Atomic force microscopy and infrared spectroscopy studies of the thermal degradation of Nomex aramid fibers

In the present work, the thermal transformations of Nomex [poly(m-phenylene isophthalamide)] fibers have been investigated up to a temperature of 1173 K. The main stages of the pyrolytic degradation of the fibers were determined by thermal analysis, and their chemical and morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) measurements, respectively. The degradation starts with the cleaving of hydrogen bonds at approximately 633 K, which leads to a disordering of the polyaramide chains on the nanometer scale. The next decomposition step takes place between 673 and 873 K with the disruption of the amide bonds, the subsequent breaking of the polyaramide chains into smaller units, and their condensation into large polyaromatic compounds. From 873 K onward, the reaction progresses by the dehydrogenation of the polyaromatic structures and their arrangement into graphite-like assemblies, resulting in the final fibrous carbon which is obtained at 1173 K.