Shellac-paper composite as a green substrate for printed electronics

Printed electronic (PE) devices that sense and communicate data will become ubiquitous as the Internet of things continues to grow. Devices that are low cost and disposable will revolutionize areas such as smart packaging, but a major challenge in this field is the reliance on plastic substrates such as polyethylene terephthalate. Plastics discarded in landfills degrade to form micro- and nanoplastics that are hazardous to humans, animals, and aquatic systems. Replacing plastics with paper substrates is a greener approach due to the biodegradability, recyclability, low cost, and compatibility with roll-to-roll printing. However, the porous microstructure of paper promotes the wicking of functional inks, which adversely affects printability and electrical performance. Furthermore, truly sustainable PE must support the separation of electronic materials, particularly metallic inks, from the paper substrate at the end of life. This important step is necessary to avoid contamination of recycled paper and/or waste streams and enable the recovery of electronic materials. Here, we describe the use of shellac-a green and sustainable material-as a multifunctional component of green, paper-based PE. Shellac is a cost-effective biopolymer widely used as a protective coating due to its beneficial properties (hardness, UV resistance, and high moisture- and gas-barrier properties); nonetheless, shellac has not been significantly explored in PE. We show that shellac has great potential in green PE by using it to coat paper substrates to create planarized, printable surfaces. At the end of life, shellac acts as a sacrificial layer. Immersing the printed device in methanol dissolves the shellac layer, enabling the separation of PE materials from the paper substrate.