Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MODIFYING STARCH FOR INCREASED PAPERMACHINE
'RETENTION AND DRAINAGE PERFORMANCE
FIELD OF THE INVENTION
[0001] The present invention relates to modifying starch with metal
silicates, and the use of the modified starch in the preparation of cellulosic
fiber
compositions. The present invention further relates to cellulosic fiber
compositions, such as paper and paperboard, which incorporate the starch
modified with metal silicates.
BACKGROUND OF THE INVENTION
[0002] The making of cellulosic fiber sheets, particularly paper and
paperboard, includes the following: 1) producing an aqueous slurry of
cellulosic
fiber; which may also contain inorganic mineral extenders or pigments; 2)
depositing this slurry on a moving papermaking wire or fabric; and 3) forming
a
sheet from the solid components of the slurry by draining the water.
[0003] The foregoing is followed by pressing and drying the sheet to
further remove water. Organic and inorganic chemicals are often added to the
slurry prior to the sheet-forming step to make the papermaking method less
costly, more rapid, and/or to attain specific properties in the final paper
product.
[0004] The paper industry continuously strives to improve paper quality,
increase productivity, and reduce manufacturing costs. Chemicals are often
added to the fibrous slurry before it reaches the papermaking wire or fabric,
to
improve the drainage/dewatering and solids retention; these chemicals are
called retention and/or drainage aids.
[0005] Drainage or dewatering of the fibrous slurry on the papermaking
wire or fabric is often the limiting step in . achieving faster method speeds.
Improved dewatering can also result in a dryer sheet in the press and dryer
sections, resulting in reduced energy or steam consumption. Yet further, this
is
the stage in the papermaking method that determines many sheet final
properties.
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[0006] Papermaking retention aids are used to increase the retention of
fine furnish solids in the web during the turbulent method of draining and
forming the paper web. Without adequate retention of the fine solids, they are
either lost to the method effluent or accumulate to high levels in the
recirculating white water loop, potentially causing deposit buildup.
Additionally,
insufficient retention increases the papermakers' cost due to loss of
additives
intended to be adsorbed on the fiber to provide the respective paper opacity,
strength, or sizing property.
[0007] Cationic starch is utilized extensively in the paper industry. It is
introduced into the pulp slurry to increase interfiber bonding and to obtain
paper
strength properties, to emulsify synthetic internal sizing agents, such as
alkenyl
succinic anhydride (ASA), or to provide drainage.
[0008] Metal silicates, which include sodium silicate, potassium silicate,
and sodium metasilicate, are commodity chemicals utilized widely in many
industries, including paper and water treatment.
[0009] In US Patent 5,185,206, Rushmere teaches an improved
drainage aid and retention aid for papermaking which is added to an aqueous
paper furnish containing pulp and which comprises a silicated cationic starch
composition which is a dry solid which contains from about 1 to 25 wt % silica
and consists essentially of granules of a cationized starch having the silica
in
the form of a water soluble polysilicate microgel deposited on the surfaces
thereof and, optionally, the composition further containing discreet
agglomerates of silica microgels in admixture with the silicated starch
granules.
The one-component product is a dry solid which offers convenience and
economy over colloidal silica combinations because shipping large quantities
of
water can be avoided. In practicing the invention, it is preferred that as
much
microgel as possible be deposited onto the surface of each starch granule..
Thereby, optimum redispersion of the microgels will be achieved when the
starch is subsequently heated in water just prior to being used.
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[0010] It has been unexpectedly discovered that the addition of metal
silicate to cationic starch provides a remarkable increase in retention and
drainage performance.
SUMMARY OF THE INVENTION
[0011] This invention describes a method for improving the retention
and drainage properties during the papermaking process by the addition of a
cationic or amphoteric polysaccharide or polysaccharide derivative that has
been modified with a metal silicate.
[0012] The present method also provides for a method of modifying a
cationic or amphoteric polysaccharide or polysaccharide derivative by the
addition of a metal silicate.
[0013] The present invention also provides for a cationic or amphoteric
polysaccharide or polysaccharide derivative modified with a metal silicate
[0014] In one embodiment of the invention the' cationic or amphoteric
polysaccharide or polysaccharide derivative is a cationic or amphoteric
starch.
[0015] Also disclosed is a papermaking process comprising adding to a
papermaking slurry, at least one polysaccharide or polysaccharide derivative,.
wherein the polysaccharide or polysaccharide derivative has been modified
with at least one metal silicate, wherein the at least one polysaccharide or
polysaccharide derivative is selected from the group consisting of
polysaccharide derivatives containing a cationic nitrogen group, a blend of
cationic and anionic polysaccharides and combinations thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0016] It has been discovered that the addition of metal silicate to
cationic starch will provide a dramatic increase in the drainage. Best results
are
obtained when the metal silicate is added to the starch after the starch has
been cooked. The metal silicate can be added while the starch is still at an
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elevated temperature or after the starch has been cooled to ambient
temperatures. Improved retention and drainage performance has also been
observed with adding the metal silicate to the water prior to adding the
starch
and cooking. In one embodiment of the invention the metal silicate is sodium
silicate. The metal silicate may also be potassium silicate or sodium
metasilicate.
