Note: Descriptions are shown in the official language in which they were submitted.
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Pulp and Paper Having Increased Brightness
FIELD OF THE INVENTION
The present invention relates to a method of increasing the brightness of
pulp, pulp made
from such methods and methods of using such pulp.
BACKGROUND OF THE INVENTION
Bleaching is a common method for increasing the whiteness of pulp. Industry
practice for
improving appearance of fluff pulp is to bleach the pulp to ever-higher levels
of brightness (the
Technical Association of the Pulp & Paper Industry ("TAPPI") or the
International Organization
for Standardization ("ISO")). However, bleaching is expensive, environmentally
harsh and often
is a source of manufacturing bottleneck. Widespread consumer preference for a
brighter, whiter
pulp drives manufacturers to pursue ever more aggressive bleaching strategies.
While highly
bleached pulps are "whiter" than their less-bleached cousins, they are still
yellow-white in color.
A yellow-white product is undesirable. Countless studies suggest that
consumers clearly favor a
blue-white over a yellow-white color. The former is perceived to be whiter,
i.e., "fresh", "new"
and "clean", while the latter is judged to be "old", "faded", and "dirty".
While bleaching directly elevates brightness, it only indirectly elevates
whiteness. Due to
the latter, bleaching is not always the most efficient method for boosting
product whiteness. For
example, even after aggressive bleaching, a product's whiteness can always be
extended beyond
that achievable with bleaching alone by judicious addition of colorant.
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The practice of pre-coloring papermaking pulp is not usually done nor is it
necessarily
desired. With the former, intentional alteration of optical properties often
ends up degrading
product specifications such as TAPPI brightness, which is undesirable. With
the latter, one runs
the risk that colorants may not survive the unpredictable manufacturing
environments of
downstream processes. This is because previously applied colorant can be
adversely affected
chemically and/or physically during post-processing operations resulting in
unexpected or
undesirable color changes or even full loss of color. Furthermore, some
colorants can be lost or
rendered ineffective during various post-processing operations disrupting
process health and
reliability. Therefore, any optical enhancement is usually accomplished by
addition of tinting
colorants, fillers, and/or fluorescent dye during the papermaking stage. A
process for enhancing
the whiteness, brightness, and chromaticity of papermaking fibers has been
described in U.S. Pat.
No. 5,482,514. The process relates to adding photoactivators, particularly
water-soluble
phthalocyanines, to papermaking fibers to enhance their optical properties by
a catalytic
photosensitizer bleaching process. The resulting bleached papermaking fibers
can be
advantageously incorporated into paper sheets.
With fluff pulp, as well as most pulp and paper, products, TAPPI brightness
serves as the
de facto standard in lieu of an industry-specific whiteness specification such
as CIE Whiteness
(Commission Internationale d'Eclairage). Because of this, brightness serves
two key roles. First,
brightness is a manufacturing parameter. Second, brightness is a specification
for classifying
finished product grades. The implicit, but dubious, assumption to this day has
been that
brightness is equivalent to whiteness. Common papermaking practice is to
either add blue tinting
dyes or tinting pigments and/or different types of blue-violet fluorescent
dyes to boost whiteness
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properties. Tinting colorants are either finely ground colored pigments
suspended in a dispersant
or synthetically produced direct dyes. Tinting dyes have some affinity to
cellulose while tinting
pigments have little to none.
Fluorescent whitening agents (FWA) or optical brightening agents (OBA) are
used in the
pulp and paper industry are of three types: di-, tetra-, or hexasulphonated
stilbene compounds,
for example. These chemicals require ultraviolet (UV) light to excite
fluorescence. While there
is strong UV content in daylight, even common office lights produce enough UV
light to permit
some excitation.
During papermaking, OBAs are added at the wet end of papermaking processes,
which include
for example, the machine chest and/or the fan pump, where the fiber solution
is at low
consistencies that are less than about 3% solids. At these conventional
addition points, much
OBA is lost to waste as the OBA does not necessarily have a strong affinity to
the fibers in
solution. Accordingly, the OBA must be added at high concentrations (lbs/ton
of fiber or pulp)
in order to achieve high quality fibers having high brightness and high
brightness improvements.
Accordingly, there exists a need for a pulp having improved whiteness and
brightness. A
need also exists for a method for making whitened/brightened pulp for any use,
especially
papermaking and fluff pulp, while using less OBA to obtain such levels of
whiteness and
brightness at less cost. The present invention seeks to fulfill these needs
and provides further
related advantages.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1: Graphs of ISO Brightness v.s OBA Level of Handsheets made from pulp
treated
with OBA, full data set.
