阅读说明：本技术 纤维素微细纤维及其制造方法 (Cellulose microfine fiber and process for producing the same ) 是由 松末一紘 于 2018-05-08 设计创作，主要内容包括：[课题]提供一种在将纤维素微细纤维制成分散液的情况下使该分散液的透明度和粘度极高的纤维素微细纤维及其制造方法。[解決手段]对于纤维素纤维而言,纤维素纤维的羟基的一部分被规定的官能团取代而导入了磷酸的酯、并且被氨基甲酸酯基取代而导入了氨基甲酸酯。另外,关于纤维素微细纤维的制造方法,在纤维素纤维中添加添加物(A)以及含有脲和脲衍生物中的至少任一者的添加物(B),在100～210℃进行加热,清洗后进行开纤,使所述添加物(B)的添加量相对于1mol所述添加物(A)为0.01～100mol。([ problem ] to provide a cellulose microfiber which has extremely high transparency and viscosity when the cellulose microfiber is made into a dispersion liquid, and a method for producing the cellulose microfiber. [ solving means ] in the cellulose fiber, a part of hydroxyl groups of the cellulose fiber is substituted with a predetermined functional group to introduce an ester of phosphoric acid and is substituted with a carbamate group to introduce carbamate. In addition, the method for producing the cellulose microfiber comprises adding an additive (A) and an additive (B) containing at least one of urea and a urea derivative to cellulose fibers, heating the mixture at 100 to 210 ℃, washing the mixture, and then opening the mixture to make the amount of the additive (B) 0.01 to 100mol based on 1mol of the additive (A).)

1. A cellulose microfine fiber characterized in that,

In the cellulose fibers, a part of hydroxyl groups are substituted with functional groups represented by the following structural formula (1) to introduce esters of oxyacids of phosphorus, and are substituted with carbamate groups to introduce carbamates,

[ structural formula (1) ]

[ solution 1]

In the structural formula 1, a, b, m and n are natural numbers,

At least one of A1, A2, …, An and A' is O^-The balance being any one of R, OR, NHR OR absent; r is any one of a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, an aromatic group, and a derivative thereof; α is a cation formed from an organic or inorganic substance.

2. The cellulose microfine fiber according to claim 1, wherein the degree of substitution of said carbamate groups is 0.01 to 0.38.

3. The cellulose microfine fiber according to claim 1 or 2, wherein the degree of substitution of the functional group represented by the structural formula (1) is 0.01 to 0.64.

4. A method for producing a cellulose microfiber, characterized in that,

Adding an additive (A) and an additive (B) containing at least one of urea and a urea derivative to cellulose fibers, heating the mixture at 100 to 210 ℃, washing the mixture, and then opening the mixture,

The additive (B) is added in an amount of 0.01 to 100mol based on 1mol of the additive (A).

5. The method for producing cellulose microfine fibers according to claim 4, wherein said heating is carried out at a pH of 3 to 12.

Technical Field

The present invention relates to a cellulose microfiber and a method for producing the same.

Background

In recent years, as natural fibers, there are cellulose microfibers (cellulose nanofibers (CNF)) having a fiber width of 1 μm or less, in addition to cellulose fibers having a fiber width of about 20 to 30 μm. The cellulose microfine fibers are usually obtained by opening cellulose fibers. In order to effectively open cellulose fibers, various proposals have been made.

For example, patent document 1 proposes a cellulose microfiber in which a mechanical opening (fibrillation) treatment is performed by stirring with a stirrer, and the damage to the fiber is small, but the stirrer treatment time is also long and the damage to the fiber is also large in order to obtain a dispersion having a higher transparency. Patent document 2 proposes a method of "preparing a polybasic acid half-esterified cellulose by half-esterifying a polybasic acid anhydride to introduce a carboxyl group into a part of hydroxyl groups of cellulose" before opening. However, according to this proposal, it is considered that the cellulose fibers cannot be sufficiently refined by the subsequent opening.

Therefore, patent document 3 proposes a method of "treating a fiber raw material containing cellulose with at least one compound selected from oxyacids of phosphorus and salts thereof while heating at 100 to 170 ℃. This proposal suggests that "microfibrous cellulose having a fiber width of 1 to 1000nm and having phosphorus-containing oxoacid groups introduced thereto by substituting a part of hydroxyl groups of cellulose constituting the fiber with a predetermined functional group" can be obtained by this method. However, the fine fibrous cellulose dispersion obtained by this proposal still has room for improvement in transparency and viscosity.

