Synergistic effect between a novel triazine charring agent and ammonium polyphosphate on flame retardancy and thermal behavior of polypropylene

A novel oligomeric charring agent (PTCA) containing triazine and diphenyl group was synthesized by cyanuric trichloride, diphenylamine and ethylenediamine through nucleophilic reaction. The structure and thermal stability of PTCA were characterized by Fourier transform infrared spectrometry (FT-IR), element analysis testing and thermogravimetric analysis (TGA). The effectiveness of the novel intumescent flame retardant system (ammonium polyphosphate and PTCA, abbrev. IFRs) on fire retardancy and thermal stability of polypropylene (PP) was investigated through UL-94, limiting oxygen index (LOI) tests, cone calorimeter tests and thermogravimetric analysis (TGA). UL-94 vertical burning test revealed that the addition of 20 wt% IFRs into neat PP was enough to reach V-0 rating. LOI value of PP by addition of 20 wt% IFRs rose from 17.5 to 31 vol%. Moreover, a remarkable decrease in peak heat release rate (PHRR: −90%), total heat release (THR: −54%) and total smoke release (TSR: −51%) was revealed when the loading of IFRs was 20 wt%. TGA results showed that PTCA presented good char formation ability, and it would greatly increase the thermal stability of PP when combined with APP. The Fourier transformed infrared spectra (FTIR) revealed that the flame retardant mechanism might be ascribed to aromatic and phosphoric char formed during combustion. Additionally, the structure and morphology of char residues were further studied by SEM and Raman spectra.