U.S. patent application number 14/081296 was filed with the patent office on 2014-03-13 for cellulose nanofibers and method for producing same, composite resin composition, molded body.
This patent application is currently assigned to Olympus Corporation. The applicant listed for this patent is Olympus Corporation. Invention is credited to Lianzhen Lin, Kohei Shiramizu.
Application Number | 20140073722 14/081296 |
Document ID | / |
Family ID | 47755948 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140073722 |
Kind Code |
A1 |
Shiramizu; Kohei ; et
al. |
March 13, 2014 |
CELLULOSE NANOFIBERS AND METHOD FOR PRODUCING SAME, COMPOSITE RESIN
COMPOSITION, MOLDED BODY
Abstract
Cellulose nanofibers have an average degree of polymerization of
600 or more to 30000 or less, an aspect ratio of 20 or more to
10000 or less, an average diameter of 1 nm or more to 800 nm or
less, and an I.beta.-type crystal peak in an X-ray diffraction
pattern, in which a hydroxyl group is chemically modified by a
modifying group.
Inventors: |
Shiramizu; Kohei;
(Kawasaki-shi, JP) ; Lin; Lianzhen; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Olympus Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Olympus Corporation
Tokyo
JP
|
Family ID: |
47755948 |
Appl. No.: |
14/081296 |
Filed: |
November 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2012/069038 |
Jul 26, 2012 |
|
|
|
14081296 |
|
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|
Current U.S.
Class: |
524/35 ; 428/401;
536/56 |
Current CPC
Class: |
D06M 23/10 20130101;
D06M 2101/06 20130101; C08B 3/06 20130101; C08L 1/08 20130101; C08J
5/005 20130101; B82Y 30/00 20130101; D06M 13/513 20130101; Y10T
428/298 20150115; D06M 13/188 20130101; D01F 2/28 20130101; D06M
13/08 20130101; C08J 5/045 20130101 |
Class at
Publication: |
524/35 ; 428/401;
536/56 |
International
Class: |
D01F 2/28 20060101
D01F002/28 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2011 |
JP |
2011-185040 |
Claims
1. Cellulose nanofibers, having an average degree of polymerization
of 600 or more to 30000 or less, an aspect ratio of 20 or more to
10000 or less, an average diameter of 1 nm or more to 800 nm or
less, and an I.beta.-type crystal peak in an X-ray diffraction
pattern, wherein a hydroxyl group is chemically modified by a
modifying group.
2. The cellulose nanofibers according to claim 1, wherein a thermal
decomposition temperature of the cellulose nanofibers is equal to
or more than 330.degree. C.
3. The cellulose nanofibers according to claim 2, wherein a
saturated absorptivity of the cellulose nanofibers in an organic
solvent having an SP value of 8 or more to 13 or less is 300% or
more to 5000% or less by mass.
4. The cellulose nanofibers according to claim 3, wherein the
organic solvent is a water-insoluble solvent.
5. The cellulose nanofibers according to claim 1, wherein the
hydroxyl group of the cellulose nanofibers is esterified or
etherified by the modifying group.
6. The cellulose nanofibers according to claim 1, wherein a
modification rate of the cellulose nanofibers is 0.01% or more to
50% or less based on all of the hydroxyl groups.
7. A composite resin composition, comprising the cellulose
nanofibers according to claim 1 in a resin.
8. A composite resin composition, comprising the cellulose
nanofibers according to claim 3 in a resin.
9. A molded body which is formed by molding the composite resin
composition according to claim 8.
10. A method for producing cellulose nanofibers, comprising a
process of: swelling a cellulose raw material in a solution
containing an ionic liquid; and adding a modifier thereto,
filtering, and washing the cellulose raw material.
11. The cellulose nanofibers according to claim 1, wherein a
saturated absorptivity of the cellulose nanofibers in an organic
solvent having an SP value of 8 or more to 13 or less is 300% or
more to 5000% or less by mass.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of and the benefit of
Japanese Patent Application No. 2011-185040 filed on Aug. 26, 2011,
and is a continuous application of international application
PCT/JP2012/069038 filed on Jul. 26, 2012, the disclosures thereof
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to cellulose nanofibers, a
method for producing the same, a composite resin composition, and a
molded body.
[0004] 2. Description of Related Art
[0005] Cellulose nanofibers have been used as a reinforcing
material of a polymer composite material in the related art.
[0006] The cellulose nanofibers are generally obtained by
mechanically shearing cellulose fibers such as pulp or the like,
however, in recent years, a method for defibrating a fibrous raw
material using an ionic liquid has been proposed (Japanese
Unexamined Patent Application, First Publication No.
2009-179913).
[0007] In the method disclosed in Japanese Unexamined Patent
Application, First Publication No. 2009-179913, since it is not
necessary to sufficiently perform mechanical shearing, there is no
concern that the fibers are damaged, and the method is excellent in
terms of its ability to easily obtain cellulose nanofibers with
high strength and high aspect ratio.
[0008] Further, a method for modifying a hydroxyl group of
cellulose nanofibers by a modifying group in order to increase
affinity with a polymer composite material has been proposed
(Japanese Unexamined Patent Application, First Publication No.
2009-144262).
