Printed electronics suit well for the current mega trends, like internet of things and growing interest in monitoring your own health. The products produced by printed electronics vary from displays and sensors to energy storage and flexible conductors. For example, small sensors can be printed on food packaging to follow the quality of food as well as warn the consumer when the product is out of date. For such reasons, the interest for developing materials for printed electronics is growing. How can cellulose fibrils and other cellulose based materials be used in such applications?
Printed electronics refer to electronic devices that are produced by printing on a substrate. This allows low-cost production compared to traditional electronic devices. In addition, the substrate can be flexible. Low cost, easy production and flexible substrate create an opportunity to make products such as wearable electronics, disposable electronics or sensors on consumer packaging. The substrates have traditionally been made of plastic, ceramics or silicon. There is, however, a need for recyclable, flexible, smooth and low-cost substrate material and improved conductive inks.
Substrate for printed electronics with cellulose fibrils
Katariina Torvinen, a researcher at VTT (Technical Research Centre in Finland), has been developing with her colleagues a substrate for printed electronics based on cellulose fibrils. In her doctoral thesis, she produced supercapacitors, transistors and antennas using a composite of cellulose fibrils and inorganic pigments (kaolin and precipitated calcium carbonate) as a substrate. The material contained up to 90% inorganic pigment. The composite made a flexible substrate which tolerates high sintering temperatures. Moreover, to achieve a good printing result, the surface porosity of the substrate must be controlled and that was possible with these composites.
Inks for printed electronics
According to Ink World magazine, the conductive inks for printed electronics today are metal-based (for instance, silver and copper), carbon-based materials (graphite and carbon nanotubes) and nanoparticles of metals (like silver and gold). Cellulose-based material, cellulose nanocrystals (CNC), can be utilized in the inks as well. PhD student Fanny Hoeng at Grenoble INP-Pagora has studied how silver nanoparticle ink can be improved with CNC. The traditional silver nanoparticle ink is rather expensive, has problems with the sintering process, makes fragile films and is not transparent. By using CNC in the ink, the stability was improved and they were able to create transparent films.
--> Learn more: how do cellulose fibrils improve inks?
Printed electronics are certainly coming to our everyday life but material development is still needed before they fulfill all expectations. Cellulose as a renewable, flexible and easily available material is a good candidate for both the substrates and inks. For substrate, cellulose fibrils can give desired mechanical properties, control porosity and enable recycling. In the inks, cellulose fibrils can bring rheological properties and stability.
--> Read also what we wrote earlier about flexible displays and electronics.