JP6276900B2 - Method for producing cellulose nanofiber - Google Patents

Description

  The present invention relates to a method for producing cellulose nanofibers.

  Natural fibers or synthetic fibers having a diameter of about 1 to 100 nm are generally called nanofibers. Cellulose nanofibers, one of the nanofibers, are expected to be used in various applications such as composite reinforcement materials.

  Cellulose nanofibers can be obtained by oxidizing cellulose fibers in water in the presence of an N-oxyl compound, removing impurities, applying a dispersion force (Patent Document 1), or mechanically defibrating ( Patent document 2) is known.

  With the development of cellulose nanofibers for various uses, development of cellulose nanofibers having various characteristics is desired. For example, cellulose nanofiber having a short fiber length is one of them. Examples of applications of cellulose nanofibers having a short fiber length include coating a cellulose nanofiber dispersion on a substrate to form a film on the substrate, and a coating containing a pigment, binder, etc. on the cellulose nanofiber dispersion. To be mixed. When a cellulose nanofiber dispersion is applied to a substrate to form a film on the substrate, the dispersion cannot be uniformly applied if the viscosity of the dispersion is too high. On the other hand, if the cellulose nanofiber dispersion is diluted and used in order to apply uniformly, the application and drying must be repeated many times until the desired film thickness is achieved. There's a problem. Further, when the cellulose nanofiber dispersion is mixed with a paint containing a pigment and a binder, there is a problem that the dispersion cannot be uniformly mixed in the paint if the viscosity of the dispersion is too high. In such a case, it is conceivable to prepare and use a low-viscosity cellulose nanofiber dispersion from cellulose nanofibers having a short fiber length.

  As a method for producing a low-viscosity cellulose nanofiber dispersion, before defibrating oxidized cellulose, an enzyme treatment, a method of adding hydrogen peroxide and ozone to an oxidative decomposition treatment, a method of ultraviolet irradiation, an acid A method of adding and hydrolyzing, a method of using dissolved pulp by a kraft method as a raw material, and a method of using wood flour made from planted trees from 1 to 10 years old (Patent Document 3) have been reported.

JP 2008-001728 A JP 2010-216021 JP 2011-236398 A

  According to the above method, it is possible to produce a low-viscosity cellulose nanofiber dispersion, but since the pulp before defibration is subjected to chemical or biological treatment, the fiber is greatly damaged, and when dried There was a problem that coloration was likely to occur. Further, when wood powder is used as a raw material, there is a problem that transparency is lowered. In addition to this, when wood flour is used as a raw material, the pulp fiber in the wood flour is too short and it is very difficult to clean the residual chemicals after chemical modification, and the wood is made into wood flour. There was also a problem that since the mechanical treatment was very strong in the process, the fiber was damaged greatly and coloring was likely to occur during heating and drying.

  An object of the present invention is to provide a cellulose nanofiber dispersion having a low viscosity, and to provide a method for producing cellulose nanofibers that has a stable quality with little coloring even when heated.

The above problems are solved by the present invention described below.
[1] Production of cellulose nanofibers having a number average fiber length of 500 μm or less and a number average fiber diameter of 100 nm or less, comprising a step (1) of preparing wood-derived pulp and a step (2) of defibrating the pulp A method,
When the wood was pulped under kraft pulp production conditions of 15% active alkali addition, 25% sulfidity, 2.5 L / kg liquid ratio, H-factor 830, measured according to ISO 16065-2, 1.00 mm The manufacturing method of the cellulose nanofiber which is a wood from which the pulp which has the fiber length distribution whose ratio of the above fiber length component is 20% or less is obtained.
[2] When the wood is pulped under the above conditions, the ratio of fiber length components of 1.00 mm or more is 20% or less, and the ratio of fiber length components of 0.20 mm or less is 20% or less. The production method according to [1], which is wood from which a pulp having a fiber length distribution is obtained.
[3] In [1] or [2], wherein the wood is a wood from which a pulp having a number average fiber length of 0.65 mm or less measured according to ISO 16065-2 when pulped under the above conditions The manufacturing method as described.
[4] The production method according to any one of [1] to [3], including a step of anion-modifying the raw pulp.

  INDUSTRIAL APPLICABILITY According to the present invention, a cellulose nanofiber dispersion having a low viscosity can be provided, and a method for producing cellulose nanofiber having stable quality with little coloring even when heated can be provided.

