Fascination with Technology Researchers Develop Biodegradable Computer Mouse

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In our "Fascination with Technology" section, we present impressive research and development projects to engineers every week. Today: How researchers succeeded in developing a nearly fully compostable computer mouse made of wood.

They are the "heart" of every electronic device, from laptops to electric toothbrushes: circuit boards, also known as PCBs, short for "printed circuit boards." The rigid boards are covered with copper traces and soldered electronic components, usually coated in a characteristic green. But they are not particularly environmentally friendly.

As a substrate for the copper traces and electronic components, a laminate made of fiberglass-reinforced epoxy resin is typically used. This composite material is made from petroleum and cannot be recycled. Proper disposal is complex, for example, requiring a special pyrolysis furnace with exhaust air treatment—an issue given the large quantities of discarded circuit boards that need to be disposed of each year.

Base Material Made of Wood—A Waste Product

Researchers led by Thomas Geiger from the "Cellulose and Wood Materials" lab at Empa are working on a "green," sustainable alternative. As part of the EU research project "HyPELignum," they have developed a substrate material for circuit boards based on wood that can compete with conventional epoxy resin—and is also fully biodegradable. The circuit boards made from it have been installed by the researchers into functioning computer mice.

The base material for the substrate is a natural mixture of cellulose with a small amount of lignin. Strictly speaking, it is a waste product. "Our partners at the TNO research institute in the Netherlands have developed a process to extract the raw materials lignin and hemicellulose from wood," Geiger explains. "What remains is the brownish lignocellulose, which previously had no use." Geiger, who has been researching electronics made from cellulose for a long time, recognized the potential of this raw material.

• In order for fluffy lignocellulose to become a high-tech product like a circuit board, it must first be ground with the addition of water to break down the relatively thick cellulose fibers into fine cellulose fibrils.
• This creates a fine network of ultra-thin fibrils that are interconnected.
• In the next step, the water is pressed out of the mass under high pressure. The fibrils move closer together and dry into a solid mass. The researchers call this process "hornification."

Challenge Water

The resulting hornified board is almost as resilient as a conventional circuit board made of fiberglass and epoxy—almost. This compostable board is still sensitive to water and high humidity. But water is necessary, because, "if no water can penetrate the substrate at all, microorganisms, like fungi, can no longer grow in it—thus biodegradability would no longer be possible," Geiger explains.

Initial Applications: Compostable Computer Mouse And RFID Card

Nevertheless, the researchers are confident that the resistance of the lignocellulose-based biocomposite can be further improved with the right processing. "For certain applications, however, we also need to rethink our relationship with electronics," says Thomas Geiger. "Many electronic devices are only used for a few years before they become obsolete—so it is not necessarily sensible to manufacture them from materials that can last for hundreds of years."

The researchers, in collaboration with their industrial partner Profactor GmbH in Austria, printed circuit traces onto their sustainable circuit boards and assembled them with components to create functioning electronic devices, such as a computer mouse or an RFID card. At the end of its lifecycle, such a device could be composted under the right conditions. Once the substrate material decomposes, the metallic and electronic components can be extracted from the compost and recycled.

About the Project "HyPELignum"

The EU research project "HyPELignum" aims to develop a holistic approach to functional, CO₂-neutral electronics. To achieve this, the international project partners from research and industry are combining wood-based raw materials and minimally critical transition metals with additive manufacturing and advanced sustainability analyses. The project is funded under the "Horizon Europe" program and by the State Secretariat for Education, Research and Innovation (SBFI) and runs from October 2022 to September 2026. Researchers from Empa are contributing to the development of sustainable circuit boards as well as to lifecycle analysis.

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