Chemical and technical properties

Polyurethanes, or PU for short, are a particularly versatile group of plastics that can be found in many different areas of everyday life. Polyaddition of isocyanates with polyols generates plastics containing the urethane group, NH-CO-O, hence the name polyurethane. The main ingredients in PU foam cans are polyol, isocyanate (diphenylmethane-4,4‘-diisocyanate) and propellants as well as stabilizers, accelerators, flameproofing agents and other additives.

There are two different functional principles for canned PU foam, the one-component foam (1-C PU foam) and the two-component foam (2-C PU foam). In the case of one-component foams, the mixture of the so-called prepolymer and the propellant reacts outside the can through contact with the ambient moisture. The foam hardens from the outside (where the ambient moisture acts first) to the inside. After use, the can still contains a liquid residue composed of prepolymer and propellant.

In two-component foams, the mixture reacts with a second component. This hardener is an additional packaging unit that is contained either in the can itself or added separately. As a result, no ambient moisture is required for the reaction. Shortly before application, both components are mixed in the can through a special mechanism. Two-component foams must be used up in one single application. After being sprayed from the can, the foam hardens very quickly from the inside to the outside, thereby allowing more control over the hardening process.