Phosphorus PIN FRs tested in carbon-fibre reinforced epoxy reduced generation of respirable fibres in fire tests. Samples were produced using epoxy resin* and carbon fibre fabric, with 0 – 15% loading of three different phosphorus PIN FRs** and also a combination of silicon dioxide nanoparticles with these. All three P-FRs showed flame retardant effectiveness, e.g. reducing MARHE*** from 242 to 194 – 230 (at 10% loadings), with the phosphazene and the phosphate showing the higher flame retardant efficiencies and acting respectively in the gas and condensed phases. All three P-FRs were effective in reducing levels of carbon fibres on the sample surface and also led to nearly two times higher average fibre diameter after testing (i.e. lower levels of respirable fibres), with the phosphate PIN FR showing the greatest effect against respirable fibres.
* tetraglycidyl methylene dianiline and aromatic aminic hardeners.
** an oligomeric bis(phenoxy)phosphazene, a condensed adduct of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and salicylaldehyde [i.e. a phosphinate], an oligomeric resorcinol bis(diphenyl phosphate).
*** MARHE = maximum average rate of heat emission.
“Prevention of the formation of respirable fibers in carbon fiber reinforced epoxy resins during combustion by phosphorus or silicon containing flame retardants”, L. Greiner et al., Polymer Degradation and Stability 185 (2021) 109497 https://doi.org/10.1016/j.polymdegradstab.2021.109497