Empa researchers have developed a cellulose-based material that enables 3D printing of biodegradable sensors and displays. The mixture of hydroxypropyl cellulose water carbon nanotubes and cellulose anofibrils changes color when heated or stretched – without the addition of pigments.
HPC forms liquid crystals that reflect different colors depending on their structure and concentration, even though they are colorless. This phenomenon, known as structural coloring, is found in nature in peacock feathers, butterfly wings and chameleon skin. The color of HPC liquid crystals changes with concentration and temperature.
The researchers led by Gustav Nyström supplemented the HPC-water mixture with 0.1 mass percent carbon nanotubes, making it electrically conductive. This allowed them to control the color of the liquid crystals by applying an electrical voltage. In addition, the carbon intensified the colors. By adding cellulose nanofibers, the mixture could be 3D printed.
The scientists made several applications, including a strain sensor that changes color depending on deformation and a simple, electrically controlled display.
“Our lab has already developed different disposable electronic components based on cellulose, such as batteries and sensors,” says Xavier Aeby, co-author of the study. “This is the first time we were able to develop a cellulose-based display.”
Lab head Nyström hopes to discover other applications for the cellulose-based ink, such as in biodegradable electronics and the Internet of Things.
“Sustainable materials that can be 3D printed are of great interest, especially for applications in biodegradable electronics and the Internet of Things,” says Nyström, head of the laboratory. “There are still many open questions about how structural coloring is generated and how it changes with different additives and environmental conditions.”
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