Ammonium polyphosphate (APP) is not a single substance, but a vast "family", and its performance differences are mainly determined by two dimensions: degree of aggregation (n-value) and crystal structure.
Classified by degree of polymerization:
- Oligomeric APP (n=10-20): High water solubility, poor thermal stability, mainly used as a fire extinguishing agent, paper flame retardant, or as a slow-release fertilizer.
-High polymerization APP (n>20): With low water solubility and good thermal stability, it is the main flame retardant in industries such as plastics and coatings.
-Ultra high polymerization degree APP (n>1000): Almost insoluble in water, with a decomposition temperature of over 350 ℃, specifically designed for high-end engineering plastics and high temperature resistant scenarios.
Classified by crystal form:
- Type I APP: mostly amorphous, highly hygroscopic, prone to clumping, suitable for low-end applications with low water resistance requirements.
-Type II APP: Crystalline state, excellent hydrolysis resistance and thermal stability, it is currently the mainstream choice in industry and widely used in high-performance flame retardant materials. This refined classification system enables the app to accurately match the needs of different application scenarios.
The reason why the APP stands out in the flame retardant market is due to its comprehensive and balanced performance. Its core advantages can be summarized into four points:
Firstly, excellent environmental friendliness. The APP does not contain halogens and does not release toxic hydrogen halide gas during combustion. It complies with international environmental standards such as RoHS and REACH and is an ideal choice to replace traditional bromine based flame retardants.
Secondly, it has high flame retardant efficiency. Adding 5% -25% to plastic can achieve the highest flame retardant level of UL-94 V-0, which means that the material will extinguish immediately upon ignition without any melting droplets.
Thirdly, it has strong processing adaptability. The initial decomposition temperature of Type II APP is ≥ 260 ℃, which is much higher than the processing temperature of common engineering plastics such as PP and PA, ensuring stability and non decomposition during injection molding and extrusion processes.
Fourthly, it has excellent smoke suppression properties. The smoke generated during combustion is minimal and does not cause secondary damage, making it particularly important in enclosed spaces such as subways and tunnels.
Compared with traditional flame retardants, the advantages of the APP are clear at a glance. Compared to halogenated flame retardants, it is more environmentally friendly; Compared with aluminum hydroxide (ATH), it has better flame retardant effect at the same addition amount, and the decomposition temperature of ATH is only about 180 ℃, which limits its application in high-temperature processing materials.
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