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Longitudinal permeability within Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) growth increments Bramhall, George

Abstract

An apparatus was constructed to measure the longitudinal gas-permeability of wood microsections about 150 microns thick. This apparatus was used to examine low surface tension drying methods of wood (freeze-drying and alcohol-benzene extraction) believed to maintain the bordered pit tori of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) in the non-aspirated condition. Results were compared with drying methods believed to aspirate tori (air-drying, oven-drying and boiling-under-vacuum). Dry nitrogen gas-permeability measurements were made under "steady state" conditions. Similar drying techniques were used to prepare gross specimens which were subsequently subjected to “non-steady state" pressure treatment in end-penetration. Sapwood and heartwood specimens from impermeable interior-type and permeable coast-type Douglas fir were tested. With both gross sections and microsections, the two low surface tension drying methods provided more permeable wood than did air-drying. Boiling-under-vacuum was as effective as low surface tension methods in improving gas-permeability, but not creosote-permeability, whereas oven-drying was as effective as low surface tension methods in improving creosote-permeability, but not gas-permeability. The improvement was most striking in all sapwood samples, less in coast-type heartwood, and nil or not measurable in interior-type heartwood. Under the experimental conditions, latewood gas-permeability was about 2 darcies for all specimens and drying methods. Heartwood early-wood gas-permeability ranged from 0.02 to 2 darcies but was unaffected by drying methods. Sapwood earlywood gas-permeability was improved from 8 to 30 times by low surface tension drying. The greatest gas-permeability was found in the first-formed earlywood, which ranged from 2 to 100 darcies. The later-formed earlywood ranged from 0.02 to 100 darcies, depending on wood origin and drying method. Creosote-permeability of interior-type heartwood was uniformly low by all drying methods. Interior-type sapwood and coast-type sapwood and heartwood were much more permeable after low surface tension drying or oven-drying. By visual observations, after all drying methods, latewood was more permeable than earlywood. Low surface tension drying methods improve earlywood gas-permeability of sapwood, and latewood creosote-permeability of sapwood and coast-type heartwood.

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