Printed Humidity Sensors from Renewable and Biodegradable Materials

Abstract

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.

Biopolymer Cryogels for Transient Ecology‐Drones

“…[ 47 ] Additionally, materials other than carbon particles could be explored to realize resistive sensors. [ 48 ] For example, zinc‐ or magnesium‐based ink could reduce the environmental impact of the sensors, while achieving higher conductivity. Especially, the lower resistivity renders the manufacturing of transient antennas [ 49 ] possible, which enables wireless transmission of environmental data.…”

Advances in Bioresorbable Materials and Electronics

“…(b) Left: Schematic illustration of a capacitive humidity/temperature sensor on a shellac substrate, where egg albumin is coated onto interdigitated electrodes for humidity sensing. Right: Capacitive response of the humidity sensor . Reproduced with permission from ref .…”

“…Several examples rely on capacitive effects. One case involves an interdigitated carbon electrode printed on a shellac substrate for capacitive sensing of both humidity and temperature (Figure b) . Coated with egg albumin as a responsive layer, the sensor demonstrates high sensitivity (∼0.011% RH –1 ) to relative humidity (RH) from 35% to 65% with a response time of 12–100 s.…”

“…Right: Capacitive response of the humidity sensor . Reproduced with permission from ref . Copyright 2022 Wiley-VCH.…”

Additively Manufactured Degradable Piezoelectric Microsystems for Sensing and Actuating

“…[22][23][24] For printed conductive materials, both carbon and zinc are promising candidates, with degradable screen-printing inks realized for both conductive materials in recent years. [25][26][27] Readily degradable, carbon is the standard for many biodegradable electronics applications, however its poor conductivity makes carbon non-ideal for widespread industrial use. [26,28] Conversely, zincbased conductive layers show remarkably better electrical performance relative to carbon, but complicated multi-step postprinting treatments are required in order to produce longlifetime conductive layers (as recently described by Fumeaux).…”