Several leading materials fire scientists have proposed a dimensionless “Flame Retardance Index” for flame retarded (compounds), based on cone calorimetry data: pHRR (peak heat release rate), THR (total heat release) and TTI (time to ignition). Each of these reflects a different aspect of fire performance. This is an extension of the “Fire Performance Index” proposed by M. Hirschler in 2017. The key paper (1) defining the index is based on over 100 data points from around 20 publications, covering four thermoplastic polymers (PP, PMMA, EVA, PLA) either neat or with known and specified loadings of different PIN flame retardants. A second paper (2) assess nearly 900 data points from over 100 publications, covering these and other polymers, including epoxies, again neat or with flame retardants (in all cases PIN FRs). The “Flame Retardancy Index” proposed is calculated as THR x PHRR / TTI for [ neat polymer / polymer with FR ]. This Index, on a logarithmic scale, show to effectively differentiate compounds into three groups defined as Poor, Good and Excellent. The Index was then used (3) to model, then test, optimal combinations of phosphorus and mineral PIN FRs for EVA after compression molding (APP ammonium polyphosphate, CC calcium carbonate and ethylene vinyl acetate copolymer, respectively). The best Flame Retardancy Index was achieved with 15% APP + 5% CC, with limited reduction in mechanical properties, considered to be the result of synergy between the two PIN FRs in char formation, and optimisation of reduction of TTI by APP and reduction in total heat release by the mineral FR.
(1) “Flame Retardancy Index for Thermoplastic Composites”, H. Vahabi B. Kandola M. Reza Saeb, Polymers 2019, 11, 407; https://doi.org/10.3390/polym11030407
(2) “Flame Retardant Epoxy Composites on the Road of Innovation: An Analysis with Flame Retardancy Index for Future Development”, E. Movahedifar et al., Molecules 2019, 24, 3964; https://doi.org/10.3390/molecules24213964
(3) “Description of complementary actions of mineral and organic additives in thermoplastic polymer composites by Flame Retardancy Index”, H. Vahabi, F. Laoutid et al., Flame Retardancy Index. Polym Adv Technol. 2019; 30: 2056– 2066 https://doi.org/10.1002/pat.4638