Wood and Wood Based Materials. Air Permeability in Wood of Cryptomeria Japonica D.Don. Relationship between Moisture Content and Air Permeability in Logs Obtained from Trees Felled Beforehand, and in Several Stages of Natural Drying.
Abstract
To investigate the relationship between moisture content and the air permeability in logs of Cryptomeria japonica, the log specimens were obtained from one standing tree and 7 trees that were felled 2-4 months beforehand, in several stages of natural drying. Each log section consisting of heartwood, white zone wood and sapwood was set in a vacuum chamber which was connected to a mercury manometer, and the changes in pressures were measured during the different stages of vacuuming. Several experiments were carried out on logs of different conditions, ranging from green to relatively dry. Furthermore, the conditions of exposing and sealing of the transverse section were changed, and the relationship between the moisture content and the ratio of volume of air space and air permeability of longitudinal and radial directions were investigated with respect to each of the points.The results obtained were as follows.1) In heartwood, air permeation was scarcely detected regardless of the moisture contents, which ranged from 51% to 142%.2) In white zone wood, the air permeability was remarkably high regardless of the moisture contents, which ranged from 43% to 75%.3) In sapwood, the air permeability became remarkably higher with the decrease in moisture contents, which ranged from 70% to 191%.4) In sapwood, an inverse relationship was detected between the ratio of volume of air space and the elapsed time from beginning of vacuuming (760mmHg (101KPa)) until the pressure of each of the points attained the value of 400mmHg (53KPa).5) In sapwood, the air permeability of longitudinal direction became higher with the decrease in moisture content and the increase in the ratio of volume of air space.6) The air permeability between white zone wood and sapwood in the radial direction became higher with the decrease in moisture content and the increase in the ratio of volume of air space in sapwood.