The world generates over 140,000 tons of electronic waste every single day. This waste is complex, made of many different materials, making it very hard to separate and recycle.
Researchers have turned to the humble fungus for help. In a new Science Advances study, they show how processed mushroom skin could be a biodegradable substrate for computer chips, taking us one step closer to recyclable electronics.
Electronic circuits are made of multiple computer chips and other components sitting on circuit boards made of conventional plastics. These boards are a major hurdle in recycling electronics, says Martin Kaltenbrunner of Johannes Kepler University in Austria. “They are difficult if not impossible to be reused or taken apart. It is often not economically viable to recycle them, so they are either incinerated or landfilled.”
Meanwhile, the world is producing ever more small electronics that don’t need to last for too long. These include sensors, electronic tags for store products, and wearable health monitoring devices. Making degradable versions of these short-lived devices could be a big step forward in sustainability. And a good place to start is the plastic circuit board.
Mushrooms are already being used to make sustainable leather and Styrofoam-like packaging materials. Kaltenbrunner and his colleagues came upon mushroom skins for circuit boards by serendipity. One of his PhD students is studying wood–mushroom composite materials for insulation materials. He found that Ganoderma lucidum mushrooms grow a compact protective skin around the wood shavings on which they grow. He was able to peel off large sheets of this material, which resembled thin sheets of paper.
Drying the sheets gave a strong, flexible and current- and heat-resistant material that was perfect for a circuit substrate. The material could be bent more than 2,000 times and folded over multiple times without losing its electrical resistance.
The researchers could solder electronic components and construct metal circuits on the skin. They also made a mostly biodegradable battery from the fungal material. Mushroom skin soaked in a conductive liquid electrolyte was the battery’s central separator, with metal pastes on either side as the electrodes. Its outer case was made of the dry mushroom skin. It could power small devices such as a Bluetooth module and a humidity sensor.
The fungal skin also hits the “sweet spot” for degradability, Kaltenbrunner says. Other naturally derived materials that either degrade too quickly or need industrial composting facilities to break down. The mushroom skin by contrast “lasts for a long time when kept reasonably dry, but in a standard household compost, it would degrade entirely within two weeks or less. No special facilities needed. Also, no post-processing or chemical treatment needed.”
Others have made biodegradable electronic substrates from paper and silk. But growing and processing silk for thin films is complex, while producing paper is energy- and water-intensive. Making one ton of paper requires about 300 million liters of water and roughly 33 Gigajoules of energy, says Kaltenbrunner, making it less than idea for large scale, cheap electronics.
Mushrooms, meanwhile, cultivate easily on waste wood, and the skin grows naturally and does not need much processing, he adds. “Our fungus-based materials do have the potential to be scaled at low costs to the needs of the everyday electronics industry, while being less resource and energy intensive than other approaches.”
The team is now looking into processing methods that let them reliably grow uniform mushroom skins. And they also aim to combine the sustainable substrate with electronics components that are degradable themselves to make fully biodegradable circuits.
Source: Doris Danninger et al. MycelioTronics: Fungal mycelium skin for sustainable electronics. Science Advances, 2022.
Image ©Anthropocene Magazine