U.S. patent application number 13/511956 was filed with the patent office on 2013-01-03 for method for manufacturing nanofibrillated cellulose pulp and use of the pulp in paper manufacturing or in nanofibrillated cellulose composites.
This patent application is currently assigned to UPM-KYMMENE CORPORATION. Invention is credited to Antti Laukkanen, Markus Nuopponen, Taru Paivalainen, Jouni Paltakari.
Application Number | 20130000855 13/511956 |
Document ID | / |
Family ID | 41395280 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130000855 |
Kind Code |
A1 |
Nuopponen; Markus ; et
al. |
January 3, 2013 |
METHOD FOR MANUFACTURING NANOFIBRILLATED CELLULOSE PULP AND USE OF
THE PULP IN PAPER MANUFACTURING OR IN NANOFIBRILLATED CELLULOSE
COMPOSITES
Abstract
A method for manufacturing pulp. The manufactured pulp includes
at least 30 w-% nanofibrillated cellulose material measured from
the dried pulp. A raw material is introduced to a system. The raw
material includes cellulose. At least one type of an optical
brightening agent is dosed as a refining additive to the system.
The raw material is refined in the presence of the dosed optical
brightening agent in at least one pre-refining stage or
fibrillation stage to form fibrillar cellulose material.
Inventors: |
Nuopponen; Markus;
(Helsinki, FI) ; Paivalainen; Taru; (Lappeenranta,
FI) ; Laukkanen; Antti; (Helsinki, FI) ;
Paltakari; Jouni; (Espoo, FI) |
Assignee: |
UPM-KYMMENE CORPORATION
Helsinki
FI
|
Family ID: |
41395280 |
Appl. No.: |
13/511956 |
Filed: |
November 5, 2010 |
PCT Filed: |
November 5, 2010 |
PCT NO: |
PCT/FI2010/050897 |
371 Date: |
September 18, 2012 |
Current U.S.
Class: |
162/76 ; 162/158;
162/72 |
Current CPC
Class: |
D21H 21/30 20130101;
D21H 11/18 20130101; D21H 21/32 20130101 |
Class at
Publication: |
162/76 ; 162/72;
162/158 |
International
Class: |
D21C 3/00 20060101
D21C003/00; D21H 23/00 20060101 D21H023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2009 |
FI |
20096233 |
Claims
1. A method for manufacturing pulp, wherein the manufactured pulp
contains at least 30 w-% nanofibrillated cellulose material
measured from the dried pulp, the method comprising: introducing
raw material to a system which raw material includes cellulose,
dosing at least one type of an optical brightening agent as a
refining additive to the system, and refining the raw material in
the presence of the dosed optical brightening agent in at least one
pre-refining stage or fibrillation stage in order to form fibrillar
cellulose material.
2. The method according to claim 1, wherein the refining is made in
the presence of the dosed optical brightening agent in at least one
fibrillation stage in order to form fibrillar cellulose
material.
3. The method according to claim 1, wherein manufactured pulp
contains at least 40 w-%, at least 50 w-%, at least 60 w-%, or at
least 70 w-% nanofibrillated cellulose material measured from the
dried pulp.
4. The method according to claim 1, wherein at least part of the
raw material is selected from the following group: unbleached
chemical pulp, bleached chemical pulp, unbleached chemithermo pulp,
and bleached chemithermo pulp.
5. The method according to claim 1, wherein at least one type of
the optical brightening agent is dosed before the pre-refining
stage.
6. The method according to claim 1, wherein at least one type of
the optical brightening agent is added to the pre-refining
stage.
7. The method according to claim 1, wherein at least one type of
the optical brightening agent is dosed before the fibrillation
stage.
8. The method according to claim 1, wherein at least one type of
the optical brightening agent is dosed to the fibrillation
stage.
9. The method according to claim 1, wherein at least one dosed
optical brightening agent type is selected from the group of
stilbene, coumarin and pyrazoline compounds.
10. The method according to claim 1, further comprising: using the
pulp in nanofibrillated cellulose composites.
11. The method according to claim 1, further comprising: utilizing
the pulp in manufacturing of paper or paperboard including base
paper production, and finishing stages of paper or paperboard.
12. The use according to claim 11, wherein said finishing stages
comprise coatings for the paper or paperboard.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method of manufacturing
nanofibrillated cellulose pulp. The invention further relates to
use of the pulp in paper manufacturing or in nanofibrillated
cellulose composites.
