WO2010116826A1

WO2010116826A1 - Process for producing cellulose nanofibers

Info

Publication number: WO2010116826A1
Application number: PCT/JP2010/053570
Authority: WO
Inventors: 正一宮脇; 志穂勝川; 裕阿部; 夕子飯嶋; 明磯貝
Original assignee: 日本製紙株式会社
Priority date: 2009-03-30
Filing date: 2010-03-04
Publication date: 2010-10-14

Abstract

A cellulosic raw material is oxidized with an oxidizing agent in water in the presence of (1) an N-oxyl compound and (2) a bromide, an iodide, or a mixture thereof to prepare an oxidized cellulosic raw material, and the oxidized material is subjected to a viscosity reduction treatment and then to a fibrillation/dispersion treatment, thereby efficiently producing, with low energy, a high-concentration cellulose nanofiber dispersion having excellent flowability and transparency. Examples of the viscosity reduction treatment include ultraviolet irradiation, hydrolysis with cellulase and/or hemicellulase, oxidative decomposition with ozone and hydrogen peroxide, hydrolysis with an acid, and combinations of these. It is preferred to remove the N-oxyl compound from the oxidized cellulosic raw material by heating the oxidized cellulosic raw material to 50-120ºC at a pH of 3-10 and washing the resultant material with water.

Description

Method for producing cellulose nanofiber

The present invention relates to a method for producing a cellulose nanofiber dispersion liquid having a lower energy and a higher concentration than conventional materials from a cellulose raw material oxidized with an N-oxyl compound.

Cellulose-based raw materials in the presence of a catalytic amount of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and an inexpensive oxidizing agent sodium hypochlorite When treated, carboxyl groups can be efficiently introduced onto the surface of cellulose microfibrils. Cellulosic raw materials into which these carboxyl groups have been introduced are highly viscous and transparent by performing a simple mechanical treatment with a mixer in water. It is known that it can be prepared into an aqueous cellulose nanofiber dispersion (Non-Patent Document 1).

Cellulose nanofiber is a new biodegradable water-dispersible material. Since the carboxyl group is introduced into the surface of the cellulose nanofiber by an oxidation reaction, the cellulose nanofiber can be freely modified with the carboxyl group as a base point. In addition, since the cellulose nanofibers obtained by the above method are in the form of a dispersion, the quality can be modified by blending with various water-soluble polymers or by combining with organic / inorganic pigments. it can. Furthermore, cellulose nanofibers can be made into sheets or fibers. Taking advantage of such characteristics of cellulose nanofibers, it is envisaged to be applied to highly functional packaging materials, transparent organic substrate members, highly functional fibers, separation membranes, regenerative medical materials, and the like. In the future, it is expected to develop new high-functional products that are essential for the formation of a recycling-type safety and security society by making the best use of the characteristics of cellulose nanofibers.

However, the cellulose nanofiber dispersion obtained by oxidizing the above-described method, that is, oxidizing the cellulosic raw material with TEMPO and defibrating with a mixer is 0.3 to 0.5% (w / v). Even at a low concentration, the B-type viscosity (60 rpm, 20 ° C.) has a very high viscosity such as 800 to 4000 mPa · s, it is not easy to handle, and its application range is actually limited. It was. For example, 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, so the B-type viscosity of the dispersion (60 rpm, 20 ° C.) must be adjusted to about 500 to 3000 mPa · s, and for this purpose, the concentration of cellulose nanofibers in the dispersion is reduced to a low concentration of about 0.2 to 0.4% (w / v). I had to set it. However, when such a low-concentration dispersion is used, there is a problem that the application and drying must be repeated many times until the desired film thickness is achieved, resulting in poor efficiency.

In addition, when the cellulose nanofiber dispersion is mixed with a paint containing a pigment and a binder and applied to paper or the like, the dispersion cannot be uniformly mixed if the viscosity of the dispersion is too high. However, if such a low-concentration dispersion liquid is used, the concentration of the paint becomes dilute, making it difficult to apply the sufficient viscosity necessary for application and increasing the drying load. In addition, there is also a problem that the desired function expected for the coating film such as gloss development, surface strength, and suppression of printing unevenness does not appear because the effective coating film becomes thin by the penetration of the paint into the base paper. .

Thus, in the conventional method in which the cellulose-based raw material obtained by oxidation using TEMPO is defibrated using a mixer, the viscosity of the obtained dispersion becomes very high, causing various problems. . Further, when the viscosity is too high, the dispersion proceeds only around the stirring blade, so that the dispersion becomes non-uniform and the dispersion becomes low in transparency.

In addition, if the oxidized cellulosic material is defibrated using a homogenizer with higher defibration / dispersion power than the mixer, the cellulosic material will thicken significantly in the initial stage of dispersion and fluidity will deteriorate. There is a problem that the amount of power consumption required sometimes increases significantly, the cellulose nanofiber dispersion liquid adheres to the inside of the apparatus and the dispersion is not sufficiently performed, and operations such as taking out the dispersion liquid from the apparatus are performed. There is also a problem that the yield of the dispersion is lowered due to difficulty.

In view of the above problems, an object of the present invention is to provide a method capable of efficiently producing a high-concentration cellulose nanofiber dispersion excellent in fluidity and transparency with low energy.

As a result of diligent studies to solve the problems of the prior art, the present inventors have used an oxidizing agent in the presence of (1) N-oxyl compound and (2) bromide, iodide or a mixture thereof. By oxidizing the cellulose raw material in water to prepare an oxidized cellulose raw material, and subjecting the oxidized cellulose raw material to a viscosity reduction treatment before subjecting to a defibration / dispersion treatment, 1 to 3 It has been found that a cellulose nanofiber dispersion excellent in fluidity and transparency can be efficiently produced even at a high concentration of about% (w / v), and the present invention has been completed. Here, the viscosity reduction treatment is a treatment for appropriately cutting the cellulose chain of the oxidized cellulose raw material (shortening fiber) and lowering the viscosity of the raw material, and specifically, an ultraviolet irradiation treatment. And hydrolytic treatment with enzymes, oxidative degradation treatment with hydrogen peroxide and ozone, and hydrolysis treatment with acid.

