Synthesis of a Phosphorus/Nitrogen/Sulphur Containing Phosphazene Micro-Nanotube and Its Flame Retardancy on Epoxy Nanocomposite

A highly cross-linked poly (cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) nanotubes were synthesized via an in situ template method using cyclotriphosphazene (HCCP) and 4,4'-sulfonyldiphenol (BPS) as raw materials. PZS micro-nanotubes were applied on epoxy resin (EP) and the flame retarded mechanism was studied. The PZS micro-nanotubes were characterized by SEM, TEM, EDS and element Mapping. The thermalstability of PZS/EP nanocomposites were explored through TG, as compared to that of EP, and the flammability was investigated by microscale combustion calorimeter (MCC) and limit oxygen index (LOI) tests. The TGA results showed that a decreased initial degradation temperature, the residue chars were greatly improved. The flame retardancy was significantly enhanced by the addition of PZS micro-nanotubes. The residue char was improved 46% and the heat release rate was reduced 40% under addition of PZS micronanotubes (5%). The LOI value was also improved from 26.0% to 30.6%. The mechanical strength was also improved by the addition of PZS micro-nanotubes. The improvement of flame retardancy can be ascribed to the good dispersion and the formation of graphene-like structure during combustion of PZS/EP nanocomposites. In conclusion, PZS micro-nanotube is a kind of excellent flame retardant with potential application value.