The flame retardancy and pyrolysis mechanism of polyimide fibers investigated by cone calorimeter and pyrolysis–gas chromatography–mass spectrometry

In the present research, the flame retardancy and pyrolysis mechanism of polyimide fibers were investigated by cone calorimeter, scanning electron microscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and pyrolysis–gas chromatography–mass spectrometry. As it turned out, the polyimide fibers possessed excellent thermal stability and flame retardancy. The onset thermal degradation temperature ( T _{onset 10%} ) of polyimide was 587℃ and 610℃ at nitrogen and air atmospheres, respectively. The polyimide fibers cannot be ignited at the heat flux of 35 and 50 kW/m ² , while they can be ignited at the heat flux of 75 kW/m ² with the time to ignition of 33 s and peak heat release rate of 53.4 kW/m ² . Moreover, the flame retardancy of woven and knitted fabrics was also discussed, which demonstrated that knitted fabric was easier to become thermally thick than woven fabric. Scanning electron microscopy analysis of the residual chars of fibers showed that the shape of fiber can be maintained irrespective of heat flux, but the chemical structure of the fiber was destroyed at the heat flux of 75 kW/m ² . The pyrolysis combustible volatiles at 700℃ include benzonitrile, aniline, and phenol, which can interpret the ignition of polyimide fibers. The results obtained in the present research revealed the flame retardancy and pyrolysis mechanism of polyimide fibers, which can guide its application and further modification.