Tarja Oksanen

Treatment of recycled kraft pulps with Trichoderma reesei hemicellulases and cellulases

Effects of recycling ECF-bleached softwood kraft pulp on pulp properties were evaluated in the laboratory. The tensile strength, fiber flexibility and WRV lost during drying of the pulp were recovered by refining between the cycles which, however, resulted in deteriorated drainage properties. The recycled pulps were treated with purified Trichoderma reesei cellulases and hemicellulases and the changes in fiber properties due to enzymatic treatments were characterized. The endoglucanases (EG I and EG II) significantly improved pulp drainage already at low dosage levels, and EG II was found to be more effective at a given level of carbohydrate solubilization. Combining hemicellulases with the endoglucanase treatments increased the positive effects of the endoglucanases on pulp drainage. However, as a result of the endoglucanase treatments a slight loss in strength was observed. Combining mannanase with endoglucanase treatments appeared to increase this negative effect, whereas the impact of xylanase was not significant. Although the drainage properties of the pulps could be improved by selected enzymes, the water retention capacity of the dried hornified fibers could not be recovered by any of the enzymes tested.

CELLULASES IN PULP AND PAPER PROCESSING

The enzymatic modification of cellulose, the major carbohydrate in different pulp fibres, offers unique opportunities for new applications, due to the different modes of action of individual cellulases. Although they all act on the same glycosidic β-1,4-linkage, different structural and functional modifications can be obtained depending on the type of fiber, enzyme and process phase used. Thus, cellulase based applications have been developed aiming at energy saving in refining, improvement of beatability, drainage and runnability of the paper machine, or enhancing de-inking processes. In these applications, the enzymatic treatment has been carried out on coarse or refined mechanical pulps, chemical pulps or recycled fibers at different phases of the processing. When applying cellulases, it is important to minimize the detrimental effects of these enzymes on the yield and strength properties of fibers. In this paper, the mode of action and effects of different types of cellulases; cellobiohydrolases and endoglucanases, are reviewed in the light of present applications.