Synthesis of a cyclomatrix-type polyphosphazenes microspheres and its flame retardancy on polycarbonate

Abstract

A highly cyclomatrix-type poly(cyclotriphosphazene- co -4,4 ¢ -sulfonyldiphenol) microsphere (PZS) was successfully synthesized and applied to polycarbonate (PC) as a novel flame retardant. The PZS microspheres were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM). The thermal stability of PC/PZS composites were explored through thermogravimetric analysis (TG) and the flammability was studied by limiting oxygen index (LOI) tests and cone calorimetric tests (CONE). The TG results showed a high thermal stability and excellent carbonization ability. The corporation of PZS microspheres can significantly improve the performance of the flame retardancy of polycarbonate. With a 5 wt% addition of PZS microspheres, the LOI value was improved from 27.4 % to 31.5 %. The results of CONE tests showed that the heat release rates (HRR), total heat release (THR) and average mass loss rates (av-MLR) were all significantly reduced. Moreover, the ignition time ( t ign) was greatly extended. The char residue was investigated by SEM and FTIR and the results showed that phosphoric acid was produced in the process of combustion, which promotes the cross-linking and carbonization of the PC substrate, leading the formation of a compact carbon layer on the outer surface. The compacted carbon layer acts as a barrier to the transportation of heat and oxygen.