Ultrahigh solid loading biorefinery with deep eutectic solvent pretreatment for lignin fractionation and nanoparticle preparation

The large-scale application of deep eutectic solvents (DESs) in biorefineries has been limited by low biomass loading. This study introduces a novel ZnCl 2 /lactic acid (LA) DES for the efficient isolation of lignin from poplar at ultrahigh solid loading. The results show that 67.41% delignification was achieved under extreme solid loading of 50 wt%. The recovered lignin exhibited unique amphiphilicity, enabling the fabrication of lignin nanospheres (∼123 nm in diameter) with uniform, monodisperse morphology, superior colloidal stability, and excellent Pickering emulsification stability. Reduced density gradient (RDG) analysis demonstrated that the ZnCl 2 /LA DES outperformed the conventional ChCl/LA system due to Zn 2+ coordination with the carboxyl group of LA and stronger noncovalent interactions with lignin, facilitating targeted β-O-4 bond cleavage. Over 95% of cellulose was recovered and processed into lignin-containing cellulose nanofibers, achieving an outstanding tensile strength of 139.17 MPa. The ZnCl 2 /LA DES system demonstrated exceptional recyclability, maintaining 84.41% delignification efficiency even after five consecutive reuse cycles at 33 wt% solid loading.