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The role of different alkali sources in deinking and bleaching processes


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Mahagaonkar, Madhu S 1995 , 'The role of different alkali sources in deinking and bleaching processes', PhD thesis, University of Tasmania.

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This thesis is divided into two parts. The first and major part deals with deinking and
the second part deals with peroxide bleaching.
The use of deinked fibre in the paper industry has increased dramatically in recent
times. Enormous progress has been made in recent years in improving the deinking
process. However, deinking chemistry remains one area which is not well understood
and not completely optimized. There is widely held belief that the inclusion of
approximately 10% ash in the feed is desirable for effective removal of ink from
newsprint. However, some recently reported studies have found that the inclusion of
magazines does not enhance deinking of newsprint. Many factors can have an
influence on the efficiency of flotation deinking of newsprint and magazines. In order
to have a better understanding of this complex process, the influence of some important
process variables (flotation time and pH, different magazine type and quality, influence
of sodium silicate and water hardness) during flotation deinking of newsprint and
magazines have been examined in this thesis. No evidence could be found to support
the idea that ash components from magazines facilitate the removal of ink from
newsprint. There has been significant recent interest in attempting to improve the strength and
optical properties of recycled fibre. However, no study has been reported which
investigates comprehensively the effect of dein king on the properties of recycled paper
after the deinking stages of pulping and flotation. This work also addresses the effects
of different stages of deinking on the physical and optical properties of recycled paper.
Furnishes of mixed magazine (coated) and newsprint were used to investigate changes
in properties of recycled paper during deinking. In most cases, optical and physical
properties showed reverse trends after pulping and flotation stages. These differences can be explained by the change in proportions of mechanical and chemical fibre, filler,
fines and ink during flotation. After the pulping stage, trends in strength properties
were influenced by detrimental effects of filler from magazines. However, after the
flotation stage, due to loss of most of the filler and fines, an enhancement in all strength
properties occurred. Brightness and light absorption coefficient appeared to be
influenced more by ink content, when large amounts of filler are present. The light
scattering coefficient was dominated by the fibre type. Extended periods of flotation
(greater than ten minutes) had no significant effect on properties of the recycled paper
Studies have also been carried out to examine the effects of the various alkali sources on
flotation deinking of newsprint and coated magazines. At the same time, the effects of
each alkali used in the deinking process with regard to the strength, optical and surface
properties of recycled paper have been investigated. This study also addresses the
effect of sodium silicate on the deinking efficiency of each alkali. Significant
differences in the strength and optical properties of recycled paper occurred with the use
of different alkalis. These observed differences can be explained by the hydrolysing
effect of the alkalis. BLEACHING
Recently there has been interest in the use of other sources of alkali in peroxide
bleaching, particularly magnesium oxide and calcium oxide. These bases may offer the
advantage of decreased pollution problems associated with salinity, which arise when
discharging conventional effluents into a fresh water system. Magnesia as an
alternative alkali source may be particularly attractive in the Australian context as there
are very large deposits of high quality mineral available at Kunwarara in Northern
Queensland. In this study, sodium hydroxide and magnesium oxide have been
compared as alkali sources in single-stage and two-stage bleaching of Eucalyptus regnans cold caustic soda (CCS) and Pinus radiata thermomechanical pulp (TMP). The
effects of peroxide stabilizers have also been studied in the presence of individual alkali.
Several studies have been reported on recycling spent liquor in the bleaching process
for mechanical pulps using sodium hydroxide as an alkali source. However, no work
has been reported in the literature using magnesium oxide as an alkali source employed
in multi-stage bleaching of mechanical or chemical pulps.
In this work, the possibilities of internal recycling of residual liquor during sequential
two-stage peroxide bleaching processes using either sodium hydroxide or magnesium
oxide as an alkali have been investigated. This study includes the investigation of
various recirculation strategies for bleaching of Pinus radiata TMP and Eucalyptus
regnans CCS pulp, without altering the pulp concentration in the first and second stage
of the bleaching processes. In general, there was a small to no improvement in
brightness response in going from one-stage to a two-stage process, although some
exceptions show interesting results. Under certain conditions, recycling residual
peroxide produces detrimental effects on the bleaching response of Pinus radiata TMP.

Item Type: Thesis - PhD
Authors/Creators:Mahagaonkar, Madhu S
Keywords: Wood-pulp, Newsprint, Printing ink
Copyright Holders: The Author
Copyright Information:

Copyright 1995 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1996. Includes bibliographical references

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