We examined structural and chemical changes in heartwood of oak (Quercus sp.), related to wood ageing. The research was made on samples of construction wood of various ages from different objects in Slovenia. The age of wood was determined dendrochronologically. Structural and anatomical properties were determined with help of light microscopy (techniques: bright field, polarized light, epi-flourescence) and Fourier Transform Infra Red (FT-IR) spectroscopy. It has been visually confirmed that the heartwood becomes visually darker due to ageing. Its colour proved to depend on variable wood anatomy, with different proportions of vessels, traheids, libriform fibres and rays. FT-IR spectroscopy showed that the percentage of hemicellulose and lignin decreased in comparison with basic wood components during the process of ageing. The decrease of hemicellulose proportion was statistically significant, whereas the decrease of lignin was not. Degradation of cellulose during the ageing was also shown by using polarized light. In the case of more than 600 years old sample of subfossil wood, which was preserved underwater, all techniques confirmed an increased proportion of lignin and decreased proportion of cellulose and hemicellulose. Different degree of changes in similarly old samples could be ascribed to variable (and partly unknown) conditions of wood exposure during its service life.
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