Engineers have Developed Fully Recyclable Printed Electronics

Engineers have created printed electronics that are completely recyclable. The researchers hope to inspire a new generation of recyclable electronics to help fight the growing global epidemic of electronic waste by demonstrating a crucial and relatively complex computer component – the transistor – created with three carbon-based inks.

Duke University engineers have created the world’s first fully recyclable printed electronics. The researchers hope to inspire a new generation of recyclable electronics to help fight the growing global epidemic of electronic waste by demonstrating a crucial and relatively complex computer component – the transistor – created with three carbon-based inks.

The work appears online April 26 in the journal Nature Electronics.

“Silicon-based computer components are probably here to stay, and we don’t expect easily recyclable electronics like ours to replace existing technology and devices,” said Aaron Franklin, the Addy Professor of Electrical and Computer Engineering at Duke. “However, we hope that by developing new, fully recyclable, easily printed electronics and demonstrating their capabilities, they will become widely used in future applications.”

Engineers have developed the world’s first fully recyclable printed electronics. By demonstrating a crucial and relatively complex computer component – the transistor – created with three carbon-based inks.

As people around the world incorporate more electronics into their lives, there is an ever-growing pile of discarded devices that either no longer work or have been replaced by a newer model. According to estimates from the United Nations, less than a quarter of the millions of pounds of electronics discarded each year is recycled. And the problem will only worsen as the world transitions to 5G devices and the Internet of Things (IoT) expands.

Electronic devices are difficult to recycle, which contributes to the problem. Hundreds of workers are employed in large plants to hack at bulky devices. But while scraps of copper, aluminum and steel can be recycled, the silicon chips at the heart of the devices cannot.

Franklin and his colleagues present a completely recyclable, fully functional transistor made of three carbon-based inks that can be easily printed onto paper or other flexible, environmentally friendly surfaces in their new study. For semiconductors and conductors, carbon nanotubes and graphene inks are used, respectively. While these materials are not new to the world of printed electronics, Franklin claims that the path to recyclability was paved with the development of nanocellulose, a wood-derived insulating dielectric ink.

“Nanocellulose is biodegradable and has been used in applications such as packaging for many years,” Franklin explained. “While its potential applications as an insulator in electronics have long been known, no one has yet figured out how to use it in a printable ink. That is one of the keys to making these completely recyclable devices work.”

Fully recyclable printed electronics developed

The researchers created a method for suspending nanocellulose crystals extracted from wood fibers that, when mixed with a little table salt, yields an ink that performs admirably as an insulator in their printed transistors. Using the three inks in an aerosol jet printer at room temperature, the team demonstrates that their all-carbon transistors perform well enough for use in a wide range of applications, even six months after printing.

The team then shows how recyclable their design is. Carbon nanotubes and graphene are sequentially recovered with an average yield of nearly 100 percent by immersing their devices in a series of baths, gently vibrating them with sound waves, and centrifuging the resulting solution. Both materials can then be reused in the same printing process with very little loss of performance viability. Because the nanocellulose is made of wood, it can be recycled alongside the paper on which it was printed.

A transistor, in comparison to a resistor or a capacitor, is a relatively complex computer component used in devices such as power control or logic circuits, as well as various sensors. Franklin explains that by first demonstrating a fully recyclable, multifunctional printed transistor, he hopes to take a first step toward the technology that is currently being pursued commercially for simple devices. Franklin, for example, envisions the technology being used in a large building that requires thousands of simple environmental sensors to monitor its energy use or customized biosensing patches to track medical conditions.

“By no means are recyclable electronics like this going to go out and replace an entire half-trillion-dollar industry, and we’re certainly nowhere near printing recyclable computer processors,” Franklin said. “However, demonstrating these types of new materials and their functionality is hopefully a first step toward a new type of electronics lifecycle.”