Posted on 28/05/2024 in Fire Safety 2024
Functionalised APP for different polymers

Ammonium polyphosphate is an effective, non-toxic PIN FR. Innovative coatings improve performance and compatibility.

Peil et al. encapsulated APP in cross-linked lignin (a bio-based polymer from plants) stabilised by polyglycerin polyricinoleate (PGCR, a food additive ). The encapsulated APP was tested as a PIN flame retardant in PLA foams (poly lactic acid, a bio-based plastic). Encapsulation improved dispersion in the polymer matrix, resulting in smaller foam cells and higher foam density. LOI (limiting oxygen index) increased from 21% to 24.5% (20% PIN FR) and UL 94 V-0 (3 mm) was achieved with only 9% PIN FR. The PIN FR foam could provide a bio-based and biodegradable material for lightweight packaging and construction applications.

Chu et al. review over sixty studies of application of APP in unsaturated polyester resins. Microencapsulation or surface modification are widely used to improve interfacing with the polyester matrix, so improving mechanical performance of the PIN FR resin, and to reduce water absorption by APP. Synergy with compounds used in the surface treatment of the APP can also enhance the smoke reduction effect of APP. In particular, nitrogen compounds (e.g. chitosan, imidazoles, amines) and silicon compounds (e.g. silanes) are cited. Studies of different synergists with APP are also reviewed, including metal oxides/hydroxides, phosphorus FRs, clays.

Zheng et al. review studies of differently functionalised APP in epoxy resins. Compounds combined with APP include metal compounds, which catalyse char production and suppress smoke release, and can also facilitate crosslinking of APP to the epoxy, in particular iron, copper, zirconium, cobalt compounds. Studies also show a range of organic molecules used to functionalise APP, enabling cross linking with epoxy and improving mechanical performance. These can include P or N, so also improving fire performance. Bio-based organic molecules are also reported. Studies of synergies with inorganics such as silicates or carbon nano-fillers are also noted.

“Encapsulation of Ammonium Polyphosphate in Lignin Nanocontainers Enhances Dispersion and Flame Retardancy in Polylactic Acid Foams”, S. Peil et al., ACS Appl. Polym. Mater. 2024,

“The application of ammonium polyphosphate in unsaturated polyester resins: A mini review”, T. Chu et al., Polymer Degradation and Stability 225 (2024) 110796

“Review. Recent advances in constructing new type of epoxy resin flame retardant system using ammonium polyphosphate”, P. Zheng et al., Safety Science and Resilience 5 (2024) 179–193,

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