DENITROGENATION BEHAVIOR AND TENSILE-STRENGTH INCREASE DURING CARBONIZATION OF STABILIZED PAN FIBERS

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