JP2020111673A - Ester-modified cellulose nanofiber and method for producing the same - Google Patents

Abstract

To provide a cellulose-based fiber capable of providing a resin composition which is excellent in compatibility with a resin when being blended with various resins, and can be produced at a comparatively low temperature and a low cost with less specification chemicals, and a resin composition containing the composite body.SOLUTION: There are provided a cellulose nanofiber having an ester group obtained by reacting cellulose having a carboxyl group or a cellulose nanofiber with alcohol, and a method for producing the same, in which an esterified cellulose fiber or a cellulose nanofiber is obtained by allowing cellulose fiber having a carboxyl group containing water or a cellulose nanofiber to form an azeotropic mixture with an organic solvent, dehydrating the mixture, mixing an organic acid and alcohol in the organic solvent to progress an esterification reaction and simultaneously removing the water purified by the esterification reaction by the azeotropy.SELECTED DRAWING: None

Description

The present invention relates to cellulosic fibers suitable for composite materials.

Conventionally, plastic materials derived from petroleum, which is a finite resource, have been heavily used, but in recent years, technologies that have a low impact on the environment have come into the limelight, and under such a technological background, there is a large amount of biomass that exists naturally Materials using cellulose fibers have been attracting attention.

For example, Patent Document 1 reports that a composite material having both high mechanical strength and transparency can be obtained by incorporating a fine cellulose fiber composite having a surfactant adsorbed therein into various resins. ing. Further, in Patent Documents 2 and 3, it is reported that a fine cellulose fiber composite having an amide group bonded thereto is mixed with various resins to obtain a composite material having both high mechanical strength and transparency. ing.
Furthermore, Patent Document 4 has high mechanical strength and transparency by incorporating a fine cellulose fiber composite that is bound via an ionic bond and/or a covalent bond and introduced a modifying group into various resins. It has been reported that a composite material can be obtained.

Japanese Patent No. 5722021 Japanese Patent No. 5944098 Japanese Patent No. 6238971 JP, 2018-24967, A

When the cellulose nanofiber is made into a composite with another polymer material, it is necessary to chemically modify the surface of the cellulose in order to have compatibility and compatibility with the material. In the chemical modification, there is a problem that an expensive condensing agent is used and a large amount of solvent is spent for solvent substitution.

The above problems can be solved by the present invention of the following [1] to [4].
[1] Method for producing esterified cellulose nanofiber having the following steps (1) to (4) (1) Step of introducing carboxy group into hydroxyl group of cellulose fiber to obtain carboxylated cellulose fiber (2) A step of defibrating carboxylated cellulose fibers in water to obtain an aqueous dispersion of carboxylated cellulose nanofibers (3) A step of dehydrating and washing after adding an acid to the aqueous dispersion of carboxylated cellulose nanofibers (4) Azeotropically dewatering the carboxylated cellulose nanofiber aqueous dispersion with an organic solvent to obtain a carboxylated cellulose nanofiber solvent dispersion (5) azeotropically adding alcohol to the carboxylated cellulose nanofiber solvent dispersion Process for obtaining esterified cellulose nanofibers by performing esterification and dehydrating the produced water [2] A method for producing esterified cellulose nanofibers (6) having the following steps (6) to (10) Step (7) of introducing a carboxy group into a hydroxyl group of the cellulose fiber to obtain a carboxylated cellulose fiber, treating the carboxylated cellulose fiber with an acid, and then dehydrating and washing (8) the carboxylated cellulose fiber together with an organic solvent. Azeotropically dehydrating to obtain a carboxylated cellulose fiber solvent dispersion (9) Alcohol is added to the carboxylated cellulose fiber solvent dispersion to perform azeotropic esterification, and the generated water is dehydrated, Step (10) of obtaining esterified cellulose fibers Step (3) of defibrating the esterified cellulose fibers to obtain esterified cellulose nanofibers [3] The organic solvent is a water-insoluble organic solvent [1] to [1] 2] Production method [4] The production method according to [1] to [3], wherein the organic solvent is toluene, xylene, cyclohexane, or hexane.

In the present invention, a carboxylated cellulose fiber containing water is azeotropically distilled with an organic solvent and dehydrated to form a carboxylated cellulose solvent dispersion, which is then subjected to an ester reaction with an alcohol, and water molecules produced are azeotropically distilled with an organic solvent. Is used for dehydration, and the equilibrium reaction is allowed to proceed in the esterification direction to obtain esterified cellulose fibers and esterified cellulose nanofibers.