[0017] The materials utilized in the method of the invention include
cellulosic pulp and at least one starch modified with a metal silicate. There
can
also be employed one or more additional materials, including, but not limited
to,
additional unmodified starch,. filler, inorganic or organic coagulant,
conventional
flocculant, and at least one organic or inorganic drainage aid.
[0018] In one embodiment of the invention the cationic or amphoteric
polysaccharide or polysaccharide derivative is a 'cationic or amphoteric
starch.
[0019] The order in which the different materials are introduced into the
method of the invention is not limited to that set forth in the preceding
discussion, but will generally be based on practicality and performance for
each
specific application.
[0020] Suitable cellulosic fiber pulps for the method of the invention
include conventional papermaking stock such as traditional chemical pulp. For
instance, bleached and unbleached sulfate pulp and sulfite pulp, mechanical
pulp such as groundwood, thermomechanical pulp, chemi-thermomechanical
pulp, recycled pulp such as old corrugated containers, newsprint, office
waste,
magazine paper and other non-deinked waste, deinked waste, and mixtures
thereof, may be used.
[0021] Fillers are used in papermaking. Filler provides optical
properties to the cellulosic product. It provides opacity and brightness to
the
finished sheet, and improves its printing properties. Fillers which are
suitable
include calcium carbonate (both naturally occurring ground carbonate and
synthetically produced precipitated carbonate), titanium oxide, talc, clay,
and
gypsum. The amount of filler employed can be that which results in a
cellulosic
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product of up to about 50 weight percent filler, based on the dry weight of
the
pulp.
[0022] Coagulants are utilized to enhance retention and drainage.
Coagulants may be either inorganic or organic. The most common inorganic
coagulant is an alumina species. Suitable examples include, but are not
limited
to, technical grade aluminum sulfate (alum), polyaluminum chloride,
polyhydroxy aluminum chloride, polyhydroxy aluminum sulfate, sodium
aluminate, and the like. The organic coagulant is typically a synthetic,
polymeric
material. Suitable examples include, but are not limited to, polyamines,
poly(amido amines), polyDADMAC (poly(diallyldimethylammonium chloride)),
polyethyleneimine, hydrolyzates and quaternized hydrolyzates of N-vinyl
formamide polymers and copolymers, and the like.
[0023] Coagulants are generally employed in a proportion of from
about 0.05 lb. per ton to about 50 lbs. per ton of cellulosic pulp, based on
the
dry weight of the pulp. The coagulant concentration can be from about 0.5 lbs.
per ton to about 20 lbs. per ton, and or from about 1 lb. per ton to about 10
lbs.
per ton, of the pulp.
[0024] Ionic flocculants are conventionally used in the papermaking
art.. Cationic, anionic, nonionic, and amphoteric flocculants--particularly,
.cationic, anionic, nonionic, and amphoteric polymers--can be used. Polymers
suitable as flocculants include, but are not limited to, homopolymers of a
nonionic ethylenically unsaturated monomer. Copolymers of monomers
comprising two or more nonionic ethylenically unsaturated monomers can also
be used, as can copolymers of monomers comprising at least one nonionic
ethylenically unsaturated monomer and at least one cationic ethylenically
unsaturated monomer and/or at least one anionic ethylenically unsaturated
monomer. Suitable nonionic ethylenically unsaturated monomers include, but
are not limited to, acrylamide; methacrylamide; N-alkylacrylamides, such as N-
methylacrylamide; N,N-dialkylacrylamides, such as N,N-dimethylacrylamide;
methyl acrylate; methyl methacrylate; acrylonitrile; N-vinyl methylacetamide;
N-
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vinyl methyl formamide; vinyl acetate; N-vinyl pyrrolidone; hydroxyetkyl(meth)
acrylates such as hydroxyethyl(meth) acrylate or hydroxypropyl(meth) acrylate;
mixtures of any of the foregoing and the like. Of the foregoing, acrylamide,
methacrylamide, and the N-alkylacrylamides are preferred, with acrylamide
being particularly preferred.
[0025] The cationic ethylenically unsaturated monomers which may be
used include, but are not limited to, diallylamine, the (meth)acrylates of
dialkylaminoalkyl compounds, the (meth)acrylamides of dialkylaminoalkyl
compounds, the N-vinylamine hydrolyzate of N-vinylformamide, and the salts
and quaternaries thereof. The N,N-dialkylaminoalkyl acrylates and
methacrylates, and their acid and quaternary salts, are preferred, with the
methyl chloride quaternary of N,N-dimethylaminoethylacrylate being
particularly
preferred.
