JP2014040530A - Method for producing oxidized cellulose and method for producing cellulose nanofiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing oxidized cellulose which uses as a catalyst an N-oxyl compound capable of efficiently introducing a carboxyl group into cellulose in a short time.SOLUTION: A method for producing oxidized cellulose includes the steps of: (A) preparing cellulose having a cellulose II type crystal content of 5-90%; and (B) making oxidized cellulose by oxidizing pulp in water using an oxidizing agent in the presence of (1) an N-oxyl compound and (2) a compound selected from the group consisting of a bromide, an iodide and their mixture.

Description

  The present invention relates to an efficient method for producing oxidized cellulose and cellulose nanofibers.

  When the cellulosic material is treated in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and sodium hypochlorite which is an inexpensive oxidant, Carboxyl groups can be efficiently introduced onto the surface of cellulose microfibrils. It is known that cellulose nanofiber aqueous dispersions can be obtained by treating the cellulose-based raw material (oxidized cellulose) introduced with a carboxyl group in water with a mixer or the like (Non-patent Document 1, Patent Documents 1 and 2).

JP 2008-001728 A JP 2010-235679 A

Saito, T .; , Et al. Cellulose Commun. , 14 (2), 62 (2007)

  The cellulose oxidation method using the above N-oxyl compound as a catalyst can uniformly introduce many carboxyl groups into the cellulose, but the carboxyl group introduction time (oxidation reaction time) is long and the production efficiency is low. There was a problem.

  Therefore, the present invention relates to a method for producing oxidized cellulose using an N-oxyl compound that can efficiently introduce a carboxyl group into cellulose in a short time as a catalyst, and cellulose nanofibers obtained by defibrating this oxidized cellulose. It is an object to provide a manufacturing method.

The present invention provides the following [1] to [2].
[1] Step (A) of preparing cellulose having a cellulose crystal II type content of 5 to 90%,
Oxidized cellulose is prepared by oxidizing the pulp in water in the presence of (1) N-oxyl compound and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof. The manufacturing method of the oxidized cellulose including the process (B) to do.
[2] A method for producing cellulose nanofibers, comprising the step (C) of producing cellulose nanofibers by fibrillating and dispersing the oxidized cellulose.

  According to the present invention, a method for producing oxidized cellulose using an N-oxyl compound that can efficiently introduce a carboxyl group into cellulose in a short time as a catalyst, and cellulose nanofibers obtained by defibrating this oxidized cellulose are provided. A manufacturing method can be provided.

Hereinafter, the present invention will be described in detail. In the present specification, “to” includes values at both ends.
1. Method for Producing Oxidized Cellulose The method for producing oxidized cellulose of the present invention comprises a step (A) of preparing cellulose having a cellulose crystal II type content of 5 to 90%, and (1) an N-oxyl compound and the pulp. (2) including a step (B) of preparing oxidized cellulose by oxidation in water using an oxidizing agent in the presence of a compound selected from the group consisting of bromide, iodide or a mixture thereof.

1-1. Process A
Step A is a step of preparing a pulp having a cellulose crystal II type content of 5 to 90% by subjecting the cellulose-based raw material to an alkali treatment.
The content of cellulose crystal type II was calculated from the area ratio of the peak at the diffraction angle 2θ of the graph obtained by the measurement by the wide angle X-ray diffraction method. The procedure is as follows.
First, the cellulose is frozen with liquid nitrogen and compressed to produce tablet pellets. Thereafter, the measurement result (graph) obtained from this sample by an X-ray diffraction measurement apparatus (LabX XRD-6000, manufactured by Shimadzu Corporation) is peak-separated by graph analysis software PeakFit (manufactured by Hulinks), and crystal I The ratio of type to type II was calculated. At this time, for peak separation, crystal type I and type II were distinguished based on the following diffraction angles.
Crystal type I: 2θ = 14.7 °, 16.5 °, 22.5 °
Crystal type II: 2θ = 12.3 °, 20.2 °, 21.9 °

(1) Cellulose-based raw materials Cellulose-based raw materials are wood-derived kraft pulp or sulfite pulp, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer, a mill or the like, or microcrystals purified by chemical treatment such as acid hydrolysis. Cellulose powder and the like. In addition to these, cellulosic materials derived from plants such as kenaf, hemp, rice, bacus, and bamboo can also be produced. However, if a large amount of hardwood-derived lignin remains in the cellulosic raw material, there is a risk of inhibiting the oxidation reaction of the raw material. Therefore, in the present invention, the cellulosic raw material obtained by the method for producing chemical pulp is preferred. . In order to further remove lignin, it is more preferable to subject the cellulosic raw material thus obtained to a known bleaching treatment.

