Electronic upcycling of corn straw: bio-based, elastic, conductive, cross-linked, eco-friendly hydrogels with multifunctionalities for flexible wearable sensors

Abstract

Conductive hydrogels based on biomaterials have garnered much attention. However, the utilization of corn straw, an agricultural waste, as a gel substrate can achieve the recycling of agro-waste and the development of advanced electronic materials, which has a dual benefit, but it seems to be overlooked. In this study, a corn straw pith (CSP)-based multifunctional conductive hydrogel (CSP-MCG) was prepared by introducing CSP, which presents oxygen-rich groups, into the three-dimensional crosslinking network system of a hydrogel. The CSP-MCG exhibits mechanical elasticity (maximum tensile rate of 340%) and responsiveness to multiple external environmental factors (mechanical strain, temperature, and humidity). Under different tensile strain conditions, it demonstrates sensitive response properties (GF = 2.8, R² = 0.996, and T_res = 0.075 s). In the temperature range of 20 °C–50 °C, it exhibits great performance (R² = 0.993, TCR = 1.34% per °C, and T_res = 0.5 s). Within the humidity range of RH29%–79%, the signal changes steadily, and the response time is short (T_res = 0.2 s). In addition, CSP-MCG not only exhibits responsiveness to various external stimuli but also demonstrates the ability to differentiate between these stimuli based on variation trends in its resistance and capacitance. Owing to its exceptional multi-functional sensing capabilities and environmental attributes (recyclability and degradability), CSP-MCG can be a green flexible electronic material in practical applications, such as electronic skin, human-computer interaction and flexible wearable sensors.