The manufacturing process differs depending on the form of the carboxylated cellulose fiber containing water.
That is, the form of carboxylated cellulose containing water,
i) In the case of an aqueous dispersion of carboxylated cellulose nanofibers,
ii) Hydrous carboxylated cellulose fibers dispersed in fiber form by a refiner iii) Pulped carboxylated cellulose fibers

When the form of the carboxylated cellulose fiber containing water is a carboxylated cellulose nanofiber aqueous dispersion,
(1) A step of introducing a carboxy group into a hydroxyl group of the cellulose fiber to obtain a carboxylated cellulose fiber (2) A step of defibrating the carboxylated cellulose fiber in water to obtain a carboxylated cellulose nanofiber aqueous dispersion (3) After adding an acid to the carboxylated cellulose nanofiber aqueous dispersion, dehydration/washing step (4) The carboxylated cellulose nanofiber aqueous dispersion is azeotropically dehydrated together with an organic solvent to obtain a carboxylated cellulose nanofiber solvent. Step (5) of obtaining a dispersion liquid, which comprises azeotropically adding alcohol to the carboxylated cellulose nanofiber solvent dispersion liquid to effect esterification, and dehydrating the produced water to obtain esterified cellulose nanofibers. ..

The form of the carboxylated cellulose fibers containing water is the case of hydrous carboxylated cellulose fibers in which pulp-like cellulose fibers are dispersed in a fiber form by a refiner,
(6) A step of introducing a carboxy group into a hydroxyl group of the cellulose fiber to obtain a carboxylated cellulose fiber (7) A step of treating the carboxylated cellulose fiber with an acid, followed by dehydration/washing (8) the carboxylated cellulose fiber, Azeotropically azeotropically dehydrating with an organic solvent to obtain a carboxylated cellulose fiber solvent dispersion (9) Alcohol is added to the carboxylated cellulose fiber solvent dispersion to azeotropically esterify and dehydrate the produced water. This comprises a step (10) of obtaining esterified cellulose fibers, and a step of defibrating the esterified cellulose fibers to obtain esterified cellulose nanofibers.

The form of the carboxylated cellulose fibers containing water is pulp-like carboxylated cellulose fibers,
(6) A step of introducing a carboxy group into the hydroxyl group of the cellulose fiber to obtain a carboxylated cellulose fiber (7) A step of treating the carboxylated cellulose fiber with an acid, followed by dehydration/washing (8) the carboxylated cellulose fiber, Azeotropically dehydrating with an organic solvent to obtain a carboxylated cellulose fiber solvent dispersion (9) Alcohol is added to the carboxylated cellulose fiber solvent dispersion to effect azeotropy and dehydrate the produced water. Thereby, the step (10) of obtaining the esterified cellulose fiber comprises the step of defibrating the esterified cellulose fiber to obtain the esterified cellulose nanofiber.

<Carboxylated cellulose fiber>
The carboxylated cellulose fiber used in the present invention means a modified cellulose fiber having at least one carboxy group. A carboxy group may be bonded to the cellulose skeleton, or a group containing a carboxy group (eg, carboxyalkyl group such as carboxymethyl group) may be bonded.

<Introduction of a substituent containing a carboxy group>
The method for producing the carboxy-based cellulose fiber is not particularly limited, and examples thereof include a modification method in which the cellulose raw material is modified and a carboxy group or a substituent containing a carboxy group can be introduced. The modification method is not particularly limited, but examples thereof include oxidation, etherification, and esterification. Of these, oxidation and carboxymethylation are preferable.

<Cellulose fiber>
The origin of the cellulose fibers is not particularly limited, and examples thereof include plants (eg, wood, bamboo, hemp, jute, kenaf, agricultural land waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP)). ), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), hardwood unbleached sulfite pulp (LUSP), hardwood bleached Examples include sulfite pulp (LBSP), thermomechanical pulp (TMP), recycled pulp, (recycled paper, etc.), animals (for example, ascidians), algae, microorganisms (for example, acetic acid bacteria (acetobacter)), microbial products, and the like. The cellulose fiber used in the present invention may be any of these or a combination of two or more thereof, but is preferably a plant- or microorganism-derived cellulose fiber, more preferably a plant-derived cellulose fiber. Is.

<Oxidation>
The method of oxidation is not particularly limited, but as one example, oxidation in water using an oxidant in the presence of an N-oxy compound and a compound selected from the group consisting of bromide, iodide or a mixture thereof. There is a method of doing. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized to generate an aldehyde group and a group selected from the group consisting of a carboxy group and a carboxylate group. The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.

