Semi-bleached pulps

The repeatability of the measurement is high for semi-bleached pulps but decreases with increasing kappa numbers and becomes fairly constant for kappa numbers above 20. With semi-bleached pulps with kappa numbers below 20, the method will have a minimum repeatability of 0.2 kappa number. Repeatability decreases systematically from 13% for kappa numbers below 2 to 2.3% for kappa numbers between 10 and 20. The average repeatability is 3.8% for kappa numbers between 2.5 and 20. With unbleached pulps having kappa numbers above 20, the repeatability varies unsystematically between 0.9 and 1.5%. The average repeatability is 1.2% for kappa numbers between 20 and 190. 

The kappa number determination is applicable to all types and grades of semichemical, unbleached, and semi-bleached pulps obtained in yields under 60% and for pulps in yields of up to 70% if the pulp has been well screened prior to the test. Typical values for representative pulps are listed in Table 2.2.7. In... 

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... 

All residual lignins isolated by the enzymatic method are contaminated with enzymes to varying extents. This is especially true for the residual lignins isolated from semi-bleached pulps (Jiang et al. 1987). The contamination can be largely removed by the following procedure ... 

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). 

The isolation of enzymatic residual LCCs from unbleached softwood Kraft pulps is a well-established procedure producing preparations with high yields (estimated as lignin in isolated preparations per lignin in the original pulp) and relatively low enzyme impurities [46 8]. In contrast, significant problems are encountered when similar procedures are applied to the isolation of enzymatic residual LCCs from hardwood Kraft pulps and semi-bleached pulps [47]. Low yields (25-30%) make these preparations nonrepresentative for the whole pulp LCC. A very large amount of protein impurities... 

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