[0026] Suitable anionic ethylenically unsaturated monomers include,
but are not limited to, acrylic acid, methylacrylic acid, and their salts; 2-
acrylamido-2-methyl-propane sulfonate; sulfoethyl-(meth)acrylate;
vinylsulfonic
acid; styrene sulfonic acid; and maleic and other dibasic acids and their
salts.
Acrylic.acid, methacrylic acid and their salts are preferred, with the sodium
and
ammonium salts of acrylic acid being particularly preferred.
[0027] Cationic polymer flocculants will generally contain one or more
of the cationic monomers described above. The level of total cationic monomer,
based upon molar concentrations, can range from about 1 to about 99%,
preferably from about 2 to about 50%, and still more preferably from about 5
to
about 40 mole % cationic monomer, with the remaining monomer being one of
the previously described non-ionic monomers.
[0028] Anionic polymer flocculants will generally contain one or more of
the anionic monomers described above. The level of total anionic monomer,
based upon molar concentrations, will range from about 1 to about 99%,
preferably from about 2 to about 50%, and still more preferably from about 5
to
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about 40 mole % anionic monomer, with the remaining monomer being one of
the previously described non-ionic monomers.
[0029] Amphoteric polymer flocculants will contain a combination of
one or more of the described cationic and anionic monomers. Any combination
of cationic and anionic monomer(s) can be used, provided at least one cationic
and one anionic monomer are utilized. The polymer may contain an excess of
cationic monomer, an excess of anionic monomer, or equivalent amounts of
both cationic and anionic monomers. The level of total ionic monomer, being
the combined amount of both cationic and anionic monomers, based upon
molar concentrations, will range from about I to about 99%, preferably from
about 2 to about 80%, and still more preferably from about 5 to about 40 mole
% ionic monomer, with the remaining monomer being one of the previously
described non-ionic monomers. The flocculant can be employed, in,a
proportion of from about 0.01 lb. per ton to about 10 lbs. per ton of
cellulosic
pulp,,based upon active polymer weight and on the dry weight of the pulp. The
concentration of flocculant is more preferably from about 0.05 lb. per ton to
about 5 lbs. per ton, and still more preferably from about 0.1 lb. per ton to
about
1 lb. per ton, of the pulp.
[0030] In addition to the conventional flocculants, inorganic or organic
drainage aids, known in the art as microparticles, micropolymers, organic
microbeads, or associative polymers, may also be employed.
[0031] The inorganic microparticles employed include any of the
materials selected from the group consisting of silica based particles, silica
microgels, colloidal silica, silica sols, silica gels, polysilicates,
polysilicate
microgels, aluminosilicates, polyaluminosilicates, borosilicates,
polyborosilicates and zeolites. The inorganic microparticle may also be a
swellable clay, including, but not limited to, clays often referred to as
hectorite,
smectites, montmorillonites, nontronites, saponite, sauconite, hormites,
attapulgites and sepiolites.
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[0032] The micropolymers or organic microbeads are crosslinked,
cationic or anionic, polymeric, organic microparticles having an unswollen
number average particle size diameter of less than about 750 nanometers and
a crosslinking agent content of above about 4 molar parts per million based on
the monomeric units present in the polymer and are generally formed by the
polymerization of at least one ethylenically unsaturated cationic or anionic
monomer and, optionally, at least one non-ionic comonomer in the presence of
said crosslinking agent. One example of a micropolymer is Polyflex (CIBA
Corporation, Tarrytown, NY)
[0033] The associative polymer useful in the present invention can be
described as a water-soluble copolymer composition, wherein the associative
properties of the inverse emulsion anionic copolymer are provided by an
emulsification surfactant chosen from diblock and triblock polymeric
surfactants. The associative inverse emulsion anionic copolymer contains at
least one nonionic polymer segment and at least one anionic polymer segment,
and has a Huggins' constant (k') determined in 0.01 M NaCl greater than 0.75
and a storage modulus (G) in a 1.5 wt. % actives polymer solution at 4.6 Hz
greater than 175 Pa. Examples of associative polymers include, but are not
limited, to PerForm 9232 and PerForm 7200 (Hercules Incorporated,
Wilmington, DE)
[0034] Starch adds strength properties to the cellulose products,
particularly dry strength by increasing inter-fiber bonding. Starch will also
affect
drainage properties. Starch is the common name for a polymer of glucose that
contains alpha-1,4 linkages. Starch is a naturally occurring material; this
carbohydrate can be found in the leaves, stems, roots and fruits of most land
plants. The commercial sources of starch include, but are not limited to, the
seeds of cereal grains (corn, wheat, rice, etc.), and certain roots (potato,
tapioca, etc.). Starch is described by its plant source; reference would be
made
to, for example, corn starch, potato starch, tapioca starch, rice starch, and
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wheat starch.. Starch can be considered to be a condensation polymer of
glucose.