It is a figure which shows fiber length distribution of the raw material pulp used in Example 1 and Comparative Example 1.

  Hereinafter, the present invention will be described in detail. In the present invention, “to” includes values at both ends thereof. That is, “X to Y” includes X and Y.

1. Production Method Cellulose nanofibers are fibers having a number average fiber length of 500 μm or less and a number average fiber diameter of 100 nm or less. The fiber diameter is preferably 20 nm or less, more preferably 2 to 10 nm. The number average fiber length and the number average fiber diameter of the cellulose nanofiber can be measured by observing the cellulose nanofiber with a microscope such as an electron microscope or an atomic force microscope. The manufacturing method of the cellulose nanofiber of this invention includes the process (1) of preparing the raw material pulp prepared from the specific wood chip, and the process (2) of defibrating the said pulp.

1-1. Process (1)
In this step, wood-derived pulp is prepared. Specifically, when the wood is pulped under specific pulping conditions (hereinafter also referred to as “specific pulp conditions”), the ratio of fiber length components of 1.00 mm or more (hereinafter “long” measured according to ISO 16065-2). It is wood which gives a pulp having a fiber length distribution whose fiber ratio is also 20% or less. The fiber length distribution can be measured using a pulp analyzer “FiberLab” manufactured by Metso Automation. In the fiber length distribution, the ratio of the fiber length component of 0.20 mm or less is preferably 20% or less. The number average fiber length of the pulp is preferably 0.65 mm or less.

The specific pulping conditions are the conditions for producing kraft pulp using wood chips at an active alkali addition amount of 15%, a sulfidity of 25%, a liquid ratio of 2.5 L / kg, and an H factor of 830.
The activated alkali is a term defined in JIS P0001, and indicates the alkalinity of the Kraft method and soda method cooking liquor. The amount of active alkali is expressed as NaOH + Na ₂ S.
The degree of sulfidization is a term defined in JIS P0001, and is the amount of sulfide in the Kraft process cooking liquor. The degree of sulfidation (%) is expressed as Na ₂ S / (NaOH + Na ₂ S) × 100.
H-factor is a term defined in JIS P0001, and is a cooking degree that comprehensively represents the effects of cooking temperature and cooking time in a chemical pulping method. The pulping effect when digested for 1 hour at 100 ° C. is defined as H-factor 1.

1) Wood The tree species is not limited as long as it is a wood from which such fiber length distribution can be obtained, but a hardwood is preferable as the tree species. Although it does not specifically limit as a tree species of hardwood, For example, Eucalyptus (eucalyptus), Fagus (beech), Quercus (nara, oak etc.), Beluta (hippopotamus), Acacia (acacia) etc. are mentioned, for example. Among these, tree species belonging to the genus Eucalyptus are preferred. These are generally good in growth and contain a large number of tree species, so it is relatively easy to find a suitable tree species for the plantation. The tree species belonging to the genus Eucalyptus is preferably at least one selected from the group consisting of Eucalyptus globulas, Eucalyptus grandis, Eucalyptus nighttens, Eucalyptus eurofila, Eucalyptus perita, and Eucalyptus camaldrensis. Moreover, these hybrids etc. may be sufficient.

2) Pulpping Examples of pulping methods for hardwoods include mechanical pulping using the kraft pulp method, soda pulp method, sulfite pulp method, refiner, and the like. In addition to pulp obtained by these methods, pulp obtained by pulverizing these pulps with a high-pressure homogenizer, a cutting mill, or the like, or pulp purified by chemical treatment such as acid hydrolysis can be used. However, if a large amount of lignin remains in the pulp material, chemical modification in the next step may be hindered. Use chemical pulp produced by the kraft pulp method, soda pulp method, sulfite pulp method, etc. Is preferred.

  The pulping conditions for obtaining the raw material pulp prepared in the step (1) (also referred to as “pulping conditions in the step (1)”) need not be the same as the “specific pulping conditions” described above. That is, the pulping conditions in step (1) may be milder conditions or severer conditions than the specific pulping conditions. However, the “long fiber ratio” of the raw material pulp prepared in step (1) is preferably 20% or less. Moreover, it is preferable that the ratio of the fiber length component of 0.20 mm or less of raw material pulp is 20% or less. Furthermore, the number average fiber length of the raw pulp is preferably 0.65 mm or less.

