The impact of low consistency refining of eucalyptus species on the fibre morphology and strength properties of pulp.
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Date
2005
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Abstract
It is a well-known fact that the selection of the raw material and how it is further treated
within the stock preparation system has a major affect on the quality of paper obtained. While
the pulp selection is important for a good product, the refining treatment received by that pulp
is the determining factor for the properties of the product. It is for these reasons that it is
interesting and beneficial to study the pulp quality and refining results. The focus of this
research work was to study the behaviour of selected clones of Eucalyptus materials from
different site indices under different refining conditions. Poor and good sites were
investigated. The strength properties of the resulting refined pulp were investigated.
The project was conducted in three phases with the focus of the project being phase 3. The
work began with refining of commercial Eucalyptus pulp obtained from Mondi Richards Bay
(phase 1). The objective here was to get an understanding of the influence of the various
parameters affecting refining. This knowledge could then be used on a more focused research
program on the well defined pulps with limited refining variables being considered. The
results indicated that of the three variables investigated (i.e. stock flow rate, stock consistency
and refiner speed of rotation) the parameter speed of rotation gave the most repeatable results
when varied and also resulted in the largest range of refining intensity (SEL) achievable
compared to the variation of the other two parameters. It was decided that the work on the
different pulps investigated in phase 3 would be carried out using the parameter speed of
rotation to vary the SEL and multiple passes through the refiner to vary the specific refining
energy (SRE).
A comparison between the refining characteristic of bleached and unbleached pulp was
carried out (phase 2). It was seen that there were differences in the refining characteristics
between bleached and unbleached pulp. These differences however, occurred in a predictable
manner. This indicated that with further investigations on the differences in refining
characteristics, it would be possible to extend the results obtained from refining studies using
unbleached pulp to what can be expected from the refining of bleached pulp.
Phase 3 of the project considered the refining of different pulps. Two different clones of
Eucalyptus (GU A380 and GC G438) each from two site indices (good and poor), were
selected to provide raw materials having different wood anatomy. These were pulped under
similar cooking conditions using the kraft pulping process. The kappa numbers were in the
range of 18 to 21. The refining trials were then conducted to determine how the different
pulps affected the refining process and also how the refining process affected the pulp
properties. Refining was carried out at three different refiner speeds. It was seen that for the
overall results SRE was a good predictor of all the pulp properties measured except for the
tear. The pulp fibre length was able to predict the tear best. It was seen that refining higher
intensities reduced the SRE required to obtain a pulp freeness of 400 ml.
Description
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005
Keywords
Theses--Chemical engineering.