With the rapid decrease of forest resources worldwide and the implementation of natural forest resources protection projects in China, small wood veneer requires better adhesive strength and durability than wood itself. The amount of adhesives used has become a symbol to measure the technological development level of wood industry.
In the past, most wood adhesives were urea-formaldehyde resin, phenolic resin and melamine-formaldehyde resin, which mainly used formaldehyde as raw materials. However, due to the existence of free formaldehyde, formaldehyde gas will gradually emit to the surrounding during the use of products, causing environmental pollution. Wood processing industry has begun to focus on the new environmental friendly adhesive polyurethane adhesive in order to reduce environmental pollution. The one-component moisture curable polyurethane adhesives used in woodworking industry are liquid and used at room temperature. Usually it has high bonding strength, good flexibility and water resistance, and can be bonded with many non-wood substrates (such as textile fibers, metals, plastics, rubber, etc.). The dry and wet strength of one-component polyurethane adhesives is better than that of phenolic adhesives. Before bonding, coating hydroxymethyl resorcinol (HMR) coupling agent on the surface of the bonding base material can improve the bonding strength, and HMR can strengthen the bonding strength of all thermosetting wood adhesives. When HMR coupling agent is pre-coated on wood surface, the strength and durability of one-component polyurethane adhesives can meet most of the stringent testing requirements.