JP2022051300A - Method for Producing Chemically Modified Microfibril Cellulose Fiber - Google Patents

Abstract

To provide a method for producing a chemically modified microfibril cellulose fiber dispersion that prevents the viscosity from decreasing during its storage and also reduces malodors therefrom.SOLUTION: A method for producing a chemically modified microfibril cellulose fiber includes the following steps (A)-(B): (A) a chemically modified cellulose is prepared; and (B) the chemically modified cellulose is fibrillated at 55°C or higher, to produce a chemically modified microfibril cellulose fiber.SELECTED DRAWING: None

Description

The present invention relates to a method for producing chemically modified microfibrillose cellulose fibers. More specifically, the present invention relates to a method for producing a chemically modified microfibril cellulose fiber in which a decrease in viscosity and an odor are suppressed during storage.

Chemically modified microfibrillose fibers are obtained by defibrating or crushing cellulose raw materials such as pulp, and are used as additives for improving paper strength and water retention, foods, and cosmetics. Is expected.

For example, Patent Document 1 describes a fine fibrous cellulose-containing substance having a viscosity measured at 3 rpm and 25 ° C. using a B-type viscometer at 2800 mPa · s or more and a haze value of 10% or more and 50% or less. Has been done. Further, Patent Document 2 describes microfibrillated cellulose having a Canadian standard drainage degree of less than 200 ml and an average fiber diameter of 500 nm or more. Patent Document 3 describes a carboxymethylated microfibril cellulose fiber paper having a Canadian standard drainage degree of 200 ml or more and an average fiber diameter of 500 nm or more.

Japanese Unexamined Patent Publication No. 2017-57390 International Publication No. 2019/189588 International Publication No. 2019/189595

However, when manufactured by the methods described in Patent Documents 1 to 3, chemically modified microfibrillose cellulose fibers can be obtained, but the viscosity is lowered due to putrefaction during storage. In view of the above, it is an object of the present invention to provide a method for producing a chemically modified microfibrillose fiber that suppresses a decrease in viscosity.

The inventors have found that the above-mentioned problems can be solved by producing chemically modified microfibrillose fibers by defibrating at a temperature of 55 ° C. or higher and treating them with chemically modified cellulose. Therefore, the above-mentioned problem is solved by the following invention.
(1) A method for producing a chemically modified microfibril cellulose fiber, which comprises the following steps (A) to (B).
(A) Step of preparing chemically modified cellulose (B) Step of defibrating the chemically modified cellulose at a temperature of 55 ° C. or higher to obtain chemically modified microfibrillose fibers (2) Cellulose having a carboxyl group in the chemically modified cellulose The manufacturing method according to (1).
(3) The production method according to (1), wherein the chemically modified cellulose is carboxymethylated cellulose.

The chemically modified microfibril cellulose fiber produced by the present invention is characterized in that a decrease in viscosity is suppressed during storage and an odor is also reduced.

The present invention will be described in detail. In the present invention, "X to Y" includes X and Y which are fractional values thereof.

The method for producing a chemically modified microfibril cellulose fiber of the present invention is (A) a step of preparing a chemically modified cellulose, and (B) defibrating the chemically modified cellulose at a temperature of 55 ° C. or higher to obtain a chemically modified microfibril cellulose fiber. It is essential to include the step of obtaining.

(1) Step A
<Chemically modified cellulose>
The chemically modified cellulose used in the chemically modified microfibrillose fiber of the present invention is one in which the cellulose chains constituting the fiber are chemically modified. The type of chemically modified cellulose is not limited to these, for example, carboxylated cellulose having a carboxyl group introduced, carboxyalkylated cellulose having an ether bond of a carboxyalkyl group such as a carboxymethyl group, and phosphorus having a phosphate group introduced. Examples thereof include acid esterified cellulose. Of these, oxidation (carboxylation), etherification (for example, carboxyalkylation), cationization, and esterification are preferable, and oxidation (carboxylation) and carboxyalkylation are more preferable. These manufacturing methods will be described later.

The chemically modified cellulose may be in the form of a salt, and the term “chemically modified cellulose” as used herein also includes a salt-type chemically modified cellulose. Examples of the salt-type chemically modified cellulose include those forming a metal salt such as a sodium salt.

The chemically modified cellulose used in the chemically modified microfibrillose cellulose fiber of the present invention maintains at least a part of the fibrous shape even when dispersed in water. That is, when the aqueous dispersion of chemically modified cellulose fibers is observed with an electron microscope or the like, a fibrous substance can be observed, and when measured by X-ray diffraction, the peak of cellulose type I crystal can be observed. It is a thing.

<Chemically modified microfibril cellulose fiber>
The chemically modified microfibrillose fiber of the present invention is obtained by appropriately beating or defibrating (fibrillating) a chemically modified cellulose raw material using a refiner or the like. Chemically modified microfibrils Cellulose fibers show fluffing of cellulose microfibrils on the fiber surface as compared to chemically modified cellulose fibers that have not been beaten or defibrated. In addition, the fiber diameter is larger than that of chemically modified cellulose nanofibers, and the fiber surface is efficiently fluffed (external fibrillation) while suppressing the miniaturization (internal fibrillation) of the fiber itself.

Further, the chemically modified microfibril cellulose fiber of the present invention has features such as high water retention and high chicosis due to chemical modification as compared with the non-chemically modified microfibril cellulose fiber.

Further, the chemically modified microfibrillose fiber obtained by fibrillating the chemically modified cellulose raw material of the present invention has cellulose at the time of fibrillation as compared with the one chemically modified after beating the chemically modified cellulose raw material. Since the fibers are chemically modified, the strong hydrogen bonds existing between the fibers are weakened, and the fibers are easily loosened during fibrillation, and the fibers are less damaged.

The chemically modified microfibril cellulose fiber of the present invention has an average fiber diameter of 500 nm or more, preferably 1 μm or more, and more preferably 2 μm or more. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, still more preferably 20 μm or less. By appropriately fibrillating to the extent that the average fiber diameter is within this range, it exhibits higher water retention than undefibrated cellulose fibers, and even in a small amount compared to finely defibrated cellulose nanofibers. A high strength-imparting effect and a yield-improving effect can be obtained.

The average fiber length of the chemically modified microfibril cellulose fiber is preferably 5 μm or more, preferably 10 μm or more, and more preferably 20 μm or more. The upper limit of the average fiber length is not particularly limited, but is preferably 3000 μm or less, preferably 2500 μm or less, further preferably 2000 μm or less, still more preferably 1500 μm or less. According to the present invention, since the chemically modified cellulose raw material is used for beating or defibration, fibrillation can be promoted without making the fibers extremely short. Further, since the affinity with water is improved by the chemical denaturation, the water retention can be increased even when the fiber length is long.

