Internal sizing of different hardwood species

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Helsinki University of Technology | Diplomityö
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Puunjalostuksen kemia
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iii + 97 s. + liitt. 4
In order to improve profitability, uncoated fine paper mills nowadays utilize large proportion fast-growing hardwood pulp, calcium carbonate filler, and in Asia also non-wood pulp, which raw materials could contribute good optical properties and favourable formation to paper. On the other hand, some challenges from papermaking and paper-printing are apparently induced and naturally related to these raw materials, such as high consumption wet-end chemicals consumption and printing picking problem. Botnia has already supplied Asia markets eucalyptus pulp with high fiber property. The objective of this thesis was to characterize the performance of two hardwood pulp grades at internal sizing process during uncoated fine paper making and to clarify the differences between pulp grades. The comparison of two wheat straw pulp grades as complement pulp was also included into this study. The fiber and pulp properties of raw pulp and stock pulp have been thoroughly analyzed in several laboratories according to industry standards, which fundamental properties or modified ones by mechanical treatments contribute the performance of pulp grades in final paper products. After papermaking trials, the parameters of papermaking process, and the properties of ASA sized fine paper have been also measured to be evident for the various performance of pulp materials. The released organic substances (COD, cationic demand) and WRV of Euca pulp reach higher level than Acacia pulp after refining, which differences drive Euca pulp to consume more ASA size and to receive lower dry content after press than Acacia pulp. Acacia pulp possesses large fiber population per gram, which may lead at same basis weight into high dense, low porosity, and high smoothness for uncalendered paper. Low porosity of uncoated fine paper enables high initial pressure for liquid penetration, which is favourable for good sizing degree. Generally, more wheat straw pulp content in paper furnishes more difficulty it is for ASA sizing. With low amount of released organic substances, however, Novel straw pulp has performed inferior sizing efficiency in comparison with Soda straw pulp, which phenomenon is opposite to hardwood or traditional pulp.
Laine, Janne
Thesis advisor
Hirvonen, Kirsi
internal sizing, uncoated fine paper, hardwood pulp, wheat straw pulp
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