No abstract

A nitrogen-, phosphorus-and chlorine-containing flame retardant, hexachlorocyclotriphosphazene (HCTP), has been covalently grafted onto the surface of multi-wall carbon nanotubes (MWNT) to obtain MWNT-HCTP. Polyamide 6 (PA6)/MWNT composites were then prepared via melt compounding. The flammability of PA6/MWNT composite was characterized by cone calorimetry, limiting oxygen index (LOI) and UL-94 tests. The results showed that peak heat release rate of samples containing 3 wt% MWNT-HCTP was only 460 kW/m 2 , which decreased by 35.2% compared with that of a neat PA6 sample. The LOI value was increased from 22.7% to 26.5%, and UL-94 test performance was also significantly improved by the presence of MWNT-HCTP. Scanning electron microscope (SEM) and optical microscope analysis showed that modified MWNT had a better dispersion and compatibility in PA6 than unmodified MWNT. The composition of residue chars and volatile products was investigated by SEM/energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric-FTIR, respectively. It was proposed that grafted HCTP was mainly functioned in the condensed phase, where P, N can synergistically promote char formation and Cl element can catch free radicals to terminate the chain reaction during combustion of the PA6 composite.