The above average fiber diameter and average fiber length can be obtained by an image analysis type fiber analyzer such as L & W Fiber Tester Plus manufactured by ABB Ltd. or a fractionator manufactured by Valmet Co., Ltd. Specifically, when a fractionator is used, it can be obtained as length-weighted fiber width and length-weighted average fiber length, respectively.

The aspect ratio of the chemically modified microfibril cellulose fiber is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more. The upper limit of the aspect ratio is not particularly limited, but is preferably 1000 or less, more preferably 100 or less, and even more preferably 80 or less. The aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length / average fiber diameter

Regarding the chemically modified microfibril cellulose fiber, the fibrillation rate (Fibrillation%) measured using a fractionator manufactured by Valmet Co., Ltd. is preferably 0.5% or more, more preferably 0.8% or more. It is preferably 1.0% or more, and more preferably 1.0% or more. The fibrillation rate differs depending on the type of cellulose raw material used, but if it is within the above range, it is considered that fibrillation has been performed. Further, in the present invention, it is preferable to carry out fibrillation so that the fibrillation rate (f ₀ ) of the chemically modified cellulose raw material before fibrillation is improved. Assuming that the fibrillation rate of the chemically modified cellulose fiber fibrillated is f, the difference Δf = ff ₀ of the fibrillation rate may be more than 0, preferably 0.1% or more, more preferably. Is 0.2% or more, more preferably 0.3% or more.

<Crystallinity of cellulose type I>
The crystallinity of cellulose in the chemically modified microfibrillose fiber of the present invention is more preferably 50% or more, and more preferably 60% or more for crystal I type. The crystallinity of cellulose can be controlled by the degree of chemical denaturation. The upper limit of the crystallinity of cellulose type I is not particularly limited. In reality, about 90% is considered to be the upper limit.

The method for measuring the crystallinity of cellulose type I of the chemically modified cellulose fiber is as follows. :
The sample is placed on a glass cell and measured using an X-ray diffraction measuring device (LabX XRD-6000, manufactured by Shimadzu Corporation). The crystallinity is calculated using a method such as Segal, and the diffraction intensity of the 002 surface of 2θ = 22.6 ° and 2θ = with the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram as the baseline. It is calculated by the following formula from the diffraction intensity of the amorphous part of 18.5 °.
Xc = (I002c-Ia) / I002c × 100
Xc: Cellulose type I crystallinity (%)
I002c: 2θ = 22.6 °, diffraction intensity of 002 surface Ia: 2θ = 18.5 °, diffraction intensity of amorphous part

<Degree of anionization>
The degree of anionization (anion charge density) of the chemically modified microfibril cellulose fiber of the present invention is usually 2.50 meq / g or less, preferably 2.30 meq / g or less, more preferably 2.00 meq / g or less. It is more preferably 1.50 meq / g or less and 1.00 meq / g or less. As a result, it is considered that the chemical denaturation is made uniform throughout the cellulose as compared with the chemically modified cellulose fiber having a higher degree of anionization, and it is possible to obtain more stable effects peculiar to the chemically modified cellulose fiber such as water retention. It is thought that it can be done. The lower limit is usually 0.08 meq / g or more, preferably 0.10 meq / g or more, more preferably 0.30 meq / g or more, but is not particularly limited. Therefore, it is preferably 0.08 meq / g or more and 2.50 meq / g or less. The degree of anionization is the equivalent of anion per unit mass of modified cellulose microfibrils and can be calculated from the equivalent of diallyldimethylammonium chloride (DADMAC) required to neutralize the anionic group in the unit mass of modified cellulose microfibrils. .. In the present invention, the method for measuring the degree of anionization is as follows. :
The chemically modified cellulose fiber is dispersed in water to prepare an aqueous dispersion having a solid content of 10 g / L, and the mixture is stirred with a magnetic stirrer at 1000 rpm for 10 minutes or more. After diluting the obtained slurry to 0.1 g / L, 10 ml was collected, titrated with a 1/1000 normal diallyldimethylammonium chloride (DADMAC) using a flow current detector (Mutek Particle Charge Detector 03), and flowed. Using the amount of DADMAC added until the current becomes zero, the degree of anionization is calculated by the following formula. :
q = (V × c) / m
q: Degree of anionization (meq / g)
V: Addition amount (L) of DADMAC until the flow current becomes zero
c: DADMAC concentration (meq / L)
m: Mass (g) of chemically modified microfibrillose cellulose fibers in the measurement sample

<Water retention capacity>
The chemically modified microfibril cellulose fiber of the present invention preferably has a water retention capacity of 15 or more as measured by the following method. The method for measuring the water retention capacity is as follows. :
Prepare 40 mL of a slurry (medium: water) having a solid content of 0.3% by mass of chemically modified microfibril cellulose fibers. Let A be the mass of the slurry at this time. Then, the entire amount of the slurry is centrifuged at 25000 G at 30 ° C. for 30 minutes with a high-speed cooling centrifuge to separate the aqueous phase and the sediment. Let B be the mass of the sediment at this time. Further, the aqueous phase is placed in an aluminum cup and dried at 105 ° C. for 24 hours to remove water, and the mass of the solid content in the aqueous phase is measured. Let C be the mass of the solid content in this aqueous phase. The water retention capacity is calculated using the following formula. :
Water retention capacity = (B + C-0.003 × A) / (0.003 × AC)

As described above, the water retention capacity corresponds to the mass of water in the sediment with respect to the mass of the solid content of the fiber in the sediment. The higher the value, the higher the ability of the fiber to retain water. The water retention capacity of the fibrillated chemically modified cellulose fiber of the present invention is preferably 15 or more, more preferably 20 or more, still more preferably 30 or more. The upper limit is not particularly limited, but in reality, it seems to be about 200 or less.

The above-mentioned method for measuring the water retention capacity is intended for fibrillated fibers, and for fibers that have not been fibrillated or defibrated, or cellulose nanofibers that have been defibrated to single microfibrils. Is usually not applicable. Attempts to measure the water retention capacity of unfibrillated or defibrated cellulose fibers by the method described above may result in the inability to form dense sediments under the above-mentioned centrifugation conditions and the separation of sediments from the aqueous phase. Have difficulty. In addition, the cellulose nanofibers hardly settle under the above-mentioned centrifugation conditions.

<B type viscosity>
In the present invention, the method for measuring the B-type viscosity is as follows. :
Chemically modified microfibrillose fibers are weighed in a polypropylene container, dispersed in 160 ml of ion-exchanged water, and the aqueous dispersion is adjusted so that the solid content is 1% by mass. Adjust the aqueous dispersion to 25 ° C. After that, the viscosity after 1 minute is measured at a rotation speed of 60 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) according to the method of JIS-Z-8803.