[0009] The method disclosed in Japanese Unexamined Patent
Application, First Publication No. 2009-144262 excels in terms of
improving affinity with polymer composite materials and showing
excellent dispersibility by forming a graft on the surface of the
cellulose nanofibers using polyvinyl acetal.
SUMMARY OF THE INVENTION
[0010] According to a first aspect of the present invention,
cellulose nanofibers have an average degree of polymerization of
600 or more to 30000 or less, an aspect ratio of 20 or more to
10000 or less, an average diameter of 1 nm or more to 800 nm or
less, and an I.beta.-type crystal peak in an X-ray diffraction
pattern, and a hydroxyl group which is chemically modified by a
modifying group.
[0011] According to a second aspect of the present invention, in
the first aspect, a thermal decomposition temperature of the
cellulose nanofibers may be equal to or more than 330.degree.
C.
[0012] According to a third aspect of the present invention, in the
first aspect or the second aspect, a saturated absorptivity of the
cellulose nanofibers in an organic solvent having an SP value of 8
or more to 13 or less may be 300% or more to 5000% or less by
mass.
[0013] According to a fourth aspect of the present invention, in
the third aspect, the organic solvent may be a water-insoluble
solvent.
[0014] According to a fifth aspect of the present invention, in any
one of the first aspect to the fourth aspect, the hydroxyl group of
the cellulose nanofibers may be esterified or etherified by the
modifying group.
[0015] According to a sixth aspect of the present invention, in any
one of the first aspect to the fifth aspect, a modification rate of
the cellulose nanofibers may be 0.01% or more to 50% or less based
on all of the hydroxyl groups.
[0016] According to a seventh aspect of the present invention, a
composite resin composition may contain the cellulose nanofibers
according to any one of the first aspect to the sixth aspect in a
resin.
[0017] According to an eighth aspect of the present invention, a
molded body may be formed by molding the composite resin
composition according to the seventh aspect.
[0018] According to a ninth aspect of the present invention, a
method for producing cellulose nanofibers may include a process of:
swelling a cellulose raw material in a solution containing an ionic
liquid; and adding a modifier thereto, filtering, and washing the
cellulose raw material.
BRIEF DESCRIPTION OF THE DRAWING
[0019] FIG. 1 illustrates results of analyzing X-ray diffraction of
cellulose nanofibers according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] [Cellulose nanofibers]
[0021] The average degree of polymerization of cellulose nanofibers
according to an embodiment of the present invention is in the range
of from 600 to 30000, preferably in the range of from 600 to 5000,
and more preferably in the range of from 800 to 5000. In the case
where the average degree of polymerization is 600 or more,
sufficient reinforcement efficacy can be obtained. For example,
such cellulose nanofibers can be produced by a method using an
ionic liquid. In the case where the average degree of
polymerization is 30000 or less, a problem such that kneading with
resins is difficult to perform does not occur, because the
viscosity during the kneading does not become high.
[0022] The aspect ratio of the cellulose nanofibers according to
the embodiment of the present invention is 20 to 10000, and
preferably 20 to 2000, from the viewpoint of reinforcement
efficacy. The term "aspect ratio" of the present specification and
claims means the ratio of an average fiber length to an average
diameter (average fiber length/average diameter) in cellulose
nanofibers. In the case where the aspect ratio is 20 or more,
sufficient reinforcement efficacy can be obtained. Further, the
aspect ratio is 10000 or less, moldability of a composite resin
composition containing the cellulose nanofibers is excellent.
Furthermore, the aspect ratio is in the range described above, in
the cellulose nanofibers, the entanglement between molecules and
the network structure become strong, thereby improving the
mechanical strength of a molded body.
[0023] The average diameter of the cellulose nanofibers according
to the embodiment of the present invention is 1 nm to 800 nm,
preferably 1 nm to 300 nm, and more preferably 1 nm to 100 nm. In
the case where the average diameter thereof is 1 nm or more, the
cost for production is low, and in the case where the average
diameter thereof is 800 nm or less, the aspect ratio thereof is
hard to decrease. As a result, sufficient reinforcement efficacy
can be obtained at low cost.
[0024] A cellulose type I is composite crystals of I.alpha.-type
crystals and I.beta.-type crystals, and cellulose derived from
high-grade plants such as cotton includes a large quantity of
I.beta.-type crystals, on the other hand, bacteria cellulose
includes a large quantity of I.alpha.-type crystals.
[0025] Since the cellulose nanofibers according to the embodiment
of the present invention include an I.beta.-type crystal peak in an
X-ray diffraction pattern, the X-ray diffraction pattern indicates
a pattern unique to the I.beta.-type crystals as shown in FIG.
1.
[0026] Further, since the cellulose nanofibers according to the
embodiment of the present invention mainly includes the
I.beta.-type crystals, the reinforcement efficacy thereof is
excellent when compared to the bacteria cellulose with a large
quantity of I.alpha.-type crystals.
