Controlled Preparation of Corncob Lignin Nanoparticles and their Size-Dependent Antioxidant Properties: Toward High Value Utilization of Lignin

Lignin nanoparticles (LNPs) offer a versatile platform for its high-value applications. A controlled LNP process is essential to ensure the quality of produced nanoparticles and integrity of their applications. The lignins used in this work were extracted using an enzymatic mild acidolysis procedure from corncob residue after acid-catalyzed steam explosion pretreatment. Their structure was investigated by 31P NMR and 2D-HSQC NMR, and the molecular weight of them was measured by GPC. LNPs were prepared by adding antisolvent (sodium acetate buffer, pH = 4.8) to DMSO/lignin colloidal dispersions. Process parameters (volume of buffer addition, buffer concentration (sodium acetate molarity), dilution rate with the buffer, and initial lignin concentration) were varied to identify their relative significance in determination of the size of LNPs by using surface response methodology. The morphology and size of LNPs were characterized by DLS and AFM, and the diameters of obtained LNPs varied from 60 to 200 nm. This work demonstrates a reproducible route for manufacturing of LNPs. Total phenolic content was found to be proportional to antioxidant activity of extracted lignin, consistent with literature studies. The antioxidant properties of LNPs were studied as a function of particle size for the first time. LNPs showed different antioxidant activity from the extracted lignin. Thermal stability of LNPs/poly­(vinyl alcohol) (PVA) composite films was investigated by TGA.