FIGURE 2: Graphs of ISO Brightness v.s OBA Level of Handsheets made from pulp
treated
with OBA, dose data set.
FIGURE 3: Graphs of ISO Brightness v.s OBA Level of Handsheets made from pulp
treated
with OBA, effect of OBA dose in the presence of 10 and 20% filler.
FIGURE 4: Graphs of ISO Brightness v.s OBA Level of Handsheets made from pulp
treated
with OBA effect of OBA dose in the presence of 10 and 20% filler, regression
lines added.
FIGURE 5: Raman spectra of OBA only and pulp with different levels of OBA
added
conventionally.
FIGURE 6: Raman spectra of pulp with different levels of OBA added according
to one aspect
of the present invention.
FIGURE 7: Raman spectra of pulp with different levels of OBA added
conventionally and
added according to one aspect of the present invention.
FIGURE 8: Graph of the peak ratio (1604/900cm 1) within Raman spectra of pulp
with different
levels of OBA added conventionally and added according to one aspect of the
present invention
(Hardwood and Softwood) as depicted in Table 10.
FIGURE 9: UV/VIS absorbance at 350 nm of water estract vs. Actual Amount of
OBA on
fibers, lbs/ton.
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FIGURE 10: OBA peak height vs. OBA added (lbs/ton) via the conventional
addition method
and added according to one aspect of the present invention (Hardwood and
Softwood).
FIGURE 11: OBA peak height vs. OBA added (lbs/ton) via the conventional
addition method
and added according to one aspect of the present invention (Hardwood and
Softwood).
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DETAILED DESCRIPTION OF THE INVENTION
The present inventor has surprisingly found an method of efficiently
increasing the
brightness and whiteness of pulp and paper while using less OBA applied
thereto, thereby
providing for a much more efficient manner of providing a fiber-OBA complex
containing
greater fiber-OBA interaction on the whole than conventional methodologies of
creating a fiber-
OBA complex. Such a fiber-OBA complex made by the method according to the
present
invention has greater increases in brightness and whiteness than the fiber
alone as compared to
traditional methodologies as described below.
The present invention relates, in part, to a method of making pulp. The pulp
may be fluff
or papermaking pulp. The method may be used and added to any traditional
methods of making
papermaking or fluff pulp. The pulp may be used in any conventional uses of
pulp, including
any conventional papermaking processes of making paper and/or paperboard
substrates. Such
conventional pulp and papermaking processes in the pulp, paper and paperboard
art may be
found, for example, in "Handbook For Pulp & Paper Technologies", 2nd Edition,
G.A. Smook,
Angus Wilde Publications (1992) and references cited therein.
A typical pulp/paper making process may include, but is not limited to, the
following
stages:
A. Digesting stage where wood chips are digested to release pulp fibers from
the lignin;
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B. Brownstock Washing Stage where the pulp from the Digesting Stage is washed;
C. Bleaching/Extraction Stages where the pulp is extracted with and bleached
with
various chemicals such as oxygen in oxygen delignification, chlorine dioxide,
elemental
chlorine, peroxide, ozone, and the like followed by one or more washing
stages;
D. High Density Storage Stage where the bleached/washed pulp is stored at
relatively
high density as for example more than about 7%, preferably from about 7.5 to
about 15%, and
preferably from about 10 to about 12%;
E. Low Density Storage Stage where the bleached/washed pulp is stored at
relatively
low density as for example equal to or less than about 7%, preferably from
about 3% to 7%, and
more preferably from about 10 to about 12%;
D. Pulp Refining Stage where the pulp is refined at a consistency preferably
of from
about 4 to about 5%;
E. Blend Chest/Machine Chest Stages where the pulp having a consistency
preferably
from about 3 to about 4% is mixed with wet end chemicals used in paper making
such as fillers,
retention aids, dyes and optical brighteners and the like. Such a traditional
processes may
include repeats of any one or more of the above-mentioned steps. In addition,
the present
invention may be combined with traditional methods of adding OBA to fibers,
such as the
conventional wet-end addition points as well as size press addition points and
coating addition
points, when making paper and/or paperboard.
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The present invention relates, in part, to a method of adding OBA to fibers at
any point
after the last bleaching/extraction stage and up to and prior to the Blend
Chest/Machine Chest
Stages.
The source of the fibers may be from any fibrous plant. The paper substrate of
the
present invention may contain recycled fibers, deinked fibers and/or virgin
fibers. Examples of
such fibrous plants are trees, including hardwood and softwood fibrous trees,
including mixtures
thereof. In certain embodiments, at least a portion of the pulp fibers may be
provided from non-
woody herbaceous plants including, but not limited to, kenaf, hemp, jute,
flax, sisal, or abaca
although legal restrictions and other considerations may make the utilization
of hemp and other
fiber sources impractical or impossible. Either bleached or unbleached pulp
fiber may be utilized
in the process of this invention. Recycled pulp fibers are also suitable for
use.
