JP7250455B2 - Composition containing anion-modified cellulose nanofibers - Google Patents

Description

The present invention relates to compositions containing anion-modified cellulose nanofibers. Specifically, it relates to a composition containing anion-modified cellulose nanofibers that are less likely to be colored when heated.

When cellulose as a raw material is treated in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (hereinafter referred to as TEMPO) and sodium hypochlorite as an oxidizing agent, cellulose carboxyl groups can be efficiently introduced onto the surface of the microfibrils. It is known that mechanical treatment of cellulose into which carboxyl groups have been introduced in water using a mixer or the like can convert the cellulose into cellulose nanofibers having a nanoscale fiber diameter (Patent Document 1).

Japanese Unexamined Patent Application Publication No. 2008-001728

However, the cellulose nanofiber disclosed in Patent Literature 1 has a problem of coloring when heated. When such cellulose nanofibers are heat-processed to obtain a product, the resulting product shows discoloration, which poses a problem that it is difficult to use it industrially.

Accordingly, an object of the present invention is to provide a composition containing anion-modified cellulose nanofibers that is less likely to be colored when heated.

As a result of intensive studies, the present inventors found that a phosphine compound (general formula: RR'R''P) (R, R ', R'' are hydrogen or an organic group), it was found that the coloration of anion-modified cellulose nanofibers due to heat is suppressed.

The present invention includes, but is not limited to, the following.
(1) A composition containing nanofibers of anion-modified cellulose and a phosphine compound.
(2) The composition according to (1), wherein the phosphine compound has a hydroxyl group.
(3) The composition according to (1) or (2), wherein the phosphine compound is one or more compounds selected from the group consisting of trishydroxypropylphosphine, trishydroxyethylphosphine, and trishydroxymethylphosphine. .
(4) The composition according to any one of (1) to (3), wherein the anion-modified cellulose has a carboxyl group.
(5) The anion-modified cellulose according to any one of (1) to (4), wherein the anion-modified cellulose is cellulose having carboxyl groups obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent. Composition.
(6) The composition according to any one of (1)-(5), wherein the composition is a dispersion.
(7) The composition according to (6), wherein the dispersion medium of the dispersion is water or an organic solvent, or a mixture thereof.
(8) A composition obtained by at least partially removing the dispersion medium from the dispersion described in (6) or (7).
(9) The composition according to any one of (1) to (5), which is in the form of a film.

According to the method of the present invention, it is possible to obtain an anion-modified cellulose nanofiber-containing composition that is less likely to be colored when heated. The composition of the present invention also has the effect that wrinkles are less likely to occur on the surface when formed into a film (membrane).

1 is a photograph of a film-like dried product of Example 1. FIG. On the same date as the filing of this application, I submitted the color photograph of Fig. 1 in the article submission form. 1 is a photograph of a film-like dried product of Comparative Example 1. FIG. On the same date as this application, I submitted the color photograph of FIG. 4 is a photograph of a film-like dried product of Comparative Example 2. FIG. On the same date as this application, I submitted the color photograph of FIG.

In the present invention, by allowing a phosphine compound to coexist with nanofibers obtained by defibrating cellulose (anion-modified cellulose) into which an anionic group such as a carboxyl group has been introduced, the anion-modified cellulose nanofibers are colored during heating. is suppressed.

<Cellulose>
In the present invention, cellulose means a polysaccharide having a structure in which D-glucopyranose (also referred to simply as "glucose residue" or "anhydroglucose") is linked by β-1,4 bonds. Cellulose is generally classified into natural cellulose, regenerated cellulose, fine cellulose, microcrystalline cellulose excluding non-crystalline regions, etc., according to its origin, production method, and the like. In the present invention, any of these celluloses can be used as a raw material for anion-modified cellulose.

Examples of natural cellulose include bleached or unbleached pulp (bleached wood pulp or unbleached wood pulp); linters, purified linters; cellulose produced by microorganisms such as acetic acid bacteria. Raw materials for bleached or unbleached pulp are not particularly limited, and examples thereof include wood, cotton, straw, bamboo, hemp, jute, and kenaf. Also, the method for producing the bleached pulp or the unbleached pulp is not particularly limited, and may be a mechanical method, a chemical method, or a combination of the two. Examples of bleached pulp or unbleached pulp classified by manufacturing method include mechanical pulp (thermomechanical pulp (TMP), groundwood pulp), chemical pulp (softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) ), softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP) and other kraft pulps). Further, dissolving pulp may be used in addition to paper pulp. Dissolving pulp is pulp that has been chemically refined, and is mainly used by dissolving it in chemicals, and serves as a main raw material for artificial fibers, cellophane, and the like.

