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Evaluating Durability of Adhesive-Bonded Wood Joints,
FOREST PRODUCTS LAB MADISON WI
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A wood joint properly bonded with a phenolic adhesive is said to be stronger and more durable than wood itself. But what happens to both wood and adhesive during natural aging, and how long might both materials last The literature reveals that wood, when subjected to only the chemical effects of aging, can last for up to thousands of years with remarkably small changes in mechanical properties, chemical composition, and morphology. Durability of adhesives can be compared with that of wood by rate process methods of analysis under conditions that accelerate the chemical reactions occurring during natural aging. Results demonstrated that moisture plays a predominant role in determining the durability of both adhesives and wood and that all degrading reactions are highly dependent on temperature. A procedure is proposed for comparing the durability of any new adhesive with that of wood, based on the time each requires to lose 25 percent of its original shear strength under prescribed conditions of exposure. This procedure requires a small number of test specimens and a short time for evaluation. Results are of high precision which can be related to centuries of use in natural aging and directly compare performance of phenolic and melamine adhesives as commonly recognized benchmarks for two levels of durability in service. Author
APPROVED FOR PUBLIC RELEASE