JPWO2011074301A1 - Method for oxidizing cellulose and method for producing cellulose nanofiber - Google Patents

Abstract

Provided is a method for efficiently introducing a carboxyl group by promoting oxidation of a primary hydroxyl group of a cellulose-based raw material. Further, the present invention provides a method for efficiently producing a cellulose nanofiber dispersion excellent in fluidity, transparency and thermal stability with low energy. In the presence of (1) an N-oxyl compound, and (2) a compound selected from the group consisting of bromide, iodide, or a mixture thereof, a cellulosic raw material is obtained with hypohalite under the conditions of pH 8-11. Oxidize and introduce 1.0 mmol / g or more of carboxyl groups with respect to the absolute dry mass of the cellulosic raw material, and then further oxidize with halite under pH 4-6 conditions. The obtained oxidized cellulose raw material is defibrated and dispersed to obtain a cellulose nanofiber dispersion.

Description

  The present invention provides a method for obtaining an oxidized cellulosic raw material by efficiently converting primary hydroxyl groups of the cellulosic raw material to carboxyl groups, and fluidity, transparency, and from the oxidized cellulosic raw material obtained as described above. The present invention relates to a method for producing cellulose nanofibers excellent in thermal stability.

  Hypochlorous acid, which is an inexpensive oxidant, using cellulose raw material as a catalyst with 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and bromide or iodide. When treated in the presence of sodium acid, the primary hydroxyl group at the C6 position of cellulose is selectively oxidized, and a carboxyl group can be introduced on the surface of the microfibril. It is known that it can be prepared (Non-patent Document 1).

  This technique for producing cellulose nanofibers is superior in environmental harmony as a reaction process, such as the use of water as a solvent and the fact that the reaction byproduct is only sodium chloride. However, in the oxidation method described above, not only carboxyl groups but also aldehyde groups are mixed in the oxidized pulp due to insufficient oxidation of the cellulosic material. It has been found that oxidized pulp containing an aldehyde group and having a relatively small amount of carboxyl groups requires a larger amount of energy for defibrating and dispersing treatment than oxidized pulp having a relatively large amount of carboxyl groups. This is because in oxidized pulp with a large amount of carboxyl groups, microscopic gaps are created between the pulps due to the charge repulsion between the carboxyl groups, and it becomes easy to fibrillate, but oxidation with a large amount of aldehyde groups and a small amount of carboxyl groups In the pulp, unlike the carboxyl group, the aldehyde group does not have a negative charge, so the charge repulsion is weak, and it is considered that the gap between the pulps contributing to the promotion of defibration and dispersion is not formed so much. Moreover, in the oxidized pulp which has an aldehyde group, a hemiacetal bond and / or an acetal bond are formed between the aldehyde group in a cellulose, and a hydroxyl group, and it is thought that a pulp bridge | crosslinks and dispersibility deteriorates.

  Furthermore, it has been found that films obtained from nano dispersions of oxidized pulp containing aldehyde groups are susceptible to thermal fading, and aldehyde groups are considered to be causative substances that impair the transparency of cellulose nanofiber films.

  Therefore, it is desired to develop a method capable of accelerating the oxidation of the primary hydroxyl group in the cellulosic raw material and efficiently oxidizing the primary hydroxyl group to the carboxyl group.

  In the method of oxidizing lignocellulose using TEMPO, it has been reported that it is preferable to maintain the pH of the aqueous medium at 8 to 11 when sodium hypochlorite is used as the oxidizing agent. It has been reported that it is preferable to maintain the pH of the aqueous medium at 4 to 7 when using sodium chlorite (Patent Document 1).

  In addition, as a method of oxidizing a primary hydroxyl group in an aromatic compound to a carboxyl group using TEMPO, a method in which sodium hypochlorite and sodium chlorite are simultaneously added and reacted in a phosphate buffer solution at pH 6.7. Has been proposed (Non-Patent Document 2).

