U.S. patent application number 17/374009 was filed with the patent office on 2021-11-11 for method for evaluating cellulose nanofiber dispersion.
The applicant listed for this patent is NIPPON PAPER INDUSTRIES CO., LTD.. Invention is credited to Koji Kimura, Takeshi Nakatani, Shinji Sato.
Application Number | 20210349072 17/374009 |
Document ID | / |
Family ID | 1000005726673 |
Filed Date | 2021-11-11 |
United States Patent
Application |
20210349072 |
Kind Code |
A1 |
Nakatani; Takeshi ; et
al. |
November 11, 2021 |
METHOD FOR EVALUATING CELLULOSE NANOFIBER DISPERSION
Abstract
Herein provided are methods for evaluating cellulose nanofiber
dispersions, comprising the steps of: (1) preparing a cellulose
nanofiber dispersion; (2) adding a color material into the
cellulose nanofiber dispersion; and (3) observing the cellulose
nanofiber dispersion to which a colored pigment has been added with
a light microscope. The methods allow for easy evaluation of
whether or not agglomerates of cellulose nanofibers exist in
cellulose nanofiber dispersions, which cannot be visually
determined.
Inventors: |
Nakatani; Takeshi; (Tokyo,
JP) ; Sato; Shinji; (Tokyo, JP) ; Kimura;
Koji; (Yamaguchi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON PAPER INDUSTRIES CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
1000005726673 |
Appl. No.: |
17/374009 |
Filed: |
July 13, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15550882 |
Aug 14, 2017 |
11092587 |
|
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PCT/JP2016/054416 |
Feb 16, 2016 |
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17374009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2015/1493 20130101;
C08J 3/05 20130101; G02B 21/34 20130101; G01N 2015/0053 20130101;
C08J 3/215 20130101; D21H 11/20 20130101; G01N 2015/0092 20130101;
G01N 1/38 20130101; G01N 15/1463 20130101; C08J 2301/02 20130101;
D21H 17/67 20130101; C08J 3/03 20130101; G01N 33/343 20130101; G01N
33/36 20130101; C08L 1/02 20130101; G01N 15/0227 20130101; D21H
11/18 20130101; C08J 3/09 20130101 |
International
Class: |
G01N 33/36 20060101
G01N033/36; C08J 3/05 20060101 C08J003/05; G01N 33/34 20060101
G01N033/34; G01N 15/02 20060101 G01N015/02; G01N 15/14 20060101
G01N015/14; C08L 1/02 20060101 C08L001/02; C08J 3/03 20060101
C08J003/03; C08J 3/09 20060101 C08J003/09; C08J 3/215 20060101
C08J003/215; D21H 11/18 20060101 D21H011/18; D21H 11/20 20060101
D21H011/20; D21H 17/67 20060101 D21H017/67; G01N 1/38 20060101
G01N001/38; G02B 21/34 20060101 G02B021/34 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 17, 2015 |
JP |
2015-028609 |
Claims
1-8. (canceled)
9. A food containing a cellulose nanofiber dispersion wherein the
cellulose nanofiber dispersion contains no agglomerates of
cellulose nanofibers as evaluated by the following method: (1)
preparing a cellulose nanofiber dispersion; (2) adding a color
pigment into the cellulose nanofiber dispersion; and (3) observing
the cellulose nanofiber dispersion to which the color pigment has
been added with a light microscope to determine whether or not
agglomerates of cellulose nanofibers exist in a cellulose nanofiber
dispersion, which cannot be visually determined, wherein the
colored pigment is less transparent to light during observation
with a light microscope, wherein the agglomerates have a size of
150 .mu.m or more and cannot be visually determined.
10. A cosmetic containing a cellulose nanofiber dispersion wherein
the cellulose nanofiber dispersion contains no agglomerates of
cellulose nanofibers as evaluated by the following method: (1)
preparing a cellulose nanofiber dispersion; (2) adding a color
pigment into the cellulose nanofiber dispersion; and (3) observing
the cellulose nanofiber dispersion to which the color pigment has
been added with a light microscope to determine whether or not
agglomerates of cellulose nanofibers exist in a cellulose nanofiber
dispersion, which cannot be visually determined, wherein the
colored pigment is less transparent to light during observation
with a light microscope, wherein the agglomerates have a size of
150 .mu.m or more and cannot be visually determined.
11. A rubber composition containing a cellulose nanofiber
dispersion wherein the cellulose nanofiber dispersion contains no
agglomerates of cellulose nanofibers as evaluated by the following
method: (1) preparing a cellulose nanofiber dispersion; (2) adding
a color pigment into the cellulose nanofiber dispersion; and (3)
observing the cellulose nanofiber dispersion to which the color
pigment has been added with a light microscope to determine whether
or not agglomerates of cellulose nanofibers exist in a cellulose
nanofiber dispersion, which cannot be visually determined, wherein
the colored pigment is less transparent to light during observation
with a light microscope, wherein the agglomerates have a size of
150 .mu.m or more and cannot be visually determined.
12. The food of claim 9, wherein the colored pigment has an average
particle size of 10 .mu.m or less.
13. The food of claim 9, wherein the step (2) comprises adding a
dispersion of a colored pigment to the cellulose nanofiber
dispersion.
15. The cosmetic of claim 10, wherein the colored pigment has an
average particle size of 10 .mu.m or less.
16. The cosmetic of claim 10, wherein the step (2) comprises adding
a dispersion of a colored pigment to the cellulose nanofiber
dispersion.
17. The rubber composition of claim 11, wherein the colored pigment
has an average particle size of 10 .mu.m or less.
18. The rubber composition of claim 11, wherein the step (2)
comprises adding a dispersion of a colored pigment to the cellulose
nanofiber dispersion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 15/550,882, filed on Aug. 14, 2017, which is
the U.S. national stage filing, under 35 U.S.C. .sctn. 371(c), of
International Application No. PCT/JP2016/054416, filed on Feb. 16,
2016, which, in turn, claims priority to Japanese Patent
Application No. 2015-028609, filed on Feb. 17, 2015. The entire
contents of each of the aforementioned applications are
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to methods for evaluating
cellulose nanofiber dispersions.
