Studies on pyrolysis of Nomex polyaramid fibers

Abstract

The pyrolysis behavior of Nomex [poly( m-phenylene isophtalamide)] fibers under argon was studied using thermoanalytical and infrared spectroscopic methods to get direct information on the progressive changes undergone by the solid material and its carbon fiber residues. Simultaneous thermogravimetry (TG)–differential thermal analysis (DTA) measurements were carried out in a thermobalance in order to establish the different steps in the thermal degradation of Nomex. Samples pyrolyzed to various carefully controlled extents were prepared in the same thermobalance by heating under the same conditions to different temperatures selected as a function of the TG/DTA results. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) spectra of all samples were obtained in order to follow changes in chemical composition along the pyrolysis process. Rupture of hydrogen bonds takes place in the 300–400°C interval, being followed by a complex thermal event involving two weight loss steps and three endothermal DTA peaks. An intermediate aryl nitrile forms from heterolytic decomposition of Nomex above 433°C and decomposes totally at 698°C. From 473°C onwards, the DRIFTS spectra evidence a drop in intensity of amide bands in parallel with increases in primary amine and carbonyl groups. Total disappearance of amide bands (607°C) is followed by a DTA exotherm at 627°C attributed to condensation reactions. Accordingly, CC skeletal vibrations in polyaromatic networks develop confirming the occurrence of a progressive loss of heteroatoms and an increase in aromaticity.