Visualization of a microscopic chemical changes in wood cell walls due to weathering degradation

Confocal Raman microscopy reveals changes in chemical composition of wood surfaces exposed to artificial weathering

Toru Kanbayashi (a), Yutaka Kataoka (a), Atsuko Ishikawa (a), Masahiro Matsunaga (a), Masahiko Kobayashi (a), Makoto Kiguchi (b)

(a) Department of Wood Improvement, FFPRI, Tsukuba, Ibaraki, Japan.
(b) Nihon University, Fujisawa, Kanagawa, Japan.

Journal of Photochemistry and Photobiology, B: Biology, 187:136-140, October 2018, DOI：10.1016/j.jphotobiol.2018.08.016( External link )

Wood is being more frequently used as an exterior material, such as in wood decks and outer walls of buildings. A surface-protecting treatment, including painting, is required when wood is used outdoors because the surface of wood deteriorates more easily due to weather factors, such as sunlight, wind, and rain. The mechanism of weathering degradation on the surface of wood needs to be elucidated in detail to effectively perform this protection treatment required to prevent wood deterioration.

This study aimed to examine how the cell walls at the surface and the chemical components were affected by weather factors after the exposure of wood to artificial sunlight and rain. For this study, we used a micro-spectrometer * capable of performing the chemical analysis of microscopic regions that are ten times smaller than the regions analyzed using conventional methods. Visualization based on the analysis of the main chemical components of wood, polysaccharides (cellulose and hemicellulose), and lignin showed no big difference in the polysaccharides. However, a significant decrease in lignin content was observed in the surface layer of wood where the ultraviolet light penetrates easily and the inside of the cell wall where liquid moisture penetrates easily.

The results of this study suggested that the properties capable of repelling rainwater as well as protecting from ultraviolet light are important to protect wood from weathering degradation. The study has successfully obtained a clue to prevent wood deterioration, based on which the control technology for wood deterioration will be progressed further.

* A device capable of visualizing chemical changes in a microscopic region by combining microscope and chemical analyses using spectroscopy.


Figure: Cross-section of the surface layer of wood with weathering degradation (yellow rectangle, measured region; white dotted line, the position of the wood surface prior to degradation; white arrow, the parts where lignin decreased inside the cell wall; H denotes the thickness)