BACKGROUND OF THE INVENTION
[0002] Many stages of pulp production, especially refining stages,
consume lots of energy. Specially a production of nanofibrillated
cellulose consumes a great deal of energy due to several
fibrillarion passages that are needed to achieve nano-sized
material. Because the energy consumption of the manufactured pulp
increases hugely when the produced pulp includes nanofibrillated
cellulose, there may be an efficiency problem when the produced
pulp consist at least partly of nanofibrillated cellulose.
Sometimes another problem in the nanofibrillated cellulose pulp
production is poor water removal due to several strong bonds
between cellulose fibers and the water to be removed.
[0003] Due to the above mentioned problems, it is beneficial to add
at least one compound capable of substantially inhibiting hydrogen
bonding of fibrils in cellulose, especially in a process preparing
nanofibrillated cellulose. For this purpose some polyhydroxy
compounds, such as sucrose, are used in prior art. However, those
known compounds have some problems. For example, known additives
have generally been used only for refining stages, which will cause
extra additive costs. Thus, it would be more beneficial to use
those kind of additives which were anyway added to the process for
another purpose on later process stages instead of those known
additives used only for the above mentioned purpose.
[0004] There is, therefore, a need for a new solution for
increasing the efficiency of the nanofibrillated cellulose pulp
production. There is, thus, a need for an additive that could cause
a smaller energy consumption of pre-refining and/or fibrillation
stages and a better water removability in the pulp production. The
new additive would preferably have features to reduce the
inter-fiber bonding and, thus, increase a refining efficiency due
to decreased energy consumption of the refining stage. In addition,
the additive would preferably have features to reduce fiber-water
and fiber-fiber bonding that occurs during drying and
concentrating. Moreover, the additive would preferably be some of
those additives that are often added for another purpose on later
process stages.
SUMMARY OF THE INVENTION
[0005] The present invention solves at least some of the above
mentioned problems by providing a method for pulp manufacturing
wherein the produced pulp consist at least partly of
nanofibrillated cellulose. The method comprises a step in which at
least one type of optical brightening agent (OBA) is dosed before
and/or during at least one pre-refining and/or fibrillation stage.
The invention further discloses a use of the produced pulp in
nanofibrillated cellulose composites or in paper or paperboard
manufacturing including base paper manufacturing and finishing
stages like, for example, the use in paper or paperboard
coatings.
[0006] Aspects of the invention are characterized by what is stated
in the independent claims 1, 10 and 11. Various embodiments of the
invention are disclosed in the dependent claims.
[0007] The inventors of the present invention have surprisingly
found that optical brightening agents can increase the production
efficiency of the nanofibrillated cellulose pulp if the additives
are dosed before or during a pre-refining stage and/or a
fibrillation stage. Optical brightening agents have been found to
be able to create bonding with cellulose in such a way that the
optical brightening agents can act as substituents in inter-fiber
bonding and, thus, inhibiting hydrogen bonding of fibrils in
cellulose. The increased production efficiency is mainly due to
decreased energy consumption of the fibrillation stage because of
the substituent effect. Optical brightening agents are also able to
create bonding with water and, thus, to increase the efficiency of
drying and concentrating processes.
[0008] Due to the above mentioned things, optical brightening
agents are able to enable redispersing of nanofibrillated
containing cellulose. Due to the dispersive effect, an optical
brightening agent can be used as a dispersing agent in
nanofibrillated concentrating and/or redispersing process and,
therefore, help the process. In addition, due to the dispersive
effect, the quality of the nanofibrillated cellulose pulp can be
increased.
[0009] According to an embodiment of the present invention, at
least one kind of optical brightening agent is added before a pulp
pre-refining stage. According to another embodiment, at least one
kind of optical brightening agent is added before a pulp
fibrillation stage. According to another embodiment, at least one
kind of optical brightening agent is dosed into the pulp at the
pre-refining stage. According to another embodiment, at least one
kind of optical brightening agent is dosed into the pulp at the
fibrillation stage.
[0010] According to an embodiment, the amount of the
nanofibrillated cellulose in the produced pulp is more than 30 w-%,
preferably more than 40 w-%, 50 w-%, 60 w-% or 70 w-%, and can be
even up to 100 w-% measured from the dried pulp.
