A lignin-based gel preparation enabled by a deep eutectic solvent pretreatment recycling liquor: towards a full utilization of lignocellulose.

Deep eutectic solvents (DESs) are widely applied in lignocellulosic biomass pretreatment for their green, reusable, and lignin-selective merits. However, lignin accumulation during DES cycling significantly increases solvent viscosity and reduces pretreatment efficiency, severely limiting its sustainable application. To address this bottleneck, we innovatively combined recycled lactic acid/zinc chloride (LA/ZnCl2) DES with acrylic acid (AA), leveraging the synergistic effect of lignin and metal ions to drive free radical polymerization. This strategy enables a simple and efficient preparation for lignin eutectic gels with excellent mechanical properties and low-temperature resistance. The optimized gels (with 3 wt% lignin) exhibited high tensile stress (1.2 MPa), elongation at break (580%), multi-surface adhesion (32 kPa), and maintained a stable electrical conductivity of 1.1 mS cm-1 even at -18 °C. At room temperature, the assembled flexible sensors possessed a fast response speed (160 ms), linear deformation response, and robust electrical stability (<5% signal decay over 700 cycles of 100% deformation). This study pioneered the coupling of DES pretreatment and eutectic gel preparation, facilitating full utilization of lignocellulose and DES components to advance DES-based lignocellulose fractionation, valorization, and the entire biorefinery industry.