The upper limit of the B-type viscosity (25 ° C., 60 rpm) of the chemically modified microfibrillose fiber of the present invention is 4,000 mPa · s or less, preferably 3,000 mPa · s or less, and more preferably 2,000 mPa · s or less. Is. The lower limit is 10 mPa · s or more, preferably 20 mPa · s or more, and more preferably 50 mPa · s or more.

<Others>
The chemically modified microfibril cellulose fiber of the present invention preferably has an electric conductivity of 500 mS / m or less when made into an aqueous dispersion having a solid content concentration of 1.0% by mass. It is more preferably 300 mS / m or less, further preferably 200 mS / m or less, still more preferably 100 mS / m or less, still more preferably 70 mS / m or less. The lower limit of the electric conductivity is preferably 5 mS / m or more, and more preferably 10 mS / m or more. The electrical conductivity can be measured by the following method. :
200 g of an aqueous dispersion having a solid content concentration of 1.0% by mass of chemically modified microfibril cellulose fibers is prepared and stirred sufficiently. Then, the electric conductivity is measured using an electric conductivity meter (ES-71 type manufactured by HORIBA).

The chemically modified microfibril cellulose fiber of the present invention has a BET specific surface area of preferably 30 m ² / g or more, more preferably 50 m ² / g or more, and further preferably 70 m ² / g or more. When the BET specific surface area is high, for example, when it is used as an additive for papermaking, it is easy to bind to pulp, and there are advantages such as improvement in yield and enhancement of the effect of imparting strength to paper. The BET specific surface area can be measured by the following method with reference to the nitrogen gas adsorption method (JIS Z 8830). :
(1) About 2% slurry (dispersion medium: water) of chemically modified microfibril cellulose fibers is separately placed in a centrifuge container so that the solid content becomes about 0.1 g, and 100 ml of ethanol is added.
(2) Add a stirrer and stir at 500 rpm for 30 minutes or more.
(3) The stirrer is taken out, and the chemically modified microfibril cellulose fibers are settled in a centrifuge under the conditions of 7000 G, 30 minutes and 30 ° C.
(4) Remove the supernatant while trying not to remove the chemically modified microfibril cellulose fibers as much as possible.
(5) Add 100 ml of ethanol, add a stirrer, stir under the condition of (2), centrifuge under the condition of (3), remove the supernatant under the condition of (4), and repeat this three times.
(6) The solvent of (5) is changed from ethanol to t-butanol, and stirring, centrifugation, and supernatant removal are repeated three times in the same manner as in (5) at room temperature above the melting point of t-butanol.
(7) After the final removal of the solvent, add 30 ml of t-butanol, mix lightly, transfer to an eggplant flask, and freeze using an ice bath.
(8) Cool in the freezer for 30 minutes or more.
(9) Attach to a freeze-dryer and freeze-dry for 3 days.
(10) BET measurement is performed (pretreatment conditions: 105 ° C. for 2 hours under a nitrogen stream, relative pressure 0.01 to 0.30, sample volume of about 30 mg).

The chemically modified microfibrillose fiber of the present invention preferably has a transparency (transmittance of 660 nm light) of less than 60%, more preferably 50% or less, when made into an aqueous dispersion having a solid content of 1% by mass. 400% or less is more preferable, and 35% or less is further preferable. The lower limit is not particularly limited and may be 0% or more. When the transparency is in such a range, the degree of fibrillation is appropriate, and the effect of the present invention can be easily obtained. Transparency can be measured by the following method. :
An aqueous dispersion of chemically modified microfibrill cellulose fibers (solid content 1% (w / v), dispersion medium: water) was prepared, and a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) was used to length the optical path. The transmittance of light having a wavelength of 660 nm is measured using a 10 mm square cell.

When water is used as a dispersion medium, the chemically modified microfibrillose fiber of the present invention becomes a translucent to white gel, cream or paste at a solid content concentration of about 2% or more.

The chemically modified microfibrillose fiber may be in the form of a dispersion obtained after production, may be dried if necessary, or may be redispersed in water. The drying method is not limited, but for example, a freeze-drying method, a spray-drying method, a shelf-stage drying method, a drum drying method, a belt drying method, a method of thinly spreading and drying on a glass plate, a fluidized bed drying method, and a microwave drying method. Known methods such as the method and the heating fan type vacuum drying method can be used. After drying, it may be crushed with a cutter mill, a hammer mill, a pin mill, a jet mill or the like, if necessary. Further, the method of redispersion to water is not particularly limited, and a known disperser can be used.

The use of the chemically modified microfibril cellulose fiber of the present invention is used for various uses. Since it has a high specific surface area, its strength is improved when it is blended with paper. In addition, since the degree of defibration is not too strong and the fiber diameter is maintained at an appropriate level, it can be particularly optimally used for applications that require fiber strength and applications that require high fiber yield. it is conceivable that. However, it may be used for other purposes. The fields in which chemically modified microfibril cellulose fibers are used are not limited, and various fields in which additives are generally used, such as foods, beverages, cosmetics, pharmaceuticals, papermaking, various chemical supplies, paints, sprays, pesticides, and civil engineering. , Buildings, electronic materials, flame retardants, household goods, adhesives, cleaning agents, fragrances, lubricating compositions, etc., thickeners, gelling agents, sizing agents, food additives, excipients, additives for paints, etc. It can be used as an agent, adhesive additive, papermaking additive, abrasive, rubber / plastic compounding material, water retention agent, shape retention agent, muddy water conditioner, filtration aid, mud prevention agent, etc. Conceivable.

<Manufacturing method of chemically modified microfibrillose cellulose fiber>
The chemically modified microfibrillose fiber of the present invention can be produced by first preparing a chemically modified cellulose raw material and then fibrillating it. As described above, examples of the type of chemical denaturation include, but are not limited to, carboxylation, carboxyalkylation, and phosphoric acid esterification of cellulose. As the chemically modified cellulose raw material to be subjected to fibrillation, a commercially available product may be used, or for example, a cellulose raw material described later may be chemically modified by a method described later to be produced.

<Cellulose raw material>
The cellulose used as a raw material for the chemically modified microfibrillose fiber of the present invention is not particularly limited, but for example, for plants, animals (for example, squirrels), algae, microorganisms (for example, acetobacter), and microbial products. The origin is mentioned. Plant-derived materials include, for example, wood, bamboo, hemp, jute, kenaf, farmland waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleached kraft pulp (NBKP), broadleaf unbleached kraft pulp (NBKP). LUKP), broad-leaved bleached kraft pulp (LBKP), coniferous unbleached sulphite pulp (NUSP), coniferous bleached sulphite pulp (NBSP), thermomechanical pulp (TMP), coniferous melted pulp, broadleaf tree melted pulp, recycled pulp, used paper, etc. ). Further, the cellulose powder obtained by pulverizing the above-mentioned cellulose raw material may be used. Any one or a combination of these may be used as the cellulosic raw material, but it is preferably a cellulosic fiber derived from a plant or a microorganism, more preferably a cellulosic fiber derived from a plant, and further preferably a wood-based pulp.

