Prediction of Moisture Content and Moisture Gradient of an Overlaid Particleboard1

Equilibrium moisture contents (EMCs) and diffusion coefficients of a high pressure laminate (HPL) overlay, a wood particleboard (PB) substrate, and an HPL backer (BCK) were measured at different levels of relative humidity (RH). The EMCs as a function of RH were fitted to the Nelson's sorption isotherm. It was found that Nelson's model reproduced accurately the experimental data of these different materials. Over a given RH interval, the PB face layer had a smaller diffusion coefficient than the core layer. Diffusion coefficients for both PB face and core layers decreased with increase in moisture content (MC). For overlays, diffusion coefficients increased with MC for both HPL and HPL backer. A model based on the diffusion theory was developed to predict MC and moisture distribution for a multi-ply wood composite panel. The model's prediction of the mean MC for a three-layer PB, a two-ply HPL+PB panel, and a three-ply HPL+ PB+BCK panel compared favorably with experimental data. Developments of asymmetric moisture distributions within the HPL+PB and HPL+PB+BCK laminates were demonstrated, and their implication for the panel's warping potential was discussed.