WO2011118746A1

WO2011118746A1 - Method for producing cellulose nanofibers

Info

Publication number: WO2011118746A1
Application number: PCT/JP2011/057283
Authority: WO
Inventors: 志穂勝川; 宮脇　正一; 裕阿部; 知章小柳
Original assignee: 日本製紙株式会社
Priority date: 2010-03-26
Filing date: 2011-03-25
Publication date: 2011-09-29
Also published as: JPWO2011118746A1

Abstract

Provided is a method for producing a highly concentrated cellulose nanofiber dispersion liquid with outstanding fluidity and transparency, with low energy and high efficiency. Specifically, in the presence of (1) an N-oxyl compound and (2) bromides, iodides, or a mixture thereof, a cellulose starting material is oxidized in water using an oxidizing agent to prepare an oxidized cellulose starting material, and in the presence of cellulase and/or hemicellulase, an ultra-high pressure homogenizer is used to perform defibration/dispersion at a pressure of at least 100 MPa.

Description

Method for producing cellulose nanofiber

The present invention relates to a method capable of producing a cellulose nanofiber dispersion liquid having a lower concentration and lower energy than conventional cellulose-based raw materials 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 these characteristics of cellulose nanofibers, it is envisaged to be applied to highly functional packaging materials, transparent organic base members, high performance 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, if the viscosity is too high, the dispersion proceeds only around the stirring blades, resulting in non-uniform dispersion, resulting in a dispersion with low 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.

The present invention provides a method capable of efficiently producing a cellulose nanofiber dispersion having low viscosity even at high concentration, excellent fluidity, and excellent transparency with low energy. With the goal.

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. An oxidized cellulosic material is prepared by oxidizing a cellulosic material in water, cellulase and / or hemicellulase is added to the oxidized cellulosic material, and an ultrahigh pressure homogenizer is used in the presence of these enzymes. By defibrating and dispersing at a pressure of 100 MPa or more, it is possible to efficiently produce a cellulose nanofiber dispersion excellent in fluidity and transparency even at a high concentration of about 1 to 3% (w / v). As a result, the present invention has been completed.

According to the present invention, a cellulosic material is oxidized in the presence of an N-oxyl compound and bromide, iodide, or a mixture thereof, and cellulase and / or hemicellulase is added to the resulting oxidized cellulosic material. In the presence of these enzymes, defibration and dispersion at a pressure of 100 MPa or more using an ultra-high pressure homogenizer enables low viscosity even at high concentrations, excellent fluidity, and easy handling. A dispersion of cellulose nanofibers having excellent transparency can be efficiently produced with lower power consumption than in the past. 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, the cellulose-based raw material is oxidized in water using an oxidizing agent in the presence of (1) N-oxyl compound, and (2) bromide, iodide, or a mixture thereof to obtain an oxidized cellulose-based raw material. Cellulose and / or hemicellulase is added, and in the presence of these enzymes, fibrillation / dispersion is performed at 100 MPa or more with an ultra-high pressure homogenizer, so that power consumption in defibration / dispersion treatment can be reduced, and cellulose nanofiber Can be efficiently manufactured with low energy.

(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.)

Of the compounds 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 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 cellulose nanofibers having a high degree of polymerization can be produced 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 them, from the viewpoint of cellulose nanofiber production cost, sodium hypochlorite, which is currently most widely used in industrial processes and has a low environmental load, 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.

(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 6 hours.

(Defibration / dispersion treatment in the presence of enzyme)
In the cellulose nanofiber of the present invention, cellulase, which is a cellulose-degrading enzyme, or hemicellulase (for example, xylanase or mannase), which is a degrading enzyme of hemicellulase, is used alone or in combination with the oxidized cellulose obtained by the above-described method. It mixes and adds, It can manufacture by carrying out a fibrillation and a dispersion | distribution process by the pressure of 100 Mpa or more using an ultrahigh pressure homogenizer.

