Study proposes N-P flame retardant, derived from phenyl hypophosphite, achieving UL 94 V-0 (3.2 mm) in TPU (thermoplastic polyurethane). Phenyls hypophosphite was reacted with N, N’-bis(salicylidene)ethylenediamine, to produce a Schiff-base derivative (SMAE). At 4% loading in TPU, LOI (Limiting Oxygen Index) increased from 22 to 32% and UL 94 V-0 (3.2 mm) was achieved. Melt-dripping occurred but did not transit fire. Analysis showed that the SMAE generated phosphonic acid in heat, causing dense charring. SMAE also generated PO. radicals, inhibiting flame, and released inert gases (carbon dioxide and ammonia), diluting combustible gases. The authors conclude that the synthesised SMAE has good thermal stability and char forming capacity, making it an effective PIN flame retardant for TPU at low loadings.
“Highly effective flame retarded TPU introduced by a new phosphorus-containing Schiff base derivative at low addition”, F. Hao et al., J Polym Res 30, 313 (2023) https://doi.org/10.21203/rs.3.rs-2827935/v