[0011] The nanofibrillated cellulose pulp that can be produced
according to the invention and, thus, contains one or more optical
brightening agents, may be used in various end product
applications. The cellulose pulp may be used, for example, in
nanofibrillated cellulose composites, and/or in paper
manufacturing, for example, in a base paper and/or in a finishing
stage of produced paper. The finishing stages of produced paper
includes, for example, coating stages.
DESCRIPTION OF THE DRAWINGS
[0012] In the following, the invention will be illustrated by
drawings in which
[0013] FIGS. 1a-d show microscopy pictures of cellulose pulp,
refined cellulose pulp and nanofibrillated cellulose pulps;
[0014] FIG. 2a-c show some viscosity results of experimental test
together with some optical microscopy pictures taken during
experimental test from Masuko grinded samples;
[0015] FIG. 3a-b show optical microscopy images of some fluidisator
samples taken during experimental test;
[0016] FIG. 4a-b show SEM (scanning electron microscope) pictures
of the samples shown also in FIGS. 3a-3b; and
[0017] FIG. 5 shows some turbidity and centrifugation experimental
test results of the fluidized samples.
DETAILED DESCRIPTION OF THE INVENTION
[0018] In this application, the term "cellulose raw material"
refers to any cellulose raw material source that can be used in a
production of cellulose pulp, refined pulp, or microfibrillar
cellulose. The cellulose raw material can be based on any plant
material that contains cellulose, for example wood material. The
wood material can be from softwood trees, such as spruce, pine,
fir, larch, douglas-fir or hemlock, or from hardwood trees, such as
birch, aspen, poplar, alder, eucalyptus or acacia, or from a
mixture of softwoods and hardwoods. Non-wood material can be from
agricultural residues, grasses or other plant substances such as
straw, leaves, bark, seeds, hulls, flowers, vegetables or fruits
from cotton, corn, wheat, oat, rye, barley, rice, flax, hemp,
manila hemp, sisal hemp, jute, ramie, kenaf, bagasse, bamboo or
reed.
[0019] The term "cellulose pulp" refers in this application to
cellulose fibers, which are isolated from any cellulose raw
material using chemical, mechanical, thermomechanical, or
chemithermo--mechanical pulping process(es). Typically the diameter
of the fibers varies between 15-25 .mu.m and the length exceeds 500
.mu.m, but the present invention is not intended to be limited to
these parameters.
[0020] In this application, the term "paper manufacturing" refers
to manufacturing process of any paper-like material, for example,
paperboards, papers and/or paper composites.
[0021] According to an example embodiment of the invention, at
least part of the lignin that has been included in cellulose raw
material is advantageously removed from the cellulose raw material
when it is processed into cellulose pulp to be used in the
nanofibrillated cellulose production. Thus, chemical pulp may be
used more preferably for nanofibrillated cellulose production than
mechanical pulp. According to an example embodiment of the
invention, the yield of the process wherein cellulose raw material
is processed into cellulose pulp to be used in the nanofibrillated
pulp production has been at least 50%, at least 60%, at least 70%
or at least 80%.
[0022] According to an example embodiment, the cellulose pulp used
in the nanofibrillated cellulose production may be preferably
unbleached or bleached chemithermo or chemical pulp, more
preferably unbleached or bleached chemical pulp, and the most
preferably unbleached chemical pulp, because the method of the
invention may be the most advantageous compared to other processes
when the used cellulose pulp is chemically produced unbleached
pulp.
[0023] The term "refined pulp" refers to refined cellulose pulp.
The refining of cellulose pulp is carried out with suitable
equipment such as a refiner, grinder, homogenizer, colloider,
friction grinder, fluidizer such as microfluidizer, macrofluidizer
or fluidizer-type homogenizer or ultrasound sonicator. Typically,
all cellulose fibers have not been fully fibrillated; a large
fraction of cellulose fibers with unchanged dimensions are still
present in addition to refined cellulose material. The large fibers
in the refined pulp may have fibrillated surface. The finest
fraction of cellulose based material in the "refined pulp" consists
of nanofibrillated cellulose, i.e. cellulose microfibrils and
microfibril bundles with diameter less than 200 nm.
[0024] The term "nanofibrillated cellulose, (NFC)" refers to a
collection of isolated cellulose microfibrils or microfibril
bundles derived from cellulose raw material. Microfibrils have
typically high aspect ratio: the length might exceed one micrometer
while the number-average diameter is typically below 200 nm. The
diameter of microfibril bundles can also be larger but generally
less than 1 .mu.m. The smallest microfibrils are similar to the so
called elementary fibrils, which are typically 2-12 nm in diameter.