BACKGROUND ART
[0003] Cellulose nanofibers (CNFs) are fine fibers having a fiber
diameter in the order of about 4 to several hundred nanometers with
high dispersity in water-based media so that they are expected to
be applied as reinforcing materials for resins; for maintaining the
viscosity of foods, cosmetics, medical products or coatings or the
like; for strengthening doughs as precursors of foodstuffs and
holding water in them; for improving food stability; and as
low-calorie additives or emulsion stabilizing aids (patent document
1 and the like). In cases where CNFs are used as additives, they
are typically used in a dispersed state in water (i.e., in a wet
state).
CITATION LIST
Patent Literature
[0004] Patent document 1: JPA No. 2008-1728.
SUMMARY OF INVENTION
Technical Problem
[0005] CNFs are expected to be applied for various purposes, but
CNFs may associate with each other to form agglomerates in CNF
dispersions, thus inviting various problems. Therefore, it should
be necessary to ascertain whether or not agglomerates exist in CNF
dispersions in advance, and to remove or disintegrate any possible
agglomerates in the CNF dispersions as appropriate. However, CNFs
are very thin fibers so that their dispersions are highly
transparent, which caused the problem that agglomerates of CNFs
could not be visually identified if they existed.
[0006] Under these circumstances, the present invention aims to
provide methods for evaluating whether or not agglomerates of CNFs
exist in CNF dispersions, which cannot be visually determined.
Technical Problem
[0007] [1] A method for evaluating a cellulose nanofiber
dispersion, comprising the steps of: (1) preparing a cellulose
nanofiber dispersion; (2) adding a color material into the
cellulose nanofiber dispersion; and (3) observing the cellulose
nanofiber dispersion to which the color material has been added
with a light microscope. [2] The method of [1], wherein the color
material is a colored pigment. [3] The method of [2], wherein the
colored pigment has an average particle size of 10 .mu.m or less.
[4] The method of any one of [1] to [3], wherein the step (2)
comprises adding a dispersion of a colored pigment to the cellulose
nanofiber dispersion. [5] The method of any one of [1] to [4],
further comprising the step of: (4) determining the CNF dispersion
index as follows: 1) sandwich the dispersion between two glass
plates to form a film having a thickness of 0.15 mm; observe the
film with a microscope to measure the major axes of agglomerates;
and classify the agglomerates as follows: agglomerates having a
size of 100 to 150 .mu.m: large particles; agglomerates having a
size of 50 to 100 .mu.m: medium-sized particles; agglomerates
having a size of 20 to 50 .mu.m: small particles; and 2) calculate
the CNF dispersion index by the equation below:
CNF dispersion index=(the number of large particles.times.64+the
number of medium-sized particles.times.8+the number of small
particles.times.1)/2.
[6] A cellulose nanofiber dispersion containing no agglomerates
having a size of 150 .mu.m or more as evaluated by the method of
any one of [1] to [4]. [7] A cellulose nanofiber dispersion having
a CNF dispersion index of 500 or less as determined by the method
defined in [5]. [8] The cellulose nanofiber dispersion of [6] or
[7], which is a dispersion obtained by drying a cellulose nanofiber
dispersion once prepared and then redispersing it in a dispersion
medium. [9] A food containing the cellulose nanofiber dispersion of
any one of [6] to [8] or a cellulose nanofiber from the dispersion.
[10] A cosmetic containing the cellulose nanofiber dispersion of
any one of [6] to [8] or a cellulose nanofiber from the dispersion.
[11] A rubber composition containing the cellulose nanofiber
dispersion of any one of [6] to [8] or a cellulose nanofiber from
the dispersion.
Advantageous Effects of Invention
[0008] The present invention makes it possible to provide methods
for evaluating whether or not agglomerates of CNFs exist in CNF
dispersions, which cannot be visually determined.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 shows an image of the CNF dispersion in Example 1
observed with a light microscope.
[0010] FIG. 2 shows an image of the CNF dispersion in Example 2
observed with a light microscope.
[0011] FIG. 3 shows an image of the CNF dispersion in Example 3
observed with a light microscope.
[0012] FIG. 4 shows an image of the CNF dispersion in Example 4
observed with a light microscope.
[0013] FIG. 5 shows an image of the CNF dispersion in Example 5
observed with a light microscope.
[0014] FIG. 6 shows an image of the CNF dispersion in Comparative
example 1 observed with a light microscope.
[0015] FIG. 7 shows an image of the CNF dispersion in Comparative
example 2 observed with a light microscope.
DESCRIPTION OF EMBODIMENTS
[0016] The methods for evaluating cellulose nanofiber (CNF)
dispersions according to the present invention comprise the steps
of: (1) preparing a dispersion of a cellulose nanofiber; (2) adding
a color material into the cellulose nanofiber dispersion; and (3)
observing the cellulose nanofiber dispersion to which the color
material has been added with a light microscope. As used herein,
the range "A to B" includes its endpoint values, i.e., A and B. The
expression "A or B" includes either one or both of A and B.
[0017] As used herein, the term "agglomerates of cellulose
nanofibers (CNFs)" refers to poorly disintegrated fibers produced
during the disintegration process described later, CNF network
structures produced in dispersions, or agglomerates produced during
the concentration or drying of CNFs or the like. These agglomerates
contain the dispersion media of the dispersions within them so that
they are highly transparent in the visible region and cannot be
visually identified.
Cellulose Nanofibers
[0018] Cellulose nanofibers (CNFs) are fine fibers having a fiber
width of about 4 to 500 nm and an aspect ratio of 100 or more that
can be obtained by disintegrating cellulose fibers having undergone
a chemical treatment such as cationization or anionization.
Anionization treatments include carboxylation (i.e., oxidization),
carboxymethylation, esterification, functionalization and the
like.
