U.S. patent application number 10/305929 was filed with the patent office on 2003-08-07 for process for making paper.
This patent application is currently assigned to COOPERATIEVE VERKOOP-EN PRODUCTIEVERENIGING VAN AARDAPPELMEEL EN DERIVATEN AVEBE B.A.. Invention is credited to Hendriks, Jan, Terpstra, Jacob.
Application Number | 20030145966 10/305929 |
Document ID | / |
Family ID | 8233797 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030145966 |
Kind Code |
A1 |
Terpstra, Jacob ; et
al. |
August 7, 2003 |
Process for making paper
Abstract
The invention relates to a process for making paper wherein an
anionic starch, which is based on a starch comprising at least 95
wt. %, based on dry substance of the starch, of amylopectin, or a
derivative of said starch, is used in combination with a fixative
as a strengthening agent.
Inventors: |
Terpstra, Jacob; (Assen,
NL) ; Hendriks, Jan; (Grolloo, NL) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Assignee: |
COOPERATIEVE VERKOOP-EN
PRODUCTIEVERENIGING VAN AARDAPPELMEEL EN DERIVATEN AVEBE
B.A.
|
Family ID: |
8233797 |
Appl. No.: |
10/305929 |
Filed: |
November 27, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10305929 |
Nov 27, 2002 |
|
|
|
09701820 |
Jan 10, 2001 |
|
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Current U.S.
Class: |
162/175 ;
162/164.1; 162/164.6; 162/168.3; 162/181.2 |
Current CPC
Class: |
D21H 23/76 20130101;
D21H 17/28 20130101; D21H 21/20 20130101 |
Class at
Publication: |
162/175 ;
162/181.2; 162/164.6; 162/164.1; 162/168.3 |
International
Class: |
D21H 017/28; D21H
017/29; D21H 017/56 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 1998 |
EP |
98201943.2 |
Claims
1. A process for making paper wherein an anionic starch, which is
based on a starch comprising at least 95 wt. %, based on dry
substance of the starch, of amylopectin, or a derivative of said
starch, is used in combination with a fixative as a strengthening
agent.
2. A process according to claim 1, wherein the starch is a root or
tuber starch.
3. A process according to claim 2, wherein the starch is a potato
or tapioca starch.
4. A process according to any one of claims 1-3, wherein the
derivative of the starch is obtained by an etherification or
esterification reaction, or a combination thereof.
5. A process according to any one of the preceding claims, wherein
the fixative is a cationic compound having a charge density of at
least 1 .mu.eq/mg.
6. A process according to any one of the preceding claims, wherein
the fixative is chosen from the group of polyaluminum compounds,
alum, cationic starch or a derivative thereof,
polydimethyldiallylammonium chlorides, polyamines, polyvinylamines,
polyethylene imines, and dicyandiamide polycondensates.
7. Paper obtainable by a process according to any one of the
preceding claims.
8. The use of an anionic starch, which is based on a starch
comprising at least 95 wt. %, based on dry substance of the starch,
of amylopectin, or a derivative of said starch, as a strengthening
agent in paper.
9. The use of an anionic starch, which is based on a starch
comprising at least 95 wt. %, based on dry substance of the starch,
of amylopectin, or a derivative of said starch, for reducing the
amount of a fixative in a process for making paper wherein an
anionic starch is used as a strengthening agent.
Description
[0001] The invention relates to a process for making paper and to
the use of starch in said process.
[0002] In order to increase the strength properties of paper, it
has been common practice during the last thirty years to add
cationic starch at the wet-end stage of the papermaking process.
The wet-end of the papermaking process refers to-the stages of the
papermaking process, wherein a pulp of fibers, obtained from
cellulose-based materials, such as recycled, used paper, wood,
cotton, or alternative sources, is being processed. The term
"wet-end" originates in the large amounts of water, in the presence
of which the pulp is processed.
