Étude par spectroscopie de résonance paramagnétique électronique de la photodégradation des lignines extraites du bois de pin radiata (Pinus radiata D. Don)

Abstract

Cellulose in lignocellulosic materials is protected from photochemical degradation by the lignin which can play a three-fold role: to filter near UV radiation by absorbing photons, to deactivate the excited state of cellulose, and by acting as an antioxidant by forming stable phenoxy radicals by radical transfer reactions. In the work presented we have studied by electron paramagnetic resonance (EPR) the photodegradation of lignins extracted and isolated from Pinus radiata wood. The kinetics of the intermediate radical species concentrations have been followed during irradiation of solid specimens as well as for lignins in solution both for the raw and for modified extracts alter stop-ping light irradiation and stocking the samples in the dark in order to quantify the stability of the formed radicals. Attribution of EPR signals to phenoxy radicals formed by abstraction of an hydrogen atom from the phenolic chromophore groups of lignin has been confirmed by the study of radical transfer reactions from the DPPH° radical to the lignins. The lignin ability to form resonance stabilized phenoxyl radicals confers on these materials antioxidant properties which allow the value-added use of this by-product of the pulp and paper industry. © 1999 Éditions scientifiques et médicales Elsevier SAS.