JP 2008-308802 A

Saito, T., et al., Cellulose Commun., 14 (2), 62 (2007) Zhao, M., et al., J. Org. Chem., 64, 2564 (1999)

  However, the addition of only sodium hypochlorite and the addition of sodium chlorite (Patent Document 1) and the simultaneous addition of sodium hypochlorite and sodium chlorite (Non-Patent Document 2) It was practically insufficient to efficiently oxidize the primary hydroxyl group in the raw material to the carboxyl group.

  Therefore, it is desired to develop a method capable of accelerating the oxidation of the primary hydroxyl group in the cellulosic raw material and efficiently oxidizing the primary hydroxyl group to the carboxyl group. In addition, development of a method capable of efficiently producing a cellulose nanofiber dispersion excellent in fluidity, transparency and thermal stability with low energy is desired.

Means to solve the problem

  As a result of intensive studies, the present inventors have conducted (1) N-oxyl compound, and (2) oxidation of a cellulosic raw material in the presence of a compound selected from the group consisting of bromide, iodide, or a mixture thereof. First, hypohalite is added to cause the oxidation reaction of the cellulosic raw material under the conditions of pH 8 to 11, and 1.0 mmol / g or more of the carboxyl relative to the absolute dry mass of the cellulosic raw material. After the reaction is completed and the reaction is completed, the pH of the reaction system is adjusted to 4 to 6 with an acid or the like without filtering and washing the cellulosic raw material. It has been found that the primary hydroxyl group in the cellulosic material can be efficiently converted to a carboxyl group by carrying out the oxidation reaction. In addition, the oxidized cellulose raw material (also referred to as “oxidized cellulose-based raw material” or “oxidized pulp” in the present specification) thus obtained is defibrated and dispersed, whereby fluidity, transparency and heat are obtained. The inventors have found that a cellulose nanofiber dispersion excellent in stability can be efficiently produced with low energy, and have completed the present invention.

  In the present invention, a cellulose system is used at a pH of 8 to 11 using hypohalite in the presence of (1) N-oxyl compound and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof. After the raw material is oxidized and 1.0 mmol / g or more of carboxyl groups are introduced with respect to the absolute dry mass of the cellulosic raw material, the pH is subsequently adjusted without subjecting the cellulosic raw material to filtration and washing. Is adjusted to 4-6, and further an oxidation reaction is carried out with a halite, thereby promoting the oxidation of the cellulosic material and obtaining an oxidized cellulosic material in which carboxyl groups are introduced at a higher rate than before. it can. In the oxidized cellulose-based raw material obtained by the present invention, since the aldehyde group generated at the initial stage of the oxidation reaction is further oxidized to a carboxyl group, the amount of the aldehyde group is small and the content ratio of the carboxyl group is high. Therefore, formation of a microscopic gap between cellulosic raw materials due to charge repulsion between carboxyl groups is promoted, and formation of cross-linking of pulps by aldehyde groups is suppressed. Therefore, the oxidized cellulose raw material obtained by the present invention can be efficiently defibrated with lower energy than before. And it is thought that the B-type viscosity of the resulting dispersion is remarkably lowered and the fluidity is improved by shortening the cellulose chain. In addition, the cellulose nanofibers obtained in this way have less aldehyde groups that cause thermal fading, so they are more transparent and more stable than cellulose nanofibers using oxidized cellulose-based raw materials obtained by conventional methods. Is excellent.

FIG. 1 is an explanatory diagram of a method for measuring the amount of carboxyl groups.

(N-oxyl compound)
As the N-oxyl compound used in the present invention, any compound can be used as long as it promotes the target oxidation reaction. For example, the N-oxyl compound used in the present invention includes a substance represented by the following general formula (Formula 1).

（式１中、Ｒ¹〜Ｒ⁴は同一又は異なる炭素数１〜４程度のアルキル基を示す。）

(In Formula 1, R ^{1 to} R ⁴ represent the same or different alkyl groups having about 1 to 4 carbon atoms.)