[0035] Generally starches consist of a mixture of two polysaccharide
types: amylose, an essentially linear polymer, and amylopectin, a highly
branched polymer. The relative amounts of amylose and amylopectin vary with
the source, with the ratio of amylose to amylopectin typically being 17:83 for
tapioca, 21:79 for potato, 28:72 for corn and 0:100 for waxy maize corn.
Although these are the typical starch ratios found the present invention
contemplates that any ratio of amylose to amylopectin can be useful in the
present invention. For the purposes of this invention waxy maize is considered
a type of corn starch.
[0036] Starch is synthesized by plants and accumulates in granules
that are distinctive for each plant. Starch granules are separated from the
plant
through a milling and grinding process. The granules are insoluble in cold
water
and must be heated above a critical temperature in order for the granules to
swell and rupture, allowing the polymer to dissolve in solution.
[0037] Starch can be modified to provide specific properties of value in
selected applications. This includes modification to either or both the
physical
and chemical structure of the material. Physical modification includes
reduction
in molecular weight, which is most often achieved by hydrolysis. Such modified
materials are often referred to as derivatized starch or starch derivatives.
[0038] The present invention modifies a cationic or amphoteric
polysaccharide or polysaccharide with a metal silicate. The cationic or
amphoteric polysaccharide or polysaccharide derivative is preferably a
cationic
or amphoteric starch or starch derivative.
[0039] Starches that may be used in the method of the invention
include cationic and amphoteric starches. Suitable starches include those
derived from corn, potato, wheat, rice, tapioca, and the like. Cationicity is
imparted by the introduction of cationic groups, and amphotericity by the
further
introduction of anionic groups. For instance, cationic starches may be
obtained
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by reacting starch with tertiary amines or with quaternary ammonium
compounds, e.g., dimethylaminoethanol and 3-chloro-2-
hydroxypropyltrimethylammonium chloride. Cationic starches preferably have a
cationic degree of substitution (D.S.)--i.e., the average number of cationic
groups substituted for hydroxyl groups per anhydroglucose unit--of from about
0.01 to about 1.0, more preferably about 0.01 to about 0.10, more preferably
about 0.02 to 0.04.
[0040] Amphoteric starches can be provided by adding anionic groups
to cationic starches. Preferred amphoteric starches are those with a net
cationicity. As an example, anionic phosphate groups can be introduced into
cationic starches through reaction with phosphate salts or phosphate
etherifying reagents. Where the cationic starch starting material is starch
diethylaminoethyl ether, the amount of phosphate reagent employed in the
modification preferably is that which will provide about 0.07-0.18 mole of
anionic groups per mole of cationic groups.
[0041] Other amphoteric starches that may be used are those made by
introduction of sulfosuccinate groups into cationic starches. This
modification is
accomplished by adding maleic acid half-ester groups to a cationic starch and
reacting the maleate double bond with sodium bisulfite.
[0042] Cationic starch can also be etherified with 3-chloro-2-
sulfopropionic acid, carboxyl groups can be introduced into starches by
reaction
with sodium chloroacetate or by hypochlorite oxidation, and propane sultone
can be employed to treat cationic starches to provide amphotericity.
[0043] Further useful amphoteric starches can be obtained by
xanthation of diethylaminoethyl- and 2-(hydroxypropyl)trimethylammonium
starch ethers.
Yet additionally, the modification can be extended by the introduction of
nonionic or hydroxyalkyl groups from treatment with ethylene oxide or
propylene oxide.
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[0044] Starches that require gelatinizing or "cooking" at the use
location, or pre-gelatinized, cold-water dispersion starches can be used.
Starch
granules are insoluble in water. The gelatinization of starch at elevated
temperatures results in water penetrating the starch granule, rupturing the
granule and releasing the starch molecule into solution. The release of the
starch molecule into solution results in an increase in the solution
viscosity. The
starch is cooked by heating an aqueous solution of starch for 10 to 90 minutes
at temperatures of 50 to 98 C until a thick, clear solution is obtained.
[0045] In some embodiments of the present invention aqueous
solutions of starch are prepared at concentrations typically ranging from I to
5%. The Starch is added to cellulosic pulp, in a proportion of from about 1
lb.
per ton to about 100 lbs. per ton of cellulosic pulp, based on the dry weight
of
the pulp. The starch concentration is more preferably from about 2.5 lbs. per
ton to about 50 lbs. per ton, and still more preferably from about 5 lbs. per
ton
to about 25 lbs. per ton, of the pulp. These weights do not include the weight
of
the metal silicate used to modify the starch. In the present invention the
starch
or a portion of the starch will be modified by metal silicate prior to being
added
to the cellulosic pulp.
