Recycling for smaller electronics like fitness trackers and smartwatches has proven to be less than optimal in practice. On top of that, these types of devices often get refreshed with new updated models, meaning that the older ones end up in hazardous waste streams.

To solve this problem, scientists have created a two-metal nanocomposite that disintegrates when submerged in water. They published their findings in the science journal ACS Applied Materials & Interfaces.

The team effectively showed circuits in a prototype device (a functional smartwatch) that dissolved within 40 hours!

Smartwatches are very nifty devices but a nightmare when it comes to recycling - Image Credit: Drean Drobot via Shutterstock / HDR tune by Universal-Sci

Due to planned obsolescence and the rapid speed of technological advancements, new gadgets are constantly replacing older models, resulting in millions of tons of electronic trash being generated each year.

Recycling may help minimize the amount of e-waste produced and is required in many places around the world. On the other hand, small consumer electronics are frequently considered not worth the trouble to recycle since their components must be recovered by hand, and some processing procedures, such as open burning and acid leaching, can create health problems and pollution.

Both of these issues can potentially be solved by dissoluble gadgets that disintegrate on demand. Xian Huang from the Department of Biomedical Engineering at Tianjin University and his colleagues had previously produced a zinc-based nanocomposite that dissolved in water and could be used in temporary circuits, but it turned out not to be conducive enough for use in consumer devices.

As a result, the team aimed to enhance the electrical characteristics of their dissolvable nanocomposite while also constructing circuits that could endure regular use by consumers. They added silver nanowires to the zinc-based nanocomposite to make it more conductive. The metallic solution was then screen-printed onto bits of poly(vinyl alcohol) — a polymer that dissolves in water — and the circuits were then hardened by adding tiny droplets of water that stimulate chemical reactions and then evaporate.

The prototype smartwatch inside a poly(vinyl alcohol) case (top) dissolves in water within 40 hours (bottom). (Credit: Adapted from ACS Applied Materials & Interfaces 2021, DOI: 10.1021/acsami.1c07102)

The researchers used this method to create a smartwatch that had several nanocomposite-printed circuit boards within a 3D printed poly(vinyl alcohol) casing.

It was a fully functional smartwatch as well as it had sensors capable of correctly monitored a person's heart rate, blood oxygen levels, and step count. In addition, using Bluetooth functionality, data could be transmitted to a smartphone.

Furthermore, The exterior packaging withstood perspiration, but after submerging the entire gadget in water for 40 hours, both the polymer casing and circuitry disintegrated in their entirety.

All that was left after submersion were the watch's components, such as an organic light-emitting diode (OLED) screen and microprocessor, as well as resistors and capacitors incorporated into the circuits.

According to the research team, their two-metal nanocomposite can be used to create transient devices with performance comparable to that of commercial models, which all in all might go a long way toward addressing the problem of tiny electronics waste.

If you are interested in further details about the work of Xian Huang and his team, check out the paper listed below.

Sources and further reading: