Printed Humidity Sensors from Renewable and Biodegradable Materials

Increasing environmental concerns raised by the accumulation of electronic waste draws attention to the development of sustainable materials for short-lived electronics. In this framework, printed capacitive humidity sensors and temperature resistive detectors composed exclusively of biodegradable materials: shellac, carbon-derived particles, and egg-albumin are reported. The sensor platform comprises interdigitated electrodes serving as a capacitive transducer for humidity sensing, and a serpentine used as a resistive temperature detector. Both the interdigitated and serpentine electrodes are manufactured by screen-printing carbon ink on a shellac substrate. The humidity sensors are constructed by drop-coating egg albumin on the interdigitated carbon electrodes and the temperature detector is prepared by encapsulating the serpentine design with shellac. Shellac is shown to be a biodegradable alternative to hydrophilic cellulose-derived substrates, with the capacitive humidity sensors demonstrating a sensitivity of 0.011% RH-1. The response and recovery times on shellac are 12 and 20 times faster than on cellulose-based substrate, and the serpentine resistive temperature detectors have a temperature coefficient of 5300 ppm K-1. At the end of their service-life, the sensors produced are home compostable and can be environmentally friendly disposed, potentially enabling their future use for sustainable and environmentally friendly smart-packaging, agricultural sensing, or point-of-care testing.

Automated summary

This study presents printed capacitive humidity sensors and temperature resistive detectors made from biodegradable materials as an alternative to electronic waste. The sensors and detectors are manufactured using shellac, carbon-derived particles, and egg-albumin. The use of shellac as a substrate proves to be biodegradable and demonstrates faster response and recovery times compared to cellulose-based substrates. The sensors are home compostable and can potentially be used for sustainable smart-packaging, agricultural sensing, or point-of-care testing.