Controlling lignin nanoparticle morphology and properties via tailoring molecular weight and interunit linkage from...

Lignin nanoparticles (LNPs) offer a sustainable pathway for the high-value valorization of lignin. However, controlling LNP morphology remains challenging due to the structural heterogeneity of lignin. This study systematically investigates how pretreatment-induced and extraction-mediated structural changes in enzymatic residual lignin (ERL) dictate LNP self-assembly behavior. Through dilute acid, alkaline, and liquid hot water pretreatments combined with specific solvent extraction, distinct LNP morphologies were successfully fabricated. Characterization using 2D-HSQC NMR and gel permeation chromatography demonstrates that high-molecular-weight fractions (Mn > 1500 Da) rich in flexible β-O-4 linkages (up to 58.1%) preferentially assemble into spherical LNPs with lower hydrophobicity. Low-molecular-weight fractions (Mn < 1000 Da) enriched with β-5 and CC linkages aggregate into sheet-like nanostructures with small sizes (42-99 nm), superior colloidal stability, and pronounced hydrophobicity (137°). Furthermore, modulating the extraction solvent polarity from LHW-ERL successfully shifted the morphology from sheets to highly uniform porous hollow spheres. Molecular dynamics simulations confirm flexible β-O-4 linkages promote isotropic folding into spheres, whereas rigid CC bonds direct anisotropic π-π stacking into sheets. Molecular weight tunes particle size and morphological regularity. These findings provide a framework and a rational strategy for tailoring LNPs through biomass processing, bridging the gap between biomass refining and targeted high-value applications.