[0003] During the last decade, there have been several trends in
the papermaking process which either call for more starch in the
paper than is feasible with cationic starch, or which make the
application of cationic starch more difficult. One of these trends
is the environmental demand to recycle paper. As paper is recycled,
the fibers of the paper tend to become shorter and weaker, the
latter of which is due to reduced interactions among the fibers. As
a result, increased amounts of starch are necessary in the wet-end
of the papermaking in-order to produce a paper which is
sufficiently strong. It has been found that after paper has been
recycled a certain number of times, the loss of strength due to
recycling cannot be compensated by adding cationic starch, leading
to paper having an inferior paper strength.
[0004] Another trend is the urge to produce cheaper paper. This can
be achieved by incorporating large amounts of a cheap filler into
the paper. However, a larger filler content of the paper results in
a deterioration of paper strength, which gives rise to a demand for
the addition of increased amounts of starch in the wet-end.
[0005] Yet another trend concerns a change in the apparatuses used
in the papermaking process. The conventionally used size-press is
more and more being replaced by a premetering size-press. The use
of a premetering size-press often has the effect that starch
penetrates to lesser degree into the paper sheet than when a
conventional size-press is used. As a result, the starch provides a
smaller contribution to the strength of the paper. Moreover, the
use of a premetering size-press for pigmentizing diminishes the
internal strength of the paper even more. Therefore, it is desired
to provide an increase of the strength of the paper obtained in the
wet-end.
[0006] In "Anionic starch: an effective wet-end concept for
enhancing paper strength", Proceedings of the PITA Annual
Conference, 87-91, Manchester, October 1997, J. Terpstra and R. P.
Versluijs have proposed to use anionic starch-instead of cationic
starch as a strengthening agent in the wet-end of the papermaking
process, in order to achieve a greater, internal strength of the
paper produced. This concept of using anionic starch has also been
described in P. Brouwer, Wochenblatt fur Papierfabrikation, 19
(1997), 928-937, WO-A-93/01353 and WO-A-96/05373, and may be
explained as follows.
[0007] The fibers and filler particles, which are used to produce
paper from, are negatively charged. When cationic starch is used as
a paper strengthening agent, its retention is mainly caused by the
interaction between the positively charged starch and the
negatively charged fibers and filler particles. In order to adhere
anionic starch molecules onto anionic fibers and filler particles,
use is made of a so-called cationic fixative. In principle, any
cationic paper and can be used as a fixative for the anionic
starch, although some lead to better results than others. Because
they are cheap and hardly affected by water hardness, polyaluminum
chlorides are considered very attractive fixatives. Other materials
that have been proposed for use as a fixative in this regard are,
inter alia, alum, or cationic polymers, such as
polydimethyldiallylammonium chloride and polyamines.
[0008] It has been found that, by using anionic starch in
combination with a suitable fixative, it is possible to incorporate
up to five times as much starch into a paper sheet in comparison
with the case wherein only cationic starch is used as a
strengthening agent. Of course, this results in a much stronger
paper sheet. At the same time, the retention of the starch in a
papermaking process is much higher when anionic starch and a
fixative are used instead of cationic starch. This means, that a
much smaller part of the starch, which is added to the pulp in the
wet-end of the papermaking process, is lost to the processing
water. Furthermore, by using anionic starch in combination with a
suitable fixative, it has been found that the retention of fines
and fillers is increased substantially, and it is possible to
reduce the refining. Also, an increase in dewatering speed has been
observed.
[0009] A disadvantage of the use of anionic starch instead of
cationic starch in the wet-end of the papermaking process resides
in the necessity of using a fixative. Even though some of the
fixatives proposed in the art are relatively cheap, the costs of
the paper that is produced may increase considerably because of the
use of the fixative. Also, as the fixative is a cationic compound;
it is inevitable that anionic counterions are added to the paper
along with the fixative. Often, the counterions are chloride ions
which are corrosive. Furthermore, the use of a fixative may lead to
a hardening of the process water and to the production of salts,
which may interfere with other papermaking aids.
