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Since wood chemical components can be depolymerized and modified by weathering, a better understanding of the mechanisms governing these processes in needed to develop effective protection methods for wood surfaces. Unfortunately, very little has been reported about the micro-scale chemical changes in wood, particularly hardwood, during weathering. The purpose of the present work is to determine the degradation behavior of Japanese beech (Fagus crenata Blume) under artificial weathering at the cellular-level. Herein, the structural and micro-distributional changes in wood components during weathering were investigated using micro-Raman spectral and chemical mapping analyses. The Raman spectra showed that weathering facilitated lignin degradation and modification. The degradation behavior of lignin differed depending on the type of wood tissue. The rate of lignin reduction followed a descending order: vessel element > axial parenchyma cell > wood fiber. Raman mapping determined that cellular-level lignin reduction on the surface layers differed for wood species. Although lignin degradation of cedar tracheids proceeded from both the surface and the cell lumen, the lignin in beech fibers degraded according to the depth.

Japanese cedar (Cryptomeria japonica) was treated with the ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which is a solvent for cellulose, and the changes in the chemical components and their distribution in wood cell walls have been investigated by Raman microscopy. Raman spectra, recorded from various areas of the cell walls, showed that lignin in the compound middle lamellae (CML) and cell corners (CC) was resistant to the reaction with [C2mim][Cl], but its molecular structure changed partially. The reactivity of cellulose and hemicelluloses with [C2mim][Cl] was higher than that of lignin in the cell wall, and the cell wall structure was maintained even in an advanced state of the reactions. The effects of [C2mim]-[Cl] on cellulose and hemicelluloses in the cell wall were homogeneous, whereas that of lignin was inhomogeneous.