In this article, the laboratory-made poly(p-ethylene terephthalamide) (PETA) was used as a novel charring agent; it was characterized by Fourier transform infrared spectroscopy and 1H NMR. PETA combined with ammonium polyphosphate (APP) to prepare the intumescent flame retardant (IFR), which was applied in polypropylene (PP). The flame retardancy of IFR on PP was investigated by the limiting oxygen index (LOI), the UL-94 (vertical flame) test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that the LOI value of the IFR-PP (30/70) system reached the highest 35%, and the system passed V-0 rating, when the weight ratio of PETA to APP was 1 : 3. The TGA data indicated that the charring ability of PETA was relatively poor with 18.0 wt % char residue at 800 degrees C. However, the residual weight of the IFR was promoted with 28.1 wt % at 800 degrees C, while it was 22.8 wt % based on calculation. The SEM showed that the intumescent and dense charring layer was formed after the combustion of the IFR-PP(30/70) system. In addition, the thermal degradation mechanism of PETA and IFR was studied by thermogravimetry-Fourier transform infraredspectroscopy and IR, and it demonstrated that the reaction between APP and PETA was happened and the P?O?C structure was got. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013