The amount of the N-oxy compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 mmol or more is preferable, and 0.02 mmol or more is more preferable for 1 g of absolutely dried cellulose. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, still more preferably 0.5 mmol or less. Therefore, the amount of the N-oxy compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.02 to 0.5 mmol, per 1 g of absolutely dry cellulose.

The N-oxy compound means a compound capable of generating a nitroxy radical. Examples of the N-oxy compound include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). As the N-oxy compound, any compound can be used as long as it is a compound that promotes the desired oxidation reaction.

The bromide is a compound containing bromine, and examples thereof include alkali metal bromide capable of dissociating and ionizing in water, such as sodium bromide. The iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used may be selected within a range that can accelerate the oxidation reaction. The total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, based on 1 g of absolutely dried cellulose. The upper limit is preferably 100 mmol or less, more preferably 10 mmol or less, and further preferably 5 mmol or less. Therefore, the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol, based on 1 g of absolutely dried cellulose.

The oxidizing agent is not particularly limited, and examples thereof include halogen, hypohalous acid, halogenous acid, halogenic acid, perhalogenic acid, salts thereof, halogen oxides and peroxides. Among them, hypohalous acid or a salt thereof is preferable, hypochlorous acid or a salt thereof is more preferable, and sodium hypochlorite is further preferable, because it is inexpensive and has a low environmental load. The amount of the oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, still more preferably 3 mmol or more, based on 1 g of absolutely dried cellulose. The upper limit is preferably 500 mmol or less, more preferably 50 mmol or less, further preferably 25 mmol or less. Therefore, the amount of the oxidizing agent used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and particularly preferably 3 to 25 mmol based on 1 g of absolutely dry cellulose. When using the N-oxy compound, the amount of the oxidizing agent used is preferably 1 mol or more per 1 mol of the N-oxy compound. The upper limit is preferably 40 mol. Therefore, the amount of the oxidizing agent used is preferably 1 to 40 mol per 1 mol of the N-oxy compound.

Conditions such as pH and temperature during the oxidation reaction are not particularly limited, and generally, the reaction proceeds efficiently even under relatively mild conditions. The reaction temperature is preferably 4°C or higher, more preferably 15°C or higher. The upper limit is preferably 40°C or lower, more preferably 30°C or lower. Therefore, the reaction temperature is preferably 4 to 40°C, and may be about 15 to 30°C, that is, room temperature. The pH of the reaction solution is preferably 8 or higher, more preferably 10 or higher. The upper limit is preferably 12 or less, more preferably 11 or less. Therefore, the pH of the reaction solution is preferably 8 to 12, more preferably about 10 to 11. Usually, a carboxy group is generated in cellulose as the oxidation reaction progresses, so that the pH of the reaction solution tends to decrease. Therefore, in order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous solution of sodium hydroxide to maintain the pH of the reaction solution within the above range. Water is preferable as the reaction medium during oxidation 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 0.5 hours or more. The upper limit is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time in the oxidation is usually 0.5 to 6 hours, for example, 0.5 to 4 hours.

The oxidation may be carried out in two or more steps. For example, by oxidizing the oxidized cellulose obtained by filtering after the completion of the reaction in the first step again under the same or different reaction conditions, the reaction efficiency due to the salt produced as a by-product in the reaction in the first step is not increased, and the efficiency is improved. Can be well oxidized.

Included in the carboxy group-containing modified cellulose nanofibers obtained by modifying the cellulose raw material by oxidation (oxidized cellulose nanofibers), the amount of carboxy groups relative to the absolute dry mass of the cellulose nanofibers is preferably 0.6 mmol/g or more, It is more preferably 0.8 mmol/g or more, still more preferably 1.0 mmol/g or more. The upper limit is preferably 2.2 mmol/g or less, more preferably 2.0 mmol/g or less, and further preferably 1.8 mmol/g or less. Therefore, 0.6 mmol/g to 2.2 mmol/g is preferable, 0.8 mmol/g to 2.0 mmol/g is more preferable, and 1.0 mmol/g to 1.8 mmol/g is further preferable.

The amount of carboxy groups contained in the oxidized cellulose nanofibers can be adjusted by controlling the addition amount of the above-mentioned oxidizing agent and the reaction time.

