The investigation of intumescent flame-retarded polypropylene using poly(hexamethylene terephthalamide) as carbonization agent

A novel intumescent flame retardant, containing ammonium polyphosphate (APP), and poly(hexamethylene terephthalamide) (PA6T), was prepared for flame retarding polypropylene (PP). The flame retardation of the PP composites was characterized by limiting oxygen index (LOI). The thermal degradation of the composites was investigated by means of thermogravimetric analysis (TG) and TG coupled with Fourier transform infrared spectroscopy (TG-FTIR). The morphology of the char obtained after combustion of the composites was studied by scanning electron microscopy. It has been found the intumescent flame retardant showed good flame retardancy, with the LOI value of the PA6T/APP/PP (5/25/70) system increasing from 17.5 to 32. Meanwhile, the TG and TG-FTIR work indicated that PA6T could be effective as a carbonization agent and there was a synergistic reaction between PA6T and APP, which effectively promoted the char formation of the PP composites. Moreover, it was revealed that uniform and compact intumescent char layer was formed after combustion of the intumescent flame retarded PP composites.