Synthesis Of Metallic Ferrites（ZnFe₂04_、BiFe0₃、LaFe0₃）And Their Flame-retarding Application On Poly（vinyl Chloride） And Polypropylene

Fire hazard is one of the most serious disaster that influences the society development and our personal safety. Therefore, the investigation of combustion behavior and its mechnism have attracted the attention of researchers. Currently, several kinds of flame retardants, such as halogenate, phosphorus-nitrogen intumescent, antimonide, metal hydroxide, stannate and metallic ferrites have been used to control the flammability of polymer. In this article, three metallic ferrites, lanthanum ferrite(La Fe O3), zinc ferrite(Zn Fe2O4) and bismuth ferrite(Bi Fe O3) were successfully synthesized and used as flame retardants and smoke suppressants for flexible poly(vinyl chloride)(PVC). The limiting oxygen index(LOI), smoke density rating(SDR) and cone calorimeter tests indicated that Bi Fe O3 is an excellent flame retardant and smoke suppressant for flexible PVC. Then Bi Fe O3 was used in polypropylene(PP) with intumescent flame retardant(IFR). The effect of Bi Fe O3 on the char formation, thermal behavior and burning process of PP was investigated. More details are as follows:Firstly, La Fe O3 was synthesized by a coprecipitation method, Zn Fe2O4 was prepared by wet air oxidation and Bi Fe O3 was synthesized via hydrothermal route. The optimal synthesis conditions of Bi Fe O3 and La Fe O3 was discussed. The products were characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM).Secondly, La Fe O3, Zn Fe2O4 and Bi Fe O3 were used as flame retardants and smoke suppressants for flexible PVC. The LOI, SDR and cone calorimeter tests indicate that Bi Fe O3 is an excellent flame retardant and smoke suppressant for flexible PVC. Thermogravimetric analysis(TG), differential thermal analysis(DTG) and TGA coupled with fourier transform infrared spectrometry(TG-FTIR) showed that Bi Fe O3 promoted the dehydrochlorination reaction of PVC effectively and generated a large amount of stable char residue in a condensed phase. The morphology and composition of the char residue of PVC/ferrite composites were characterized by SEM, laser raman spectra(LRS) and X-ray photoelectron spectroscopy(XPS). The results demonstrated that Bi Fe O3 can not only effectively inhibit the production of smoke from PVC during combustion but it also has an effect similar to that of Sb2O3 in flame-retardant PVC.Thirdly, the Bi Fe O3 was used in PP with the synergist of intumescent flame retardant system(IFR). IFR is composed with ammonium polyphosphate(APP) and pentaerythritol(PER). The LOI, UL-94 tests showed that there is an optimal loading for Bi Fe O3 with APP/PER synergistic flame retardant PP. TG-DTG of PP/APP/PER/Bi Fe O3 showed that the moderate of Bi Fe O3 can reduce the rate of decomposition at high temperatures, and retained more carbon in the condensed phase. TG-DTG of APP/PER/Bi Fe O3 showed that the third mass loss stage of APP/PER was affected by Bi Fe O3. The morphology and composition of the char residue of APP/PER/Bi Fe O3 composites were characterized by SEM, XRD, XPS and LRS. An appropriate amount of Bi Fe O3 can react with APP/PER and form P-O-Bi and P-O-Fe bond, so that more P elements involved in a crosslinking reaction to form carbon. The formation of more expansive char can increase the flame retardancy.