Disclosure of Invention

problems to be solved by the invention

The present invention addresses the problem of providing a cellulose microfiber which, when the cellulose microfiber is prepared as a dispersion liquid, has extremely high transparency and viscosity of the dispersion liquid, and a method for producing the cellulose microfiber.

Means for solving the problems

The means for solving the above problems is a cellulose microfiber characterized in that,

an ester of an oxyacid of phosphorus, in which a part of hydroxyl groups of cellulose fibers is substituted with a functional group represented by the following structural formula (1),

And a carbamate group is substituted by the carbamate group to introduce the carbamate.

[ structural formula (1) ] [ formula 1]

In the structural formula 1, a, b, m and n are natural numbers.

At least one of A1, A2, …, An and A' is O^-And the remainder are any of R, OR, NHR OR absent. R is any of a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, an aromatic group, and a derivative thereof. α is a cation formed from an organic or inorganic substance.

Further, a means for solving the above problems is a method for producing a cellulose microfiber,

Adding an additive (A) and an additive (B) containing at least one of urea and a urea derivative to cellulose fibers, heating at 100 to 210 ℃, washing, and opening,

The additive (B) is added in an amount of 0.01 to 100mol based on 1mol of the additive (A).

Effects of the invention

According to the present invention, a cellulose microfiber having extremely high transparency and viscosity of a dispersion liquid obtained when the cellulose microfiber is prepared into the dispersion liquid, and a method for producing the cellulose microfiber are obtained.

Detailed Description

Next, a description will be given of a specific embodiment of the present invention. The present embodiment is an example of the present invention.

(cellulose microfine fiber)

In the cellulose microfine fibers of the present embodiment, esters (esterified) of oxyacids of phosphorus are introduced (modified or modified) by substituting a part of hydroxyl groups (-OH groups) of the cellulose fibers with functional groups represented by the following structural formula (1). In the cellulose fibers of the present embodiment, a carbamate (ester of carbamate) is introduced by substituting a part of the hydroxyl groups of the cellulose fibers with a carbamate group.

[ structural formula (1) ] [ formula 1]

In the structural formula 1, a, b, m and n are natural numbers.

At least one of A1, A2, …, An and A' is O^-and the remainder are any of R, OR, NHR OR absent. R is any of a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, an aromatic group, and a derivative thereof. α is a cation formed from an organic or inorganic substance.

The esters of oxyacids of phosphorus are the following compounds: a hydroxyl group (— OH) and an oxo group (═ O) are bonded to the phosphorus atom, and the hydroxyl group provides an acidic proton. Since esters of oxyacids of phosphorus have a high negative charge, introduction of esters of oxyacids of phosphorus results in strong repulsion between cellulose molecules and facilitates opening of cellulose fibers. Further, when a carbamate is introduced together with an ester of an oxyacid of phosphorus, the transparency and viscosity of the dispersion are greatly improved. In this regard, it is considered that the carbamate has an amino group. Thus, if a carbamate is introduced, it interacts with the ester of the oxyacid of phosphorus. Therefore, when urethane is also introduced, the shear force of the dispersion increases, and the viscosity increases.

The ester of the oxyacid of phosphorus to be introduced is more preferably an ester of phosphorous acid. When the phosphite ester is introduced, yellowing is reduced and transparency of the dispersion of the cellulose microfiber is improved. In addition, the viscosity also increases. In the case of introducing the ester of phosphorous acid, a part of the hydroxyl groups (-OH groups) of the cellulose fibers is substituted with a functional group represented by the following structural formula (2).

[ structural formula (2) ] [ formula 2]

In structural formula (2), α is either absent or is either R and NHR. R is any of a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, an aromatic group, and a derivative thereof. Beta is a cation formed from an organic or inorganic substance.