The pulp of the present invention may contain from 1 to 99 wt%, preferably
from 5 to 95
wt%, cellulose fibers originating from hardwood species and/or softwood
species based upon the
total amount of cellulose fibers. This range includes 1, 2, 5, 10, 15, 20, 25,
30, 35, 40, 45, 50,
55, 60, 65, 70, 75, 80, 85, 90, 95, and 100wt%, including any and all ranges
and subranges
therein, based upon the total amount of cellulose fibers.
When the pulp may contain both hardwood and softwood fibers, it is preferable
that the
hardwood/softwood ratio be from 0.001 to 1000. This range may include 0.001,
0.002, 0.005,
0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,
55, 60, 65, 70, 75, 80, 85,
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90, 95, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 including any
and all ranges and
subranges therein and well as any ranges and subranges therein the inverse of
such ratios.
Optical brighteners are dye-like fluorescent compounds which absorb the short-
wave
ultraviolet light not visible to the human eye and emit it as longer-wave blue
light, with the result
that the human eye perceives a higher degree of whiteness and the degree of
whiteness is thus
increased. The optical brighteners used in the paper industry are generally
1,3,5-triazinyl
derivatives of 4,4'-diaminostilbene-2,2'-disulfonic acid, which may carry
additional sulfo groups,
for example altogether 2, 4 or 6. An overview of such brighteners is to be
found, for example, in
Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, 2000 Electronic
Release,
OPTICAL BRIGHTENERS--Chemistry of Technical Products. However, recent
brightener
types are also suitable, for example derivatives of 4,4'-distyrylbiphenyl, as
likewise described in
the abovementioned Ullmann's Encyclopedia of Industrial Chemistry.
While the present invention prefers methods
and fiber-OBA complexes using the above-mentioned OBA, the present invention
is in no way
limited to such exemplified embodiments and any OBA may be utilized.
The present invention relates in part, to a fiber:OBA complex in which the
affinity of the
OBA added to the fiber according to present invention is preferably greater
than that when the
OBA is added to the fiber conventionally. When the OBA is added to the fiber
according to the
method of the present invention, there is 30 to 60% reduction in the OBA
required to be added
than that of conventional methods and addition points. The reduction may be
30, 31, 32, 33, 34,
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35, 40, 45, 50, 55, 56, 57, 58, 59, and 60 % compared to that required in
conventional methods
and addition points, including any and all ranges and subranges therein.
The increased affinity of the OBA to the fiber may be measured by extraction
methods
using any solvent, preferably water, at any temperature. Because the OBA has
increased affinity
to the fiber overall in the present inventive pulps and paper substrates made
therefrom compared
to conventional pulp, it will take a longer period of time for the OBA to be
extracted from the
pulp:OBA complex of the present invention (pulp and/or paper) at a given time
period and
temperature for a given solvent.
In addition, the present invention preferably relates to a method of
increasing the
penetration of OBA into the cell wall of a fiber. Preferably, there is a
greater amount of OBA
that has penetrated the cell wall of a fiber treated according to the present
invention than that of
fibers treated by conventional methods. More preferably, the amount of OBA
present within the
cell wall of the fiber is increased by at least 1 % than the amount of OBA
present within the cell
wall of fiber that was treated in conventional methods. However, it is more
preferred that the
amount of OBA present within the cell wall of the fiber is increased by at
least 2, 3, 4, 5, 6, 7, 8,
9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 100,
200, 300, 500, and
1000% than the amount of OBA present within the cell wall of fiber that was
treated in
conventional methods, including any and all ranges and subranges therein.
The amount of OBA present within the cell wall of fiber may be measured, for
example,
by microscopy, more specifically fluorescent microscopy.
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While any amount of OBA may be added to the fiber so long as it is added at
any point
after the last bleaching/extraction stage and up to and prior to the Blend
Chest/Machine Chest
Stages, it is preferable that from 1 to 60 lbs of OBA per ton of fiber, more
preferably not more
then 30 lbs/ton, most preferably, not more than 15 lbs/ton OBA/fiber. This
range includes 60,
55, 50, 45, 40, 30, 35, 30, 25, 20, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4,
3, 2, and 1 lbs of OBA
per ton of fiber (lbs/ton) including any and all ranges and subranges therein.
In addition, the fiber may be in solution, or added to solution at the same
time, as the
OBA. Preferably, the fiber is in solution prior to contacting the OBA thereto.
