SINGLET OXYGEN DEGRADATION OF LIGNIN

Lignin obtained by steam explosion of straw, beech (a hardwood plant), and pine (a softwood plant) was isolated and characterized by using s tandard methods, The irradiation of lignins with visible light in the presence of oxygen and of a singlet oxygen sensitizer (Rose Bengal) in duced several modifications in the lignin structures that were monitor ed by using gel permeation chromatography (GPC) and UV spectroscopy, W e observed a remarkable reduction of the mass distribution by GPC when monitoring at 280 nm and the shift of the residual chromatograms to m ass values lower than the native lignins. These data are in agreement with a depolymerization reaction of lignins. The UV spectra showed tha t all the chemical species of lignins undergo several modifications du ring the irradiation reaction. Thus, the E-1 band reduced its absorban ce and underwent a hypsochromic shift. The E-2 and the B band were gre atly reduced during the irradiation. (C) 1998 Elsevier Science S.A.