[0010] Surprisingly, it has now been found that the above described
disadvantages of the use of anionic starch as a strengthening agent
in paper may be mitigated by using an anionic starch which
primarily comprises amylopectin.
[0011] Hence, the invention relates to a process for making paper
wherein an anionic starch, which is based on a starch comprising at
least 95 wt. %, based on dry substance of the starch, of
amylopectin, or a derivative of said starch, is used in combination
with a fixative as a strengthening agent.
[0012] The use of the specific anionic starch has been found to
make it possible to use significantly smaller amounts of a
fixative, when compared with the use of a conventional anionic
starch. Moreover, the incorporation of an anionic starch which
primarily comprises amylopectin into a paper sheet leads to a paper
sheet having a superior strength.
[0013] Most starch, types consist of granules in which two types of
glucose-polymers are present. These are amylose (15-35 wt. % on dry
substance) and amylopectin (65-85 wt. %, on dry substance). Amylose
consists of unbranched or slightly branched molecules having an
average degree of polymerization of 1000 to 5000, depending on the
starch type. Amylopectin consists of very large, highly branched
molecules having an average degree of polymerization of 1,000,000
or more. The commercially most important starch types (maize
starch, potato starch, wheat starch and tapioca starch) contain 15
to 30 wt. % amylose.
[0014] Of some cereal types, such as barley, maize, millet, wheat,
milo, rice and sorghum, there are varieties of which the starch
granules nearly completely consist of amylopectin. Calculated as
weight percent on dry substance, these starch granules contain more
than 95%, and usually more than 98% amylopectin. The amylose
content of these cereal starch granules is thus less than 5%, and
usually less than 2%. The above cereal varieties are also referred
to as waxy-cereal grains, and the amylopectin-starch granules
isolated therefrom as waxy cereal starches.
[0015] In contrast to the situation of different cereals, root and
tuber varieties of which the starch granules nearly exclusively
consist of amylopectin are not known in nature. For instance,
potato starch granules isolated from potato tubers usually contain
about 20% amylose and 80% amylopectin (wt. % on dry substance).
During the past 10 years, however, successful efforts have been
made to cultivate by genetic modification potato plants which, in
the potato tubers, form starch granules consisting for more than 95
wt. % (on dry substance) of amylopectin. It has even been found
feasible to produce potato tubers comprising substantially only
amylopectin.
[0016] In the formation of starch granules, different enzymes are
catalytically active. Of these enzymes, the granule-bound starch
synthase (GBSS) is involved in the formation of amylose. The
presence of the GBSS enzyme depends on the activity of genes
encoding for said GBSS enzyme. Elimination or inhibition of the
expression of these specific genes results in the production of the
GBSS enzyme being prevented or limited. The elimination of these
genes can be realized by genetic modification of potato plant
material or by recessive mutation. An example thereof is the
amylose-free mutant of the potato (amf) of which the starch
substantially only contains amylopectin through a recessive
mutation in the GBSS gene. This mutation technique is described in,
inter alia, J. H. M. Hovenkamp-Hermelink et al., "Isolation of
amylose-free starch mutant of the potato (Solanum tuberosum. L.)",
Theor. Appl. Gent., (1987), 75:217-221, and E. Jacobsen et al.,
"Introduction of an amylose-free (amf) mutant into breeding of
cultivated potato, Solanum tuberosum L., Euphytica, (1991),
53:247-253.
[0017] Elimination or inhibition of the expression of the GBSS gene
in the potato is also possible by using so-called antisense
inhibition. This genetic modification of the potato is described in
R. G. F. Visser et al., "Inhibition of the expression of the gene
for granule-bound starch synthase in potato by antisense
constructs", Mol. Gen. Genet., (1991), 225:289-296.
[0018] By using genetic modification, it has been found possible to
cultivate and breed roots and tubers, for instance potato, yam, or
cassave (Patent South Africa 97/4383), of which the starch granules
contain little or no amylose. As referred to herein,
amylopectin-potato starch is the potato starch granules isolated
from potato tubers and having an amylopectin content of at least 95
wt. % based on dry substance.
