THERMAL TRANSFORMATIONS OF KEVLAR ARAMID FIBERS DURING PYROLYSIS - INFRARED AND THERMAL-ANALYSIS STUDIES

The main objective of this work was to get some further insight into t he chemistry involved in the carbonization of aramid fibers. For this, the pyrolysis behavior of Kevlar [poly(p-phenylene terephthalamide)] fibers under argon was studied using thermoanalytical and FT-IR spectr oscopic methods to get direct information on the progressive changes u ndergone by the solid material and its carbon fiber residues. Variatio ns in concentration of major elements (C, H, N, S, and O) were also mo nitored as a function of pyrolysis temperature. Below 500-degrees-C on ly minor changes associated with loss of hydrogen bonds occur. Above 5 00-degrees-C the weight loss becomes significant. However, no noticeab le framework changes take place until about 545-degrees-C. Kevlar appe ars to be chemically stable up to this temperature. The main pyrolytic transformation occurs over a narrow temperature interval (550-575-deg rees-C) leading to the collapse of the initial framework, which procee ds mainly through the progressive decomposition of amide groups by C=O and C-N bond cleavage. Intermediate aryl nitrile products are formed during this process. Above 600-degrees-C depolymerization gives way to progressive aromatization/condensation reactions leading to polynucle ar aromatic compounds, the degree of condensation of the network incre asing with treatment temperature.