The amount of the ester of an oxyacid of phosphorus introduced is preferably 0.06 to 3.94mmol, more preferably 0.47 to 2.54mmol per 1g of the cellulose microfine fiber. If the amount of introduction is less than 0.06mmol, there is a possibility that the cellulose fibers are not easily opened. In addition, the aqueous dispersion of the cellulose microfine fibers may become unstable. On the other hand, if the amount of cellulose fibers introduced exceeds 3.94mmol, the cellulose fibers may be dissolved in water.

the amount of the ester of an oxyacid of phosphorus introduced is a value evaluated based on elemental analysis. X-Max50001 manufactured by horiba, Ltd was used for the elemental analysis.

The amount of urethane introduced is preferably 0.06 to 2.34mmol, more preferably 0.15 to 1.28mmol, and particularly preferably 0.21 to 0.94mmol per 1g of the cellulose microfiber. If the amount of incorporation is less than 0.06mmol, the transparency and viscosity of the dispersion may not be sufficiently improved. On the other hand, if the amount of cellulose fibers introduced exceeds 2.34mmol, the cellulose fibers may be dissolved in water. The method of calculating the introduced amount of carbamate was performed by the kjeldahl method.

The Degree of Substitution (DS) of the functional group represented by the structural formula (1) is preferably 0.01 to 0.64, more preferably 0.08 to 0.41. If the degree of substitution is less than 0.01, the opening of the cellulose fibers may become difficult. On the other hand, if the degree of substitution exceeds 0.64, the cellulose fibers may be dissolved in water.

The degree of substitution of the carbamate group is preferably 0.01 to 0.38, more preferably 0.02 to 0.21, and particularly preferably 0.03 to 0.15. If the degree of substitution is less than 0.01, the transparency and viscosity may not be sufficiently high. On the other hand, if the degree of substitution exceeds 0.38, the cellulose fibers may be dissolved in water.

The substitution degree refers to the average substitution number of the functional group (the functional group represented by the structural formula (1), the carbamate group) with respect to one glucose unit in cellulose. The degree of substitution can be controlled by, for example, the reaction temperature and the reaction time. If the reaction temperature is increased or the reaction time is prolonged, the degree of substitution increases. Among them, if the substitution degree is excessively increased, the polymerization degree of cellulose is remarkably decreased.

The cellulose microfine fibers preferably have a fiber width (average diameter of single fibers) of 1 to 1,000nm, more preferably 2 to 400nm, and particularly preferably 3 to 100 nm. If the fiber width is less than 1nm, the cellulose dissolves in water, and physical properties such as strength, rigidity, dimensional stability and the like as cellulose microfibers may not be obtained. On the other hand, if the fiber width exceeds 1,000nm, the fiber cannot be called a cellulose microfiber any more, and is changed to a general cellulose fiber. When the fiber width exceeds 1,000nm, the wavelength of visible light becomes about 1/10, and therefore, when the cellulose fine fibers are dispersed in water (in the case of an aqueous dispersion), refraction and scattering of visible light occur, and the transparency may be insufficient.

The fiber width of the cellulose microfiber was measured using an electron microscope as follows.

First, 100ml of an aqueous dispersion of cellulose microfibers having a solid content concentration of 0.01 to 0.1 mass% was filtered through a teflon (registered trademark) membrane filter, and 1 solvent substitution was performed with 100ml of ethanol and 3 solvent substitutions were performed with 20ml of t-butanol. Subsequently, freeze-drying was performed, and osmium coating was performed to prepare a sample. For this sample, observation based on an electron microscope SEM image was performed at any of 5,000 times, 10,000 times, or 30,000 times depending on the width of the fiber constituted. In this observation, 2 diagonal lines are drawn on the observation image, and further, 3 straight lines passing through the intersection points of the diagonal lines are arbitrarily drawn. The width of a total of 100 fibers intersecting the 3 lines was then measured visually. The median diameter of the measurement was taken as the fiber width.

The axial ratio (fiber length/fiber width) of the cellulose microfine fibers is preferably 3 to 1,000,000, more preferably 6 to 340,000, and particularly preferably 10 to 340,000. If the axial ratio is less than 3, it cannot be said to be fibrous. On the other hand, if the axial ratio exceeds 1,000,000, the viscosity of the dispersion (slurry) may be excessively high.