[0046] Metal silicate is preferably employed, in the method of the
invention, in a proportion of from about 0.1 lb. per ton to about 10 lbs. per
ton of
cellulosic pulp, based on the dry weight of the pulp. The metal silicate
concentration is more preferably from about 0.5 lbs. per ton to about 5 lbs.
per
ton, and still more preferably from about 1 lb. per ton to about 2 lbs. per
ton, of
the pulp.
[0047] The weight ratio of cationic starch to metal silicate (as Si02) can
vary from 1:10 to 100:1 or can vary for 1:1 to 50:1. The preferred weight
ratio is
from about 20:1 to about 2:1, or from 15:1 to 2:1, or from 10:1 to 2:1 or from
10:1 to 3:1.
[0048] Other polysaccharides may also be employed for modification
with metal silicates. These include, but are not limited to, guar, cellulose
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derivatives such as hydroxyethylcellulose, hydroxypropylcellulose,
methylcellulose, chitin and the like. The other polysaccharides may be
unsubstituted, or substituted with cationic, anionic, or combined cationic or
anionic moieties. These polysaccharides are in a proportion of from about 1
lb.
per ton to about 100 lbs. per ton of cellulosic pulp, based on the dry weight
of
the pulp, preferably from about 2.5 lbs. per ton to about 50 lbs. per ton, and
still
more preferably from about 5 lbs. per ton to about 25 lbs. per ton, of the
pulp.
These weights do not include the weight of the metal silicate used to modify
the
polysaccharide. -
[0049] The metal silicate can be any of the alkali silicate commonly
utilized, including, for example sodium silicate, aka "water glass", potassium
silicate, and-sodium metasilicate or. any combination of the metal silicates.
Sodium silicate can vary in the Si02:Na2Oweight ratio, which is controlled
during manufacture by the ratio of the two reactants. The ratio of Si02:Na2O
for
commercially available sodium silicates can vary from about 3.22 to about 2Ø
The weight ratio of potassium silicate Si02:K20 can vary from about 1.65 to
about 2.50. The metal silicates are available as an aqueous solution or a dry
powder version. The preferred metal silicate is a sodium silicate solution
with
a Si02:Na2O ratio of 3.22:1.
[0050] In the present invention a polysaccharide or derivitized,
polysaccharide is modified by.at least one metal silicate. The modified
polysaccharide or derivitized polysaccharide modified with the at least one
metal silicate is then added to a papermaking process.
[0051] In one embodiment of the invention the polysaccharide or
polysaccharide derivative is a cationic or amphoteric starch. The metal
silicate
can be added to the cationic or amphoteric starch after the starch has been
cooked, while the starch is still warm (> 65 C), has moderately cooled (30 to
65 C) or has been cooled to ambient temperatures (< 30 C). The addition of
the metal silicate to the cooked starch results in slight increases in the
turbidity
and viscosity of the starch solution.
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[0052] The metal silicate can also be added to the aqueous starch
slurry before the starch has been cooked such that the starch granules are
gelatinized in the presence of the metal silicate. In this embodiment the
starch
is then cooked in the presence of the metal silicate. This process also
produces
a starch solution which is more turbid, but less viscous, than a starch
solution
cooked without the addition of metal silicate.
[0053] The starch modified with metal silicate may be added to the
thick stock, in the machine chest or blend chest. Alternatively the starch
modified with metal silicate may be added to the thin stock, after or before
any
of the typical thin stock addition points, i.e. fan pump, cleaners, or screen.
[0054] In the present invention, the metal silicate may be added to all
of the starch, or may treat a side stream of the starch to modify a fraction
of the
starch. In a preferred embodiment the metal silicate is added to all of the
starch. The starch modified with metal silicate may also be added
simultaneously, before, or after any of the conventional wet-end additives,
untreated starch, coagulants, flocculants, sizing agents, drainage aids,
fillers,
and the like.
[0055] The present invention will now be further described with
reference to a number of specific examples that are to be regarded solely as
iiiustrative and not restricting the scope of the present invention.