  As bleaching treatment methods, chlorine treatment (C), chlorine dioxide bleaching (D), alkali extraction (E), hypochlorite bleaching (H), 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 / D-E-H-D, Z-E-D-P , Z / D-Ep-D, Z / D-Ep-DP, D-Ep-D, D-Ep-DP, D-Ep-PD, Z-Eop-DD, Z / D-Eop-D, Z / D-Eop-D-ED, or the like. “/” In the sequence means that the processes before and after “/” are continuously performed without cleaning. The amount of lignin in the cellulose raw material is preferably small, and the cellulose raw material (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 that

  In addition, it is preferable to use powdered cellulose or microcrystalline cellulose powder as a cellulose-based raw material because cellulose nanofibers that give a dispersion having a high concentration and a lower viscosity can be produced. Powdered cellulose is a rod-like particle made of microcrystalline cellulose obtained by removing a non-crystalline part of wood pulp by acid hydrolysis and then pulverizing and sieving. The degree of polymerization of cellulose in the powdered cellulose is about 100 to 500, the degree of crystallinity of the powdered cellulose by X-ray diffraction method is 70 to 90%, and the volume average particle diameter by a laser diffraction type particle size distribution analyzer is preferably 100 μm. Or less, more preferably 50 μm or less. When the volume average particle diameter is 100 μm or less, a cellulose nanofiber dispersion excellent in fluidity can be obtained. As the powdered cellulose, for example, an undegraded residue obtained after acid hydrolysis of a selected pulp is purified, dried, crushed and sieved, and a crystal having a rod-shaft shape and a constant particle size distribution Cellulose powder can be used. Alternatively, commercially available products such as KC Flock (registered trademark) (manufactured by Nippon Paper Chemicals Co., Ltd.), Theolas (trademark) (manufactured by Asahi Kasei Chemicals), and Avicel (registered trademark) (manufactured by FMC) may be used.

(2) Alkali treatment In step A, cellulose having a cellulose crystal II type content of 5 to 90% can be obtained by treating the cellulose raw material in an alkaline solution. Hereinafter, this treatment is also simply referred to as “alkali treatment”. The alkali treatment can be performed by dispersing the cellulose raw material in water, adding an alkali to the aqueous dispersion to adjust the hydroxide ion concentration in the water to the above range, and stirring the reaction system. Alternatively, the alkali treatment can be performed by dispersing the cellulose raw material in water having a hydroxide ion concentration prepared in advance.

  In the present invention, by using cellulose having a cellulose crystal II type content of 5 to 90%, a carboxyl group can be efficiently introduced into cellulose in a short time, and the mechanism is considered as follows.

  Cellulose has a high molecular orientation when the crystal is type I and is dense, whereas cellulose has a low molecular orientation when type II. For this reason, it is estimated that the pulp which has a cellulose crystal II type becomes easy to permeate an oxidizing agent and can efficiently introduce a carboxyl group into cellulose in a short time. If the content of cellulose crystal II in the pulp is less than 5%, the oxidant does not sufficiently permeate, so that carboxyl groups cannot be introduced efficiently. On the other hand, when the content of crystal II type exceeds 90%, it becomes polyseurouronic acid by the oxidation reaction in the next step B and dissolves in water, so that it cannot be obtained as oxidized cellulose fiber.

  In particular, when bleached kraft pulp or bleached sulfite pulp is used as the cellulosic raw material, hemicellulose covering the cellulose microfibril surface is eluted with alkali. For this reason, the microfibril surface is exposed and oxidation in the next step B is promoted. As a result, the oxidation reactivity of the cellulose raw material is enhanced, the oxidation reaction proceeds in a short time, and many carboxyl groups are introduced.

