In a new spin on green electronics, researchers have made a biodegradable electronic circuit board from tree leaves. Such leaf-based electronics, or “leaftronics” as the team from Dresden University of Technology (TU Dresden) has dubbed it, could reduce millions of tons of waste that humans produce every year.

Today, the world produces over 50 million metric tons of electronic waste a year. That number that is slated to double by 2050. And printed circuit boards (PCBs) – the flat boards onto which all the circuit chips, wires and other components of an electronic gadget are soldered–-constitute a big share of this e-waste.

PCBs are typically made of fiberglass or a composite plastic. The material is difficult to recycle and is usually either dumped in landfills or burned to separate the valuable metals for reuse.

As detailed in the journal Science Advances, the team used the veiny, webbed skeleton of leaves to create their biodegradable substrates. This fine branched structure is made of the same lignocellulose compounds that give its toughness. Postdoctoral researcher Rakesh Nair and colleagues started by stripping away the cells of a magnolia leaf to leave behind the white veined skeleton. They dipped the scaffold into ethyl cellulose, a tough biodegradable polymer.

The resulting leaftronics substrate is smooth, flexible, transparent, and can handle high temperatures. In that sense it rivals plastic and glass, Nair says, but is biodegradable. The researchers could use a laser to cut the substrate, print circuits on it, as well as solder electronic components on top.

To degrade the substrate, the researchers placed it in an ultrasonic acid bath to remove the metals and circuit components. The boards began to degrade after about a month in compost.

“Up until now, substrates made of biodegradable polymers could not be used for electronic device or circuit fabrication, since they naturally do not handle elevated temperatures well,” Nair says. There are ways to improve the thermal and mechanical properties of biodegradable polymers. But, he says, they “often result in these polymers either no longer being biodegradable or requiring complex, high carbon-footprint, chemical processes,” he says.

Others have also made degradable PCBs using paper, silk, and mushroom skins. But the new method that relies on dipping a leaf scaffold in a biodegradable polymer is much simpler and should allow researchers to make specific biodegradable substrates with superior properties.

For example, the researchers also made leaftronics substrates using gelatin, which is a hydrophilic, biodegradable, solution processable material. “But is difficult to work with since it melts around 50-60°C,” Nair says. “However, with reinforcement using leaf-derived lignocellulose [scaffolds], it appears that gelatin could be used as a film even at 180°C.”

Leaftronics should be reliable enough for mass production, he says. But the challenge will be in convincing electronics manufacturers to adopt the technology because of the extremely high PCB durability standards it has set itself. “Currently, circuit boards are made of materials that can last for thousands of years but are put into electronic products designed to become obsolete within a few years. This makes it difficult for biodegradable PBCs to clear the industrial durability standards, even if they can survive the regular production processes.”

Source: Rakesh R. Nair et al. Leaftronics: Natural lignocellulose scaffolds for sustainable electronics. Sci. Adv. 2024.

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