Expanded flame retardants are not a single type of flame retardant, but rather halogen-free composite flame retardants mainly composed of phosphorus, nitrogen, and carbon, which have internal synergistic effects within their system. Due to the foaming and expansion of this type of flame retardant when heated, it is called an expanding flame retardant.
It is generally believed that the flame retardant mechanism of the expansion system is condensed phase flame retardant.
Firstly, polyphosphate amine is thermally decomposed to generate phosphoric acid and pyrophosphate with strong dehydration effect, which esterizes pentaerythritol and then dehydrates and carbonizes it. The water vapor formed by the reaction and the ammonia gas decomposed by melamine cause the carbon layer to expand, ultimately forming a layer of microporous carbon layer, which isolates air and heat conduction, protects the polymer body, and achieves the purpose of flame retardant. The addition of expandable flame retardants to polymer materials must possess the following properties: good thermal stability, able to withstand high temperatures above 200 ℃ during polymer processing; Due to the release of a large amount of volatile substances and the formation of residues during thermal degradation, this process should not have adverse effects on the expansion and foaming process; This type of flame retardant is uniformly distributed in polymers and can form a layer of expanded carbon that completely covers the surface of the material during combustion; Flame retardants must have good compatibility with the flame retardant polymer, and must not have adverse effects on the polymer and additives, nor excessively deteriorate the physical and mechanical properties of the material. The advantages of expandable flame retardants over general flame retardants are halogen-free and antimony oxide free: low smoke, less toxic, and non corrosive gases; The carbon layer generated by the expansion flame retardant can adsorb the melted and ignited polymer, preventing it from dripping and spreading the fire.
Expanded flame retardants have basically overcome the shortcomings of traditional flame retardant technology, with the following advantages: high flame retardancy, no droplet behavior, and good resistance to prolonged or repeated exposure to flames; Halogen-free and antimony free; Low smoke, less toxic, and non corrosive gas production.
Ammonium polyphosphate (APP) belongs to inorganic phosphorus flame retardants
Phosphorus based and nitrogen based flame retardants, as well as metal hydroxides and other flame retardants, have synergistic effects and can produce synergistic flame retardant and smoke reducing effects.
Inorganic phosphorus flame retardants have poor water resistance and usually require modification for use.
Property: White powder, water absorption decreases with increasing polymerization degree. The APP decomposes above 250 ℃, releasing water and ammonia, and generating phosphoric acid. The flame retardant mechanism is to absorb heat, cool down, and dilute combustible gases. Due to the presence of phosphorus and nitrogen in its molecules, APP has a good synergistic effect and flame retardant effect, mainly used in fireproof coatings.