  In the present invention, the alkali used in the alkali treatment of the cellulose raw material is not particularly limited as long as it is water-soluble, inorganic alkali such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, tetramethylammonium hydroxide, And organic alkalis such as tetraethylammonium hydroxide. Of these, sodium hydroxide is preferable because it is easily available and relatively inexpensive. Further, an aqueous solution containing a plurality of alkalis such as white liquor and green liquor produced in a pulp factory and other components can also be used.

  The hydroxide ion concentration of the alkaline solution is preferably 0.75 to 4 mol / L, and more preferably 1.25 to 3.75 mol / L. When the hydroxide ion concentration exceeds 4 mol / L, the cellulose crystal II type content of the cellulose to be oxidized exceeds 90%. On the other hand, when the hydroxide ion concentration is less than 0.75 mol / L, the alkali concentration is low, and the cellulose crystal II type content of the resulting pulp is less than 5%.

  The alkali treatment may be performed under atmospheric pressure, under pressure, or under reduced pressure. The treatment temperature is preferably 0 ° C to 100 ° C, more preferably 10 ° C to 60 ° C, and further preferably 20 ° C to 40 ° C. The treatment time is preferably 5 minutes to 24 hours, more preferably 15 minutes to 12 hours, and even more preferably 30 minutes to 6 hours. The concentration of the cellulose-based raw material is preferably 0.1 to 60% by mass in the reaction mixture, more preferably 1 to 50% by mass, and further preferably 5 to 40% by mass. If the concentration is higher than the above range, the production of cellulose type II becomes non-uniform, and if the concentration is low, the production efficiency is poor and uneconomical.

In the present invention, from the viewpoint of the yield of oxidized pulp and the oxidation reaction time, the content of crystal II type of cellulose to be oxidized needs to be 5 to 90%. By making the content of crystal II type of cellulose to be oxidized 10 to 80%, further 20 to 70%, the amount of addition of N-oxyl compound as an oxidation catalyst can be greatly reduced to obtain oxidized pulp The influence of the N-oxyl compound remaining on the oxidized pulp or nanofiber and the removal process of the N-oxyl compound can be greatly reduced.

  From the viewpoint of avoiding a side reaction or the like in the next step B, the cellulose having a cellulose crystal II type content of 5 to 90% obtained in step A is preferably neutralized and washed.

1-2. Process B
In step B, the presence of a compound selected from the group consisting of N-oxyl compounds and bromides, iodides, or mixtures thereof, wherein the cellulose crystal II type content obtained in step A is 5 to 90% Below, it is the process of oxidizing using an oxidizing agent to obtain oxidized cellulose.

(1) N-oxyl compound (a1)
An N-oxyl compound is a compound capable of generating a nitroxy radical. 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 compound represented by the following general formula (Formula 1).

(In Formula 1, R _{1 to} R ₄ represent the same or different alkyl groups having about 1 to 4 carbon atoms.)
Of the substances represented by Formula 1, 2,2,6,6-tetramethyl-1-piperidine-oxy radical (hereinafter referred to as TEMPO) is preferable. Further, the N-oxyl compound represented by any one of the following formulas 2 to 5, 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. A 4-hydroxy TEMPO derivative or 4-acetamido TEMPO having an appropriate hydrophobicity by acetylating the amino group of 4-amino TEMPO is particularly preferable because it is inexpensive and can provide uniform oxidized cellulose.

(In formulas 2 to 5, R is a linear or branched carbon chain having 4 or less carbon atoms.)
Furthermore, an N-oxyl compound represented by the following formula 6, that is, an azaadamantane-type nitroxy radical, is preferable because it can efficiently oxidize a cellulose-based raw material in a short time and is less likely to break the cellulose chain.

(In Formula 6, 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 to be used is not particularly limited as long as it is a catalyst amount capable of forming nanofibers of cellulose having a cellulose crystal II type content of 5 to 90%. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.05 to 0.5 mmol is further added to cellulose having a cellulose crystal II type content of 1 to 90 g of absolutely dry. preferable.

