ESR studies on the free radical generation in wood by irradiation with selected sources from UV to IR wavelength regions

Abstract

Abstract The formation of free radicals in pine and kwila woods and cellulose and kraft lignin was studied to understand better the impact of radiation on wood degradation. Wood specimens were irradiated with sources emitting in the UV, Vis, and IR regions and then analyzed by electron spin resonance (ESR) spectroscopy and the increment of free radicals generated was measured. In addition, samples were irradiated by color filtered light. Lignin was found to be more susceptible to radiation than cellulose. Kwila wood is more photostable than pine, probably due to the photoprotective extractive contents in the former. As expected, lower energy wavelengths generated fewer free radicals. However, fluorescent lighting generated as many free radicals as UV irradiation indicating that high-energy visible radiation is equally harmful to wood surfaces. Light-colored filters absorbing the latter wavelength region reduced the photodegrading damage. Accordingly, transparent stains containing colored pigments which imitate the filter effect should provide better protection of wood surfaces against sunlight.