Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The use of arabinoxylans as additive in paper production
The present invention concerns the use of arabinoxylans as additive in paper
production.
The mechanical properties of paper are influenced by a series of different
parameters of a
chemical and physical nature. Several theories to explain the tear resistance
properties of
paper have been suggested, most of which emphasise the special relevance of
fibre-fibre
bonding. Amongst the most frequently cited is the theory that includes the
factors of interfibre
bonding force of the bonded surface and the length of the fibre.
It is generally agreed that the hemicelluloses native to the pulp improves the
tear resistance
and contributes to the formation of stronger fibre bonding. Depending upon the
raw material
and the pulping method, these hemicelluloses are modified greatly during pulp
preparation
and are destroyed to a considerable extent.
The use of xylans as additive in paper manufacture is basically known. Thus
Naterova et al.
(Papir a celuloza, 41, (7-8), V23-V30, 1986) describe the addition of 2% maize
xylan to
packaging paper. In this way the flexural strength is increased by about 172%
by the addition
of 2% xylan.
DE 44 09 372 Al, US 5 810 972 and WO 2004/031477 Al describe the addition of
highly
refined birch pulp and Lenzing xylan in the range of 0.005 to 0.14% (WO
2004/031477 Al)
or 0.15 to 1.5% (US 5 810 972, DE 44 09 372 Al) to tissue products. A positive
effect of the
xylans and xylan-rich, highly refined birch pulp on the softness of the tissue
product and the
behaviour of the paper web on the drying drum is described. The breaking
strength was
increased by 15 to 73% in the machine way and'17 to 90% transverse to the
direction of
travel. Allegedly the behaviour of the dry end was positively influence but
not reported
numerically, but assessed according to the experience of the paper maker.
In the aforementioned applications the use of xylans from the raw material
wood and its
secondary product pulp is discussed. In particular, the use of acetyl-4-O-
methylglucuronoxylan from deciduous wood and arabino-4-O-methylglucuronoxylan
from
coniferous wood is cited. The examples on the use of xylans cites Lenzing
xylan. This
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product is obtained by alkaline extraction of beech wood pulp in the viscose
process and
exhibits only a low degree of polymerisation of about 35.
Consequently different xylans have been investigated in respect of their
attributes for the fibre
properties or as paper additive. However, the work cited shows that an
improvement in tear
length is associated with a deterioration in other strength properties or in
an unacceptable
deterioration in optical properties.
There is therefore still the requirement for a cost-effective paper additive
that brings about an
improvement in paper properties, in particular strength, bulk and optical
properties.
It has now been surprisingly found that the addition of arabinoxylans to pulp
during paper
production brings about a significant improvement in paper properties. By the
use of
arabinoxylan the tear length, the tear resistance and the bulk, i.e. the
volume of the paper, is
improved. The improvement in the bulk improves both the strength properties
and the optical
properties of the paper. Surprisingly a significantly greater improvement of
the paper
properties is achieved in comparison to other xylans such as 4-0-
methylglucuronoxylans
from deciduous wood or Lenzing xylans.
The subject matter of the invention is therefore the use of arabinoxylans as
additive in paper
manufacture.
Suitable arabinoxylans are polysaccharides that are present in, for example,
different annual
plants and agricultural residues such as oat husks, straw or maize. The
arabinoxylans can be
obtained by different extraction techniques, e.g. with water, steam or
solvents with the aid of
the most different of auxiliary chemicals, as well as by enzymatic isolation
and purification
steps. Preferably alkali-extracted arabinoxylans are used, especially
arabinoxylans from oat
husks that can be obtained, for example, by extraction of oat husks with
aqueous alkali
solution, separation of the alkaline extract and subsequent precipitation of
the alkaline extract
in a precipitation bath of water and a water-miscible organic solvent A, with
the alkaline
extract not neutralised before precipitation.
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The special feature of the arabinoxylans from oat husks in comparison to
xylans from
deciduous wood and coniferous wood is that they have a comparably high number
of
arabinose substituents but not the 4-O-methylglucuronic acids occurring in
deciduous and
coniferous xylans. In comparison to xylans from pulp such as the Lenzing
xylans, the
arabinoxylans exhibit a much higher chain length.
