Lignin nanoparticles with excellent performance by regulating the molecular structure of lignin in DES pretreatment of choline chloride/5-sulfosalicylic acid/γ-valerolactone

Lignin nanoparticles (LNPs) can significantly address the heterogeneity of lignin and enhance its application potential. However, the structure activity relationship between the structure of lignin and LNPs has been underexplored. In this study, lignin was extracted using a ternary deep eutectic solvents (DES) of choline chloride (ChCl)/5-sulfosalicylic acid (5Saa)/γ-valerolactone (GVL). The molecular structures of DES Ⅰ-L, DES Ⅱ-L, and DES Ⅲ-L were regulated by varying the temperature (85, 105, and 125 °C). Compared to softwood kraft lignin (SKL), lignin with small molecular weight was obtained. In particular, good homogeneity (PDI 1.55, 1.58, and 1.59) was found. The dispersion stability and pH response of DES Ⅰ-LNPs, DES Ⅱ-LNPs, and DES Ⅲ-LNPs were remarkable. In particular, DES Ⅱ-LNPs was the smallest (32 nm) and exhibited the highest stability (no flocculation within 90 d). DES-LNPs exhibited high shear viscosity, a gentle shear decay trend, low yield stress and shear sensitivity. The phenolic hydroxyl groups rich in lignin promoted the interaction, leading to an increase in the size of LNPs. Fortunately, its smaller molecular weight formed an effective complement. The structure activity relationship between the structure of lignin and LNPs was established, providing theoretical support for the efficient conversion and application of LNPs.