In order to maintain the crystallinity of cellulose type I of 50% or more in the chemically modified microfibril cellulose fiber, it is preferable to use cellulose having a high crystallinity of cellulose type I as a raw material. The crystallinity of cellulose type I, which is a raw material for cellulose, is preferably 70% or more, and more preferably 80% or more. The method for measuring the crystallinity of cellulose type I is the same as described above.

<Carboxylation of cellulose raw material>
As an example of the chemically modified cellulose raw material, a carboxylated (introducing a carboxyl group into cellulose, also referred to as "oxidation") cellulose raw material can be used. As the carboxylated cellulose raw material (also referred to as “oxidized cellulose raw material”), a commercially available product may be used, or the above-mentioned cellulose raw material is produced by carboxylating (oxidizing) it by a known method. May be good. The amount of the carboxyl group is preferably 0.1 to 2.5 mmol / g, more preferably 0.6 mmol / g to 2.5 mmol / g, and 1.0 mmol / g to 1.0 mmol / g with respect to the absolute dry mass of the carboxylated cellulose fiber. 2.0 mmol / g is more preferable.

The amount of carboxyl group of carboxylated cellulose can be measured by the following method. :
60 ml of a 0.5 mass% slurry (aqueous dispersion) of carboxylated cellulose was prepared, a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5, and then a 0.05 N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11. The electric conductivity is measured until the pH becomes equal to, and the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid in which the change in the electric conductivity is gradual is calculated by using the following formula.
Amount of carboxyl group [mmol / g carboxylated cellulose] = a [ml] x 0.05 / mass of carboxylated cellulose [g]
The amount of carboxyl groups in the carboxylated cellulose raw material before fibrillation and the amount of carboxyl groups in the carboxylated cellulose fibers after fibrillation are usually the same.

As an example of the carboxylation (oxidation) method, a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromide, iodide, and a mixture thereof. You can mention how to do it. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose is selectively oxidized, and the cellulose raw material having an aldehyde group and a carboxyl group (-COOH) or a carboxylate group (-COO- ⁾ on the surface. Can be obtained. The concentration of the cellulose raw material at the time of the reaction is not particularly limited, but is preferably 5% by mass or less.

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

The bromide is a compound containing bromine, and examples thereof include alkali metals bromide that can be dissociated and ionized in water. Further, the iodide is a compound containing iodine, and an example thereof includes an alkali metal iodide. The amount of bromide or iodide used can be selected within the range in which the oxidation reaction can be promoted. 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, still more preferably 0.5 mmol to 5 mmol with respect to 1 g of an absolute dry cellulose raw material.

As the oxidizing agent, known ones can be used, and for example, halogens, hypohalogenic acids, subhalogen acids, perhalonic acids or salts thereof, halogen oxides, peroxides and the like can be used. Of these, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferable. The 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, still more preferably 1 mmol to 25 mmol, and most preferably 3 mmol to 10 mmol with respect to 1 g of the dry dry cellulose raw material. preferable. Further, for example, 1 mol to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

In the oxidation step of the cellulose raw material, the reaction can 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. As the reaction progresses, a carboxyl group is generated in the cellulose chain, so that the pH of the reaction solution is lowered. In order to efficiently proceed the oxidation reaction, 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 to 12, preferably about 10 to 11. Water is preferable as the reaction medium because it is easy to handle and side reactions are unlikely to occur. The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually about 0.5 hour to 6 hours, for example, about 0.5 hour to 4 hours.

Further, the oxidation reaction may be carried out in two stages. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

As another example of the carboxylation (oxidation) method, there is a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, the hydroxyl groups at at least the 2-position and the 6-position of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. The ozone concentration in the gas containing ozone is preferably 50 g / m ³ to 250 g / m ³ , and 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 part by mass to 30 parts by mass, and more preferably 5 parts by mass 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, it is possible to prevent the cellulose raw material from being excessively oxidized and decomposed, and the yield of oxidized cellulose becomes good. After the ozone treatment, the additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine 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 the carboxyl group in the carboxylated cellulose raw material can be adjusted by controlling the reaction conditions such as the addition amount of the oxidizing agent and the reaction time described above.

<Carboxyalkylation of cellulose raw material>
As an example of the chemically modified cellulose raw material, a cellulose raw material (carboxyalkylated cellulose raw material) in which a carboxyalkyl group such as a carboxymethyl group is ether-bonded can be used. Such a raw material may be a commercially available material, or may be produced by carboxyalkylating the above-mentioned cellulose raw material by a known method. The degree of carboxyalkyl substitution of cellulose per anhydrous glucose unit is preferably 0.01-0.50. The upper limit is preferably 0.40 or less. If the degree of carboxyalkyl substitution exceeds 0.50, dissolution in water is likely to occur, and the fiber morphology cannot be maintained in water. In order to obtain the effect of carboxyalkylation, it is necessary to have a certain degree of substitution. For example, if the degree of substitution is less than 0.02, there is an advantage of introducing a carboxyalkyl group depending on the application. It may not be obtained. Therefore, the degree of substitution of carboxyalkyl is preferably 0.02 or more, more preferably 0.05 or more, further preferably 0.10 or more, still more preferably 0.15 or more. , 0.20 or more, more preferably 0.25 or more. The degree of substitution of carboxyalkyl can be adjusted by controlling the amount of the carboxyalkylating agent to be reacted, the amount of the mercerizing agent, the composition ratio of water and the organic solvent, and the like.

As used herein, the term anhydrous glucose unit means individual anhydrous glucose (glucose residue) constituting cellulose. The degree of carboxyalkyl substitution (also referred to as the degree of etherification) is the ratio of hydroxyl groups in the glucose residues constituting cellulose that are substituted with carboxyalkyl ether groups (carboxyalkyl per glucose residue). The number of ether groups) is shown. The degree of carboxyalkyl substitution may be abbreviated as DS.

