AbstractThere is much research on nanomaterial from natural polymer because of its biocompatibility, abundance, and non-toxicity. This work is devoted to the study of free radical scavenging activities (FRSA) of nanoscale lignin biomaterials, which are recognized as promising natural antioxidants. The nanoscale lignin biomaterials were prepared from alkaline lignin by a solution-precipitation method with either ethylene glycol (NL1) or alkaline solution (NL2). Structural analysis of the nanoscale lignin biomaterials were conducted by Scanning electron microscopy (SEM), laser particle size analyzer, Fourier transform-infrared spectroscopy (FT-IR), potentiometric titration, and gel permeation chromatography (GPC). The results indicated that NL2 had a smaller average particle size (278±13 nm) than NL1 (375±18 nm) and contained more phenolic hydroxyl groups (2.35±0.11 mmol/g) and had a lower weight-average molecular weight (Mw=6510±320). The FRSA of the biomaterials towards hydroxyl free radicals were measured and compared with the alkaline lignin. Some structure-activity relationships were proposed based on the analysis of experiment data, which revealed NL2 (IC50=0.18±0.01 mg/mL) had a 3.33 fold higher activity than NL1 (IC50=0.60±0.05 mg/mL), which could be attributed to the smaller particle size, more phenolic hydroxyl group, and lower weight-average molecular weight.