Reaction of PIN flame retardants into polymers avoids risk of migration of the FR out of the product into the environment, enables an optimal distribution of the PIN FR throughout the polymer, can avoid polymer mechanical performance deterioration and has also been show for some phosphorus PIN FRs to improve the fire protection performance.
Tributyl(ethyl)phosphonium diethylphosphate (IL169), an ionic phosphorus-containing liquid, was shown to initiate anionic polymerisation and react into the resin of DGEBA (bisphenol-A-diglycidyl) epoxy resin, a polymer used in aircraft engineering applications. Resins were tested with 10 to 30% IL169 (1.5 – 3.7% phosphorus) showed no deterioration of resin thermal stability whilst significantly improving fire performance: peak heat release rate was reduced by nearly 75% and total heat release by c. 50%. Residue after burning was considerable (40% of initial weight) corresponding to formation of a fire-protecting layer of expanded char. The phosphorus content showed to also have a significant gas phase flame retardancy effect.
“Résines époxy intrinsèquement ignifuges à base de liquides ioniques phosphorés”, R. Sonnier et al., Polyflame n°11, December 2016 (in French) http://gcf-scf.lmops.univ-lorraine.fr/files/2017/01/PolyFlame-N%C2%B011.pdf