Cellulose Base Materials
[0019] Cellulose base materials for preparing chemically modified
cellulose include, for example, those derived from plant materials
(e.g., wood, bamboo, hemp, jute, kenaf, farm wastes, cloth, pulp),
animal materials (e.g., Ascidiacea), algae, products produced by
microorganisms (e.g., acetic acid bacteria (Acetobacter)), and the
like. Pulps include softwood unbleached kraft pulp (NUKP), softwood
bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP),
hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite
pulp (NUSP), softwood bleached sulfite pulp (NBSP),
thermomechanical pulp (TMP), recycled pulp, waste paper pulp, and
the like. Any of these materials can be used, but cellulose fibers
derived from plants or microorganisms are preferred, among which
cellulose fibers derived from plants are more preferred.
Carboxymethylation
[0020] When a carboxymethylated cellulose is used as a chemically
modified cellulose in the present invention, the carboxymethylated
cellulose may be obtained by carboxymethylating any one of the
cellulose base materials listed above by a known method, or may be
commercially available. In either case, the degree of carboxymethyl
substitution per anhydrous glucose unit of the cellulose is
preferably 0.01 to 0.50. An example of a process for preparing such
a carboxymethylated cellulose is as follows. A cellulose is used as
a starting material in a solvent consisting of water or a lower
alcohol in an amount of 3 to 20 times the mass of the cellulose.
Specifically, water, methanol, ethanol, N-propyl alcohol, isopropyl
alcohol, N-butanol, isobutanol, tert-butanol or the like can be
used alone or as a combination of two or more of them. When a mixed
solvent of water and a lower alcohol is used, the proportion of the
lower alcohol is 60 to 95% by mass. A mercerizing agent consisting
of an alkali metal hydroxide such as sodium hydroxide or potassium
hydroxide is used in an amount of 0.5 to 20 molar equivalents per
anhydrous glucose residue of the starting material. The starting
material, solvent, and mercerizing agent are mixed to perform a
mercerization process at a reaction temperature 0 to 70.degree. C.,
preferably 10 to 60.degree. C. for a reaction period of 15 minutes
to 8 hours, preferably 30 minutes to 7 hours. Then, a
carboxymethylating agent is added in an amount of 0.05 to 10.0
molar equivalents per glucose residue to perform an etherification
reaction at a reaction temperature of 30 to 90.degree. C.,
preferably 40 to 80.degree. C. for a reaction period of 30 minutes
to 10 hours, preferably 1 hour to 4 hours.
Carboxylation
[0021] When a carboxylated (oxidized) cellulose is used as a
chemically modified cellulose in the present invention, the
carboxylated cellulose (also referred to as "oxidized cellulose")
can be obtained by carboxylating (oxidizing) any one of the
cellulose base materials by a known method. The carboxyl group
content is preferably, but not limited to, 0.6 to 2.0 mmol/g, more
preferably 1.0 mmol/g to 2.0 mmol/g based on the bone dry mass of
the anionically modified cellulose nanofibers.
[0022] An example of a carboxylation (oxidation) method comprises
oxidizing a cellulose base material using an oxidizing agent in
water in the presence of a compound selected from the group
consisting of an N-oxyl compound, a bromide, an iodide and a
mixture thereof. This oxidation reaction allows the primary
hydroxyl group at the C6 position of the glucopyranose ring on the
surface of the cellulose to be selectively oxidized to give
cellulose fibers having an aldehyde group and a carboxyl group
(--COOH) or a carboxylate group (--COO.sup.-) on their surface.
During the reaction, the concentration of the cellulose is not
specifically limited, but preferably 5% by mass or less.
[0023] The term "N-oxyl compound" refers to a compound capable of
generating nitroxyl radicals. Any N-oxyl compounds can be used so
far as they promote the intended oxidation reaction. Examples
include 2,2,6,6-tetramethylpiperidin-1-oxy radical (TEMPO) and
derivatives thereof (e.g., 4-hydroxy-TEMPO).
[0024] The amount of the N-oxyl compound used is not specifically
limited so far as it is a catalytic amount enough to oxidize the
cellulose used as a base material. For example, it is preferably
0.01 to 10 mmol, more preferably 0.01 to 1 mmol, still more
preferably 0.05 to 0.5 mmol per gram of bone dry cellulose. It is
also preferably about 0.1 to 4 mmol/L of the reaction system.
[0025] The term "bromide" refers to a compound containing bromine,
examples of which include alkali metal bromides that can be ionized
by dissociation in water. Similarly, the term "iodide" refers to a
compound containing iodine, examples of which include alkali metal
iodides. The amount of the bromide or iodide used can be selected
in a range that can promote the oxidation reaction. The total
amount of the bromide and iodide is preferably, for example, 0.1 to
100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5
to 5 mmol per gram of bone dry cellulose.
[0026] Any known oxidizing agents can be used, including, for
example, halogens, hypohalous acids, halous acids, perhalogenic
acids or salts thereof, halogen oxides, peroxides and the like.
Among others, sodium hypochlorite is preferred because it is
inexpensive and less environmentally harmful. The amount of the
oxidizing agent used is preferably 0.5 to 500 mmol, more preferably
0.5 to 50 mmol, still more preferably 1 to 25 mmol, most preferably
3 to 10 mmol per gram of bone dry cellulose, for example. It is
also preferably 1 to 40 mol per mole of the N-oxyl compound.
[0027] During the oxidation process of the cellulose, the reaction
efficiently proceeds even under relatively mild conditions. Thus,
the reaction temperature is preferably 4 to 40.degree. C., or may
be room temperature around 15 to 30.degree. C. As the reaction
proceeds, the pH of the reaction solution is found to decrease
because carboxyl groups are generated in the cellulose. To ensure
that the oxidation reaction efficiently proceeds, an alkaline
solution such as an aqueous sodium hydroxide solution is preferably
added to maintain the pH of the reaction solution in the order of 8
to 12, preferably 10 to 11. The reaction medium is preferably water
because of easy handling, low likelihood of side reactions and the
like.
[0028] The reaction period in the oxidation reaction can be
appropriately selected depending on the extent to which oxidation
proceeds, typically in the order of 0.5 to 6 hours, for example 0.5
to 4 hours.