(2) Bromide or iodide Bromide is a compound containing bromine, and examples thereof include alkali metal bromide that can be dissociated and ionized in water. Further, an 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, preferably from 0.1 to 100 mmol, more preferably from 0.1 to 10 mmol, based on cellulose having a dry crystal content of 1 g of cellulose crystal II of 5 to 90%. 0.5 to 5 mmol is more preferable.

(3) Oxidizing agent As the oxidizing agent used in the oxidation of cellulose having a cellulose crystal II type content of 5 to 90%, known ones can be used, for example, halogen, hypohalous acid, halogenous acid, Perhalogen acids or their salts, halogen oxides, peroxides and the like can be used. Among these, from the viewpoint of cost, sodium hypochlorite, which is the most widely used in industrial processes and has a low environmental load, is particularly preferable. The appropriate amount of the oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, based on cellulose having a dry crystal content of 1 g of cellulose crystals II of 5 to 90%. 1 to 25 mmol is more preferable, and 3 to 10 mmol is most preferable.

(4) Oxidation reaction conditions This step allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. As the reaction proceeds, a carboxyl group is generated in the cellulose constituting the pulp, 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.

  The reaction time in the oxidation reaction can be appropriately set according to the progress of oxidation, and is usually 0.5 to 6 hours, preferably 2 to 6 hours, more preferably about 4 to 6 hours. However, in the present invention, since the oxidation time can be reduced as described above, the reaction time is preferably 30 minutes to 120 minutes, more preferably 30 to 100 minutes, and even more preferably 30 to 70 minutes.

  The oxidation reaction may be performed in two stages. For example, oxidized cellulose obtained by filtration after the completion of the first stage reaction is oxidized again under the same or different reaction conditions, so that the cellulose is not subject to reaction inhibition by the salt produced as a by-product in the first stage reaction. Carboxyl groups can be efficiently introduced into cellulose having a crystal II type content of 5 to 90%, and oxidation of cellulose having a cellulose crystal II type content of 5 to 90% can be promoted.

  In this step, conditions are set so that the amount of carboxyl group of cellulose having an oxidized cellulose crystal type II content of 5 to 90% is 0.2 mmol / g or more based on the absolute dry mass of the pulp. It is preferable. The amount of carboxyl groups in this case is more preferably 0.3 mmol / g to 3.0 mmol / g, further preferably 1.0 mmol / g to 2.5 mmol / g, particularly preferably 1.5 mmol / g to 2.0 mmol. / G. The amount of the carboxyl group can be adjusted by adjusting the oxidation reaction time, adjusting the oxidation reaction temperature, adjusting the pH during the oxidation reaction, adjusting the addition amount of the N-oxyl compound, bromide, iodide, or oxidizing agent.

  In order to efficiently perform defibration in the next step C, the oxidized cellulose-based material obtained in step B is preferably washed.

1-3. Process C
In Step C, a dispersion containing the oxidized cellulose obtained in Step B is prepared, and the oxidized cellulose is fibrillated to form nanofibers. “To make nanofiber” means to process oxidized cellulose into cellulose nanofiber which is a single microfibril of cellulose having a width of about 2 to 5 nm and a length of about 0.1 to 5 μm. A dispersion is a liquid in which the oxidized cellulose is dispersed in a dispersion medium. From the viewpoint of ease of handling, the dispersion medium is preferably water.

  In order to disentangle the oxidized cellulose and disperse it in the dispersion medium, a strong shearing force is applied to the dispersion liquid using a high-speed rotation type, colloid mill type, high pressure type, roll mill type, ultrasonic type device or the like. It is preferable to apply. In particular, in order to efficiently obtain cellulose nanofibers, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer that can apply a pressure of 50 MPa or more to the dispersion and can apply a strong shearing force. The pressure is more preferably 100 MPa or more, and further preferably 140 MPa or more. By this treatment, the oxidized cellulose-based raw material is defibrated to form cellulose nanofibers, and the cellulose nanofibers are dispersed in the dispersion medium.

  The concentration of oxidized cellulose in the dispersion subjected to the treatment is 0.3% (w / v) or more, preferably 1 to 2% (w / v), more preferably 3 to 5% (w / v). ).