The crystallinity of the cellulose microfine fiber is preferably 50 to 100%, more preferably 60 to 90%, and particularly preferably 65 to 85%. If the crystallinity is less than 50%, strength and heat resistance may be insufficient. The crystallinity can be adjusted by, for example, selection of pulp fibers, pretreatment, fiber opening, and the like. The crystallinity is a value measured by X-ray diffraction method according to JIS-K0131(1996) "X-ray diffraction analysis general rules". The cellulose fine fibers have an amorphous portion and a crystalline portion, and the crystallinity is a ratio of the crystalline portion to the entire cellulose fine fibers.

The light transmittance (solid content 0.2% solution) of the cellulose microfine fibers is preferably 40.0% or more, more preferably 60.0% or more, and particularly preferably 70.0% or more. If the light transmittance is less than 40.0%, the transparency may be insufficient. The light transmittance of the cellulose microfine fibers can be adjusted by, for example, selection of pulp fibers, pretreatment, opening, and the like.

The light transmittance is a value obtained by measuring the transparency (transmittance of 350 to 880nm light) of a cellulose microfiber dispersion liquid of 0.2% (w/v) using a spectrophotometer U-2910 (Hitachi, Ltd.).

the B-type viscosity of the dispersion is preferably 10 to 300,000cps, more preferably 1,000 to 200,000cps, and particularly preferably 10,000 to 100,000cps when the concentration of the cellulose microfine fibers is 1 mass% (w/w). The type B viscosity is a value obtained by measuring an aqueous dispersion of cellulose microfibers at a solid content concentration of 1% according to JIS-Z8803(2011) "method for measuring viscosity of liquid". The type B viscosity is a resistance torque when the slurry is stirred, and the higher the viscosity, the more energy is required for stirring.

(method for producing cellulose microfine fiber)

In the production method of this embodiment, the additive (a) and the additive (B) are added and heated to introduce the ester of oxyacid of phosphorus and carbamate into the cellulose fiber. Then, the cellulose fiber into which the ester of an oxyacid of phosphorus and carbamate have been introduced is washed and then opened to obtain a cellulose microfiber.

(cellulose fiber)

As the cellulose fiber, for example, a plant-derived fiber (plant fiber), an animal-derived fiber, a microorganism-derived fiber, or the like can be used. These fibers may be used alone or in combination of plural kinds as required. Among these, as the cellulose fiber, a plant fiber is preferably used, and a pulp fiber which is one of plant fibers is more preferably used. When the cellulose fiber is pulp fiber, the physical properties of the cellulose microfiber can be easily adjusted.

Examples of the plant fiber include wood pulp using broad-leaved trees, coniferous trees, and the like as a raw material, non-wood pulp using straw, bagasse, and the like as a raw material, and waste paper pulp (DIP) using recycled waste paper, broke, and the like as a raw material. These fibers may be used alone or in combination of plural kinds.

as the wood pulp, for example, chemical pulp such as hardwood kraft pulp (LKP) and softwood kraft pulp (NKP), mechanical pulp (TMP), waste paper pulp (DIP), and the like can be used. These pulps may be used alone or in combination of plural kinds.

The hardwood kraft pulp (LKP) may be bleached kraft pulp, unbleached kraft pulp, or semi-bleached kraft pulp. The softwood kraft pulp (NKP) may be softwood bleached kraft pulp, may be softwood unbleached kraft pulp, or may be softwood semi-bleached kraft pulp. The used paper pulp (DIP) may be magazine used paper pulp (MDIP), newspaper used paper pulp (NDIP), paper machine used paper pulp (WP), or other used paper pulp.

(additive (A))

The additive (A) contains at least one of an oxygen-containing acid compound of phosphorus and an oxygen-containing metal salt of phosphorus. Examples of the additive (a) include phosphorous acid compounds such as phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate, lithium dihydrogen phosphate, trilithium phosphate, dilithium hydrogen phosphate, lithium pyrophosphate, lithium polyphosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium polyphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium polyphosphate, phosphorous acid, sodium hydrogen phosphite, ammonium hydrogen phosphite, potassium hydrogen phosphite, sodium dihydrogen phosphite, sodium phosphite, lithium phosphite, potassium phosphite, magnesium phosphite, calcium phosphite, triethyl phosphite, triphenyl phosphite, and pyrophosphorous acid. These phosphoric acids and metal phosphate salts, phosphorous acids or metal phosphite salts may be used alone or in combination of two or more. Among them, sodium hydrogen phosphate or sodium hydrogen phosphite is preferably used. It is more preferable to use a phosphorous acid or a metal salt of phosphorous acid because yellowing of the cellulose fiber can be prevented.