[0029] In addition, the oxidation reaction may be performed in two
stages. For example, the oxidized cellulose obtained by filtration
after the end of a first stage reaction can be oxidized again under
the same or different reaction conditions, whereby the reaction is
not inhibited by the salt produced as a by-product during the first
stage reaction and efficient oxidation can be achieved.
[0030] Another example of a carboxylation (oxidation) method may
comprise contacting a cellulose base material with an
ozone-containing gas. This oxidation reaction allows hydroxyl
groups at least at the 2- and 6-positions of the glucopyranose ring
to be oxidized and cellulose chains to be cleaved. The ozone
concentration in the ozone-containing gas is preferably 50 to 250
g/m.sup.3, more preferably 50 to 220 g/m.sup.3. The amount of ozone
added to the cellulose base material is preferably 0.1 to 30 parts
by mass, more preferably 5 to 30 parts by mass per 100 parts by
mass of the cellulose base material on a solids basis. The
ozonation temperature is preferably 0 to 50.degree. C., more
preferably 20 to 50.degree. C. The ozonation period is not
specifically limited, but in the order of 1 to 360 minutes,
preferably 30 to 360 minutes. If the ozonation conditions are
within these ranges, the cellulose can be prevented from being
excessively oxidized and cleaved, thereby improving the yield of
the oxidized cellulose. The ozonation may be followed by a
post-oxidation process using an oxidizing agent. The oxidizing
agent used in the post-oxidation process is not specifically
limited, but may include chlorine compounds such as chlorine
dioxide and sodium chlorite; as well as oxygen, hydrogen peroxide,
persulfuric acid, peracetic acid and the like. For example, the
post-oxidation process can be performed by dissolving one of these
oxidizing agents in water or a polar organic solvent such as an
alcohol to prepare a solution of the oxidizing agent and immersing
the cellulose base material in the solution.
[0031] The carboxyl group content of the oxidized cellulose can be
adjusted by controlling the reaction conditions described above
such as the amount of the oxidizing agent added, the reaction
period and the like.
Cationization
[0032] When a cationized cellulose is used as a chemically modified
cellulose in the present invention, the cationically modified
cellulose can be obtained by reacting any one of the cellulose base
materials with a cationizing agent such as
glycidyltrimethylammonium chloride,
3-chloro-2-hydroxypropyltrialkylammonium hydride or a halohydrin
form thereof and an alkali metal hydroxide (sodium hydroxide,
potassium hydroxide or the like) as a catalyst in the presence of
water or an alcohol containing 1 to 4 carbon atoms. In this
process, the degree of cationic substitution per glucose unit of
the resulting cationically modified cellulose can be adjusted by
controlling the amount of the reactant cationizing agent added or
the proportion of water and the alcohol if they are used as a mixed
solvent.
[0033] The degree of cationic substitution of the cationically
modified cellulose is preferably 0.02 to 0.50 per glucose unit.
When a cationic substituent is introduced into cellulose fibers,
the cellulose fibers electrically repel each other. Therefore, the
cellulose fibers into which a cationic substituent has been
introduced can be readily disintegrated into nanofibers. If the
degree of cationic substitution is lower than 0.02 per glucose
unit, they cannot be sufficiently disintegrated into nanofibers. If
the degree of cationic substitution is higher than 0.50 per glucose
unit, however, they may be swollen or dissolved and may fail to
form nanofibers. For efficient disintegration, the cationized
cellulosic base material obtained as described above is preferably
washed.
Esterification
[0034] An esterified cellulose can also be used as a chemically
modified cellulose. Esterification may take place by mixing a
cellulose base material with a powder or an aqueous solution of
phosphate-based compound A; or adding an aqueous solution of
phosphate-based compound A to a slurry of a cellulose base
material, or the like. Examples of phosphate-based compound A
include phosphoric acid, polyphosphoric acid, phosphorous acid,
phosphonic acid, polyphosphonic acid or esters thereof. These may
be in the form of a salt. Among these examples, phosphate
group-containing compounds are preferred because they are
inexpensive and easy to handle and the disintegration efficiency
can be improved by introducing a phosphate group into cellulose
pulp fibers. Phosphate group-containing compounds include
phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen
phosphate, trisodium phosphate, sodium pyrophosphate, sodium
metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen
phosphate, tripotassium phosphate, potassium pyrophosphate,
potassium metaphosphate, ammonium dihydrogen phosphate, diammonium
hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate,
ammonium metaphosphate, and the like. These can be used alone or as
a combination of two or more of them. Among them, phosphoric acid,
sodium salts of phosphoric acid, potassium salts of phosphoric
acid, and ammonium salts of phosphoric acid are preferred because
phosphate groups are introduced efficiently, disintegration is
promoted in the disintegration process described below and they are
readily industrially applied, and specifically, sodium dihydrogen
phosphate and disodium hydrogen phosphate are more preferred.
Further, the phosphate-based compound A is desirably used as an
aqueous solution because the reaction can proceed uniformly and
phosphate groups are introduced more efficiently. The pH of the
aqueous solution of the phosphate-based compound A is preferably 7
or less to introduce phosphate groups more efficiently, whereas the
pH is preferably 3 to 7 to reduce the hydrolysis of pulp
fibers.
[0035] An example of a process for preparing a cellulose phosphate
ester is as follows: To a suspension of a cellulose base material
having a solids content of 0.1 to 10% by weight is added
phosphate-based compound A with stirring to introduce a phosphate
group into the cellulose. The amount of the phosphate-based
compound A added is preferably 0.2 to 500 parts by weight, more
preferably 1 to 400 parts by weight expressed as the amount of
elemental phosphorus per 100 parts by weight of the cellulose base
material. If the proportion of the phosphate-based compound A is
equal to or higher than the lower limit indicated above, the yield
of microfibrous cellulose can be further improved. However, it is
not preferable in terms of costs to exceed the upper limit
indicated above because the yield cannot be further improved.
