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Effects of the partial removal of wood hemicelluloses on the properties of kraft pulp

Saukkonen, Esa (2014-12-04)

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Saukkonen_A4.pdf (9.539Mb)
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Saukkonen, Esa
04.12.2014
Lappeenranta University of Technology

Acta Universitatis Lappeenrantaensis

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Julkaisun pysyvä osoite on
http://urn.fi/URN:ISBN:978-952-265-679-7

Tiivistelmä

The objective of this work was to study the effects of partial removal of wood hemicelluloses
on the properties of kraft pulp.The work was conducted by extracting hemicelluloses (1) by a
softwood chip pretreatment process prior to kraft pulping, (2) by alkaline extraction from
bleached birch kraft pulp, and (3) by enzymatic treatment, xylanase treatment in particular, of
bleached birch kraft pulp. The qualitative and quantitative changes in fibers and paper
properties were evaluated. In addition, the applicability of the extraction concepts and
hemicellulose-extracted birch kraft pulp as a raw material in papermaking was evaluated in a
pilot-scale papermaking environment. The results showed that each examined hemicellulose
extraction method has its characteristic effects on fiber properties, seen as differences in both
the physical and chemical nature of the fibers.
A prehydrolysis process prior to the kraft pulping process offered reductions in cooking time,
bleaching chemical consumption and produced fibers with low hemicellulose content that are
more susceptible to mechanically induced damages and dislocations. Softwood chip
pretreatment for hemicellulose recovery prior to cooking, whether acidic or alkaline, had an
impact on the physical properties of the non-refined and refined pulp. In addition, all the
pretreated pulps exhibited slower beating response than the unhydrolyzed reference pulp.
Both alkaline extraction and enzymatic (xylanase) treatment of bleached birch kraft pulp
fibers indicated very selective hemicellulose removal, particularly xylan removal.
Furthermore, these two hemicellulose-extracted birch kraft pulps were utilized in a pilot-scale
papermaking environment in order to evaluate the upscalability of the extraction concepts.
Investigations made using pilot paper machine trials revealed that some amount of alkalineextracted
birch kraft pulp, with a 24.9% reduction in the total amount of xylan, could be used
in the papermaking stock as a mixture with non-extracted pulp when producing 75 g/m2
paper. For xylanase-treated fibers there were no reductions in the mechanical properties of the
180 g/m2 paper produced compared to paper made from the control pulp, although there was a
14.2% reduction in the total amount of xylan in the xylanase-treated pulp compared to the
control birch kraft pulp.
This work emphasized the importance of the hemicellulose extraction method in providing
new solutions to create functional fibers and in providing a valuable hemicellulose co-product
stream. The hemicellulose removal concept therefore plays an important role in the integrated
forest biorefinery scenario, where the target is to the co-production of hemicellulose-extracted
pulp and hemicellulose-based chemicals or fuels.
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LUT-yliopisto
PL 20
53851 Lappeenranta
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