1-4. Low Viscosity Treatment In the present invention, before the step C, the oxidized cellulose-based raw material (hereinafter simply referred to as “ It is preferable to reduce the viscosity of the cellulose raw material). The viscosity reduction treatment is to appropriately cut the cellulose chain of the oxidized cellulose raw material (shorten the cellulose chain). Since the raw material thus treated has a low viscosity when used as a dispersion, the viscosity reduction treatment can be said to be a treatment for obtaining a cellulosic raw material that gives a low-viscosity dispersion. The viscosity-reducing treatment may be any treatment that reduces the viscosity of the cellulosic raw material. For example, the treatment of irradiating the oxidized cellulosic raw material with ultraviolet rays, the oxidized cellulosic raw material with hydrogen peroxide and ozone. Examples thereof include a treatment for oxidative decomposition, a treatment for hydrolyzing an oxidized cellulose-based raw material with an acid, and a combination thereof.

2. Cellulose nanofiber The cellulose nanofiber produced by the present invention is a single microfibril of cellulose having a width of about 2 to 5 nm and a length of about 0.1 to 5 μm. The dispersion of cellulose nanofibers obtained by the present invention has excellent transparency. The dispersion medium in the dispersion is preferably water. In the present invention, the transparency is evaluated by a light transmittance of 660 nm. Specifically, the transparency is transmitted through a test body in which a 0.1% dispersion liquid is put in a quartz cell (optical path 10 mm) using an ultraviolet / visible spectrophotometer. It is obtained by measuring the amount of light to be performed.

  The amount of carboxyl groups of the cellulose nanofiber obtained by the present invention is preferably 0.3 mmol / g or more. The amount of carboxyl groups was prepared by preparing 60 ml of 0.5% by weight slurry (aqueous dispersion) of cellulose nanofibers, adding 0.1M hydrochloric acid aqueous solution to pH 2.5, and then dropping 0.05N aqueous sodium hydroxide solution dropwise. Then, the electrical conductivity is measured until the pH reaches 11, and the amount of sodium hydroxide consumed in the neutralization step of the weak acid whose change in electrical conductivity is gradual can be calculated using the following equation. it can.

Carboxyl group amount [mmol / g pulp] = a [ml] × 0.05 / oxidized pulp mass [g]
The aqueous dispersion of cellulose nanofibers obtained by the present invention has a light transmittance of 660 nm at a concentration of 0.1% (w / v), preferably 94% or more, more preferably 95% or more, and still more preferably. It is 97% or more, particularly preferably 99% or more. When the transparency is 95% or more, it can be used without problems for general film applications, and when the transparency is 99% or more, high optical properties (transparency) such as a display and a touch panel are required. Can be used without problems for film applications. Since the cellulose nanofibers obtained by the present invention have a large amount of carboxyl groups on the fiber surface, the fibers are less likely to aggregate with each other and the dispersion into the dispersion medium is good. .

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
Step A: 20 g of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous tree (absolutely dry) is charged into an aqueous sodium hydroxide solution having a hydroxide ion concentration of 2.5 mol / L, and the pulp concentration is 5 mass. Adjusted to be%. The mixture was stirred at room temperature (25 ° C.) for 2 hours, neutralized with an acid, and washed with water.
Step B: 5 g of alkali-treated pulp (absolutely dried) was added to 500 ml of an aqueous solution in which 7.8 mg of TEMPO (Sigma Aldrich) and 755 mg of sodium bromide were dissolved, and stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system to 5.5 mmol / g to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 3M aqueous sodium hydroxide solution was successively added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system no longer changed. The reaction mixture was filtered through a glass filter to separate pulp, and the pulp was sufficiently washed with water to obtain oxidized pulp. The pulp yield at this time was 86%, and the time required for the oxidation reaction was 115 minutes.
Process C: The said oxidized pulp was adjusted to 1% (w / v), and it processed 10 times with the ultrahigh pressure homogenizer (20 degreeC, 140 Mpa), and obtained the transparent gel-like dispersion liquid.