[0036] In addition to the phosphate-based compound A, a powder or
an aqueous solution of compound B may be mixed. The compound B is
not specifically limited, but preferably a basic
nitrogen-containing compound. The term "basic" as used here is
defined to mean that the compound in aqueous solution turns
pink-red in the presence of the phenolphthalein indicator or the
compound in aqueous solution has a pH of more than 7. The basic
nitrogen-containing compound used in the present invention is not
limited so far as the advantages of the present invention are
achieved, but it is preferably an amino-containing compound. Such
compounds include urea, methylamine, ethylamine, trimethylamine,
triethylamine, monoethanolamine, diethanolamine, triethanolamine,
pyridine, ethylene diamine, hexamethylene diamine and the like.
Among others, urea is preferred because it is inexpensive and
excellent in handling. The amount of compound B added is preferably
2 to 1000 parts by weight, more preferably 100 to 700 parts by
weight per 100 parts by weight of the cellulose base material on a
solids basis. The reaction temperature is preferably 0 to
95.degree. C., more preferably 30 to 90.degree. C. The reaction
period is not specifically limited, but about 1 to 600 minutes,
more preferably 30 to 480 minutes. If the esterification reaction
conditions are within these ranges, the cellulose can be prevented
from being excessively esterified and readily dissolved, thereby
improving the yield of the cellulose phosphate ester. After the
resulting cellulose phosphate ester suspension is dehydrated, it is
preferably heated at 100 to 170.degree. C. to reduce the hydrolysis
of the cellulose. Further, it is heated at 130.degree. C. or less,
preferably 110.degree. C. or less while water is contained during
the heat treatment, and after water has been removed, it is
preferably heated at 100 to 170.degree. C.
[0037] Preferably, the degree of phosphate substitution of the
cellulose phosphate ester is 0.001 to 0.40 per glucose unit. When a
phosphate substituent is introduced into cellulose fibers, the
cellulose fibers electrically repel each other. Therefore, the
cellulose fibers into which a phosphate group has been introduced
can be readily disintegrated into nanofibers. If the degree of
phosphate substitution is lower than 0.001 per glucose unit, they
cannot be sufficiently disintegrated into nanofibers. If the degree
of phosphate substitution is higher than 0.40 per glucose unit,
however, they may be swollen or dissolved and may fail to form
nanofibers. For efficient disintegration, the cellulosic base
material esterified by phosphate groups obtained as described above
is preferably boiled and then washed with cold water.
Color Materials
[0038] The term "color material" refers to a material having a
color such as white, black, blue, red, yellow, green or the like.
In the present invention, a colored pigment or a dye can be used as
a color material.
Colored Pigments
[0039] As used herein, the term "colored pigment" refers to a
pigment having a color such as white, black, blue, red, yellow,
green or the like in any particle shapes including, but not
specifically limited to, plate-like, spherical, flaky and other
particles. Colored pigments include inorganic pigments and organic
pigments. Examples of inorganic pigments include carbon black,
black iron oxide, black complex metal oxides, zinc chromate, lead
chromate, red lead, zinc phosphate, vanadium phosphate, calcium
phosphate, aluminum phosphomolybdate, calcium molybdate, aluminum
tripolyphosphate, bismuth oxide, bismuth hydroxide, basic bismuth
carbonate, bismuth nitrate, bismuth silicate, hydrotalcite, zinc
dust, micaceous iron oxide, calcium carbonate, barium sulfate,
alumina white, silica, diatomaceous earth, kaolin, talc, clay,
mica, barium oxide, organic bentonite, white carbon, titanium
oxide, zinc oxide, antimony oxide, lithopone, white lead, perylene
black, molybdenum red, cadmium red, red iron oxide, cerium sulfide,
chrome yellow, cadmium yellow, yellow iron oxide, yellow ochre,
bismuth yellow, sienna, amber, green earth, Mars Violet,
ultramarine blue, Prussian blue, basic lead sulfate, basic lead
silicate, zinc sulfide, antimony trioxide, calcium complexes,
phthalocyanine blue, phthalocyanine green, ochre, aluminum powder,
copper powder, brass powder, stainless steel powder, titanium
oxide-coated mica, iron oxide-coated mica, copper zinc oxide,
silver particles, anatase titanium oxide, iron oxide-based calcined
pigments, conductive metal powder, microwave-absorbing ferrites and
the like. Organic pigments include Quinacridone Red, Polyazo
Yellow, Anthraquinone Red, Anthraquinone Yellow, Polyazo Red, Azo
Lake Yellow, Perylene, Phthalocyanine Blue, Phthalocyanine Green,
Isoindolinone Yellow, Watching Red, Permanent Red, Para Red,
Toluidine Maroon, Benzidine Yellow, Fast Sky Blue, Brilliant
Carmine 6B and the like. These pigments can be used alone or as a
combination of two or more of them.
[0040] The colored pigments have an average particle size of 10
.mu.m or less, preferably 0.01 or more and 10 .mu.m or less, more
preferably 0.03 or more and 1 .mu.m or less. If the average
particle size is 10 .mu.m or less, preferably 1 .mu.m or less,
evaluation will be easier because the dispersity of colored
pigments in CNF dispersions becomes stable. On the other hand, the
lower limit is not limited, but if the average particle size is
smaller than 0.01 .mu.m, agglomerates may be difficult to observe
with a light microscope because colored pigments may infiltrate
into the agglomerates. The average particle size is measured by a
laser diffraction particle size distribution analyzer (e.g.,
Mastersizer 3000 or Zetasizer Nano ZS from Malvern). In the case of
non-spherical pigments, the average of the major axis lengths is
taken as the average particle size.
Dyes
[0041] The term "dye" refers to an organic colorant which
selectively absorbs or reflects visible light to exhibit its own
color and with which fibers, pigments and the like are stained by
an appropriate staining method. Dyes include azo dyes, diphenyl-
and triphenylmethane dyes, azine dyes, oxazine dyes, thiazine dyes
and the like. These dyes may be used alone or as a combination of
two or more of them.
Pigment Dispersions
[0042] In the present invention, a colored pigment dispersion
containing a colored pigment stably dispersed in a water-based
solvent using a dispersant or the likes is preferably added to the
CNF dispersion. The use of the colored pigment dispersion helps
make observation with a light microscope easier.
