BLEACHED KRAFT PULP FROM PRE-EXTRACTED BEECH WOOD

Beech chips were pre-extracted with hot water and green liquor prior to kraft pulping. The total pulp yield of green liquor pre-extracted chips equivalent to 10 % wood weight was approximately the same as that from the original chips, while the pulp yield from hot water pre-extracted chips was lower by 4.2 %. Effective alkali charge was reduced by about 3 % in kraft pulping of green liquor pre-extracted chips, and by about 1 % in kraft pulping of hot water pre-extracted chips when compared with original chips. The pulps from pre-extracted chips demonstrated higher oxygen delignification efficiency and bleachability in the sequence D-0(EO)D1D2 as in case of reference pulp from original chips. Consumption of chlorine dioxide in bleaching of pulps from hot water pre-extracted chips was lower by about 17 % at 5 % wood weight loss and 20.5 % at 10 % wood weight loss, while in case of pulp from green liquor pre-extracted chips it was lower only by about 5 % at the same weight loss compared with the reference pulp. The overall yield of bleached pulps from hot water pre-extracted chips was lower by 1.2 and 3.1 %, respectively (at 5 and 10 % wood weight loss), of the pulp from green liquor pre-extracted chips by 0.2 % in comparison with the reference pulp. Brightness reversion and beatability of bleached pulps from pre-extracted chips was lower as compared with the reference pulp, mainly in case of pulps from hot water pre-extracted chips. Tensile index of bleached pulps prepared from pre-extracted chips was lower, however tear index was higher in comparison with the bleached reference kraft pulp.