Freeze-resistant, rapidly polymerizable, ionic conductive hydrogel induced by Deep Eutectic Solvent (DES) after lignocellulose pretreatment for flexible sensors

In this paper, ternary DES (choline chloride, glycerol, Lewis acid) was used to pretreat lignocellulose, and the DES solution with dissolved lignin was utilized as the medium of hydrogel to prepare DES-based polyacrylic acid/polyvinyl alcohol (PAA/PVA) double network hydrogels with great mechanical properties, self-adhesion, and high electrochemical sensitivity. The entanglement of PAA with PVA chains, the covalent linkage between Al3+ and PAA chains and the metal phenol network (MPN) formed by Al3+ and lignin improved the mechanical properties of the hydrogels, enabling the prepared hydrogels to achieve a tensile strain of 400 % and an elongation at break of 150 kPa. Secondly, the introduction of DES solution endowed the hydrogel with excellent electrical sensing ability and anti-freezing property, so that the hydrogel still maintains good flexibility and ionic conductivity at −20 °C. It was also found that the above hydrogel can achieve a high gauge factor of 4.19 as a flexible sensor, which provides scientific ideas for the application of the pretreated DES solution in the field of flexible wearable.