In one
embodiment of the present invention, the fiber may have any consistency.
However, it is
preferably to have a consistency that is equal to or greater than 4% solids,
more preferably, not
less than about 5 % solids, most preferably, not less than about 10% solids.
In addition, it is
preferable that the fibers have a consistency that is not more than about 35%
solids, preferably
not more than 20% solids, more preferably not more than about 15% solids.
These ranges
include 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and
20% solids as the fiber
consistency at the time the OBA is added thereto, including any and all ranges
and subranges
therein.
At the time of the addition of the OBA to the fiber, the pH may be any pH.
Preferably,
the pH may range from 2.5 to 8.0, more preferably from 3.5 to 5.5. This range
includes 2.5, 3.0,
3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, and 8.0, including any and all
ranges and subranges
therein.
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At the time of the addition of the OBA to the fiber, the temperature may be
any
temperature. However, it is preferable that means be applied, such as heating,
so as to generate a
temperature that is from 35 to 95 C, preferably from 50 to 90 C, more
preferably from 60 to
80 C. This range includes 35, 40, 45, 50, 55, 60, 61, 62, 63, 64, 65, 66, 67,
68, 69, 70, 71, 72,
73, 74, 75, 76, 77, 78, 79, 80, 85, 90 and 95 C, including any and all ranges
and subranges
therein.
The time in which the OBA is contacted with the fiber may be for any duration
of time.
Preferably, the OBA and fiber may be contacted from 30 minutes to 12 hours,
more preferably
from 45 minutes to 8 hours, most preferably from lhour to 6 hours. This range
includes 0.5,
0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25,
4.5, 4.75, 5, 5.25, 5.5, 5.75,
6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, and 12 hrs, including any and all
ranges and subranges
therein.
At the time of contacting the OBA with the fiber, retention aids may
optionally be present
or added therewith. Alum and/or cationic retention aids are examples of such
retention aids.
Examples of retention aids is found in
United States Patent Number 6,379,497.
However, any retention aid commonly used
with OBAs may be used. While the retention aid may be present in any amount,
or not at all,
preferably, the amount of retention aid present is less than that required
during conventional
processes and addition points used to contact OBA with fibers. Most
preferably, no retention
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aids are used. If retention aids are used, it is preferable that there is at
least a 1% reduction in the
amount of retention aid present as compared to that of conventional methods
and addition points
for contacting OBA with fiber. The preferred reduction is at least 2, 3, 4, 5,
10, 15, 20, 25, 30,
35, 40, 50, 60, 75, 100, 200, 300, 500, and 1000% reduction in the amount of
retention aid
present in the present invention as compared to conventional methods and
addition points for
contacting OBA with fiber, including any and all ranges and sub-ranges
therein.
While the fiber may be refined at any time, preferably, the fiber is refined
after the OBA
is contacted with the fiber. Therefore, the fiber:OBA complex of the present
invention is refined.
Accordingly, any conventional refining may occur, including but not limited
the chemical
refining, mechanical refining, thermochemical refining, thermomechanical
refining,
chemithermomechanical refining, etc may occur. Therefore the pulp produced may
include
TMP, CTMP, MP, BCTMP, etc.
The pulp of the present invention and method of making the same may be
incorporated
into any traditional papermaking process. The pulp and/or paper substrate may
also include other
conventional additives such as, for example, starch, mineral and polymeric
fillers, sizing agents,
retention aids, and strengthening polymers. Among the fillers that may be used
are organic and
inorganic pigments such as, by way of example, minerals such as calcium
carbonate, kaolin, and
talc and expanded and expandable microspheres. Other conventional additives
include, but are
not restricted to, wet strength resins, internal sizes, dry strength resins,
alum, fillers, pigments
and dyes. Dyes that are especially preferably are those of the blue dye type
which are capable of
increasing the CIE Whiteness of the pulp and/or paper substrate. Preferably,
pulp and paper
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substrate of the present invention made according to the present invention is
capable of achieving
CIE Whiteness that is much higher than conventional pulps and substrates made
by conventional
methods, even at CIE Whiteness levels that usually result in decreased ISO
brightness levels.
The pulp and/or paper substrate of the present invention may have any CIE
whiteness,
but preferably has a CIE whiteness of greater than 70, more preferably greater
than 100, most
preferably greater than 125 or even greater than 150. The CIE whiteness may be
in the range of
from 125 to 200, preferably from 130 to 200, most preferably from 150 to 200.
The CIE
whiteness range maybe greater than or equal to 70, 80, 90, 100, 110, 120, 125,
130, 135, 140,
145, 150, 155, 160, 65, 170, 175, 180, 185, 190, 195, and 200 CIE whiteness
points, including
any and all ranges and subranges therein. Examples of measuring CIE whiteness
and obtaining
such whiteness in a fiber and paper made therefrom can be found, for example,
in United States
Patent 6,893,473.
