Singlet oxygen mediated degradation of Klason lignin

After some results concerning photochemical generated singlet oxygen on lignins from steam explosion, the reactions of chemically generated singlet oxygen with Klason lignins from pine and beech are described. Singlet oxygen was produced through the reaction of hydrogen peroxide with sodium hypochlorite. The degradation of lignin was followed by uv spectroscopy and gel permeation chromatography. Extensive degradation of the lignins was observed when 20 mg of Klason lignin was treated with 1 ml of 30% hydrogen peroxide and 8.56 mi of 1.093 M sodium hypochlorite. In the uv spectra registered after the treatment with singlet oxygen the absorptions typical of lignin (210-220 nm) and 250-280 nm were completely absent. The gpc analysis of lignin after a treatment with 0.1 mi of hydrogen peroxide and 0.86 ml of sodium hypochlorite showed a clear reduction of signals due to the lignin and a shift to lower molecular weight. The potential use of this procedure in the bleaching procedure was tested by using recycled paper. A maximum reduction of 51% in the amount of lignin in this paper was observed. (C) 1999 Elsevier Science Ltd. All rights reserved.