Rapid fabricated in-situ polymerized lignin hydrogel sensor with highly adjustable mechanical properties

Conductive hydrogels have been widely used as sensors owing to their tissue-like properties. However, the synthesis of conductive hydrogels with highly adjustable mechanical properties and multiple functions remains difficult to achieve yet highly needed. In this study, lignin hydrogel characterized by frost resistance, UV resistance, high conductivity, and highly adjustable mechanical properties without forming by-products was prepared through a rapid in-situ polymerization of acrylic acid/zinc chloride (AA/ZnCl₂) aqueous solution containing lignin extract induced by the reversible quinone-catechol redox of the ZnCl₂-lignin system at room temperature. Results revealed that the PAA/ZnCl₂/lignin hydrogel exhibited mechanical properties with tensile stress (ranging from 0.08 to 3.28 MPa), adhesion to multiple surfaces (up to 62.05 J m^-2), excellent frost resistance (-70-20 °C), UV resistance, and conductivity (0.967 S m^-1), which further endow the hydrogel as potential strain and temperature sensor with wide monitor range (0-300 %), fatigue resistance, and quick response (70 ms for 150 % strain). This study proposed and developed a green, simple, economical, and efficient processing method for a hydrogel sensor in flexible wearable devices and man-machine interaction fields.