[0027] The cellulose nanofibers according to the embodiment of the
present invention are chemically modified for improving
functionality. In order to use the cellulose nanofibers as a
composite material, it is necessary to chemically modify hydroxyl
groups on the surface of the cellulose nanofibers by a modifying
group so as to reduce the number of the hydroxyl groups. The
cellulose nanofibers are easily dispersed into a polymer material
by preventing strong adherence between cellulose nanofibers due to
hydrogen bonds, and therefore, excellent interfacial bonds can be
formed between the cellulose nanofibers and the polymer
material.
[0028] The ratio of the hydroxyl groups, which are chemically
modified by a modifying group, to the total hydroxyl groups in the
cellulose nanofibers according to the embodiment of the present
invention is preferably 0.01% to 50%, more preferably 10% to 30%,
and particularly preferably 10% to 20%.
[0029] It is preferable that a hydroxyl group be etherified or
esterified by the modifying group in view of convenience and high
efficiency.
[0030] Preferred examples of etherification agents may include an
alkyl halide such as methyl chloride, ethyl chloride, or propyl
bromide; dialkyl carbonate such as dimethyl carbonate, or diethyl
carbonate; dialkyl sulfate such as dimethyl sulfate or diethyl
sulfate; and alkylene oxide such as ethylene oxide or propylene
oxide. Further, the etherification is not limited to alkyl
etherification caused by the above etherification agents, and
aralkyl etherification caused by benzyl bromide, silyl
etherification, and the like are preferable.
[0031] Examples of silyl etherification agents may include
alkoxysilane, and specific examples thereof may include
alkoxysilane such as n-butoxy trimethylsilane,
tert-butoxytrimethylsilane, sec-butoxytrimethylsilane,
isobutoxytrimethylsilane, ethoxytriethylsilane,
octyldimethylethoxysilane, or cyclohexyloxytrimethylsilane,
alkoxysiloxane such as butoxypolydimethylsiloxane, and disilazane
such as hexamethyldisilazane, tetramethyldisilazane, or
diphenyltetramethyldisilazane. In addition, silyl halides such as
trimethylsilyl chloride or butyl diphenyl silyl chloride, and silyl
trifluoromethane sulfonate such as t-butyldimethylsilyl
trifluoromethane sulfonate may also be used.
[0032] Examples of esterification agents include a carboxylic acid
that may include a hetero atom, a carboxylic acid anhydride, and a
carboxylic halide. As the esterification, an acetic acid, a
propionic acid, a butyric acid, an acrylic acid, a methacrylic acid
and derivatives thereof are preferred, and an acetic acid, acetic
anhydride, and butyric anhydride are more preferable.
[0033] Alkyl etherification, alkyl silylation, and alkyl
esterification from among etherification and esterification are
preferable for improving dispersibility into a resin.
[0034] In the case where the cellulose nanofibers which are
chemically modified in this way are used for a lipophilic resin, it
is preferable that the saturated absorptivity of the cellulose
nanofibers in an organic solvent with a solubility parameter
(hereinafter, referred to as an "SP value") of 8 or more to 13 or
less is 300% by mass to 5000% by mass. The cellulose nanofibers
which are dispersed in the organic solvent having the
above-described SP value have high affinity with a lipophilic
resin, and high reinforcement efficacy.
[0035] Examples of the organic solvents having an SP value of 8 or
more to 13 or less may include an acetic acid, ethyl acetate, butyl
acetate, isobutyl acetate, isopropyl acetate, methyl propyl ketone,
methyl isopropyl ketone, xylene, toluene, benzene, ethyl benzene,
dibutyl phthalate, acetone, 2-propanol, acetonitrile,
dimethylformamide, ethanol, tetrahydrofuran, methyl ethyl ketone,
cyclohexane, carbon tetrachloride, chloroform, methylene chloride,
carbon disulfide, pyridine, n-hexanol, cyclohexanol, n-butanol, and
nitromethane.
[0036] As the organic solvent, a water-insoluble solvent (a solvent
that is not mixed with water of 25.degree. C. at an arbitrary
ratio) is more preferable, and examples thereof may include xylene,
toluene, benzene, ethyl benzene, dichloromethane, cyclohexane,
carbon tetrachloride, methylene chloride, ethyl acetate, carbon
disulfide, cyclohexanol, and nitromethane. The cellulose nanofibers
which are chemically modified in the above way can be dispersed in
a water-insoluble solvent, and easily dispersed in a lipophilic
resin in which the conventional cellulose nanofibers are hard to
disperse.
[0037] Since the cellulose nanofibers according to the embodiment
of the present invention have heat resistance by being chemically
modified, it is possible to impart the heat resistance to other
materials by allowing the cellulose nanofibers to be mixed with
other materials.
[0038] The thermal decomposition temperature of the cellulose
nanofibers according to the embodiment of the present invention is
preferably 330.degree. C. or more, and more preferably 350.degree.
C. or more. A thermal decomposition temperature of 330.degree. C.
or more is too high temperature for conventional cellulose
nanofibers to withstand.
[0039] The degree of crystallinity of the cellulose nanofibers
having the above-described structure according to the embodiment of
the present invention is 80% or more. Accordingly, the cellulose
nanofibers according to the embodiment of the present invention
have exceedingly excellent reinforcement efficacy on resins.
[0040] [Composite Resin Composition]
[0041] The composite resin composition according to the embodiment
of the present invention includes the cellulose nanofibers in a
resin.
