INFLUENCE OF BEECH WOOD PRE-EXTRACTION ON BLEACHING AND STRENGTH PROPERTIES OF KRAFT PULPS

摘要

Kraft pulps prepared from beech chips, with 10% wood weight loss, pre-extracted with green liquor solution, hot water and dilute oxalic acid, were more effectively delignified by a double-stage oxygen system in comparison with the reference pulp from original chips. The highest delignification efficiency was demonstrated for pulps prepared from dilute oxalic acid and hot water pre-extracted chips. The bleachability of oxygen delignified kraft pulps in the sequence D-0( EO) D1D2 was better in the case of the pulps from pre-extracted chips, first for those extracted with dilute oxalic acid and then for the hot water extracted ones. The consumption of ClO2 in bleaching was lower for these pulps by about 40% and 20%, respectively, while for the pulp from green liquor solution pre-extracted chips it was lower only by about 5% compared with the reference pulp. Brightness reversion of the bleached pulps from pre-extracted chips was lower in comparison with the reference pulp, which correlates with lower content of hexenuronic acids. The loss of pulp yield in oxygen delignification and bleaching was of 1.4% for the pulp from dilute oxalic acid pre-extracted chips, 1.6% for the pulp from hot water pre-extracted chips, while in the case of the pulp from green liquor pre-extracted chips it was 2.4% and for the reference pulp - 2.5%. The beatability of bleached pulps from dilute oxalic acid and hot water pre-extracted chips was much worse than that of the bleached reference pulp, but in the case of the pulp from green liquor pre-extracted chips it was only slightly lower. The tensile index and burst index of the bleached pulps prepared from dilute oxalic acid and hot water pre-extracted chips were lower, while the tear index was higher, compared with those of the reference bleached pulp.