Distribution of inorganic elements in wood impregnated with preservative solutions. I. Visualization of inorganic element distribution in wood by SEM-EDXA

Japanese larch (Larix Kaempferi) heartwood extracted with ethanol and radiata pine (Pinus radiata) wood including heartwood and sapwood were impregnated by vacuum treatment with 0.6 M CuSO₄, aq. and 0.5% toluidine blue dye. The distribution of sulfur (S) and copper (Cu) elements in wood was examined by SEM-EDXA (Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis). For Japanese larch heartwood, both inorganic elements were distributed in some tracheids, axial resin canals and parts of ray tracheids. Distribution of both inorganic elements was also evident in bordered pits between tracheids. It seemed to be difficult for both inorganic elements to diffuse from an axial resin canal to adjacent tracheids. On the other hand, for radiata pine sapwood, both S and Cu elements were distributed in earlywood and latewood but the concentration was observed to be different. When S and Cu elements were distributed in tracheids, both were observed throughout the cell walls. In latewood both inorganic elements showed a concentration near the growth ring boundary. In heartwood both inorganic elements were observed in ray perenchyma cells but not in tracheids and ray tracheids. SEM-EDXA was found to be an effective way of visualizing inorganic element distribution in wood as it was possible to examine two inorganic elements at the same time and map the concentration differences in color.