RATES OF ACTIVATION AND SCANNING ELECTRON-MICROSCOPY OF POLYARYLAMIDE-DERIVED CHARS

Fibrous activated carbons were prepared from Kevlar(R) (poly (p-phenyl ene terephthalamide)) and Nomex(R) (poly (m-phenylene isophthalamide)) by carbonisation in nitrogen and subsequent activation in steam of ca rbon dioxide to varying burn-offs at 1123 K. The resultant chars were characterised by activation rate studies, scanning electron microscopy and, in the case of the Nomex chars, energy dispersive X-ray analysis . It was found for both the polyarylamide-derived chars that significa nt differences existed between the chars activated in steam and carbon dioxide. Steam reacts much faster than carbon dioxide with these char s at elevated temperatures. This may be due to its smaller molecular s ize, resulting in an increase in diffusion and accessibility in and ou t of the constricted char structure, its higher intrinsic reactivity, or to specific reactions with metallic residues. The catalytic activit y of metallic residues, rather than the crystallinity differences betw een the two polymers, is the suggested reason why Kevlar chars are nea rly three times more reactive than Nomex chars. The appearance of the external surfaces of all the chars can be related to the percentage bu rn-off and the activation gas used. The presence of metallic residues leads to pitting on activation, which increases with progressive burn- off. At high burn-offs, the action of metallic residues in steam and c arbon dioxide results in homogeneous and localised surface pits, respe ctively.