An example of the method for measuring the amount of carboxy groups will be described below. 60 mL of 0.5% by mass slurry of oxidized cellulose fiber (aqueous dispersion) was prepared and adjusted to pH 2.5 by adding 0.1 M hydrochloric acid aqueous solution, and then 0.05 N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11 Measure the electrical conductivity until. It can be calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of a weak acid with a gradual change in electrical conductivity using the following formula:
Amount of carboxyl group [mmol/g oxidized cellulose fiber or oxidized cellulose nanofiber]=a [mL]×0.05/mass of oxidized cellulose fiber or oxidized cellulose nanofiber [g]

<Carboxymethylation>
The method of carboxymethylation is not particularly limited, and examples thereof include a method of mercerizing a cellulose raw material as a starting raw material and then etherifying the raw material. Examples of the solvent include water, alcohol (for example, lower alcohol), and a mixed solvent thereof. Examples of the lower alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and tertiary butanol. The mixing ratio of the lower alcohol in the mixed solvent is usually 60% by mass or more or 95% by mass or less, and preferably 60 to 95% by mass. The amount of solvent is usually 3 times the mass of the cellulose raw material. The upper limit is not particularly limited, but it is preferably 20 times by mass. Therefore, the amount of the solvent is preferably 3 to 20 times by mass.

The mercerization is usually performed by mixing a starting material and a mercerizing agent. Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of the mercerizing agent used is preferably 0.5 times mol or more, more preferably 0.7 times mol or more, and further preferably 0.8 times mol or more per unit of glucopyranose ring as a starting material. The upper limit is usually 20 times mol or less, preferably 10 times mol or less, more preferably 5 times mol or less, therefore, 0.5 to 20 times mol is preferable, 0.7 to 10 times mol is more preferable, and 0 is. More preferably, the molar ratio is 8 to 5 times.

The reaction temperature for mercerization is usually 0°C or higher, preferably 10°C or higher. The upper limit is 70°C or lower, preferably 60°C or lower. Therefore, the reaction temperature is usually 0 to 70°C, preferably 10 to 60°C. The reaction time is usually 15 minutes or longer, preferably 30 minutes or longer. The upper limit is usually 8 hours or less, preferably 7 hours or less. Therefore, the reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include sodium monochloroacetate. The amount of the carboxymethylating agent added is usually 0.05 times mol or more, preferably 0.5 times mol or more, more preferably 0.7 times mol or more, per unit of glucopyranose ring of the cellulose raw material. More preferable. The upper limit is usually 10.0 times mol or less, preferably 5 times mol or less, more preferably 3 times mol or less, and therefore preferably 0.05 to 10.0 times mol, more preferably 0.5 to 5 times. The molar ratio is twice, and more preferably 0.7 to 3 times. The reaction temperature is usually 30° C. or higher, preferably 40° C. or higher, and the upper limit is usually 90° C. or lower, preferably 80° C. or lower. Therefore, the reaction temperature is usually 30 to 90°C, preferably 40 to 80°C. The reaction time is usually 30 minutes or longer, preferably 1 hour or longer. The upper limit is usually 10 hours or less, preferably 4 hours or less. Therefore, the reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. The reaction solution may be stirred during the carboxylation reaction if necessary.

Carboxymethyl-containing modified cellulose fibers obtained by carboxymethylation and glucopyranose ring in carboxymethylated cellulose nanofibers, the carboxymethyl substitution degree per unit is preferably 0.01 or more, more preferably 0.05 or more, It is more preferably 0.10 or more. The upper limit is preferably 0.50 or less, more preferably 0.40 or less, and further preferably 0.35 or less. Therefore, the carboxymethyl group substitution degree is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and further preferably 0.10 to 0.35.

Examples of the method for measuring the glucopyranose ring of carboxymethylated cellulose fiber and the degree of carboxymethyl substitution per unit include the following methods: 1) About 2.0 g of carboxymethylated cellulose fiber (extra dry) is precisely weighed Then, put it in a 300 mL Erlenmeyer flask with a ground stopper. 2) Add 100 mL of a liquid containing 100 mL of special grade concentrated nitric acid to 1,000 mL of nitric acid methanol, and shake for 3 hours to convert carboxymethyl cellulose salt (CM cellulose fiber) into hydrogen type CM cellulose fiber. 3) 1.5 to 2.0 g of hydrogenated CM-modified cellulose (absolutely dry) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 4) Wet the hydrogenated CM cellulose fibers with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. 5) Back titration of excess NaOH with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. 6) The carboxymethyl substitution degree (DS) is calculated by the following formula.