[0043] Such water-based solvents include water, methanol, ethanol,
N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol,
tertiary butanol, linear or branched pentanediol, aliphatic ketones
(e.g., acetone, methyl ethyl ketone, diacetone alcohol, etc.),
polyols (e.g., ethylene glycol, diethylene glycol, triethylene
glycol, etc.), polyglycols having a molar mass of 200 to 2000
g/mol, propylene glycol, dipropylene glycol, tripropylene glycol,
trimethylolpropane, glycerol, thiodiglycol, 2-pyrrolidone,
N-methylpyrrolidone, M-ethylpyrrolidone,
1,3-dimethylimidazolidinone, dimethylacetamide, dimethylformamide,
and combinations thereof.
[0044] Dispersants include higher fatty acids, higher fatty acid
amides, metallic soaps, glycerin esters, hydrotalcite, polyethylene
waxes, polypropylene waxes, glue, gelatin and the like, alone or as
a combination of two or more of them.
[0045] The amount of the colored pigment in the colored pigment
dispersion is not limited, but preferably about 5 to 20% by mass.
If the amount of the colored pigment contained is low, the
photographs taken through a light microscope look pale, but if the
amount of the colored pigment contained is high, agglomerates of
the colored pigment may be generated.
[0046] In the present invention, preferred colored pigments are
those providing a high contrast and less transparent to light
(i.e., highly absorptive to light) during observation with a light
microscope, among which black pigments are more preferred. Further,
they preferably resist secondary agglomeration or agglomeration due
to interaction with CNFs during observation. For example, colored
pigment dispersions that can be used include predispersed liquid
sumi inks for brush calligraphy and paintings including those
available under the brand name Bokuteki, pigment inks for inkjet
printers and the like. Sumi is surface-treated carbon black coated
with a water-based resin on the surface and shows high dispersity
and resists secondary agglomeration when it is mixed with a binder
resin so that it achieves sufficiently high blackness even in CNF
dispersions at relatively low concentrations. Predispersed liquid
sumi inks including those available under the brand name Bokuteki
are water-based dispersions containing surface-treated carbon black
and they are prepared by, for example, coating the surface of
amorphous furnace black made by the furnace process involving
incomplete combustion of a petroleum- or coal-derived oil in a
high-temperature gas or the like with a water-based resin, adding a
glycol-based anti-freezing agent and a preservative as appropriate,
mixing them and slurring the mixture. In the present invention,
commercially available products (e.g., those available under the
brand name "Bokuteki" from Kuretake Co., Ltd. and the like) can be
used. Surface-treated carbon black or water-based dispersions
thereof can also be prepared according to known methods (e.g., JPA
No. 1995-188597 or JPA No. 1994-234946). Predispersed liquid sumi
inks including those available under the brand name Bokuteki, and
pigment inks for inkjet printers may be used alone or as a
combination of two or more of them.
Observation With a Light Microscope
[0047] In the present invention, the concentration of the CNF
dispersion is not specifically limited, but preferably about 0.01
to 10% by mass, more preferably about 0.1 to 2% by mass. If the
concentration is low, the amount of agglomerates decreases, but if
the concentration is high, the viscosity increases to make it
difficult to disperse the colored pigment, whereby the precision
decreases in either case.
[0048] In the present invention, the light microscope with which
the cellulose nanofiber dispersion containing a color material is
observed is not specifically limited, and any conventional light
microscopes (including digital microscopes) can be used. The
magnification at which the CNF dispersion is observed with the
light microscope is not limited, but preferably 50 to 1000
times.
[0049] In the present invention, CNF dispersions containing no
agglomerates having a size of 150 .mu.m or more are judged to have
good dispersity when they are observed with a light microscope.
[0050] Alternatively, the dispersity of the CNF dispersion may be
evaluated by using the CNF dispersion index. The CNF dispersion
index refers to an indicator of the dispersity of CNFs as a
modification of the NEP index (e.g., disclosed in JPA No.
1996-134329), which is an indicator of the dispersity of fibers.
Specifically, the CNF dispersion index is determined as
follows:
1) Sandwich the dispersion between two glass plates to form a film
having a thickness of 0.15 mm; observe the dispersion with a
microscope to measure the major axes of agglomerates; and classify
them as follows: agglomerates having a size of 100 to 150 .mu.m:
large particles; agglomerates having a size of 50 to 100 .mu.m:
medium-sized particles; agglomerates having a size of 20 to 50
.mu.m: small particles. 2) Calculate the CNF dispersion index by
the equation below:
CNF dispersion index=(the number of large particles.times.64+the
number of medium-sized particles.times.8+the number of small
particles.times.1)/2.
3) Evaluate as follows: Dispersions having a CNF dispersion index
of 500 or less: good dispersity; Dispersions having a CNF
dispersion index of 100 or less: very good dispersity.
[0051] CNF redispersions evaluated to have good dispersity in
dispersion media according to the present invention not only show
high solubility in applications for foods, cosmetics, chemical
products and the like but also contain little undispersed
materials, thereby providing smooth touch and improving the mouth
feel when they are added to foods or the like. Thus, transparency,
light transmittance, reproducibility of viscosity and the like are
improved if the CNFs are used in liquid products such as cosmetics,
and on the other hand, transparency, light transmittance and the
like are improved if they are used in chemical products such as
optical films.
