Lignin Degradation via Chlorine Dioxide at Room Temperature: Chemical Groups and Structural Characterization

Lignin degradation is an effective means of achieving the high-value application of lignin, but degradation usually requires the use of high temperatures and harsh reaction-conditions. This study describes a green, mild approach for the degradation of lignin, in which chlorine dioxide (ClO2) was used for the oxidative degradation of lignin (IL) in an acidic aqueous suspension at room temperature. The optimal process conditions were: 30 mL of ClO2 solution (2.5 mg·L−1), pH 4.5 and 3 h. The FT-IR, NMR (1H NMR, 2D-HSQC and 31P NMR), XPS and GPC analyses indicated that lignin could be degraded by ClO2 relatively well at room temperature, to form quinones and muconic acids. Additionally, DIL was reduced to substances with a high phenolic-hydroxyl (OH) content (RDIL) under the presence of NaBH4, which further confirmed the composition of DIL and which can be applied to the development of lignin-based phenolic resins, providing a reference for the further modification as well as the utilization of DIL.