Gas and solid phase phosphonate FR action
Analysis of P and PO from three different phosphonate FRs neat and on cotton shows gas and solid phase FR behaviours. The phosphonate PIN FRs tested were a classical phosphonate TRI/DPTS*, a triazine derivative 2DTA** (electron-rich) and a carbamoylphosphonate ID*** (electron-poor). Analysis combined standardised fire testing with thermal analysis, molecular beam mass spectrometry and characterisation of evolved gases and residues, under both pyrolytic and oxidative conditions. Volatilisation of P-containing gases, release of PO radicals and char formation varied between the different phosphonates tested between neat FR and FR treated cotton. Conclusions suggest that the electron-rich 2DTA generated significantly more PO radicals (gas phase fire protection effect) under all conditions, whereas TRI/DPTS generated more HOPO2, and PO formation was inversely correlated release of phosphorus containing gases, and so to char generation (solid phase fire protection effect). At temperatures below 500°C PO / HOPO2 formation from coated cotton can involve condensed-phase and interface processes rather than being related to phosphorus volatisation.
* TRI/DPTS = 1:3 rimethoxysilyl)propyl]diethylenetriamine : Diethylphosphatoethyltriethoxysilane.
** 2DTA = a synthesised triazine derivative described in the paper’s supplementary material.
*** ID = a carbamoylphosphonate synthetised from 3-Isocyanatepropyltriethoxysilane and diethyl phosphite.
See also “Phosphorus FR radical FR mechanism” in pinfa Newsletter n°180.
“In situ elucidation of PO radical formation pathways in phosphonate flame retardants with different P–C linkage motifs”, R. Otto et al., Polymer Degradation and Stability (in print) https://doi.org/10.1016/j.polymdegradstab.2026.112440
