Lignin nanoparticles for hydrogel-based pressure sensor

The preparation of high lignin content hydrogels with good mechanical and multifunctional properties remains a huge challenge. In this study, a novel polymer-nanoparticle hydrogel was developed by a covalent crosslinking strategy, which not only preserved the characteristics of nanoparticles but also gives them good mechanical properties. Herein, lignin-silver nanoparticles (Lig-Ag NPs) were prepared from industrial lignin starting material and crosslinked into hydrogel with poly(ethylene glycol) diglycidyl ether. The obtained hydrogel (Lig-Ag NPs/PEG, LANP) exhibited good mechanical properties (elongation at break 53%, tensile strength 94.67 kPa, toughness 277.32 kJ m−3), adhesiveness, conductivity, pressure- and pH-stimuli-responsiveness, which benefited from the appropriate degree of crosslink, the generated catechol groups and redox-active quinone/semiquinone free radicals from Lig-Ag NPs. These functional properties can also be tuned by the contents of Lig-Ag NPs. Based on the above properties, a LANP sensor was assembled and showed good application for pressure- and pH-monitoring. This work provides a green and facile strategy of lignin valorization towards new multi-functional and smart applications.