[0052] Foods according to the present invention contain the CNF
dispersion or CNFs from the dispersion. Such foods include desserts
and snacks such as flour-based baked foods (e.g., biscuits,
crackers, etc.), Japanese rice crackers (including those made from
non-glutinous rice called senbei, those made from glutinous rice
called okaki, bite-sized crackers made from glutinous rice called
arare, etc.), sweet buns (e.g., rusks, etc.), fried dough foods
(including a traditional Japanese sweet and deep-fried snack food
called karinto, etc.), chocolates, pastries and desserts, candies
and caramels, higashi (i.e., a general term for traditional
Japanese dry confectionery), uchigashi (i.e., a type of higashi
made from rice or other cereal flour and sugar pressed in wood
molds), mamegashi (i.e., traditional Japanese bean snacks), and
yokan (i.e., a bar of gelled sweet bean paste); and manju (i.e.,
traditional Japanese steamed buns with sweet paste fillings),
breakfast cereals, snacks, and dough products such as breads and
noodles. The foods according to the present invention are
preferably obtained by adding CNFs and optional ingredients such as
sugar, oils and fats, eggs, dairy products, leavening agents,
common salt, emulsifiers, flavorings and the like to a flour of a
cereal such as wheat, corn, rye, oat, or rice to prepare a dough,
which is then subjected to kneading and baking steps or subjected
to kneading, fermentation and baking steps to prepare a food
containing the flour as the primary ingredient such as biscuits,
cookies, crackers, wafers, snacks, breakfast cereals, breads, as
well as Japanese rice crackers such as senbei (made from
non-glutinous rice), okaki (made from glutinous rice), arare
(bite-sized crackers made from glutinous rice) and the like. It
should be noted that baking also includes frying with oil.
[0053] Cosmetics according to the present invention contain the CNF
dispersion or CNFs from the dispersion. Such cosmetics include skin
care products such as creams, milky lotions, toners, and serums;
personal cleansing products such as soaps, facial cleansers,
shampoos, and rinses; hair care products such as hair tonics, and
hairstyling products; makeup products such as foundations, eye
liners, mascaras, and lipsticks; oral care products such as
toothpastes; bath products; etc.
[0054] Rubber compositions according to the present invention
contain the CNF dispersion or CNFs from the dispersion. Rubbers in
the rubber compositions are typically based on organic polymers and
have a high elastic limit and a low elastic modulus. Rubbers are
mainly classified into natural rubbers and synthetic rubbers, and
either may be used or both may be combined in the present
invention. Natural rubbers may be natural rubbers in the narrow
sense that have not been chemically modified, or may be chemically
modified natural rubbers such as chlorinated natural rubbers,
chlorosulfonated natural rubbers, epoxylated natural rubbers,
hydrogenated natural rubbers, deproteinized natural rubbers and the
like. Synthetic rubbers include, for example, diene rubbers such as
butadiene rubbers (BR), styrene-butadiene copolymer rubbers (SBR),
isoprene rubbers (IR), butyl rubbers (IIR), acrylonitrile-butadiene
rubbers (NBR), chloroprene rubbers (CR), styrene-isoprene copolymer
rubbers, styrene-isoprene-butadiene copolymer rubbers,
isoprene-butadiene copolymer rubbers and the like; as well as
ethylene-propylene rubbers (EPM, EPDM), acrylic rubbers (ACM),
epichlorohydrin rubbers (CO, ECO), fluorinated rubbers (FKM),
silicone rubbers (Q), urethane rubbers (U), and chlorosulfonated
polyethylene (CSM).
EXAMPLES
Preparation of a CNF Dispersion
[0055] To 500 ml of an aqueous solution containing 39 mg of TEMPO
(from Sigma Aldrich) and 514 mg of sodium bromide dissolved therein
was added 5 g (on a bone dry basis) of an unbeaten softwood
bleached kraft pulp (brightness 85%), and the mixture was stirred
until the pulp was homogeneously dispersed. An aqueous sodium
hypochlorite solution was added to the reaction system in an amount
of 5.5 mmol/g to start an oxidation reaction. During the reaction,
the pH in the system decreased, and therefore, a 3M aqueous sodium
hydroxide solution was added as appropriate to adjust the reaction
system to pH 10. The reaction was terminated when sodium
hypochlorite has been consumed and the pH in the system became
constant. After the reaction, the mixture was filtered through a
glass filter to separate the pulp, and the pulp was thoroughly
washed with water to give an oxidized pulp (carboxylated
cellulose). The pulp yield was 90%, the time required for the
oxidation reaction was 90 minutes, and the carboxyl group content
was 1.6 mmol/g.
[0056] The oxidized pulp obtained in the process described above
was adjusted to 1.0% (w/v) (=1.0% by mass) with water, and treated
in a ultra-high pressure homogenizer (20 .degree. C., 150 Mpa) for
three cycles to give an anionically modified cellulose nanofiber
dispersion. The resulting fibers had an average fiber diameter of
40 nm and an aspect ratio of 150.
Determination Method of the Carboxyl Group Content
[0057] The carboxylated cellulose was prepared into 60 ml of a 0.5%
by mass slurry (aqueous dispersion) and adjusted to pH 2.5 by
adding a 0.1M aqueous hydrochloric acid solution, and then a 0.05N
aqueous sodium hydroxide solution was added dropwise while the
electric conductivity was measured until the pH reached 11. The
carboxyl group content was calculated from the amount of sodium
hydroxide (a) consumed during the neutralization stage of the weak
acid characterized by a moderate change in electric conductivity
using the equation below:
Carboxyl group content [mmol/g carboxylated cellulose]=a
[ml].times.0.05/mass [g] of carboxylated cellulose.
Determination Methods of the Average Fiber Diameter and Aspect
Ratio
[0058] The average fiber diameter and average fiber length of the
anionically modified CNFs were analyzed on randomly chosen 200
fibers using a field emission scanning electron microscope
(FE-SEM). The aspect ratio was calculated by the equation
below:
Aspect ratio=average fiber length/average fiber diameter.
Example 1
[0059] The carboxylated CNFs described above (having a carboxyl
group content of 1.6 mmol/g, an average fiber diameter of 40 nm and
an aspect ratio of 150) were used as CNFs. To 1 g of a 1.0% by mass
aqueous suspension of the CNFs were added two drops of Bokuteki (a
brand name for a predispersed liquid sumi ink for brush calligraphy
and paintings having a solids content of 10% available from
Kuretake Co., Ltd.), and the suspension was stirred in a vortex
mixer for 1 minute. Using Zetasizer Nano ZS (from Malvern), the
average particle size of the liquid sumi ink was measured three
times to be, on average, 0.22 .mu.m. The dispersion was observed
with a light microscope (the digital microscope KH-8700 (from HIROX
Co., Ltd.)) at a magnification of 100.times.. The results are shown
in FIG. 1. The CNF dispersion index was 0.