[0019] Regarding production possibilities and properties, there are
significant differences between amylopectin-potato starch on the
one hand, and the waxy cereal starches on the other hand. This
particularly applies to waxy maize starch, which is commercially by
far the most important waxy cereal starch. The cultivation of waxy
maize, suitable for the production of waxy maize starch is not
commercially feasible in countries having a cold or temperate
climate, such as The Netherlands, Belgium, England, Germany,
Poland, Sweden and Denmark. The climate in these countries,
however, is suitable for the cultivation of potatoes. Tapioca
starch, obtained from cassave, may be produced in countries having
a warm climate, such as is found in regions of South East Asia and
South America.
[0020] The composition and properties of root and tuber starch,
such as amylopectin-potato starch and amylopectin-tapioca starch,
differ from those of the waxy cereal starches. Amylopectin-potato
starch has a much lower content of lipids and proteins than the
waxy cereal starches. Problems regarding odor and foaming, which,
because of the lipids and/or proteins, may occur when using waxy
cereal starch products (native and modified), do not occur, or
occur to a much lesser degree when using corresponding
amylopectin-potato starch products. In contrast to the waxy cereal
starches, amylopectin-potato starch contains chemically bound
phosphate groups. As a result, amylopectin-potato starch products
in a dissolved state have a distinct polyelectrolyte character.
[0021] The invention contemplates the use of anionic starch
obtained from cereal and fruit sources on the one hand, and root
and tuber sources on the other hand. Of the cereal starches, waxy
maize starch has proven very suitable. In general, however, root
and tuber starches are more preferred. As has been indicated above,
it is often advantageous to use a starch having a very low content
of lipids and/or proteins. The use of anionic amylopectin-potato
starch and amylopectin-tapioca starch as a strengthening agent in
paper has been found to lead to a particularly strong paper
sheet.
[0022] By the term anionic starch is meant a starch having a charge
density of at least 0.03 seq/mg starch, preferably at least 0.15
.mu.eq/mg starch. In the context of the invention, the charge
density is defined as the amount of a cationic polymer (methyl
glycol chitosan iodide, Sigma M-3150) which has to be added to a
known amount of dissolved starch in order to reach the equivalence
point. This equivalence point may be determined by measuring the
electrophoretic zetapotential of the dispersion to which silicate
particles are added as indicator. The zetapotential can for
instance be measured by using a Malvern Zetasizer 3.
[0023] The anionic starch, which, according to the invention, is
used in combination with a fixative as a strengthening agent in
paper, may be prepared from the starch comprising at least 95 wt.
%, based on dry substance of the starch, of amylopectin, or the
derivative of said starch, on which it is based in any manner known
for regular starch comprising both amylopectin and amylose. For a
description of a possible manner of preparing an anionic starch,
reference may be made to O. B. Wurzburg (Ed.), "Modified Starches:
Properties and Uses", CRC Press Inc., Boca Eaton, Fla., 1986.
[0024] Examples of anionic starch may be obtained by introduction
of any anionic substituents or by any oxidation process known in
the derivatization of starch. Suitable examples of anionic
substituents are phosphate, phosphonate, sulfonate, sulfate,
(alkyl)succinate, anionic graft copolymers and combinations
thereof. An example of a suitable oxidation is oxidation by
hypochlorite. Preferably, a carboxymethyl of phosphated starch is
used. The degree of substitution (DS), which is the molar ratio
between the amount of substituted hydroxyl groups of a glucose unit
in the starch and the amount of glucose units in the starch, may
range between 0.005 and 0.5, preferably between 0.01 and 0.2, more
preferably between 0.01 and 0.1.
[0025] Suitable derivatives of a starch comprising at least 95 wt.
