Porosity development in chars from thermal degradation of poly(p-phenylene benzobisoxazole)

The main objective of this work was to investigate porosity development in carbonaceous materials formed by thermal degradation of the high thermal stability polymer, poly(p-phenylene benzobisoxazole) (PBO). Two varieties of PBO, as-spun (AS) and high-modulus (HM) were studied. Chars obtained at various polymer decomposition temperatures (selected on the basis of thermogravimetric and differential thermal analysis results) were characterized by elemental analysis, infrared spectroscopy, X-ray diffraction and CO₂ adsorption at 273 K. The obtained adsorbents essentially contained narrow micropores, and maximum pore development took place at ca. 1000 K, when the polymer was not yet completely decomposed. At higher temperatures, there is a certain pore widening along with a displacement towards smaller pore sizes, and the pore volume significantly decreases.