A=[(100×F×0.1−(0.1N H ₂ SO ₄ )(mL)×F′)×0.1]/(absolute dry mass (g) of hydrogenated CM cellulose fiber)
DS=0.162×A/(1-0.058×A)
A: 1N NaOH amount (mL) required to neutralize 1 g of hydrogenated CM-modified cellulose fiber
F′: Factor of 0.1 N H ₂ SO ₄ F: Factor of 0.1 N NaOH

<Pickling treatment>
As a method for washing carboxylated cellulose fibers such as oxidized cellulose fibers and carboxymethylated cellulose fibers obtained by the above method, a method of washing while forming a salt with an alkali, a method of washing with an acid to add a carboxylic acid There is a method, a method of adding an organic solvent to make it insoluble, and washing. From the viewpoint of handleability and yield, a method of adding an acid to form a carboxylic acid and washing is preferable. Water is preferable as the washing solvent. By carrying out pickling with a washing solution having a pH value adjusted to 2 to 3, the counter ion of the carboxy group is replaced with a proton, and the metal ion can be removed.

<defibration>
Next, the step of making the carboxylated cellulose fibers fine (nanofiber) will be described.
The carboxylated cellulose fiber is used in the state of a dispersion liquid dispersed in water or an organic solvent as a dispersion medium. The solid content concentration of the carboxylated cellulose fibers in the dispersion is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more. As a result, the liquid amount with respect to the amount of carboxylated cellulose fibers becomes appropriate and efficient. The upper limit is usually 10% by mass or less, preferably 6% by mass or less. This makes it possible to maintain fluidity.

The apparatus used for defibration is not particularly limited, for example, high-speed rotation type, colloid mill type, high pressure type, roll mill type, ultrasonic type and other types of devices, high pressure or ultra high pressure homogenizer is preferred, wet high pressure or An ultra high pressure homogenizer is more preferred. The device is preferably capable of applying a strong shearing force to the carboxylated cellulose fibers (usually a dispersion). The pressure that can be applied by the device is preferably 50 MPa or more, more preferably 100 MPa or more, and further preferably 140 MPa or more. The apparatus is preferably a wet high-pressure or ultra-high-pressure homogenizer capable of applying the above-mentioned pressure to the cellulose raw material or modified cellulose (usually a dispersion liquid) and applying a strong shearing force. Thereby, defibration can be efficiently performed. The number of treatments (passes) in the defibrating device may be once, twice or more, and preferably twice or more.

The order of the defibration treatment and the dispersion treatment is not particularly limited, and either may be performed first or may be performed at the same time, but the defibration treatment is preferably performed after the dispersion treatment. The combination of each treatment may be performed at least once, and may be repeated twice or more.

Prior to the defibration treatment or the dispersion treatment, a preliminary treatment may be performed if necessary. The pretreatment may be carried out using a mixing, stirring, emulsifying and dispersing device such as a high speed shear mixer.

<Dehydration>
As a method for dehydrating water from an aqueous dispersion of cellulose nanofibers, there are a solvent replacement method, a spray dryer, a drying method using a hot air dryer, and a freeze-drying method.However, the solvent replacement method uses a large amount of a plurality of solvents, and it takes time and time. It takes.
Redispersion in a solvent is a major problem in a spray dryer, a drying method using a hot air dryer, and a freeze-drying method.
In the present invention, the carboxylated cellulose fibers containing water are dehydrated by azeotropically boiling water with an organic solvent to reduce the amount of solvent used, and in the liquid phase, the water and the organic solvent are replaced to form the carboxylated cellulose fibers. It facilitates dispersion in solvents.

The organic solvent used for azeotropic distillation is not particularly limited, but an organic solvent insoluble in water is preferable. Preferred organic solvents include carbon tetrachloride, chloroform, dichloromethane, 1,2-dichloroethane, benzene, toluene, xylene, cyclohexane, nitromethane, etc., but safety, ease of handling, solvent reuse, azeotropic liquid From the viewpoint of the solvent fraction therein, toluene, xylene, cyclohexane, and hexane are more preferable.

As the alcohol that reacts with the carboxy group of the carboxylated cellulose fiber to form an ester, one or more alcohols can be used from primary alcohols, secondary alcohols, and tertiary alcohols.

The primary alcohol, secondary alcohol and tertiary alcohol having a hydrocarbon group may be commercially available products or may be prepared according to known methods.

Specific examples of the primary to tertiary alcohols include, for example, methanol, ethanol, propanol, isopropanol, n-butanol, sec-butanol, t-butanol, n-pentanol, sec-butanol, 2-methyl-2. -Saturated aliphatic alcohols such as butanol, neopentyl alcohol, 1-docosanol, 1-triacontanol, 3-buten-1-ol, 2-buten-1-ol, cis-6-nonen-1-ol, 9 -Decen-1-ol, 5-hexen-1-ol, 8-nonen-1-ol, oleyl alcohol, linoleyl alcohol (cis,cis-9,12-octadecadien-1-ol), elaidyl alcohol (Trans-9-octadecenol Elaidyl Alcohol) and other unsaturated aliphatic alcohols, cyclohexanemethanol, cyclohexaneethanol, 3-cyclohexyl-1-propanol, alcohols having a cycloaliphatic exo-norborneol, benzyl alcohol, 2-( (Benzyloxy) ethanol, 4-methoxyphenethyl alcohol

The esterification reaction is a reversible reaction as in formula (1), and the equilibrium constant can be represented by formula (2).

