Biphasic Free‐Radical Synergistic Strategy Induced by Combining Fullerene and Hindered Amine for Intumescent Flame‐Retardant Polypropylene

ABSTRACT Free‐radical scavengers (FRSs) can influence the combustion behavior and flame retardancy of polymers by quenching free radicals. To explore the influences of FRSs on the combustion behavior and flame‐retardant performance of polymers, in this paper, fullerene (C 60 ) was selected as the condensed‐phase FRS and hindered amines (NOR) as the gaseous‐phase FRS, and they were applied in flame‐retardant polypropylene (PP). Thermogravimetric analysis (TGA), vertical burning, limiting oxygen index (LOI), and cone calorimetry tests were used to characterize the thermal stability and flame‐retardant performance. The combination of C 60 and NOR increased the LOI of flame‐retardant PP to 30.5%, the vertical combustion test reached the V‐1 rating, and the peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) all decreased. Morphology, composition, and structure of the carbon layer were characterized by scanning electron microscope (SEM) and x‐ray photoelectron spectroscopy (XPS). Thermogravimetric infrared spectroscopy coupling analysis (TG‐FTIR) and pyrolysis gas chromatography–mass spectrometry (Py‐GC/MS) were used to monitor the gas‐phase products. It was found that the biphasic free‐radical synergistic effect of C 60 and NOR promoted the formation of a high‐quality carbon layer, thereby enabling flame‐retardant PP to exhibit the optimal fire safety performance, which not only reduced the possibility of comprehensive combustion of flame‐retardant PP but also minimized the risk of fire spread.