EPR spin trapping – A new technique for observation and characterisation of free radicals during photodegradation of wood

Absorption of UV light by wood or its components promotes the formation of free radicals. These radicals induce the depolimerization of lignin and cellulose. We found Electron Paramagnetic Resonance (EPR) spin-trapping technique was a useful method to observe and characterize free radicals formed during photodegradation of wood or its components. During photodegradation of wood, using a spin trap DEPMPO three types of radicals were identified: hydroxy and carbon-centered as well as hydroperoxide species. We calculated proportions between free radical-DEPMPO adducts after UV-irradiation of wood, cellulose and brown rotted wood (as a model for lignin). As copper is known as a photo-stabilizing agent, we also investigated photodegradation of copper treated wood. Proportions between DEPMPO-radical adduct in UV-irradiated treated and untreated wood, or its components, significantly differed.