Near-infrared spectroscopic monitoring of the water adsorption/desorption process in modern and archaeological wood

We investigated the adsorption/desorption mechanism of water and the variation of water adsorption for modern and archaeological wood using near-infrared spectroscopy. A mixture model of water was used to decompose the near-infrared difference spectra into three components (free water molecules (S-0), those with one OH group engaged in hydrogen bonding (S-1), and those with two OH groups engaged in hydrogen bonding (S-2)) based on a principal component analysis. The variations of each water component with relative humidity could be explained by proposing a model that describes water absorption in three stages. It was concluded that the aging phenomenon in wood is due to the decrease of adsorption sites on hemicellulose and amorphous cellulose.