[0042] As the above-described lipophilic resin in which the
cellulose nanofibers according to the embodiment of the present
invention can be dispersed, a resin which is sparingly soluble in
water and widely used as an industrial material for which water
resistance is needed is preferable. The lipophilic resin may be a
thermoplastic resin or a thermosetting resin, and examples thereof
may include a plant-derived resin, a resin using carbon dioxide as
a raw material, an acrylonitrile-butadiene-styrene (ABS) resin, an
alkylene resin such as polyethylene or polypropylene, a styrene
resin, a vinyl resin, an acrylic resin, an amide resin, an acetal
resin, a carbonate resin, an urethane resin, an epoxy resin, an
imide resin, a urea resin, a silicone resin, a phenol resin, a
melamine resin, an ester resin, an acrylic resin, an amide resin, a
fluorine resin, a styrole resin, and engineering plastic. In
addition, as the engineering plastic, polyamide, polybutylene
terephthalate, polycarbonate, polyacetal, modified polyphenylene
oxide, modified polyphenylene ether, polyphenylene sulfide,
polyether ether ketone, polyether sulfone, polysulfone, polyamide
imide, polyether imide, polyimide, polyarylate, or polyallyl ether
nitrile is preferably used. Further, two or more kinds of these
resins may be used as a mixture. Among these, polycarbonate is
particularly good due to its high impact strength.
[0043] As the polycarbonate, generally used polycarbonate can be
used. For example, aromatic polycarbonate which is produced by
reacting an aromatic dihydroxy compound and a carbonate precursor
can be preferably used.
[0044] Examples of the aromatic dihydroxy compound may include
2,2-bis(4-hydroxyphenyl)propane ("bisphenol A"),
bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,
2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane,
4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl)cycloalkane,
bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone,
bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)ether, and
bis(4-hydroxyphenyl)ketone.
[0045] Examples of the carbonate precursor may include a carbonyl
halide, carbonyl ester, and a haloformate, and specific examples
thereof may include phosgene, dihaloformate of a dihydric phenol,
diphenyl carbonate, dimethyl carbonate, and diethyl carbonate.
[0046] As the polycarbonate used in the embodiment of the present
invention, polycarbonate that does not contain an aromatic group
may be used. As the polycarbonate that does not contain an aromatic
group, alicyclic polycarbonate or aliphatic polycarbonate are
exemplary examples. A polycarbonate resin may be linear or
branched. In addition, the polycarbonate resin may be a copolymer
of a polymer, which is obtained by polymerizing the aromatic
dihydroxy compound and the carbonate precursor, and other
polymers.
[0047] The polycarbonate resin may be produced by a conventionally
known method, and examples thereof may include an interfacial
polymerization, a melt transesterification method, a pyridine
method, and the like.
[0048] As the types of the resin in the composite resin composition
according to the embodiment of the present invention, a hydrophilic
resin may be included in addition to the lipophilic resin described
above. With regard to the hydrophilic resin, unmodified cellulose
nanofibers, and cellulose nanofibers which are chemically modified
by a hydrophilic functional group such as a sulfonic acid group, a
carboxylic acid group and these chlorides may be preferably used
due to high dispersibility into the hydrophilic resin.
[0049] As the hydrophilic resin, polyvinyl alcohol and a resin
which is subjected to a hydrophilic treatment are listed as
examples. Among these, polyvinyl alcohol is particularly preferred
for its low cost and high dispersibility of the cellulose
nanofibers. The composite resin composition according to the
embodiment of the present invention may include an additive such as
a filler, a flame retardant aid, a flame retardant, an antioxidant,
a release agent, a colorant, or a dispersant in addition to those
described above.
[0050] Examples of the filler to be used may include a carbon
fiber, a glass fiber, clay, titanium oxide, silica, talc, calcium
carbonate, potassium titanate, mica, montmorillonite, barium
sulfate, a balloon filler, a bead filler, and a carbon
nanotube.
[0051] Examples of the flame retardant to be used may include a
halogen-based flame retardant, a nitrogen-based flame retardant, a
metal hydroxide, a phosphorous based-flame retardant, an organic
alkali metal salt, an organic alkali earth metal salt, a
silicone-based flame retardant, and expanded graphite.
[0052] As the flame retardant aid, polyfluoroolefin, antimony
oxide, or the like may be used.
[0053] As the antioxidant, a phosphorous-based antioxidant, a
phenyl-based antioxidant, or the like may be used.
[0054] As the mold release agent, higher alcohol, carboxylic acid
ester, a polyolefin wax, or polyalkylene glycol may be used.
[0055] As the colorant, an arbitrary colorant such as carbon black
or phthalocyanine blue may be used.
[0056] As the dispersant, a dispersant in which the cellulose
nanofibers can be dispersed in a resin may be used, and examples
thereof may include an anionic, cationic, nonionic, or amphoteric
surfactant, and a polymer dispersant, and these may be used in
combination.
[0057] Since the cellulose nanofibers according to the embodiment
of the present invention have reinforcement efficacy as described
above, the composite resin composition containing the cellulose
nanofibers according to the embodiment of the present invention is
excellent in terms of strength. Therefore, the composite resin
composition according to the embodiment of the present invention is
suitable for use in an application requiring strength.
