Abstract
The flame retardant properties of the epoxy resin thermosets incorporated with hexa-phenoxyl- cyclophosphazene (HPCP) were investigated via limited oxygen index (LOI) and cone calorimeter. The results show that the LOI value increased, the peak of heat release rate (pk-HRR) and total heat release (THR) decreased, the time to ignition are shortened, the temperature of onset degradation are reduced and the pyrolysis velocity of HPCP/EP thermoset are accelerated compared with that of pure epoxy resin thermoset. The pyrolysis route and mechanism of HPCP and the epoxy resin thermoset were explored via analysis of the thermogravimetric analysis (TGA), the real time fourier transform infrared spectra (FTIR), TGA/infrared spectrometry (TGA-FTIR), X-ray photoelectron spectroscopy (XPS) and pyrolysis-gas chromatography mass/spectrometry (Py-GC/MS). The pyrolysis route of HPCP is that the phenoxyl fragments were dissociated from HPCP firstly, then carried on a disproportionation reaction and subsequently the cyclotriphosphazene and benzene ring from HPCP were pyrolyzed to some smaller fragments. Meanwhile, the flame-retardant epoxy resin thermoset was decomposed earlier under the existence of HPCP and the decomposed fragments interacted with the fragments from HPCP and then the more char was produced. Therefore, the phenoxyl free radical and its disproportionated products exert the gaseous-phase flame-retardant effect and the promotion on charring of matrix implies the condensed-phase flame-retardant effect.
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