  Among the compounds represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) and 4-hydroxy-2,2,6,6-tetramethyl-1 -Piperidine-oxy radical (hereinafter referred to as 4-hydroxy TEMPO) is preferred. Further, the N-oxyl compound represented by any one of the following formulas 2 to 4, that is, the hydroxyl group of 4-hydroxy TEMPO was etherified with alcohol or esterified with carboxylic acid or sulfonic acid to impart moderate hydrophobicity. The 4-hydroxy TEMPO derivative is particularly preferable because it is inexpensive and can obtain a uniformly oxidized cellulose raw material.

（式２〜４中、Ｒは炭素数４以下の直鎖又は分岐状炭素鎖である。）

(In formulas 2 to 4, R is a linear or branched carbon chain having 4 or less carbon atoms.)

  Furthermore, an N-oxyl compound represented by the following formula 5, that is, an azaadamantane type nitroxy radical, is particularly preferable because it can obtain a uniformly oxidized cellulose raw material in a short time.

（式５中、Ｒ⁵及びＲ⁶は、同一又は異なる水素又はＣ₁〜Ｃ₆の直鎖若しくは分岐鎖アルキル基を示す。）

(In Formula 5, R ⁵ and R ⁶ represent the same or different hydrogen or a C _{1 to} C ₆ linear or branched alkyl group.)

  The amount of the N-oxyl compound used is not particularly limited as long as it is a catalyst amount that can make the cellulose-based raw material into nanofibers. For example, about 0.01 to 10 mmol, preferably 0.01 to 1 mmol, and more preferably about 0.05 to 0.5 mmol can be used with respect to 1 g of the cellulosic raw material.

(Bromide or iodide)
As the bromide or iodide used in oxidizing the cellulosic raw material, a compound that can be dissociated and ionized in water, such as an alkali metal bromide or an alkali metal iodide, can be used. The amount of bromide or iodide used can be selected as long as the oxidation reaction can be promoted. For example, 0.1 to 100 mmol, preferably 0.1 to 10 mmol, and more preferably about 0.5 to 5 mmol can be used for 1 g of cellulosic raw material.

(Cellulosic material)
The cellulose-based raw material used in the present invention is not particularly limited, and kraft pulp or sulfite pulp derived from various woods, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer or a mill, or chemical treatment such as acid hydrolysis. The microcrystalline cellulose powder refined by the above can be used. In addition, plants such as kenaf, hemp, rice, bagasse and bamboo can also be used. Of these, bleached kraft pulp, bleached sulfite pulp, or powdered cellulose is preferably used from the viewpoint of mass production and cost.

  Powdered cellulose is a rod-like particle made of microcrystalline cellulose obtained by removing a non-crystalline portion of wood pulp having a high cellulose purity by acid hydrolysis, and then pulverizing and sieving. The degree of polymerization of cellulose is about 100 to 500, the degree of crystallinity of powdered cellulose by X-ray diffractometry is 70 to 90%, and the average particle size by a laser diffraction type particle size distribution measuring device is 100 μm or less.

(Hypohalite)
In the oxidation method of the present invention, hypohalite is first used in the presence of the above-mentioned (1) N-oxyl compound and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof. Then, the cellulosic material is oxidized under the condition of pH 8-11. The type of hypohalite that can be used is not particularly limited. For example, ammonium hypochlorite, ammonium hypobromite, and ammonium hypoiodite, and hypochlorous acid and hypobromite. , And alkali metal or alkaline earth metal salts of hypoiodous acid can be used alone or in combination of two or more. Among them, it is particularly preferable to use sodium hypochlorite, which is most widely used in industrial processes at present and has a low environmental impact.

  The amount of hypohalite used can be selected as long as the oxidation reaction can be promoted. For example, 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol can be used for 1 g of cellulosic raw material.

(Halogenite)
In the oxidation method of the present invention, following the oxidation using the hypohalite at pH 8 to 11, the pH is adjusted to 4 to 6 without filtering and washing the cellulosic raw material. Halogenate is added to further oxidize the cellulosic material. There are no particular limitations on the type of halite salt that can be used. For example, ammonium chlorite, ammonium bromate, and ammonium iodate, as well as alkalis of chlorous acid, bromic acid, and iodic acid. Metals or alkaline earth metal salts can be used alone or in combination of two or more.

