Abstract
Cleanliness is a very important quality parameter of a bleached chemical pulp . The main objective of bleaching kraft pulp to full brightness is to produce a white, strong, clean, and stable pulp that is suitable for high-quality grades of printing paper. It is natural to stress brightness and cleanliness while properties such as strength are given a lower priority. However, for most purposes, cleanliness is more critical than brightness and the advantages of bleaching to a very high brightness are, therefore, not always evident. The reason for bleaching to a very high brightness is that this indirectly guarantees an acceptable cleanliness or that customer demands are not always necessarily related to the end product demand. For many paper grades, a significantly lower bleached pulp brightness can be accepted if the cleanliness is sufficient. During most of the bleaching operation, the shives decrease significantly. Normally, bleaching to make market pulp removes 95–99% of the shives. Better cleanliness is obtained using bleaching in short sequences. Some advances in mill techniques such as whole tree utilization intensify the cleanliness problems. Another is closing up of the screening department including recycling the screenings. On the other hand, improved bleaching techniques with more extensive use of chlorine dioxide permit prolonged cooking without excessive carbohydrate degradation during cooking and bleaching. The resulting pulp has fewer and probably less shives. Xylanase enzymes have also been found to be effective in removing shives. By treating the brown stock with xylanases, mills can substantially increase the degree of shive removal in the subsequent bleaching. Xylanase enzymes can increase the degree of shive removal by 50% in the subsequent bleaching . At a given bleached brightness , Xylanase treatment results in a lower shive count. Xylanase treatment, therefore, helps to remove shives from the pulp beyond the associated gain in the brightness. Removal of shives and ease of pulp bleaching by the use of xylanases also helps in reducing the energy requirement.
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Bajpai, P. (2018). Removal of Shives. In: Biotechnology for Pulp and Paper Processing. Springer, Singapore. https://doi.org/10.1007/978-981-10-7853-8_14
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DOI: https://doi.org/10.1007/978-981-10-7853-8_14
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