printed circuit boards for sustainable electronics. Nature Sustainability, 2024.

Image credit: Mark Stone/University of Washington

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