Print Version

Polyurethane Foam

To make polyurethane foam, a polyether such as polypropylene glycol is treated with a diisocyanate in the presence of water and a catalyst (amines, tin soaps, organic tin compounds), as well as fillers, dispersing and emulsifying agents, etc. Simultaneously with the polymer-forming reactions the water reacts with the isocyanate group to cause cross linking and curing, and also produces carbon dioxide which causes foaming. In some foams, a volatile material such as Freon is incorporated to serve as a blowing agent. Foam is normally made by one of two basic methods, the prepolymer system or the one-shot system.

The prepolymer system brings two streams together at the foaming head. Component A is a mixture of a polyol, catalyst, surfactant and blowing agent, while component B is a polyol isocyanate mixture. Both components are quite viscous.

The one-shot system brings all components together at the spray head through independent lines from separate supplies. This system requires more equipment and precise metering, but once controls are established the uniformity of the foam is much better than with the prepolymer system.

Viscosity: Varies widely from thin for the blowing agents, catalyst and amines to the order of 5,000 for the polyols or resins.