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69: Cell phone components, nanocellulose

Problem:

Approximately 150 million mobile phones are discarded each year in the USA. Although cell phones have the highest recycling market of any electronic material only 10% of these are recycled while the rest may end up in a landfill, but more likely to end up in desk drawers or garages.

Solution:

In recent years, researchers have demonstrated that nanocellulose, which is made by breaking wood fibers down to the nanoscale, can be a viable support material for a variety of electronic devices, including solar cells.


John Rogers, a professor of materials science at the University of Illinois at Urbana-Champaign, developed the method for transferring small amounts of semiconducting material from a large wafer to the nanocellulose surface.

In 2015, researchers at the University of Wisconsin-Madison, led by Zhenqiang (Jack) Ma, a professor of electrical and computer engineering, collaborated with researchers in the Madison-based U.S. Department of Agriculture Forest Products Laboratory (FPL), to innovate wood-based semi-conductor chips, by making the gallium arsenide electronic components in a similar way but then using a rubber stamp to lift them from the wafer and transfer them to a new surface made of nanocellulose.

The challenge was to produce a smooth-enough surface that also had the capacity for thermal expansion. The final product evolved from the concept of breaking wood down further from individual fibre, at the micron stage, to the nanoscale.

The result is a material which is very strong, transparent, flexible, and, most-importantly, biodegradable, cellulose nanofibril (CNF).

An epoxy coating is added to the surface to ensure a smooth layer and eliminate the hydroscopic nature, both of which were previously barriers for using wood-derived materials. This reduced the amount of semiconducting material used by a factor of up to 5,000, without sacrificing performance.

Their results also show that a transparent, wood-derived material called nanocellulose paper is an attractive alternative to plastic as a surface for flexible electronics.

In conventional chip manufacturing, electronic components such as transistors are made on the surface of a rigid wafer made of a semiconducting material such as silicon.

In two recent demonstrations, Ma and his colleagues showed they can use nanocellulose as the support layer for radio frequency circuits that perform comparably to those commonly used in smartphones and tablets. They also showed that these chips can be broken down by a common fungus.

In 2019, researchers at the Institute of Materials Science of Barcelona (ICMAB-CSIC) created a new concept of thermoelectric material, published in the journal Energy & Environmental Science (“Farming thermoelectric paper”).

It is a device composed of cellulose, produced in situ in the laboratory by bacteria, dispersed in an aqueous culture medium containing sugar and carbon nanotubes, producing the nanocellulose fibres that end up forming the device, in which the carbon nanotubes are embedded.

The intention is to approach the concept of circular economy, using sustainable materials that are not toxic for the environment, which are used in small amounts, and which can be recycled and reused.

Tomorrow’s solution: a healthier overall central heating system

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