  The amount of halite used can be selected within a range that can promote the oxidation reaction. For example, 0.5 to 500 mmol, preferably 0.5 to 50 mmol, and more preferably about 2.5 to 25 mmol can be used for 1 g of cellulosic raw material.

(Oxidation reaction conditions)
In the oxidation method of the present invention, oxidation is first performed using hypohalite. At this time, the amount of carboxyl groups of the oxidized cellulose-based material obtained by the oxidation reaction with hypohalite is the cellulose-based material. 1.0 mmol / g or more, preferably 1.0 mmol / g to 2.5 mmol / g, more preferably 1.2 mmol / g to 2.5 mmol / g, particularly preferably 1.3 mmol The conditions are set to be / g to 2.0 mmol / g. Specifically, by adjusting the oxidation reaction time, adjusting the oxidation reaction temperature, adjusting the oxidation reaction pH, adjusting the addition amount of N-oxyl compound, bromide, iodide, hypohalite, etc. The amount of the carboxyl group can be determined.

  In the oxidation method of the present invention, the pH is adjusted to 8 to 11 when oxidation is performed using hypohalite. More preferably, the pH is 9-11. Below pH 8, the oxidation reaction hardly proceeds. Moreover, since reaction will become slow when pH exceeds 11, it is disadvantageous. Although the pH of the reaction solution decreases with the progress of the oxidation reaction, the pH of the reaction solution is adjusted to 8 to 8 by adding an alkaline solution such as an aqueous sodium hydroxide solution in order to advance the oxidation reaction efficiently. 11, preferably 9 to 11.

  In the oxidation method of the present invention, following the oxidation reaction with the hypohalite, an oxidation reaction with the halite is performed without filtering and washing the cellulosic material. In the present invention, “filtering and washing the cellulose-based raw material” means separating (filtering) the cellulose after reaction and unreacted cellulose by filtering the suspension after completion of the reaction. This refers to the operation of washing with an appropriate liquid. In the present invention, the cellulosic raw material is not filtered and washed after the oxidation reaction with the hypohalite and before the oxidation reaction with the halite. That is, in the present invention, the reaction system after the oxidation reaction with hypohalite is used as it is for the oxidation reaction with halite in the next step. Therefore, the oxidation reaction of the present invention can be performed in one pot. By performing the oxidation reaction in one pot, the procedure for the reaction can be simplified, and the yield can be improved. Further, in addition to these, it was found that, by performing filtration and washing anew this time, surprisingly, a highly transparent oxidized cellulose-based raw material can be obtained (results of Example 1 and Comparative Example 6). See In the oxidation reaction with the halite, the carboxyl group amount of the oxidized cellulose-based material obtained by oxidation with the halite is 1.1 mmol / g or more, preferably 1 with respect to the absolute dry mass of the cellulose-based material. The conditions are set so as to be 1 mmol / g to 2.6 mmol / g, more preferably 1.3 mmol / g to 2.6 mmol / g, and particularly preferably 1.4 mmol / g to 2.1 mmol / g.

  When performing the oxidation reaction with a halite, the pH of the reaction system is adjusted to 4 to 6 in advance using a mineral acid such as hydrochloric acid, sulfuric acid, nitric acid, sulfurous acid, nitrous acid, and phosphoric acid. When the pH is less than 4, the halite is destabilized and decomposes. Moreover, when pH exceeds 6, an oxidation reaction rate falls and it is disadvantageous.

  In general compounds, when an aldehyde group is oxidized using a halite, the pH gradually increases. Therefore, it is usually performed to add an acid or the like to maintain the pH within an appropriate range. During the reaction with the halite of the present invention, there is no particular increase in pH. The reason is unknown, but due to the oxidation reaction with hypohalite performed prior to the oxidation reaction with halite, some water-soluble acidic substances are eluted from the cellulosic raw material into the reaction solution, It is thought that the buffer action is produced. Therefore, in the oxidation reaction of the present invention, at the time of the reaction with the halite, if the pH is adjusted to 4-6 at the beginning of the reaction, it is necessary to adjust the pH by adding an acid or the like thereafter. Absent.

