Forest Products Laboratory

Title: Strength and durability of one-part polyurethane adhesive bonds to wood

Author: Vick, C. B.; Okkonen, E. A.

Date: 1998

Source: Forest products journal. Vol. 48, nos. 11/12 (Nov./Dec. 1998).:p. 71-76.

Description: One-part polyurethane wood adhesives comprise a new class of general purpose consumer products. Manufacturersa claims of waterproof bonds brought many inquiries to the Forest Products Laboratory (FPL) from users constructing aircraft, boats, lawn furniture, and other laminated materials for outdoor use. Although FPL has technical information on several types of polyurethane and isocyanate-based adhesives for wood, no information was available on this new class of adhesives. Four commercial polyurethane adhesives, along with a resorcinol-formaldehyde adhesive to represent a standard of performance, were subjected to a series of industry-accepted tests that assess varying levels of bond strength and durability. In bonds to yellow birch and Douglas-fir, the polyurethanes did not differ significantly from each other in their performance; as a group, though, their dry shear strengths showed that they were significantly stronger than the resorcinol. Dry wood failures by the polyurethanes were high and did not differ significantly from the resorcinol. After three water-saturating procedures, wet shear strengths of polyurethanes and the resorcinol were statistically comparable. Wet wood failures, however, were very low among polyurethanes, which is a sharp contrast to the high wood failure by the resorcinol. A moderately severe delamination test indicated varying levels of water resistance among the polyurethanes, but the resorcinol was completely resistant to delamination. A very severe cyclic delamination test caused severe delamination of polyurethane bonds. However, a recently discovered hydroxymethylated resorcinol (HMR) coupling agent dramatically increased delamination resistance of polyurethane adhesives. In a test of resistance to deformation under static loads, polyurethane bonds withstood extreme exposures of temperature and relative humidity for 60 days without deformation.

Keywords: Adhesives, Glued joints, Bond strength., Polyurethanes

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Citation

Vick, C. B.; Okkonen, E. A.  1998.  Strength and durability of one-part polyurethane adhesive bonds to wood .   Forest products journal. Vol. 48, nos. 11/12 (Nov./Dec. 1998).:p. 71-76..