DOPO itself has been shown to be an effective PIN flame retardant for the bio-sourced polymer PLA (poly lactic acid), achieving UL94-V0 at 3 mm and LOI (limiting oxygen index) of 35% (increased from 20% for pure PLA) with 5% DOPO loading (Jiang 2015).
In this study, three different bridged DOPO derivatives were synthesised by reacting DOPO with phosphorus oxychloride (the chlorine is the carrier for the phosphorus, not included into the final product), resulting in DOPO molecules linked by carbon-carbon bonds and with increased phosphorus contents. These bridged DOPOs, at 10% loading, achieved UL94-V0 @ 3.2mm in PLA, peak heat release rate was reduced by 10-30% and dripping was inhibited. Analysis showed that the bridged DOPOs act both in the gaseous phase and by generating char in which cross linking is made with PLA molecules. The bridged DOPOs also improve the thermal stability of PLA.
“Effects of bridged DOPO derivatives on the thermal stability and flame retardant properties of poly(lactic acid)”, L. Long et al., Polymer Degradation and Stability 2017, http://dx.doi.org/10.1016/j.polymdegradstab.2017.03.016 See Xie et al., pinfa Newsletter n°79