Green and tough eutectogel from demethylated lignin: bridging renewable biomass and harsh-environment sensing

Abstract

Despite growing interest in gel-based wearable electronics, developing reliable strain sensors for harsh environments remains a challenge, primarily due to the susceptibility of conventional hydrogels to freezing, swelling, and poor adhesion. In this study, we report a sustainable strategy inspired by mussel adhesion to transform industrial lignin—an underutilized biomass—into a green and tough eutectogel for adaptive electronics. First, demethylated lignin rich in catechol-like structures is prepared via an eco-friendly demethylation process that transforms methoxy groups into phenolic hydroxyls. This modified lignin is then copolymerized with a polymerizable deep eutectic solvent (acrylic acid-choline chloride) and hydrophobic dodecyl acrylate through a facile and green UV-initiated polymerization, yielding a multifunctional eutectogel. The resulting material exhibits integrated features essential for high-performance flexible sensors, including excellent adhesion strength (0.41 MPa to glass in air, 165 kPa to wet metal and 91 kPa to metal underwater), remarkable mechanical properties (toughness: 8.18 MJ m⁻³; elongation at break: 1792.54%; Young's modulus: 0.22 MPa), high conductivity (0.51 S m⁻¹), significant strain sensitivity (gauge factor = 3.33), freeze tolerance (flexibility at −20 °C and no crystallization down to −80 °C), as well as self-healing and anti-swelling properties. Thanks to the high crosslinking density and multiple interactions, as a proof-of-concept, the eutectogel-sensor demonstrates reliable real-time monitoring of human motion and accurate Morse code transmission even under extreme environments. This work not only establishes a sustainable valorization route for industrial lignin but also pioneers a bioinspired material platform for next-generation adaptive electronics.