Insights into the Synergistic Mechanism of a Polyol-Assisted Ternary Deep Eutectic Solvent for the Production of Lignocellulosic Nanofibers and Lignin Nanoparticles from Sunflower Stalks

The use of traditional acidic deep eutectic solvents (DESs) causes substantial lignin condensation and thus limits the subsequent downstream valorization of lignocellulosic biomass into lignocellulosic nanofibers (LCNFs) and lignin nanoparticles (LNPs). Herein, a ternary DES comprising choline chloride, lactic acid, and one of three polyols (glycerol, 1,2-propanediol, or ethylene glycol) is evaluated for its efficacy to produce LCNFs and LNPs from sunflower stalks, a high-volume renewable resource. The incorporation of polyols decreased the solvent acidity and led to a reduction in delignification. The resultant LCNFs had uniform crystallinity (36.34–41.49%), uniform size dispersity (13.46–18.84 nm diameter), and their water retention value (WRV) increased from 16.3 to 21.7% on increasing the polyol content. Simultaneously, LNPs recovered from polyol-assisted DES pretreatment retained aromatic ring structures and exhibited a spherical morphology with particle sizes between 23.52 and 63.26 nm. Interestingly, the LNPs displayed moderate and homogeneous molecular weights and preserved β-O-4 substructures, while the degree of condensation decreased significantly from 21.8 to 10.3%, highlighting the stabilization effect of polyols. In conclusion, this study demonstrates the significant potential of polyol-assisted ternary DESs for the sustainable and high-quality production of lignocellulosic nanomaterials from sunflower stalks.