Chemical characterization of birch, maple and spruce kraft and kraft-borate pulps

Abstract

To evaluate kraft pulping in the presence of sodium metaborate at 35% borate autocausticizing, the chemical constituents of birch, maple, and spruce kraft and kraft-borate pulps produced under the same conditions were analyzed. The contents of Klason lignin, hexenuronic acid groups (HexA), phenolic hydroxyl groups (PhOH), holocellulose and pentosans in the pulps of decreasing kappa number were determined. Calculated conversion factors between Klason lignin and kappa number/HexA-free kappa number were equal for kraft and corresponding kraft-borate pulps. While dissolution of pentosans was approximately the same in kraft and kraft-borate pulping, an observed stabilization of hexosans might be the reason for an increased screened yield found in spruce kraft borate pulping. The equal PhOH content of the residual lignin of kraft and corresponding kraft-borate pulps, in combination with the same rate of lignin removal, is a good indicator that the delignification path is similar for both kraft and kraft-borate pulping of the species studied.