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Some aspects of western hemlock air permeability Rayirath, Prasad

Abstract

This study is indented to explore the variability in longitudinal and radial air permeability of western hemlock and to determine the effect of tracheid length and wood density on measured permeability. Western hemlock (Tsuga heterophylla) is one the most abundant species in British Columbia’s and it is one of the demanding species in North America and Asian market. An important attribute of hemlock is the ease with which it can be pressure impregnated with wood preservatives. In spite of its reputation for treatability, hemlock still varies quite widely in its receptivity to treatment. Although this variability exists, there is little information known on the relative differences in permeability within hemlock, despite of its importance as a treatable wood. Ten western hemlock trees were randomly selected and samples were selected from three different tree heights of each tree. The specimens were then conditioned to 12% moisture content to nullify the effect of moisture content on permeability. The air permeability of sapwood and heartwood specimens in longitudinal direction at three different tree heights was measured using a dynamic method. Tracheid lengths were measured with a fiber quality analyzer and density of each specimen was measured by water displacement. The effect of tree height, tracheid length and density on longitudinal permeability was then evaluated. Data analysis revealed that tree height has no effect on heartwood longitudinal permeability whereas in sapwood the longitudinal permeability at 7m height was found to be significantly higher than that of 1m or 4m. It was also clearly apparent that longitudinal permeability was not influenced by the tracheid length and wood density. The radial permeability of heartwood and sapwood samples were also measured at three different heights and observed that radial permeability of both the samples at 7m is significantly higher than that of 1m or 4m.

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