A huge portion of electronic devices that are discarded at the end of their lives are never recycled, and a big part of the problem is the difficulty in separating out and recovering the valuable materials that make them up. With a view to solving this problem, engineers at Duke University 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 waves.
This latest advance in the world of printable electronics, where conductive inks combine with common printing techniques to create thin and flexible electronic circuits, came about through experimentation with nanocellulose. Derived from plants and often wood waste, we've seen how this common material could find use in advanced water filters, squishy batteries and eco-friendly plastics.
We've also seen previously how it can be used as a substrate for wood-based computer chips, though the Duke University engineers have set their sights a little higher, looking to leverage its potential as an insulating material to produce an even more eco-friendly computer component.
“Nanocellulose is biodegradable and has been used in applications like packaging for years,” says 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.”
Franklin and his team appear to have worked out a way to incorporate nanocellulose into printable ink, by reducing it to a crystalline form and adding a sprinkling of salt. This insulating, dielectric ink was combined with a conductive ink made with graphene and a semiconductive ink made from carbon nanotubes, to form an all-carbon transistor that can be printed onto a paper substrate using aerosol jet printing at room temperature.
In testing, the team demonstrated its abilities as a paper-based lactate sensor and say the transistor performed well enough to serve a a range of uses, remaining stable over six months.
The recycling process for the transistor starts by plunging it into a series of baths, and vibrating it gently with sound waves. Subjecting the resulting solution to a centrifuge then allows the carbon nanotubes and graphene to be recovered at a yield close to 100 percent, for re-use with the same printing process. The nanocellulose, meanwhile, can be recycled along with the paper substrate.
“Recyclable electronics like this aren’t going to go out and replace an entire half-trillion-dollar industry by any means, and we’re certainly nowhere near printing recyclable computer processors,” says Franklin. “But demonstrating these types of new materials and their functionality is hopefully a stepping stone in the right direction for a new type of electronics lifecycle.”
The research was published in the journal Nature Electronics.
Source: Duke University