% amylopectin (based on dry substance) are starches wherein,
besides an anionic substituent, also one or more non-ionic or
cationic substituents may be introduced. Suitable examples of
non-ionic or cationic substituents may be introduced by
etherifcation idem esterifcation reactions, such as methylation,
ethylation, hydroxyethylation, hydroxypropylation,
alkylglycidylation (wherein the length of the alkyl chain varies
from 1 to 20 carbon atoms), acetylation, propylation,
carba-imidation, diethylamino-ethylation, and/or
trimethylammoniumhydroxy- propylation. Further, the starch may be
crosslinked by any crosslinking known in the derivatization of
starch. Examples of suitable crosslinking agents include
epichlorohydrine, dichloropropanol, sodium trimethaphosphate,
phosphorousoxychloride and adipic acid anhydride of course, care
should be taken that the overall charge of the starch is
anionic.
[0026] As has been indicated hereinabove, it is essential to use a
fixative, when anionic starch is used in the wet-end to provide
strength in paper. In accordance with the invention, suitable
fixatives are cationically charged compounds, which are capable of
binding anionic starch to anionic paper fibers and filler
particles. In principle, any cationic compound that has been
proposed for use as a fixative for anionic starch in the wet-end of
a papermaking process can be used. Examples include alum, cationic
starch or derivatives thereof, polyaluminum compounds, and cationic
polymers, such as polydimethyldiallylammonium chlorides,
polyamines, polyvinylamines, polyethylene imines, dicyandiamide
polycondensates, or other high molecular weight cationic polymers
or copolymers, e.g. comprising a quaternized nitrogen atom or
polyvinyl alcohol, and combinations thereof. Such cationic polymers
preferably should have a weight average molecular weight of at
least about 10,000, preferably at least about 50,000, more
preferably at least 100,000. In a preferred embodiment, the
cationic polymers have a weight average molecular weight in the
range from about 50,000 to about 2,000,000.
[0027] Preferably, a fixative having a high charge density is used.
In this regard, a charge density higher than 1 seq/mg. is
considered a high charge density. The charge density of the
fixative is defined as the amount of an anionic polymer (sodium
polystyrenesulfonate, Aldrich cat. no. 24,305-1) which has to be
added to a known amount of fixative (typically a few milliliters of
the fixative in 500 ml demineralized water) in order to reach the
equivalence point. This equivalence point may be determined by
measuring the electrophoretic zetapotential of the dispersion to
which silicate particles are added as indicator. The zetapotential
can for instance be measured by using a Malvern Zetasizer 3. It has
been found that the use of a fixative having a higher charge
density leads to a decreased sensitivity of the papermaking process
for the hardness and conductivity of the process water. Preferred
fixatives having a high charge density are polyaluminum compounds,
such as polyaluminum chloride or polyaluminum sulfate,
polydimethyldiallylammoniu- m chlorides, polyamines, and
combinations thereof.
[0028] In a process for making paper, the anionic starch, which is
based on a starch comprising at least 95 wt. %, based on dry
substance of-the starch, of amylopectin, or a derivative of said
starch, and the fixative are added at the wet-end of the process.
This means that they are added to a pulp comprising fibers obtained
from recycled paper or from wood and water. It is common practice
to add a filler compound to the pulp. In accordance with the
invention, any of the commonly used filler compounds, such as clay,
ground CaCO.sub.3, precipitated CaCO.sub.3, talc or
titaniumdioxide, may be employed. Preferably, the filler compound
is added to the pulp prior to the addition of the anionic starch
and the fixative. Further, the anionic starch is preferably added
to the pulp before the fixative is added.
[0029] The amount in which the anionic starch is added to the pulp
will depend on the desired paper strength. Generally, the amount
will vary between 0.1 and 10 wt. %, preferably between 1 and 5
wt.-, based on (consistency) the weight-of the solids in the pulp
(fibers, filler compounds, fines, and so forth).
[0030] The amount of the fixative which is added depends on the
nature of the fixative and the pulp that is being used and on the
amount of anionic starch that is to be incorporated into the paper.
