The action mechanism of laccase/1-hydroxybenzotriazole system on pulp residual lignin

Residual lignins isolated from pine kraft pulp and from oxygen-delignified pine kraft pulp were treated with laccase with and without 1-hydroxybenzotriazole (HBT). Gel permeation chromatography was used to follow the changes in lignin molar mass and the reactions of HBT during the treatment, while the structural changes in lignin were followed by oxidative degradation. The results were compared with those obtained from the corresponding pulp treatments. Analysis of the lignins isolated from the pulps after laccase/HBT treatments and of the isolated lignins treated with laccase/HBT indicated similar degradative reactions. The reactions between isolated lignin and laccase were similar with and without HBT, although the reactions proceeded further in the presence of HBT. The high reactivity with the HBT radical was predicted theoretically for biphenyl structures, especially those carrying a-carbonyl substituents. The prediction was supported by the experimental results.