Old electronics are tricky to recycle, meaning they clog up landfills while locking valuable metals away. Now scientists have demonstrated printed circuits that can be degraded on demand, returning their materials to reusable forms.

While many of us chase the excitement of a new phone every year or two, the problem of electronics waste only grows. Many of these devices aren’t built with recyclability in mind, and it’s hard to extract the precious metals like gold and silver from them for reuse. Instead, much of this e-waste ends up in landfill, where it can leach toxic chemicals into the environment.

A growing field of research is what is known as transient electronics – those made to degrade after a certain amount of time, or when they encounter a specific trigger like heat or water. These could not only help reduce e-waste, but make for sensors in the human body or the environment that can biodegrade when their work is done.

For the new study, researchers at Berkeley Lab and UC Berkeley have developed and demonstrated printed circuits that can break down into reusable materials, including precious metals, on demand.

The new design builds on the team’s previous work, where they created biodegradable plastics with embedded enzymes that would break apart the material’s polymer chains in hot water or in soil, degrading the plastic in a matter of days. A molecule called RHP disperses the enzymes into clusters within the plastic, which keeps them from destroying the material too early.

This time, the researchers tweaked the recipe to use cocktails of inexpensive enzymes, to streamline production and reduce costs. They used their biodegradable plastic as a substrate, and onto that they printed electronic circuits made of a conductive ink. This is made up of silver flakes or carbon black particles to provide electrical conductivity, polyester binders that hold it all together, and the enzyme cocktails that eventually unravel the whole thing by degrading the binders.

The team tested the entire proposed lifecycle of the circuits. First they stored them in a drawer for seven months under normal conditions, exposed to everyday fluctuations in temperature and humidity. Then they ran an electrical current through them continuously for a month. The stored circuits worked just as well as brand new ones, the team says, indicating they hadn’t started prematurely degrading.

Finally, the researchers tested their biodegradability. They let them sit in warm water for a few days, and found that within 72 hours the silver particles separated from the polymers, which had broken down into monomers. The team says that 94% of the silver could be recycled, as could the monomers.

The team also tested the biodegradable, conductive ink on a range of other materials, like flexible plastic and cloth, and found that it still worked as a circuit in all cases. This could make it useful for wearables. The next steps are to create an entire microchip that’s biodegradable, the team says.

The research was published in the journal Advanced Materials. The team describes the work in the video below.

Source: Berkeley Lab