Formaldehyde Adhesives

Formaldehyde adhesives are the adhesives that use formaldehyde in the process of formation. The formaldehyde in the composition serves as the cross-linking agent in the bond-forming. The formaldehyde adhesive is widely used in the woodworking industry because it has some advantages, such as water resistance, ease of application and handling, and a reasonable price. In the woodworking industry, glue is used for the wood laminating, finger joint, plywood laminating, and veneer paneling. It is the main glue for the hot press in the process of making the plywood or wood veneer panel. The glue is heated with a metal plate until around 100 °C, and the glue will cure in a few minutes. A similar process is also done in the manufacturing of the finger joint laminating board.

Some resins are used to make the formaldehyde adhesives, including phenol formaldehyde, resorcinol formaldehyde, urea formaldehyde, and melamine formaldehyde. Each material will have different properties and characters. Urea-formaldehyde adhesive is durable, but they have poor durability in wet conditions; it is not proper for outdoor uses. Phenol-formaldehyde glue offers a good balance between cost and resistance to water. Melamine is more expensive, but they provide good resistance to water and have a lighter color than the phenol resin. Resorcinol-formaldehyde resin is very useful because it can be cured at room temperature, but it is expensive. For more explanation, you can go to this link: "Wood adhesive and adhesion," e-book by Charles Frihat. The co-reactants or their combinations used for formaldehyde can be selected to accord to the price, production conditions, and the expected performance of the product.

The glue is emitting formaldehyde, a poisonous gas that can interfere with human health. The "formaldehyde" could make some people don’t like this product. Although, once the product is dry, it will no longer emit formaldehyde gas and can be used safely. In many countries there is tight regulation about the formaldehyde emission allowed. And now most of the glue manufacturers have made modifications in formulation according to the regulation. So most of the glues available now are actually quite safe for human health. 

Here are some things to be considered in the uses of formaldehyde glue.

• Read the product specification, technical data, and instructions on how to use it.

The adhesive is a two-component adhesive that must be mixed in the proper ratio before it is applied to the wood surface. The glue also has some types; each of them may have different character and specification. The curing time, the mixing ratio, the temperature, and even the thickness are factors that affect the adhesion result. Make sure we know the instruction and follow it.

•  Preparation of wood.

The surface where the glue is applied is the other important factor that determines the quality of adhesion resulted. Make sure we cut the wood pieces properly to let them be able to be attached together tightly. Make sure that the pieces of wood are completely dry with uniform moisture content before laminated. The high moisture content will cause poor adhesion since the water in the wood pieces will reduce the concentration of the glue. Too much variation of wood MC will lead to the splitting or crack problem because of the wood movement at each piece of the wood.

• Beware for the gas emissions

Although many improvements have been made by the glue manufacturer to minimize the gas emission, this glue will emit gas during its drying process. Then make sure we handle this glue properly and safely. Do the application of the glue in the room with good air circulation to avoid the gas accumulation in the room. Although the chemical is quite safe, we better minimize the direct contact with the glue. Wear the gloves and masker when handling and applying this glue.