EXAMPLES
[0056] To evaluate the performance of the inventive process, a series
of drainage tests were conducted utilizing a vacuum drainage test (VDT). The
results of this testing demonstrate the ability of starch modified with a
metal
silicate to improve the drainage of the system. The device setup is similar to
the
Buchner funnel test as described in various filtration reference books, for
example see Perry's Chemical Engineers' Handbook, 7th edition, (McGraw-Hill,
New York, 1999) pp.18-78. The VDT consists of a 300-ml magnetic Gelman
filter funnel, a 250-ml graduated cylinder, a quick disconnect, a water trap,
and
a vacuum pump with a vacuum gauge and regulator. The VDT test was
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conducted by first setting the vacuum toll 0 inches Hg, and placing the funnel
properly on the cylinder. Next, 250 g of 0.5 wt. % paper stock was charged
into
a beaker and then the required additives according to treatment program (e.g.,
starch, alum, flocculants and drainage aids) were added to the stock under the
agitation provided by an overhead mixer. The stock was then poured into the
filter funnel and the vacuum pump was turned on while simultaneously starting
a stopwatch. The drainage efficacy is reported as the time required to obtain
230 ml of filtrate.
[0057] Lower quantitative drainage time values represent higher levels
of drainage or dewatering, which is the desired response. The values reported
are the average values of two runs.
[0058] The Britt jar retention test (Paper Research Materials, Inc., Gig
Harbor, WA) is known in the art. In the Britt jar retention test a specific
volume
of furnish was mixed under dynamic conditions and an aliquot of the furnish
was drained through the bottom screen of the jar, so that the level of fine
materials which were retained can be quantified. The Britt jar utilized for
the
present tests was equipped with 3 vanes on the cylinder walls to induce
turbulent mix, and a 76 m screen in the bottom plate.
[0059] The Britt jar retention tests were conducted with 500 ml of the
synthetic furnish, having a total solids concentration of 0.5 %. The test was
conducted at 1,200 rpm with the sequential addition of starch, followed by
alum,
followed by polymer flocculant, followed by drainage aid; the materials were
all
mixed for specified interval times. After the drainage aid had been.
introduced
and mixed, the filtrate was collected.
[0060] The retention values calculated are fines retention where the
total fines content in the furnish is first determined by washing 500 ml of
furnish
with 10 liters of water under mixing conditions to remove all the fine
particles,
defined as particles smaller than the Britt jar 76 m screen. The fines
retention
for each treatment was then determined by draining 100 ml of filtrate after
the
described addition sequence, then filtering the filtrate through a pre-weighed
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1.5 m filter paper. The fines retention are calculated according to the
following equation:
% Fines retention = (filtrate wt. - fines wt.)/filtrate wt.
wherein the filtrate and fines weight are both normalized to 100 ml. The
retention values obtained represent the average of 2 replicate runs.
[0061] The furnish employed in the series of tests was a synthetic
alkaline furnish. This furnish was prepared from hardwood and softwood dried
market lap pulps, and from water and further materials. First the hardwood and
softwood dried. market lap pulp were separately refined in a laboratory Valley
Beater (Voith, Appleton, Wis.). These pulps were then added to an aqueous
medium. The aqueous medium utilized in preparing the furnish comprises a
local tap water, and was further modified with inorganic salts added in
amounts
so as to provide this medium with a m-alkalinity of 75-100 ppm as NaHCO3 and
a total solution conductivity of 750 - 1000 pS/cm. To prepare the furnish, the
hardwood and softwood were dispersed into the aqueous medium at weight
ratios of about 67% hardwood and 33% softwood Precipitated calcium
carbonate (Albacar 5970, Minerals Technologies, Bethlehem, PA) was
introduced into the furnish at 25 weight percent, based on the combined dry
weight of the pulps, so as to provide a final furnish comprising 80% fiber and
20% PCC filler. The furnish had a consistency of 0.5% (total solids of 0.5 lbs
per 100 lbs of water).
[0062] The modified starch utilized in the present system is presented
in Table 1. Stalok 400 is a cationic potato starch (A. E. Staley, Decatur,
III.).
The metal silicate is Silicate 0, a liquid sodium silicate possessing a
Si02:Na2O
ratio of 3.22:1 (PQ Corporation, Valley Forge, PA); the dosage of metal
silicate
in all examples is based upon active Si02. The alum is aluminum sulfate-
octadecahydrate available as a 50% solution (Delta Chemical Corporation,
Baltimore, Md.). Perform PC 8138 is a cationic emulsion flocculant (Hercules
Incorporated, Wilmington, DE). Perform SP 7200 is an advanced structured
organic microparticulate (Hercules Incorporated, Wilmington, DE).
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[0063] A 2% starch solution was prepared by heating adding 4 grams
Stalok 400 cationic starch to 196 grams deionized water and heating the
starch to 95 C for 30 minutes until a clear, viscous solution was produced.
The
starch solution was allowed to cool to ambient temperatures.
[0064] A blend of cationic starch and sodium silicate at the indicated
ratio was prepared by adding the indicated amount of metal silicate to the
cooked starch solution. For example, a 10:1 starch:metal silicate solution was
prepared by adding 0.68 grams of Silicate 0 (29% active sodium silicate) to
100 grams of 2% starch cooked starch solution.