3) Bleaching treatment In order to further remove lignin, the raw material pulp is preferably subjected to a known bleaching treatment. The bleaching method is not particularly limited, but chlorine treatment (C), chlorine dioxide bleaching (D), alkali extraction (E), hypochlorite bleaching (H), oxygen treatment (O), hydrogen peroxide bleaching (P ), Alkaline hydrogen peroxide treatment stage (Ep), alkaline hydrogen peroxide / oxygen treatment stage (Eop), ozone treatment (Z), chelate treatment (Q) and the like. For example, C / DE / O-HD, ZE / OD, C / D-EHD, ZEDP, Z / D-Ep-D, Z / D-Ep-DP, D-Ep-D, D-Ep-DP, D-Ep-PD, ZEop-DD, Z / D-Eop-D, Z / D-Eop- Bleaching can be performed in a sequence such as D-E-D. “/” In the sequence means that the processes before and after “/” are continuously performed without cleaning. The amount of lignin in the pulp is preferably small, and the pulp (bleached kraft pulp, bleached sulfite pulp) obtained by using the pulping treatment and the bleaching treatment has a whiteness (ISO 2470) of 80% or more. It is more preferable.

4) Chemical modification In order to efficiently perform defibration in the next step, it is preferable to subject the raw material pulp to chemical modification such as anion modification or cation modification.
4-1) Anion modification i) Carboxymethylation A raw material pulp is used as a bottoming raw material, and a mixed medium of 3 to 20 times by weight of a lower alcohol and water is used as a solvent. Specifically, the lower alcohol is methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol or the like, or a mixture of two or more. The mixing ratio of the lower alcohol is 60 to 95% by weight in the mixed medium. As the mercerizing agent, 0.5 to 20 times moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide is used per glucose residue of the bottoming material. A bottoming raw material, a solvent, and a mercerizing agent are mixed and subjected to mercerization treatment at a reaction temperature of 0 to 70 ° C., preferably 10 to 60 ° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times mol per glucose residue, a reaction temperature of 30 to 90 ° C., preferably 40 to 80 ° C., and a reaction time of 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.

  The degree of carboxymethyl substitution per glucose unit in the anion-modified cellulose is preferably 0.02 to 0.50. By introducing a carboxymethyl substituent into cellulose, the celluloses are electrically repelled. For this reason, the cellulose which introduce | transduced the carboxymethyl substituent can be nano-defibrated easily. If the carboxymethyl substituent per glucose unit is smaller than 0.02, nanofibrosis cannot be sufficiently achieved. On the other hand, if the carboxymethyl substituent per glucose unit is larger than 0.50, it may swell or dissolve, and may not be obtained as a nanofiber.

ii) Oxidation The raw material pulp is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide and a mixture thereof, thereby converting the carboxyl group into cellulose. Oxidized cellulose introduced in can be obtained.

  An N-oxyl compound is a compound capable of generating a nitroxy radical. The N-oxyl compound used in the present invention is not limited as long as it is a compound that promotes the target oxidation reaction.

  The amount of the N-oxyl compound is not particularly limited as long as the amount of N-oxyl compound is a catalyst amount that can sufficiently oxidize the pulp so that the resulting oxidized pulp can be converted into nanofibers. For example, it is about 0.01 to 10 mmol, preferably 0.02 to 1 mmol, and more preferably about 0.05 to 0.5 mmol with respect to 1 g of absolutely dry pulp.

  The bromide used in the oxidation of the pulp is a compound containing bromine, and examples thereof include alkali metal bromide that can be dissociated and ionized in water. Iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, about 0.1 to 100 mmol, preferably 0.1 to 10 mmol, and more preferably about 0.5 to 5 mmol with respect to 1 g of absolutely dry pulp.

  As the oxidizing agent used in the oxidation of the pulp, known oxidizing agents such as halogen, hypohalous acid, halogen acid, perhalogen acid or salts thereof, halogen oxide, peroxide, and the like can be used. Sodium hypochlorite is preferable because it is inexpensive and has a low environmental impact. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. The amount is, for example, about 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol with respect to 1 g of absolutely dry pulp.

