Many monomers in PP halogen-free flame retardants, such as ammonium polyphosphate, aluminum hypophosphite, and MPP, are raw materials for composite halogen-free flame retardants. pp halogen-free flame retardant LXF-C5800A is a general-purpose, environmentally friendly, and highly efficient composite P-N flame retardant. Inorganic salt monomers often absorb a large amount of heat generated during the combustion of PP, playing a role in delaying further combustion and reducing surface temperature. What is the endothermic effect mechanism of PP halogen-free flame retardants, and what is the essence of heat absorption?

Ammonium polyphosphate, zinc borate, magnesium hydroxide, aluminum hydroxide, borax, and other inorganic salts all contain a certain amount of water of crystallization and are common raw materials for halogen-free flame retardants. When these inorganic salts reach their decomposition temperature, they need to absorb a large amount of heat from the surrounding environment, lose their water of crystallization, and generate water vapor, thereby slowing down the heating rate of the polymer PP material. The flame-retardant effect of aluminum hydroxide also stems from its dehydration upon heating, generating a large amount of water vapor that absorbs heat from PP and lowers the surface temperature. Some phosphorus-nitrogen-based flame retardants do not rely on the endothermic effect of water of crystallization for flame retardancy, but primarily rely on the synergistic effect of phosphorus and nitrogen.

The endothermic effect mechanism of halogen-free PP flame retardants shows that the water of crystallization of inorganic salts is key to generating the flame-retardant endothermic effect. The relationship between the amount of water of crystallization and the endothermic and flame-retardant effects is complex and requires continuous exploration and summarization based on the characteristics of each product in the field of plastic flame retardancy. However, the moisture content of the flame retardant cannot be too high, especially since a high free water content has a significant negative impact on the flame-retardant effect. A reasonable water of crystallization content has a positive effect on improving flame-retardant efficiency.