The method for measuring the degree of carboxyalkyl substitution is as follows. :
Weigh about 2.0 g of the sample and place it in a 300 mL Erlenmeyer flask with a stopper. Add 100 mL of methanol nitrate (1000 mL of methanol plus 100 mL of special grade concentrated nitric acid) and shake for 3 hours to convert salt-type carboxyalkylated cellulose to hydrogen-type carboxyalkylated cellulose. Weigh 1.5 to 2.0 g of hydrogen-type carboxyalkylated cellulose (absolutely dry) and place in a 300 mL Erlenmeyer flask with a stopper. Wet with 15 mL of 80% methanol, add 100 mL of 0.1N-NaOH, and shake at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH is back titrated at 0.1 N—H ₂ SO ₄ , and the degree of carboxyalkyl substitution (DS value) is calculated by the following equation.
A = [(100 x F'-0.1N-H ₂ SO ₄ (mL) x F) x 0.1] / (absolute dry mass (g) of hydrogen-type carboxyalkylated cellulose)
Degree of substitution = 0.162 x A / (1-0.058 x A)
F': 0.1N-H ₂ SO ₄ factor F: 0.1N-NaOH factor

The degree of carboxyalkyl substitution in the carboxyalkylated cellulose raw material before fibrillation and the degree of carboxyalkyl substitution in the carboxyalkylated cellulose fiber after fibrillation are usually the same.

As an example of a method for producing a carboxyalkylated cellulose raw material, an example of producing a carboxymethylated cellulose raw material will be described below.

First, the cellulose raw material is mixed with a solvent and a mercerizing agent, and the reaction temperature is 0 to 70 ° C., preferably 10 to 60 ° C., and the reaction time is 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Mercerize. Then, a carboxymethylating agent was added in an amount of 0.05 to 10.0 times per glucose residue, and the reaction temperature was 30 to 90 ° C., preferably 40 to 80 ° C., and the reaction time was 30 minutes to 10 hours, preferably 1 hour. Carboxymethylation is performed for ~ 4 hours.

As the solvent, 3 to 20 times by mass of water or an organic solvent or a mixture thereof can be used, and the organic solvent is not limited to these, but methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol. , Isobutanol, tertiary butanol and other alcohols, acetone, diethyl ketone, methyl ethyl ketone and the like, and dioxane, diethyl ether, benzene, dichloromethane and the like. Of these, monohydric alcohols having 1 to 4 carbon atoms are preferable, and monohydric alcohols having 1 to 3 carbon atoms are more preferable because of their excellent compatibility with water. As the mercerizing agent, it is preferable to use 0.5 to 20 times mol of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, per anhydrous glucose residue of the cellulose raw material. Examples of the carboxymethylating agent include monochloroacetic acid, sodium monochromoacetate, methyl monochromoacetate, ethyl monochloroacetate, isopropyl monochromoacetate and the like. Of these, monochloroacetic acid or sodium monochloroacetate is preferable in terms of availability of raw materials. The amount of the carboxymethylating agent used is not particularly limited, but in one embodiment, it is preferably added in the range of 0.5 to 1.5 mol per anhydrous glucose unit of cellulose. The lower limit of the above range is more preferably 0.6 mol or more, further preferably 0.7 mol or more, and the upper limit is more preferably 1.3 mol or less, still more preferably 1.1 mol or less. The carboxymethylating agent can be added to the reactor as an aqueous solution of, for example, 5 to 80% by mass, more preferably 30 to 60% by mass, without limitation, and is added in a powder state without being dissolved. You can also do it.

The molar ratio of the mercerizing agent to the carboxymethylating agent (mercerizing agent / carboxymethylating agent) is generally 0.90 to 2.45 when monochloroacetic acid or sodium monochloroacetic acid is used as the carboxymethylating agent. Will be adopted by. The reason is that if it is less than 0.90, the carboxymethylation reaction may be insufficient, and unreacted monochloroacetic acid or sodium monochloroacetate may remain, resulting in waste. If the amount exceeds the above, a side reaction between the excess marcel agent and monochloroacetic acid or sodium monochloroacetic acid may proceed to form an alkali metal glycolic acid salt, which may be uneconomical.

When carboxymethylating a cellulose raw material, usually, both marcelification and carboxymethylation are performed in a solvent mainly containing water (water medium method), and both marcelation and carboxymethylation are performed with water. There is a method (solvent method) in which the solvent is mixed with an organic solvent, but in the present invention, a solvent mainly containing water is used for marcel formation, and an organic solvent and water are used for carboxymethylation. A mixed solvent with and may be used. By doing so, even when the crystallinity of cellulose was maintained at 50% or more, the carboxymethyl group was introduced uniformly rather than locally (that is, the absolute value of the anionization degree was small). The raw material for modified cellulose can be obtained economically.

The term "water-based solvent" as a solvent mainly used for water means a solvent containing water in a proportion higher than 50% by mass. The water in the solvent mainly containing water is preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more. It is more preferably 90% by mass or more, still more preferably 95% by mass or more. Particularly preferably, the solvent mainly containing water is 100% by mass (that is, water) of water. The higher the proportion of water during mercerization, the more the advantage that the carboxymethyl group is uniformly introduced by the cellulose. As the solvent other than water (used by mixing with water) in the solvent mainly composed of water, the above-mentioned organic solvent can be used. The amount of the organic solvent in the solvent mainly containing water is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, still more preferably 20% by mass or less. It is more preferably 10% by mass or less, further preferably 5% by mass or less, and even more preferably 0% by mass.

At the same time as the addition of the carboxymethylating agent, or immediately before or immediately after the addition of the carboxymethylating agent, an organic solvent or an aqueous solution of the organic solvent is appropriately added to the reactor, or water other than the water used for the marcelification treatment by reducing the pressure or the like. It is preferable to appropriately reduce the amount of the organic solvent and the like to form a mixed solvent of water and the organic solvent, and to proceed the carboxymethylation reaction under the mixed solvent of the water and the organic solvent. The timing of addition or reduction of the organic solvent may be between the end of the mercerization reaction and immediately after the addition of the carboxymethylating agent, and is not particularly limited, but for example, 30 minutes before and after the addition of the carboxymethylating agent. Within is preferable.

The ratio of the organic solvent in the mixed solvent at the time of carboxymethylation is preferably 20% by mass or more, more preferably 30% by mass or more, based on the total amount of water and the organic solvent. It is more preferably 40% by mass or more, further preferably 45% by mass or more, and particularly preferably 50% by mass or more. The higher the proportion of the organic solvent, the more likely it is that uniform substitution of carboxymethyl groups will occur, and thus the quality of the obtained carboxymethylated cellulose raw material will be stable. The upper limit of the proportion of the organic solvent is not limited and may be, for example, 99% by mass or less. Considering the cost of the organic solvent to be added, it is preferably 90% by mass or less, more preferably 85% by mass or less, still more preferably 80% by mass or less, still more preferably 70% by mass or less.