[0065] A solution was also prepared by cooking the starch in the
presence of the metal silicate. In this example, a 10:1 cooked solution was
prepared by mixing 1.38 grams of Silicate 0 (29% active sodium silicate) with
198.62 grams of deionized water. 4 grams of Stalok 400 cationic starch was
added and the solution was heated to 95 C for 30 minutes until a turbid,
viscous solution was produced. The starch solution was allowed to cool to
ambient temperatures.
[0066] The data in Table 1 illustrate the improved retention and
drainage performance of the invention, where starch modified with a metal
silicate provides better drainage compared to the unmodified starch. The data
further iiiustrate the metal silicate can be blended with the starch after
cooking,
or added to the starch slurry prior to cooking.
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[0067]
TABLE I
Ratio Metal
Starch Metal Starch: Silicate Drain Fines
Starch Dose*, Silicate Metal Dose*, Time, Retention, Comments
#1T Silicate #/T seconds %
Stalok 400 10 None 0 19.1 82.8
Stalok 400 10 Silicate O 10:1 1 16.5 cooked
together
Stalok 400 10 Silicate O 10:1 1 15.4 89.3 Blend
Stalok 400 10 Silicate 0 2:1 5 15.8 cooked
together
Stalok 400 10 Silicate 0 2:1 5 15.9 Blend
Starch was modified with metal silicate prior to addition to the pulp slurry.
Dose #
indicates individual qualities of starch and metal silicate prior to
modification and
subsequent addition to the pulp slurry. Total #/T of modified starch including
metal
silicate is found by adding starch dose and metal silicate dose. The Metal
Silicate
Dose is measured as Active metal silicate.
[0068] The addition sequence is as follows, with 10 seconds mix time
between each additive:
Starch or modified starch;
Alum at a dosage level of 5 lb./ton;
Perform PC 8138 at a dosage level of 0.4 lb./ton;
Perform SP 7200 at a dosage level of 0.4 lb./ton.
[0069] A series of drainage tests was conducted with the starch blended
with the metal silicate at the indicated ratio utilizing the VDT, and the data
are
presented in Table 2. The materials, methods, and addition sequence are as
specified in Table 1. The data in Table 1 illustrate the improved drainage of
the
17
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inventive process compared to a starch that is not modified with metal
silicate.
Improved drainage is noted with higher levels of metal silicate.
TABLE 2
Ratio Metal
Starch Metal Starch: Silicate Drain Time,
Starch Dose*, #/T Silicate Metal Dose*, #/T seconds
Silicate
Stalok 400 10 None 0 21.6
Stalok 400 10 Silicate 0 20:1 0.5 18.1
Stalok 400 10 Silicate 0 10:1 1 15.9
Stalok 400 10 Silicate 0 5:1 2 14.4
Starch was modified with metal silicate prior to addition to the pulp slurry.
Dose #
indicates individual qualities of starch and metal silicate prior to
modification and
subsequent addition to the pulp slurry. Total #/T of modified starch including
metal
silicate is found by adding starch dose and metal silicate dose. The Metal
Silicate
Dose is measured as Active metal silicate.
[0070] A series of drainage tests was conducted with the starch blended
with the metal silicate at the indicated ratio using the VDT, and the data are
presented in Table 3. Cato 232 is a cationic waxy maize starch (National
Starch,
Bridgewater, NJ). Stalok 300 is a cationic corn starch (A. E. Staley,
Decatur, !!!.).
The materials, methods, and addition sequence are as specified in Table 1. The
data in Table 3 illustrate the drainage improvement provided with the
inventive
process compared to an unmodified starch, using example of waxy maize and
corn starch.
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TABLE 3
Ratio
Metal Starch: Metal
Starch Starch Silicate Metal Silicate Drain Time,
Dose*, #/T Silicate Dose*, seconds
#/T
Cato 232 10 None 0 20.4
Cato 232 10 Silicate 0 20:1 0.5 16.9
Cato 232 10 Silicate O 10:1 1 15.7
Cato 232 10 Silicate 0 5:1 2 13.7
Stalok 300 10 None 0 19.2
Stalok 300 10 Silicate 0 20:1 0.5 17.3
Stalok 300 10 Silicate 0 10:1 1 17.0
Stalok 300 10 Silicate 0 5:1 2 13.7
Starch was modified with metal silicate prior to addition to the pulp slurry.
Dose #
indicates individual qualities of starch and metal silicate prior to
modification and
subsequent addition to the pulp slurry. Total #/T of modified starch including
metal
silicate is found by adding starch dose and metal silicate dose.
