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.