When the additive (a) is added, the cellulose fibers may be in a dry state, a wet state, or a slurry state. The additive (a) may be in the form of powder or an aqueous solution. Among them, it is preferable to add the additive (a) in an aqueous solution state to the cellulose fibers in a dry state for the reason of high uniformity of the reaction.

The amount of the additive (A) added is preferably 1 to 10,000g, more preferably 100 to 5,000g, and particularly preferably 300 to 1,500g, based on 1kg of the cellulose fiber. If the amount is less than 1g, the effect of the addition of the additive (A) may not be obtained. On the other hand, even if the amount exceeds 10,000g, the effect of the addition of the additive (A) may not be further improved.

(additive (B))

The additive (B) contains at least one of urea and a urea derivative. Examples of the additive (B) include urea, thiourea, biuret, phenylurea, benzylurea, dimethylurea, diethylurea, and tetramethylurea. These ureas or urea derivatives may be used alone or in combination of two or more, respectively. Among them, urea is preferably used.

When heated, the additive (B) decomposes into isocyanic acid and ammonia as shown in the following reaction formula (1). Further, isocyanic acid has very high reactivity and forms hydroxyl groups and carbamate groups of cellulose as shown in the following reaction formula (2).

NH₂-CO-NH₂→HN＝C＝O+NH₃…(1)

Cell-OH+H-N＝C＝O→Cell-O-C-NH₂…(2)

The amount of the additive (B) to be added is preferably 0.01 to 100mol, more preferably 0.2 to 20mol, and particularly preferably 0.5 to 10mol based on 1mol of the additive (A). If the amount of addition is less than 0.01mol, the urethane may not be sufficiently introduced into the cellulose fibers, and the cellulose fibers may not be easily opened. On the other hand, even if the amount exceeds 100mol, the effect of urea addition may not be further improved.

(heating)

The heating temperature for heating the cellulose fiber to which the additive (a) and the additive (B) are added is preferably 100 to 210 ℃, more preferably 100 to 200 ℃, and particularly preferably 100 to 160 ℃. When the heating temperature is 100 ℃ or higher, the ester of the oxyacid of phosphorus can be introduced. In particular, when the heating temperature exceeds 210 ℃, the deterioration of the cellulose rapidly progresses, and may cause coloring and a decrease in viscosity. When the heating temperature exceeds 160 ℃, the B-type viscosity of the cellulose microfiber may be reduced and the light transmittance may be reduced.

The cellulose fibers to which the additive (A) and the additive (B) are added preferably have a pH of 3 to 12, more preferably 4 to 11, and particularly preferably 6 to 9 when heated. When the pH is low, esters and carbamates of oxyacids of phosphorus can be easily introduced. However, if the pH is less than 3, the deterioration of the cellulose may progress rapidly.

the heating of the cellulose fiber to which the additive (a) and the additive (B) are added is preferably performed until the cellulose fiber is dried. Specifically, the cellulose fibers are dried until the moisture content of the cellulose fibers is preferably 10% or less, more preferably 0.1% or less, and particularly preferably 0.001% or less. Of course, the cellulose fibers may be in an absolutely dry state without moisture.

The heating time of the cellulose fiber to which the additive (a) and the additive (B) are added is, for example, 1 to 1,440 minutes, preferably 10 to 180 minutes, and more preferably 30 to 120 minutes. If the heating time is too long, the introduction of the ester or carbamate of the oxoacid of phosphorus may be excessively advanced. In addition, if the heating time is too long, the cellulose fibers may be yellowed.

Examples of the device for heating the cellulose fibers to which the additive (a) and the additive (B) are added include a hot air dryer, a baking furnace, a heated kneader, a paper machine, and a dry pulp machine.

(pretreatment)

Before or after introducing the ester and carbamate of an oxyacid of phosphorus into the cellulose fibers, the cellulose fibers may be subjected to pretreatment such as beating, if necessary. By pretreating the pulp fibers before opening the cellulose fibers, the number of opening times can be greatly reduced, and the energy for opening can be reduced.

