Effective smoke suppression and flame retardancy for epoxy with “eco-friendly” phosphorus – nitrogen PIN FR. A commercially available phosphonate (titrilotriemthylene triphosphonic acid ATMPA) was reacted in water with piperazine to produce a polymeric n- P salt (poly-amino trimethylene phosphonic acid piperazine salt PTPAP). This was then tested at 0 – 8 % loading in epoxy resin. UL 94 V-0 (3.2 mm) was achieved at 6% PTPAP with no dripping and LOI increased to 28 from 21 (neat epoxy). At 6% PTPAP, total smoke production (TSP, m2/kg) was reduced to 20 from 29 (neat epoxy). Analysis suggests that the FR and smoke suppression effects result from early degradation and charring of the epoxy and generation of intumescent and sealed char, as well as release of PO- which traps radicals in fire gases and inert gases which dilute fire gases. The authors consider that the synthesis of PTPAP is “eco-friendly”. See also in pinfa Newsletter n°129 a biobased N-P FR synthesised from piperazine and phytic acid, but which required 15% loading in epoxy to achieve UL 94 V-0 (3 mm).
“Eco-friendly phosphonic acid piperazine salt toward high-efficiency smoke suppression and flame retardancy for epoxy resins”, X. Xu et al., Journal of Materials Science volume 56, pages16999–17010 (2021) https://doi.org/10.1007/s10853-021-06384-1