[Example 2]
Steps A and B were carried out in the same manner as in Example 1 except that the hydroxide ion concentration of the aqueous sodium hydroxide solution was 3.13 mol / L. The time required for the oxidation reaction was 100 minutes, and the yield was 80%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 3]
Steps A and B were carried out in the same manner as in Example 1 except that the hydroxide ion concentration of the aqueous sodium hydroxide solution was 3.75 mol / L. The time required for the oxidation reaction was 150, and the yield was 91%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 4]
Steps A and B were performed in the same manner as in Example 1 except that the hydroxide ion concentration of the aqueous sodium hydroxide solution was 0.75 mol / L. The time required for the oxidation reaction was 180 minutes, and the yield was 98%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 5]
Steps A and B were carried out in the same manner as in Example 1 except that the amount of TEMPO (Sigma Aldrich) added in step B was 78 mg. The time required for the oxidation reaction was 85 minutes, and the yield was 92%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 6]
Steps A and B were carried out in the same manner as in Example 2 except that the amount of TEMPO (Sigma Aldrich) added in step B was 78 mg. The time required for the oxidation reaction was 30 minutes, and the yield was 86%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 7]
Steps A and B were carried out in the same manner as in Example 3 except that the amount of TEMPO (Sigma Aldrich) added in step B was 78 mg. The time required for the oxidation reaction was 25 minutes, and the yield was 78%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 8]
Steps A and B were performed in the same manner as in Example 4 except that the amount of TEMPO (Sigma Aldrich) added in step B was 78 mg. The time required for the oxidation reaction was 110 minutes, and the yield was 98%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 9]
Steps A and B were carried out in the same manner as in Example 1 except that the cellulose raw material was hardwood kraft pulp. The time required for the oxidation reaction was 105 minutes, and the yield was 82%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 10]
Steps A and B were carried out in the same manner as in Example 1 except that the cellulose raw material was softwood sulfite pulp. The time required for the oxidation reaction was 110 minutes, and the yield was 89%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 11]
Steps A and B were carried out in the same manner as in Example 1 except that the cellulose raw material was softwood kraft dissolving pulp. The time required for the oxidation reaction was 95 minutes, and the yield was 87%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 12]
Step B was carried out in the same manner as in Example 1 except that the cellulose raw material was softwood kraft dissolving pulp manufactured by Bakay (content of cellulose crystal II type: 54%). The time required for the oxidation reaction was 105 minutes, and the yield was 80%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Example 13]
Step B was carried out in the same manner as in Example 1 except that the cellulose raw material was softwood kraft dissolving pulp manufactured by Leonia (content ratio of cellulose crystal II type: 78%). The time required for the oxidation reaction was 75 minutes, and the yield was 73%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got.

[Comparative Example 1]
Step B was performed in the same manner as in Example 1 except that the alkali treatment in Step A was not performed. Since the reaction was not completed even when the oxidation reaction exceeded 300 minutes, the reaction was stopped.

[Comparative Example 2]
Steps A and B were performed in the same manner as in Example 1 except that the hydroxide ion concentration of the aqueous sodium hydroxide solution was 5.00 mol / L. The time required for the oxidation reaction was 70 minutes. When this oxidized pulp was washed with water, it swelled and could not be recovered.

[Reference Example 1]
Step B was performed in the same manner as in Example 5 except that the alkali treatment in Step A was not performed. The oxidation reaction time was 130 minutes, and the yield was 93%. The obtained oxidized pulp was prepared into a 1% (w / v) aqueous dispersion, and the aqueous dispersion was treated 10 times with an ultra-high pressure homogenizer (20 ° C., 140 MPa) to obtain a transparent cellulose nanofiber aqueous dispersion. Got. In addition, the carboxyl group amount of the obtained cellulose nanofiber was 1.55 mmol / g.

From the above examples, comparative examples, and reference examples, when the reaction is carried out under the same oxidation conditions, the pulp containing cellulose crystal type II has high reactivity, so that the oxidation reaction can be completed in a short time. On the other hand, if the content of crystal type II is too high, the fibers become short and cannot be recovered.

Claims (2)

A step of preparing cellulose having a cellulose crystal II type content of 5 to 90% (A),
Oxidized cellulose is prepared by oxidizing the pulp in water in the presence of (1) N-oxyl compound and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof. The manufacturing method of the oxidized cellulose including the process (B) to do.   A method for producing cellulose nanofibers, comprising a step (C) of producing cellulose nanofibers by defibrating and dispersing the oxidized cellulose.