Characterization and evaluation of antioxidation of lignin from bamboo powder using a formic acid-catalyzed ethanol organosolv process

The antioxidant activity of lignin for producing biochemicals has attracted attention. In this paper, a separation method for lignin is proposed, with high-yield and high-antioxidant activity by using a formic acid-catalyzed subcritical ethanol process. The formic acid-catalyzed ethanol lignin (EOL/FA) and ethanol organosolv lignin (EOL) were first prepared using a high-pressure autoclave at different formic acid dosages. Then, the antioxidant activity and the structural and thermal properties of EOL/FA, EOL, alkali lignin, and sodium lignosulfonate were analyzed using antioxidant analysis, Fourier transform infrared (FTIR) spectroscopy analysis, and thermogravimetric analysis (TGA). The phenolic hydroxyl content of the four lignins was also determined by the Folin–Ciocalteau colorimetric method. Results showed EOL/FA had a higher radical scavenging ability and higher total phenolic hydroxyl content than industrial lignin. It indicated that the formic acid-catalyzed subcritical ethanol process was effective for enhancing the antioxidant activity of lignin.