Examples of regenerated cellulose include those obtained by dissolving cellulose in some solvent such as cuprammonium solution, cellulose xanthate solution, morpholine derivative, and spinning again.
The fine cellulose is obtained by subjecting cellulosic materials such as the natural cellulose and regenerated cellulose to depolymerization (for example, acid hydrolysis, alkaline hydrolysis, enzymatic decomposition, explosion treatment, vibration ball mill treatment, etc.). and those obtained by mechanically processing the above cellulosic materials.

<Anion-modified cellulose>
(1) Anion Modification Anion modification is the introduction of an anionic group into cellulose, specifically the introduction of an anionic group into a pyranose ring by an oxidation or substitution reaction. In the present invention, the oxidation reaction means a reaction of directly oxidizing a hydroxyl group of a pyranose ring to a carboxyl group. Further, in the present invention, a substitution reaction means a reaction for introducing an anionic group into a pyranose ring by a substitution reaction other than the oxidation.

(2) Carboxylation Carboxylated (oxidized) cellulose can be used as anion-modified cellulose. The carboxy group in the present invention means -COOH (acid form) or -COOM (salt form) (wherein M is a metal ion). Carboxylated cellulose (also referred to as “oxidized cellulose”) can be obtained by carboxylating (oxidizing) the above cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.6 mmol/g to 3.0 mmol/g, more preferably 1.0 mmol/g to 2.0 mmol, relative to the absolute dry mass of anion-modified cellulose or anion-modified cellulose nanofibers. /g is more preferred.

The carboxyl group content of anion-modified cellulose or anion-modified cellulose nanofibers can be measured by the following method:
60 ml of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. and calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid, where the change in conductivity is gradual, using the following formula:
Carboxyl group amount [mmol/g carboxylated cellulose]=a [ml]×0.05/carboxylated cellulose mass [g].

As an example of a carboxylation (oxidation) method, a cellulose feedstock is oxidized in water with an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, and mixtures thereof. You can mention how to do it. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface, resulting in a cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or carboxylate group ( ^-COO- ) on the surface. can be obtained. Although the concentration of cellulose during the reaction is not particularly limited, it is preferably 5% by mass or less.

An N-oxyl compound means a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy TEMPO). The amount of the N-oxyl compound to be used is not particularly limited as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, it is preferably 0.01 mmol to 10 mmol, more preferably 0.01 mmol to 1 mmol, even more preferably 0.05 mmol to 0.5 mmol, relative to 1 g of absolute dry cellulose. Further, it is preferable that the concentration is about 0.1 mmol/L to 4 mmol/L with respect to the reaction system.

Bromides are compounds containing bromine, examples of which include alkali metal bromides that can be dissociated and ionized in water. Also, iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, and even more preferably 0.5 mmol to 5 mmol, relative to 1 g of absolute dry cellulose. The modification is modification by an oxidation reaction.

Known oxidizing agents can be used, for example, halogens, hypohalous acids, halogenous acids, perhalogenates or salts thereof, halogen oxides, peroxides and the like can be used. Among them, sodium hypochlorite is preferable because it is inexpensive and has less environmental load. An appropriate amount of the oxidizing agent to be used is, for example, preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, even more preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol, relative to 1 g of absolute dry cellulose. . Further, for example, 1 mol to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

The oxidation process of cellulose allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4°C to 40°C, and may be room temperature of about 15°C to 30°C. Since carboxyl groups are generated in the cellulose as the reaction progresses, the pH of the reaction solution decreases. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8-12, preferably about 10-11. Water is preferable as the reaction medium because it is easy to handle and less likely to cause side reactions. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 hours to 6 hours, for example, about 0.5 hours to 4 hours.

Moreover, the oxidation reaction may be carried out in two steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the reaction in the first step, again under the same or different reaction conditions, the reaction can be efficiently It can be oxidized well.

Another example of the carboxylation (oxidation) method is a method of oxidizing by contacting a cellulose raw material with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring and causes degradation of the cellulose chain. The ozone concentration in the gas containing ozone is preferably 50 g/m ³ to 250 g/m ³ , more preferably 50 g/m ³ to 220 g/m ³ . The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by mass, more preferably 5 to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. . The ozone treatment temperature is preferably 0°C to 50°C, more preferably 20°C to 50°C. The ozone treatment time is not particularly limited, but is about 1 minute to 360 minutes, preferably about 30 minutes to 360 minutes. When the ozone treatment conditions are within these ranges, cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the additional oxidation treatment is not particularly limited, but examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

The amount of carboxyl groups in the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time. The amount of carboxyl groups in the anion-modified cellulose and the amount of carboxyl groups when the anion-modified cellulose is used as nanofibers are usually the same.