The dimensions of the fibrils or fibril bundles are dependent on
the raw material and disintegration method. The nanofibrillated
cellulose may also contain some hemicelluloses; the amount may be
dependent on the plant source.
[0025] Mechanical disintegration of nanofibrillated cellulose from
cellulose raw material, cellulose pulp, or refined pulp is carried
out with suitable equipment such as a refiner, grinder,
homogenizer, colloider, friction grinder, ultrasound sonicator,
fluidizer such as microfluidizer, macrofluidizer or fluidizer-type
homogenizer. Nanofibrillated cellulose can also be any chemically
or physically modified derivate of cellulose microfibrils or
microfibril bundles. The chemical modification could be based for
example on carboxymethylation, oxidation, esterification, or
etherification reaction of cellulose molecules. Modification could
also be realized by physical adsorption of anionic, cationic, or
non-ionic substances or any combination of these on cellulose
surface. The described modification can be carried out before,
after, or during the production of nanofibrillated cellulose.
[0026] There are several widely used synonyms for nanofibrillated
cellulose. For example: nanocellulose, microfibrillar cellulose,
nanofibrillar cellulose, cellulose nanofiber, nano-scale
fibrillated cellulose, microfibrillated cellulose (MFC), or
cellulose microfibrils. Nanofibrillated cellulose described in this
application is not the same material as the so called cellulose
whiskers, which are also known as: cellulose nanowhiskers,
cellulose nanocrystals, cellulose nanorods, rod-like cellulose
microcrystals or cellulose nanowires. In some cases, similar
terminology is used for both materials, for example by
Kuthcarlapati et al. (Metals Materials and Processes 20(3):307-314,
2008) where the studied material was called "cellulose nanofiber"
although they clearly referred to cellulose nanowhiskers. Typically
these materials do not have amorphous segments along the fibrillar
structure as microfibrillar cellulose, which leads to more rigid
structure. Cellulose whiskers are also shorter than microfibrillar
cellulose; typically the length is less than one micrometer.
[0027] In conventional pulp production, it is usually an aim to get
long, quite undamaged, fibrillated fibers, while in the
nanofibrillated cellulose production an aim is to crush fibers into
small pieces. Nanofibrillated cellulose and normal cellulose are
usually produced using different kind of refiners, because the
refiners that are used conventionally in the pulp refiner
production may not, at least efficiently, be used in
nanofibrillated cellulose production. However, the refiners used in
the conventional pulp production may be used as pre-refiners in
nanofibrillated cellulose production. In this application, the term
"fibrillation stage" means the stage that causes more fibrillar
cellulose, and the term "pre-refiner stage" means the stage that
may advantageously be used for pre-refining before a fibrillation
stage in nanofibrillated cellulose production.
[0028] Properties of nanofibrillated cellulose pulp differs hugely
from conventional cellulose pulp due to many nano-sized particles
of the nanofibrillated cellulose pulp and, thus, nanofibrillated
cellulose cannot be though as a same material as conventional
cellulose pulp. Nanofibrillated cellulose is, for example, gel-like
material even in low consistency, and its water removal rate is
usually slow. Paper sheets that contain a lot of nanofibrillated
cellulose have special properties comparing to the sheets made from
normal cellulose pulp, for example, they have usually high strength
properties, their porosity is very low, and the sheets are usually
(at least partly) transparent.
[0029] The differences between cellulose pulp, refined cellulose
pulp and nanofibrillated cellulose pulp are illustrated in FIGS.
1a-1d in optical microscopy pictures. Magnification is the same in
the FIGS. 1a-1c. FIG. 1a shows an optical microscopy picture of
typical cellulose pulp. FIG. 1b shows an microscopy picture of
typical refined cellulose pulp. FIGS. 1c and 1d show microscopy
pictures of typical nanofibrillated cellulose pulp. As can be seen
in FIG. 1c, the large cellulose fibers shown in FIGS. 1a and 1b are
not anymore clearly visible. FIG. 1d shows the same situation as
FIG. 1c but with higher magnification wherein individual
microfibrils and microfibril bundles with diameter less than 100 nm
can be detected.
[0030] According to an example embodiment the present invention
provides a method for manufacturing nanofibrillated cellulose pulp
by pre-refining and/or fibrillating the pulp with a presence of at
least one kind of optical brightening agent. In addition, according
to another example embodiment, the present invention provides the
use of the produced pulp in paper manufacturing or in
nanofibrillated cellulose composites.
