Qualification of wood adhesives for structural softwood glulam with large juvenile wood content

This paper reports on an experimental study to assess the bond quality achieved when bonding softwood spruce containing large proportions of juvenile wood with a range of conventional wood laminating adhesives. Adhesives examined comprised two phenol resorcinol formaldehydes, a melamine urea formaldehyde, a polyurethane, an emulsion polymer isocyanate and a polyvinyl acetate. The notched block shear test was utilised in which both non-moisture cycled and moisture cycled specimens were tested. The grain orientation of the wood, was carefully studied in the bonding process. Results indicated that the integrity of the bond was highly dependent on the adhesive under examination. No significant difference was observed at the interface when bonding to juvenile wood or to mature wood . Furthermore, no distinct performance difference for both nonmoisture cycled and moisture cycled specimens was recorded when bonding to tangential grained or radial grained wood.