(2) Carboxyalkylation Cellulose into which a carboxyalkyl group such as a carboxymethyl group has been introduced can be used as the anion-modified cellulose. The carboxyalkyl group in the present invention means -RCOOH (acid form) or -RCOOM (salt form). Here, R is an alkylene group such as a methylene group or ethylene group, and M is a metal ion. Since the carboxyalkyl group contains a carboxyl group moiety (-COOH or -COOM moiety), in the present invention, when referring to cellulose "having a carboxyl group", the above carboxylation (oxidation ) include not only cellulose but also carboxyalkylated cellulose.

Carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. Preferably, the degree of carboxyalkyl substitution per anhydroglucose unit of the cellulose is less than 0.40. Furthermore, when the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably less than 0.40. If the degree of substitution is 0.40 or more, the dispersibility of the cellulose nanofibers is lowered. Also, the lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. Considering workability, the degree of substitution is particularly preferably 0.02 to 0.35, more preferably 0.10 to 0.30. The anhydroglucose unit means an individual anhydroglucose (glucose residue) constituting cellulose, and the degree of carboxyalkyl substitution refers to the hydroxyl group (—OH) in the glucose residue constituting cellulose. The percentage of those substituted with ether groups (-ORCOOH or -ORCOOM) (the number of carboxyalkyl ether groups per glucose residue) is shown.

An example of a method for producing carboxyalkylated cellulose includes the following steps. The modification is modification by a substitution reaction. Carboxymethylated cellulose will be described as an example.

i) Mixing the raw material with the solvent and the mercerizing agent, and mercerizing at a reaction temperature of 0° C. to 70° C., preferably 10° C. to 60° C., and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. the process of processing,
ii) then, 0.05 to 10.0 times mol of a carboxymethylating agent per glucose residue is added, the reaction temperature is 30° C. to 90° C., preferably 40° C. to 80° C., and the reaction time is 30 minutes to 10 hours; A step of conducting the etherification reaction preferably for 1 hour to 4 hours.

The above-mentioned cellulose raw material can be used as the bottom raw material. As the solvent, 3 to 20 times by weight of water or a lower alcohol, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc. alone, or two Mixed media of more than one species can be used. When a lower alcohol is mixed, the mixing ratio is preferably 60% by mass to 95% by mass. As the mercerizing agent, it is preferable to use an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, in an amount of 0.5 to 20 times the moles of the anhydroglucose residue of the starting material.

As described above, the degree of carboxymethyl substitution per glucose unit of cellulose is less than 0.40, preferably 0.01 or more and less than 0.40. By introducing carboxymethyl substituents into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which carboxymethyl substituents have been introduced can be nano-fibrillated. If the number of carboxymethyl substituents per glucose unit is less than 0.02, nano-fibrillation may not be sufficient. The degree of carboxyalkyl substitution in the anion-modified cellulose is usually the same as the degree of carboxyalkyl substitution when the anion-modified cellulose is made into nanofibers.

The degree of carboxymethyl substitution per glucose unit can be measured by the following method:
About 2.0 g of carboxymethylated cellulose fiber (absolute dry) is precisely weighed and placed in a 300 mL conical flask with a common stopper. 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 900 mL of methanol is added and shaken for 3 hours to convert carboxymethylated cellulose salt (CM cellulose) into hydrogenated CM cellulose. 1.5 to 2.0 g of hydrogenated CM cellulose (absolutely dried) is precisely weighed and put into a 300 mL Erlenmeyer flask equipped with a common stopper. Hydrogenated CM-cellulose is wetted with 15 mL of 80% by mass methanol, 100 mL of 0.1 N NaOH is added, and shaken at room temperature for 3 hours. Excess NaOH was back-titrated with 0.1 N H2SO4 using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) is calculated by the formula:
A=[(100×F′−(0.1N H ₂ SO ₄ ) (mL)×F)×0.1]/(absolute dry weight of hydrogen-type CM cellulose (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogenated CM-cellulose
F: factor of 0.1N _H2SO4 F': factor of 0.1N _NaOH .