  The temperature during the oxidation reaction may be a room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution is reduced. In order to advance the oxidation reaction efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11. The reaction medium is preferably water because it is easy to handle and hardly causes side reactions.

  By the above oxidation reaction, the primary hydroxyl group at the 6-position in the cellulose pyranose ring of the pulp is oxidized to a carboxyl group or a salt thereof. A pyranose ring is a six-membered ring carbohydrate consisting of five carbons and one oxygen. The 6-position primary hydroxyl group is an OH group bonded to a 6-membered ring via a methylene group. In the oxidation reaction of cellulose using an N-oxyl compound, this primary hydroxyl group is selectively oxidized. The cellulose thus oxidized is easily nano-defibrated in the next defibrating process. This mechanism is explained as follows. Natural celluloses are nanofibers when they are biosynthesized, but many of these converge by hydrogen bonding to form fiber bundles. When the cellulose fiber is oxidized using an N-oxyl compound, the primary hydroxyl group at the C6 position of the pyranose ring is selectively oxidized, and this oxidation reaction remains on the surface of the microfibril, so that the concentration is high only on the surface of the microfibril. A carboxyl group is introduced. Since the carboxyl groups are negatively charged, they repel each other, and when dispersed in water, the aggregation of the microfibrils is prevented. It becomes a certain cellulose nanofiber.

  The carboxyl group introduced at the C6 position of the cellulose may form a salt with an alkali metal or the like. The amount of the carboxyl group and its salt (hereinafter collectively referred to as “carboxyl group and the like”) is preferably 0.10 mmol / g or more with respect to the dry mass of the cellulose nanofiber. Since the carboxyl group or the like is a polar group, when the amount is large, the cellulose nanofibers are more likely to be firmly adhered to each other when the film or laminate is formed, and the oxygen barrier property is improved. Furthermore, since the cellulose nanofibers are firmly adhered to each other to form a smooth film, the gloss when formed into a sheet is also improved. Therefore, the lower limit of this amount is more preferably 1.20 mmol / g or more, and further preferably 1.40 mmol / g or more. However, under conditions where a large amount of carboxyl groups is obtained, the cellulose is likely to be cleaved as a side reaction during the oxidation reaction, and the yield decreases, which is uneconomical. For this reason, the upper limit of the amount of carboxyl groups and the like is preferably 3.00 mmol / g or less, and more preferably 2.00 mmol / g or less.

The amount of carboxyl groups and the like is adjusted by adding 60 ml of a 0.5% by mass slurry of oxidized pulp and adding 0.1 M hydrochloric acid aqueous solution to pH 2.5, then adding 0.05 N sodium hydroxide aqueous solution dropwise to adjust the pH. The electric conductivity is measured until it becomes 11, and the amount can be calculated from the amount (a) of sodium hydroxide consumed in the neutralization step of the weak acid where the change in electric conductivity is slow, using the following formula.
Carboxyl group amount [mmol / g pulp] = a [ml] × 0.05 / oxidized pulp mass [g]

As another example of the oxidation method, a method of oxidizing by contacting a gas containing ozone and a cellulose raw material can be mentioned. By this oxidation reaction, at least the 2-position and 6-position hydroxyl groups of the glucopyranose ring are oxidized and the cellulose chain is decomposed. Ozone concentration in the ozone containing gas is preferably 50 to 250 g / ^{m 3,} more preferably 50~220g / ^{m 3.} The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass when the solid content of the cellulose raw material is 100 parts by mass. The ozone treatment temperature is preferably 0 to 50 ° C, and more preferably 20 to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, and preferably about 30 to 360 minutes. When the conditions for the ozone treatment are within these ranges, the cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, an additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, these oxidizing agents can be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and a cellulose raw material can be immersed in the solution for additional oxidation treatment. The amount of carboxyl groups in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the added amount of the oxidizing agent and the reaction time.

4-2) Cation modification The above cellulose raw material is used as a starting material, and the above cellulose raw material is converted into a cationizing agent and a catalyst such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydride or a halohydrin type thereof. A cation-modified cellulose can be obtained by reacting alkali metal hydroxide (sodium hydroxide, potassium hydroxide, etc.) in the presence of water or an alcohol having 1 to 4 carbon atoms. The degree of cation substitution per glucose unit in the resulting cation-modified cellulose can be adjusted by controlling the amount of the cationizing agent to be reacted, the composition ratio of water or an alcohol having 1 to 4 carbon atoms.

