The extractives, especially ferruginol and its derivatives, from the woods of sugi (
Cryptomeria japonica) are responsible for low brightness and intense color reversion of its bleached sulfate pulps (BKP). The improved methods for better bleaching were suggested as follows.
1) In the case of mixed sulfate pulps involving less ratios of sugi, which requires a slight impovement in brightness, better bleaching can be achieved simply by adequate increase in ClO
2 dosage at D
2-stage in the sequence of CE, D
1E
2D
2. Slight improvement in P.C.number may also, but not always, be expectable by this methods.
2) In the case of more increased ratios of sugi in the mixed pulps, improvement in both brightness and P. C. number can be attained by dosing hydrogen peroxide (P) into E
2-stage (i. e. P/E-stage).
3) Better improvement in brightness and P. C. number is accomplished by adding a slight amount of phase transfer catalyt (PTC) at P/E-stage mentioned above.
4) Even in case of 100% sugi heartwood pulps, oxygen bleaching affords fully bleached pulps having satisfiable brightness and P. C. number by adopting ODED sequence.
The improved methods for bleaching of sugi sulfate pulps mentioned above may also be applicable to bleaching of pulps from the other wood species having difficulties due to extractives.
View full abstract