The degree of substitution with carboxyalkyl groups other than carboxymethyl groups can also be measured in the same manner as described above.
(3) Esterification Esterified cellulose can also be used as anion-modified cellulose. Examples of the esterification method include a method of mixing a cellulose raw material with powder or an aqueous solution of a phosphoric acid compound, a method of adding an aqueous solution of a phosphoric acid compound to a slurry of a cellulose raw material, and the like. Phosphoric acid compounds include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among the above, a compound having a phosphate group is preferable because it is low cost, easy to handle, and can introduce a phosphate group into the cellulose of the pulp fiber to improve defibration efficiency. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, phosphorus Tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. Phosphate groups can be introduced into cellulose by using one or more of these in combination. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of introduction of phosphate group, easy fibrillation in the fibrillation process described below, and easy industrial application is preferred. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Further, it is desirable to use the phosphoric acid-based compound in the form of an aqueous solution, since the reaction can proceed uniformly and the efficiency of introduction of the phosphoric acid group is increased. The pH of the aqueous solution of the phosphoric acid-based compound is preferably 7 or less because the efficiency of introducing phosphoric acid groups is increased, but from the viewpoint of suppressing hydrolysis of pulp fibers, pH 3 to 7 is preferable.

Examples of the method for producing the phosphorylated cellulose include the following method. A phosphoric acid compound is added to a suspension of a cellulosic raw material having a solid concentration of 0.1% by mass to 10% by mass while stirring to introduce a phosphoric acid group into the cellulose. When the cellulosic raw material is 100 parts by mass, the amount of the phosphoric acid compound added is preferably 0.2 parts by mass to 500 parts by mass, and 1 part by mass to 400 parts by mass, as the elemental amount of phosphorus. is more preferred. If the proportion of the phosphoric acid-based compound is at least the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the above upper limit is exceeded, the effect of improving the yield reaches a ceiling, which is not preferable from the viewpoint of cost.

In addition to the phosphoric acid-based compound, powders or aqueous solutions of other compounds may be mixed. The compound other than the phosphoric acid-based compound is not particularly limited, but a basic nitrogen-containing compound is preferable. "Basic" here is defined as a pink to red color of the aqueous solution in the presence of the phenolphthalein indicator or pH of the aqueous solution greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as the effect of the present invention is exhibited, but a compound having an amino group is preferable. Examples include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like. Among them, urea is preferable because it is inexpensive and easy to handle. The amount of the other compound added is preferably 2 parts by mass to 1000 parts by mass, more preferably 100 parts by mass to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0°C to 95°C, more preferably 30°C to 90°C. Although the reaction time is not particularly limited, it is about 1 minute to 600 minutes, more preferably 30 minutes to 480 minutes. When the esterification reaction conditions are within these ranges, cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of phosphate-esterified cellulose is improved. After dehydrating the obtained phosphate-esterified cellulose suspension, it is preferable to heat-treat at 100° C. to 170° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, it is preferable to heat at 130° C. or less, preferably 110° C. or less while water is contained in the heat treatment, and heat at 100° C. to 170° C. after removing the water.

The degree of phosphate group substitution per glucose unit of the phosphated cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which a phosphate group has been introduced can be easily nano-fibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, the nanofibers may not be obtained due to swelling or dissolution. In order to defibrate efficiently, it is preferable to wash the cellulose-based raw material obtained above with cold water after boiling it. Modification by these esterifications is modification by a substitution reaction. The degree of substitution in the anion-modified cellulose and the degree of substitution when the anion-modified cellulose is used as nanofibers are usually the same.

(4) Anion-Modified Cellulose Anion-modified cellulose can be obtained by subjecting the raw material cellulose to anion modification as exemplified above. By anionically modifying cellulose to obtain anionically modified cellulose, it becomes possible to bond with a basic phosphine compound. As for the type of anion-modified cellulose, an anion-modified cellulose having a carboxyl group, such as carboxylated cellulose or carboxyalkylated cellulose, is preferred because the effect of suppressing coloration by coexistence of a phosphine compound is most commonly observed. In particular, in carboxylated cellulose obtained by oxidizing cellulose with an N-oxyl compound and an oxidizing agent, carboxyl groups are uniformly introduced, and a phosphine compound binds to the carboxyl groups to form a phosphine compound. Uniform distribution in anion-modified cellulose or anion-modified cellulose nanofibers is preferable because a high coloration suppression effect can be obtained.

In the present invention, as the anion-modified cellulose, one that maintains at least a part of its fibrous shape even when dispersed in water or an organic solvent is used. Nanofibers cannot be obtained by using materials that do not maintain their fibrous shape (that is, materials that dissolve). The expression that at least a part of the fibrous shape is maintained when dispersed means that a fibrous substance can be observed when an anion-modified cellulose dispersion is observed with an electron microscope. In addition, anion-modified cellulose is preferable, since a peak of cellulose type I crystals can be observed when measured by X-ray diffraction.