  In the present invention, the degree of cation substitution per glucose unit of the cation-modified cellulose is preferably 0.02 to 0.50. By introducing a cationic substituent into cellulose, the celluloses repel each other electrically. For this reason, the cellulose which introduce | transduced the cation substituent can be nano-defibrated easily. In addition, when the cation substitution degree per glucose unit is smaller than 0.02, nano-fibrosis cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is more than 0.50, it may swell or dissolve, and may not be obtained as a nanofiber. In order to efficiently perform the next defibration, the oxidized cellulose raw material obtained above is preferably washed.

1-2. Process (2)
In this step, raw material pulp is defibrated to obtain cellulose nanofibers. Defibration can be performed, for example, by mixing or stirring, emulsifying, or dispersing apparatus such as a high-speed shear mixer or a high-pressure homogenizer alone or in combination of two or more. At this time, the size of the pulp (fiber diameter) decreases simultaneously with the loosening of the fibers. In particular, when an ultra-high pressure homogenizer that enables a pressure of 100 MPa or more, preferably 120 MPa or more, more preferably 140 MPa or more is used, defibration and dispersion of cellulose nanofibers proceed efficiently, and are low when used as an aqueous dispersion. This is preferable because cellulose nanofibers having a viscosity can be efficiently produced.

  Since the raw pulp subjected to the above-mentioned chemical modification is easily defibrated, in the present invention, further, a treatment for cutting the cellulose chain (shortening the cellulose chain) (also referred to as “low viscosity treatment”) is not performed. It is preferable. However, the raw material pulp may be subjected to a mild viscosity-reducing treatment so that coloring or the like does not occur. Examples of such a viscosity-reducing treatment include a treatment of irradiating pulp with ultraviolet rays, a treatment of oxidizing and decomposing with hydrogen peroxide and ozone, a treatment of hydrolyzing with acid, a treatment of hydrolyzing with alkali, and an enzyme such as cellulase. Treatment, or a combination thereof.

  For example, for the hydrolysis with alkali, an oxidized pulp dispersion (preferably an aqueous dispersion) is prepared, and the pH of the dispersion is adjusted to 8 to 14, preferably 9 to 13, and more preferably 10 to 12. By reacting at a temperature of 20 to 120 ° C., preferably 50 to 100 ° C., more preferably 60 to 90 ° C., for 0.5 to 24 hours, preferably 1 to 10 hours, more preferably 2 to 6 hours. It can be carried out. For adjusting the pH of the dispersion, an alkaline aqueous solution such as sodium hydroxide can be used. Moreover, it is preferable to add an oxidizing agent or a reducing agent as an auxiliary agent. As the oxidizing agent or reducing agent, those having activity in an alkaline region of pH 8-14 can be used. Examples of the oxidizing agent include oxygen, ozone, hydrogen peroxide, hypochlorite, etc. Among these, oxygen, hydrogen peroxide, hypochlorite, etc., which are less likely to generate radicals, are preferable. Hydrogen peroxide is most preferred. Examples of the reducing agent include sodium borohydride, hydrosulfite, sulfite and the like.

2. Cellulose nanofiber The cellulose nanofiber of the present invention can be used as a dispersion. The dispersion is a liquid in which the cellulose nanofibers of the present invention are dispersed in a dispersion medium. The dispersion medium is a medium, and water is preferable from the viewpoint of handleability. The dispersion is useful from the viewpoint of industrial use of cellulose nanofibers.

  The B-type viscosity of the cellulose nanofiber dispersion using the cellulose nanofiber of the present invention is 2000 mPa · s or less at a concentration of 1% (w / v). The viscosity was 20 ° C., 60 rpm, rotor No. 4 is measured. The lower limit of the B-type viscosity is not particularly set, but actually, the lower limit is about 10 mPa · s at a concentration of 1% (w / v).