Within the context of the present invention arabinoxylans are understood to be
such xylans
that bear 5 to 20% (w/w relative to the whole sample), preferably 7 to 15%,
most preferably 8
to 13% arabinose substituents in their main chain and less than 5%, preferably
less than 2%,
most preferably less than 1% 4-O-methylglucuronic acid substituents
(chromatographic sugar
determination after acid hydrolysis).
Arabinoxylans that are obtained by extraction of oat husks with aqueous
alkaline solution
with isolation of an alkaline extract and subsequent precipitation of the
alkaline extract in a
precipitation bath of water with a water-miscible organic solvent A with the
alkaline extract
not neutralised before precipitation are particularly preferred. Such
arabinoxylans exhibit a
chain length of at least 100 also after a possible bleaching stage. Usually
the chain lengths of
these arabinoxylans lie in the range 120 to 240.
A further subject matter of the invention is a method for the preparation of
cellulose pulps
comprised of contact with a concentrated solution or suspension of an
arabinoxylan with pulp
or stock system that contains pulp.
In one embodiment of the invention the arabinoxylan solution or suspension is
added to the
fibre suspension before sheet making. The action of the arabinoxylan is also
carried out in
combination with other paper chemicals which are added to the fibre before,
after or together
with the arabinoxylan. In this way the use of arabinoxylan is advantageous for
the most
different of products in the paper industry.
Other normal paper chemicals are for example wet-strength agents, fillers,
retention agents,
fixatives, defoamers, deaerators, sizing agents, optical brighteners and
colours.
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A homogeneous solution or suspension of the arabinoxylan can be achieved, for
example, by
intense mechanical loading such as stirring, by the effect of temperature or
with the help of
chemicals, preferably basic chemicals such as alkali or alkaline earth
hydroxides, preferably
NaOH. The concentration of the arabinoxylan solution or suspension can be
varied over a
wide range of 0.1 to 40% (w/w). Preferred is the range of 0.1 to 25% (w/w),
especially
preferred is the range from 0.5% to 10% (w/w).
The arabinoxylan solution or suspension can be incubated with the pulp and the
desired paper
auxiliaries and additives in high pulp density (solids content) of up to 20%
before the pulp
enters the headbox of the paper machine. Then by squeezing out the supematant
solution any
unabsorbed chemicals can be used for the next batch.
In a further embodiment of the invention the pulp is mixed with the additives
and the
arabinoxylan solution or suspension in any desired sequence in the headbox,
that is
immediately before entry into the machine for paper production. The addition
of the
arabinoxylan in the headbox usually achieves better results than the pevious
incubation with
the pulp.
In a further embodiment of the invention the arabinoxylan solution or
suspension is added to
the pulp suspension before the refinement of the pulp fibres.
Usually after achieving the optimal quantities no further increase in strength
and bulk is
achieved by further increase in the amount of arabinoxylan in a product
formulation. The
optimal amount is dependent upon which other paper auxiliaries are used in the
mass so that
that the amount of arabinoxylan used relative to pulp can be varied in a wide
range of 0.1 % to
40% (w/w). Preferably, however, an amount between 0.5 and 10% arabinoxylan is
used.
Usually with the use of paper additives the optimal increase in strength is
achieved at even
lower arabinoxylan concentration.
The invention is illustrated but not limited in the following by a number of
embodiment
examples.
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Examples
Unless otherwise stated in the following examples the compositions of xylans
are given as %
w/w relative to the whole sample, determined by chromatographic sugar
determination after
acid hydrolysis.
Example 1 (of the invention)
An arabinoxylan from oat husks (9.5% arabinose, < 1% 4-O-methylglucuronic
acid, DP ca.
160) was dissolved in water with heating with formation of a 5% solution. 20 G
coniferous
sulfite pulp was suspended in water and treated with the xylan solution in the
amounts given
in Table 1. For experiments with higher amounts of xylan solution
correspondingly lower
amounts of water were used in each case for suspension of the pulp. After
addition of the
xylan suspensions the pulp density was 7.1% in each case. The experimental
batches were all
incubated for 2 h at 50 C. After incubation the pulp was filtered off through
a nutsch.
The pulp was refined for 2.5 min in a Jockro mill in accordance with ISO 5264-
3 and
laboratory sheets produced in accordance with ISO 5269-2 (rapid K6then
method). Testing
for strength was carried out in accordance with ISO 1974 (DIN EN 21974).
