Water Relations in Phenolic (Plywood) Bonds

Good hot-press phenolic resin bonds using liquid resins can only be obtained when the water content of the glue at the instant of pressing is at or near optimum. It is immaterial how the water is dissipated, whether by evaporation, by diffusion into the wood, or by other means. Heat treatment of wood tends to reduce the wettability of the wood, and this reduced wettability interferes with the normal diffusion of glue moisture into the wood, requiring longer assembly time. The caustic of the glue acts to restore the wettability of the veneer surface so that spreading both contacting faces of a glue line and increasing the assembly time results in a good bond. The interrelationship between the heat treatment to which veneer is subjected during manufacture, moisture content, glue spread, veneer roughness, assembly time, and the resulting bond quality is much more complicated than had been generally considered. There is need to intensify work in this area to clarify the interrelationships between veneer drying and/or redrying as done in industry, veneer roughness, glue spread, and assembly time.

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