  The aqueous dispersion of cellulose nanofibers prepared using the cellulose nanofibers of the present invention is a liquid that is visually transparent because the cellulose nanofibers are uniformly dispersed in water. The transparency of the cellulose nanofiber dispersion can be determined by measuring the transmittance of light having a wavelength of 660 nm with a spectrophotometer. The light transmittance (wavelength 660 nm) at a concentration of 0.1% (w / v) of the cellulose nanofiber aqueous dispersion using the cellulose nanofiber of the present invention is preferably 90% or more, and more preferably 95% or more.

  The dispersion can be prepared by any method. For example, after preparing oxidized pulp, a dispersion medium such as water is added and dispersed while defibrating using an ultrahigh pressure homogenizer or the like, whereby a dispersion can be prepared.

  The cellulose nanofiber dispersion (1% (w / v)) obtained by the conventional method has a B-type viscosity (60 rpm, 20 ° C.) of about 2000 to 10,000 mPa · s, whereas it is produced by the method of the present invention. The viscosity of the cellulose nanofiber dispersion (1% (w / v)) is as low as 2000 mPa · s or less. Therefore, it is possible to increase the concentration of the cellulose nanofiber dispersion. For example, the concentration of the cellulose nanofiber dispersion obtained in the present invention is preferably 1.1 to 10% (w / v), and more preferably 2 to 8% (w / v). Moreover, the cellulose nanofiber of this invention has the characteristics that the coloring degree at the time of heat drying is small. Therefore, for example, when a film is formed by coating on a substrate, there is an advantage that a film having a transparent, smooth and uniform surface can be formed.

The reason why cellulose nanofibers having such performance can be produced by using a specific raw pulp is not limited, but is considered as follows.
For example, when a conventional alkali treatment is performed on pulp, some of the fibers are excessively cut, and a colored material that is extremely shortened is generated. This substance causes coloring upon heating when cellulose nanofibers are formed. Furthermore, since the fiber length distribution becomes wider and extremely short fibers to long fibers exist, the viscosity is increased when a cellulose nanofiber dispersion is obtained. In addition, when wood flour is used as a raw material, the fibers are mechanically destroyed excessively, so there are many colored substances, and the degree of coloring during heating when cellulose nanofibers are obtained is large. On the other hand, from the wood used in the present invention, a raw material having a relatively narrow fiber length distribution and a certain amount or less of a long fiber component without using wood powder or conventional alkali treatment. Since the pulp can be prepared, it is possible to produce cellulose nanofibers that give a dispersion having a low viscosity and a low degree of coloring during heating.

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.
<B-type viscosity>
The B type viscosity (60 rpm, 20 ° C.) was measured using a TV-10 type viscometer (Toki Sangyo Co., Ltd.).

<Pulp viscosity>
The measurement of pulp viscosity is described in It carried out according to TAPPI 44.

<Number average fiber length of cellulose nanofiber>
The fiber length was measured from the atomic force microscope image (3000 nm × 3000 nm) of the cellulose nanofiber fixed on the mica section, and the number average fiber length was calculated. The fiber length was measured using image analysis software WinROOF (Mitani Corporation) in the range of 100 nm to 2000 nm in length.

<Number average fiber diameter of cellulose nanofiber>
A cellulose nanofiber aqueous dispersion diluted so that the concentration of the cellulose nanofibers was 0.001% by mass was prepared. The diluted dispersion is thinly spread on a mica sample stage, dried by heating at 50 ° C. to prepare a sample for observation, the cross-sectional height of the shape image observed with an atomic force microscope (AFM) is measured, and the number average is obtained. The fiber diameter was calculated.

<Number average fiber length and fiber length distribution of pulp>
Measured according to ISO 16065-2.

<Wood>
The following wood was prepared. The ratios (long fiber ratio) of fiber length components of 1.00 mm or more measured according to ISO 16065-2 when each wood was pulped under specific pulping conditions were as follows.
Specific pulping conditions:
Production of kraft pulp using wood chips with 15% active alkali addition, 25% sulfidity, liquid ratio 2.5L / kg, H factor 830 (maximum temperature is 160 ° C, hold 90 minutes after maximum temperature is reached) Condition Wood A: Eucalyptus maldorensis 2 years old, long fiber ratio 8.8%
Wood B: 3 years old Eucalyptus maldorensis, long fiber ratio 17.6%
Wood C: 3 years old acacia, long fiber ratio 10.1%
Wood D: 8 year old hardwood mixed material, long fiber ratio 28.6%
Wood E: Eucalyptus globulus, 8 years old, long fiber ratio 36.2%

[Example 1]
<Step (1): Preparation of raw material pulp>
Wood A (2 years old Eucalyptus maldrensis) was used. Bleached unbeaten kraft pulp (whiteness 85%) (manufactured by Nippon Paper Industries Co., Ltd.) obtained by pulping wood A chips as raw materials under the same conditions as the specific pulping conditions was prepared. FIG. 1 shows the fiber length distribution of this pulp. The long fiber ratio was 8.8%.

