Spectroscopic monitoring of wood characteristics variation by light-irradiation

This study deals with the feasibility of near-infrared (NIR) spectroscopy to qualitatively monitor the variation in wood characteristics caused by ultraviolet light-irradiation. It was found from the second derivative NIR spectra that OH groups in the amorphous regions in cellulose, hemicellulose, and lignin could be easily decomposed into low molecular matter by light-irradiation. The degradation rates for the amorphous regions in cellulose and hemicellulose were faster than that for lignin. Such degradation of main chemical compounds in wood by light-irradiation was closely associated with yellowing of the samples. The ratio of the second derivative of absorbance (Rλ) at λ nm after light-irradiation to before irradiation, was investigated. In the case of OH groups in the amorphous region, we could not find an obvious difference in the trend of Rλ between wood species. However, it was suggested from Rλ that the decomposition state of lignin by light-irradiation varied characteristically with wood species. Furthermore, we found a strong correlation between Rλ due to lignin and chroma coordinates (I.e.; Δb), independent of wood species. In the case of hemicellulose, there were considerable differences in R λ vs. Δb between softwoods and hardwoods.