One of the main reasons why so many electronics end up as e-waste instead of getting recycled at the end of their life is the fact that it’s really difficult to separate and recover the valuable materials that make them up. Now, a new technique developed by scientists at Duke University may help solve that problem.
As part of their effort to slow the stream of e-waste, the engineers have developed the world’s first fully recyclable printed electronics, demonstrated in the form of a transistor that can be reduced to its original building blocks, with the help of baths and sound.
The development is one of the latest in the field of printable electronics, which involves combining common printing equipment together with conductive ink to create thin and flexible electronic circuits. The key component of the new technology is nanocellulose, a substance derived from plants and wood waste.
“Nanocellulose is biodegradable and has been used in applications like packaging for years,” said study author Aaron Franklin. “And while people have long known about its potential applications as an insulator in electronics, nobody has figured out how to use it in a printable ink before. That’s one of the keys to making these fully recyclable devices functional.”
To create the recyclable transistor, Franklin and his team incorporated nanocellulose into printable ink by reducing it to a crystalline form and adding a sprinkling of salt. This insulating, dielectric ink was then combined with conductive ink and a semiconductive ink to form an all-carbon transistor that can be printed onto a paper sheet. Tests then demonstrated that the transistor performed well enough to serve a variety of uses, remaining stable over six months.
Finally, recycling the electronic component involved first dipping it in a series of baths, then vibrating it with sound waves. Next, the resulting solution was centrifuged, which allowed the carbon nanotubes and graphene to be recovered at a yield close to 100 percent and be reused to create another transistor.