Influence of TEMPO-mediated oxidation on the lignin of thermomechanical pulp

The influences of various factors in 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation on delignification, lignin aromatic ring and side chain structures of thermomechanical pulp (TMP) were investigated. The results indicate neither TEMPO nor NaBr alone can provoke changes in lignin content or lignin structure under weakly alkaline conditions. However, NaClO and NaClO–NaBr were able to remove lignin effectively, causing remarkable changes in lignin structure. Delignification was promoted when TEMPO was used with NaBr and NaClO. In contrast to NaClO alone, an additional 15% lignin was removed when TEMPO-mediated oxidation system was used, but it did not induce further changes on lignin structure. Increased doses of oxidizing agent and reaction time also improved the oxidation of cellulose and delignification, but they did not have a significant impact on lignin aromatic and side chain structures.