06-05-2021 | | By Robin Mitchell
Recently, researchers from Duke University have demonstrated the world’s first fully recyclable printed electronics. What challenges may disposable electronics create, how were the researchers able to achieve this, and will this technology replace modern methods for electronics production?
As electronics continue to power everyday life, there is an increasing demand for disposable electronics. The idea behind disposable electronics is an electronic device that can be used once and then discarded similarly to the product packaging and plastic bags. However, while most disposable packaging can be easily recycled, electronics are not so easily recycled—the inability to recycle electronics results in e-waste that is harmful to the environment.
Disposable electronics already exist in some forms, and by far the most common is the RFID tag found on expensive products in shops. These devices integrate an antenna loop and a microchip, and if not scanned correctly at the till, will trigger alarms at the shop entrance.
However, these devices cannot be disposed of, and the result is that potentially toxic compounds found in the semiconductor are finding their way into the ground. Printable electronics could provide a cheaper alternative to traditional semiconductors in the disposable field. Still, if printable electronics cannot be recycled, disposable electronics will continue the creation of e-waste.
A material is considered recyclable if it can be taken apart and reused later. For example, glass is a fully recyclable material as it can be broken down, reheated, and formed into new glassware. However, while electronic devices can be broken down into their individual parts (with some being reused), most electronic components cannot be recycled.
However, a team of researchers from Duke University (Durham), have developed the world’s first fully recyclable printable electronics. The first important step that the researchers accomplished was to create a printable transistor as this allows for the creation of all other electronics. The second step was to use then materials that can be broken down and either reused or safely disposed of.
Their printed transistor is comprised of three separate carbon inks and nanocellulose. The semiconductor material used by the transistor is carbon nanotubes (in one of the carbon-based inks), while the conductive inks were made using graphene. The dielectric ink is made from nanocellulose that is extracted from wood and then suspended with salt in an ink-form.
The transistor itself can be easily constructed at room temperature using an aerosol jet spray. Furthermore, the inks can be printed directly onto many surfaces including flexible substrates such as paper allowing for flexible electronics. However, the real trick comes when the devices are disposed of!
Disposing of the printed electronics is done using a multistage bath. Each successive bath removes one of the inks in order and suspends that ink in solution. The end result is the original substrate with the electronics totally removed, and several solutions with different compounds. These solutions can be processed to extract the materials, and these can then be reused to make new printed electronics. The nanocellulose can be left in paper-based substrates as it is a biodegradable material that is already found in paper. As such, paper substrates can be recycled back into paper.
The short answer to this question is no, but that is not to say that what the researchers have developed is not game-changing. On the contrary, what the researchers have demonstrated is the possibility of future electronic components that are easily recycled using a solution-based dissolving method, and those solutions can have the active compounds extracted with ease.
For such printed electronics to become mainstream (and compete with commercial devices), the individual active components would need to be reduced significantly in size. This does not require nanometre features as electronics designed in the late 90s (i.e. 250nm) are more than sufficient for many disposable applications such as RFID tags and product identifiers. Current technology does not permit this, but that is not to say that in the future extremely small nozzles can be produced (remember that commercial printers can already achieve more than 1200DPI on printable mediums).
Overall, the researchers of this project have demonstrated a real-world practical example of fully recyclable electronics that can be used to produce active components that are key to all electronic devices.