Nanolignin filled conductive hydrogel with improved mechanical, anti-freezing, UV-shielding and transparent properties for strain sensing application

Herein, we innovatively synthesized an ionic conductive PVA/LNP hydrogel with integrated excellent mechanical, anti-freezing, moisturizing, transparent and UV-shielding performances via incorporating nanolignin (also called lignin nanoparticle, LNP) and aluminum chloride (AlCl3) into polyvinyl alcohol (PVA) matrix containing ethylene glycol/water (EG/H2O) binary solvent. The rigid porous network structure was well constructed by the hydrogen bond interactions among the evenly distributed LNP and PVA chains, thus providing abundant ion transport channels, which attributed to the outstanding ionic conductivity (up to 1.35 × 10-2 S/m, at -24 °C) with improved mechanical strength and flexibility. The tensile strength and elongation at break of PVA/LNP hydrogel were greatly increased from 574.6 kPa and 363.7% to 1241.4 kPa and 589% at the addition of 0.35% LNP, respectively. In addition, the UV-resistance ability was 95% at 365 nm, while the transparency was 74% at 550 nm. The binary solvent of EG and H2O ensured long-term moisturizing capability (10 days) of the hydrogel at 35 °C and 60 RH%, as well as possessing superior anti-freezing performance over the temperature range of -62.6 to 24 °C. As a result, the fabricated PVA/LNP hydrogel was successfully used as strain sensor for detecting diverse human motions and electrophysiological signals.