A phosphorus – nitrogen PIN flame retardant was developed for PA6 providing gas phase fire performance and anti-drip. ‘CBPB’ was synthesised by reacting p-Cyanobenzaldehyde (CBAD with 2-aminobenzimidazole (2-AB), then with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10- oxide (DOPO). CBPB offered improved thermal stability compared to DOPO and a melt processing temperature (Tp) close to that of PA6. 8% loading of CBPB reduced peak heat release rate of PA6 by nearly 20% and increased LOI by nearly 50%, enabling UL 94 V-0 (3 mm) and self-extinguishing (in 4s), nearly no drips for extruded PA6 fibres. Smoke release was however increased, indicating that the FR effect was in the gas phase. The anti-drip effect is considered to be by cross-linking by trimerization of nitrile groups at c. 290°C, that is lower than the initial degradation temperature (T5%) of PA6 which is c. 350°C.
“A phosphorus-containing flame retardant with thermal feature suitable for polyamide 6 and its filaments with enhanced anti-dripping performance”, Y. Sun et al., Polymer Degradation and Stability 200 (2022) 109936 https://doi.org/10.1016/j.polymdegradstab.2022.109936