Researchers produced and tested in polypropylene a new PIN flame retardant, combining in one molecule phosphorus, nitrogen (in melamine) and mineral kaolin. Designated MPPK (melamine salt of pentaerythritol phosphate with kaolin) the substance was synthesised in three steps: pentaerythritol (a simple molecule with 5 carbons and four OH groups) was reacted with phosphoric acid, then with kaolin, then with melamine dispersed in methanol. The MPPK was tested at 15 – 25% loading in polypropylene, and compared to neat polymer, 25% kaolin and 25% melamine phosphate. MPPK showed to improve thermal stability of polypropylene at high temperatures, enabled to achieve UL94-V0 (2mm) at 20% loading (similar to melamine phosphate) and reduced peak heat release rate and total heat release rate by c. 80% (compared to neat polymer). MPPK resulted in cellular and coherent char production and resulted in the inner half of the sample not burning in cone calorimeter test. The authors conclude that this molecule is an effective flame retardant for polypropylene, more so than melamine phosphate.
“Manufacturing, thermal stability, and flammability properties of polypropylene containing new single molecule intumescent flame retardant”, A. Abdelkhalik, G. Makhlouf, M. Hassan, Polym Adv Technol. 2019;30:1403–1414 https://doi.org/10.1002/pat.4573