Effect of Phosphoric Acid on Chemical Transformations during Nomex Pyrolysis

The thermal degradation of Nomex [poly(m-phenylene Sisophthalamide)] impregnated with phosphoric acid has been investigated by the analysis of the corresponding pyrolysis products, which were fractionated into gases, liquids, and char. Gas chromatography (GC) and\or gas chromatography\mass spectrometry (GC\MS) were used to study the volatiles evolved whereas the solid residue was examined by elemental analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). For the sake of comparison, a parallel study of unimpregnated Nomex was carried out in the same conditions. The main product of unimpregnated Nomex degradation in the conditions of this work was found to be m-benzenediamine, which is the result of a heterolytic process. Aromatic nitriles are also produced through homolytic reactions. Most of the products of impregnated Nomex degradation were also detected with its unimpregnated counterpart, except for isophthalic acid, carbon monoxide, and elemental phosphorus. Aromatic nitriles are the preeminent products from pyrolysis of unimpregnated Nomex, there being no trace of m-benzenediamine. Reaction mechanisms for impregnated Nomex degradation consistent with these findings are proposed, including a nonhomolytic process for the formation of nitriles in the presence of phosphoric acid.