Polyurethane foams are produced by reacting polyols and diisocyanates, both products derived from crude oil. Some polyols can however also be derived from renewable sources.
Two different aromatic diisocyanates are being used in the production of polyurethane foam: MDI (Methylene diphenyl diisocyanate) and TDI (Toluene diisocyanate ). When mixed with polyols, which are long alcoxyether chains, these chemicals form the building blocks of polyurethane.
To produce flexible polyurethane foam, and depending on the specifications of the foam to be produced, other substances are mixed with the diisocyanates and the polyols:
- Catalysts are used to increase the reaction rate between diisocyanates and polyols. There is a wide variety, with metals salts or amine-based catalysts the most commonly used.
- Blowing agents are used to produce the foam’s cellular structure. The blowing agents for flexible polyurethane foam are simply water and carbon dioxide (CO2).
In some instances – notably when required by local legislation – flame retardants are added to formulations to increase the fire resistance of polyurethane foam. It should be noted that spontaneous ignition is not possible for flexible foams under normal operating temperature.
Also, to facilitate the removal of the foam from its mould (“demoulding”), release agents are being used. These are typically silicone or wax-based.