Chemical transformations resulting from pyrolysis and CO2 activation of Kevlar flocks

The chemical and structural transformations which result from the pyrolisis of Kevlar (poly[p-phenyleneterephthalamide]) fibres in argon, and from subsequent activations to differing levels of burn-off, under differing activation conditions in CO2, have been investigated using XPS, SEM and XRD. XPS indicates a marked decrease in surface oxygen after pyrolysis followed by the formation of oxygen functionalities at various levels depending upon the activation regime. Nitrogen levels appear relatively constant after pyrolysis indicating the condensation of stable aromatic nitrogen during pyrolysis. The corresponding oxygen and nitrogen chemistry obtained from chemical shift data is also discussed. SEM indicates that the lamellar structure of polyaramid is preserved after carbonization and activation which is consistent with the observations of other authors. XRD shows that the carbons produced are generally more ordered than those resulting from coal, other organic precursors and some ex-PAN fibres. (C) 1997 Elsevier Science Ltd.