Several additives have been used in research and on an
industrial scale to improve the pulp yield and to increase
the rate of delignification. One such additive is 1,4-
dihydro- 9,10-dihydroxyanthracene (DDA), also called soluble
anthraquinone. This chemical is widely used in Japan and
some other countries, especially with the eucalyptus
species; however, there is little information on this
additive in the literature for pulping softwoods. The
behavior of this chemical in the kraft pulping of Douglas-fir
(Pseudotsuga menziesii), a predominant species of the
northwest, was studied using DDA and the more common
anthraquinone (AQ) additives. DDA was found to be a superior
additive compared to AQ as the total pulp yields improved by
1 to 2% over AQ or 3 to 4% over control kraft, for kappa
numbers below 90 (at 0.1% additive level). A decrease of 80
to 400 in the H-Factor is possible during cooking for pulps with kappa numbers between 25 and 80. For cooks producing
pulps with kappa number of 90 or higher, DDA was actually
detrimental. The brightness of the unbleached DDA pulps
improved by 1 to 2% (TAPPI) over the AQ and control pulps.
No significant difference was found in the beating
performance of the three types of pulps and also there was
no significant difference in the pulp viscosities or the
strength properties of the handsheets made from these pulps
