Enhanced dispersibility and uniform distribution of iron phosphonate to intensify its synergistic effect on polypropylene-based intumescent flame-retardant system

Good dispersion and distributed nanoscaled synergists are expected to greatly enhance the performance of flame retardants. Here, a new type of iron organic-phosphonate (FeP) nanoparticles was synthesized and utilized as the synergist for polypropylene-based intumescent flame-retardant system (IFR/PP). To improve the dispersion of the FeP in the IFR/PP system, a master-batch method was used to achieve separation between the FeP particles, which included hydrogen bonding with ammonium polyphosphate (APP). To improve its compatibility with PP, the hybrid synergist FeP@APP@CS was produced by electrostatic interaction with chitosan (CS). The results showed that the FeP@APP@CS nanoparticles were homogeneously dispersed in the PP matrix and selectively located on the IFR particles, achieving compatibility between the PP and IFR. The FeP@APP@CS/IFR/PP system exhibited an enhanced limiting oxygen index (LOI) of up to 28.5%, and achieved an improved vertical burning rating of V-0 (UL-94), compared to the IFR/PP system. The improved flame-retardant properties, even at low levels of IFR loading, were attributed to the homogeneous dispersion of the FeP@APP@CS throughout the IFR system and the fine synergistic effect between the FeP@APP@CS and IFR.