[0058] Further, since the cellulose nanofibers according to the
embodiment of the present invention have excellent dispersibility
in a resin, the composite resin composition containing the
cellulose nanofibers according to the embodiment of the present
invention is excellent in terms of transparency. Accordingly, the
composite resin composition according to the embodiment of the
present invention can maintain its transparency, and therefore the
composite resin composition is suitable for use in an application
requiring transparency.
[0059] Furthermore, since the cellulose nanofibers according to the
embodiment of the present invention have excellent heat resistance
when compared to the cellulose nanofibers in the related art, the
composite resin composition containing the cellulose nanofibers
according to the embodiment of the present invention is excellent
in terms of heat resistance. Therefore, the composite resin
composition according to the present invention is suitable for use
in an application requiring heat resistance while maintaining
transparency.
[0060] [Molded Body]
[0061] The molded body according to the embodiment of the present
invention is formed by molding the composite resin composition. The
method for molding the molded body is not particularly limited, but
examples thereof may include various conventionally known methods
such as an injection molding method, an injection compression
molding method, an extrusion molding method, a blow molding method,
a press molding method, a vacuum molding method, and a foam molding
method.
[0062] Since the molded body according to the embodiment of the
present invention contains the cellulose nanofibers according to
the embodiment of the present invention, the strength or the heat
resistance thereof is excellent. As the molded body, although not
particularly limited, medical equipment, audio equipment, or the
like are listed as examples. Such a molded body may be used for a
molded body for a camera, a lens barrel, or the like, which
particularly requires strength.
[0063] [Method for Producing Cellulose Nanofibers]
[0064] A method for producing cellulose nanofibers according to the
embodiment of the present invention includes a process of swelling
a cellulose raw material in a solution containing an ionic liquid,
adding a modifier thereto, filtering, and washing the
resultant.
[0065] The method for producing the cellulose nanofibers according
to the embodiment of the present invention is a method for
performing a process of defibrating a cellulose raw material in a
solvent containing an ionic liquid and a process of chemically
modifying a hydroxyl group of the cellulose nanofibers using a
modifying agent in one step (hereinafter, referred to a one-step
method).
[0066] In the process of defibrating the cellulose raw material in
a solvent containing an ionic liquid, the solution in which the
cellulose raw material is dissolved is thickened. Consequently, in
the method for producing the cellulose nanofibers using an ionic
liquid in the related art, a sulfate treatment hydrolyzing a low
crystalline cellulose part using sulfate is necessary in order to
decrease the viscosity thereof, therefore, a method for performing
a process of defibration and a process of chemical modification in
two steps (hereinafter, referred to as a "two-step method") has
been used.
[0067] Since the one-step method according to the embodiment of the
present invention has a fewer number of processes compared to the
two-step method in the related art, the one-step method has
advantages in terms of management and cost. In addition, the amount
of a solvent being used is small, so that the burden on the
environment may be reduced.
[0068] The cellulose raw material according to the embodiment of
the present invention is not particularly limited, however,
examples thereof may include raw materials of natural cellulose
such as linter, cotton, and hemp; pulp obtained by chemically
treating wood such as kraft pulp or sulfide pulp; semi-chemical
pulp; used paper or recycle pulp thereof, and the like. Among
these, pulp obtained by chemically treating wood is preferable,
linter with high average degree of polymerization is more
preferable when the cost, quality, and the burden on the
environment are considered.
[0069] The shape of the cellulose raw material is not particularly
limited, however, it is preferable that the cellulose raw material
is used after being appropriately pulverized from the viewpoints of
easiness of mechanical sheerness and accelerating permeation of
solvents.
[0070] As the solution containing the ionic liquid (hereinafter,
referred to as a treatment solution), a solution containing an
ionic liquid represented by the following chemical formula 1 and an
organic solvent is preferable.
##STR00001##
[In the formula, R.sup.1 represents an alkyl group having 1 to 4
carbon atoms, R.sup.2 represents an alkyl group having 1 to 4
carbon atoms or an ally! group. X'' represents a halogen ion,
pseudo-halogen, carboxylate having 1 to 4 carbon atoms, or
thiocyanate.]
[0071] Examples of the ionic liquid may include
1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium
bromide, 1-allyl-3-methylimidazolium chloride,
1-allyl-3-methylimidazolium bromide, and
1-propyl-3-methylimidazolium bromide.
[0072] It is also possible to defibrate the fiber raw material
using only the ionic liquid, however, in the case where even fine
fibers are likely to be dissolved due to excessively high
solubility, it is preferable to add an organic solvent to the ionic
liquid for use.
[0073] The type of the organic solvent to be added may be selected
in consideration of compatibility with the ionic liquid, affinity
with cellulose, solubility of a mixed solvent, viscosity, and the
like, and particularly, it is preferable to use any one or more of
organic solvents from among N,N-dimethylacetamide,
N,N-dimethylformamide, 1-methyl-2-pyrrolidone, dimethylsulfoxide,
acetonitrile, methanol, and ethanol.