According to the present invention, the cellulose raw material is oxidized in the presence of the N-oxyl compound and bromide, iodide, or a mixture thereof, and the resulting oxidized cellulose raw material is reduced in viscosity and then defibrated.・ By dispersing, cellulose nanofiber dispersions that are excellent in fluidity, easy to handle and excellent in transparency even at high concentrations can be efficiently produced with low power consumption. Can do. The cellulose nanofiber dispersion obtained by the present invention is excellent in fluidity even at a high concentration.For example, when a cellulose nanofiber is applied to a substrate to form a film on the substrate, A paint containing cellulose nanofibers at a high concentration of 1 to 3% (w / v) can be prepared at a low viscosity of 500 to 3000 mPa · s (B type viscosity, 60 rpm, 20 ° C.). There is an advantage that a film having a thickness of about 5 to 30 μm can be formed only by coating. Conventionally, in order to prepare a coating material having a viscosity of about 500 to 3000 mPa · s (B type viscosity, 60 rpm, 20 ° C.), the concentration of cellulose nanofiber is 0.2 to 0.4% (w / v). In order to produce a film having a thickness of about 5 to 30 μm, it was necessary to repeat coating and drying many times. The feature of the cellulose nanofiber dispersion obtained by the present invention having a high fluidity at a high concentration is very excellent.

In the present invention, a cellulose raw material oxidized by oxidizing a cellulosic raw material in water using an oxidizing agent in the presence of (1) an N-oxyl compound and (2) bromide, iodide or a mixture thereof. It is prepared and subjected to a viscosity reduction treatment before defibration and dispersion treatment. By subjecting the oxidized cellulose raw material to a viscosity reduction treatment before defibration / dispersion treatment, power consumption in the defibration / dispersion treatment can be reduced, and cellulose nanofibers can be produced efficiently with low energy. can do.

(N-oxyl compounds)
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, examples of the N-oxyl compound used in the present invention include substances represented by the following general formula (Formula 1).

(In Formula 1, R ₁ to R ₄ are 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 A -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. A 4-hydroxy TEMPO derivative is particularly preferable because it is inexpensive and can provide uniform oxidized cellulose.

(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 produce uniform cellulose nanofibers in a short time.

(In Formula 5, R ⁵ and R ⁶ represent the same or different hydrogen or a C ₁ -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 capable of converting the cellulose raw material into nanofibers. For example, 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 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.

(Oxidant)
As the oxidizing agent used for oxidizing the cellulosic raw material, the target oxidation reaction such as halogen, hypohalous acid, halous acid, perhalogen acid or salts thereof, halogen oxide, peroxide can be promoted. Any oxidizing agent can be used as long as it is an oxidizing agent. Among these, from the viewpoint of nanofiber production costs, sodium hypochlorite, which is currently most widely used in industrial processes and has low environmental impact, is particularly suitable. The amount of the oxidizing agent used can be selected within a range that can promote the oxidation reaction. For example, about 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.

(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. In addition to the microcrystalline cellulose powder purified by the above, plants such as kenaf, hemp, rice, bacus, and bamboo can also be used. Of these, bleached kraft pulp, bleached sulfite pulp, powdered cellulose, or microcrystalline cellulose powder is preferably used from the viewpoint of mass production and cost. In addition, it is particularly preferable to use powdered cellulose and microcrystalline cellulose powder because a cellulose nanofiber dispersion having a lower viscosity can be produced even at a high concentration.

Powdered cellulose is rod-like particles made of microcrystalline cellulose obtained by removing the non-crystalline part of wood pulp by acid hydrolysis and then pulverizing and sieving. The degree of polymerization of cellulose in powdered cellulose is about 100 to 500, the degree of crystallinity of powdered cellulose by X-ray diffraction is 70 to 90%, and the volume average particle size 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 used in the present invention, for example, a fixed particle size in the form of a rod shaft produced by a method of purifying and drying an undegraded residue obtained after acid hydrolysis of a selected pulp, pulverizing and sieving. Crystalline cellulose powder having a distribution may be used, KC Flock (registered trademark) (manufactured by Nippon Paper Chemical Co., Ltd.), Theolas (trademark) (manufactured by Asahi Kasei Chemicals), Avicel (registered trademark) (manufactured by FMC), etc. Commercial products may be used.

(Oxidation reaction conditions)
The method of the present invention is characterized in that the oxidation reaction can proceed smoothly even under mild conditions. Therefore, the reaction temperature may be a room temperature of about 15 to 30 ° C. In addition, since a carboxyl group produces | generates in a cellulose with progress of reaction, the fall of pH of a reaction liquid is recognized. In order to advance the oxidation reaction efficiently, it is desirable to maintain the pH of the reaction solution at about 9 to 12, preferably about 10 to 11, by adding an alkaline solution such as an aqueous sodium hydroxide solution. The reaction time in the oxidation reaction can be appropriately set and is not particularly limited, but is, for example, about 0.5 to 4 hours.

(Low viscosity treatment)
In the present invention, the viscosity-reducing treatment is performed on the oxidized cellulose raw material obtained by the above oxidation reaction. The viscosity reduction treatment refers to a treatment that moderately cuts the cellulose chain of the oxidized cellulose raw material (shortens the cellulose chain) and lowers the viscosity of the raw material. Any treatment can be used as long as the viscosity of the cellulosic raw material is lowered. For example, the treatment of irradiating the oxidized cellulosic raw material with ultraviolet rays, the treatment of hydrolyzing the oxidized cellulosic raw material with an enzyme, and the oxidation Examples thereof include a process of oxidizing and decomposing the cellulose-based raw material with hydrogen peroxide and ozone, a process of hydrolyzing the oxidized cellulose-based raw material with an acid, and combinations thereof.

(UV irradiation)
In the low viscosity treatment of the present invention, when the oxidized cellulose raw material is irradiated with ultraviolet rays, the wavelength of the ultraviolet rays is preferably 100 to 400 nm, more preferably 100 to 300 nm. Among these, ultraviolet rays having a wavelength of 135 to 260 nm are particularly preferable because they can directly act on cellulose and hemicellulose to cause low molecular weight and shorten the fiber.

As a light source for irradiating ultraviolet rays, a light source having a wavelength of 100 to 400 nm can be used. Specifically, a xenon short arc lamp, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, A hydrogen lamp, a metal halide lamp, etc. are mentioned as an example, These 1 type (s) or 2 or more types can be used in arbitrary combinations. In particular, it is preferable to use a combination of a plurality of light sources having different wavelength characteristics, because ultraviolet rays having different wavelengths are simultaneously irradiated to increase the number of cut portions in the cellulose chain and hemicellulose chain, thereby promoting shortening of the fiber.