Generally, the amount of fixative is chosen such that at least 60%,
preferably at least 80%, more preferably at least 90% adsorption of
the anionic starch is attained. It is noted that in this regard a
distinction should be made between adsorption and retention.
Retention refers to the amount of starch added in the wet-end that
is eventually incorporated in the paper, while adsorption refers to
the amount of starch added in the wet-end that adsorbs to the paper
fibers in the pulp in the wet-end. The skilled person will be able
to adjust the amount of the fixative to the circumstances at hand.
Typical values differ for inorganic and organic fixatives. When
normal, amylose containing anionic starch is used, the weight ratio
of fixative to anionic starch is about 1:1 for inorganic fixatives
and about 1:4 for organic fixatives. When, in accordance with the
invention, an amylopectin type anionic starch is used, these
amounts may be reduced by a factor of about 8-10 for organic
fixatives and a factor of about 4-6 for inorganic fixatives.
[0031] The pulp that is used for making paper in a process
according to the invention may be any aqueous suspension of
cellulose-based fibers that can be used to make paper from. After
the anionic starch and the fixative have been added to the pulp,
the pulp may be processed into paper in any known manner.
[0032] The invention will now be further elucidated by the
following, non-restrictive examples.
EXAMPLE I
[0033] A solution of 30 g urea and 31.1 g phosphoric acid (85%) in
85 ml of water was neutralized to pH 6.0 with 50% NaOH. This
solution was mixed with 600 g of amyopectin-potato starch (moisture
20%) for 30 minutes in a Hobart mixer. The mixture was equilibrated
and subsequently dried in a Retsch fluid bed dryer for 30 minutes
at 60.degree. C., and for 30 minutes at 90.degree. C. the mixture
was heated at 145.degree. C. in a fluid bed reactor for 30 minutes.
The resulting product was HK4017A and had a charge density of 0.47
.mu.eq/mg.
EXAMPLE II
[0034] A solution of 30 g urea and 31.1 g phosphoric acid (85%) in
85 ml of water was neutralized to pH 6.0 with 50% NaOH. This
solution was mixed with 600 g of amyopectin-potato starch (moisture
20%) for 30 minutes in a Hobart mixer. The mixture was equilibrated
and subsequently dried in a Retsch fluid bed dryer for 30 minutes
at 60.degree. C., and for 30 minutes at 90.degree. C. the mixture
was heated at 140.degree. C. in a fluid bed reactor for 30 minutes.
The resulting product was HK4041B and had a charge density of 0.34
.mu.eq/mg.
EXAMPLE III
[0035] The adsorption of the starch on to solid pulp components was
studied as follows. To a pulp (consistency of 1%) anionic starch
was added (dosage 3% on consistency). The pulp was stirred in a
baffled beaker at 800 rpm. After 60 seconds a fixative was added
and after another 60 seconds the pulp was filtered. The starch
adsorption was determined by measuring the amount of non-adsorbed
starch in the filtrate.
[0036] The pulp was a birch sulfate pulp beaten to 35.degree.SR
(measured at 21.degree. C.) at a consistency of 2% in tap-water
using a Hollander. After beating the pulp was diluted to a
consistency of 1% with tap-water.
[0037] The pulp was divided in three separate batches., The
conductivity of one batch was set to 3.01 mS/cm with sodium
sulphate (Na.sub.2SO.sub.4.10H.sub.2O, Merck reinst). The water
hardness of the second batch was increased from ca. 11 to ca.
80.degree.GH by adding calcium chloride (CaCl.sub.2.2H.sub.2O,
Merck reinst). The resulting conductivity of this batch was 3.01
ms/cm. To the third batch no salt was added. The conductivity and
water hardness was 0.51 mS/cm and ca. 11.degree.GH, respectively.
The conductivity of the pulp was measured with a Radiometer CDM 80
conductivity meter.
