Spectral analysis of changes to pine and oak wood natural polymers after short-term waterlogging

Non-destructive spectroscopic methods (UV-Vis, FT-NIR and XRF) were utilized to evaluate the degradation state of natural polymers of contemporary wood exposed to short-term (eight years) waterlogging. Experimental samples included both softwood (Scots pine) and hardwood (Penduculate oak) degraded in two differing environments (peat and water). The species investigated exhibited diverse mechanisms of degradation. Differing sites also seem to have influenced degradation kinetics. Samples of both species placed in trenches filled with water show slightly more intense degradation. However, interpretation of FT-NIR spectra revealed that different woody polymers (functional groups) were degraded in waterlogged pine and oak respectively. Characteristic darker color was observed in oak wood with progressive waterlogging. XRF analysis identified deposition of iron in the external zone of oak samples. Partial Least Square prediction models for exposure time of wood decomposed in wet environment were also developed. The degradation stage of the short-term waterlogged samples was compared to archaeological oak dated at 13th century, and to pine dated at 17th century. Archaeological pine wood exhibits more intense degradation relative to the oak, even though the latter was 400 years older. Spectral analysis in the near-infrared range confirmed that amorphous and semi-crystalline regions of cellulose, hemicelluloses and lignin changed due to waterlogging. Conversely, the crystalline regions of cellulose seem not to be degraded.