The reaction medium for carboxymethylation (cellulose-free, mixed solvent of water and organic solvent, etc.) has a smaller proportion of water than the reaction medium for mercerization (in other words, the proportion of organic solvent is higher). Many) is preferable. By satisfying this range, it becomes easy to maintain the crystallinity of the obtained carboxymethylated cellulose raw material, and the fiber of the present invention can be obtained more efficiently. In addition, when the reaction medium for carboxymethylation has a smaller proportion of water (more proportion of organic solvent) than the reaction medium for mercerization, the transition from the mercerization reaction to the carboxymethylation reaction occurs. Another advantage is that a mixed solvent for the carboxymethylation reaction can be formed by a simple means of adding a desired amount of an organic solvent to the reaction system after the completion of the mercerization reaction.

In carboxymethylation, the effective utilization rate of the carboxymethylating agent is preferably 15% or more. It is more preferably 20% or more, further preferably 25% or more, and particularly preferably 30% or more. The effective utilization rate of the carboxymethylating agent refers to the ratio of the carboxymethyl group introduced into cellulose among the carboxymethyl groups in the carboxymethylating agent. By using a solvent mainly composed of water for marcel formation and using a mixed solvent of water and an organic solvent for carboxymethylation, the effective utilization rate of the carboxymethylating agent is high (that is, the carboxymethylating agent). It is possible to obtain a carboxymethylated cellulose raw material economically without significantly increasing the amount of the solvent used. The upper limit of the effective utilization rate of the carboxymethylating agent is not particularly limited, but in reality, the upper limit is about 80%. The effective utilization rate of the carboxymethylating agent may be abbreviated as AM.

The method for calculating the effective utilization rate of the carboxymethylating agent is as follows. :
AM = (DS x number of moles of cellulose) / number of moles of carboxymethylating agent DS: degree of carboxymethyl substitution degree number of moles of cellulose: pulp mass (dry mass when dried at 100 ° C. for 60 minutes) / 162
(162 is the molecular weight of cellulose per glucose unit)

<Phosphoric acid esterification of cellulose raw material>
As an example of the chemically modified cellulose raw material, a phosphoric acid esterified cellulose raw material can be used. Examples of the esterification method include a method of mixing a powder or an aqueous solution of a compound having a phosphoric acid group with a cellulose raw material, a method of adding an aqueous solution of a compound having a phosphoric acid group to a slurry of a cellulose raw material, and the like. Compounds having a phosphoric acid group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, and potassium hypophosphite. , Sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate , Ammonium pyrophosphate, ammonium metaphosphate and the like. A phosphoric acid group can be introduced into a cellulose raw material by using one of these or two or more of them in combination. Of these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, and phosphoric acid from the viewpoint of high efficiency of introduction of phosphoric acid group, easy defibration in the following defibration step, and easy industrial application. Ammonium salt is preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. In addition, it is desirable to use the compound having a phosphoric acid group as an aqueous solution because the reaction can proceed uniformly and the efficiency of introducing the phosphoric acid group is high. The pH of the aqueous solution of the compound having a phosphoric acid group is preferably 7 or less because the efficiency of introducing the phosphoric acid group is high, but the pH is preferably 3 to 7 from the viewpoint of suppressing the hydrolysis of the fiber.

The following methods can be mentioned as an example of a method for producing a phosphoric acid esterified cellulose raw material. A compound having a phosphate group is added to a suspension of a cellulose raw material having a solid content concentration of 0.1 to 10% by mass with stirring to introduce a phosphate group into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of the compound having a phosphoric acid group added is preferably 0.2 to 500 parts by mass, and more preferably 1 to 400 parts by mass. ..

After dehydrating the obtained suspension of the phosphoric acid esterified cellulose raw material, it is preferable to heat-treat it at 100 to 170 ° C. from the viewpoint of suppressing the hydrolysis of the cellulose. Further, it is preferable to heat at 130 ° C. or lower, preferably 110 ° C. or lower while water is contained in the heat treatment, remove water, and then heat-treat at 100 ° C. to 170 ° C.

The degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose raw material is preferably 0.001 or more and less than 0.40. The degree of phosphoric acid group substitution in the phosphoric acid esterified cellulose raw material before fibrillation and the degree of phosphoric acid group substitution in the phosphoric acid esterified cellulose fiber after fibrillation are usually the same.

(2) Step B
In this step, the chemically modified cellulose is defibrated at a temperature of 55 ° C. or higher. By this treatment, it is possible to obtain a chemically modified microfibril cellulose fiber in which the decrease in viscosity due to the generation of various germs is suppressed during storage and the generation of odor is reduced. The temperature is preferably 55 ° C. or higher, and more preferably 57 ° C. or higher and 150 ° C. or lower.

In step B, the chemically modified microfibrillose fiber is obtained by defibrating or beating the chemically modified cellulose raw material. For fibrillation or beating, a refiner such as a disc type, conical type, cylinder type, etc., a high-speed defibrator, a shear type stirrer, a colloid mill, a high-pressure injection disperser, a beater, a PFI mill, a kneader, a disperser, etc. are used. Therefore, it is necessary to carry out the process in a wet manner (that is, in the form of a dispersion using water or the like as a dispersion medium), but the device is not particularly limited to these devices, and any device that imparts mechanical defibration force in a wet manner. Any can be used.

The solid content concentration of the raw material in the dispersion of the chemically modified cellulose raw material to be subjected to fibrillation is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1.0% by mass or more. 2.0% by mass or more is more preferable. The upper limit of the concentration is preferably 60% by mass or less, more preferably 45% by mass or less.

The pH of the aqueous dispersion of the chemically modified cellulose raw material at the time of defibration is preferably 13 or less, more preferably 12 or less, still more preferably 11 or less at the time of mechanical treatment. The lower limit of pH is not particularly limited, but is usually 2 or more, preferably 3 or more, and more preferably 3.5 or more. The pH can be adjusted, for example, by adding an acid (eg, hydrochloric acid, sulfuric acid) or an alkali (eg, caustic soda) to the aqueous dispersion.

Before preparing the dispersion for fibrillation, the chemically modified cellulose raw material obtained by the above method may be dried and pulverized in advance. Then, the dry-pulverized chemically modified cellulose raw material may be dispersed in a dispersion medium and subjected to fibrillation (wet). The apparatus used for dry pulverization of raw materials is not particularly limited, and examples thereof include impact mills such as hammer mills and pin mills, medium mills such as ball mills and tower mills, and jet mills.

As described above, fibrillation is carried out within a range in which the average fiber diameter is maintained at 500 nm or more, preferably 1 μm or more, and more preferably 4 μm or more. The upper limit of the average fiber diameter is preferably 60 μm or less, more preferably 40 μm or less, further preferably 30 μm or less, still more preferably 20 μm or less. By appropriately fibrillating to the extent that the average fiber diameter is within this range, it exhibits higher water retention than undefibrated cellulose fibers and a smaller amount than finer defibrated cellulose nanofibers. However, a high strength-imparting effect and a yield-improving effect can be obtained.

