The thermal degradation behaviors of polyp-phenylene-benzimidazole-terephthalamide (PBIA), poly-m-phenylene isophthalamide (PMIA) and poly-pphenylene terephthalamide (PPTA) fibers are investigated by thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy (TGA-FTIR). The results demonstrate that PBIA fiber exhibits better thermal-and thermo-oxidative stability than that of the other two polymers. PBIA shows the highest onset degradation temperature, both in nitrogen and air. TGA-FTIR provides information on compositions of pyrolyzates and their relationship with the structures of polyamides. Analysis of the compositions and distributions of all pyrolyzates, at different temperatures, indicates that a hydrolytic mechanism plays a leading role at lower temperature, and a homolytic mechanism is dominant at higher temperature.

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