Example 2
[0060] The CNFs used in Example 1 were dried in a forced air drying
oven at 105.degree. C., and water was added again to prepare an
aqueous CNF dispersion (having a solids content of 1.0% by mass),
which was stirred by using T.K. HOMO MIXER (6,000 rpm) for 60
minutes. To the dispersion were added two drops of Bokuteki and the
dispersion was stirred in a vortex mixer for 1 minute in the same
manner as in Example 1. The dispersion was observed with a light
microscope. The results are shown in FIG. 2. The CNF dispersion
index was 1825.
Example 3
[0061] To 500 ml of an aqueous solution containing 39 mg of TEMPO
(from Sigma Aldrich) and 514 mg of sodium bromide dissolved therein
was added 5 g (on a bone dry basis) of an unbeaten softwood
bleached kraft pulp (brightness 85%), and the mixture was stirred
until the pulp was homogeneously dispersed. An aqueous sodium
hypochlorite solution was added to the reaction system in an amount
of 5.7 mmol/g to start an oxidation reaction. During the reaction,
the pH in the system decreased, and therefore, a 3M aqueous sodium
hydroxide solution was added as appropriate to adjust the reaction
system to pH 10. The reaction was terminated when sodium
hypochlorite has been consumed and the pH in the system became
constant. After the reaction, the mixture was filtered through a
glass filter to separate the pulp, and the pulp was thoroughly
washed with water to give an oxidized pulp (carboxylated
cellulose). The pulp yield was 90%, the time required for the
oxidation reaction was 90 minutes, and the carboxyl group content
was 1.67 mmol/g.
[0062] The oxidized pulp obtained in the process described above
was adjusted to 1.0% (w/v) (=1.0% by mass) with water, and treated
in a ultra-high pressure homogenizer (20.degree. C., 150 Mpa) for
five cycles to give an anionically modified cellulose nanofiber
dispersion. The resulting fibers had an average fiber diameter of 4
nm and an aspect ratio of 150.
[0063] The same experiment as described in Example 2 was performed
except that the CNFs thus obtained were dried in a forced air
drying oven at 105.degree. C., and water was added again as well as
40 parts of carboxymethyl cellulose per 100 parts by weight of the
bone dry solids of the CNFs to prepare an aqueous CNF dispersion
(having a solids content of 1.0% by mass), and the dispersion was
observed with a light microscope. The results are shown in FIG. 3.
The CNF dispersion index was 24.
Example 4
[0064] The CNFs used in Example 3 were dried in a forced air drying
oven at 105.degree. C., and water was added again as well as 40
parts of carboxymethyl cellulose per 100 parts by weight of the
bone dry solids of the CNFs to prepare an aqueous CNF dispersion
(having a solids content of 1.0% by mass), which was stirred by
using T.K. HOMO MIXER (1,000 rpm) for 60 minutes. To the dispersion
were added two drops of Bokuteki and the dispersion was stirred in
a vortex mixer for 1 minute in the same manner as in Example 1. The
dispersion was observed with a light microscope. The results are
shown in FIG. 4. The CNF dispersion index was 252.
Example 5
[0065] The CNFs used in Example 3 were dried in a forced air drying
oven at 105.degree. C., and water was added again as well as 40
parts of carboxymethyl cellulose per 100 parts by weight of the
bone dry solids of the CNFs to prepare an aqueous CNF dispersion
(having a solids content of 1.0% by mass), which was stirred by
using T.K. HOMO MIXER (600 rpm) for 180 minutes. To the dispersion
were added two drops of Bokuteki and the dispersion was stirred in
a vortex mixer for 1 minute in the same manner as in Example 1. The
dispersion was observed with a light microscope. The results are
shown in FIG. 5. The CNF dispersion index was 942.
Example 6
[0066] A dispersion was prepare by the same procedure as described
in Example 1 except that the liquid sumi ink used was changed from
Bokuteki (from Kuretake Co., Ltd.) to another commercially
available predispersed liquid sumi ink (from KAIMEI & Co.,
Ltd.), and the dispersion was observed with a light microscope. As
a result, it could be confirmed that no agglomerates were contained
in the CNF dispersion. Using Zetasizer Nano ZS (from Malvern), the
average particle size of the liquid sumi ink was measured three
times to be, on average, 0.09 .mu.m.
Example 7
[0067] A dispersion was prepare by the same procedure as described
in Example 1 except that the liquid sumi ink used was changed to a
liquid sumi ink obtained by grinding an inkstick (from Kuretake
Co., Ltd.) against an inkstone with water, and the dispersion was
observed with a light microscope. As a result, it could be
confirmed that no agglomerates were contained in the CNF
dispersion. Using Zetasizer Nano ZS (from Malvern), the average
particle size of the liquid sumi ink was measured three times to
be, on average, 0.51 .mu.m.
Example 8
[0068] A dispersion was prepare by the same procedure as described
in Example 1 except that the liquid sumi ink used was changed to an
"aqueous pigment ink" prepared according to the process described
in "Example 1" of JPA No. 2015-199966, and the dispersion was
observed with a light microscope. As a result, it could be
confirmed that no agglomerates were contained in the CNF
dispersion.
Comparative Example 1
[0069] The CNFs used in Example 1 were observed with a light
microscope without adding any drops of liquid sumi ink. The results
are shown in FIG. 6. The CNF dispersion index was 0.
Comparative Example 2
[0070] The CNFs used in Example 2 were observed with a light
microscope without adding any drop of liquid sumi ink. The results
are shown in FIG. 7. The CNF dispersion index was 0.
Results
[0071] Observation results from the CNF dispersions having
undergone no drying step and containing no agglomerates (FIGS. 1
and 6) showed no difference depending on whether or not a liquid
sumi ink exists, but observation results from the CNF dispersions
having undergone a drying step and containing agglomerates (FIGS. 2
to 5, and 7) showed a difference depending on whether or not a
liquid sumi ink exists. These results demonstrated that whether or
not agglomerates exist in CNF dispersions can be easily determined
by observing the CNF dispersions to which a liquid sumi ink has
been added with a light microscope, though it had been previously
difficult to determine.
* * * * *