E-Waste : Scientists find way to recover nanowires from consumer electronics

Researchers at North Carolina State University have developed a new method for recycling nanowires in electronics.

Yong Zhu, corresponding author of a paper on the subject and the Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State, pointed out that the new technique differs from conventional recycling methods.

Whereas the latter would see the entirety of a product melted down prior to repurposing, the new way would entail the complete separation of silver nanowire networks from a device.

In order for this to work, the first order of business is the development of electronic goods made from polymers that are soluble in solvents meant to extract nanowires. The leftover nanowire network is then dunked in another solvent and consequently hit with ultrasound. Said process allows for the separation of the condensed nanowires into single strands that can be reused.

The research team discovered that the application of ultrasound needs to be regulated in order to ensure proper material recovery. A too long exposure to the relevant soundwaves can result in breakage while a too short exposure to ultrasound levels could lead to nanowire clumping.

For the separate solvent used for the nanowire network, low surface tension was equally identified as a necessary requirement, as this is what ‘facilitates the disassembling of the network’.

To prove the sustainability of their proposed recycling method, the researchers made a health sensor patch used to track a patient’s hydration and temperature levels. This device contained nanowire networks embedded within in a plastic structure. They then proceeded to strip said network from the polymer frame, disassembled it into individual nanowires, and then used those separate wires to build another health sensor patch. They were able to do this four times without compromising the device’s performance.

"Using our approach, you get far more use from the nanowires," Zhu says. "And even after the nanowires have broken down many times, to the point where they can't be reused, we can still use them as feedstock for conventional recycling. It's a tremendous reduction in waste."