Effects of Different Lignin Contents and Water Contents on the Performance of DES-Based Hydrogels

Abstract

This study fabricated choline–acrylic acid deep eutectic solvent (DES) hydrogels via in situ free-radical polymerization and systematically investigated the individual and co-optimization effects of lignin dosage and water content on the chemical structure, micromorphology, compressive mechanical properties, swelling behavior, and thermal stability of the hydrogels. This work quantitatively uncovers the co-optimization mechanism between the two variables in modulating crosslink density and pore architecture, thereby filling a research gap in the dual-factor co-optimization of biomass-based DES hydrogels. The results reveal that a moderate lignin dosage (0.02 g) generates abundant dynamic hydrogen bonds, densifying the crosslinked network and raising the maximum compressive stress from 0.378 MPa to 0.426 MPa, whereas excessive lignin triggers molecular aggregation and deteriorates mechanical performance. Higher water content dilutes crosslinking sites, reduces network compactness, boosts the swelling ratio while lowering compressive strength, and exerts negligible impacts on thermal degradation characteristics. FTIR analysis confirms that lignin participates in network formation solely through non-covalent hydrogen bonds, without forming new covalent bonds. A comprehensive performance evaluation identifies the optimal formulation as 0.02 g lignin and 60 g water. Although this two-factor optimization strategy provides clear experimental and theoretical guidance for designing sustainable soft materials, the present work still has limitations, including the use of only static laboratory characterizations, with no cyclic mechanical measurements or aging assessments. This study advances the customized performance tuning of lignin-derived DES hydrogels and facilitates the high-value valorization of lignin, which is promising for multifunctional green-material applications, including adsorption, flexible electronics, and biological carriers.