Printed electronics made of compostable materials

E-waste levels in Germany are rising, with the increase in disposable printed electronics — such as interactive packaging and smart Band-Aids — at least partially to blame. With this in mind, researchers from the Karlsruhe Institute for Technology (KIT) have developed printed electronics made of compostable natural materials and processes for industrial production.

Conventional printed electronics, such as organic light-emitting diodes (OLEDs), are not necessarily environmentally compatible. For instance, the carrier foil of OLED — the paper equivalent for electronic inks — is made of the same plastic material as conventional beverage bottles. The advantages of plastic materials are that they are bendable, cheap and can be processed into miles of printing foil, enabling production of printed electronics on an industrial scale.

KIT’s Biolicht Young Investigator Group, however, only uses easily biodegradable materials that can be found in nature — with starch, cellulose and chitin suitable as carrier foil — and rarely uses metals or metalloids, such as silicon. According to Dr Gerardo Hernandez-Sosa, leader of the Biolicht Young Investigator Group of KIT, “These may not be as long-lived as the inorganic alternatives, but they easily survive the service life of disposable electronics.” After use, he said, the electronics can simply be thrown away into the biowaste bin or on compost heaps, where it will rot like a banana skin.

As part of the group’s work, electronic components have to be printed onto the compostable foils similar to letters onto paper. Their function depends on the ink used: instead of dye particles, conducting, semiconducting or insulating materials are dissolved in the ink. Upon application, the liquid solvent dries and the remaining layer forms the corresponding component.

The group also needs to develop biodegradable inks which can be adapted to the new foil material and suitable for printing with existing equipment, so manufacturers can swap to environmentally compatible materials without having to exchange their printer arsenal. The scientists have to identify environmentally compatible materials for the inks with the desired electrical properties; hard gelatin that is used for making drug capsules is suitable for insulation, for instance.

Selection of the solvent is also a precise process: it has to be in liquid form at temperatures used for printing; it must not penetrate into the carrier material, but should form a closed liquid film on it without dripping off; it cannot be so thick that it plugs the pores of the printer; and it cannot be so thin that it disperses on the carrier foil and does not cover it homogeneously. The properties of the dry material film are also crucial to the function of the electronic components: its thickness that is less than a thousandth of a millimetre must not vary by more than 5%.

The scientists expect to have compostable organic electronics ready for the market three years from now.

Image caption: Organic light-emitting diodes (OLEDs) can be produced easily and at low cost. Thanks to compostable materials, they can also be made sustainable. Image credit: KIT.

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