Adhesives can also be referred to as resins.
Many engineered wood products, including finger-joined lumber, plywood, oriented strand board (OSB), glulam, cross-laminated timber (CLT), wood I-joists and other structural composite lumber products, require the use of adhesives to transfer the stresses between adjoining wood fibres. Waterproof adhesives and heat resistant adhesives are commonly used in the manufacture of structural wood products.
Advances in adhesive technology to address challenges associated with increased production rates, visual appearance, process emissions and environmental impact concerns, have resulted in a wider range of innovative structural adhesive products. It is imperative that this new generation of adhesives achieve the same level of performance as traditional structural wood product adhesives such as phenol-formaldehyde (PF) or phenol-resorcinol formaldehyde (PRF).
Examples of different structural wood product adhesives families include, but are not limited to:
- Emulsion polymer isocyanate (EPI);
- One-component polyurethane (PUR);
- Phenolic resins such as phenol-formaldehyde (PF) and phenol-resorcinol formaldehyde (PRF).
Various types of extenders such as walnut shell flour, Douglas fir bark flour, alder bark flour, and wood flour are sometimes used to reduce cost, control penetration into the wood fibre or moderate strength properties for the specific materials being bonded.
There are several industry standards that may be used to evaluate the performance of structural wood product adhesives, including:
Phenol and phenol-resorcinol resin adhesives for wood (high-temperature curing)
Resorcinol and phenol-resorcinol resin adhesives for wood (room- and intermediate-temperature curing)
Evaluation of adhesives for structural wood products (exterior exposure)
Evaluation of adhesives for structural wood products (limited moisture exposure)
Formaldehyde emissions standard for composite wood products
Standard Test Method for Evaluating the Shear Strength of Adhesive Bonds in Laminated Wood Products at Elevated Temperatures
Standard Practice for Evaluating Elevated Temperature Performance of Adhesives Used in End-Jointed Lumber