The degree of crystallinity of cellulose in the anion-modified cellulose is preferably 50% or more, more preferably 60% or more for crystalline type I. By adjusting the crystallinity to the above range, it is possible to sufficiently obtain crystalline cellulose fibers that do not dissolve even after the fibers are refined by fibrillation. The crystallinity of cellulose can be controlled by the crystallinity of the raw material cellulose and the degree of anion modification. The method for measuring the crystallinity of anion-modified cellulose is as follows:
A sample is placed in a glass cell and measured using an X-ray diffraction measurement device (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using the method of Segal et al. Using the diffraction intensity at 2θ = 10° to 30° in the X-ray diffraction diagram as a baseline, the diffraction intensity at 2θ = 22.6° at the 002 plane and 2θ = It is calculated from the diffraction intensity of the amorphous portion at 18.5° by the following equation.
Xc=(I002c−Ia)/I002c×100
Xc: Crystallinity of type I of cellulose (%)
I002c: 2θ=22.6°, diffraction intensity of 002 plane Ia: 2θ=18.5°, diffraction intensity of amorphous portion.

The proportion of cellulose type I crystals in the anion-modified cellulose and the proportion of cellulose type I crystals when the anion-modified cellulose is used as nanofibers are usually the same.
<Nanofibers of anion-modified cellulose>
Nanofibers of anion-modified cellulose can be obtained by mechanically defibrating the above-described anion-modified cellulose.

For defibration, although not limited to this, a dispersion of anion-modified cellulose is prepared. The dispersion medium is preferably water for ease of handling, but may contain a polar organic solvent that has a high affinity for hydroxyl groups in cellulose. Such organic solvents include methanol, ethanol, isopropanol, isobutanol, sec-butanol, tert-butanol, methyl cellosolve, ethyl cellosolve, ethylene glycol, glycerin, ethylene glycol dimethyl ether, 1,4-dioxane, tetrahydrofuran, acetone, Methyl ethyl ketone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide and the like can be mentioned. These may be used alone or in combination of two or more. The concentration of anion-modified cellulose in the dispersion is preferably 0.01% by mass to 10% by mass in consideration of workability during fibrillation.

Although the device used for fibrillation is not limited, it is preferable to use a device capable of applying a strong shearing force to the dispersion, such as a high-speed rotation type, colloid mill type, high pressure type, roll mill type, and ultrasonic type. For efficient fibrillation, it is preferable to use a wet high-pressure or ultrahigh-pressure homogenizer capable of applying a pressure of 50 MPa or more to the dispersion and a strong shearing force. The pressure is more preferably 100 MPa or higher, still more preferably 140 MPa or higher. A high-pressure or ultra-high-pressure homogenizer pressurizes (high-pressures) a fluid with a pump and ejects it from very fine gaps provided in the flow path. Equipment for emulsifying, dispersing, crushing, pulverizing, and ultra-fine. Prior to fibrillation and dispersion treatment with a high-pressure homogenizer, pretreatment can be performed using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer, if necessary.

A dispersion of nanofibers of anion-modified cellulose can be obtained by the above defibration. Anion-modified cellulose nanofibers are fibers having an average fiber diameter of about 3 nm to 500 nm, preferably about 3 nm to 150 nm, more preferably about 3 nm to 20 nm. The aspect ratio is 30 or more, preferably 50 or more, more preferably 100 or more. Although the upper limit of the aspect ratio is not limited, it is about 500 or less.

The average fiber diameter and average fiber length of nanofibers of anion-modified cellulose are measured using an atomic force microscope (AFM) when the diameter is less than 20 nm, and a field emission scanning electron microscope (FE-SEM) when the diameter is 20 nm or more. , can be measured by analyzing 200 randomly selected fibers and calculating the average. Also, the aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length/average fiber diameter.

The dispersion of anion-modified cellulose nanofibers may be dried (removing the dispersion medium) based on the drying method described later, but since coloration may occur during drying, the phosphine compound described later is allowed to coexist before drying. It is preferable to let

<Phosphine compound>
The composition of the present invention contains a phosphine compound in addition to the anion-modified cellulose nanofibers. As a result, coloring of the nanofibers during heating is suppressed.

A phosphine compound is a phosphorus compound represented by the general formula RR'R''P (wherein R, R', and R'' are hydrogen or an organic group). In the present invention, the types of R, R′, and R″ in the above general formula are not limited, but tertiary phosphines in which R, R′, and R″ are all organic groups are highly basic and anionic cellulose. It is most preferable because of its high binding strength with As for the type of the organic group, for example, when water is selected as the dispersion medium, R, R′, and R″ in the above general formula are alkyl having about 1 to 3 carbon atoms in consideration of affinity with water. It is preferable to use a phosphine compound as a group, and when an organic solvent is selected as a solvent, one having a larger number of carbon atoms may be appropriately selected. Among phosphine compounds, those having a hydroxyl group are preferred because they are highly stable in water and air and are excellent in handleability. Examples of such phosphine compounds include, but are not limited to, tris(hydroxypropyl)phosphine, tris(hydroxyethyl)phosphine), tris(hydroxymethyl)phosphine, and the like.