[0074] Since the production method according to the embodiment of
the present invention is a one-step method which does not include a
process of a sulfate treatment, the ionic liquid after the
defibration treatment does not contain a hydrolytic agent.
Therefore, recycling of the ionic liquid after the defibration
treatment is easy to perform.
[0075] The amount of the ionic liquid in the treatment solution may
be appropriately adjusted since the amount of the ionic liquid
depends on the types of the cellulose raw material, the ionic
liquid, and the organic solvent, but the amount thereof is
preferably 20% by mass or more from the viewpoints of swelling and
solubility. In the case where an organic solvent having high
solubility is used, the amount thereof is preferably 30% by mass or
more, and in the case where an organic solvent having low
solubility such as methanol is used, the amount thereof is
preferably 50% by mass or more.
[0076] The amount of the cellulose raw material is preferably in
the range of 0.5% by mass to 30% by mass based on the treatment
liquid. In view of economic efficiency, the amount thereof is
preferably 0.5% by mass or more, and more preferably 1% by mass or
more. In view of uniformity of the defibration degree, the amount
thereof is preferably 30% by mass or less, and more preferably 20%
by mass.
[0077] In the method for producing the cellulose nanofibers
according to the embodiment of the present invention, the cellulose
raw material is swollen in the solution containing an ionic liquid.
The cellulose raw material is constituted by crystalline cellulose
with high degree of crystallinity, and a binding substance
including lignin which is present between the crystalline
cellulose, hemicellulose, and amorphous cellulose. The fine
structure constituting cellulose is somewhat slackened by swelling
the cellulose raw material, and enters a state in which it can be
easily cleaved by the external force.
[0078] According to the embodiment of the present invention, a
process of adding a modifier to the cellulose raw material in such
a state, filtering, and washing the resultant is included.
[0079] As the modifier used in the production method according to
the embodiment of the present invention, the same modifier as
described in the method of producing the cellulose nanofibers
according to the embodiment of the present invention may be
used.
[0080] In the method for producing cellulose nanofibers according
to the embodiment of the present invention, it is possible to
obtain cellulose nanofibers having the properties described in the
cellulose nanofibers according to the embodiment of the present
invention.
[0081] That is, according to the embodiment of the present
invention, it is possible to obtain cellulose nanofibers having an
average degree of polymerization of from 600 to 30000, an aspect
ratio of 20 to 10000, an average diameter of 1 nm to 800 nm, and an
I.beta.-type crystal peak in an X-ray diffraction pattern, in which
a hydroxyl group is chemically modified by a modifying group.
[0082] Further, according to the embodiment of the present
invention, since the process of a sulfide treatment is not
included, there is no concern that the cellulose nanofibers are
damaged, cellulose nanofibers having heat resistance with a thermal
decomposition temperature of 330.degree. C. or more can thereby be
obtained.
[0083] Furthermore, the obtained cellulose nanofibers have high
degree of crystallinity. The reason why such effects can be
obtained is not clear, but it can be speculated as follows.
[0084] In the process of defibration in the solution containing an
ionic liquid, the cellulose raw material is swollen in the solution
containing an ionic liquid. That is, the fine structure
constituting cellulose is somewhat slackened and enters a state in
which it can be easily cleaved by the external force. Here, among
three hydroxyl groups which are present in the constituent unit of
the cellulose, one hydroxyl group is exposed to the surface of the
cellulose, and the other two hydroxyl groups are assumed to be
related to formation of the crystal structure. In the one-step
method for the present invention, since a modifier is directly
added to the swollen crystalline cellulose, it is speculated that
the hydroxyl group exposed to the surface of the cellulose is
efficiently modified.
[0085] In the two-step method, amorphous cellulose or the like,
which is unnecessary, present in the cellulose raw material is
removed while the swollen cellulose raw material is being
hydrolyzed by the sulfate treatment.
[0086] On the other hand, in the one-step method according to the
embodiment of the present invention, it can be speculated that
since a hydroxyl group is hydrophobized and amorphous cellulose
becomes easily dissolved in a solvent by modifying the hydroxyl
group of the swollen amorphous cellulose, the hydroxyl group is
therefore easily removed by filtration.
EXAMPLES
[0087] Hereinafter, the embodiment of the present invention will be
specifically described by Examples and Comparative Examples, but
the embodiment of the present invention is not limited to the
following Examples.
Example 1
[0088] 15 g filter paper cut into a 3 mm square with scissors was
put into a 300 ml flask, and then 100 ml of N,N-dimethylacetamide
and 100 g of an ion liquid 1-butyl-3-methylimidazolium chloride
were added to the flask, followed by stirring. Subsequently, 90 g
of acetic anhydride was added thereto to react with each other, and
filtered to wash the solid content. The resultant was treated with
a homogenizer, thereby obtaining acetylated cellulose nanofibers by
the one-step method. The modification rate of the acetylated
cellulose nanofibers obtained at this time was 17%, and the thermal
decomposition temperature thereof was 350.degree. C.
[0089] Subsequently, polycarbonate which was dissolved in
dichloromethane in advance (PC, manufactured by Teijin Chemicals
Ltd., Panlite L-1225L, refractive index: 1.58) was mixed with the
acetylated cellulose nanofibers in the dichloromethane, and then
dried, thereby obtaining a polycarbonate composite resin
composition containing the acetylated cellulose nanofibers.
