The nature of functional groups on the surface of oxidized carbon fiber was investigated through the chemical reactions, particularly with focussing on the weaker acidic groups than carbonic acid.
A pitch-based carbon fiber, prepared by 1000°C heat treatment, was oxidized with 60% nitric acid under various conditions and the cation exchange capacities of the oxidized fibers for NaOH and Na
2 CO
3 (Ct-NaOH and Ct-Na
2 CO
3, respectively) were determined. The proportion of the less acidic groups (Ct-NaOH-Ct-Na
2CO
3) to the total acidic groups (Ct-NaOH) was found to increase with the increasing Ct-NaOH value. One of the oxidized fibers, whose Ct-NaOH and -Na
2CO
3 were 2.84 meq/g and 1.98 meq/g, was treated with hexamethylenediamine resulting in a weight increase of about 5%, a nitrogenintake of 1.28 matom/g, and a Ct-NaOH decrease of 2.42 meq/g. On the basis of stoichiometry from these results it was concluded that the surface of the oxidized carbon fiber in question must be tightly covered mainly with quinone-type carbonyl groups and carboxyl groups, some of the carboxyl groups exist in the form of intramolecular acid anhydride, and, as a result, the fiber can combine directly with an amine reagent forming the imide group.
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