Air Permeability, Shrinkage, And Moisture Sorption of Lodgepole Pine Stemwood
Keywords:
Permeability, lodgepole pine, latitude, elevation, specific gravity, sapwood, heartwood, shrinkage, moisture, sorptionAbstract
The longitudinal air permeabilities, shrinkage (from fully swollen to oven-dry), and moisture sorption characteristics of two varieties (latifotia and murrayana) of lodgepole pine (Pinus contorta) were measured, based on wood samples taken from ten latitudes (37.5° to to 60°N) in western North America, from 279 trees of three diameter classes (76, 152, 228 mm DBH).
The mean permeabilities of the sapwood and heartwood were 0.13 and 0.014 darcy, respectively. Geographical latitude and elevation of trees did not affect permeability. The mean calculated radius of pit pores in the sapwood was 1.5 μm, with median values between 12-13 pit pores per mm2. There was a fair correlation between water retention in an empirical water-soaking test and axial gas permeability.
The volumetric and radial shrinkages, as well as the ratio of radial to tangential shrinkage, all increased with increasing specific gravity for both varieties. Tree size and latitude also affected shrinkage somewhat, primarily through their effects on specific gravity. The mean ratio of percent volumetric shrinkage to specific gravity was 30.7 2.9% for the two varieties combined.
The moisture sorption study gave adsorption and desorption equilibrium moisture content (EMC) values at 30 C at relative humidities of 34.4, 65.0, and 83.2% for both varieties, on each of 62 test samples, representing the three different tree sizes and nine different latitudes. The mean adsorption-desorption (A/D) ratio was 0.79. The EMCs generally decreased with increasing latitude, with no significant difference between varieties at corresponding latitudes.
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