Denitrogenation behavior and tensile strength increase during carbonization of stabilized pan fibers

Carbonization of stabilized PAN fibers was studied by focusing nitrogen using elemental analysis and XPS, in relation to mechanical properties. A difference in denitrogenation on the surface and in the bulk of the fibers was observed in a range of carbonization temperatures between 600 and 1000 degrees C, with denitrogenation on the surface occurring much earlier (600-800 degrees C) than in the bulk (> 800 degrees C). The chemical state of nitrogen seemed to be different between the surface and the core; more tertiary nitrogen (-N-) was present at the surface than in the core in a temperature range between 600 and 1000 degrees C. This difference might be responsible for the retardation in the tensile strength development of the fibers while increasing the HTT from 700 to 800 degrees C. (C) 1998 Elsevier Science Ltd. All rights reserved.