Example 2
[0090] Butylated cellulose nanofibers in which the one-step method
was used and a polycarbonate composite resin composition containing
the butylated cellulose nanofibers were obtained by the same
procedures as Example 1 except that butyric anhydride was added
instead of acetic anhydride. The modification rate of the butylated
cellulose nanofibers obtained at this time was 12% and the thermal
decomposition temperature thereof was 350.degree..
Example 3
[0091] Silylated cellulose nanofibers in which the one-step method
was used and a polycarbonate composite resin composition containing
the silylated cellulose nanofibers were obtained by the same
procedures as Example 1 except that hexamethyl disilazane was added
instead of acetic anhydride. The modification rate of the silylated
cellulose nanofibers obtained at this time was 15% and the thermal
decomposition temperature thereof was 350.degree. C.
Example 4
[0092] Propylated cellulose nanofibers in which the one-step method
was used and a polycarbonate composite resin composition containing
the propylated cellulose nanofibers were obtained by the same
procedures as Example 1 except that propyl bromide was added
instead of acetic anhydride. The modification rate of the
propylated cellulose nanofibers obtained at this time was 15% and
the thermal decomposition temperature thereof was 350.degree.
C.
Reference Example 1
[0093] 2 g filter paper cut into a 3 mm square with scissors was
put into a 200 ml flask, and then 50 ml of N,N-dimethylacetamide
and 60 g of an ion liquid 1-butyl-3-methylimidazolium were added to
the flask, followed by stirring. Subsequently, a sulfuric acid
aqueous solution was added thereto, stirred, and filtered to wash
the solid content. The resultant was treated with a homogenizer,
thereby obtaining cellulose nanofibers by the two-step method. The
obtained cellulose nanofibers were reacted with acetic anhydride to
be acetylated, and the resultant was washed, thereby obtaining
acetylated cellulose nanofibers. The modification rate of the
acetylated cellulose nanofibers obtained at this time was 17%, and
the thermal decomposition temperature thereof was 320.degree.
C.
[0094] Subsequently, polycarbonate which was dissolved in
dichloromethane in advance (PC, manufactured by Teijin Chemicals
Ltd., Panlite L-1225L, refractive index: 1.58) was mixed with the
acetylated cellulose nanofibers in the dichloromethane, and then
dried, thereby obtaining a polycarbonate composite resin
composition containing the acetylated cellulose nanofibers.
Reference Example 2
[0095] Butylated cellulose nanofibers in which the two-step method
was used and a polycarbonate composite resin composition containing
the butylated cellulose nanofibers were obtained by the same
procedures as Example 1 except that butyric anhydride was added
instead of acetic anhydride. The modification rate of the butylated
cellulose nanofibers obtained at this time was 16% and the thermal
decomposition temperature thereof was 320.degree. C.
Comparative Example 1
[0096] A polycarbonate composite resin composition was obtained by
the same method as Reference Example 1 and using bacteria cellulose
nanofibers obtained by drying Nata de COCO (manufactured by Fujicco
Co., Ltd., average degree of polymerization: 3000 or more, average
aspect ratio: 1000 or more, average diameter: 70 nm).
Comparative Example 2
[0097] A polycarbonate composite resin composition was obtained by
the same method as Reference Example 1 and using fine crystalline
cellulose (manufactured by Merck Ltd., average degree of
polymerization: 250, average aspect ratio: 10, crystals having a
diameter of 1 .mu.m to 10 .mu.m are mixed).
[0098] The cellulose nanofibers and the composite resin
compositions obtained from respective Examples, Reference Examples,
and Comparative Examples were measured by the following test
method, and the results thereof are listed in Table 1.
[0099] (1) Measurement of Average Degree of Polymerization
[0100] The molecular weight was evaluated by viscometry (reference:
Macromolecules, volume 18, page 2394 to 2401, 1985).
[0101] (2) Aspect ratio and Average Diameter
[0102] The number average fiber diameter and the number average
length of the cellulose nanofibers were evaluated by SEM
analysis.
[0103] Specifically, a cellulose nanofiber dispersion was cast on a
wafer so as to be observed by SEM. The values of fiber diameter and
length were read out with respect to 20 or more strands of fibers
for each of the obtained images. This operation was performed on at
least 3 sheets of images of non-overlapping regions, thereby
obtaining information on the diameter and length of a minimum of 30
strands of fibers.
[0104] From the data of the diameter and the length of the fibers
obtained as above, the number average fiber diameter and the number
average length could be calculated, and the aspect ratio was then
calculated from the ratio of the number average length to the
number average fiber diameter. In the case where the aspect ratio
was in the range of from 20 to 10000, it was indicated as
excellent, and in the case where the aspect ratio was not in the
range of from 20 to 10000, it was indicated as poor.
[0105] (3) Crystal Structure Analysis (XRD)
[0106] The crystal structure of the cellulose nanofibers was
analyzed using a powder X-ray diffractometer Rigaku Ultima IV. In
the case where the crystal structure of the cellulose nanofibers
was an I.beta.-type crystal structure, it was indicated as
.smallcircle. (excellent), and in the case where the crystal
structure of the cellulose nanofibers was not the I.beta.-type
crystal structure, it was indicated as .times. (poor) in Examples,
Reference Examples, and Comparative Examples.
