Adhesive penetration of hardwood: a generic penetration model

An analytical model to predict the penetration of adhesives into hardwood is proposed. Penetration into hardwood is dominated by the vessel network which prohibits porous medium approximations. The model considers two scales: (1) a one dimensional capillary fluid transport of a hardening adhesive through a single, straight vessel with diffusion of solvent through the walls of the vessel; and (2) a mesoscopic scale based on topological characteristics of the vessel network. Given an initial amount of adhesive and applied bonding pressure, the portion of the filled structure could be calculated. The model was applied to beech samples joined with three different types of adhesive (PUR, UF, PVAc) under various growth ring angles as described by Hass et al. (2011). The model contains one free parameter that can be adjusted in order to fit the experimental data.