As a container for storing the oxidized cellulosic raw material when performing ultraviolet irradiation, for example, when ultraviolet rays having a wavelength longer than 300 nm are used, those made of hard glass can be used, but ultraviolet rays having a shorter wavelength than that can be used. In the case of using, it is better to use a quartz glass that transmits ultraviolet rays more. In addition, about the material of the part which does not participate in the light transmission reaction of a container, a suitable thing can be selected from the materials with little deterioration with respect to the wavelength of the ultraviolet-ray used.

The concentration of the oxidized cellulose raw material when irradiated with ultraviolet rays is preferably 0.1% by mass or more because energy efficiency is increased, and if it is 12% by mass or less, the concentration of cellulose raw materials in the ultraviolet irradiation device is preferable. It is preferable because the fluidity is good and the reaction efficiency is increased. Therefore, the range of 0.1 to 12% by mass is preferable. More preferably, it is 0.5 to 5% by mass, and still more preferably 1 to 3% by mass.

The temperature of the cellulosic raw material when irradiated with ultraviolet rays is preferably 20 ° C. or higher because the efficiency of the photooxidation reaction is increased. This is preferable because there is no fear and there is no possibility that the pressure in the reactor exceeds atmospheric pressure. Therefore, the range of 20 to 95 ° C. is preferable. Within this range, there is also an advantage that there is no need to design a device in consideration of pressure resistance. More preferably, it is 20 to 80 ° C., and further preferably 20 to 50 ° C.

Further, the pH at the time of irradiation with ultraviolet rays is not particularly limited. However, in view of simplification of the process, it is preferable to perform the treatment in a neutral region, for example, pH 6.0 to 8.0.

The degree of irradiation received by the cellulosic raw material in the ultraviolet irradiation reaction can be arbitrarily set by adjusting the residence time of the cellulosic raw material in the irradiation reaction apparatus, adjusting the amount of energy of the irradiation light source, or the like. Also, for example, by adjusting the concentration of the cellulosic material in the irradiation device by diluting with water, or by adjusting the concentration of the cellulosic material by blowing an inert gas such as air or nitrogen into the cellulosic material. The irradiation amount of ultraviolet rays received by the cellulosic material in the irradiation reaction apparatus can be arbitrarily controlled. These conditions such as residence time and concentration can be appropriately set in accordance with the quality (fiber length, cellulose polymerization degree, etc.) of the oxidized cellulose raw material after the target ultraviolet irradiation reaction.

In addition, when the ultraviolet irradiation treatment in the present invention is performed in the presence of an auxiliary such as oxygen, ozone, or peroxide (hydrogen peroxide, peracetic acid, sodium percarbonate, sodium perborate, etc.), photooxidation is performed. Since the efficiency of reaction can be improved more, it is preferable.

In the present invention, particularly when ultraviolet rays having a wavelength region of 135 to 242 nm are irradiated, ozone is generated because air is usually present in the gas phase around the light source. In the present invention, while continuously supplying air to the periphery of the light source, the generated ozone is continuously extracted, and this extracted ozone is injected into the oxidized cellulosic raw material, so that the outside of the system is removed. Without supplying ozone, ozone can be used as an auxiliary for the photo-oxidation reaction. Furthermore, by supplying oxygen to the gas phase around the light source, a larger amount of ozone can be generated in the system, and the generated ozone can be used as an auxiliary agent for the photooxidation reaction. As described above, in the present invention, it is also a great advantage that ozone generated by the ultraviolet irradiation reactor can be used.

In the present invention, the ultraviolet irradiation treatment can be repeated a plurality of times. The number of repetitions can be appropriately set according to the relationship with the target quality of the oxidized cellulosic raw material and the post-treatment such as bleaching. For example, although not particularly limited, ultraviolet rays of 100 to 400 nm, preferably 135 to 260 nm are irradiated for 1 to 10 times, preferably about 2 to 5 times, for a length of about 0.5 to 3 hours per time. be able to.

The reason why the oxidized cellulose raw material can be efficiently reduced in viscosity by irradiation with ultraviolet rays is presumed as follows. A carboxyl group is localized on the surface of the cellulosic raw material oxidized with the N-oxyl compound, and a hydrated layer is formed. Therefore, it is considered that there is a microscopic gap between the raw materials which is not found in ordinary pulp due to the action of the charge repulsive force between the carboxyl groups. When the raw material is irradiated with ultraviolet rays, active oxygen species having excellent oxidizing power such as ozone are generated from oxygen dissolved in the hydrated layer on the surface of the raw material or pore water of the raw material, and the cellulose chain is efficiently formed. It is considered that the oxidative decomposition eventually promotes shortening of the fiber of the cellulosic material and lowers the viscosity of the cellulosic material.

(Enzymatic hydrolysis)
In the low viscosity treatment of the present invention, cellulase that is a cellulose degrading enzyme or hemicellulase that is a degrading enzyme of hemicellulose (for example, xylanase or mannase) is added to the oxidized cellulose raw material to hydrolyze the cellulose chain. When performing, there are no particular restrictions on the cellulase or hemicellulase that can be used. Cellulase or hemicellulase-producing filamentous fungi, bacteria, actinomycetes, basidiomycetes, or genetic engineering such as genetic recombination or cell fusion were used. A thing can be used individually or in mixture of 2 or more types. Commercial products can also be used. Examples of commercially available cellulases include Novozymes 476 from Novozymes Japan, Cellulase AP3 from Amano Enzyme, Cellulase Onozuka RS from Yakult Pharmaceutical Co., Ltd., Optimase CX40L from Genencor Kyowa Co., Ltd. Cellulase XL-522 manufactured by Chemtex, Enchiron CM manufactured by Nitto Kasei Kogyo Co., Ltd., etc. can be used. As commercially available hemicellulases, for example, Pulpzyme manufactured by Novozymes Japan, Hemicellulase Amano 90 manufactured by Amano Enzyme, and Sumiteam X manufactured by Shin Nippon Chemical Industry Co., Ltd. can be used.

If the amount of the enzyme added is 0.001% by mass or more with respect to the absolutely dry cellulosic raw material, it is sufficient to cause the desired enzyme reaction from the viewpoint of treatment time and efficiency, and 10% by mass. The following is preferable because excessive hydrolysis of cellulose can be suppressed and a decrease in the yield of cellulose nanofibers can be prevented. Therefore, the addition amount of the enzyme is preferably 0.001 to 10% by mass with respect to the absolutely dry cellulosic material. More preferably, the content is 0.01 to 5% by mass, and still more preferably 0.05 to 2% by mass. The “enzyme amount” here refers to the dry solid content of the enzyme aqueous solution.

