Isolation of Residual Lignins from Semi-Bleached Pulps

3 Isolation of Residual Lignins from Semi-Bleached Pulps 

The residual lignin in a semi-bleached pulp such as oxygen-bleached pulps or chlorinated and alkali extracted pulps can be isolated using the same procedure as described previously. However, during the successive enzymatic hydrolyses, some residual lignin in the semi-bleached pulp becomes soluble in the acetate buffer solution. The water-soluble residual lignin can be isolated by combining 

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Contamination by enzymes is a main drawback of the procedure, especially in the isolation of residual lignin from semi-bleached pulps. The contaminants cannot be completely removed by the purification procedure described above. Consequently, it is important to determine the nitrogen content of the residual lignin. Typical values of nitrogen content are 2.5% and 7.3% before purification and 0.6% and 2.3% after purification for residual lignins isolated from an unbleached and a semi-bleached southern pine kraft pulp, respectively (Jiang et al. 1987). 

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