[0107] (4) Thermal Decomposition Temperature (TG-DTA)
[0108] The cellulose nanofibers were measured using a thermal
analysis apparatus THERMO plus TG8120. A graph in which the weight
decreasing rate was plotted on vertical axis and the temperature
was plotted on the horizontal axis was drawn, and the temperature
of the intersection point of a tangent at the time when the weight
was largely reduced and a tangent before the weight was reduced was
set to the thermal decomposition temperature.
[0109] (5) Evaluation Method for Modification Rate Al of Hydroxyl
group
[0110] The modification rate of the hydroxyl group was calculated
from a strength of corresponding characteristic band/a strength of
characteristic band of CH (before and after 1367 cm.sup.-1) in the
cellulose ring by FT-IR. For example, in the case where a C.dbd.O
group (before and after 1736 cm.sup.-1) was obtained by
modification, the value in which the strength thereof was divided
by the strength of CH was obtained, and then the modification rate
was calculated by standard curve that was created by a quantitative
measurement method such as NMR or the like in advance.
[0111] (6) Evaluation of Saturated Absorptivity R
[0112] First, cellulose nanofibers of a weight (W1) were dispersed
in dimethylacetamide (SP value: 11.1), thereby preparing a
dispersion of 2% by weight. Subsequently, the dispersion was put in
a centrifuge flask, followed by centrifugation for 30 minutes at
4500 G, and a transparent solvent layer in the upper portion of the
centrifuged dispersion was removed, and then a weight (W2) of a gel
layer in the lower portion of the centrifuged dispersion was
measured, thereby calculating the saturated absorptivity by the
following formula.
R=W2/W1.times.100%
[0113] In the case where the saturated absorptivity was in the
range of from 300% by mass to 5000% by mass, it was indicated as
.smallcircle. (excellent).
TABLE-US-00001 TABLE 1 Reference Reference Comparative Comparative
Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Example
1 Example 2 Polymerization 800 800 800 800 800 800 3000 250 degree
Aspect ratio 100 100 100 100 50 50 1000 10 Average 30 30 30 30 30
30 70 1000 diameter (nm) Crystal .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. x
.smallcircle. structure Thermal 350 350 350 350 320 320 300 300
decomposition temperature (.degree. C.) Modification 17 12 15 15 17
16 0 0 rate A1 (%) Saturated .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. x x
absorptivity R (%)
[0114] As shown in Table 1, the composite resin compositions of
Examples 1 to 4 and Reference Examples 1 and 2 were excellent in
terms of the saturated absorptivity. In addition, the composite
resin compositions of Examples 1 to 4 in which the cellulose
nanofibers produced by the one-step method was used were excellent
in terms of the thermal decomposition temperature.
[0115] The molded bodies of the respective Examples, Reference
Examples, and Comparative Examples were measured by the following
test method, and the results thereof were listed in Table 2.
[0116] (1) Moldability
[0117] The obtained composite resin compositions containing the
cellulose nanofibers were thermally melted and molded, and the
molded state was determined by visual observation. "o" indicates
cases where the moldability was excellent, and ".times." indicates
cases where the moldability was poor.
[0118] (2) Linear Thermal Expansion Coefficient
[0119] A linear thermal expansion coefficient between 100.degree.
C. and 180.degree. C. was measured using Thermo plus TMA8310
(manufactured by Rigaku Corporation) in an air atmosphere at a
heating rate of 5.degree. C./min. The size of a test sample was set
to 20 mm (length).times.5 mm (width). First, a first-run was
carried out at a temperature range of room temperature to Tg, and
then the temperature was cooled to room temperature and a
second-run is carried out. From the results, a linear thermal
expansion coefficient was calculated by the following formula.
Linear thermal expansion coefficient(%)=(length at a time point of
180.degree. C.-length at a time point of 40.degree. C.)/length at a
time point of 40.degree. C..times.100
[0120] In the case where the linear thermal expansion coefficient
was 5% or more, it was indicated as o (excellent), and in the case
where the linear thermal expansion coefficient was less than 5%, it
was indicated as .times. (poor).
TABLE-US-00002 TABLE 2 Reference Reference Comparative Comparative
Example 1 Example 2 Example 3 Example 4 Example 1 Example 2 Example
1 Example 2 Moldability .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. x x Linear .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. x thermal expansion coefficient
[0121] As shown in Table 2, the molded bodies of Examples 1 to 4
showed moldability and linear thermal expansion coefficient
superior to those of the molded bodies of Comparative Examples 1
and 2.
[0122] Furthermore, the entire components described in the
above-mentioned embodiments, and various modified examples can be
carried out by suitably changing or deleting the combination within
the scope of the technical idea of the invention.
[0123] While preferred embodiments of the present invention have
been described, the present invention is not limited to the
embodiments. Additions, omissions, substitutions, and other
variations may be made to the present invention within the scope
that does not depart from the scope of the present invention. The
present invention is not limited by the above description, but only
by the appended claims.
* * * * *