The hydrolysis treatment with an enzyme is performed at pH 4 to 10, preferably pH 5 to 9, more preferably pH 6 to 8, temperature 40 to 70 ° C., preferably 45 to 65 ° C., more preferably 50 to 60 ° C. The reaction time is preferably 0.5 to 24 hours, preferably 1 to 10 hours, and more preferably 2 to 6 hours from the viewpoint of enzyme reaction efficiency.

The reason why the oxidized cellulose raw material can be efficiently reduced in viscosity by enzyme treatment is presumed as follows. A carboxyl group is localized on the surface of the cellulosic raw material oxidized with the N-oxyl compound, and a hydrated layer is formed. Therefore, it is considered that there is a microscopic gap between the raw materials which is not found in ordinary pulp due to the action of the charge repulsive force between the carboxyl groups. And, when an enzyme is added to the raw material for hydrolysis, a strong network of cellulose molecules is broken, the specific surface area of the raw material is increased, the shortening of the cellulose-based raw material is promoted, and the cellulose-based raw material is It is thought that the viscosity is lowered.

(Oxidative decomposition with hydrogen peroxide and ozone)
In the low viscosity treatment of the present invention, when the oxidized cellulose raw material is oxidatively decomposed with hydrogen peroxide and ozone, ozone can be generated by a known method using an ozone generator using air or oxygen as a raw material. . The addition amount (mass) of ozone in the present invention is preferably 0.1 to 3 times the absolute dry mass of the cellulosic material. If the amount of ozone added is at least 0.1 times the absolute dry mass of the cellulosic material, the amorphous part of the cellulose can be sufficiently decomposed, greatly increasing the energy required for the defibration / dispersion treatment in the next step. Can be reduced. Moreover, if it is 3 times or less, the excessive decomposition | disassembly of a cellulose can be suppressed and the fall of the yield of a cellulose raw material can be prevented. The amount of ozone added is more preferably 0.3 to 2.5 times, more preferably 0.5 to 1.5 times the absolute dry mass of the cellulosic material.

The addition amount (mass) of hydrogen peroxide is preferably 0.001 to 1.5 times the absolute dry mass of the cellulosic material. When hydrogen peroxide is used in an amount of 0.001 times or more of the addition amount of the cellulosic material, a synergistic effect between ozone and hydrogen peroxide is exhibited. In addition, it is sufficient to use hydrogen peroxide in an amount about 1.5 times or less that of the cellulosic raw material for decomposing the cellulosic raw material, and it is thought that a larger addition amount leads to an increase in cost. The amount of hydrogen peroxide added is more preferably 0.1 to 1.0 times the absolute dry mass of the cellulosic material.

The oxidative decomposition treatment with ozone and hydrogen peroxide is pH 2 to 12, preferably pH 4 to 10, more preferably pH 6 to 8, and temperature is 10 to 90 ° C., preferably 20 to 70 ° C., more preferably 30. From the viewpoint of oxidative decomposition reaction efficiency, it is preferable to carry out the reaction at -50 ° C. for 1-20 hours, preferably 2-10 hours, more preferably 3-6 hours.

As a device for performing treatment with ozone and hydrogen peroxide, a device commonly used by those skilled in the art can be used. For example, a normal chamber equipped with a reaction chamber, a stirrer, a chemical injection device, a heater, and a pH electrode. A reactor can be used.

After the treatment with ozone and hydrogen peroxide, ozone and hydrogen peroxide remaining in the aqueous solution can effectively work in the defibration / dispersion treatment in the next step, and can further promote the lowering of the viscosity of the cellulose nanofiber dispersion. .

The reason why the viscosity of the oxidized cellulose raw material can be efficiently reduced by hydrogen peroxide and ozone is presumed as follows. A carboxyl group is localized on the surface of the cellulosic raw material oxidized with the N-oxyl compound, and a hydrated layer is formed. Therefore, it is considered that there is a microscopic gap between the raw materials which is not found in ordinary pulp due to the action of the charge repulsive force between the carboxyl groups. Then, when the raw material is treated with ozone and hydrogen peroxide, hydroxy radicals having excellent oxidizing power are generated from ozone and hydrogen peroxide, and the cellulose chains in the raw material are efficiently oxidized and decomposed, and finally the cellulose-based raw material It is considered that the fiber is shortened to lower the viscosity of the cellulosic material.

(Hydrolysis with acid)
In the viscosity reduction treatment of the present invention, when an acid is added to the oxidized cellulose raw material to hydrolyze the cellulose chain (acid hydrolysis treatment), the acid used is sulfuric acid, hydrochloric acid, nitric acid, or phosphorus. It is preferred to use a mineral acid such as an acid.

The conditions for the acid hydrolysis treatment can be set as appropriate as long as the acid acts on the amorphous part of the cellulose, and are not particularly limited. For example, the amount of acid added is preferably 0.01 to 0.5% by mass, more preferably 0.1 to 0.5% by mass, based on the absolute dry mass of the cellulosic material. When the amount of acid added is 0.01% by mass or more, hydrolysis of cellulose proceeds and the fibrillation / dispersion efficiency of the cellulose-based raw material in the next step is improved, and preferably 0.5% by mass or less. For example, excessive hydrolysis of cellulose can be prevented, and a decrease in the yield of cellulose nanofibers can be prevented. The pH of the reaction solution during acid hydrolysis is 2.0 to 4.0, preferably 2.0 or more and less than 3.0. The acid hydrolysis treatment is preferably performed at a temperature of 70 to 120 ° C. for 1 to 10 hours from the viewpoint of acid hydrolysis efficiency.

Moreover, after the acid hydrolysis treatment, it is preferable to neutralize by adding an alkali such as sodium hydroxide from the viewpoint of the efficiency of the subsequent defibration / dispersion treatment.

The reason why the oxidized cellulose raw material can be efficiently reduced in viscosity by the acid hydrolysis treatment is presumed as follows. A carboxyl group is localized on the surface of the cellulosic raw material oxidized with the N-oxyl compound, and a hydrated layer is formed. For this reason, it is considered that there is a microscopic gap between the raw materials which is not found in ordinary pulp due to the action of the electric repulsion between carboxyl groups. Then, when an acid is added to the raw material for hydrolysis, a strong network of cellulose molecules is broken, the specific surface area of the raw material is increased, shortening of the cellulose-based raw material is promoted, and the cellulose-based raw material is It is thought that the viscosity is lowered.