R ¹ OH + R ² COOH ⇔ R ² COOR ¹ + H ₂ O (1)

K _eq =[R ² COOR ¹ ][H ₂ O]/[R ¹ OH][R ² COOH]<<1 (2)

In order to proceed the production of the ester, it is necessary to remove the produced water from the reaction system.
As this method, dehydration of water utilizing azeotropic distillation with the organic solvent is useful.

Examples of the method for confirming the ester group formation include infrared spectroscopy and acid value measurement.

In the infrared spectroscopy, infrared spectroscopy of the sample obtained by the reaction is performed, and the presence of the ester group can be confirmed by the presence of ester-induced C═O stretching vibration at 1750 to 1735 cm ⁻¹ . If the ester group does not generated, C = O stretching vibration of carboxylic acids resulting from 1720-1700cm ^-1, or, C = O stretching vibration of the carboxylate due is observed 1610-1550cm ^-1.

Samples obtained by drying the carboxylated cellulose fibers and the carboxylated cellulose nanofibers, filtering the acid value measured according to JIS K 5601-2-1 and the product obtained by the reaction, washing with a solvent and drying. The production of ester can be indirectly confirmed from the acid value measured in step 1.
The acid value of the sample with advanced esterification is smaller than the acid value of carboxy-modified cellulose fiber and carboxylated cellulose nanofiber, and the acid value that almost all raw materials can be regarded as esterified is carboxy-modified cellulose fiber before esterification treatment. , And 10% or less of the acid value of the carboxylated cellulose nanofibers, and more preferably 5% or less.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In addition, when the method of measuring/calculating each numerical value in each example is not particularly described, it is measured/calculated by the method described in the specification.

<Production Example of TEMPO Oxidized Cellulose Fiber>
Bleached unbeaten kraft pulp from softwood (whiteness 85%) 500 g (extremely dried), TEMPO (Sigma Aldrich Co.) 1.95 g (0.025 mmol per 1 g of absolutely dried cellulose) and sodium bromide 51.4 g (1 mmol of absolutely dry cellulose 1 mmol) was added to 500 mL of an aqueous solution, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system so that the amount of sodium hypochlorite was 6.0 mmol/g, and the oxidation reaction was started. Although the pH in the system was lowered during the reaction, the pH was adjusted to 10 by sequentially adding a 3M sodium hydroxide aqueous solution. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system stopped changing. The mixture after the reaction was filtered with a glass filter to be separated, and washed sufficiently with water to obtain oxidized TEMPO oxidized cellulose fiber. The yield of the obtained TEMPO oxidized cellulose fiber was 90%, the time required for the oxidation reaction was 90 minutes, the amount of carboxy groups was 1.6 mmol/g, and the acid value was 90.0.

<Production Example of Carboxymethyl Cellulose Fiber>
Bleached unbeaten kraft pulp from softwood (whiteness 85%) 253 g (absolutely dry), sodium hydroxide 56.3 g (glucopyranose ring of pulp, 0.9 times mole per unit) added, pulp Water was added so that the solid content was 20% (w/v). Then, after stirring at 30° C. for 30 minutes, 127 g of sodium monochloroacetate (glucopyranose ring of pulp, 0.7 times mol per unit) was added. After stirring for 30 minutes, the temperature was raised to 70° C. and the mixture was stirred for 1 hour. Then, the reaction product was taken out and washed to obtain a carboxymethylated cellulose fiber having a glucopyranose ring, a carboxymethyl substitution degree of 0.25 per unit, and an acid value of 28.0.

