Polyureas have a lot of similarity to polyurethanes, but they are two-component systems based on reacting an isocyanate with a multifunctional amine rather than with a polyol. This chemical reaction is extremely fast, quite often just a few seconds. Polyureas are widely used as coatings in many industries, where they are applied using plural spray equipment (i.e., two or more coating materials are mixed together and sprayed at the same time onto an object or surface).
Polyureas are even faster than cyanoacrylate super glues. However, this cure speed leads to potential problems. It is very difficult to mix the two parts together, and a lot of heat can be generated that can damage sensitive materials. (I remember formulating very fast-curing epoxy adhesives years ago that could cure so quickly that they would melt plastic lap shears.)
Furthermore, you do have to be careful with surface preparation. Polyureas cure so quickly that complete wetting of the surface is sometimes difficult, leading to reduced adhesion. Thorough cleaning and the use of primers when necessary should solve this problem.
Despite these difficulties, some polyamines have been shown to slow down the curing somewhat. Polyurea adhesives can be highly effective in wood bonding applications like edge banding and bonding profiles, giving high productivity. However, special mixing equipment has to be used.
Any views or opinions expressed in this column are those of the author and do not represent those of ASI, its staff, Editorial Advisory Board or BNP Media.
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