The more than one trillion transistors or semiconductors produced each year, the things that populate computer chips and make them work, are indispensable and also a biblical-scale trash problem: relatively few chips are recycled because breaking them down and extracting the metals used to make them is neither easy nor reliably profitable and also consumes noxious chemicals and lots of energy.
No problem for engineers making next-generation computer chips out of cellulose – the fibrous strands that makeup wood and other plants – instead of the petroleum-based plastics that chips are made of now.
At the University of Wisconsin in Madison, scientists are crafting chips from nanofibrillated cellulose (NC), which is made by adding water to wood waste from lumber mills, grinding the mix into a gel of nano-width fibers, then freeze-drying it to remove the water.
The Wisconsin researchers then covered the NC with epoxy to make it waterproof and leave a smooth surface.
When the chip is no longer useful, it can decompose in a landfill, just as a wood chip might.
Scientists at Duke University are complementing Wisconsin’s work by creating a transistor that can be printed on paper, then broken up into its constituent parts using water and sound waves.
Printing electrical circuits using conductive ink isn’t new, but using cellulose as an element in printable ink is.
The trick the Duke group discovered is to make a crystalline form of nanocellulose and sprinkle in some salt.
The team then mixed this insulating ink with a conducting ink made from graphene and a semi-conducting ink fashioned from carbon nanotubes.
The mix delivered an all-carbon transistor printable on paper using conventional printing technology at room temperature.
The resulting paper transistor remained stable for six months in tests and worked about as well as a conventional semiconductor in a range of uses, the researchers reported.
To break down the gadget and reclaim its components, the engineers submerged it in a series of water baths and vibrated it gently with sound waves. The water bath containing the dissolved elements was put through a centrifuge, which separated the components.
The carbon nanotubes and graphene are almost 100-percent recoverable, the group found, to re-use in making more paper transistors; the nanocellulose and paper underlayment can be recycled using conventional methods.
TRENDPOST: With an Internet of Everything in the offing, demand for transistors – and the resulting heaps of e-waste to follow – will continue to grow relentlessly. Making biodegradable electronics and recycling parts that can be will be recognized as an urgent necessity as devices break down, become antiquated, and we run out of places to pile them.
The use of stable cellulose chips and environmentally benign inks is a breakthrough that could make reclaiming and recycling transistors practical, a big step in reducing the 60 million tons of electronic waste humans turn out annually, with less than 15 percent being recycled now.
Photo credit: Duke University
