Almond shells provide an innovative solution for green electronics. The new discovery in a study coordinated by the Sant'Anna School of Advanced Studies in Pisa

Transforming almond shells into biodegradable electronics. This is not science fiction, but the result of a study coordinated by the Sant'Anna School of Advanced Studies in Pisa and published in the journal Advanced Functional Materials. A team of researchers led by Francesco Greco, associate professor of bioengineering, has demonstrated the possibility of producing completely bio-derived and biodegradable circuits and sensors using almond shells.
The study, carried out as part of the LIGASH (Laser Induced Graphene from waste Almond Shells) project, funded by the MUR, was made possible thanks to the contribution of DAMIANO Organics SpA, a world leader in organic almonds. This is an interdisciplinary collaboration between two research institutes of the Sant'Anna School of Advanced Studies in Pisa: the BioRobotics Institute, with the group coordinated by Greco, and the Institute of Crop Science, with Luca Sebastiani and Alessandra Francini, respectively full professor and RTT of General Arboriculture and Tree Cultivation.
The team also collaborated with Graz University of Technology and the Italian Institute of Technology for some experimental analyses.
Specifically, almond shells were used as raw material for the sustainable production of Laser Induced Graphene (LIG): a highly conductive material obtained through laser irradiation of carbon-rich materials.

"The study is an excellent example of upcycling: converting biological waste with no commercial value into a resource. It is a significant step towards more sustainable electronics, with possible applications in the creation of degradable electronic devices that will prevent the formation of microplastics and electronic waste, minimising the impact on the environment" says Francesco Greco, coordinator of the study.

Why almond shells?

Almond shells are an abundant and voluminous agri-food waste product, the disposal of which is economically disadvantageous and for which there are currently no valorisation processes that can transform it into high added-value materials.
Thanks to DAMIANO Organics SpA, which provided shells from various types of almonds, researchers at the Sant'Anna School of Advanced Studies first determined the chemical characterisation of the various shells, highlighting the high concentration of lignin, an organic polymer that is an excellent precursor to graphene. Subsequently, by combining almond shell powder and chitosan (a biopolymer derived from crustacean shells), flexible films were produced, optimised as a substrate for electronics and as precursors for Laser Induced Graphene. The materials proved to be completely biodegradable in soil in about 90 days.

"We wrote the LIG with two types of lasers (ultraviolet and infrared). The materials obtained were successfully used to make circuits and sensors: in particular, various circuit elements (resistors and capacitors) and a humidity sensor" says Yulia Steksova, PhD student at the Sant'Anna School and first author of the study.

A new paradigm for sustainable electronics

The bio-derived composite in film form, compared to the raw material, has proven to be more suitable for flexible and biodegradable electronics applications. This paves the way for the creation of zero-impact electronic devices, such as environmental or medical sensors designed to degrade naturally after use.
In addition to developments in the field of circuits and sensors, researchers have identified the composite as a potential alternative to tanned leather: by modifying its composition, it is possible to obtain a flexible, resistant material that can be sewn and has a similar appearance to natural leather.
Experiments are also underway with other almond processing waste, such as skins, and with the shells of other nuts (hazelnuts, pistachios): the preliminary results are promising. A further development of the project involves exploring the 3D printing of similar materials for the production of customised devices on a large scale.

"We would like to apply these results to the development of environmental monitoring devices. For example, for air and soil humidity, water quality and more, in a truly circular approach, developed by nature for nature. Our desire is also to contribute to the growth of the scientific community: we hope that this method will encourage other researchers to focus on completely natural and degradable materials" explains Yulia Steksova.

"In addition to being a project that brings together two souls of the School, LIGASH has allowed us to demonstrate how research and innovation are valuable tools for making agriculture an increasingly sustainable process. In this case, recycling waste and transforming it into biodegradable, low-cost sensors. After characterising the plant matrices in this study, we will evaluate the application of these sensors in the field in the future," says Luca Sebastiani, professor at the Institute of Crop Science.