The pretreatment of the cellulose fibers can be carried out by physical or chemical methods, preferably physical and chemical methods. The pretreatment by a physical method and the pretreatment by a chemical method may be performed simultaneously or separately.

As the pretreatment by physical means, beating is preferably employed. When the cellulose fibers are beaten, the cellulose fibers are aligned. Whereby the cellulose fibers can be prevented from intertwining with each other (aggregation is prevented). From this point of view, beating is preferably performed until the degree of beating of the cellulose fibers is 700ml or less, more preferably 500ml or less, and particularly preferably 300ml or less. The freeness of the cellulose fibers was determined in accordance with JISP8121-2 (2012). Further, the beating may be performed using, for example, a refiner, or the like.

Examples of the pretreatment by a chemical method include hydrolysis of polysaccharide by an acid (acid treatment), hydrolysis of polysaccharide by an enzyme (enzyme treatment), swelling of polysaccharide by an alkali (alkali treatment), oxidation of polysaccharide by an oxidizing agent (oxidation treatment), reduction of polysaccharide by a reducing agent (reduction treatment), and the like. Among them, as the pretreatment by a chemical method, it is preferable to carry out an enzyme treatment, and more preferably 1 or 2 or more kinds of treatments selected from an acid treatment, an alkali treatment and an oxidation treatment are further carried out. The enzyme treatment and the alkali treatment are described below in this order.

As the enzyme used for the enzyme treatment, at least either one of cellulase-based enzymes and hemicellulase-based enzymes is preferably used, and both are more preferably used in combination. When these enzymes are used, the opening of cellulose fibers becomes easier. The cellulase enzyme causes the decomposition of cellulose in the presence of water. In addition, hemicellulase enzymes cause decomposition of hemicellulose in the presence of water.

Examples of the cellulase enzyme include enzymes produced by the genus Trichoderma (filamentous fungi), the genus Acremonium (filamentous fungi), the genus Aspergillus (filamentous fungi), the genus Phanerochaete (Phanerochaete, Basidiomycetes), the genus Trametes (Trametes, Basidiomycetes), the genus Humicola (Humicola, filamentous fungi), the genus Bacillus (Bacillus, bacteria), the genus Schizophyllum (Schizophyllum, Basidiomycetes), the genus Streptomyces (bacteria), and the genus Pseudomonas (Pseudomonas). These cellulase enzymes can be purchased as reagents or commercially available products. Examples of commercially available products include CellulosinT2 (HBI), Meicelase (Mingzhi Korea), Novozymes 188 (Novozymes), multifectCX10L (Genencor), and cellulase GC220 (Genencor).

Further, as the cellulase enzyme, any of EG (endoglucanase) and CBH (exoglucanase) may be used. EG and CBH may be used alone or in combination. In addition, the compound may be used in combination with a hemicellulase enzyme.

Examples of the hemicellulase enzyme include xylanase (xylanase) which is an enzyme that degrades xylan, mannanase (mannase) which is an enzyme that degrades mannan, and arabinase (arabinanase) which is an enzyme that degrades arabinan. In addition, pectinase, which is an enzyme that decomposes pectin, may also be used.

Hemicellulose is a polysaccharide other than pectins located between cellulose microfibrils of plant cell walls. Hemicellulose is various in kind and also varies depending on the kind of wood, and between wall layers of cell walls. In the secondary wall of the conifer, glucomannan is used as a main component; 4-O-methylglucuronoxylan is the main component in the secondary wall of broad-leaved trees. Therefore, in the case of obtaining cellulose microfibers from bleached softwood kraft pulp (NBKP), it is preferable to use mannanase. In addition, when cellulose microfibers are obtained from hardwood bleached kraft pulp (LBKP), xylanase is preferably used.

The amount of the enzyme added to the cellulose fiber is determined by, for example, the type of the enzyme, the type of wood (coniferous tree, hardwood tree) as a raw material, the type of mechanical pulp, and the like. The amount of the enzyme added to the cellulose fiber is preferably 0.1 to 3% by mass, more preferably 0.3 to 2.5% by mass, and particularly preferably 0.5 to 2% by mass. If the amount of the enzyme added is less than 0.1 mass%, the effect of the enzyme addition may be insufficient. On the other hand, if the amount of the enzyme added exceeds 3 mass%, cellulose may be saccharified and the yield of the cellulose microfibers may be reduced. Further, there is a problem that an increase in the effect commensurate with the increase in the amount added cannot be observed.

