Using TG-FTIR and XPS to understand thermal degradation and flame-retardant mechanism of flexible poly(vinyl chloride) filled with metallic ferrites

The effect of three metallic ferrites, LaFeO3, ZnFe2O4, and BiFeO3, on the thermal degradation and flame retardancy of flexible poly(vinyl chloride) (PVC) was investigated using thermogravimetric analysis (TG), differential thermal analysis, and TG coupled with Fourier transform infrared spectrometry. In combination with X-ray photoelectron spectroscopy techniques, the charring and flame-retardant mechanism has been obtained. The results show that compared with LaFeO3 and ZnFe2O4, BiFeO3 promoted the dehydrochlorination reaction of PVC more effectively and generated a large amount of stable char residue in a condensed phase. In the char residue of PVC/BiFeO3, the Fe2p spectra are assigned to FeCl2 and FeOCl, which acts as effective catalysts for the ionic dehydrochlorination of PVC owing to their strong Lewis acidity. Bi exists as BiOCl, which has a lower melting point and boiling point and can more easily decompose to form BiCl3 gas at the flame temperature. The results demonstrated that BiFeO3 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.