Cellulase to be added, hemicellulase is not particularly limited, cellulase or hemicellulase-producing filamentous fungus, bacteria, actinomycetes, basidiomycete-derived, those produced by genetic manipulation such as genetic recombination, cell fusion, It can be used alone or in combination of two or more. Commercial products can also be used. Examples of commercially available cellulases include Novozymes® 476 manufactured by Novozymes Japan, Cellulase AP3 manufactured by Amano Enzyme, Cellulase Onozuka RS manufactured by Yakult Pharmaceutical Co., Ltd., Optimase CX40L manufactured by Genencor Kyowa Co., Ltd. Chemtex Cellulase XL-522, Nitto Kasei Kogyo Entilon CM, and other commercially available hemicellulases include Novozymes Japan Pulpzyme (registered trademark), Amano Enzyme Hemicellulase Amano 90, Shin Nippon Chemical Co., Ltd. Sumiteam X manufactured by Kogyo Co., Ltd. can be used.

If the amount of the enzyme added is 0.001% by mass or more based on the absolutely dry cellulosic material, it is sufficient to cause the desired enzyme reaction from the viewpoint of processing time and efficiency, and 10% by mass or less. If so, it 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.

In the present invention, in the presence of cellulase and / or hemicellulase, the oxidized cellulose raw material is defibrated and dispersed at a pressure of 100 MPa or more using an ultrahigh pressure homogenizer. As the ultra-high pressure homogenizer apparatus, a known apparatus can be used alone or in combination of two or more as required.

The pressure during defibration / dispersion treatment is 100 MPa or more. When the pressure is less than 100 MPa, the B-type viscosity of the obtained dispersion increases, the fluidity of the dispersion deteriorates, and the transparency also deteriorates remarkably. The pressure is preferably 120 MPa or more, more preferably 140 MPa or more.

The present inventors have found that by placing cellulase and / or hemicellulase under an ultra-high pressure of 100 MPa or more, the thermal stability of the enzyme is improved and the hydrolysis activity of cellulose and hemicellulose is also improved. Therefore, the pressure of 100 MPa or more is preferable not only for mechanical defibration / dispersion of cellulose nanofibers but also from the viewpoint of promoting enzyme reaction.

The pH, temperature, and treatment time when performing defibration / dispersion treatment in the presence of the enzyme are not particularly limited as long as the hydrolysis reaction by the enzyme proceeds, but pH 4 to 10, preferably pH 5 to 9, More preferably, the pH is 6 to 8, the temperature is 40 to 70 ° C., preferably 45 to 65 ° C., more preferably 50 to 60 ° C., and the treatment time and the number of passes are appropriately changed until the desired viscosity is obtained. Is preferable from the viewpoint of enzyme reaction efficiency.

Prior to defibration / dispersion treatment with an ultra-high pressure homogenizer, if necessary, the oxidized cellulosic raw material is pretreated using a known mixing, stirring, emulsifying and dispersing device such as a high-speed shear mixer or high-pressure homogenizer. May be.

(Enzyme deactivation)
In the present invention, the enzyme may be deactivated by irradiating the cellulose nanofiber dispersion liquid treated with the enzyme with ultraviolet rays and / or heating as necessary.

When the enzyme is deactivated by heating, it may be treated at a temperature of 90 to 120 ° C. for about 5 to 30 minutes using a pressure autoclave or the like according to the heat resistance of the enzyme.

When the enzyme is inactivated by irradiation with ultraviolet rays, the wavelength of the ultraviolet rays used is preferably 100 to 400 nm, more preferably 100 to 300 nm. Among these, ultraviolet rays having a wavelength of 135 to 260 nm not only act on the enzyme, but also act on cellulose and hemicellulose to promote further shortening of the cellulose nanofibers. In particular, it is also preferable from the viewpoint of lowering the viscosity of the cellulose nanofiber.

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 ultra-high pressure mercury lamp, a high-pressure mercury lamp, a low-pressure mercury lamp, a deuterium 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, when multiple light sources with different wavelength characteristics are used in combination, the number of cut sites in the enzyme, cellulose chain, and hemicellulose chain increases by simultaneously irradiating ultraviolet rays of different wavelengths, deactivating the enzyme and shortening the cellulose nanofibers. Is preferable because it is promoted.

When an enzyme is deactivated by irradiating with ultraviolet rays, an auxiliary agent such as oxygen, ozone, or peroxide (hydrogen peroxide, peracetic acid, sodium percarbonate, sodium perborate, etc.) is added. The efficiency of the photo-oxidation reaction due to can be further increased, which is preferable.

