Effect of Panel Moisture Content and Density on Moisture Movement in MDF
Keywords:Medium density fiberboard, effective water conductivity, diffusion coefficient, sorption isotherm, moisture content, density
AbstractThis study examined the effect of medium density fiberboard (MDF) density and sorption state on the sorption isotherms and the effect of panel moisture content and density on the effective water conductivity and diffusion coefficient of MDF panels. A total of 39 laboratory-made MDF panels with dimensions 650 mm X 650 mm X 12 mm divided into 3 density groups (540 kg/m3, 650 kg/m3, and 800 kg/m3) was produced. The surface layers of each panel were removed, and the thickness of the remaining core layer of homogeneous density was reduced by sanding to 6 mm. The sorption isotherms were determined by exposing MDF samples to controlled relative humidities. The effective water conductivity was determined by the instantaneous profile method. Medium density fiberboard from all density levels displayed a marked sorption hysteresis. Both in adsorption and in desorption, the MDF specimens with higher density levels equilibrated at higher levels of moisture content. Moisture content had a stronger effect than density on the effective water conductivity. In desorption, the higher the moisture content level, the higher the effective water conductivity. Conversely, in adsorption, the effective water conductivity decreased as moisture content increased. The effective water conductivity in desorption and the diffusion coefficients both in desorption and adsorption were significantly higher for panels with a density of 540 kg/m3 than for densities of 650 and 800 kg/m3. In adsorption, the effective water conductivity of panels with a density of 540 kg/m3 was significantly higher than for a density of 800 kg/m3.
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