When a cellulase-based enzyme is used as the enzyme, the pH at the time of the enzyme treatment is preferably in a weakly acidic region (pH 3.0 to 6.9) from the viewpoint of reactivity of the enzyme reaction. On the other hand, when a hemicellulase enzyme is used as the enzyme, the pH at the time of the enzyme treatment is preferably in a weakly alkaline region (pH 7.1 to 10.0).

The temperature during the enzyme treatment is preferably 30 to 70 ℃, more preferably 35 to 65 ℃, and particularly preferably 40 to 60 ℃ when either of cellulase and hemicellulase is used as the enzyme. When the temperature during the enzyme treatment is 30 ℃ or higher, the enzyme activity is not easily decreased, and the treatment time can be prevented from being prolonged. On the other hand, when the temperature at the time of the enzyme treatment is 70 ℃ or lower, the inactivation of the enzyme can be prevented.

the time of the enzyme treatment can be determined by, for example, the kind of enzyme, the temperature of the enzyme treatment, the pH at the time of the enzyme treatment, and the like. Wherein the time for the enzyme treatment is generally 0.5 to 24 hours.

The enzyme is preferably inactivated after the enzyme treatment. Examples of the method for inactivating the enzyme include a method of adding an alkaline aqueous solution (preferably, pH10 or more, more preferably, pH11 or more), and a method of adding hot water at 80 to 100 ℃.

The method of the alkali treatment will be described below.

As a method of alkali treatment, for example, there is a method of immersing cellulose fibers into which an ester of an oxyacid of phosphorus or the like is introduced in an alkaline solution.

The alkali compound contained in the alkaline solution may be an inorganic alkali compound or an organic alkali compound. Examples of the inorganic basic compound include hydroxides of alkali metals or alkaline earth metals, carbonates of alkali metals or alkaline earth metals, and oxyacids of phosphorus of alkali metals or alkaline earth metals. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the alkaline earth metal hydroxide include calcium hydroxide and the like. Examples of the carbonate of an alkali metal include lithium carbonate, lithium hydrogencarbonate, potassium carbonate, potassium hydrogencarbonate, sodium carbonate, sodium hydrogencarbonate, and the like. Examples of the carbonate of an alkaline earth metal include calcium carbonate. Examples of the alkali metal salt of phosphorus with an oxygen acid include lithium phosphate, potassium phosphate, trisodium phosphate, and disodium hydrogen phosphate. Examples of the alkaline earth metal phosphate include calcium phosphate and calcium hydrogen phosphate.

Examples of the organic basic compound include ammonia, aliphatic amines, aromatic amines, aliphatic ammonium, aromatic ammonium, heterocyclic compounds, and hydroxides, carbonates, phosphates thereof. Specifically, for example, ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, N-dimethyl-4-aminopyridine, ammonium carbonate, ammonium bicarbonate, diammonium hydrogen phosphate, and the like can be exemplified.

The solvent of the alkaline solution may be any of water and an organic solvent, and is preferably a polar solvent (a polar organic solvent such as water or alcohol), and more preferably an aqueous solvent containing at least water.

The pH of the alkaline solution at 25 ℃ is preferably 9 or more, more preferably 10 or more, and particularly preferably 11 to 14. When the pH is 9 or more, the yield of the cellulose microfine fibers is improved. In particular, when the pH exceeds 14, the handling property of the alkaline solution is lowered.

(cleaning)

The cellulose fibers into which the esters of oxyacids of phosphorus and the like have been introduced are washed before opening. By washing the cellulose fibers, byproducts and unreacted materials can be washed away. Further, if the cleaning is performed before the alkali treatment in the pretreatment, the amount of the alkali solution used in the alkali treatment can be reduced.

The washing of the cellulose fibers can be performed using, for example, water or an organic solvent.

(fiber opening)

The cellulose fibers into which the ester of oxyacid of phosphorus and carbamate have been introduced are washed and then opened (finely divided). By this opening, the pulp fiber is microfibrillated to become a cellulose microfiber (cellulose nanofiber).

