Synthesis of aliphatic-aromatic polyamide carbonized system with phosphoramide structure and study on its thermal degradation mechanism and flame retardancy in polypropylene system

A novel char-forming agent (PETAP) containing aliphatic-aromatic polyamide and phosphoramide structure was successfully prepared via the high-temperature and high-pressure solution reaction of terephthalic acid, ethylenediamine and phosphorous acid. Meanwhile, polypropylene (PP) composites were prepared by using different proportions of PP, ammonium polyphosphate (APP) and PETAP, and the total load of PETAP and APP was 30%. According to the results of limit oxygen index (LOI), vertical burning test (UL-94) and thermogravimetric analysis, PETAP/APP system can greatly improve the thermal stability and flame retardancy of PP. For the mass ratio of (9 mass%/21 mass%/70 mass%) APP/PETAP/PP sample (PP-4), the LOI value achieved the highest, which is 28.8%. It achieved the UL-94 V-0 rating. Then, the Fourier transform infrared spectroscopy analyzed the thermal degradation mechanism of PP composite's carbon residue at different temperatures, and the potential relationship between microstructure and flame retardancy was also evaluated and discussed. Moreover, the scanning electron microscopy of residual carbon showed that PETAP and APP were helpful to form denser char layer. This char layer has a compact structure which can effectively prevent heat transfer and plays an important role in flame retardant. Finally, the mechanical properties of PP composites were tested, which indicated the mechanical properties of PP composites have not changed much.

Automated summary

A novel char-forming agent PETAP was successfully prepared and significantly improved the flame retardancy of PP materials, as validated by a series of experiments. The study also discussed the relationship between the microstructure of PP composites and their flame retardant properties through various analysis methods.