  In the present invention, the temperature during the oxidation reaction is not particularly limited by oxidation with hypohalite or oxidation with hypohalite. For example, the efficiency of cellulosic raw materials is improved even at room temperature of about 15 to 30 ° C. Can oxidize well. Moreover, in this invention, oxidation reaction time can be suitably set in consideration of the desired use and quality of the oxidized cellulose raw material, and is not specifically limited. For example, oxidation with hypohalite at pH 8-11 (reaction temperature, 20 ° C.) can be performed for about 30 minutes to 3 hours, preferably about 1 to 3 hours. Subsequently, oxidation with a halite at a pH of 4 to 6 (reaction temperature 20 ° C.) can be performed for about 30 minutes to 5 hours, preferably about 1 to 5 hours, and more preferably about 3 to 5 hours. When oxidation by hypohalite (reaction temperature, 20 ° C.) is shorter than 30 minutes, or oxidation by hypohalite (reaction temperature, 20 ° C.) is shorter than 30 minutes, the obtained oxidized cellulose raw material The amount of the carboxyl group is small, and there is a tendency that it cannot be efficiently defibrated with lower energy than before.

  In the oxidation method of the present invention, oxidation with hypohalite and oxidation with halite can be carried out continuously in the same reaction vessel. As the reaction vessel, a vessel used for a normal oxidation reaction can be used, and is not particularly limited.

  In the oxidized cellulose-based raw material obtained by the oxidation method of the present invention, the aldehyde group generated at the initial stage of the oxidation reaction is further oxidized to a carboxyl group, and the amount of the aldehyde group is reduced. The amount of carboxyl groups in the oxidized cellulose-based raw material is 1.1 mmol / g or more, preferably 1.1 mmol / g to 2.6 mmol / g, more preferably 1.3 mmol / g to 2.6 mmol / g, particularly preferably 1. .4 mmol / g to 2.1 mmol / g. Moreover, the amount of aldehyde groups in the oxidized cellulose-based raw material is 0.05 mmol / g or less, more preferably 0.01 mmol / g or less.

(Defibration / dispersion processing)
The oxidized cellulosic raw material obtained by the oxidation method of the present invention has a sufficiently advanced oxidation reaction and has a high carboxyl group content. can do. As a specific method of defibration / dispersion treatment, for example, after sufficiently washing the oxidized cellulose raw material, using a known mixing, stirring, emulsifying, dispersing device such as a high-speed shear mixer or a high-pressure homogenizer, It can be processed into cellulose nanofibers. Examples of the type of defibrating / dispersing device used in the present invention include high-speed rotating type, colloid mill type, high pressure type, roll mill type, ultrasonic type, etc., and these may be used alone or in combination of two or more types as necessary. Can be used in combination. A shear rate during defibration / dispersion of 1000 sec ⁻¹ or more is preferable because uniform and transparent cellulose nanofibers having no aggregated structure can be obtained. Further, when treated with a wet high pressure or ultrahigh pressure homogenizer that can be dispersed under conditions of 50 MPa or more, preferably 100 MPa or more, more preferably 140 MPa or more, a cellulose nanofiber dispersion excellent in transparency and fluidity can be efficiently produced. ,preferable.

(Cellulose nanofiber)
The cellulose nanofiber produced by the present invention is a single microfibril of cellulose having a width of 2 to 5 nm and a length of about 1 to 5 μm. In the present invention, “to make nanofiber” means that a cellulose-based raw material is processed into cellulose nanofiber which is a single microfibril of cellulose having a width of about 2 to 5 nm and a length of about 1 to 5 μm.

  In the cellulose nanofiber produced according to the present invention, the aldehyde group is further oxidized to a carboxyl group in the oxidation reaction, and the amount of the aldehyde group is reduced. The amount of carboxyl groups in the cellulose nanofiber is 1.1 mmol / g or more, preferably 1.1 mmol / g to 2.6 mmol / g, more preferably 1.3 mmol / g to 2.6 mmol / g, particularly preferably 1. .4 mmol / g to 2.1 mmol / g. Moreover, the amount of aldehyde groups in the cellulose nanofiber is 0.05 mmol / g or less, more preferably 0.01 mmol / g or less.

