Synergistic effect of a novel triazine charring agent and ammonium polyphosphate on the flame retardant properties of halogen-free flame retardant polypropylene composites

•A novel triazine charring agent was prepared, and the synergistic effect has been studied between APP and novel charring agent.•The novel IFR system presents excellent flame retardant properties and smoke suppression ability.•The flame retardant mechanism shows that it has high graphitization degree and good shield properties of the char layer.

A novel triazine charring agent poly(4,6-dichloro-N-butyl-1,3,5-triazin-2-amine-ethylenediamine) (CNCD-DA) was synthesized, which had good thermal stability and char-forming ability. The synergistic effects between ammonium polyphosphate (APP) and CNCD-DA on flame retardant properties and mechanism of polypropylene (PP) were investigated by the limited oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CCT), scanning electron microscopy (SEM), laser Raman spectroscopy analysis (LRS), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results illustrated when the mass ratio of APP to CNCD-DA was 3:1 with 30% loading, the intumescent flame retardant (IFR) showed the best synergistic effect with LOI value reaching 36.5%, and the IFR could greatly suppress the generation of the flame and smoke during combustion. The results from SEM, TGA, LRS and FTIR indicated that during the combustion IFR could form a continuous and intumescent char containing POP and POC crosslinking structures and polyaromatic structures, thus effectively retard the combustion of PP.