Preferably, the pulp and/or paper substrate of the present invention has a CIE
whiteness
that is increased over conventional pulp and/or paper substrates made by
conventional methods.
The preferred increase is at least 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 50,
60, 75, 100, 200, 300,
500, and 1000% increase in CIE whiteness as compared to that of conventional
pulps, paper
substrates made by conventional methods and addition points for contacting OBA
with fiber,
including any and all ranges and sub-ranges therein.
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The pulp and paper substrate of the present invention may have any ISO
brightness, but
preferably greater than 80, more preferably greater than 90, most preferably
greater than 95 ISO
brightness points. The ISO brightness may be preferably from 80 to 100, more
preferably from
90 to 100, most preferably from 95 to 100 ISO brightness points. This range
include greater than
or equal to 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and 100 ISO
brightness points, including
any and all ranges and subranges therein. Examples of measuring ISO brightness
and obtaining
such brightness in a papermaking fiber and paper made therefrom can be found,
for example, in
United States Patent 6,893,473.
Preferably, the pulp and/or paper substrate of the present invention has an
ISO brightness
that is increased over conventional pulp and/or paper substrates made by
conventional methods.
The preferred increase is at least 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 50,
60, 75, 100, 200, 300,
500, and 1000% increase in an ISO brightness as compared to that of
conventional pulps, paper
substrates made by conventional methods and addition points for contacting OBA
with fiber,
including any and all ranges and sub-ranges therein.
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The present invention is explained in more detail with the aid of the
following
embodiment example which is not intended to limit the scope of the present
invention in any
manner.
EXAMPLES
COMPARATIVE EXAMPLE 1
Lab experiments were carried out to simulate a commercial paper making
operation, in
which T-100, a Clariant's tetrasulphonated OBA product, was added into three
bleached
hardwood Kraft pulp samples. A low speed lab Warring blender was used for
mixing pulp with
all chemicals. Prior to the optical brightener ("OBA") addition, deionized
water was added into
the 5 gm oven dry pulp sample to reduce its consistency to 1 % consistency.
Shortly after the
OBA addition, 5 ml of 5% alum solution of alum was added into the pulp mixture
to complete
the attachment of all OBA onto the fiber. After one minute mixing in the
blender, the pulp
mixture was dewatered to form a brightness pad, following the standard Tappi
pulp brightness
testing procedure. Three pulp samples and three dosage of T-100 were used in
these
experiments. Brightness results on individual pulp samples, before and after
OBA fixation, are
as follows:
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TABLE 1
Hardwood #1 Hardwood #2 Hardwood #3
Brightness Brite Brightness Brite Brightness Brite
(GE) Gain (GE) Gain (GE) Gain
0 80.5 0 84.4 0 86.6 0
4 83.1 2.6 87.7 3.3 90.0 3.5
8 84.2 3.7 89.7 5.1 90.4 3.8
16 84.9 4.3 89.4 5.0 90.7 4.1
COMPARATIVE EXAMPLE 2
Lab experiments were carried out to simulate a commercial paper making
operation in
which T-100, a Clariant's tetrasulphonated OBA product, was added into one
southern hardwood
Kraft pulp sample. A low speed lab Warring blender was used for mixing pulp
with all
chemicals. Prior to the OBA addition, deionized water was added into the 5 gm
oven dry pulp
sample to reduce its consistency to 1% consistency. For experiments in series
I, shortly after the
OBA addition, 5 ml of 5% alum solution of alum was added into the pulp mixture
to complete
the attachment of all OBA onto the fiber. No alum was used for experiments in
series II. For
both cases, after one minute mixing in the blender, the pulp mixture was
dewatered to form a
brightness pad, following the standard Tappi pulp brightness testing
procedure. Three pulp
samples and three dosage of T-100 were used in these experiments. Brightness
results on
individual pulp samples, before and after OBA fixation, are as follows:
TABLE 2
Series I - No Alum Series II - With Alum
Brightness Brite Brightness Brite
(GE) Gain (GE) Gain
0 84.0 0 84.0 0
3 87.4 3.4
6 89.0 5.0
89.7 5.7
85.8 1.8 89.1 5.1
40 86.4 2.3 86.2 2.1
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60 86.7 2.7 82.2 1.8
TABLE 3
Series I - No Alum Series II - With Alum
Brightness Brite Brightness Brite
(GE) Gain (GE) Gain
0 84.0 0 84.0 8
3 87.4 3.4
6 89.0 5.0
