HUMIDITY CONTROL PROPERTY OF HYGROSCOPIC WOOD COMPOSITES

The relative humidity in a small space with a certain amount of hygros copic material will stay constant because of sufficient moisture adsor ption or desorption of these materials with temperature changes. To cl arify this mechanism, fifteen kinds of hygroscopic composites composed of wood meals, calcium silicate, and moisture-adsorbing synthetic pol ymers were prepared. The relative humidity changes in this small space containing these composites were measured for temperature changes of the surrounding air. Humidity control efficiencies (HCEs) of these com posites were calculated from equilibrium humidities. The HCEs of wood meal composites proved to be equal or a little more than that of untre ated wood veneer. Because it was supposed that humidity control proper ties were affected by the hygroscopicities of the materials, the relat ionships between the slopes of adsorption isotherms and the HCEs of th e hygroscopic composites were investigated in relation to the weights of the materials per spacial air volumes. As a result, the HCEs could be expressed as logarithmic functions. It was suggested that the HCEs of composites at equilibrium humidities could be predicted from the ad sorption isotherms. The results obtained are not only useful in design ing hygroscopic composites but also are applicable to the finish or th e overlay of an interior wall.