The principle of the expansion and foaming process is that the coating is softened and melted when exposed to fire, the foaming agent is separated to liberate gas, and the escape of gas causes the softened coating to bubble and expand, and the thick carbonization is produced by the increase in volume. Foam layer or thermal insulation layer. When chlorinated wax and dicyandiamide are used as blowing agents, the decomposition process is as follows:
C.+H 2, +2Cl.-nC+HCl
CH Ne+0z-8C+4NH: +6Nz+2HgO
At the same time, the acid source material also decomposes to release free acids and react with the carbonized material of the polyol to dehydrate and esterify the polyol. With the progress of this process, the expanded foam layer is gradually transformed into a heat insulation layer of carbonized substances, for example, diammonium oxyphosphate produces phosphoric acid.
Phosphoric acid reacts with a carbon source (taking isopentaerythritol as an example) to form a phosphate ester.
C sHg(Ol) e+H gPO: —-C, Hy(OH) ·H gPO:
This phosphate is decomposed into phosphoric acid, water and carbonized layer:
CsH; (OH): ·HyPO→H: O+H, PO+C
Obviously, most of the carbon in the expanded foamed layer is obtained from the carbonized material contained in it through acid dehydration. It should be pointed out that in order to make the intumescent fireproof coating expand and foam to form an efficient fireproof and thermal insulation expansion layer when exposed to fire, the intumescent fireproof system in its formulation needs to undergo a series of physical and chemical reactions in an appropriate order after being heated. In the whole process, the blowing agent is required to decompose to produce gas, the acid source is separated to liberate acidic substances, and the carbon source material is dehydrated and carbonized. The three steps must be basically coordinated in terms of changing temperature, time and speed to form a small porous sponge. This is the meaning of one aspect of “cooperation” mentioned earlier.
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