Research review shows that synergies between PIN FRs in polypropylene can combine fire safety and material performance.
Seidi, Vahabi et al. assessed data on fire performance of flame retardant propylene formulations from some 150 publications, considering PIN FRs only. For each data point (formulation), the FR or FR combination, and loading are specified, and test results are indicated (as available) for time to ignition (TTI), peak heat release rate (pHRR), total heat release -THR), irradiance, LOI, sample thickness and UL-94 result. Where sufficient data is available, the dimensionless “Flame Retardancy Index” (FRI) is derived (as defined in Vahabi et al. 2019, see pinfa Newsletter n°111, combing TTI, THR, pHRR).
The authors conclude that phosphorus PIN FRs generally achieve Good FRI, and some specific phosphorus compounds achieve Excellent. Two nitrogen-phosphorus PIN FRs also achieve Excellent. Mineral and bio-based PIN FRs can also achieve Good FRI, depending on particle size and dispersion for minerals.
Combinations of PIN FRs show the best FRI, with many combinations achieving Excellent at intermediate loadings (25-30% w/w). PIN FRs generally also achieve UL94-V0.
Analysis of data showed that combining PIN FRs increased effectiveness for the same dose, compared to use of a single FR, showing the interest of synergy effects in enabling fire performance whilst limiting impact on material mechanical performance.
“Flame Retardant Polypropylenes: A Review”, F. Seidi, H. Vahabi et al., Polymers 2020, 12, 1701; https://dx.doi.org/10.3390/polym12081701