Showing papers by "Masato Yoshida published in 1998"

Relation between growth stress and lignin concentration in the cell wall: Ultraviolet microscopic spectral analysis

Abstract: Lignin content in the cell wall was investigated to examine its relation with growth stress, using an ultraviolet microscopic spectrum analyzer. Although a weak correlation existed between the growth stress and lignin concentration in the compound middle lamella, it was believed that the compound middle lamella did not contribute to compressive growth stress generation as there was no correlation between growth stress and lignin concentration in the cell corner part of the intercellular layer. In the secondary wall, larger compressive growth stress was associated with higher lignin concentration especially in the outer part. This finding confirms that lignin contributes positively to the generation of compressive longitudinal growth stresses in the compression wood and more substantially in the outer part of the secondary wall. This experimental result strongly supports our hypothesis of growth stress generation given by the model.

Studies on the softening point of wood powder as a basis for understanding the release of residual growth stresses in logs

Abstract: In a previous report, log air heating by smoking was found to reduce the residual stresses in fresh logs of larch, fir, Japanese cedar, oak, and ash. The residual stresses, evaluated by the released strain, were diminished in normal wood and reaction wood. To understand the mechanism of stress releasing, changes in the structure and chemical composition related to the thermal softening point of wood powder of these species were studied. The hemicellulose fraction was observed to be reduced because of the heat treatments done, as verified by thc sugar analysis. The thermal softening point was determined, and differences in the temperature of softening were found in untreated wood powder, among the species studied. The temperature of wood softening was always increased, after the wood powder received a heat treatment over 100°C. The results showed that hemicellulose was the main wood component influenced by the conditions of treatment. The higher thermal softening point of wood observed can be attributable to the degradation of the hemicelluloses. The release of residual stresses in logs is triggered by the heat treatment, which causes molecular motion. The hygrothermal treatment first affects the less stable elements in the wood (hemicellulose and lignin). The degradation of hemicellulose results in softening of the wood and has an important effect in the release of residual stresses.