Studies on the thermal degradation of aromatic polyamides by pyrolysis‐field ionization mass spectrometry and pyrolysis‐gas chromatography

Abstract

Abstract The thermal degradation of aromatic polyamides such as poly&(1,4‐phenyleneterephthalamide) (Kevlar) and poly&(1, 3‐phenylene‐isophthalamide) (Nomex) was studied by pyrolysis‐field ionization mass spectrometry (Py‐FIMS) and pyrolysis‐gas chromatography (Py‐GC). In Py‐FIMS, the thermal degradation products were recorded which were formed in the ion source of a double focusing mass spectrometer. Usually a temperature range from 50 to 750°C and a heating rate of 1.2°C/s were employed. Various common and characteristic products for the two samples, respectively the corresponding para‐ or meta‐isomers, were observed up to m/z 500 with significant differences in intensity. The main products observed were produced by both radical homolytic and hydrolytic decompositions. On the other hand, in flash Py‐GC the instantaneous thermal degradation products at 720°C were gas‐chromatographically separated by a fused‐silica capillary column and detected both by a flame ionization detector and a mass spectrometer with electron ionization (EI). Although many of the degradation products were identical with those observed by Py‐FIMS, the former almost entirely consisted of the fragments formed through radical homolytic degradation. In general, the differences between the samples with Py‐GC were much less than those observed in Py‐FIMS.