[Example 1]
<Esterification of TEMPO oxidized cellulose nanofibers-1>
The TEMPO-oxidized cellulose fiber and the solid content of 30 g were defibrated by a high-pressure homogenizer to obtain 3 L of 1 wt% TEMPO-oxidized cellulose nanofiber aqueous dispersion. Hydrochloric acid was added to the obtained dispersion liquid to adjust the pH to 2.4, and then the TEMPO oxidized cellulose nanofibers were thoroughly washed with water.
A 1 L, 4-neck separable flask is equipped with a stirrer, a dropping funnel, a Dean-Stark device equipped with a condenser and a thermometer for measuring the steam temperature, a liquid temperature measuring thermometer, and a nitrogen purged glass capillary.
250 mL of an acid-washed 1 wt% TEMPO oxidized cellulose nanofiber aqueous dispersion and 100 mL of toluene are placed in a flask, and water is azeotropically dehydrated while stirring. When the liquid in the flask becomes 1/3, 200 mL of the washed aqueous dispersion described above is added, water is dehydrated, addition of the aqueous dispersion and dehydration of water are repeated. When all the aqueous dispersion has been added to the flask and the liquid in the flask has reached about 1/3 of the initial liquid volume, 100 mL of toluene is added and dehydration is continued. When the vapor temperature rises from the water/toluene azeotropic temperature of 85°C to reach the boiling point of toluene of 110.6°C, the heating is stopped, the liquid temperature is cooled to 40°C, and the TEMPO oxidized cellulose nanofiber toluene dispersion liquid is obtained. Obtained.
100 g of a 20% toluene solution of stearyl alcohol is added dropwise to the TEMPO-oxidized cellulose nanofiber toluene dispersion with stirring and heating using a dropping funnel. The produced water is dehydrated by azeotropic distillation, and when the steam temperature reaches the boiling steam temperature of toluene and no more water is generated, it is confirmed that the acid value is 5 or less, the reaction is stopped, and the room temperature is reached. After natural cooling, esterified cellulose nanofibers were obtained.

[Example 2]
<Esterification of TEMPO oxidized cellulose nanofibers-2>
The TEMPO oxidized cellulose fiber and solid content of 50 g were pre-defibrated with a refiner and filtered.
Hydrochloric acid was added to the obtained pre-defibrated cellulose fiber to adjust the pH to 2.4, and the mixture was thoroughly stirred, filtered, and thoroughly washed with water.
A 1 L, 4-neck separable flask is equipped with a stirrer, a dropping funnel, a Dean-Stark apparatus equipped with a condenser and a thermometer for measuring the vapor temperature, a thermometer for liquid temperature measurement, and a nitrogen-purged glass capillary.
Preliminarily defibrating the flask, acid-washed TEMPO-oxidized cellulose fibers are added with solid content of 30 g and 200 mL of toluene, and water is azeotropically dehydrated while stirring. When the liquid in the flask becomes 2/3, 100 mL of toluene is added to continue dehydration. When the vapor temperature rises from the water/toluene azeotropic temperature of 85°C to reach the boiling point of toluene of 110.6°C, heating is stopped and the liquid temperature is cooled to 40°C to obtain a TEMPO oxidized cellulose fiber toluene dispersion liquid. It was
Stearyl alcohol 20% toluene solution 100 g is added dropwise to the TEMPO oxidized cellulose fiber toluene dispersion with stirring and heating using a dropping funnel. The produced water is dehydrated by azeotropic distillation, and when the steam temperature reaches the boiling steam temperature of toluene and no more water is generated, it is confirmed that the acid value is 5 or less, the reaction is stopped, and the room temperature is reached. Allow to cool naturally.
The toluene dispersion liquid of cellulose was defibrated with a high pressure homogenizer to obtain esterified cellulose nanofibers.

[Example 3]
<Esterification of TEMPO oxidized cellulose nanofibers-3>
Hydrochloric acid was added to 50 g of the pulp-like TEMPO oxidized cellulose fiber to adjust the pH to 2.4, and the mixture was thoroughly stirred, filtered, and washed thoroughly with water.
A 1 L, 4-neck separable flask is equipped with a stirrer, a dropping funnel, a Dean-Stark apparatus equipped with a condenser and a thermometer for measuring the vapor temperature, a thermometer for liquid temperature measurement, and a nitrogen-purged glass capillary.
The acid-washed pulp-like TEMPO-oxidized cellulose fibers having a solid content of 30 g and 200 mL of toluene are put in a flask and dehydrated by azeotropy while stirring. When the liquid in the flask becomes 2/3, 100 mL of toluene is added to continue dehydration. When the vapor temperature rises from the water/toluene azeotropic temperature of 85°C to reach the boiling point of toluene of 110.6°C, heating is stopped and the liquid temperature is cooled to 40°C.
100 g of a 20% toluene solution of stearyl alcohol is added dropwise to a pulp-like TEMPO-oxidized cellulose fiber toluene dispersion with a dropping funnel while stirring and heating. The produced water is dehydrated by azeotropic distillation, and when the steam temperature reaches the boiling steam temperature of toluene and no more water is generated, it is confirmed that the acid value is 5 or less, the reaction is stopped, and the room temperature is reached. After natural cooling, a toluene dispersion of esterified cellulose fibers was obtained.
The obtained esterified cellulose fiber toluene dispersion was defibrated with a high pressure homogenizer to obtain esterified cellulose nanofibers.

