The Sorption of Water Vapor by Domestic and Tropical Woods

The sorption of water vapor by Picea glauca, Tilia americana, Sequoia sempervirens, and Calophyllum brasilliense was measured in a glass apparatus which was initially placed under a vacuum. The pieces of wood were suspended by quartz coils and the interior of the apparatus then exposed to the vapor above a saturated solution of a salt at 90?F. Adsorption isotherms for Tilia were below those for Picea and that for Calophyllum was above both of these. The MC at saturation (relative vapor pressure 100 percent) for Sequoia was well below that for the other woods–24 percent versus 28 to 32 percent. When green wood was used an initial desorption isotherm was found for all woods above about 50 percent relative vapor pressure. The convergence of the first and second cycle desorption isotherms to a common curve indicates that the formation of permanent lateral bonds between cellulose molecules occurs in the early stages of initial drying. There is a difference in magnitude of the distance between isotherms of the hystersis loop in the species tested. At 80 percent relative vapor pressure, for example, Tilia and Calophyllum are greater than Picea which is greater than Sequoia. The great difference between the isotherms of Sequoia and Tilia is attributed to difference in distribution of cell wall capillaries.

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