EFFECT OF LIGNIN DEMETHYLATION ON OXYGEN DELIGNIFICATION

Treatment of radiata pine kraft and kraft-oxygen pulps with sodium eth anethiolate (NaSEt) in dimethylformamide (DMF) reduced the methoxyl co ntent of the fibre lignin. Demethylation increased as the level of NaS Et applied was raised. Lignin removal in a subsequent oxygen stage inc reased as the extent of demethylation was raised. For example, after N aSEt pretreatment low pulp concentration oxygen delignification reduce d the Kappa number of a kraft-oxygen pulp from 17.9 to 3.8, versus 7.9 for the non-pretreated pulp. The methoxyl content of lignin isolated from pretreated kraft or kraft-oxygen pulps was approximately linearly related to the Kappa number after oxygen delignification. Improved me thods for demethylation of the fibre lignin are required if the enhanc ed reactivity to oxygen is to be exploited as treatment with NaSEt in DMF led to significant losses in both pulp viscosity and pulp yield.