The content of the phosphine compound in the composition can be appropriately determined according to the type of phosphine compound used, the degree of anion modification of the anion-modified cellulose nanofiber, and the like. For example, it may be added in an amount of about 10% to 150%, preferably 30% to 120%, more preferably 50%, relative to the amount (number of moles) of anionic groups to which the phosphine compound can bind. % to 100%.

The phosphine compound may be added when the cellulose is anion-modified, may be added to the anion-modified cellulose dispersion before fibrillation, or may be added to the anion-modified cellulose nanofiber dispersion after fibrillation. Alternatively, it may be mixed with anion-modified cellulose nanofibers from which the dispersion medium has been removed. However, considering the favorable progress of the anion modification reaction, it is better to add the phosphine compound at least after the anion modification of the cellulose. Further, since coloration may occur when removing (drying) the dispersion medium from the dispersion of anion-modified cellulose nanofibers, it is preferable to add the phosphine compound before drying the dispersion. Therefore, the phosphine compound is preferably added to the anion-modified cellulose dispersion or the anion-modified cellulose nanofiber dispersion. Furthermore, the present inventors have found that the amount of energy required for defibration can be reduced if a phosphine compound is contained during fibrillation of anion-modified cellulose. Therefore, the phosphine compound is most preferably added to the anion-modified cellulose dispersion before defibration.

When the anion-modified cellulose is a cellulose having carboxyl groups, the carboxyl groups of the anion-modified cellulose may be converted to acid form (COOH) before adding the phosphine compound. By converting the carboxyl group of the anion-modified cellulose to an acid form before the addition of the phosphine compound, the bonding between the phosphine compound and the anion-modified cellulose is enhanced, and the effects of the present invention can be obtained to a greater extent. A method for converting to an acid form is not particularly limited, and examples include a method of adding an acid, a method of contacting an acidic ion exchange resin and an anion-modified cellulose, and the like. When an acid is added, the type of acid used is not particularly limited, and mineral acids such as hydrochloric acid, sulfuric acid, and the like, which are versatile and readily available, may be used. Examples of acidic ion exchange resins include strongly acidic cation exchange resins and weakly acidic cation exchange resins.

The pH of the anion-modified cellulose dispersion to be subjected to the fibrillation step may be appropriately adjusted using an acid or an alkali, but the range of neutral to weakly alkaline (pH 6.0 to 9.0, preferably pH 7.0 to 8) .5) is preferred. For example, when an anion-modified cellulose having a carboxyl group is converted to an acid form by adding an acid and the pH of the dispersion is acidic, a phosphine compound having a hydroxyl group is added to neutralize the pH of the dispersion. It may be adjusted to a weakly alkaline range.

<Composition containing anion-modified cellulose nanofibers and a phosphine compound>
The composition of the present invention contains anion-modified cellulose nanofibers and a phosphine compound. The form of the composition is not particularly limited, and may be in the form of a dispersion in which anion-modified cellulose nanofibers are dispersed in a dispersion medium, or in a form in which at least part of the dispersion medium is removed from the dispersion. good too.

When the composition is in the form of a dispersion, the type of dispersion medium for the dispersion is not limited, and may be water or organic, depending on the use of the dispersion, as in the case of the dispersion for fibrillating the anion-modified cellulose described above. A solvent or a mixture thereof can be selected as appropriate. From the point of view of ease of handling, the dispersion medium is preferably water, but is not limited to this. When using an organic solvent, the kind is not specifically limited. For example, although not limited to this, a dispersion using various organic solvents as a dispersion medium can be produced by performing solvent substitution from a dispersion using water as a dispersion medium.

In addition to the anion-modified cellulose nanofibers, the phosphine compound, and the dispersion medium, the dispersion may contain various additives required depending on the application.
The composition may be in the form obtained by removing all or part of the dispersion medium from the dispersion, as described above. Removal of the dispersion medium from the dispersion can be performed using, for example, centrifugal dehydration, vacuum dehydration, pressure dehydration type dehydrator, and combinations thereof. Alternatively, the dispersion medium can be removed by, for example, spray drying, squeezing, air drying, hot air drying, vacuum drying, and the like. The drying device is not particularly limited, but may be a continuous tunnel drying device, a band drying device, a vertical drying device, a vertical turbo drying device, a multi-stage disk drying device, a ventilation drying device, a rotary drying device, a flash drying device, or a spray drying device. Dryer dryer, spray dryer, cylindrical dryer, drum dryer, belt dryer, screw conveyor dryer, rotary dryer with heating tube, vibration transport dryer, batch type box dryer, ventilation dryer, vacuum Box dryers, agitator dryers, etc., and combinations thereof are included.

