Chemiluminescence and discoloration of light-irradiated wood surfaces

Very week light, called chemiluminescence, is emitted during the degradation of polymers, oils and fats by light-irradiation, heating and so on. Chemiluminescence is thought to be emitted when excited carbonyl groups return to a ground state, and singlet oxygen molecules become triplet ones. In this study, it was shown that chemiluminescence was emitted from light-irradiated wood. The intensity of chemiluminescence reached a maximum after several hours of irradiation, and then decreased gradually with increasing irradiation time. The intensity differed among the wood species used. Decreases in carbonyl groups and increases in lignin by the light irradiation were observed in PAS spectra. The color of softwood deepened by the light irradiation, and the hardwood changed to vivid or pale colors. The correlation between the sum of chemiluminescence emitted during irradiation for 50 hrs (CL50) and the color difference of the wood light-irradiated for 1000 hrs was relatively high in the 4 softwood specimens used.