Study of the thermal decomposition and flame-retardant mechanism of sulfonated polyoxadiazole fibers

Various proportions of 4,4′-oxybisbenzoic acid (OBBA) were incorporated to obtain the spinning solution of sulfonated polyoxadiazole (SPOD) copolymer through copolymerization in oleum. And the sulfonated fibers were prepared from the solution by using wet spinning approaches. The chemical structures of the fibers were characterized using Fourier transform infrared spectroscopy (FTIR) and elemental analyzer. The results indicated that sulfo groups were successfully introduced into the macromolecular chain. And the flame retardancy of the SPOD fibers was evaluated by limiting oxygen index, UL-94 and microscale combustion calorimeter tests, showing that flame-retardant properties could be significantly enhanced. And the thermal decomposition and flame-retardant mechanism were studied through various analytical methods. And thermogravimetric (TG) analyzer and scanning electron microscope results showed that the incorporation of OBBA would help fibers form more compact carbon residue. X-ray photoelectron spectroscopy and TG-FTIR results revealed that sulfur element increased carbon residue rate in the condensed phase and some converted into SO₂ in the gas phase. Py-GC/MS results showed that thermal decomposition happened at oxadiazole rings and the introduction of OBBA did not alter the decomposition mechanism of POD essentially.