Polyurethane foams generally increase the flame retardancy of foam by adding flame retardants to delay combustion, hinder smoke and even self-extinguish the fire. A polyol containing a flame retardant element (i.e., a reactive flame retardant) may also be used as the foam raw material. The flame retardant must have one or more of the following functions: it can be decomposed into non-combustible substances by heat absorption at or near the ignition temperature; it can react with foam combustion products to form non-flammable substances; it can be decomposed to terminate foam radical oxidation. The substance of the reaction.
In polyurethane foam, the phosphorus-containing flame retardant mainly acts in the condensed phase, and the phosphide can consume the combustible gas which is decomposed when the foam is burned, and converts it into a non-burnable char, and the phosphorus (P) content in the foam reaches A better flame retardant effect can be obtained at about 1.5%.
The halogen-containing flame retardant mainly functions in the gas phase, and the halogen is a chain terminator for the combustion reaction of the foam, which generates hydrogen halide to suppress the combustion reaction when the plastic is burned. According to relevant information, in order to obtain satisfactory flame retardant properties of the foam, the mass fraction of bromine (Br) in the dense body should be 12%-14%, or the mass fraction of chlorine (cl) should be 18%-20%. When phosphorus-halogen is used in combination, since there is a certain synergistic effect, 0.5% P+ (4%-5%) Br or 1% P+ (8%-12%) CI can make the polyurethane foam self-extinguishing.
A typical phosphorus-nitrogen flame retardant system may be composed of ammonium polyphosphate and melamine. In the initial stage of foam heating, the flame retardant decomposes to produce phosphoric acid, etc., which forms a flame retardant phosphate with a polyhydroxy compound and releases water vapor: Gasification of the flame retardant in the foam at high temperatures produces a non-combustible gas that carbonizes the molten foam to form a loose, porous, flame-retardant layer.
Aluminium hydroxide contains a large amount of water of crystallization (mass fraction can be as high as 34%). Crystal water is very stable in the production process of foam, but it will decompose rapidly at the burning temperature of foam, absorb heat of combustion, and in the source of fire and foam. A non-combustible barrier is formed to provide a flame retardant effect. At the same time, it is also a smoke inhibitor.
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