(N-oxyl compound removal treatment)
In the present invention, if necessary, from an oxidized cellulose raw material between the oxidation treatment and the viscosity reduction treatment of the cellulose raw material, or between the viscosity reduction treatment and the defibration / dispersion treatment, A treatment for removing the N-oxyl compound used for the oxidation of the acid may be performed. Any method may be used for the removal treatment of the N-oxyl compound. When the oxidized cellulose raw material is heated to a temperature of 50 to 120 ° C. or less under the condition of pH 3 to 10, it is washed with cellulose. This is preferable because the N-oxyl compound can be efficiently removed without reducing the yield of the system raw material.

When heating to a temperature of 50 to 120 ° C. under the condition of pH 3 to 10, it is preferable to use a cellulosic raw material in the form of an aqueous dispersion having a pulp concentration of 0.1 to 50% by mass, more preferably The pulp concentration is 1 to 30% by mass, more preferably 2 to 20% by mass.

In the removal treatment of the N-oxyl compound by the heating, the pH of the aqueous dispersion of the oxidized cellulose raw material is adjusted to pH 3 to 10, preferably pH 3 to 9, and most preferably pH 3 to 8. Is preferred. The kind of acid or alkali used for adjusting the pH is not particularly limited, and may be an inorganic compound or an organic compound. Preferably, hydrochloric acid or sulfuric acid can be used as the acid, and an aqueous sodium hydroxide solution can be used as the alkali. When the pH of the aqueous dispersion of the oxidized cellulose-based raw material exceeds 10, not only does the cellulose decompose due to excess alkali, but the pulp yield significantly decreases, and the removal rate of the N-oxyl compound also increases. Since it falls, it is not preferable.

In the removal treatment of the N-oxyl compound by the above heating, the oxidized cellulose raw material is at a temperature of 50 ° C. to 120 ° C., preferably 70 ° C. to less than 100 ° C., more preferably 70 ° C. to 90 ° C. It is preferable to heat it. When the heating temperature is less than 50 ° C., the removal rate of the N-oxyl compound is remarkably reduced, and when heated to a temperature higher than 120 ° C., the cellulose is significantly decomposed and solubilized. Since the yield is significantly reduced, it is not preferable. When the temperature during heating is less than 100 ° C., it is not necessary to use a pressure-resistant container during the heat treatment, which is advantageous from the viewpoint of equipment cost.

The pressure at the time of heating is not particularly limited, and it may be under atmospheric pressure or under pressure. The heating time can be appropriately set in the range of about 10 minutes to 10 hours, preferably about 30 minutes to 6 hours, and most preferably about 1 to 5 hours, depending on the pH and temperature.

The N-oxyl compound remaining in the raw material can be sufficiently removed by thoroughly washing the oxidized cellulose raw material treated at the above specific pH and temperature.

By sufficiently removing the N-oxyl compound from the oxidized cellulose raw material, it is possible to improve the dispersibility of the cellulose raw material in the defibration / dispersion treatment after the next step, and the cellulose nanofiber dispersion obtained The transparency of the liquid can be improved. In addition, when the cellulose nanofiber dispersion or a film prepared therefrom is used for the purpose of a cosmetic thickener or food packaging, TEMPO and its derivatives whose toxicity to the environment and human body has not yet been clarified. It is highly preferable to sufficiently remove

(Defibration / dispersion processing)
In the present invention, the oxidized cellulose raw material is subjected to a viscosity reduction treatment (and N-oxyl compound removal treatment as necessary), and then subjected to a fibrillation / dispersion treatment. Examples of the type of equipment used for defibration / dispersion include high-speed rotary type, colloid mill type, high pressure type, roll mill type, ultrasonic type, etc., but cellulose nanofiber dispersion with excellent transparency and fluidity In order to efficiently obtain the above, it is preferable to treat with a wet high pressure or ultra high pressure homogenizer that can be dispersed under conditions of 50 MPa or more, preferably 100 MPa or more, more preferably 140 MPa or more.

(Cellulose nanofiber)
The cellulose nanofibers produced by the present invention are cellulose single microfibrils having a width of 2 to 5 nm and a length of about 1 to 5 μm. In the present invention, “to form a nanofiber” means that a cellulosic 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.

The cellulose nanofiber dispersion obtained by the present invention has a B-type viscosity (60 rpm, 20 ° C.) at a concentration of 1.0% by mass (w / v) of 1000 mPa · s or less, preferably 800 mPa · s or less, more preferably It is 500 mPa · s or less, and the light transmittance (660 nm) at a concentration of 0.1% by mass (w / v) is 90% or more, preferably 95% or more. Cellulose nanofibers produced according to the present invention are excellent in fluidity and transparency, and are also excellent in barrier properties and heat resistance, and thus can be used for various applications such as packaging materials.

In the present invention, the B-type viscosity of the cellulose nanofiber dispersion can be measured using a normal B-type viscometer commonly used by those skilled in the art, for example, TV-10 type viscosity of Toki Sangyo Co., Ltd. Using a meter, it can be measured at 20 ° C. and 60 rpm.

Further, the light transmittance of the cellulose nanofiber dispersion can be measured with an ultraviolet / visible spectrophotometer.

(Operation of the present invention)
In the present invention, the B-type viscosity of the dispersion in the defibration / dispersion treatment in the next step is significantly reduced by shortening the fiber of the cellulose-based raw material oxidized using the N-oxyl compound to reduce the viscosity. The fluidity of the dispersion can be significantly improved. Moreover, the power consumption at the time of dispersion | distribution can be reduced significantly. Furthermore, the cellulose nanofiber dispersion liquid excellent in transparency can be prepared by shortening a cellulose raw material.

Next, the present invention will be described in more detail based on examples. However, the following examples are specific examples of the present invention, and the present invention is not limited to these examples. It is not something.

5 g (absolutely dried) of bleached unbeaten sulfite pulp (Nippon Paper Chemical Co., Ltd.) derived from conifers was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Sigma-Aldrich) and 755 mg (7 mmol) of sodium bromide were dissolved, Stir until the pulp is uniformly dispersed. After adding 18 ml of an aqueous sodium hypochlorite solution (effective chlorine 5%) to the reaction system, the pH was adjusted to 10.3 with an aqueous 0.5N hydrochloric acid solution to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 0.5N aqueous sodium hydroxide solution was successively added to adjust the pH to 10. After reacting for 2 hours, it was filtered through a glass filter and washed thoroughly with water to obtain an oxidized cellulose-based material.