(Low viscosity treatment)
In the present invention, the oxidized cellulose-based material may be subjected to a viscosity reduction treatment before the oxidized cellulose-based material is fibrillated and dispersed in the presence of an enzyme. 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, and oxidizing and decomposing the oxidized cellulosic raw material with hydrogen peroxide and ozone. Treatment, hydrolyzing an oxidized cellulosic 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 directly act on cellulose or hemicellulose to cause low molecular weight, and the cellulose raw material can be shortened.

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, but in consideration of simplification of the process, it is preferable to perform the treatment in a neutral region, for example, pH of about 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 is performed in the presence of an auxiliary agent such as oxygen, ozone, or peroxide (hydrogen peroxide, peracetic acid, sodium percarbonate, sodium perborate, etc.), the efficiency of the photooxidation reaction is increased. Can be further increased, which 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 applied 1 to 10 times, preferably about 2 to 5 times, 0.5 to 10 hours per time, preferably 0.5 to 3 times. It can be irradiated for as long as an hour.

(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 defibration and 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.

(Cellulose nanofiber)
The cellulose nanofiber of the present invention is a cellulose single microfibril having a width of 2 to 5 nm and a length of 1 to 5 μm. In the present invention, “to form nanofibers” means that powdered cellulose is processed into cellulose nanofibers which are single microfibrils 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 2% (w / v) of 500 to 3000 mPa · s, preferably 500 to 2000 mPa · s. Preferably, it is 600 to 1500 mPa · s. Since the cellulose nanofiber dispersion obtained by the present invention has a low viscosity and good fluidity, it has an advantage that it is easy to process such as preparation of a paint.

The cellulose nanofiber dispersion obtained by the present invention has a light transmittance (660 nm) (which is an index of transparency) at a concentration of 0.1% (w / v) of 90% or more, preferably 95%. Or more, most preferably 97% or more. When the transparency is in the above range, it can be said that cellulose that has not been made into nanofibers and aggregation of nanofibers are hardly present in the dispersion, and the film can be formed using such dispersion. When formed, a film excellent in transparency and barrier properties can be obtained.

As described above, the cellulose nanofibers produced according to the present invention are excellent in fluidity and transparency, and are also excellent in barrier properties and heat resistance, so that they are used for various applications such as packaging materials. It is possible.

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 transparency of the cellulose nanofiber dispersion can be measured as a transmittance of 660 nm light using an ultraviolet / visible spectrophotometer.

In addition, the carboxyl group amount of the cellulose nanofiber of the present invention is preferably 0.5 mmol / g or more. The amount of carboxyl groups in cellulose nanofibers was prepared by adding 60 ml of a 0.5% by weight slurry of cellulose nanofibers, adding 0.1M hydrochloric acid aqueous solution to pH 2.5, and then dropping 0.05N sodium hydroxide aqueous solution dropwise. Then, the electrical conductivity is measured until the pH reaches 11, and can be calculated from the amount of sodium hydroxide (a) consumed in the weak acid neutralization stage where the change in electrical conductivity is gradual, using the following equation. .
Amount of carboxyl group [mmol / g pulp] = a [ml] × 0.05 / oxidized pulp mass [g]

(Operation of the present invention)
In the present invention, a cellulose-based raw material oxidized using an N-oxyl compound is defibrated and dispersed under a pressure of 100 MPa or more in the presence of cellulase and / or hemicellulase, so that even at a high concentration. A cellulose nanofiber dispersion having a low viscosity and excellent fluidity and transparency can be obtained. The reason is guessed as follows. Cellulose-based raw materials oxidized with an N-oxyl compound are composed of microfibrils, carboxyl groups are localized on the surface thereof, and a hydrated layer is formed. For this reason, it is considered that there is a microscopic gap between microfibrils that cannot be seen in ordinary pulp due to the action of the charge repulsion between carboxyl groups. When the raw material is treated with cellulase and / or hemicellulase in an ultrahigh pressure of 100 MPa or more, the thermal stability of the enzyme is improved by pressurization, and hydrolysis of polysaccharides such as cellulose and hemicellulose is performed. The activity is also improved, and it is considered that hydrolysis of cellulose chains and hemicellulose chains occurs with high enzyme reaction efficiency. Furthermore, it is considered that the cellulose-based raw material is fibrillated and converted into nanofibers to increase the specific area of the cellulose-based raw material and further accelerate the polysaccharide decomposition reaction. As a result, it is considered that the cellulose chains constituting the cellulose nanofibers are efficiently divided, and finally the shortening of the cellulose nanofibers is promoted. This shortening of the cellulose chain is thought to significantly reduce the B-type viscosity of the resulting dispersion and improve the fluidity. Further, it is considered that the transparency of the dispersion is remarkably improved by shortening the fiber length of the cellulose chain.