[Example 4]
<Esterification of carboxymethyl cellulose nanofibers-1>
Esterified cellulose nanofibers esterified with carboxymethyl groups under the same conditions as in Example 1 except that the TEMPO-oxidized cellulose fibers were changed to the carboxymethylated cellulose fibers and the concentration of stearyl alcohol was changed to 6.1%. Got

[Example 5]
<Esterification of carboxymethyl cellulose nanofiber-2>
Esterified cellulose nanofibers esterified with carboxymethyl groups were obtained under the same conditions as in Example 2 except that the TEMPO-oxidized cellulose fibers were changed to the carboxymethylated cellulose fibers and the concentration of stearyl alcohol was changed to 6.1%. It was

[Example 6]
<Esterification of carboxymethyl cellulose nanofiber-3>
Esterified cellulose nanofibers obtained by esterification of carboxymethyl groups under the same conditions as in Example 3 except that the TEMPO-oxidized cellulose fibers were changed to the carboxymethylated cellulose fibers and the amount of stearyl alcohol was changed to 6.1 g. Obtained.

[Comparative Example 1]
The TEMPO oxidized cellulose fiber and a solid content of 30 g were pre-defibrated with a refiner and filtered.
100 mL of acetone was added to the obtained pre-defibrated cellulose fiber, and after stirring, suction filtration was performed and washing with acetone was repeated 4 times to replace the solvent. Next, washing with 100 mL of toluene was repeated 3 times to obtain TEMPO-oxidized cellulose fibers substituted with toluene.
A 4-neck separable flask was equipped with a stirrer, a dropping funnel, a condenser, a thermometer for measuring liquid temperature and a nitrogen-purging glass capillary, and the obtained TEMPO-oxidized cellulose fiber substituted with toluene was obtained in a solid content of 30 g. Then, 200 mL of toluene was placed in the flask.
100 g of a 20% stearyl alcohol toluene solution is added dropwise to the TEMPO-oxidized cellulose toluene dispersion with a dropping funnel while stirring and heating. The reaction was stopped 2 hours after the addition of stear alcohol was completed, and the mixture was naturally cooled to room temperature to obtain a sample.

[Comparative Example 2]
A sample was obtained under the same conditions as in Comparative Example 1, except that the TEMPO-oxidized cellulose fiber was changed to the carboxymethylated cellulose fiber and the stearyl alcohol concentration was changed to 6.1%.

Example 1-6 and Comparative Example 1-2 were applied to KBr tablets and dried, and FT-IR measurement was performed. The acid value of Comparative Example 1-2 was measured.

As described above, in the cellulose nanofiber dispersion obtained in the present invention, the used solvent was small and the esterified cellulose nanofiber was obtained.

Claims (4)

The manufacturing method of esterified cellulose nanofiber which has the following processes (1)-(5).
(1) A step of introducing a carboxy group into a hydroxyl group of the cellulose fiber to obtain a carboxylated cellulose fiber (2) A step of defibrating the carboxylated cellulose fiber in water to obtain a carboxylated cellulose nanofiber aqueous dispersion (3) After adding an acid to the carboxylated cellulose nanofiber aqueous dispersion, dehydration/washing step (4) The carboxylated cellulose nanofiber aqueous dispersion is azeotropically dehydrated together with an organic solvent to obtain a carboxylated cellulose nanofiber solvent. Step of obtaining a dispersion (5) Step of obtaining an esterified cellulose nanofiber by adding alcohol to the carboxylated cellulose nanofiber solvent dispersion to perform azeotropy for esterification, and dehydrating the produced water The manufacturing method of an esterification cellulose nanofiber which has the following processes (6)-(10).
(6) A step of introducing a carboxy group into the hydroxyl group of the cellulose fiber to obtain a carboxylated cellulose fiber (7) A step of treating the carboxylated cellulose fiber with an acid, followed by dehydration/washing (8) the carboxylated cellulose fiber, Azeotropically dehydrating with an organic solvent to obtain a carboxylated cellulose fiber solvent dispersion (9) Alcohol is added to the carboxylated cellulose fiber solvent dispersion to effect azeotropy and dehydrate the produced water. Thereby obtaining esterified cellulose fibers (10) a step of defibrating the esterified cellulose fibers to obtain esterified cellulose nanofibers The manufacturing method according to claim 1, wherein the organic solvent is an organic solvent insoluble in water. The manufacturing method according to claim 1, wherein the organic solvent is toluene, xylene, cyclohexane, or hexane.