Novel phosphorus nitrogen silicon PIN flame retardants were synthesised by a flexible sol-gel method, then applied by coating to polystyrene beads (0.7-1.1 mm) prior to expansion to form expanded polystyrene foam (EPS) boards.
The three FRs were poly-N-β-(aminoethyl)-γ-aminopropyltrimethoxysilanes (P-NMTS) and this polymer reacted with phosphoric or phosphorous acid. P-NTMS does not enable UL94 rating whereas phosphorus P-NMTS achieves UL94-V0 at 40% loading with LOI increased from 17% (neat EPS) to 27%. The authors conclude that phosphorus-P-NTMS, a phosphorus nitrogen silicon PIN FR can considerably improve fire safety of polystyrene foam by increasing char production (up to 49% residue).
“Highly Flame Retardant Expanded Polystyrene Foams from Phosphorus−Nitrogen−Silicon Synergistic Adhesives”, Z-M. Zhu et al., Ind. Eng. Chem. Res. (I&EC), 2017, 56 (16), pp 4649–4658 http://dx.doi.org/10.1021/acs.iecr.6b05065