  Add 5 g of the pulp (absolutely dry) and 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Tokyo Kasei) and 756 mg (7.35 mmol) of sodium bromide (Wako Pure Chemical Industries) are dissolved until the pulp is uniformly dispersed. Stir. To this, 2.3 mmol of sodium hypochlorite (Wako Pure Chemicals, aqueous solution) was added in the form of an aqueous solution, and then sodium hypochlorite was fed at a rate of 0.23 mmol / min per gram of pulp. Was added gradually to oxidize the pulp. The addition was continued until the total amount of sodium hypochlorite added was 22.5 mmol. During the reaction, since the pH in the system was lowered, a 3N aqueous sodium hydroxide solution was successively added to adjust the pH to 10. Addition from the start of the addition of the aqueous sodium hydroxide solution (that is, from the start of the oxidation reaction to decrease the pH), when the decrease in pH stops and the addition of the aqueous sodium hydroxide solution ends The reaction time was defined as the time until completion (that is, until the time when the oxidation reaction was finished and no pH decrease was observed). The pulp aqueous dispersion after the reaction was filtered through a glass filter and sufficiently washed with water to obtain an oxidized pulp.

<Process (2): Defibration of oxidized pulp>
When 500 mL of oxidized pulp slurry having a concentration of 1% (w / v) was treated five times with an ultra-high pressure homogenizer (20 ° C., 140 MPa), cellulose nanofibers having a number average fiber length of 290 μm were dispersed, transparency 99.4%, A transparent and low-viscosity cellulose nanofiber dispersion having a B-type viscosity of 940 mPa · s was obtained.

<Coloring evaluation after heat treatment>
The cellulose nanofiber aqueous dispersion prepared above (solid content: 1% (W / V)) was dried at 105 ° C. all day and night until there was no moisture, thereby obtaining a film having a thickness of 20 μm. The colored state of the film sample at that time was visually evaluated. Slightly colored ones were judged good, colored ones were accepted, and those with a large degree of coloring were judged defective.

[Example 2]
Wood B (3 years old Eucalyptus maldrensis) was used. Except for using pulp obtained by pulping the wood chips under the same conditions as the specific pulping conditions (long fiber ratio: 17.6%, pulp viscosity: 8.8 mPa · s, manufactured by Nippon Paper Industries Co., Ltd.) In the same manner as in Example 1, a cellulose nanofiber dispersion was obtained. As a result, a transparent and low-viscosity cellulose nanofiber dispersion having a transparency of 99.1% and a B-type viscosity of 1250 mPa · s in which cellulose nanofibers having a number average fiber length of 350 μm were dispersed was obtained. This sample was heat-dried to produce a film, and the state of coloring was evaluated.

[Example 3]
Wood C (3-year-old acacia) was used. Except using pulp obtained by pulping the wood chips under the same conditions as the specific pulping conditions (long fiber ratio is 10.1%, pulp viscosity is 5.0 mPa · s, manufactured by Nippon Paper Industries Co., Ltd.) In the same manner as in No. 1, a cellulose nanofiber dispersion was obtained. As a result, a transparent and low-viscosity cellulose nanofiber dispersion having a transparency of 98.7% and a B-type viscosity of 1300 mPa · s in which cellulose nanofibers having a number average fiber length of 400 μm were dispersed was obtained. This sample was heat-dried to produce a film, and the state of coloring was evaluated.

[Comparative Example 1]
Wood D (8-year-old hardwood mixed material) was used. Except using pulp obtained by pulping the wood chips under the same conditions as the specific pulping conditions (long fiber ratio: 28.6%, pulp viscosity: 14.5 mPa · s, manufactured by Nippon Paper Industries Co., Ltd.) In the same manner as in No. 1, a cellulose nanofiber dispersion was obtained. As a result, a cellulose nanofiber dispersion having a low viscosity of 78.2% transparency and a B-type viscosity of 8000 mPa · s in which cellulose nanofibers having a number average fiber length of 560 μm were dispersed was obtained. This sample was heat-dried to produce a film, and the state of coloring was evaluated.