89.7 5.7
85.8 0.8 89.1 5.1
40 86.4 2.3 86.2 2.1
60 86.7 2.7 82.2 1.8
TABLE 4
Water Bath at 60 C Water Bath at 75 C
T-100 Reaction Brightness Brite Brightness Brite
Charge Time (GE) Gain (GE) Gain
(lbs/ton) (Hours)
0 0 88.9 0 88.9 0
2 1 93.0 4.1 91.8 2.9
4 1 93.6 4.6 93.4 4.5
8 1 94.9 6.0 94.7 5.8
0 0 88.9 0 88.9 0
2 5 92.2 - 3.3 92.0 3.1
4 5 93.6 4.6 92.7 3.8
8 5 94.0 5.1 93.9 4.9
EXAMPLE 2
From a commercial IP pulp mill in Southern US, samples of fully bleached
hardwood and
softwood Kraft pulp at the exit of the bleach plant were collected and used in
high consistency
OBA fixation experiments. Experimental conditions, including OBA type and pulp
consistency
were identical to those described in example 1. The as-received softwood pulp
sample has a pH
of 5.2 and the pH for the hardwood pulp sample was 6.7. All experiments were
carried out for a
duration of two hours, in 65 C temperature bath. Prior to some of experiments
on hardwood
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pulp, dilute hydrochloric acid solution was also added to the as-received mill
pulp to lower its
pH to 4.9 during the reaction with OBA. The following results were obtained:
TABLE 5
Softwood at 5.2 pH Hardwood at 6.7 pH Hardwood at 4.9 pH
T-100 Brightness Brite Brightness Brite Brightness Brite
Charge (GE) Gain (GE) Gain (GE) Gain
(lbs/ton)
0 85.5 0 85.6 0 85.6 0
2.5 89.4 3.9 87.5 1.9 90.1 4.5
5.0 89.7 4.2 88.5 2.9 91.3 5.7
10.0 91.2 5.7 89.3 3.7
15.0 91.5 6.0 90.2 4.6 92.4 6.8
EXAMPLE 3
From a commercial IP pulp mill in Europe, samples of fully bleached softwood
and hardwood
pulps, leaving the bleach plant were collected and used in OBA fixation
experiments. The pH
of the filtrate of both pulp samples was 3Ø Leucophor ANO, a disulphonate
OBA product
produced by Clariant, was used in this example. Fixation experiments were
carried out with
variable OBA charges, at 10% consistency, for two hours in 65 C temperature
bath. Observed
changes in the pulp brightness as results of OBA fixation is as follows:
TABLE 6
Hardwood Softwood
Leucophor Brightness Brite Brightness Brite
Charge (GE) Gain (GE) Gain
(lbs/ton)
0 89.3 0 88.4 0
93.6 4.3 92.8 4.3
94.3 4.9 92.1 3.7
92.7 3.4 90.4 2.0
91.9 2.6 89.6 1.1
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30 89.3 0 86.0 -2.5
EXAMPLE 4
Samples of pulps and OBA of example 3 were used in this example. However,
before mixing
with OBA, dilute solution of NaOH as used to raise the pH of the pulp samples,
from 3.0 to 5.7
for the case of hardwood and to 7.0 for the case of softwood. All other
conditions were identical
to those used in example 4. Observed changes in the pulp brightness as results
of pH adjustment
and OBA fixation is as follows:
TABLE 7
Hardwood Softwood
Leucophor Brightness Brite Brightness Brite
Charge (GE) Gain (GE) Gain
(lbs/ton)
0 89.0 0 87.9 0
4 93.4 4.4 92.5 4.6
8 94.9 5.8 93.8 5.9
12 95.1 6.3 94.0 6.1
20 95.5 6.5 94.8 6.8
30 89.3 6.6 95.1 7.2
EXAMPLE 5
Experiments were carried out to fix T-100 on to commercially produced fully
bleached
softwood and hardwood Kraft pulp samples from a Northern US mill. The softwood
pulp has a
freeness of 690 csf, brightness of 90 GE and pH of 4Ø The hardwood sample
has a freeness of
570 csf, brightness of 89.2 and pH of 4Ø Variable dosages of T-100 were
mixed with pulps at
10% consistency and were kept in separate and sealed plastic bags. Bags were
placed in 70 C
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water bath for 2 hours. Change in the brightness of individual pulp samples as
a result of OBA
fixation is as follows:
TABLE 8
Softwood Hardwood
T-100 Brightness Brite Brightness Brite
Charge (GE) Gain (GE) Gain
(lbs/ton)
0 90.0 0 89.2 0
2 94.4 4.4 92.0 2.8
4 95.2 5.2 92.7 3.5
6 95.8 5.8 93.3 4.1
8 96.3 6.3 93.8 4.6
96.6 6.6 94.2 5.0
12 97.1 7.1 94.3 5.1
EXAMPLE 6
The original softwood and hardwood pulp samples of example 5, together with
samples
which were fixed with 12 lbs/bdt of T-100, were subjected to high shear
mechanical action inside
a lab PFI refiner. The extent of pulp refining was controlled so that the
freeness of the softwood
pulp is reduced from 690 CSF before refining to 450 CSF after refining. For
the hardwood pulp,
the freeness drop was from 570 CSF to 330 CSF. Brightness changes, as a result
of PFI refining,
on original pulp samples and samples containing OBA are as follows:
TABLE 9
Softwood Hardwood
Before After Gain Before After Gain
fixation fixation fixation fixation
Before 90.0 96.6 6.6 89.2 94.2 5.0
refining
After 88.4 94.7 6.3 88.4 94.0 5.6
refining
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Loss 1.6 1.9 0.8 0.2
Brightness loss as a result of pulp refining operation is well recognized in
papermaking.
