The mineral and phosphorus PIN FRs hexaphenoxycyclotriphosphazene (HPCTP) and aluminium trihydroxide (ATH) were tested separately and in combination in epoxy resin, at loadings of 15% total PIN FR. ATH decreases the tensile strength of the resin, whereas HPCTP increases it, so that combinations can be used without deterioration of mechanical properties. Combinations of the two PIN FRs enabled increase in LOI from 21.5 (pure resin) to 27 – 28, decrease of up to 31% in total and peak heat release, and decrease in horizontal burning length of up to 30%. A combination of the two PIN FRs is effective in reducing total smoke release by around 10% and reduces release of toxic carbon monoxide (COP = CO production rate). The authors conclude that these effects are due to a combination of release of water vapour from the mineral PIN FR and formation of a char residue (solid phase action) by the phosphorus PIN FR.
“Synergistic Effect of Hexaphenoxycyclotriphosphazene and Aluminium Tri-Hydroxide on Flame Retardancy and Smoke Suppression of Epoxy Resin”, M. Dong, Aust. J. Chem. (CSIRO) 2018 https://doi.org/10.1071/CH17594