Studies in Moisture Adsorption and Thickness Swelling: Low and High Humidity

Composite wood products (i.e., particleboard, medium density fiberboard, oriented strand board, plywood) used in cabinets, shelving, and base trim express varying degrees of thickness swelling when exposed to a sustained moisture source.Thickness swelling occurs when cellulose fibers adsorb water molecules and swell after attaining a moisture content of 29% to 36%.Observations of thickness swelling were made to refine water loss duration estimates.Thickness swell height is the result of several intrinsic factors (wood species, density, adhesive resin, heat pressing conditions).This study examined an extrinsic factor, humidity, at elevated (>95%RH) and ambient (50%RH) conditions.Specimens subjected to moisture for longer periods (8-10 weeks) experienced gradual darkening from accumulated biomass and fungal deterioration of the wood surfaces.The study revealed that high humidity conditions expressed higher rates of thickness swelling and that estimates of water loss duration should consider the influence of ambient humidity during and following a water release.