[0038] The starches used are: anionic potato starch PR9510 A
(commercialized as Aniofax AP25) and two anionic amylopectin potato
starches: HK4017A and HK4041B. The latter two products were
prepared as described in Examples I and II, respectively. The
starches were cooked with life steam starting with a 10% slurry in
tap-water. After cooking the starch solutions were diluted to 5%
with hot tap-water. The viscosities of the 5% solutions were
determined using a Brookfield LVTDV-II at 60 rpm (see table 1). The
degrees of substitution of phosphate in the starches were
determined as described in J. Th. L. B. Rameau and J. ten Have,
Chemisch Weekblad, No. 50 (1951), after excess of phosphate was
removed by dialysis against 0.05 N HCl solution for 48 hours and
against demineralized water for 24 hours, and neutralization to pH
7-8 with 0.10 N NaOH.
1TABLE 1 Characterization of the applied starches Viscosity DS P
(50.degree. C., 5%) Starch [mol/mol] [mPa .multidot. s] pH PR9510A
(AZM) 0.022 391 7.1 HK4017A (AAZM) 0.024 680 7.1 HK4041B (AAZM)
0.018 252 7.2
[0039] The used fixatives are Sachtoklar (obtained from Sachtleben
Chemie GmbH, Germany), Retinal 1030 (obtained from Joud, france),
and PD5-8159 (obtained from Allied Colloids Ltd., UK).
[0040] Before use, the fixatives Sachtoklar and Retinal 1030 were
diluted by a factor of 10 with demineralized water. A solution of
PD5-8159 was prepared by first dissolving 1 g of polymer in 4 g of
acetone. After stirring for 30 minutes 95 g demineralized water was
added. Some properties of the fixatives are listed in table 2.
[0041] The charge density of the fixatives was determined by adding
sodium polystyrenesulfonate to a known amount of fixative
(typically a few milliliters of the fixative in 500 ml
demineralized water). The amount necessary in order to reach the
equivalence point was the charge density. This equivalence point
was determined by measuring the electrophoretic zetapotential,
using a Malvern Zetasizer 3, of the-dispersion to which silicate
particles were added as indicator.
2TABLE 2 Characterization of the applied fixatives Viscosity
(20.degree. C., pH of as received, fixative 60 rpm) Solids Charge
density Fixative as received [mPa .multidot. s] [%] [.mu.eq/mg]
Sachtoklar 2.3 7.3 23.2 +2.0 (= Paper- PAC-N) Retinal 5.7 950 50.1
+7.6 1030 PD5-8159 6.6 2240 26.8 +7.0
[0042] The amount of starch in the filtrate was determined in an
enzymatic method. In accordance with this method, starch is first
converted into glucose with an a-amylase and an amyloglucosidase.
Subsequently, the amount of glucose is determined spectroscopically
using a hexokinase test method (Boehringer no. 716251). The amount
of starch is calculated from the obtained amount of glucose using a
correction factor for incomplete conversion of the starch into
glucose by the enzymes. The applied enzymatic conversion factor of
Aniofax AP25 is 0.78. The starch adsorption was calculated from the
enzymatically determined starch concentration in the filtrate using
the following expression: 1 A = 1 - c s .times. V G eq . A
[0043] where A is the starch adsorption, c.sub.s is the starch
concentration in the filtrate, V is the total volume of water and G
is the added amount of starch. The total amount of water is
obtained by:
V=V.sub.p-ds.sub.p+V.sub.st-ds.sub.st+V.sub.fix-ds.sub.fix eq.
B
[0044] where V.sub.p, V.sub.st and V.sub.fix represent the volume
of the batch of pulp, the volume of the starch dosage and the
volume of the fixative dosage, respectively. The total volume is
corrected for the dry solids contents ds.sub.p, ds.sub.st, and
ds.sub.fix (assuming density of dry solids is 1 g/ml).
[0045] The starch adsorption was investigated by varying three
parameters: starch, fixative and pulp properties (conductivity and
water hardness). The results will be discussed using the fixative
dosage expressed as dry on fiber.
[0046] An overview of the fixative dosages needed for a starch
adsorption of at least 90% is given in table 3 for each starch and
each experimental condition.
