Adhesive and Adhesion Problems in Particle Board Production

The controlling factors in cementing wood particles together are essentially the same as those in the gluing of woods. Next to the mechanical preparation of wood chips the spreading of the glue is the most important operation with respect to bond and board quality. Strength of bond between chips depends on surface area and adhesive spread. It increases with large contact area and thin, film-like adhesive layers. Provided chip surfaces are undamaged, a spread of 2 lbs. adhesive/1000 sq. ft. gives a good bond. Distribution of the adhesive as a continuous film rather than as discrete droplets is desirable. With present spray equipment this is difficult to realize. A better understanding of the dynamic fundamentals of adhesive atomization is needed for making progress in this field. Bonding strength is affected also by chip thickness. Optimum strength lies between very thick and very thin flakes. The moisture content of the wood particles and the moisture added with the adhesive affects both the plasticity of wood during the pressing cycle as well as the flow of resin. The role of water in the setting of resin adhesives is not fully understood. Moisture contents of 8 to 12 percent at the particle interface are found to give maximum bond strength. Methods should be sought to prevent any undesirable adhesive penetration by property chosen pressing-cycle conditions, types of catalysts, or by development of new adhesive processes.

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