2 L of 1% (w / v) slurry of oxidized cellulose raw material was subjected to a low viscosity treatment. Specifically, it was treated for 6 hours with a 20 W low-pressure mercury lamp that irradiates ultraviolet rays of 254 nm. When the oxidized cellulose raw material treated with ultraviolet rays was treated 10 times with an ultra-high pressure homogenizer (treatment pressure 140 MPa), a transparent gel dispersion was obtained.

The B-type viscosity (60 rpm, 20 ° C.) of the obtained 1% (w / v) cellulose nanofiber dispersion was measured using a TV-10 viscometer (Toki Sangyo Co., Ltd.) and 0.1% ( The w / v) cellulose nanofiber dispersion transparency (660 nm fluorescence transmittance) was measured using a UV-VIS spectrophotometer UV-265FS (Shimadzu Corporation), and the power consumption required for defibration / dispersion treatment Was determined by (power during processing) × (processing time) / (sample amount processed). The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that ultraviolet rays having a wavelength range of 260 to 400 nm and having a main peak at 310 nm were irradiated using a 20 W low-pressure mercury lamp. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that ultraviolet rays having a wavelength range of 340 to 400 nm and having a main peak at 360 nm were irradiated using a 20 W low-pressure mercury lamp. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was 100 MPa. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was 50 MPa. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was changed to 30 MPa. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 5 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 6 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that a high shear mixer (circumferential speed 37 m / s, Nippon Seiki Seisakusho) equipped with a rotating blade as a dispersing device was used instead of the ultrahigh pressure homogenizer. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that 1% (w / v) of hydrogen peroxide was added to the oxidized pulp during UV irradiation. The results are shown in Table 1.

A nanofiber dispersion was obtained in the same manner as in Example 1 except that a 20 W low-pressure ultraviolet lamp that simultaneously irradiates ultraviolet rays of 254 nm and 185 nm was used. The results are shown in Table 1.

[Comparative Example 1]
A nanofiber dispersion was obtained in the same manner as in Example 1 except that ultraviolet rays were not irradiated (that is, the viscosity was not reduced). The results are shown in Table 1.

[Comparative Example 2]
Nanofibers as in Example 1 except that a high shear mixer (circumferential speed 37 m / s, Nippon Seiki Seisakusho) equipped with a rotating blade as a dispersing device without using a low viscosity treatment was used instead of the ultra-high pressure homogenizer. A dispersion was obtained. The results are shown in Table 1.

Commercially available cellulase (manufactured by Novozymes Japan, Novozymes) was applied to 2 L (pH 7.3) of 1% (w / v) slurry of oxidized cellulose raw material obtained in the same manner as in Example 1 as a treatment for reducing viscosity. 476) was added in an amount of 2% by mass with respect to the oxidized cellulosic raw material and treated at 30 ° C. for 6 hours. The cellulase-treated oxidized cellulosic material was boiled to deactivate the cellulase, and then treated 10 times with an ultrahigh pressure homogenizer (treatment pressure 140 MPa) to obtain a transparent gel dispersion.

B-type viscosity (60 rpm, 20 ° C.) of the obtained 1% (w / v) cellulose nanofiber dispersion, transparency (660 nm light transmittance) of the 0.1% (w / v) cellulose nanofiber dispersion ) And power consumption required for defibration / dispersion treatment were measured by the method described in Example 1. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 13 except that the treatment pressure of the ultrahigh pressure homogenizer was 100 MPa. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 13 except that the treatment pressure of the ultrahigh pressure homogenizer was 50 MPa. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 13 except that the treatment pressure of the ultrahigh pressure homogenizer was changed to 30 MPa. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 13 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 15 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 16 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 13 except that a high shear mixer (circumferential speed: 37 m / s, Nippon Seiki Seisakusho) equipped with a rotating blade as a dispersing device was used instead of the ultrahigh pressure homogenizer. The results are shown in Table 2.

A nanofiber dispersion was obtained in the same manner as in Example 13 except that cellulase AP3 (manufactured by Amano Enzyme) was used as the cellulolytic enzyme. The results are shown in Table 2.

As a viscosity-reducing treatment, 2 L of 1% (w / v) slurry of the oxidized cellulose raw material obtained in the same manner as in Example 1 was added with ozone and hydrogen peroxide, respectively, with an ozone concentration of 6 g / L (cellulose type). And the hydrogen peroxide concentration is 3 g / L (corresponding to 0.3 times the absolute dry mass of the cellulosic raw material) and is added at room temperature for 6 hours. Processed. When the oxidized cellulose raw material treated with ozone and hydrogen peroxide was treated 10 times with an ultrahigh pressure homogenizer (treatment pressure 140 MPa), a transparent gel dispersion was obtained.

B-type viscosity (60 rpm, 20 ° C.) of the obtained 1% (w / v) cellulose nanofiber dispersion, transparency of the 0.1% (w / v) cellulose nanofiber dispersion (660 nm light transmittance) ) And power consumption required for defibration / dispersion treatment were measured by the method described in Example 1. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 22 except that the treatment pressure of the ultrahigh pressure homogenizer was 100 MPa. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 22 except that the treatment pressure of the ultrahigh pressure homogenizer was 50 MPa. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 22 except that the treatment pressure of the ultrahigh pressure homogenizer was 30 MPa. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 22 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 24 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 25 except that powdered cellulose (Nippon Paper Chemical Co., Ltd., particle size 75 μm) was used as the cellulose-based material. The results are shown in Table 3.

A nanofiber dispersion was obtained in the same manner as in Example 22 except that a high shear mixer (circumferential speed 37 m / s, Nippon Seiki Seisakusho) equipped with a rotary blade was used as a dispersing device. The results are shown in Table 3.

The ozone concentration is 10 g / L (corresponding to 1.0 times the absolute dry mass of the cellulosic material), and the hydrogen peroxide concentration is 3 g / L (corresponding to 0.3 times the absolute dry mass of the cellulosic material). The nanofiber dispersion was obtained in the same manner as in Example 22 except that it was added so that The results are shown in Table 3.

[Comparative Example 3]
A nanofiber dispersion was obtained in the same manner as in Example 22 except that treatment with hydrogen peroxide alone was performed. The results are shown in Table 3.

[Comparative Example 4]
A nanofiber dispersion was obtained in the same manner as in Example 22 except that treatment with ozone alone was performed. The results are shown in Table 3.