[0047] The smallest amount of fixative for a starch adsorption
>90% is needed in case of HK4017A. For PD5-8159 the fixative
dosage is 1.5 to 2.5 times larger in case of HK4041B and 2.5 to 5
times for PR9510A. For Retinal 1030 the increase of the dosage is a
factor 2 to 2.5 for HK4041B and-2 to at least 5 for PR9510A.
[0048] Also for the PAC Sachtoklar the best results are obtained
for the amylopectin starches. In case of PR9510A the PAC dosage is
1.5 to more than 3.5 times higher than in case of HK4017A.
[0049] A noteworthy difference between PR9510A and HK4017A is the
effectivity of the organic fixatives PD5-8159 and Retinal 1030 at
high water hardness. With HK4017A the starch adsorption is higher
at high hardness for both fixatives, while with PR9510A the
adsorption is the same or lower. Thus, with this anionic AAZM a
high water hardness leads to higher starch adsorptions, not only
for PACs but also for the tested organic fixatives. In case of the
other anionic AAZM, HK4041B, the same effect of water hardness is
observed for Retinal 1030, but not for PD5-8159.
[0050] These results confirm that the applied organic fixatives are
more effective in adsorbing amylopectin molecules than in adsorbing
amylose molecules.
3TABLE 3 Data for comparison of the starches. The listed fixative
dosage is the lowest dosage for which a starch adsorption higher
than 90% is obtained. The ratio of fixative dosages is the amount
of fixative needed with HK4041B or PR9510A divided by the amount
needed for HK4017A. Ratio of Exp. Cond. Hard- Fix. Starch fix. nr.
Fixative (mS/cm) ness Starch dos. ads. dos. 1 Sachtoklar 0.51 11
HK4017A 0.46 99.0 -- 2 Sachtoklar 0.51 11 HK4041B 0.46 92.6 1 3
Sachtoklar 0.51 11 PR9510A 0.70 98.6 1.5 4 Sachtoklar 3.01 11
HK4017A 0.46 93.4 -- 5 Sachtoklar 3.01 11 HK4041B 0.70 90.6 1.5 6
Sachtoklar 3.01 11 PR9510A 1.62 85.6 >3.5 7 Sachtoklar 2.98 80
HK4017A 0.23 95.0 -- 8 Sachtoklar 2.98 80 HK4041B 0.46 96.9 2 9
Sachtoklar 2.98 80 PR9510A 0.46 92.6 2 10 PD5-8159 0.51 11 HK4017A
0.10 94.5 -- 11 PD5-8159 0.51 11 HK4041B 0.15 92.6 1.5 12 PD5-8159
0.51 11 PR9510A 0.25 92.3 2.5 13 PD5-8159 3.01 11 HK4017A 0.25 98.0
-- 14 PD5-8159 3.01 11 HK4041B 0.50 91.9 2 15 PD5-8159 3.01 11
PR9510A 1.00 91.3 4 16 PD5-8159 2.98 80 HK4017A 0.10 97.0 -- 17
PD5-8159 2.98 80 HK4041B 0.25 91.7 2.5 18 PD5-8159 2.98 80 PR9510A
0.50 94.2 5 19 Retinal 0.51 11 HK4017A 0.13 95.2 -- 1030 20 Retinal
0.51 11 HK4041B 0.25 97.2 2 1030 21 Retinal 0.51 11 PR9510A 0.25
91.8 2 1030 22 Retinal 3.01 11 HK4017A 0.25 92.0 -- 1030 23 Retinal
3.01 11 HK4041B 1.00 94.6 4 1030 24 Retinal 3.01 11 PR9510A 1.00
89.9 >4 25 1030 2.00 95.7 8 26 Retinal 2.98 80 HK4017A 0.05 90.0
-- 1030 27 Retinal 2.98 80 HK4041B 0.13 91.5 2.5 1030 28 Retinal
2.98 80 PR9510A 0.25 93.3 5 1030
* * * * *