When many of us look for something new every year or twocell phoneWhen excited, the problem of waste in electronics is only going to grow. Many of these devices were not built with recyclability in mind, and it is difficult to extract precious metals such as gold and silver from them for reuse. Instead, much of this e-waste ends up in landfills, where they leach toxic chemicals into the environment.
A growing area of research is so-called transient electronics — those that dissolve naturally after a certain amount of time or when they encounter a specific trigger, such as heat or water. These could not only help reduce e-waste, but also allow sensors in the human body or the environment to biodegrade after they have done their job.
In the new study, researchers at Berkeley Lab and UC Berkeley have developed and demonstrated printed circuits that can be broken down on demand into reusable materials, including precious metals.
The new design builds on the team’s previous work to create biodegradable plastics embedded with enzymes that willhot waterOr polymer chains in the soil that break down the material, degrading the plastic within a few days. A molecule called RHP disperses enzymes into clumps within the plastic, which keeps them from prematurely destroying the material.
This time, the researchers tweaked the recipe to use a “cocktail” of inexpensive enzymes to simplify production and reduce costs. They used biodegradable plastic as a substrate and printed electronic circuits made of conductive ink on it. This is made up of silver flakes or particles of carbon black to provide conductivity, a polyester binder holds it all together, and an enzyme “cocktail” that degrades the binder eventually unravels the whole thing.
The team tested the circuit’s entire proposed life cycle. First, they stored them in a drawer for seven months under normal conditions, exposed to daily fluctuations in temperature and humidity. They then tested them continuously for a month. The stored circuits worked just as well as brand new ones, the team said, indicating that they did not begin to degrade prematurely.
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 polymer, which had broken down into monomers. The team says that 94 percent of the silver can be recovered, as can the monomer.
The team also tested the biodegradable conductive ink on a range of other materials, such as flexible plastic and cloth, and found that it still worked as a circuit in all cases. That could make it useful for wearables. The next step, the team says, is to create a biodegradable whole microchip.
The study was published inAdvanced Materials” magazine. The team describes the work in the video below.