Table 1
Amount of arabinoxylan Tear length (m)
in % (w/w) rel. to pulp
0 (reference) 2734
7.5 3473
22.5 3935
37.5 4199
The data in Table 1 show that in comparison with the reference pulp without
xylan the pulp
treated with arabinoxylan from oat husks exhibited considerably higher
strength. The tear
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lengths increased with increasing xylan amounts. The greatest increase in tear
length by
addition of arabinoxylan from oat husks is 1465 m.
Example 2 (Comparison example)
A 4-0-methylglucuronoxylan from birch wood (no arabinose side chains, 8.8%
molar ratio 4-
0-methylglucuronic acid relative to xylose units, determined by 1H NMR, DP ca.
95) was
dissolved in water with heating as 5% solution. 20 G coniferous sulfite pulp
was suspended in
water and treated with the xylan solution. For experiments with higher amounts
of xylan
solution correspondingly lower amounts of water were used to suspend the pulp.
After
addition of the xylan suspensions the pulp density was 7.1 % in each case. The
experimental
batches were each incubated for 2 hr at 50 C. After incubation the pulp was
filtered off
through a nutsch.
The pulp was refined for 2.5 min in a Jockro mill in accordance with ISO 5264-
3 and
laboratory sheets produced in accordance with ISO 5269-2 (rapid K6then method)
Testing
for strength was carried in accordance with ISO 1974 (DIN EN 21974).
Table 2
Amount of 4-0- Tear length (m)
methylglucuronoxylan in
% (w/w) rel. to pulp
0 (reference) 2734
7.5 2983
22.5 3126
37.5 3189
The data in Table 2 show that the 4-0-methylglucuronoxylan acid from birch
wood can bring
about only a very small increase in strength. The action of this xylan is less
that 31 % of the
action of arabinoxylan from oat husks.
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Experiment 3 (comparison example)
The Lenzing xylan from beech wood pulp (no arabinose side chains, 1% 4-0-
methylglucuronic acid, DP ca. 35) was dissolved in water with heating as 5%
solution. 20 G
coniferous sulfite pulp was suspended in water and treated with the xylan
solution. For
experiments with higher amounts of xylan solution correspondingly lower
amounts of water
used to suspend the pulp. After addition of the xylan suspensions the pulp
density was 7.1 %
in each case. The experimental batches were incubated for 2 hr at 50 C. After
incubation the
pulp was filtered off through a nutsch.
The pulp was refined for 2.5 min in a Jockro mill in accordance with ISO 5264-
3 and
laboratory sheets produced in accordance with ISO 5269-2 (rapid K6then
method). Testing
for strength was carried out in accordance with ISO 1974 (DIN EN 21974).
The data in Table 3 show that the "Lenzing xylan" from beech wood pulp can
bring about
only a very small increase in strength. The action of this xylan is less that
36% of the action of
arabinoxylan from oat husks.
Table 3
Amount of Lenzing xylan Tear length (m)
in % (w/w) rel. to pulp
0 (reference) 2734
7.5 3010
22.5 3000
37.5 3260
Example 4
An arabinoxylan (9.5% arabinose, < 1% 4-O-methylglucuronic acid DP ca. 160)
from oat
husks was dissolved in water with heating as 5% solution. A coniferous sulfite
pulp was then
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refined for 2.5 min. in a Jokro mill in accordance with ISO 5264-3 and
laboratory sheets
prepared in accordance with ISO 5269-2 (rapid Kothen method). The arabinoxylan
solutions
were in each case added to the pan which is used for portioning the suspension
for the
individual laboratory sheets. In each pan 16 g pulp were equalised in each
case in a total
liquid of 6.67 1 with a pulp density of 0.24%. The respective amounts of
arabinoxylan
solution was added. After 5 min portioning and preparation of the laboratory
sheets was
carried out. All experiments were carried out at room temperature. Testing for
strength was
carried out according to ISO 1974 (DIN EN 21974).
Table 4
Influence of arabinoxylan from oat husks on the tear length of coniferous
sulfite
pulp. The arabinoxylan treatment took place at a pulp density of 0.24% after
refinement of the pulp.
