Fully recyclable printed electronics ditch toxic chemicals for water
First-of-its-kind demonstration suggests a more environmentally friendly future for the electronics industry is possible

Date:
April 6, 2023
Source:
Duke University
Summary:
Engineers have produced fully recyclable printed electronics
that replace the use of chemicals with water in the fabrication
process. By bypassing the need for hazardous chemicals, the
demonstration points down a path industry could follow to reduce
its environmental footprint and human health risks.


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FULL STORY ========================================================================== Engineers at Duke University have produced the world's first fully
recyclable printed electronics that replace the use of chemicals with
water in the fabrication process. By bypassing the need for hazardous chemicals, the demonstration points down a path industry could follow
to reduce its environmental footprint and human health risks.


==========================================================================
The research appeared online Feb. 28 in the journal Nano Letters.

One of the dominant challenges facing any electronics manufacturer is successfully securing several layers of components on top of each other,
which is crucial to making complex devices. Getting these layers to
stick together can be a frustrating process, particularly for printed electronics.

"If you're making a peanut butter and jelly sandwich, one layer on either
slice of bread is easy," explained Aaron Franklin, the Addy Professor
of Electrical and Computer Engineering at Duke, who led the study. "But
if you put the jelly down first and then try to spread peanut butter on
top of it, forget it, the jelly won't stay put and will intermix with
the peanut butter. Putting layers on top of each other is not as easy
as putting them down on their own -- but that's what you have to do if
you want to build electronic devices with printing." In previous work, Franklin and his group demonstrated the first fully recyclable printed electronics. The devices used three carbon-based inks: semiconducting
carbon nanotubes, conductive graphene and insulating nanocellulose. In
trying to adapt the original process to only use water, the carbon
nanotubes presented the largest challenge.

To make a water-based ink in which the carbon nanotubes don't clump
together and spread evenly on a surface, a surfactant similar to detergent
is added. The resulting ink, however, does not create a layer of carbon nanotubes dense enough for a high current of electrons to travel across.

"You want the carbon nanotubes to look like al dente spaghetti strewn
down on a flat surface," said Franklin. "But with a water-based ink,
they look more like they've been taken one-by-one and tossed on a wall
to check for doneness. If we were using chemicals, we could just print
multiple passes again and again until there were enough nanotubes. But
water doesn't work that way. We could do it 100 times and there'd still
be the same density as the first time." This is because the surfactant
used to keep the carbon nanotubes from clumping also prevents additional
layers from adhering to the first. In a traditional manufacturing process, these surfactants would be removed using either very high temperatures,
which takes a lot of energy, or harsh chemicals, which can pose human and environmental health risks. Franklin and his group wanted to avoid both.

In the paper, Franklin and his group develop a cyclical process in which
the device is rinsed with water, dried in relatively low heat and printed
on again.

When the amount of surfactant used in the ink is also tuned down,
the researchers show that their inks and processes can create fully
functional, fully recyclable, fully water-based transistors.

Compared to a resistor or capacitor, a transistor is a relatively
complex computer component used in devices such as power control or
logic circuits and sensors. Franklin explains that, by demonstrating a transistor first, he hopes to signal to the rest of the field that there
is a viable path toward making some electronics manufacturing processes
much more environmentally friendly.

Franklin has already proven that nearly 100% of the carbon nanotubes
and graphene used in printing can be recovered and reused in the same
process, losing very little of the substances or their performance
viability. Because nanocellulose is made from wood, it can simply be
recycled or biodegraded like paper. And while the process does use a
lot of water, it's not nearly as much as what is required to deal with
the toxic chemicals used in traditional fabrication methods.

According to a United Nations estimate, less than a quarter of the
millions of pounds of electronics thrown away each year is recycled. And
the problem is only going to get worse as the world eventually upgrades
to 6G devices and the Internet of Things (IoT) continues to expand. So
any dent that could be made in this growing mountain of electronic trash
is important to pursue.

While more work needs to be done, Franklin says the approach could
be used in the manufacturing of other electronic components like
the screens and displays that are now ubiquitous to society. Every
electronic display has a backplane of thin-film transistors similar to
what is demonstrated in the paper. The current fabrication technology
is high-energy and relies on hazardous chemicals as well as toxic
gasses. The entire industry has been flagged for immediate attention
by the US Environmental Protection Agency. [https://www.epa.gov/ climateleadership/sector-spotlight-electronics] "The performance of our thin-film transistors doesn't match the best currently being manufactured,
but they're competitive enough to show the research community that we
should all be doing more work to make these processes more environmentally friendly," Franklin said.

This work was supported by the National Institutes of Health
(1R01HL146849), the Air Force Office of Scientific Research
(FA9550-22-1-0466), and the National Science Foundation (ECCS-1542015,
Graduate Research Fellowship 2139754).

* RELATED_TOPICS
o Matter_&_Energy
# Electronics # Graphene # Technology
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# Water # Sustainability # Air_Quality
o Computers_&_Math
# Spintronics_Research # Mobile_Computing #
Computers_and_Internet
* RELATED_TERMS
o Environmental_impact_assessment o Environmental_engineering
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========================================================================== Story Source: Materials provided by Duke_University. Original written
by Ken Kingery. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Shiheng Lu, Brittany N. Smith, Hope Meikle, Michael J. Therien,
Aaron D.

Franklin. All-Carbon Thin-Film Transistors Using Water-Only
Printing.

Nano Letters, 2023; 23 (6): 2100 DOI: 10.1021/acs.nanolett.2c04196 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/04/230406152644.htm

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