Preparation of Lignin Nanoparticles from Thlaspi arvense L. Rhizomes via Ultrasound-Assisted Antisolvent Precipitation: Nanostructural Characterization and Evaluation of Their Radical Scavenging Activity

The ultrasound-assisted antisolvent precipitation method was used to prepare lignin nanoparticles from <i>Thlaspi arvense</i> L. rhizomes. The influence of each experimental variable on the average particle size (APS) of the lignin nanoparticles was determined via single-factor experiments. The optimal conditions for the preparation of the lignin nanoparticles were investigated in detail, and the APS of the lignin nanoparticles was 118 ± 3 nm. Compared with those of untreated lignin, the lignin nanoparticles prepared via this method were spherical and evenly distributed, and the structure was not damaged. Ultrasound generated local extreme physical conditions through its cavitation effect to promote nucleation, triggered high-speed turbulence to refine the particle size and improve uniformity, and applied mechanical disturbance to inhibit particle agglomeration, which promoted the preparation of lignin nanoparticles with a small size and good dispersion. A solubility test revealed that the lignin nanoparticles had greater solubility, which was improved 9-fold. The determination of antioxidant capacity revealed that the lignin nanoparticles had high free radical scavenging activity, which provided a broader space for the multifaceted utilization of a kind of grass lignin with the structural characteristics of <i>T. arvense</i> lignin (<i>p</i>-hydroxyphenyl lignin).