Can You Explain Some Details Of Urethane Adheisve Systems For Bonding?

Adhesives had been an important part of our lives since they are of extensive application in many walks of life. The urethane is formed by the reaction of the hydroxyl from the polyether or polyester polyol with a suitable diisocyanate. The diisocyanate continues to react with another polyol's hydroxyl group, leading to chain extension and molecular weight build. The link thus formed is called a urethane link.

The make up of the adhesive is further complicated depending upon the starting materials. The polyol can be low to high molecular weight of singular or mixed materials, or a polyurethane prepolymer, or it could be hydroxyl terminated, and mixtures of the two as well.

These are reacted with low to medium molecular weight diisocyanate prepolymer and allowed to cross-link to form the urethane link and the final cured adhesive. This would be called a 2-part adhesive system.

In some cases, the prepolymer adhesive is created and terminated in isocyanate. This one-part adhesive is allowed to cure with ambient moisture to form a different linkage, called urea. This is sometimes called a moisture cure adhesive.

There is always the potential for water reacting with the isocyanate, even in a 2-part adhesive, due to humidity in the air and water in solvents. Though in this case the goal is to create polyurethane adhesive, there might be some small amount of polyurea formed as well.