[0031] The optical brightening agents (OBAs) are dye-like compounds
which absorb short-wave light in the ultraviolet and violet region
of the electromagnetic spectrum not visible to the human eye and
re-emit the light in the longer-wave blue region. In other words,
optical brightening agents make the material, for example paper, to
look less yellow to the human eyes and, thus, human eyes interpret
the blue light as a higher degree of whiteness. In prior art the
optical brightening agents are used to achieve better optical
properties of the produced paper, for example, for a whitening
effect of the produced paper. Optical brightening agent types that
are typically used in the pulp and paper industry are, for example,
di-, tetra-, and hexasulphonated stilbene compounds. The amount of
sulphonated groups has an effect on the chemical properties of the
optical brightening agent and, thus, the type of the used OBA may
have an effect on the method according to an example embodiment of
the invention. Generally, the more the optical brightening agent
has sulphonated groups the bigger may be the effect of the used
optical brightening agent on the method accordant with the
invention. Some other most commercially available optical
brightening agents in pulp and paper industries are based on
coumarin and pyrazoline chemistries. Those mentioned optical
brightening agent types are only some examples and also other types
of optical brightening agents known in prior art can be used in
this invention. However, according to an embodiment of the
invention, those chemical types mentioned in the application, i.e
stilbene, coumarin and pyrazoline, are preferred to use in the
practice of this invention. From those chemicals, the anionic
stilbene compounds may be the most preferably used in the
invention.
[0032] Optical brightening agents are quite expensive additives,
thus, solutions provided in this invention are intended to be the
most efficient if optical brightening agents are used in
nanofibrillated pulp production wherein the optical brightening
agent is otherwise added in a later stage to the pulp or to the end
product. In papermaking, optical brightening agents are typically
added at the wet end of the papermaking process, which include, for
example, the fan pulp or the machine chest. The use of the optical
brightening agent in accordance with some example embodiments of
the invention does not necessarily increase additive costs but,
quite the contrary, the retention of the optical brightening agent
to the nanofibrillated pulp may be improved if the optical
brightening agent is added before or during pre-refining stage or
before or during a fibrillation step and, therefore, the overall
costs of the used optical brightening agent may be decreased. In
the other words, it is possible that the total amount of the needed
optical brightening agent dosage according to an example embodiment
of the invention can be smaller if the optical brightening agent is
added accordant with some example embodiments of the invention due
to several fiber-optical brightening agent bondings that may be
formed during nanofibrillated cellulose pre-refining and/or
fibrillation stages.
[0033] Therefore, the efficiency of the nanofibrillated cellulose
production can further be increased when the optical brightening
agent is added to the produced pulp before or during the refining
stage, not only because of the decreased energy consumption but
also because of less additive costs. Moreover, the optical
brightening agent dosage to the nanofibrillated cellulose
production according to some example embodiments of this invention
may increase an ability of the nanofibrillated cellulose to carry
the optical brightening agent and, therefore, a need for other
optical brightening agent carriers e.g. Polyvinyl Alcohol (PVOH)
may decrease. Thus, the production efficiency can also be increased
this way due to the invention.
[0034] According to an embodiment of the invention, the method
comprises a step wherein at least one type of the optical
brightening agent (OBA) is dosed as a refining additive to the pulp
which contains cellulose. In the method the dosage is preferably
done before a pre-refining and/or fibrillation stage. In addition
or alternatively, one type of the optical brightening agent can be
added into the pulp at the pre-refining or the fibrillation stage.
Thus, it is possible to add the optical brightening agent to a
pre-refining stage, and/or the optical brightening agent can be
added to some or all of the following fibrillation stages.
According to an advantageous embodiment of the invention, the pulp
is fibrillated in at least one fibrillation stage after the
additive addition, no matter in which stage the additive is added
to the process.
[0035] The anionic optical brightening agent is capable of
inhibiting hydrogen bonding between the cellulose fibrils in
cellulose and can therefore be used to create a dispersive effect,
which dispersive effect can increase the quality of the produced
nanofibrillated cellulose. Due to the dispersive effect, optical
brightening agent can be used as a dispersing agent in the
nanofibrillated concentrating/redispersing process and, therefore,
may help the process.
[0036] Nanofibrillated cellulose that contains optical brightening
agent may improve not only the refining efficiency and the quality
of the produced pulp but also both the strength and the optical
properties of the end product to be produced from the pulp
manufactured according to an example embodiment of the invention.
