The flame-retardant mechanism of APP can be divided into condensed-phase flame-retardant mechanism and gas-phase flame-retardant mechanism. Condensed-phase flame-retardant mechanism: APP decomposes upon heating into phosphoric acid derivatives such as polyphosphoric acid and metaphosphoric acid. These phosphoric acid derivatives catalyze the cross-linking of polymers into char, causing dehydration and carbonization of the matrix surface, forming a non-combustible char layer. This non-combustible char layer coats the matrix surface, acting as a physical barrier, delaying the exchange of combustible substances and heat conduction, and reducing the decomposition rate of the internal matrix.
Gas-phase flame-retardant mechanism: APP decomposes upon heating to produce non-combustible gases such as NH3, NO, and water vapor. These gases not only reduce the concentration of combustible gases in the air but also cause the char layer in the condensed phase to expand, reducing the rate of heat and mass transfer. Furthermore, the phosphoric acid derivatives obtained during APP combustion undergo disproportionation reactions to generate HPO·, PO2·, and PO· free radicals. These free radicals can capture H· and OH· free radicals generated by polymer chain reactions, exerting a quenching effect and reducing heat release.
Typically, condensed-phase flame retardancy and gas-phase flame retardancy of APP work together. However, the gas-phase flame retardancy of APP requires the consumption of phosphoric acid to form free radicals. As the phosphoric acid content decreases, the total amount of porous char layer also decreases, and the formed char layer decomposes, reducing the effectiveness of condensed-phase flame retardancy. Therefore, in some cases, APP may only exhibit condensed-phase flame retardancy, and the flame retardant effect may actually be enhanced.
Sichuan Taifeng New Flame Retardant Co., Ltd was founded in 2001, mainly engaged in phosphate chemical products. In 2011, in order to keep up with the national economic trend and seize new opportunities, the company focused on ammonium polyphosphate and set up R&D department special for halogen-free flame retardant.
Ammonium polyphosphate(APP) and modified and compound based on APP are our main products. They are used throughout many industries, such as fireproof coating, textiles, paper, masterbatch and etc. We have a national and global sales network to worldwide.
Contact us for flame retardants solution.
Post time: Aug-21-2026
