Ammonium polyphosphate is an inorganic polymer of repeating phosphate units neutralised with ammonium, and it serves as an acid source in intumescent flame-retardant systems. On heating it releases ammonia and phosphoric acid, which esterifies the hydroxyl groups of the charring component and promotes dehydration and char formation [1]. Its efficiency depends strongly on the degree of polymerisation: a long chain is less water-soluble and is therefore retained in the material during processing and service [2]. In a polyolefin it is combined with a carbon source and a blowing agent, because the polymer itself does not char readily [3]. Surface treatment with a silane or with a microencapsulated coating reduces the moisture uptake and improves the compatibility with a non-polar matrix [4]. The water solubility of the short-chain grades remains the main limitation, and the additive also lowers the mechanical properties at the loading needed for a rating [5].
- intumescence
- acid source
- char formation
- degree of polymerization
- microencapsulation
- synergist
- water solubility
Flame retardant materials and properties·Polymers and Plastics·Materials Science·Physical Sciences
References
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- Pan, Y.; Luo, Z.; Wang, B. Synergistic flame retardant effect of piperazine salt and ammonium polyphosphate as intumescent flame retardant system for polypropylene. Journal of Applied Polymer Science 2021, 138, 49813. [CrossRef]
- Xu, F.; Yin, N.; Gao, S.; Shen, C. The Synergistic Effect of Ammonium Polyphosphate and a N/P/Si‐Containing Intumescent Flame Retardant on the Flame‐Retardant Properties of Polylactic Acid. Journal of Applied Polymer Science 2025, 142, e56830. [CrossRef]
- Wu, X.; Qin, Z.; Zhang, X.; Yu, Z.; Zhang, W.; Yang, R.; Li, D. Micro-Nanometer Particle Composition and Functional Design of Surface Nano-Structured Ammonium Polyphosphate and Its Application in Intumescent Flame-Retardant Polypropylene. Nanomaterials 2022, 12, 606. [CrossRef]
- Zhang, X.; Tang, S.; Quan, N.; Gao, M. Effect of seaweed extract as a novel bio-filler on the intumescent flame retardant epoxy resin with ammonium polyphosphate. Materials Today Communications 2025, 48, 113356. [CrossRef]