Question: What is the difference between a polyurethane adhesive and a polyurea adhesive?
Answer: Polyurethanes and polyureas both cure to systems that can range from rigid to very elastic solids in their final properties. The two are quite comparable, but with some obvious exceptions.
While polyurethanes have been used for many years as adhesives and sealants, polyureas are comparatively new to the industry.
Polyurethane is made from a chemical standpoint from an isocyanate reaction with a polyol, whereas a polyurea is produced from an isocyanate reacting with a multifunctional amine. It is also conceivable to make so-called “hybrid” systems, in which the isocyanate is reacted with a mixture of hydroxyl and amino combinations.
The most significant difference is that the polyurea response is much faster than the polyurethane one, and the systems can gel within a few instants after mixing. Polyureas have been used highly successfully in the coatings industry, where the two elements are mixed using plural spray machine; polyurea adhesives, however, are comparatively new.
One issue has been that the adhesives gel so suddenly that the liquid does not have time to spread and wet the bonding surface. Also, heat-sensitive substrates can be damaged by the strong exotherm generated by the fast curing. Nevertheless, slowing down the curing is feasible and has led to successful applications. Also, both polyurea adhesives and sealants are obtainable commercially. Polyurea adhesives further lead to new bonding opportunities where they can be used as a spot weld, and there is a technique possible where components are preassembled, and the adhesives are injected into the bond line through preformed grooves.