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

<Procedure for measuring the physical properties of chemically modified microfibrillose cellulose fibers>
(Chemical properties)
-Carboxylic (COOH) group amount: 60 ml of a 0.5 mass% aqueous dispersion of a sample was prepared, and a 0.1 M hydrochloric acid aqueous solution was added to adjust the pH to 2.5. Then, a 0.05 N aqueous sodium hydroxide solution was added dropwise, and the electric conductivity was measured until the pH reached 11. Calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid with a gradual change in electrical conductivity:
Amount of carboxyl group [mmol / g carboxylated cellulose] = a [ml] × 0.05 / mass of carboxylated cellulose [g].
Degree of Substitution: Approximately 2.0 g of the sample was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of methanol nitrate (a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol) was added, and the mixture was shaken for 3 hours to convert the salt-type carboxyl group into an acid type. The obtained acid type sample (absolutely dried) was precisely weighed in an amount of 1.5 to 2.0 g and placed in a 300 mL Erlenmeyer flask with a stopper. The sample was moistened with 15 mL of 80% methanol, 100 mL of 0.1N-NaOH was added, and the mixture was shaken at room temperature for 3 hours. Using phenolphthalein as an indicator, excess NaOH was back titrated at 0.1 N—H ₂ SO ₄ , and the degree of substitution (DS value) was calculated by the following formula.
A = [(100 x F'-0.1N-H ₂ SO ₄ (mL) x F) x 0.1] / (absolute dry mass (g) of acid type sample)
Degree of substitution = 0.162 x A / (1-0.058 x A)
F': 0.1N-H ₂ SO ₄ factor F: 0.1N-NaOH factor-Cellulose type I crystallinity: Place the sample on a glass cell and place an X-ray diffraction measuring device (eg, LabX XRD-6000). , Made by Shimadzu Corporation). The crystallinity is calculated using a method such as Segal. For example, using the diffraction intensity of 2θ = 10 ° to 30 ° in the X-ray diffraction diagram as the baseline, the following equation is obtained from the diffraction intensity of the 002 surface at 2θ = 22.6 ° and the diffraction intensity of the amorphous portion at 2θ = 18.5 °. Calculated by
Xc = (I _002C -Ia) / I _002C x 100
Xc: Cellulose type I crystallinity (%)
I _002C : 2θ = 22.6 °, diffraction intensity of 002 surface Ia: 2θ = 18.5 °, diffraction intensity of amorphous part The sample for measuring the degree of crystallinity is the item (1) to (1) in the measurement of the specific surface area in the subsequent stage. The freeze-dried sample prepared in the same procedure as in 9) was molded into a tablet shape and used.
-Method for measuring the degree of anionization: Chemically modified microfibril cellulose fibers were dispersed in water to prepare an aqueous dispersion having a solid content of 10 g / L, and the mixture was stirred with a magnetic stirrer at 1000 rpm for 10 minutes or more. The obtained aqueous dispersion was diluted to 0.1 g / L, 10 ml was collected, and titrated with a 1/1000 normal diallyldimethylammonium chloride (DADMAC) using a flow current detector (Mutek Particle Charge Detector 03). , The degree of anionization was calculated by the following formula using the amount of DADMAC added until the flow current became zero:
q = (V × c) / m
q: Degree of anionization (meq / g)
V: Addition amount (L) of DADMAC until the flow current becomes zero
c: DADMAC concentration (meq / L)
m: Mass (g) of chemically modified microfibrillose cellulose fibers in the measurement sample.

(Fiber characteristics)
-Average fiber length and average fiber width: A slurry of chemically modified microfibrillose fibers was diluted with water so that the solid content concentration was 0.25%, and the flow velocity was 5.7 L / min, the water temperature was 25 ± 1 ° C, and the total outflow. Approximately 250 G each (of which 50 g is used for measurement) was applied to the fractionator twice under the condition of a volume of 22 L, and the image of the chemically modified microfibrillose fiber classified inside the device was obtained by the CCD camera attached to the fractionator. Obtained about 2000 sheets.
The fiber analysis parameters of the analysis software IMG (Metso) were set as follows, and about 2000 acquired images were analyzed to obtain data such as average fiber length and average fiber width. The average value obtained by measuring and analyzing twice was adopted as the measurement data.
-Average fiber length: Length-weighted average fiber length Lc (l) mm Length-weighted average fiber length
-Average fiber width: Length-weighted average fiber width Fiber width μm Length-weighted fiber width

-Specific surface area: (1) About 2% aqueous dispersion of chemically modified microfibril cellulose fibers was separately placed in a centrifuge container so that the solid content was about 0.1 g, and 100 ml of ethanol was added.
(2) A stirrer was added and the mixture was stirred at 500 rpm for 30 minutes or longer.
(3) The stirrer was taken out, and the chemically modified microfibril cellulose fibers were settled in a centrifuge under the conditions of 7000 G, 30 minutes and 30 ° C.
(4) The supernatant was removed while trying not to remove the chemically modified microfibril cellulose fibers as much as possible.
(5) 100 ml of ethanol was added, a stirrer was added, stirring was performed under the condition of (2), centrifugation was performed under the condition of (3), and the supernatant was removed under the condition of (4), and this was repeated 3 times.
(6) The solvent of (5) was changed from ethanol to t-butanol, and stirring, centrifugation, and removal of the supernatant were repeated three times in the same manner as in (5) at room temperature above the melting point of t-butanol.
(7) After the final removal of the solvent, 30 ml of t-butanol was added, mixed lightly, transferred to an eggplant flask, and frozen using an ice bath.
(8) Cooled in a freezer for 30 minutes or more.
(9) It was attached to a freeze-dryer and freeze-dried for 3 days.
(10) BET measurement was performed (pretreatment conditions: under a nitrogen stream, 105 ° C., 2 hours, relative pressure 0.01 to 0.30, sample volume of about 30 mg).
-Water retention capacity: 40 mL of an aqueous dispersion having a solid content concentration of 0.3% by mass of chemically modified microfibril cellulose fibers was prepared. The mass of the aqueous dispersion at this time was defined as A. Then, the entire amount of the aqueous dispersion was centrifuged in a high-speed cooling centrifuge at 30 ° C. and 25,000 G for 30 minutes to separate the aqueous phase and the sediment. The mass of the sediment at this time was defined as B. Further, the aqueous phase was placed in an aluminum cup and dried at 105 ° C. for 24 hours to remove water, and the mass of the solid content in the aqueous phase was measured. The mass of the solid content in this aqueous phase was defined as C. The water retention capacity was calculated using the following formula.
Water retention capacity = (B + C-0.003 × A) / (0.003 × AC)
-B-type viscosity (25 ° C., 60 rpm): After defibration, the mixture was allowed to stand for 1 day or more, and then measured by the following method. After diluting to a predetermined concentration, leave it to stand in a water bath controlled at 25 ° C for 3 hours, and start viscosity measurement (60 rpm) using a Toki Sangyo B-type viscometer (manufactured by Toki Sangyo Co., Ltd.) for 1 minute. Later viscosity values were recorded.
-Electrical conductivity: Prepare 200 g of an aqueous dispersion having a solid content concentration of 1.0% by mass of chemically modified microfibril cellulose fibers, and stir well. Then, the electric conductivity was measured using an electric conductivity meter (ES-71 type manufactured by HORIBA).

