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    Description

    When dry wood is placed in water, the water not only fills the lumen (void in the cells) but also diffuses into the cell walls, causing them to expand. Although the wood becomes weaker via this cell wall plasticization, failure generally increases in the bondline rather than in the wood under wet conditions. Thus, the question is why water exposure often causes a greater decrease in bondline strength than in wood strength. In a few cases, such as un- crosslinked poly(vinyl acetate), bondline failure comes from the adhesive’s decreased structural integrity because of plasticization under wet conditions . For others, such as epoxies, an explanation for bond durability had not been determined prior to our recent study (1). An important aspect of our work was to determine the main failure location within the bondline and the main reason for the failure (Figure 2). This study showed that epoxy failure was mainly in the epoxy interphase adjacent to the wood surface (Figure 3). This and other studies using chemically modified wood (2) and a hydroxymethyl resorcinol primer (3) have led to the model of high interfacial strain between wood and adhesive being a critical parameter for bond durability. Wood swells going from dry to wet conditions, whereas most adhesives do not; therefore large internal stress can be generated at the bondline (4). How well wood adhesives deal with this stress caused by differential expansion and contraction has led to part of a more comprehensive chemical–mechanical wood adhesion model. An aspect of this model is in understanding how adhesives successfully deal with this difference in strain under wet conditions.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Frihart, Charles R. 2007. Model for understanding the durability performance of wood adhesives. Proceedings : 30th annual meeting of the Adhesion Society, Inc. : February 18-21, 2007, Tampa Bay, FL. [S.l. : s.n.], c2007: pages 222-224.

    Keywords

    Wood moisture, adhesion, adhesives, moisture content, testing, bondline, shrinkage, failure, failures in wood, swelling, strength, bond strength, durability, wood bonding, bonding

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