The improvements in strength properties are mainly due to the
features of nanofibrillated cellulose and the improvements in
optical properties are mainly due to the features of the optical
brightening agent.
[0037] The method according to an example embodiment of the
invention comprises at least the following: [0038] introducing raw
material to a system which raw material includes cellulose, [0039]
dosing at least one type of an optical brightening agent as a
refining additive to the system, and [0040] refining the raw
material in the presence of the dosed optical brightening agent in
at least one pre-refining or fibrillation stage in order to form
fibrillar cellulose material.
[0041] When compared to the pulp produced according to the
invention with pulp produced according to prior art, the novel
invention can provide at least some of the following advantages:
[0042] lower energy consumption to reach the targeted pulp
fibrillation degree, [0043] better quality of the produced
nanofibrillated cellulose pulp, [0044] better processing
properties, including, for example, better water removability and
better dispersing properties, [0045] better strength properties
compared to the same total energy consumption of refining, and
[0046] better optical properties compared to the same amount of the
optical brightening agent (due to better retention of the optical
brightening agent).
[0047] The amount of nanofibrillated cellulose in the pulp
manufactured according to the invention may be 30, 35, 40, 45, 50,
55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 w-%, including any and
all ranges and subranges therein.
[0048] The pulp manufacturing process according to invention has at
least one fibrillation stage, possibly at least 2, 3 or 4
fibrillation stages. According to the invention at least one type
of the optical brightening agent is added [0049] before at least
one of the mentioned fibrillation stages or before the pre-refining
stage, possibly before at least 2, 3, 4 or 5 of the mentioned
fibrillation stages or before the pre-fibrillation stage, [0050]
and/or [0051] to at least one of the mentioned fibrillation stages
or to the pre-refining stage, possibly to at least 2, 3, 4 or 5 of
the mentioned fibrillation stages or to the pre-refining stage.
[0052] In addition, according to the invention, the pulp is
fibrillated after at least one additive dosage in at least one
fibrillation stage in order to form some nanofibrillated cellulose
material.
[0053] As it presented above, the addition of the optical
brightening agent before or during the refining decreases the
cellulose-cellulose bonding through hydroxyl groups by forming
hydrogen bonds with the cellulose fibrils. At the same time, the
addition of the optical brightening agent creates a dispersive
effect to the pulp suspension through the repulsive forces between
the anionic groups.
[0054] Experimental Tests
[0055] Experimental tests were carried out in processes wherein
some amounts of optical brightening agents were dosed as refining
additives. In addition, paper sheets were made from the produced
pulps and tested afterwards.
[0056] 1. Used Pulp [0057] A bleached birch pulp made with
conventional chemical pulping process was used as raw cellulose
pulp.
[0058] 2. Used Optical Brightening Agents [0059] Two different
kinds of optical brightening agents were used as the refining
additive: disulphonic type of the optical brightening agent and
hexasulphonic type of the optical brightening agent. In addition,
reference samples without addition of the optical brightening agent
were performed.
[0060] 3. Pre-Refining [0061] The pre-refining stage was performed
with Voith refiner. Addition of the used optical brightening agent
was always 2 w-%. The whole amount was dosed to the pulp before the
pre-refiner stage, after which the samples were refined at energy
of 200 kWh/t. The pre-refinings were performed in the consistency
of 4%. [0062] The obtained pulps were diluted to 1.6% for fluidizer
and to 2% for Masuko. The optical brightening agents were dosed to
the pre-refining process in order to improve their bonding to fiber
surface.
[0063] 4. Sample Preparation [0064] 4a: Fluidizer [0065] The part
of the samples was fluidized with the M-700 Microfluidics
Processor. Those samples were dispersed with a mixer in 1.6%
consistency during 30 minutes. After dispersing, the samples were
passed three times through fluidizer so that in the first pass
there was only an APM chamber with diameter at 500 .mu.m. In the
second pass, the fiber suspension was passed through two sequential
chambers with diameters at 500 .mu.m and 200 .mu.m. The third pass
was carried out so that the fiber suspension passed through
sequential 500 .mu.m and 100 .mu.m diameter chambers. The condenser
of the fluidizer was switched off during all these trials, as it
was found to improve fibrillation in the first part of experiments.