Under refining condition used in example 6, it was 1.6 points for the original
softwood and 0.8
points for the original hardwood. Brightness losses were very similar for the
case where pulps
were fixed with OBA, suggesting that the created bonding between OBA and fiber
was very
strong and was not affected by the mechanical shear action of the refiner. The
net brightness
gain, obtained from OBA fixation, remained essentially unchanged and were not
affected by the
pulp refining process.
EXAMPLE 7: Hand Sheet Study
Summary
The handsheet study confirmed that adding Clariant Leucophor ANO optical
brightening
agent (OBA) under high consistency treatment method gave better brightness
than when the
OBA was added at low consistency.
For a fixed dose, the new addition point resulted in a brightness increase of
about 1.9 units of
ISO brightness.
Based on this study, to reach the same ISO brightness, changing to the new
addition method
would allow the OBA dosage to be decreased by 3.5 pounds/ton.
These estimates are based on data at OBA dose levels between 3.3 and 10
pounds/ton.
The designed experiment showed that two of the factors, OBA dose (nominally
3.3 and
pounds /ton) and OBA addition method (new method vs addition to low
consistency pulp)
were statistically significant in determining brightness.
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Experimental
1. Pulp
Pulp used for this study was unrefined hardwood and softwood taken from the
washer of
the last bleaching stage.
2. OBA Fixation
The hardwood and softwood pulps separately with two levels of OBA, 3.3 and 10
pounds
/ton of OBA. The OBA used was Leucophor ANO (Clariant), which is a di-
sulfonated OBA. The
conditions were 10% consistency, mixed for 2 hours at 70 C.
3. Re anin
Prior to refining, the pulps were combined into a 70:30 HWD:SWD ratio.
Refining was
performed in the LR1, a laboratory disk refiner. Two energies were used, 35
kW/T and 45 kW/T.
The freeness of the resulting pulps were -580 and -320 csf, respectively.
4. Sheet Making
Sheets were made on the dynamic sheet former with the following procedure: The
pulp
was diluted to 1 % consistency and mixed vigorously. SMI's Albacar LO PCC was
added first
and allowed to mix for 1 minute. Then a predetermined and accurate amount of
OBA was added
and mixed for 15 minutes. The sheet was then fonned. After forming, the sheets
were pressed to
^-45% solids and dried at 230 F on the drum drier. Special precautions were
made so that the
sheets with `fixed' OBA had similar amounts of OBA as the standard OBA
addition sheets. In
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addition`tb the samples pretreated with OBA and the samples prepared as
describe here, where
the PCC was added before the OBA, several controls were also made where the
order of addition
of the PCC and OBA was reversed (OBA first).
5. Testing
The handsheets were tested for various optical properties using the DataColor
Elrepho
Spectrophotometer.
6. Experimental Design
The design for this experiment included four main factors:
1) Stock consistency at which the OBA was added (10% vs. 1%)
II) Refining (35 kW/T vs. 45 kW/T)
III) Filler Level (10% vs. 20%)
IV) OBA dose (3.3 lb/T vs. 10 lb/T)
Results & Conclusions
Comparison of Handsheet Brightness for New and Traditional Fixation methods.
Adding Clariant Leucophor ANO optical brightening agent (OBA) under the new,
high
consistency treatment method gave better brightness than when added at low
consistency to
handsheets. The results are set forth in the following figures 1 to
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Figures 'i=''4"shows 'all the brightness data from the study graphed against
OBA dose. There are
several different classes of samples listed, separated by the fixation method
(high and low
consistency) and filler level (10 and 20 #Iton).