  Cellulose nanofibers are excellent in barrier properties, transparency, and heat resistance, and can be applied to various uses such as packaging materials as they are, or in the form of films or sheets. it can.

  The present invention will be described in detail below based on examples, but the present invention is not limited thereto.

1. Measurement of the amount of carboxyl groups In this example, the amount of carboxyl groups in oxidized pulp was measured by the following procedure. About 0.3 g of oxidized pulp is precisely weighed, and 60 ml of 0.5 wt% oxidized pulp slurry is prepared. After adding 0.1 M hydrochloric acid aqueous solution to pH 2.5, 0.05 N sodium hydroxide aqueous solution is prepared. Was dropped and the electrical conductivity was measured. The measurement was continued until the pH was 11. By this operation, for example, a graph as shown in FIG. 1 is obtained.

As shown by the curved line portion (A) in FIG. 1, at the initial stage of addition of sodium hydroxide, the conductivity rapidly decreases due to neutralization of protons from hydrochloric acid. Subsequently, as shown by the curved part (B), the weak acid (carboxyl group) is neutralized, and the decrease in conductivity becomes gradual. When the neutralization of the weak acid is complete, the conductivity begins to increase with the addition of sodium hydroxide, as shown in the curve section (C). In the measurement of the amount of carboxyl groups in the present invention, from the intersection D of the approximate line of the curve part (A) and the approximate line of the curve part (B), the approximate line of the curve part (B) and the approximate line of the curve part (C) From the amount of sodium hydroxide consumed up to the intersection E (a) (that is, the amount of sodium hydroxide consumed in the neutralization stage of the weak acid (a)), the amount of carboxyl groups was calculated using the following equation. The amount of carboxyl groups thus obtained is referred to as “carboxyl group amount (A)”.
Amount of carboxyl group [mmol / g pulp] = a [ml] × 0.05 / oxidized pulp weight [g]

2. Measurement of the amount of aldehyde groups In this example, the amount of aldehyde groups in oxidized pulp was measured by the following procedure. About 0.3 g of oxidized pulp was precisely weighed to prepare a slurry of 0.5 wt% oxidized pulp. Acetic acid was added to this slurry to adjust the pH to 4 to 5, and then a 2% aqueous sodium chlorite solution was added and reacted at room temperature for 48 hours to convert aldehyde groups in the oxidized pulp into carboxyl groups. After the slurry after the reaction was sufficiently washed with water, the amount of carboxyl groups was measured based on the above “1. Measurement of the amount of carboxyl groups”. The obtained amount of carboxyl groups is called the amount of carboxyl groups (B). The amount of aldehyde group was calculated by subtracting the amount of carboxyl group (B) from the amount of carboxyl group (A) previously calculated by “1. Measurement of amount of carboxyl group”.
Aldehyde group amount [mmol / g pulp] = (carboxyl group amount (A))-(carboxyl group amount (B))

3. Thermal fading test A wet sheet was prepared from about 5 g / L of oxidized pulp slurry and dried at 50 ° C. The obtained sheet was heat-treated at 120 ° C. for 2 hours, and then ISO whiteness was measured.

[Example 1]
Bleached unbeaten sulfite pulp derived from softwood as a cellulose-based raw material (manufactured by Nippon Paper Chemical Co., Ltd., carboxyl group amount: 0.003 mmol / g, aldehyde group amount: 0.005 mmol / g, ISO whiteness: 92.4 %)Using. 5 g (absolutely dry) of the sulfite pulp was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Sigma Aldrich) and 754 mg (7.3 mmol) of sodium bromide had been dissolved, and stirred until the pulp was uniformly dispersed. After adding 16.25 ml (32.5 mmol) of 2M aqueous sodium hypochlorite solution to the reaction system, the pH was adjusted to 10.3 with 0.5N aqueous hydrochloric acid solution to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 0.5N sodium hydroxide aqueous solution was sequentially added and reacted for 2 hours while adjusting the pH to 10. 2N hydrochloric acid aqueous solution was added to the reaction solution to adjust the pH to 5, and 2.3 mg (25 mmol) of sodium chlorite was added and reacted for 3 hours. After completion of the reaction, the pulp was filtered off with a glass filter and sufficiently washed with water to obtain oxidized pulp. The carboxyl group amount of the oxidized pulp was determined by measuring the aldehyde group amount and the ISO whiteness after the heating test. The results are shown in Table 1.