When the composition is in a form obtained by removing the dispersion medium from the dispersion, the composition may have various forms such as film, powder, and gel. When the composition of the present invention is formed into a film-like shape, it is possible to form a film with a smooth surface that is less likely to wrinkle. not a thing In the present invention, the term "film-like" refers to a thin film shape having a thickness of about 0.1 μm to 100 μm, preferably about 1 μm to 50 μm. A method for forming the film is not particularly limited. The dispersion may be spread thinly to a predetermined thickness and then dried. For example, among the drying devices described above, a device capable of forming a thin film may be used as appropriate, and such a drying device may be, for example, a drum or a belt that forms a thin film with a blade, die, or the like and dries it. A drying device and a belt drying device can be mentioned.

The concentrations of the anion-modified cellulose nanofibers, the phosphine compound, and the dispersion medium in the composition can be adjusted according to the form of the composition (for example, the form dispersed in the dispersion medium, or the dispersion medium dispersed in the dispersion medium). form), and the types of anion-modified cellulose nanofibers and phosphine compounds. The composition may contain 0 to 100,000 parts by mass of the dispersion medium, depending on the degree of removal of the dispersion medium, for example, when the absolute dry weight of the anion-modified cellulose nanofiber is 100 parts. For example, when the composition is in the form of a dispersion in which anion-modified cellulose nanofibers are dispersed in a dispersion medium, the concentration of the anion-modified cellulose nanofibers in the dispersion is not limited to this, but is preferably 0.5. 01% by mass to 20% by mass, more preferably 0.1% by mass to 10% by mass. Further, when the composition is in a form in which at least part of the dispersion medium is removed from the dispersion, the ratio of the dispersion medium in the composition is not limited to this, but the anion-modified cellulose nanofiber is 100 parts by mass. It is preferably about 0 parts by mass to 20 parts by mass. In addition, the content ratio of the anion-modified cellulose nanofibers and the phosphine compound in the composition varies depending on the degree of removal of the dispersion medium. The amount of the phosphine compound is about 10% to 150%, preferably 30% to 120%, more preferably 50% to 100%, relative to the amount (number of moles) of .

The composition of the present invention is characterized by a small degree of coloring when dried by heating. In addition, when a film is formed by applying the composition onto a base material, a film having a smooth surface that is less prone to wrinkles can be formed.

The use of the composition of the present invention is not particularly limited, but since the composition of the present invention has the property of being resistant to coloration when heated, it is used in applications where heat processing occurs, and in applications where coloring or discoloration is undesirable. It is considered that it can be used particularly optimally for In addition, since a smooth surface can be obtained with less wrinkles when formed into a film, it is thought that it can be optimally used for applications in which a thin film-like shape is formed. However, you may use for uses other than these. The field in which the composition of the present invention is used is not particularly limited, and various fields in which additives are generally used, such as food, beverages, cosmetics, pharmaceuticals, paper manufacturing, various chemical products, paints, sprays, pesticides, and civil engineering. , building materials, electronic materials, flame retardants, household goods, adhesives, detergents, fragrances, lubricating compositions, thickeners, gelling agents, pastes, food additives, excipients, additives for paints Additives for adhesives, additives for papermaking, abrasives, compounding materials for rubber and plastics, water retention agents, shape retention agents, mud control agents, filter aids, anti-flooding agents, etc. Conceivable.

Although the reason why the composition of the present invention is characterized by being resistant to coloration when heated is not clear, it is considered as follows. In addition to aldehyde groups present in trace amounts in cellulose, ketone groups and aldehyde groups are produced as by-products in anion-modified cellulose nanofibers due to oxidation of hydroxyl groups in the process of anion modification. When such anion-modified cellulose nanofibers are heated, a β-elimination reaction occurs with a ketone group or an aldehyde group as a scaffold. 3-diketones, α,β-unsaturated aldehydes derived from aldehyde groups are produced. Furthermore, a peeling reaction occurs from the reducing end of the newly formed cellulose, accumulating colored substances having 2,3-diketones. This is considered to be one of the causes of the coloring of ordinary anion-modified cellulose nanofibers during heating. On the other hand, the composition of the present invention contains a phosphine compound, and the phosphine compound reduces the ketone groups and aldehyde groups in the anion-modified cellulose nanofibers.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these. Unless otherwise specified, parts and % indicate parts by mass and % by mass.