Next, the present invention will be described in more detail based on examples.

[Example 1]
5 g (absolutely dried) of bleached unbeaten kraft pulp derived from coniferous tree (absolutely dried) was added to 500 ml of an aqueous solution in which 78 mg (0.5 mmol) of TEMPO (Sigma Aldrich) and 754 mg (7.4 mmol) of sodium bromide were dissolved. Stir until the pulp is uniformly dispersed. After adding 18 ml (7.2 mmol / g) of 2M aqueous sodium hypochlorite solution to the reaction system, the pH was adjusted to 10.3 with 0.5N aqueous hydrochloric acid solution to initiate the oxidation reaction. During the reaction, the pH in the system was lowered, but a 0.5N aqueous sodium hydroxide solution was successively added to adjust the pH to 10. After making it react for 2 hours, it filtered with the glass filter and obtained the cellulose-type raw material oxidized by fully washing with water. To a 2% (w / v) slurry of oxidized cellulosic raw material, 2% by mass of commercially available cellulase (Novozyme 476, manufactured by Novozymes Japan) is added to the oxidized cellulosic raw material, and ultra-high pressure is added. When a homogenizer was used 5 times at 50 ° C. and a pressure of 140 MPa (defibration / dispersion treatment), a transparent gel dispersion was obtained. The obtained gel dispersion was treated at 105 ° C. for 30 minutes to inactivate cellulase (cellulase inactivation treatment). The B-type viscosity (60 rpm, 20 ° C.) of the obtained 2% (w / v) cellulose nanofiber dispersion was measured using a TV-10 viscometer (Toki Sangyo Co., Ltd.), and 0.1% ( The transparency (w / v) of the cellulose nanofiber dispersion (660 nm light transmittance) was measured using a UV-VIS spectrophotometer UV-265FS (Shimadzu Corporation). In addition, the power consumption required for the defibration / dispersion processing was obtained by (power during processing) × (processing time) / (amount of processed sample). The results are shown in Table 1.

[Example 2]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the pressure of the ultrahigh pressure homogenizer was 100 MPa. The results are shown in Table 1.

[Example 3]
Dispersing cellulose nanofibers in the same manner as in Example 1 except that, when cellulase was deactivated, instead of treating at 105 ° C. for 30 minutes, ultraviolet rays having a main peak at 254 nm were irradiated for 2 hours using a 20 W low-pressure mercury lamp. A liquid was obtained. The results are shown in Table 1.

[Example 4]
When inactivating cellulase, a nanofiber dispersion was obtained in the same manner as in Example 1 except that instead of treatment at 105 ° C. for 30 minutes, ultraviolet rays of 254 nm and 185 nm were simultaneously irradiated using a 20 W low-pressure ultraviolet lamp. It was. The results are shown in Table 1.

[Example 5]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 3 except that 1% (w / v) of hydrogen peroxide was added to the oxidized cellulose raw material during ultraviolet irradiation. The results are shown in Table 1.

[Example 6]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1, except that bleached unbeaten kraft pulp derived from hardwood was used instead of bleached unbeaten kraft pulp derived from softwood. The results are shown in Table 1.

[Example 7]
Example 6 except that 2% by mass of commercially available cellulase (Novozymes Japan, Novozyme 476) and hemicellulase (Novozymes Japan, Pulpzyme HC) were added to the oxidized cellulose raw material. In the same manner as above, a cellulose nanofiber dispersion was obtained. The results are shown in Table 1.

[Example 8]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the temperature during the treatment with the ultrahigh pressure homogenizer was 40 ° C. The results are shown in Table 1.

[Example 9]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the temperature during the treatment with the ultra-high pressure homogenizer was 70 ° C. The results are shown in Table 1.

[Example 10]
Before adding cellulase to the oxidized cellulose raw material, the oxidized cellulose raw material (1% by mass) was irradiated with ultraviolet rays for 6 hours using a 20 W low-pressure ultraviolet lamp (main peak 254 nm) (low viscosity) A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except for the treatment. The results are shown in Table 1.

[Example 11]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 3 except that 1% (w / v) of ozone was added to the oxidized cellulose raw material at the time of ultraviolet irradiation. The results are shown in Table 1.