[Example 2]
Bleached unbeaten kraft pulp derived from conifers (manufactured by Nippon Paper Industries Co., Ltd., carboxyl group amount: 0.04 mmol / g, aldehyde group amount: not detected, ISO whiteness: 84.6%) is used as the cellulose-based raw material The oxidation reaction was carried out in the same manner as in Example 1 except that. The results are shown in Table 1.

[Example 3]
Powdered cellulose produced from bleached unbeaten sulfite pulp derived from hardwood as a cellulose-based raw material (manufactured by Nippon Paper Chemical Co., Ltd., particle size 75 μm, carboxyl group amount: 0.05 mmol / g, aldehyde group amount: 0.03 mmol / g, ISO whiteness: 91.6%) was used in the same manner as in Example 1 to carry out the oxidation reaction. The results are shown in Table 1.

[Example 4]
The oxidation reaction was carried out in the same manner as in Example 1 except that sodium hypochlorite was oxidized at pH 11 and sodium chlorite was oxidized at pH 6. The results are shown in Table 1.

[Example 5]
The oxidation reaction was carried out in the same manner as in Example 1 except that sodium hypochlorite was oxidized at pH 8 and sodium chlorite was oxidized at pH 4. The results are shown in Table 1.

[Example 6]
The oxidation reaction was performed in the same manner as in Example 1 except that sodium hypochlorite was oxidized for 30 minutes. The results are shown in Table 1.

[Example 7]
The oxidation reaction was carried out in the same manner as in Example 1 except that sodium hypochlorite was oxidized for 1 hour. The results are shown in Table 1.

[Example 8]
The oxidation reaction was carried out in the same manner as in Example 1 except that sodium chlorite was oxidized for 1 hour. The results are shown in Table 1.

[Example 9]
The oxidation reaction was carried out in the same manner as in Example 1 except that sodium hypochlorite was oxidized for 30 minutes and sodium chlorite was oxidized for 1 hour. The results are shown in Table 1.

[Comparative Example 1]
The oxidation reaction was performed in the same manner as in Example 1 except that the oxidation step with sodium chlorite was omitted. The results are shown in Table 1.

[Comparative Example 2]
The oxidation reaction was performed in the same manner as in Example 1 except that the oxidation step with sodium hypochlorite was omitted. The results are shown in Table 1.

[Comparative Example 3]
When adding sodium hypochlorite aqueous solution, sodium chlorite was added at the same time, and the reaction was carried out for 5 hours while adjusting the pH to 10 with 0.5N sodium hydroxide aqueous solution. The oxidation reaction was performed. The results are shown in Table 1.

[Comparative Example 4]
The oxidation reaction was performed in the same manner as in Example 1 except that sodium chlorite was oxidized at pH 3. The results are shown in Table 1.

[Comparative Example 5]
The oxidation reaction was performed in the same manner as in Example 1 except that sodium hypochlorite was oxidized at pH 12. The results are shown in Table 1.

[Comparative Example 6]
The oxidation reaction was carried out in the same manner as in Example 1 except that the oxidized pulp was filtered and washed after oxidation with sodium hypochlorite. The results are shown in Table 1.

[Comparative Example 7]
The oxidation reaction was performed in the same manner as in Example 1 except that sodium hypochlorite was oxidized for 15 minutes. The results are shown in Table 1.

