REDUCTION OF YIELD LOSS IN KRAFT PULPING OF HOT WATER PRE-EXTRACTED BEECH WOOD

The effect of polysaccharides stabilizing agent on kraft pulp yield from hot water preextracted beech chips was investigated. Total pulp yield from hot water pre-extracted chips exhibit a linear decrease with increasing wood weight loss, while the yield of total monosaccharides in hydrolysed extracts increased. Following that in laboratory pulping experiments pre-extracted chips with 10 % wood weight loss were used at which the total pulp yield decreased by 4.2 % in comparison with original beech chips. As reductive agent in the intermediate step sodium borohydride (SBH) in a mild alkaline sodium sulphide (SS) solution was used. The combination of reductive treatment with addition of oxidative agent anthraquinone (AQ ) in kraft pulping of hot water pre-extracted wood chips increased total yield pulp by 2.7 %. Combined simultaneous application of reductive and oxidative agents in kraft pulping of hot water pre-extracted chips increased pulp yield by 2.3 %. Both methods of pulp yield improvement have positive effect on tensile strength, but the intermediate step treatment of hot water pre-extracted chips caused slight reduction in tear strength. From economic standpoint application of polysaccharides stabilizing agents in kraft pulping is preferable to an intermediate step, even though by application of an intermediate step the yield of monosaccharides increased by about 2 % and effective alkali charge in the pulping process decreased by 3 %.