To the oxidized cellulose raw material obtained in the same manner as in Example 1, a 0.1N hydrochloric acid aqueous solution was added as a treatment for reducing the viscosity (addition amount of hydrochloric acid: 0.1% by mass relative to the absolute dry mass of the pulp). ), 5% (w / v) pulp slurry having a pH of 2.8 was prepared and subjected to acid hydrolysis treatment at 90 ° C. for 2 hours. The acid-hydrolyzed oxidized cellulosic raw material was washed with water, neutralized with a 0.1N aqueous sodium hydroxide solution, and then treated 10 times with an ultra-high pressure homogenizer (treatment pressure 140 MPa). As a result, a transparent gel dispersion was obtained. Obtained.

B-type viscosity (60 rpm, 20 ° C.) of the obtained 1% (w / v) cellulose nanofiber dispersion, transparency (660 nm light transmittance) of the 0.1% (w / v) cellulose nanofiber dispersion ) And power consumption required for defibration / dispersion treatment were measured by the method described in Example 1. The results are shown in Table 4.

A nanofiber dispersion was obtained in the same manner as in Example 31 except that the amount of hydrochloric acid added was 0.3% by mass with respect to the absolute dry mass of the pulp, and acid hydrolysis treatment was performed at pH 2.4. The results are shown in Table 4.

From the results of Tables 1 to 4, in Examples 1 to 32 in which the oxidized cellulose-based raw material was subjected to a viscosity reduction treatment, the B-type viscosity was lower and the transparency was higher than those in Comparative Examples 1 to 4 in which the viscosity reduction treatment was not performed. It can be seen that cellulose nanofibers can be obtained with low power consumption. Therefore, according to the method for producing cellulose nanofibers of the present invention, a cellulose nanofiber dispersion having high fluidity and transparency can be obtained at a high concentration and with high efficiency.

Each of the 1% (w / v) cellulose nanofiber dispersions prepared in Examples 1, 2, 7, 13, 15, 17, 22, 24, 26, and 30 to 32 was converted into a polyethylene terephthalate film (thickness 20 μm). ) Was coated with a hand-painted bar (bar No. 16) and dried at 50 ° C. to form a film. The thickness of the obtained film was measured. The results are shown in Table 5.

[Comparative Example 5]
The concentration of the 1% (w / v) cellulose nanofiber dispersion produced in Comparative Example 1 was adjusted to have a B-type viscosity of 600 mPa · s (60 rpm, 20 ° C.). The cellulose nanofiber concentration at this time was 0.4% (w / v). This dispersion was applied to one side of a polyethylene terephthalate film (thickness 20 μm) with a bar for hand coating (bar No. 16) and dried at 50 ° C. to form a film. The film thickness was about 2.0 μm. In order to form a 5.9 μm film having the same thickness as the film obtained using the cellulose nanofiber dispersion liquid of Example 1, it was necessary to repeat coating and drying at least twice.

[Comparative Example 6]
The concentration of the 1% (w / v) cellulose nanofiber dispersion produced in Comparative Example 2 was adjusted so as to have a B-type viscosity of 700 mPa · s (60 rpm, 20 ° C.). The cellulose nanofiber concentration at this time was 0.26% (w / v). This dispersion was applied to one side of a polyethylene terephthalate film (thickness 20 μm) with a bar for hand coating (bar No. 16) and dried at 50 ° C. to form a film. The film thickness was about 1.6 μm. In order to form a 5.9 μm film having the same thickness as the film obtained using the cellulose nanofiber dispersion liquid of Example 1, it was necessary to repeat coating and drying at least three times.

Next, a specific example of removing the N-oxyl compound from the oxidized cellulosic raw material before the defibration / dispersion treatment will be shown.

Using a trace nitrogen meter (Mitsubishi Chemical, TN-10), the nitrogen content of bleached unbeaten sulfite pulp (Nippon Paper Chemical Co., Ltd.) derived from conifers was measured and found to be 21 ppm. Next, this bleached unbeaten sulfite pulp was oxidized by the method described in Example 1 to prepare an oxidized cellulosic material. The amount of nitrogen in the obtained oxidized cellulose raw material was measured and found to be 32 ppm. The difference between the nitrogen content of the oxidized cellulosic raw material and the nitrogen content of the bleached unbeaten sulfite pulp that is the raw pulp is considered to be based on the nitrogen content of the N-oxyl compound (TEMPO) used in the oxidation reaction The amount of nitrogen derived from TEMPO remaining in the oxidized cellulosic material can be calculated to be 32 ppm-21 ppm = 11 ppm.

Next, 0.2 g (absolutely dry) of the oxidized cellulose raw material was dispersed in 25 ml of ultrapure water, and the pH was adjusted to 3.5 with a 0.5N hydrochloric acid aqueous solution. After heating this at 85 ° C. for 2 hours, the cellulosic material was filtered off with a glass filter and washed thoroughly with water to remove residual N-oxyl compound (TEMPO) in the cellulosic material. After the obtained cellulose raw material was dried at 70 ° C., the amount of nitrogen in the cellulose raw material was measured and found to be 23 ppm.

As described above, since the nitrogen content of the bleached unbeaten sulfite pulp that is the raw material pulp was 21 ppm, it can be seen that the residual TEMPO-derived nitrogen amount after the N-oxyl compound removal treatment is 23 ppm-21 ppm = 2 ppm. . In addition, as described above, the amount of nitrogen derived from TEMPO that existed before the removal treatment of the N-oxyl compound was 11 ppm. Therefore, the above treatment can remove 82% of TEMPO remaining in the oxidized cellulose raw material. I understand that.

Further, as an index of the amount of cellulose dissolved by heating, the total organic carbon content in the filtrate obtained by filtering the pulp after the heating was measured using a total organic carbon meter (Shimadzu Corporation, TOC-V). .

Table 6 shows the results of the residual TEMPO-derived nitrogen amount (ppm), the residual TEMPO removal rate (%), and the total organic carbon amount (ppm) in the filtrate.

Heating was performed in the same manner as in Example 34 except that the pH was set to 5.5. Table 6 shows the results of the residual TEMPO-derived nitrogen amount (ppm), the residual TEMPO removal rate (%), and the total organic carbon amount (ppm) in the filtrate, measured in the same manner as in Example 34.

Heating was performed in the same manner as in Example 34, except that the pH was 7.7. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the pH was 2.5. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the pH was adjusted to 11.9 using a 0.5N aqueous sodium hydroxide solution. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the temperature was 50 ° C. and the time was 4 hours. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the temperature was 120 ° C. and the time was 30 minutes. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the temperature was 40 ° C. and the time was 6 hours. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the temperature was 130 ° C. and the time was 10 minutes. The results are shown in Table 6.