[Example 1]
(1) Step A <Carboxymethylation of pulp>
Bleached unbeaten kraft pulp (LBKP, Nippon Paper Industries, Ltd.) derived from broadleaf tree by adding 75 parts of water and 20 parts of sodium hydroxide dissolved in 100 parts of water to a biaxial kneader whose rotation speed is adjusted to 100 rpm. ) Was charged (dry mass when dried at 100 ° C. for 60 minutes). These were stirred at 30 ° C. for 90 minutes and mixed to prepare a mercerized cellulosic raw material. Further, 100 parts of isopropanol (IPA) and 60 parts of sodium monochloroacetate were added with stirring, and after stirring for 30 minutes, the temperature was raised to 70 ° C. and a carboxymethylation reaction was carried out for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylation reaction was 37%. After completion of the reaction, the pulp is neutralized with acetic acid to a pH of about 7, and has a carboxymethylation degree of 0.21, a carboxyl group amount of 1.36 mmol / g, and a cellulose type I crystallinity of 59% (sodium). Salt) was obtained. An aqueous dispersion having a solid content concentration of 2.0% by mass was prepared from the obtained carboxymethylated pulp, and a 5% aqueous NaOH solution was added to adjust the pH to 7.5.
(2) Step B <Fibrilization>
The obtained aqueous dispersion of carboxymethylated pulp was treated with a B-50 type top finer manufactured by Aikawa Iron Works Co., Ltd. for 10 minutes (of which the temperature was 60 to 70 ° C. for 2 minutes) to obtain carboxymethylated microfibril cellulose fibers. Obtained. Table 1 shows the physical characteristics of the obtained carboxymethylated microfibril cellulose fibers. The method for measuring each physical property value is as described above.

[Example 2]
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (NBKP, manufactured by Nippon Paper Industries, Ltd., 85% whiteness) derived from coniferous trees is 39 mg (0.05 mmol per 1 g of absolute dry cellulose) of TEMPO (Sigma Aldrich). ) And 514 mg of sodium bromide (1.0 mmol with respect to 1 g of cellulose that was completely dried) were added to 500 ml of an aqueous solution, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 5.5 mmol / g, and the oxidation reaction was started at room temperature. Although the pH in the system decreased during the reaction, 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change. Hydrochloric acid was added to the mixture after the reaction to adjust the pH to 2, and then the pulp was separated by filtration through a glass filter, and the separated pulp was thoroughly washed with water to obtain TEMPO oxide pulp. The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, the amount of carboxyl groups was 1.42 mmol / g, and the pH was 4.5. An aqueous dispersion having a solid content concentration of 2.0% by mass of the obtained TEMPO oxide pulp was prepared, and a 5% aqueous NaOH solution and sodium hydrogen carbonate were added to adjust the pH to 7.5.
An aqueous dispersion having a solid content concentration of 2% by mass of the obtained TEMPO oxide pulp was prepared and treated for 10 minutes using a B-50 type top finer manufactured by Aikawa Iron Works Co., Ltd. (of which the temperature was 60 to 65 ° C. for 2 minutes). Then, cellulose oxide microfibrils (TEMPO oxide MFC) were prepared. For the obtained fibers, each physical property value shown in Table 1 was measured. The method for measuring each physical property value is as described above. The results are shown in Table 1.

[Example 3]
An aqueous dispersion having a solid content concentration of 5% by mass of TEMPO oxide pulp was prepared and treated for 14 minutes using a 14-inch laboratory refiner manufactured by Aikawa Iron Works Co., Ltd. (of which the temperature was 70 to 85 ° C for 4 minutes), and the cellulose oxide micro Cellulose-oxidized microfibrils (TEMPO-oxidized MFC) were prepared in the same manner as in Example 2 except that fibrils (TEMPO-oxidized MFC) were prepared. For the obtained fibers, each physical property value shown in Table 1 was measured. The method for measuring each physical property value is as described above. The results are shown in Table 1.

[Comparative Example 1]
Carboxymethylated microfibrillose cellulose fibers were prepared in the same manner as in Example 1 except that the defibration treatment was performed at a temperature of 18 to 48 ° C. for 5 minutes in step B. Table 1 shows the physical characteristics of the obtained carboxymethylated microfibril cellulose fibers. The method for measuring each physical property value is as described above.

[Comparative Example 2]
In step B, cellulose oxide microfibrils (TEMPO oxide MFC) were prepared in the same manner as in Example 2 except that the defibration treatment was performed at a temperature of 18 to 45 ° C. for 5 minutes. Table 1 shows the physical characteristics of the obtained chemically modified microfibril cellulose fibers. The method for measuring each physical property value is as described above.

<Decomposition / reduction confirmation test>
The samples of Examples and Comparative Examples were diluted to a concentration of 1.5% with ion-exchanged water, 180 ml each was placed in a glass bottle, covered, and allowed to stand in a constant temperature dryer set at 40 ° C. From the start of the test until 30 days had passed, the presence or absence of putrefaction due to odor was visually confirmed once every two weeks. In addition, the B-type viscosity was measured on the test start date and after 30 days, and the presence or absence of a viscosity change was confirmed. The results are shown in Table 2.

As shown in Table 2, in Examples 1 to 3, no mold or offensive odor was observed after 30 days. In addition, the decrease in B-type viscosity was suppressed after 30 days had passed.

Claims (3)

A method for producing a chemically modified microfibril cellulose fiber, which comprises the following steps (A) to (B).
(A) Step of preparing chemically modified cellulose (B) Step of defibrating the chemically modified cellulose at a temperature of 55 ° C. or higher to obtain chemically modified microfibrillose fibers. The production method according to claim 1, wherein the chemically modified cellulose is a cellulose having a carboxyl group. The production method according to claim 1, wherein the chemically modified cellulose is carboxymethylated cellulose.