[Example 10]
The oxidized pulp produced in Example 1 was treated for 30 minutes using a rotary blade mixer (Nippon Seiki Seisakusho Co., Ltd.) with a peripheral speed of 37 m / s to obtain a transparent gel-like cellulose nanofiber dispersion. The power consumption required for the treatment was determined by (power during treatment: kW) × (treatment time: hr) ÷ (amount of treated sample: kg). Moreover, the transparency (660 nm light transmittance) of a 0.1% (w / v) cellulose nanofiber dispersion was measured using a UV-VIS spectrophotometer UV-265FS (Shimadzu Corporation). Further, the B type viscosity (60 rpm, 20 ° C.) of the 0.3% (w / v) cellulose nanofiber dispersion was measured using a TV-10 type viscometer (Toki Sangyo Co., Ltd.). The results are shown in Table 2.

[Example 11]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the oxidized pulp produced in Example 6 was used. The results are shown in Table 2.

[Comparative Example 8]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the oxidized pulp produced in Comparative Example 1 was used. The results are shown in Table 2.

[Comparative Example 9]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the oxidized pulp produced in Comparative Example 2 was used. The results are shown in Table 2.

[Comparative Example 10]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the oxidized pulp produced in Comparative Example 3 was used. The results are shown in Table 2.

[Comparative Example 11]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the oxidized pulp produced in Comparative Example 7 was used. The results are shown in Table 2.

[Example 12]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the treatment was performed 10 times at a pressure of 140 MPa using an ultrahigh pressure homogenizer (Advanced Nano Technology Co., Ltd.) instead of the treatment with a rotary blade mixer. The results are shown in Table 2.

[Example 13]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the oxidized pulp produced in Example 3 was used. The results are shown in Table 2.

[Example 14]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10, except that the treatment pressure of the ultrahigh pressure homogenizer was 50 MPa. The results are shown in Table 2.

[Example 15]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 10 except that the treatment pressure of the ultrahigh pressure homogenizer was changed to 30 MPa. The results are shown in Table 2.

[Comparative Example 12]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 12 except that the oxidized pulp produced in Comparative Example 7 was used. The results are shown in Table 2.

  By the method of the present invention (Examples 10 to 15), a cellulose nanofiber dispersion liquid having high transparency and good fluidity could be produced with relatively low power consumption. In Comparative Example 9, since the introduced carboxyl groups were very few and the dispersion hardly proceeded, the transparency of the dispersion was very low. In Comparative Example 9, the viscosity is remarkably low because the oxidized pulp is hardly dispersed. Also in Comparative Example 11, since the introduced carboxyl groups were few, only a part of the oxidized pulp was dispersed, the transparency of the dispersion was lowered, and the viscosity was also apparently lowered.

Claims (6)

A hypohalite is used under the conditions of pH 8-11 in the presence of (A) (1) N-oxyl compound, and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof. The cellulosic raw material is oxidized to introduce 1.0 mmol / g or more carboxyl groups with respect to the absolute dry mass of the cellulosic raw material. (B) The cellulosic raw material from (A) is filtered and washed. Without oxidizing with halite under conditions of pH 4-6,
A method for oxidizing a cellulosic material, comprising:   The method for oxidizing a cellulosic material according to claim 1, wherein the cellulosic material is bleached kraft pulp, bleached sulfite pulp, or powdered cellulose.   An oxidized cellulose-based material having a carboxyl group content of 1.1 mmol / g or more and an aldehyde group content of 0.05 mmol / g or less, obtained by the method according to claim 1 or 2. A hypohalite is used under the conditions of pH 8-11 in the presence of (A) (1) N-oxyl compound, and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof. The cellulosic raw material is oxidized to introduce 1.0 mmol / g or more carboxyl groups with respect to the absolute dry mass of the cellulosic raw material. (B) The cellulosic raw material from (A) is filtered and washed. Without oxidizing with halite under conditions of pH 4-6,
A method for producing cellulose nanofibers, comprising: converting an oxidized cellulose raw material obtained by an oxidation method of a cellulose raw material into nanofibers by defibration and dispersion treatment.   The manufacturing method of the cellulose nanofiber of Claim 4 whose cellulosic raw material is bleached kraft pulp, bleached sulfite pulp, or powdered cellulose.   A cellulose nanofiber having a carboxyl group amount of 1.1 mmol / g or more, an aldehyde group amount of 0.05 mmol / g or less, and a width of 2 to 5 nm obtained by the method according to claim 4.

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