Raman spectroscopy study of pulp with OBA
Raman spectroscopy was used to study pulp with OBA added using the
conventional as
well as new processes. Figure 5 compares the spectrum of OBA (Leucophur ANO)
with spectra
of pulp with and without OBA added. The most intensive peak at the spectrum of
the OBA at
approximately 1600 cm 1 is visible in the spectrum of pulp with the OBA added.
Figure 6 shows
spectra of pulp (expanded region from 300 to 1700 cm 1) with different levels
of OBA added in
the process. The intensity of the peak at 1600 cm -1 increased with increased
level of the OBA.
When spectra of the pulp with OBA added in the conventional and the new
process were
compared, there were no changes in the shape of the peaks and no addition
peaks were observed
(see figure 7). In order to determine the relative amount of OBA retained on
the fibers, the ratio
of the intensity of the maximum at 1600 cm-1 to the intensity of the peak at
900 cm -1 (cellulose
peak) was calculated for pulps with different OBA levels added in the process.
The results are
presented in the table and the Figure 8.
TABLE 10
Process OBA Peak Ht ratio
added,
lb/ton
Conv 0 0.026
0.469
0.637
0.711
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New l W'-'I,. 0 0.034
------------
3.3 0.238
0.648
New SW 0 0.071
3.3 0.371
10 0.655
The results of Raman measurements indicate that the amount of OBA in the pulp
produced in the new process at 10 lb/ton in comparable to the amount of OBA in
the pulp
obtained in the conventional process at 15-20 lb/ton loading
Inductively Coupled Plasma Spectroscopy (ICP) study of OBA in pulp
Samples of softwood and hardwood pulp with OBA added during the conventional
and
new processes were hot plate digested with hydrogen peroxide and nitric acid.
A sample of OBA
used in the process was dried and digested under the same conditions. The
digested samples were
analyzed for sulfur content by ICP. The results are presented in the table
below. Untreated pulp
was also analyzed under the same conditions and determined sulfur
concentrations were
subtracted from the concentrations in the treated pulp in order to establish
the amount of OBA
present in the pulp, which is reported on the dry weight of the OBA.
Process OBA Sulfur from S from OBA on
added, ICP, ppm OBA on fiber,
lb/ton fiber, ppm ppm
(based on
S results)
Conv 0 150
10 190 40 697
250 100 1744
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NewHW 0 140
250 110 1918
New SW 0 66
10 150 84 1465
OBA (oven 57600;
dry) 57100
The sulfur concentrations in the pulp indicate that the amount of OBA present
in the pulp
treated in the new process at 10 lb/ton OBA is comparable to the amount of the
pulp from the
conventional process at 20 lb/ton loading.
Extraction Studies
Approximately 1 gram of pulp was cut into small pieces and soaked in
approximately 150
ml. of water for 6 hours at 60 degrees C.
The water extracts were filtered through a 0.45 pm filter, reduced to
approximately 2 ml
volume in a LABCONCO Rapidvap Nitrogen Evaporation System using air as the
purge gas.
The Evaporator was run at 24% vortex speed at a temperature of 30 C. After
evaporation to
approximately 2 ml. the sample was brought to 5 ml. in a volumetric flask.
A portion of this water 5 ml. extract was analyzed by high performance liquid
chromatography (HPLC).
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Aportiori of the 5 ml. water extract was diluted 1:10 for the UV/VIS analysis.
The HPLC instrumental conditions are below:
Instrument description: Waters Alliance 2695 separation module with a Waters
model 996
Photodiode Array Detector (PDA)
Mobile phase: 50% methanol 50% PIC-A buffer solution at 0.7 ml minute. PIC-A
is sold by the
Waters Corporation and is a reverse phase ion pairing buffer solution composed
of 0.005 m
tetrabutyl ammonium phosphate buffered to a pH of 7.5.
Column: Phenomenex Luna 5 t C-8 (2) 250 mm X 4.6 mm, operated at 35 C.
Detector: Waters 400 photo diode array detector (PDA) over the range of 200 -
800 nm. The
peak at 254 rim was selected for the analysis.
Run Time: 60 minutes
Injection Volume: 10 l
The UV/VIS instrumental conditions are below:
Instrument description: Shimadzu model UV-160 operated in the photometric
mode.
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Wavelength used for analysis: 350 mu.
The results are set forth in figures 9-11
Numerous modifications and variations on the present invention are possible in
light of
the above teachings. It is, therefore, to be understood that within the scope
of the accompanying
claims, the invention may be practiced otherwise than as specifically
described herein.
As used throughout, ranges are used as a short hand for describing each and
every value
that is within the range, including all subranges therein.
29
