Singlet oxygen degradation of lignin in the pulp

The lignins obtained from steam explosion of straw and beech at log R-0 3.94 and 4.35 were characterised. Elemental analysis, gel permeation chromatography, UV, H-1 and C-13 NMR spectra allow defining the characteristics of the lignins used. Pulps obtained from the steam explosion process were used as starting materials. The amount of lignin in the pulps was determined by using the Klason lignin determination. The lignins in pulp were irradiated with a visible light in the presence of Rose Bengal and oxygen in water suspension for 24 h. Extensive degradation of the lignin in the pulps was observed. In fact, the amount of lignin in the pulps dropped from 22-24% to 3-7%. The pulps from beech seem to be more sensitive to the process than that from straw. The same result was obtained by using cardboard. The irradiation with visible light of cardboard in water suspension with Rose Bengal in the presence of oxygen induced the reduction of the amount of lignin from 24% to 13%. (C) 1998 Elsevier Science S.A. All rights reserved.