The Development of Novel Latexes for Fire-Resistant, Intumescent Coatings
Intumescent coatings are coatings that react under the influence of fire and swell to many times their original thickness, producing an insulating char that protects the substrate from the effects of the fire.1,2 Steel, as we know, does not burn, but it does have a serious weakness as a construction material, in that it loses its structural strength at temperatures above approximately 550 _C. The primary function of an intumescent coating applied to structural steel is thus to protect the steel, generally for periods of up to two hours, from structural collapse during a fire, enabling fire fighters to safely evacuate people from the building. Its secondary role is to provide a smooth, aesthetically pleasing finish, which is durable and easy to maintain. The latter function is one of the main reasons why intumescent coatings are increasingly preferred over other types of passive fire protection. Thin film intumescents enable architects and designers to maximize the creative design possibilities of the steel itself, which is not possible with traditional bulky, passive fire-protection systems, such as mineral sprays and boards. This is clearly evident in new airports, shopping malls, hotels, sports stadiums, etc., where we see the architect using the steel framework as an integral part of the overall design, safe in the knowledge that the steel is fully protected against fire, with a system that has all the decorative qualities of a conventional paint.
Intumescence is generally accomplished with a minimum of three components: a source of mineral acid catalyst (typically ammonium polyphosphate, APP), a source of carbon (typically pentaerythritol or dipentaerythritol), and a blowing agent (typically melamine). When an intumescent coating is subjected to heat, a series of chemical reactions occurs: the ammonium polyphosphate decomposes to produce phosphoric acid; the phosphoric acid causes dehydration of the pentaerythritol or dipentaerythritol to produce a carbon char; the blowing agent decomposes, releasing non-flammable gases that cause the carbon char to foam, thus producing a meringue-like structure that is a highly effective insulator against heat.