Heating was carried out in the same manner as in Example 34, except that an oxidized cellulose material obtained by ultraviolet treatment obtained by the method described in Example 1 was used. The amount of nitrogen in the cellulosic material after the heat treatment (after removal of TEMPO) was 21 ppm. As described in Example 34, the nitrogen content of the bleached unbeaten sulfite pulp, which is the raw material pulp, was 21 ppm. Therefore, the nitrogen content derived from the residual TEMPO after the TEMPO removal treatment was 21 ppm-21 ppm = 0 ppm. Recognize. By the TEMPO removal treatment, TEMPO remaining in the oxidized cellulosic material could be removed 100%. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the cellulase-treated oxidized cellulose material obtained by the method described in Example 13 was used. The amount of nitrogen in the cellulosic material after the heat treatment (after removal of TEMPO) was 23 ppm. As described in Example 34, the nitrogen content of the bleached unbeaten sulfite pulp, which is the raw material pulp, was 21 ppm. Therefore, the amount of nitrogen derived from the residual TEMPO after the TEMPO removal treatment was 23 ppm-21 ppm = 2 ppm. Recognize. In addition, as described in Example 34, since the amount of nitrogen derived from TEMPO present in the oxidized cellulose raw material was 11 ppm, 82% of TEMPO remaining in the oxidized cellulose raw material by the TEMPO removal treatment. It turns out that was able to be removed. The results are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the oxidized cellulose raw material treated with ozone and hydrogen peroxide obtained by the method described in Example 22 was used. The results obtained by the method described in Example 44 are shown in Table 6.

Heating was performed in the same manner as in Example 34 except that the acid-hydrolyzed oxidized cellulose material obtained by the method described in Example 31 was used. The results obtained by the method described in Example 44 are shown in Table 6.

After neutralizing the TEMPO-removed low-viscosity oxidized cellulose-based material obtained in Example 43 with alkali, it was treated 10 times at a pressure of 140 MPa using an ultra-high pressure homogenizer, and a transparent gel dispersion was used. A cellulose nanofiber dispersion was obtained. The transparency of the obtained cellulose nanofiber dispersion, the B-type viscosity, and the power consumption required for the fibrillation / dispersion treatment were determined by the method described in Example 1. The results are shown in Table 7.

A dispersion of cellulose nanofibers, which is a transparent gel-like dispersion, was obtained in the same manner as in Example 43, except that the low-viscosity oxidized cellulose-based raw material obtained by removing TEMPO obtained in Example 44 was used. The results are shown in Table 7.

A dispersion of cellulose nanofibers, which is a transparent gel-like dispersion, was obtained in the same manner as in Example 43 except that the low-viscosity oxidized cellulose-based raw material obtained by removing TEMPO obtained in Example 45 was used. The results are shown in Table 7.

A dispersion of cellulose nanofibers, which is a transparent gel-like dispersion, was obtained in the same manner as in Example 43 except that the low-viscosity oxidized cellulose-based raw material obtained by removing TEMPO obtained in Example 46 was used. The results are shown in Table 7.

Claims

Oxidizing the cellulosic raw material using an oxidizing agent in the presence of (A) (1) an N-oxyl compound and (2) a compound selected from the group consisting of bromide, iodide or a mixture thereof;
(B) subjecting the cellulose-based raw material from (A) to a viscosity-reducing treatment; and
(C) Nanofiberization by defibrating and dispersing the cellulosic material from (B),
The manufacturing method of the cellulose nanofiber containing this.
The method according to claim 1, wherein the viscosity-reducing treatment is to irradiate the cellulosic material from (A) with ultraviolet rays.
The method according to claim 1, wherein the viscosity reduction treatment is a hydrolysis treatment by adding cellulase and / or hemicellulase to the cellulosic material from (A).
The method according to claim 1, wherein the viscosity-reducing treatment is an oxidative decomposition treatment by adding hydrogen peroxide and ozone to the cellulosic material from (A).
The method according to claim 1, wherein the viscosity reduction treatment is a hydrolysis treatment by adding an acid to the cellulosic material from (A).
The method according to claim 2, wherein the wavelength of the ultraviolet ray is 100 to 400 nm.
The method according to claim 2 or 6, wherein the ultraviolet irradiation is performed in the presence of an oxidizing agent.
8. The method according to claim 2, wherein the ultraviolet light source comprises a plurality of light sources having different wavelength characteristics.
The method according to claim 3, wherein the addition amount of the cellulase is 0.001 to 10% by mass relative to the absolutely dry mass of the cellulosic material from (A).
The method according to claim 3 or 9, wherein the hydrolysis treatment is carried out under conditions of pH 4 to 10 and temperature of 40 to 70 ° C for 0.5 to 24 hours.
The method according to claim 4, wherein the amount of ozone added is 0.1 to 3 times the absolute dry mass of the cellulosic material from (A).
The method according to claim 4 or 11, wherein the amount of hydrogen peroxide added is 0.001 to 1.5 times the absolute dry mass of the cellulosic material from (A).
The method according to claim 5, wherein the hydrolysis treatment is performed for 1 to 10 hours under conditions of pH 2 to 4 and temperature 70 to 120 ° C.
The method according to claim 5 or 13, wherein the acid is sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid.
The method according to any one of claims 5, 13, and 14, wherein the addition amount of the acid is 0.01 to 0.5 mass% with respect to the absolute dry mass of the cellulosic material from (A). .
The method according to any one of claims 1 to 15, wherein the defibrating and dispersing treatment is performed under a pressure of 50 MPa or more.
Between (A) and (B),
(D) removing the N-oxyl compound in the cellulosic raw material by heating the cellulosic raw material to 50 ° C. or higher and 120 ° C. or lower under a pH of 3 to 10 and then washing with water. The method according to any one of to 15.
Between (B) and (C),
(D) removing the N-oxyl compound in the cellulosic raw material by heating the cellulosic raw material to 50 ° C. or higher and 120 ° C. or lower under a pH of 3 to 10 and then washing with water. The method according to any one of 1 to 17.
N-oxyl compounds are 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (TEMPO), 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine-N— An oxy radical (4-hydroxy TEMPO), a 4-hydroxy TEMPO derivative obtained by etherification or esterification of a hydroxyl group of 4-hydroxy TEMPO, or an azaadamantane type nitroxy radical, or a mixture thereof. The method in any one of.
A cellulose nanofiber obtained by the method according to any one of claims 1 to 19.