Flame retardancy, thermal properties, and combustion behaviors of intumescent flame‐retardant polypropylene containing (poly) piperazine pyrophosphate and melamine polyphosphate

A (poly) piperazine pyrophosphate (PIPP) was synthesized and its chemical structure was confirmed via Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and 31P nuclear magnetic resonance. PIPP was used together with melamine polyphosphate (MPP) as an ammonium polyphosphate (APP)‐free intumescent flame retardant (IFR) to prepare several flame‐retardant polypropylene (FRPP) composites. The flame retardancy and burning behaviors of the composites were investigated via limiting oxygen index (LOI) determination, vertical burning tests (UL‐94), and cone calorimeter tests. The thermal properties were investigated by means of thermogravimetric analysis under nitrogen and air atmosphere. Use of PIPP and MPP together yielded an increase in the LOI value, a UL‐94 V‐0 rating, and a decrease in both the values of PHRR and THR in cone calorimetric analysis. Visual observations and scanning electronic microscopy confirmed the occurrence of char formation, which acted as a heat and fire barrier in the condense phase.