The effects of species, adhesive type, and cure temperature on the strength and durability of a structural finger-joint

This research project evaluated the effects of adhesive type, wood species, and cure temperature on the strength and durability properties of a finger-joint. The adhesives were a resorcinol-formaldehyde (RF), a polyurethane/aqueous emulsion polymer (PU/AEP), and a resorcinol-formaldehyde/soy-isolate (RF-Soy) honeymoon system. The species of wood were keruing (Dipterocarpus spp.), southern pine (Pinus spp.), and Douglas-fir (Pseudotsuga menziesii). The cure temperatures of the adhesives were ambient (26? to 35?C, 78? to 95?F) and elevated (43? to 49?C, 110? to 120?F). Joints were subjected to three test procedures: a tension test, a bending test, and a bending test following a cyclic delamination procedure. The response variables measured for each of the bending tests included modulus of rupture, modulus of elasticity, and percent wood failure. The response variables measured for the tension tests were tensile strength and percent wood failure. The end-joints bonded with RF adhesive performed the best in flexural and tensile strength of the three adhesives studied. However in most cases, the end-joints bonded with PU/AEP could be considered a comparable system. The RF-Soy honeymoon system generally had the lowest strength and wood failure across most species/adhesives variables. Given adequate adhesive performance, strength and stiffness of the joints studied were dependent on density of the wood species, with keruing having the greatest density.

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