[Comparative Example 2]
A 5% (w / v) aqueous dispersion of oxidized pulp used in Comparative Example 1 was prepared, and 1% (w / v) hydrogen peroxide with respect to the oxidized cellulosic raw material was prepared in the dispersion. And the pH was adjusted to 12 with 1M sodium hydroxide. This aqueous dispersion was heated at 80 ° C. for 2 hours to hydrolyze the oxidized cellulosic raw material and subjected to pre-defibration treatment. A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the pulp subjected to the defibrating pretreatment (long fiber ratio: 18.7%, pulp viscosity: 18.0 mPa · s) was used. As a result, a cellulose nanofiber dispersion having a high transparency and a low viscosity of 98.8% and a B-type viscosity of 330 mPa · s in which cellulose nanofibers having a number average fiber length of 280 μm were dispersed was obtained. This sample was heat-dried to produce a film, and the state of coloring was evaluated.

[Comparative Example 3]
Wood D (8-year-old hardwood mixed material) was used. Example 1 except that DKP (long fiber ratio: 22.3%, pulp viscosity: 4.0 mPa · s) obtained by pulping using the wood chip after pre-hydrolysis treatment was used. In the same manner as above, a cellulose nanofiber dispersion was obtained. As a result, a cellulose nanofiber dispersion having a high transparency with a transparency of 98.3% and a B-type viscosity of 130 mPa · s in which cellulose nanofibers having a number average fiber length of 190 μm were dispersed was obtained. This sample was heat-treated and dried to produce a film, and the coloring state was evaluated.

[Comparative Example 4]
Wood E (8 years old, Eucalyptus Globulus) was used. Example except that pulp obtained by pulping the wood chips under the same conditions as the specific pulping conditions (long fiber ratio: 36.2%, pulp viscosity: 21.3 mPa · s, manufactured by Nippon Paper Industries Co., Ltd.) In the same manner as in No. 1, a cellulose nanofiber dispersion was obtained. As a result, a cellulose nanofiber dispersion having a low viscosity and a transparency of 88.2% and a B-type viscosity of 10200 mPa · s in which cellulose nanofibers having a number average fiber length of 650 μm were dispersed was obtained. This sample was heat-treated and dried to produce a film, and the coloring state was evaluated.

The cellulose nanofibers of Examples 1 to 3 are highly transparent and low-viscosity in the state of dispersion compared to the cellulose nanofibers of Comparative Examples 1 to 4, and are heated and dried to produce a film. As a result of evaluation, the degree of coloring was small. Thus, the cellulose nanofiber which gives a highly transparent and low-viscosity dispersion is advantageous in industrial use. For example, when a film is formed by coating on a substrate, there is an advantage that a film having high transparency and a smooth and uniform surface can be formed. Furthermore, the range of application can be expanded due to small coloring after drying by heating.

Claims (4)

Fiber length of 1.00 mm or more measured according to ISO 16065-2 when pulped under kraft pulp production conditions of 15% active alkali addition, sulfidity 25%, liquid ratio 2.5 L / kg, H-factor 830 A step of selecting a wood from which a pulp having a fiber length distribution with a component ratio of 20% or less is obtained;
Step of preparing a pulp from the timber (1), and a step (2) for defibrating the pulp,
The number average fiber length 500μm or less and producing how the following cellulose nanofibers number average fiber diameter of 100 nm. In the selection step, when pulped under the pulp production conditions, the ratio of fiber length components of 1.00 mm or more is 20% or less, and the ratio of fiber length components of 0.20 mm or less is 20% or less. The manufacturing method of Claim 1 which selects the wood from which the pulp which has fiber length distribution is obtained. The production according to claim 1 or 2, wherein, in the selection step, a wood from which a pulp having a number average fiber length measured according to ISO 16065-2 of 0.65 mm or less is obtained when pulped under the above conditions. Method. The manufacturing method in any one of Claims 1-3 including the process of carrying out anion modification | denaturation of the raw material pulp obtained at the said process (1) .