Thermal decomposition of poly(p-phenylene benzobisoxazole) fibres:: monitoring the chemical and nanostructural changes by Raman spectroscopy and scanning probe microscopy

Thermal decomposition of poly(p-phenylene benzobisoxazole) (PBO) in two different commercial varieties (as-spun and high-modulus) has been studied between room temperature and 1123 K. Thermogravimetry and differential thermal analysis allowed the main stages of the pyrolytic degradation of the material to be established. On the basis of these results, samples were treated at several controlled temperatures and characterized by elemental analysis, X-ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). X-ray diffraction measurements indicated that, at heat treatment temperatures below 933 K, the polymer retains its original conformation and even becomes stabilized by an enhancement of its crystallinity. The decomposition takes place in a single step and the main changes occur within a very narrow temperature interval (973-993 K), as shown by Raman spectroscopy and XRD. The final carbon fibre residue is rich in nitrogen and, as AFM showed, it retains a certain degree of anisotropy. The two studied varieties of PBO differed only in their behaviour before the beginning of thermal degradation. (C) 2004 Elsevier Ltd. All rights reserved.