Interaction of Wood Surface and Adhesive Variables

Two studies were made that relate to interactions involving the chemical nature of the surface of wood, its surface permeability, and certain physical and chemical characteristics of phenolic resin adhesives. One study involved modification of the surface of thin flakes in an attempt to study the effect of drying temperature on the efficiency of resin binders in flakeboard. In the second study, an attempt was made to modify the surface of veneer by means of pretreatment with surface modifying agents for the purpose of improving the bond quality of the plywood adhesive. Results of both studies confirm the importance of efficient bonding to the optimum interactions of variables such as the chemical surface of wood, the relative molecular weight distribution of the resin, the molar ratio of formaldehyde-to-phenol, and related factors that influence the wettability of wood by the resin. It was concluded that the most efficient bonding of particleboard flakes occurred when the resin binder droplets wetted– but did not overpenetrate– the wood surfaces. For the resins used, this condition was best achieved by drying the flakes at relatively high temperatures (500?F) in a commercial dryer. Modification of veneer surfaces with a variety of commercial chromium complexes, on the other hand, did not result in improved bonding efficiency in plywood as had been expected on theoretical grounds. It is suggested that these results point up the inadequacy of the view that the veneer surface is composed of relatively uniform, highly-reactive polar groups. Results are discussed in this light.

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