Moisture-Stability Relationships in Wood-Base Composition Boards

Four types of particleboard and five types each of hardboard and insulation board were used to study the relationships of physical properties to dimensional stability characteristics of the panels. Physical properties determined were density, fiber or particle length, surface areas of fibers or particles, surface areas of panel specimens, steady state and unsteady state diffusion coefficients, and permeability to air. Dimensional stability characteristics determined included moisture absorption, linear expansion, and thickness swelling. All rate-related characteristics were found, to be dependent on interparticle capillarity as influenced by particle orientation, particle geometry, surface areas, and density. Total moisture absorption was controlled by characteristics inherent to each panel type and was found to be a function of the logarithm of time. Linear expansion and thickness swelling were found to be directly correlated with moisture absorption and, in some cases, to time. Mechanisms which reduce the rate or moisture movement had only slight value as stabilizing agents. Other methods which improve bonding conditions or which reduce the number of available absorption sites still hold the best promise as stabilizing methods.

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