Formaldehyde adhesive is 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, easiness in the application and handling and the reasonable price. In the woodworking industry, the glue is used for the wood laminating, finger joint, plywood laminating and veneer paneling. It is the main glue for hot press in 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 few minutes. The similar process is also done in manufacturing of the finger joint laminating board.
There some resins are used to make the formaldehyde adhesives include: phenol formaldehyde, resorcinol formaldehyde, urea formaldehyde and melamine formaldehyde. Each material will give 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 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 can interfere the human health. The "formaldehyde" could make some people don’t like this product. Although actually once the product is dry, he will no longer emit formaldehyde gas and can be used safely. In many country there tight regulation about the formaldehyde emission allowed. And now the most of the glue manufacturer has made modification in formulation according to the regulation. So most of the glue 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 instruction 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 is 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 make poor adhesion since the water in the wood pieces will reduce the concentration of the glue. Too big variation of wood mc will lead to the splitting, or crack problem because of the wood movement at each pieces of the wood.
- Beware for the gas emissions
Although many improvement has 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 the good air circulation to avoid the gas accumulation in the room. Although the chemical is quite safe, but we better minimize the direct contact with the glue. Wear the gloves and masker when handling and applying this glue.
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