Influence of oxidized lignin structures from chlorine dioxide delignified pulps on the kappa number test

Chlorine dioxide delignification (D-o) of kraft pulps caused the lignin/kap pa number ratio to increase from 0.15 to 0.18. It was speculated that oxidi zed structures in the D-o residual lignin, such as quinones, consumed less permanganate than unbleached residual lignin. Kraft pulps oxidized with per iodate, a method known to produce quinone structures, also showed an increa se in the lignin/kappa ratio from 0.15 to 0.18. Results from model compound studies indicated that quinones consumed similar to 25 to 40% less permang anate than corresponding phenolic or dihydroxybenzene models. Hydrosulphite reductions of periodate and D-o pulps caused the lignin/kappa ratio to ret urn to 0.15. Additional studies indicated that muconic structures in D-o re sidual lignin do not affect the lignin/kappa ratio. Based on these findings , it was estimated that the D-o residual lignin contained similar to1.9 mmo l quinones/g lignin.