According to the United Nations, less than a quarter of all US e-waste is recycled. In 2021 alone, global e-waste jumped to 57.4 million tonnes, of which only 17.4% was recycled.
Some experts predict that our e-waste problem will only get worse over time because most electronics on the market today are designed for portability, not recyclability. Tablets and readers, for example, are assembled by bonding circuitry, chips and hard drives to thin layers of plastic, which must be melted down to extract precious metals like copper and gold. Burning plastic releases toxic gases into the atmosphere, and electronic devices that degrade in landfills often contain harmful materials like mercury, lead, and beryllium.
But now, a team of researchers from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have developed a potential solution: a fully recyclable and biodegradable circuit board. The researchers, who reported on the new device in the journal Advanced Materials, say the advancement could divert wearables and other flexible electronics from landfill and mitigate the health and environmental risks posed by heavy metal waste. .
“When it comes to plastic e-waste, it’s easy to say it’s impossible to solve and walk away,” said lead author Ting Xu, a senior researcher at the Materials Science Division of Berkeley Lab and Professor of Chemistry and Materials Science and Engineering at UC Berkeley. “But scientists are finding increasing evidence of significant health and environmental problems caused by the leaching of e-waste into soil and groundwater. With this study, we show that even if we cannot yet solve the whole problem, we can at least tackle the problem of the recovery of heavy metals without polluting the environment.
Make the enzymes work
In a previous study, Xu and his team demonstrated a biodegradable plastic material incorporated with purified enzymes such as Burkholderia cepacian lipase (BC-lipase). Through this work, they discovered that hot water activated BC-lipase, prompting the enzyme to break down polymer chains into monomeric building blocks. They also learned that BC-lipase is a finicky “eater”. Before a lipase can convert a polymer chain into monomers, it must first grab the end of a polymer chain. By controlling when the lipase finds the end of the chain, it is possible to ensure that the materials do not degrade until the water has reached a certain temperature.
For the current study, Xu and his team simplified the process even further. Instead of expensive purified enzymes, biodegradable circuit boards rely on cheaper, ready-to-use lipase BC “cocktails”. This greatly reduces costs, making it easier for the circuit board to enter mass manufacturing, Xu said.
Ink adheres to a variety of materials
In doing so, the researchers advanced the technology, allowing them to develop a printable “conductive ink” composed of biodegradable polyester binders, conductive fillers such as silver flakes or carbon black, and enzyme cocktails available in the trade. The ink derives its electrical conductivity from silver or carbon black particles, and the biodegradable polyester binders act like a glue.
The researchers provided a commercial 3D printer with the conductive ink to print circuit patterns on various surfaces such as hard biodegradable plastic, flexible biodegradable plastic, and fabric. This proved that the ink adheres to a variety of materials and forms an integrated device once the ink dries.
To test its shelf life and durability, the researchers stored a circuit board in a lab drawer with no humidity or temperature control for seven months. After removing the circuit from storage, the researchers applied DC voltage to the device for a month and found that the circuit conducted electricity as well as before storage.
Next, the researchers tested the recyclability of the device by immersing it in lukewarm water. Within 72 hours, the circuit materials degraded into its building blocks – The silver particles completely separated from the polymer binders and the polymers broke down into reusable monomers, allowing researchers to easily recover the metals without further processing. At the end of this experiment, they determined that approximately 94% of the silver particles can be recycled and reused with similar device performance.
That circuit degradability continued after 30 days of operation surprised the researchers, suggesting that the enzymes were still active. “We were surprised that the enzymes ‘lived’ so long. Enzymes are not designed to work in an electric field,” Xu said.
Xu attributes the longevity of the working enzymes to the molecular structure of the biodegradable plastic. In their previous study, the researchers learned that adding an enzyme protectant called a random heteropolymer, or RHP, helps disperse the enzymes in the mixture into clusters of a few nanometers (billionths of a meter). This creates a safe place in the plastic for the enzymes to sleep until called into action.
The circuit also shows promise as a durable alternative to single-use plastics used in transient electronics – devices such as biomedical implants or environmental sensors that decay over a period of time, the author said. principal Junpyo Kwon, who holds a Ph.D. research student of the Xu and Robert Ritchie groups at UC Berkeley. Now that they have demonstrated a biodegradable and recyclable circuit board, Xu wants to demonstrate a printable, recyclable and biodegradable microchip.
“Given the current sophistication of chips, this will certainly not be easy. But we have to try to give the best of our level,” she said.
Other researchers who contributed to the study were Christopher DelRe, Philjun Kang, Aaron Hall, Daniel Arnold, Ivan Jayapurna, Le Ma, Matthew Michalek, and Robert O. Ritchie. This work was supported by the DOE Office of Science. Additional funding was provided by the US Department of Defense, Office of Army Research.
The technology is available for licensing through the UC Berkeley Technology Licensing Office.