[0071] A series of drainage tests was conducted with the VDT with the
starch blended with the metal silicate at the indicated ratio; the data are
presented
in Table 4. Silicate 0 is sodium silicate possessing a Si02:Na2O ratio of
3.22:1,
Silicate M is sodium silicate possessing a Si02:Na2O ratio of 2.58:1, and
Silicate D
is sodium silicate possessing a Si02:Na2O ratio of 2.00:1 (PQ Corporation,
Valley
Forge, PA). The materials, methods, and addition sequence are as specified in
Table 1, with the exception of the Perform SP 7200 dosage as indicated. The
data in Table 4 illustrate the improved drainage provided by the inventive
process
compared to an unmodified starch. Good drainage activity is provided with
sodium
silicates possessing various ratios of Si02:Na20.
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TABLE 4
Starch Ratio SP 7200 Drain
Dose*, Starch Metal Starch: Dose* Dose, Time,
Starch #/T Cook Silicate Metal , #/T #/T seconds
Concentration Silicate
Stalok
400 10 4 None 0 0.4 20.5
Stalok
400 10 4 Silicate D 2.5:1 4 0.4 19
Stalok
400 10 4 Silicate 0 2.5:1 4 0.4 15.6
Stalok
400 10 3 Silicate M 4:1 2.5 0.4 14.2
Stalok
400 10 4 Silicate D 10:1 1 0.4 17.6
Stalok
400 10 2 Silicate D 2.5:1 4 0.4 19.4
Stalok
400 10 2 Silicate 0 2.5:1 4 0.4 16.1
Stalok
400 10 2 Silicate D 10:1 1 0.4 18.7
Stalok
400 10 4 Silicate 0 10:1 1 0.4 15.8
Stalok
400 10 2 Silicate 0 10:1 1 0.4 15.1
Starch was modified with metal silicate prior to addition to the pulp slurry.
Dose #
indicates individual qualities of starch and metal silicate prior to
modification and
subsequent addition to the pulp slurry. Total #/T of modified starch including
metal
silicate is found by adding starch dose and metal silicate dose.
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[0072] Another series of drainage tests was conducted with the VDT with
the starch blended with the metal silicate at the indicated ratio utilizing
starches
with different degrees of substitution; the data are presented in Table 5.
Stalok
430 is a cationic com starch with a degree of substitution of 0.18; Stalok
400 is a
cationic potato starch with a DS = 0.28; and Stalok 410 is a cationic potato
starch with a DS = 0.35. (A. E. Staley, Decatur, III.)The materials, methods,
and
addition sequence are as specified in Table 1. The data in Table 5 illustrate
the
improved drainage provided by the inventive process compared to an unmodified
starch, utilizing starches with varying degrees of substitution.
TABLE 5
Starch
Degree of Starch Ratio
Starch Substitution Dose*, Metal Silicate Starch: Metal Drain
(DS) #/T Metal Silicate Time,
Silicate Dose*, seconds
#/T
Stalok 430 0.18 10 None 0 17.3
Stalok 430 0.18 10 Silicate O 10:1 1 16.8
Stalok 400 0.28 10 None 0 19.8
Stalok 400 0.28 10 Silicate 0 10:1 1 15.6
Stalok 410 0.35 10 None 0 21.4
Stalok 410 0.35 10 Silicate 0 10:1 1.0 15.5
Starch Was modified with metal silicate prior to addition to the pulp slurry.
Dose #
indicates individual qualities of starch and metal silicate prior to
modification and
subsequent addition to the pulp slurry. Total #/T of modified starch including
metal
silicate is found by adding starch dose and metal silicate dose.
[0073] Another series of drainage tests was conducted with the VDT
utilizing a cationic guar as the polysaccharide, which was blended with the
metal
silicate at the indicated ratio; the data are presented in Table 6. N-Hance
3196 is
a cationically modified guar gum (Ashland Aqualon, Wilmington, DE) The
materials, methods, and addition sequence are as specified in Table 1. The
data
in Table 6 illustrate the improved drainage provided by the inventive process
compared to an unmodified cationic guar.
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TABLE 6
PS Ratio Drain
Polysaccharide Dose*, #/T Metal PS: Metal Silicate Time,
(PS) Silicate Metal Dose*, #/T seconds
Silicate
N-Hance 10 None 0 39.2
N-Hance 10 Silicate 0 10:1 1 26.4
The polysaccharide was modified with metal silicate prior to addition to the
pulp
slurry. Dose # indicates individual qualities of starch and metal silicate
prior to
modification and subsequent addition to the pulp slurry. Total #/T of modified
starch including metal silicate is found by adding polysaccharide dose and
metal
silicate dose.
[0074] While the present invention has been described with respect to
particular embodiment thereof, it is apparent that numerous other forms and
modifications will be obvious to those skilled in the art. The appended claims
and
this invention generally should be construed to cover all such obvious forms
and
modifications, which are within the true scope of the invention.
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