Longitudinal Water Permeability of Western Hemlock II. Unsteady-State Permeability
Keywords:Tsuga heterophylla, sapwood, heartwood, wetwood, kiln-drying, wet pockets
A mathematical model was developed and used as the basis for constructing two experimental apparatuses to investigate the permeability of western hemlock to water. When unsteady-state and steady-state permeability were compared, the unsteady-state permeability of both sapwood and normal heartwood was found to be higher than the steady-state permeability, but that of wetwood was generally lower than the initial steady-state permeability and was of the order of the final steady-state permeability. The permeability of western hemlock to water, regardless of whether it is measured by steady-state or unsteady-state techniques, is the highest for sapwood, followed by wetwood and normal heartwood.
Under unsteady-state conditions, sapwood permeability is time-independent, but wetwood exhibits time-dependent behavior, probably caused by blocking of the openings on pit membranes by movable extractives when water flows through the cell lumen. Storing western hemlock wetwood in water at room temperature reduces its water permeability. Wet pockets that form when wetwood of western hemlock is subjected to kiln-drying have lower permeability than the dried portion of the lumber.
Erickson, H. D. 1960. The effects of storage conditions and time upon permeability of green sapwood. Proc. Am. Wood Preserv. Assoc. 56:156-165.nKelso, W. C., R. O. Gertjejansen and R. L. Hossfeld. 1963. The effect of air blockage upon the permeability of wood to liquids. Univ. Minn., Agric. Exp. Sta., Tech. Bull. 242.nKozlik, C. J., and L. W. Hamlin. 1972. Reducing variability in final moisture content of kiln-dried western hemlock lumber. For. Prod. J. 22(7):24-31.nLin, R. T., E. P. Lancaster, and R. L. Krahmer. 1973. Longitudinal water permeability of western hemlock. I. Steady-state permeability. Wood Fiber 4(4):278-289.nLin, R. T., and C. J. Kozlik. 1971. Permeability and drying behavior of western hemlock heartwood. Proc. West. Dry Kiln Club, 22nd Annual Meeting, Portland, Oregon.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.