[0066] 4b: Masuko ultra-fine friction grinder. [0067] The grinded
samples were dispersed in 2% consistency with a mixer during 15
minutes before the treatment with Masuko. The dispersed samples
were passed four times through Masuko in such a way that in the
first pass the gap between the grinding stones was looser than with
the following three passes. The grinder was washed after the first
and third pass.
[0068] 5. Characterization [0069] The gel-like fiber suspensions
obtained from Masuko and from fluidizer were characterized by
measuring viscosity (Brookfield) and turbidity of the samples and
by observing optical microscope and SEM images of the samples. In
addition, with centrifugation measurements the dry matter content
was measured from both the liquid and the solid phase in order to
determine the amount of nano-sized material in the sample.
[0070] 6. Preparation of Paper Sheets [0071] Paper sheets were made
in a laboratory from the produced pulps.
[0072] 7. Test Results [0073] Refining result can be estimated by
measuring the viscosity level of the nanofibrillated cellulose
sample, because the viscosity level of the pulp material goes along
with the portion of nanofibrillated cellulose in the pulp. In
general, more refined, and thus, more fibrillated nanofibrillated
cellulose is more gel-like material than less nanofibrillated
cellulose. Therefore, more gel-like material means more
nanofibrillated cellulose in the sample and this bigger part of
nanofibrillate cellulose can be seen in higher viscosity level in
the sample. Samples with optical brightening agent--dosage were
clearly more viscous than the reference samples. The amount of
unfibrillated fibers can be estimated from optical microscopy
pictures. [0074] Based on both the viscosity results and the
optical microscope images, the optical brightening agent dosage had
a clear effect on fibrillation. Some of these results can be seen
in FIGS. 2a-2c wherein viscosity results with some optical
microscopy pictures of Masuko grinded samples are shown. The FIG.
2a presents the viscosity results of the reference sample 21, the
sample with disulphonic optical brightening agent dosage 22, and
the sample with hexasulphonic optical brightening agent dosage 23.
FIG. 2b shows an optical microscopy picture of the reference sample
21 and FIG. 2c shows an optical microscopy picture of the sample 23
with hexasulphonic optical brightening agent dosage. [0075] Also,
preliminary redispersion tests on the fluidized samples were
performed when the samples were oven dried. Differences in the
disintegration of the dried films in water was detected. Reference
samples did not broken into smaller pieces almost at all, but the
optical brightening agent modified samples disintegrated clearly.
FIGS. 3a and 3b show an optical microscopy images of fluidisator
samples, wherein the reference sample (shown in FIG. 3a) and the
sample 32 with hexasulphonic optical brightening agent (shown in
FIG. 3b) are presented. The sample presented in FIG. 3b with the
dosage of the optical brightening agent is clearly better
fibrillated than the reference sample shown in FIG. 3a. FIGS. 4a
and 4b show the same situation with SEM pictures (magnification: 10
000.times.) in which the reference sample (in FIG. 4a) and the
sample with hexasulphonated optical brightening agent addition (in
FIG. 4b) are presented. As can be seen, the samples with
hexasulphonated optical brightening agent looks clearly better
compared to the reference sample, as many smaller fibrils can be
seen in the image. [0076] Quality of the nanofibrillated cellulose
can be analyzed using centrifugation of nano-sized material and
measuring the turbidity of the samples. Centrifugation results are
supposed to describe the degree of fibrillation so that the more
the nano-sized material has more efficient fibrillation than less
nano-sized material. When it comes to turbidity results, the
smaller the value for turbidity is, the more there should be
nano-sized material in the sample. FIG. 5 shows turbidity and
centrifugation results of the fluidized samples. In this figure the
reference sample 51, the sample 52 with disulphonic type of the
optical brightening agent dosage, and the sample 53 with addition
of hexasulphonic type of the optical brightening agent are
presented. As can be seen, according to the turbidity results, the
samples with OBA dosages were the most nano-sized. Also
centrifugation results indicated that amount of nano-sized material
increases along with OBA addition. [0077] The paper sheets tested
afterwards showed that internal strengths of the sheets produced
according to the invention were clearly higher than the internal
strength properties of the reference sheets produced without
optical brightening agent addition.
[0078] One skilled in the art understands readily that the
different embodiments of the invention may have applications in
environments where optimization of a nanofibrillated cellulose pulp
fibrillation is desired. Therefore, it is obvious that the present
invention is not limited solely to the above-presented embodiments,
but it can be modified within the scope of the appended claims.
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