Oxymercuration-demercuration kappa number: An accurate estimation of the lignin content in chemical pulps

In the kappa number determination, it has been found that non-lignin structures contribute to the consumption of permanganate, and thus make it difficult to estimate the lignin content in the pulp. In order to improve the accuracy of the determination, a two-step pretreatment with mercury acetate - sodium borohydride prior to a conventional kappa number determination is proposed. It has been found that such a pretreatment eliminates all interfering structures in the pulp except a, P-unsaturated carboxylic acid groups. and thus permits a very accurate estimation of the lignin content. The method has been termed "oxymercuration - demercuration (Ox-Dem) kappa number" and can be used to obtain information not only about the lignin content but also about the quantity of other oxidizable structures present in a chemical pulp. New information concerning the delignification reactions taking place in pulping and bleaching can thus be obtained.