(Example 1)
Bleached softwood pulp (manufactured by Nippon Paper Industries Co., Ltd.) was prepared as a cellulose raw material, TEMPO was used as an N-oxyl compound, sodium hypochlorite and sodium bromide were used as oxidizing agents, and the amount of carboxyl groups was 1.5 mmol/g. of carboxylated cellulose (dispersion medium: water). Hydrochloric acid was added to the aqueous dispersion of carboxylated cellulose until the pH reached 2.4 to convert the carboxyl groups to the acid form (COOH). Then, it was washed with ion-exchanged water. The solid content concentration of the dispersion after washing was 22% by mass. Tris(3-hydroxypropyl)phosphine (Hishikorin (registered trademark) p-540, manufactured by Nippon Kagaku Kogyo Co., Ltd.) was added to the washed dispersion until the pH of the dispersion reached 7.0. The solid content concentration of the obtained dispersion was adjusted to 1% by mass, and passed through an ultrahigh pressure homogenizer of 140 MPa three times to remove water containing anion-modified cellulose nanofibers and tris(3-hydroxypropyl)phosphine. A dispersion was obtained as a dispersion medium. The concentration of anion-modified cellulose nanofibers in this dispersion is 0.75% by mass, and the concentration of tris(3-hydroxypropyl)phosphine is 0.25% by mass.

The obtained dispersion was poured into a square frame and dried at 80° C. until the water content disappeared (2 to 3 hours) to obtain a film-like dried product with a thickness of 25 μm (80° C. dried product). Separately, the obtained dispersion was poured into an aluminum cup and dried by heating at 105° C. for 12 hours to obtain a dried film having a thickness of 25 μm (dried at 105° C.). A photograph of the obtained dry film is shown in FIG. The left side of FIG. 1 is the 80° C. dried product, and the right side is the 105° C. dried product. The state of coloring of the resulting film-like dried product was visually evaluated. Also, the presence or absence of wrinkles on the surface of the film was visually evaluated. Table 1 shows the results.

(Comparative example 1)
A dispersion was prepared in the same manner as in Example 1 except that sodium hydroxide was used in place of tris(3-hydroxypropyl)phosphine. The obtained dispersion was heat-dried in the same manner as in Example 1 to prepare a film-like dried product, and the coloring and formation of wrinkles due to heating were visually evaluated in the same manner as in Example 1. Table 1 shows the results. Moreover, the photograph of the obtained film-like dry matter is shown in FIG.

(Comparative example 2)
A dispersion was prepared in the same manner as in Example 1, except that tetrabutylphosphonium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of tris(3-hydroxypropyl)phosphine. The concentration of anion-modified cellulose nanofibers in the dispersion is 0.69% by mass, and the concentration of tetrabutylphosphonium hydroxide is 0.31% by mass. The obtained dispersion was heat-dried in the same manner as in Example 1 to prepare a film-like dried product, and the coloring and formation of wrinkles due to heating were visually evaluated in the same manner as in Example 1. Table 1 shows the results. Moreover, the photograph of the obtained film-like dry matter is shown in FIG.

From the results in Table 1 and FIGS. 1 to 3, it can be seen that the composition of Example 1 containing a phosphine compound was not colored even when heated (dried at a high temperature). In addition, it can be seen that the composition of Example 1 had a smooth surface with no wrinkles on the film surface. On the other hand, in the composition of Comparative Example 1, coloring and surface wrinkles were observed due to heating, and in the composition of Comparative Example 2, coloring due to heating was observed.

Claims (8)

Containing nanofibers of anion-modified cellulose and a phosphine compound having a hydroxyl group,
The amount of the phosphine compound having a hydroxyl group is 10% to 150% of the amount (number of moles) of anionic groups to which the phosphine compound having a hydroxyl group can bind in the anion-modified cellulose nanofibers. Composition. 2. The composition of Claim 1, wherein the phosphine compound having a hydroxyl group is one or more compounds selected from the group consisting of trishydroxypropylphosphine, trishydroxyethylphosphine, and trishydroxymethylphosphine. The composition according to claim 1 or 2, wherein the anion-modified cellulose has carboxyl groups. The composition according to any one of claims 1 to 3, wherein the anion-modified cellulose is cellulose having carboxyl groups obtained by oxidizing cellulose using an N-oxyl compound and an oxidizing agent. A composition according to any preceding claim, wherein the composition is a dispersion. 6. The composition according to claim 5, wherein the dispersion medium of the dispersion is water or an organic solvent, or a mixture thereof. A composition obtained by at least partially removing the dispersion medium from the dispersion according to claim 5 or 6. A film comprising the composition according to any one of claims 1 to 4.

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