When the cellulose fibers are opened, the cellulose fibers are preferably preliminarily prepared in a slurry form. The solid content concentration of the slurry is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, and particularly preferably 1.0 to 5.0% by mass. When the solid content concentration is within the above range, the fiber can be efficiently opened.

The opening of the cellulose fibers can be performed by selecting 1 or 2 or more types of means from, for example, homogenizers such as a high-pressure homogenizer and a high-pressure homogenizer, stone-mortar type grinders such as a grinder and an attritor, lapping machines such as a conical lapping machine and a disc lapping machine, and various bacteria. Among these, an apparatus and a method for refining cellulose fibers by a water stream, particularly a high-pressure water stream, are preferably used for the fiber opening. The apparatus and method can provide cellulose microfibers with very high dimensional uniformity and dispersion uniformity. On the other hand, for example, when a grinder that grinds cellulose fibers between rotating grindstones is used, it is difficult to uniformly refine the cellulose fibers, and in some cases, a part of fiber lumps that are not opened may remain.

As a grinder used for opening cellulose fibers, massscoloider, a danshin industrial co. Examples of the device for refining by the high-pressure water flow include StarBurst (registered trademark) of sugino machine corporation and Nanovater (registered trademark) of jitian machinery corporation. In addition, as the cellulose fiber opening used in the high speed rotation type homogenizer, there are Clearmix-11S manufactured by M-Technique.

The present inventors have found that, in a method of grinding between rotating grindstones and a method of refining fibers by a high-pressure water stream, when cellulose fibers are individually opened and the obtained fibers are observed under a microscope, the fiber width of the fibers obtained by the method of refining fibers by a high-pressure water stream is more uniform.

The opening by the high-pressure water flow is suitably carried out by: the dispersion of cellulose fibers is pressurized by a supercharger to, for example, 30MPa or more, preferably 100MPa or more, more preferably 150MPa or more, and particularly preferably 220MPa or more (high pressure condition), and discharged from a nozzle having a pore diameter of 50 μm or more, and the pressure is reduced such that the pressure difference is, for example, 30MPa or more, preferably 80MPa or more, and more preferably 90MPa or more (reduced pressure condition). The pulp fibers are opened by the cracking phenomenon caused by the pressure difference. When the pressure under the high-pressure condition is low or the pressure difference from the high-pressure condition to the reduced-pressure condition is small, the fiber opening efficiency is lowered, and repeated opening (blowing from a nozzle) is necessary in order to obtain a desired fiber width.

As the device for opening the fiber by the high-pressure water flow, a high-pressure homogenizer is preferably used. The high-pressure homogenizer is a homogenizer having a capability of ejecting a slurry of cellulose fibers at a pressure of, for example, 10MPa or more, preferably 100MPa or more. When cellulose fibers are treated by a high-pressure homogenizer, the cellulose fibers are subjected to collision with each other, pressure difference, micro cavitation (micro cavitation), and the like, and fiber opening of the cellulose fibers occurs efficiently. Therefore, the number of opening processes can be reduced, and the efficiency of producing cellulose microfibers can be improved.

As the high-pressure homogenizer, it is preferable to use a device in which a slurry of cellulose fibers is allowed to collide straight on the front side. Specifically, the material is, for example, a head-on collision type high-pressure homogenizer (MICROFLUIDIZER (registered trademark), wet jet mill). In this apparatus, 2 upstream side flow paths were formed so that the pressurized slurry of cellulose fibers was collided with each other at the confluence section. The pulp of cellulose fibers collides at the confluence section, and the pulp of cellulose fibers after the collision flows out from the downstream flow path. The downstream side flow path is provided perpendicular to the upstream side flow path, and the upstream side flow path and the downstream side flow path form a T-shaped flow path. When such a front collision type high-pressure homogenizer is used, the energy supplied from the high-pressure homogenizer is converted to collision energy to the maximum extent, and therefore, the cellulose fibers can be more efficiently opened.

The opening of the cellulose fibers is preferably performed in such a manner that the average fiber width, average fiber length, water retention, crystallinity, peak value of the pseudo particle size distribution, and pulp viscosity of the obtained cellulose microfibers reach the desired values or are evaluated.