[Example 12]
Dispersion of cellulose nanofibers in the same manner as in Example 6 except that, when cellulase was deactivated, instead of treating at 105 ° C. for 30 minutes, ultraviolet rays having a main peak at 254 nm were irradiated for 2 hours using a 20 W low-pressure mercury lamp. A liquid was obtained. The results are shown in Table 1.

[Comparative Example 1]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment pressure of the ultrahigh pressure homogenizer was 80 MPa. The results are shown in Table 1.

[Comparative Example 2]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that the treatment was performed at 50 ° C. for 20 minutes using a rotary blade mixer (peripheral speed 140 m / sec) instead of the ultrahigh pressure homogenizer. The results are shown in Table 1.

[Comparative Example 3]
A 2% (w / v) slurry of the oxidized cellulosic material was treated for 10 minutes using a rotary blade mixer (circumferential speed 140 m / sec), and then commercially available cellulase (Novozyme Japan, Novozymes 476). ) Was added in an amount of 2% by mass to the oxidized cellulose raw material and treated at 70 ° C. for 10 minutes using a rotary blade mixer (peripheral speed 140 m / sec), in the same manner as in Example 1, cellulose nano A fiber dispersion was obtained. The results are shown in Table 1.

[Comparative Example 4]
A cellulose nanofiber dispersion was obtained in the same manner as in Example 1 except that no cellulase was added during the treatment with the ultrahigh pressure homogenizer and the cellulase was not deactivated. The results are shown in Table 1.

In Examples 1 to 10 in which the oxidized cellulosic raw material was defibrated and dispersed under the condition of 100 MPa or more using an ultrahigh pressure homogenizer in the presence of an enzyme, Comparative Example 1 treated with less than 100 MPa and a mixer were used. It can be seen that cellulose nanofibers having a low B-type viscosity and high transparency can be obtained with relatively low power consumption as compared with Comparative Examples 2 and 3 used and Comparative Example 4 in which no enzyme was added. Therefore, according to the method for producing cellulose nanofibers of the present invention, it is possible to obtain a cellulose nanofiber dispersion liquid having a low viscosity even at a high concentration and having high fluidity and transparency with high efficiency.

[Example 13]
A 2% (w / v) cellulose nanofiber dispersion (B-type viscosity 1646 mPa · s) produced according to Example 1 was used on one side of a polyethylene terephthalate film (thickness 20 μm), and a bar exclusively for hand coating (bar No. 16). And dried at 50 ° C. to form a film. The thickness of the film was about 18.2 μm.

[Comparative Example 5]
The concentration of the 2% (w / v) cellulose nanofiber dispersion produced in Comparative Example 2 was adjusted to have a B-type viscosity of 1600 mPa · s (60 rpm, 20 ° C.). The cellulose nanofiber concentration at this time was 0.76% (w / v). This dispersion was applied to one side of a polyethylene terephthalate film (thickness: 20 μm) with a hand-painted bar (bar No. 16) and dried at 50 ° C. to form a film. The thickness of the film was about 6.9 μm. In order to form an 18.2 μm film having the same thickness as in Example 13, it was necessary to repeat coating and drying twice or more.

When the 2% (w / v) cellulose nanofiber dispersion produced in Comparative Example 2 was used at the same concentration, coating unevenness occurred and a uniform film could not be formed.

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) The cellulosic material from (A) is treated with an ultra-high pressure homogenizer in the presence of cellulase and / or hemicellulase at a pressure of 100 MPa or more, and the cellulosic material is fibrillated and dispersed to form nanofibers. thing,
The manufacturing method of the cellulose nanofiber containing this.
The method for producing cellulose nanofibers according to claim 1, wherein the obtained cellulose nanofibers have a B-type viscosity (60 rpm, 20 ° C) at a concentration of 2% (w / v) of 500 to 3000 mPa · s.
The method for producing cellulose nanofiber according to claim 1 or 2, wherein the defibrating and dispersing is performed at 40 to 70 ° C.
The method for producing cellulose nanofiber according to any one of claims 1 to 3, further comprising subjecting the cellulose-based material from (A) to a low viscosity treatment between (A) and (B).
The cellulose nanofiber according to any one of claims 1 to 4, further comprising inactivating the cellulase and / or hemicellulase by irradiating ultraviolet rays and / or heating after (B). Manufacturing method.