A note on the influence of extractives on the photo-discoloration and photo-degradation of wood

The effect of the presence of extractives on color changes (photo-discoloration) and photo-degradation of wood surfaces of Acacia auriculaeformis due to UV-visible irradiation has been examined. Unextracted and extractive free specimens were irradiated with a 1000 Watt xenon source in a weather-o-meter and exposed surfaces were analysed for color and chemical changes. Extractive free specimens exhibited a monotonous increase in color change with increasing irradiation time. Unextracted wood surfaces showed a rapid color change at initial period of exposure which decreases upon prolonged exposure. Analysis of color changes and FTIR spectra measured from irradiated wood surfaces indicate that presence of extractives increases rate of photo-discoloration and result in an apparent increase in rate of delignification of wood surfaces in the initial period of exposure. The apparently increased rate of delignification in unextrated wood has been explained on the basis of photo-degradation of polyphenolic extractives present in wood.