Amount of arabinoxylan Tear length (m)
% (w/w) rel. to pulp
Reference 2830
4.7 3759
9.4 4216
28.1 4031
The tear length can be improved by more than 1000 m by the addition of
arabinoxylan from
oat husks compared to the reference. With this method of addition the
increases in strength
can be achieved with low usage of arabinoxylan.
Example 5
An arabinoxylan from oat husks (9.5% arabinose, < 1% 4-0-methylglucuronic acid
DP ca.
160) was dissolved in water with heating as 5% solution. A coniferous sulfite
pulp was then
refined for 2.5 min. in a Jokro mill in accordance with ISO 5264-3 and
laboratory sheets
prepared in accordance with ISO 5269-2 (rapid K6then method). The xylan
solutions were in
each case added to the pan which is used for portioning the suspension for the
individual
laboratory sheets. In each pan 16 g pulp were equalised in each case in a
total liquid of 6.671
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with a pulp density of 0.24%. A cationic polyamide-epichlorhydrin resin was
added as paper
auxiliary and stirred into the suspension for 5 min. The dosage of the paper
additive
corresponded constantly to a charge density of 0.013 meq/g pulp in all
experiments carried
out. Next the respective arabinoxylan solution was added. After 5 min
portioning and
preparation of the laboratory sheets was carried out. All experiments were
carried out at room
temperature. Testing for strength was carried out according to IS01974 (DIN EN
21974).
Table 5
Influence of arabinoxylan from oat husks on the tear length of coniferous
sulfite
pulp with concomitant use of a paper additive. The arabinoxylan treatment took
place at a pulp density of 0.24% after refinement of the pulp.
Amount of xylan Arabinoxylan with paper
% (w/w) rel. to pulp additive
Tear length (m)
Reference 3944
0.09 3992
0.93 4698
2.3 5486
4.7 5629
7.0 5710
9.4 5728
The tear length can again be significantly increased by the addition of
arabinoxylan compared
to the reference. It can be clearly seen from the reference that through the
use of the paper
additive the strength generally lies at a higher level. In regard to the
effect of the arabinoxylan
a synergistic effect emerges in the interaction with the paper additive. The
increases in the
tear length are now up to as much as ca. 1800 m. The higher increases in
strength are even
effective at lower amounts of arabinoxylan than in the experiments without
paper additive.
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Example 6
An arabinoxylan from oat husks (9.5% arabinose, < 1% 4-0-methylglucuronic
acid, DP ca.
160) was dissolved in water with heating as 5% solution. A beech wood sulfite
pulp was then
refined for 2.5 min, 5 min, 10 min, 15 min and 20 min in a Jokro mill in
accordance with ISO
5264-3 and laboratory sheets were prepared in accordance with ISO 5269-2
(rapid K6then
method). The arabinoxylan solutions at 9.4% (relative to pulp) were in each
case added to the
pan which is used for portioning the suspension for the individual laboratory
sheets. In each
pan 16 g pulp were equalised in each case in a total liquid of 6.67 1 with a
pulp density of
0.24%. 5 Min after addition of the arabinoxylan solution portioning and
preparation of the
laboratory sheets was carried out. All experiments were carried out at room
temperature.
Testing for strength was carried out according to IS01974 (DIN EN 21974).
Light scattering
coefficients were determined according to Instruction SCAN C 27:76.
The experiments showed that not only the tensile strength of the pulp was
increase by
arabinoxylan addition, but also the tear strength. The tear-tensile plot
allows combined
viewing of the tensile strength and tear strength of all samples from the
refmement series
(Figure 1, Effect of arabinoxylan from oat husks (9.38% relative to pulp) on
the tear-tensile
plot of beech sulfite pulp). It is obvious that the samples show clearly
better values in both
strengths by the addition of the arabinoxylan such that the whole curve is
displaced to a
higher level.
The specific volume of the pulp is characterised by the bulk, which is plotted
in Figure 2
against the tensile breaking strength (Effect of arabinoxylan from oat husks
(9.38% relative to
pulp) on the bulk-tensile plot of beech sulfite pulp). It is clear that the
curve for the different
points of the degree of refinement is displaced to higher bulk values. In
order to produce a
product with the desired strength a higher sheet volume can be produced by the
addition of
the arabinozylan. The increased bulk leads to an increase in the light
scattering coefficients
and thus to improved optical properties.
