Some Properties of Kraft and Kraft-Borate Pulps of Different Wood Species, 2002 Fall Technical Conference

An important question with the implementation of the borate-based autocausticizing in kraft process is the effect of sodium metaborate, which is present in the pulping liquor as the product of the autocausticizing reactions on kraft pulping and properties. This study shows the results obtained for birch, maple and spruce in conventional kraft pulping and in kraft pulping with sodium metaborate added at the level corresponding to 35 % autocausticizing – kraft-borate pulping. An increase in the yield of 1.8 % was noticed in kraft-borate pulping of spruce delignified to the same kappa number, at the H-factors higher than 1,000. Also, sodium metaborate decreased the rejects in kraftborate pulping of the three studied species. Sodium borate did not affect the brightness and the contents of extractives and hexenuronic acid groups (HexA) of the kraft pulps of studied species. The kappa number corrected for the HexA component, estimating the lignin content in pulps more accurately showed, at the increasing H-factor, that kraft delignification was unchanged in the presence of sodium metaborate. An increase of holocellulose retention was found for the kraft-borate pulps of spruce at the kappa numbers lower than 60, indicating a potential of sodium metaborate to protect carbohydrates in kraft pulping.