Some properties of kraft and kraft-borate pulps of different wood species

Abstract

Comparative analyses were carried out on the properties of birch, maple, and spruce for conventional kraft pulping and kraft pulping with sodium metaborate added to correspond to 35 % autocausticizing. A 1.8 % increase was noticed in the screened yield for the kraft-borate pulping of spruce at H-factors higher than 1000. Also, at kappa numbers lower than 50, sodium metaborate increased the total yield in spruce pulping. Sodium borate did not affect the brightness nor the contents of extractives and hexenuronic acid groups (HexA) of the kraft pulps for the species studied. The kappa number corrected for the HexA component, which is a more accurate estimate of the lignin content, showed that kraft delignification was not changed by sodium metaborate at the increasing H-factor. An increase of holocellulose retention was found for the kraft-borate pulps of spruce at the kappa numbers lower than 60, indicating that sodium metaborate has the potential to protect carbohydrates in kraft pulping.