An acid-catalyzed phenolic adhesive for radiofrequency laminating of hardwood composite framing
Vick, C.
An acid-catalyzed phenolic resin, which is used in the foundry industry to bond sand into shell moldings and cores for metal castings, developed strong and highly durable bonds between hardwood veneer and flakeboard core edges in composite framing lumber. The acid-phenolic is a lower-cost and viable alternative to other thermosetting adhesives commonly used for radio-frequency laminating of wood products. Wood species, moisture content (MC), resin molecular weight, adhesive spread rate, and closed assembly time all strongly interacted and significantly impacted adhesive bond integrity. Controlling the mobility of the phenolic adhesive to prevent overpenetration of the porous edges of the flakeboard core, while maintaining adequate penetration of the veneer surface, was of critical importance when using radio-frequency heating to produce bonds of high integrity. Of the 72 combinations of material and assembly factors tested, all but a few property values far exceeded the minimum performance requirements proposed for the new composite. From the standpoint of achieving high bond integrity, practicable operating conditions, and low costs, sweetgum or yellow-poplar dried to 4-1/2 percent MC could be effectively bonded with the high-molecular-weight resin at closed assembly times between 5 and 15 minutes, even at spread rates as low as 50 lb./Mft.2
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