JP6671935B2 - Method for producing dry solid material of cellulose nanofiber - Google Patents

Description

  The present invention relates to a method for producing a dried solid of cellulose nanofiber. Further, the present invention relates to a method for producing a cellulose nanofiber dispersion in which the dried solid is redispersed in a solvent.

  Cellulose nanofiber (hereinafter, sometimes referred to as CNF) is a fine fiber having a size of about 4 to several hundreds nm, which is excellent in aqueous dispersibility, and maintains the viscosity of food, cosmetics, medical products, paints, and the like. It is expected to be used as a raw material for foodstuffs, to retain moisture, to improve food stability, to be used as a low-calorie additive, or as an emulsification stabilizing aid.

  In a solid obtained by drying CNF in a state of being dispersed in water (wet state), hydrogen bonds are formed between fine cellulose fibers. Therefore, even if water is added to this dry solid, it is not dried (wet state). Various properties such as solubility, dispersibility, degree of sedimentation, and viscosity of (state) are not restored. For this reason, CNF is usually manufactured in a state of being dispersed in water (wet state), and is usually used in various applications without being dried without being dried.

  However, in order to stabilize the wet state of CNF, several times to several hundred times of weight of water is required for CNF, and various problems such as securing storage space and increasing storage and transportation costs. There is.

  As a means for solving this problem, other than a freeze-drying method and a critical point drying method, a method of drying after substitution treatment with an organic solvent (Patent Document 1) has been proposed.

JP-A-6-233691

  However, when CNF is freeze-dried, enormous energy is required, and depending on the conditions, when water between the fine fibers of CNF is frozen, the growth of ice crystals larger than the voids between the fine cellulose fibers may occur. This causes problems such as the association of fine fibers of CNF.

  In addition, the voids between the fine fibers of CNF are very small, and a large amount of water is hydrated on the surface of the fine cellulose fibers. Required. Further, since moisture that cannot be replaced by the solvent is present therein, the surfaces of the fine cellulose fibers of CNF are strongly bonded to each other by hydrogen bonding during the drying process of the solvent. For this reason, it is difficult to restore the state of the original CNF.

  Therefore, the present invention provides a CNF dispersion obtained by re-dispersing a CNF dry solid obtained by drying a stably dispersed CNF dispersion in water, in comparison with a CNF dispersion before drying. It is an object of the present invention to provide a method for producing a CNF dry solid having characteristics (redispersibility) with little change.

The present invention provides the following [1] to [6].
[1] A method for producing a dry solid material of cellulose nanofiber,
(A) a step of fibrillating the cellulose raw material to obtain a cellulose nanofiber having an average fiber diameter of 2 to 500 nm;
(B) a step of shortening the cellulose nanofiber obtained in (A) to have a mean fiber length of 0.2 to 1.0 μm; and (C) a cellulose nanofiber obtained in (B). A method for producing a dried solid of cellulose nanofibers, comprising the step of drying
[2] The cellulose nanofiber obtained in the above (A) is a cellulose nanofiber having a carboxyl group content of 0.6 mmol / g to 3.0 mmol / g based on the absolute dry weight of the cellulose nanofiber. The method for producing a dried solid of cellulose nanofiber according to [1], which is characterized in that:
[3] The method according to [1], wherein the cellulose nanofiber obtained in (A) is a cellulose nanofiber having a degree of carboxymethyl substitution per glucose unit of the cellulose of 0.01 to 0.50. A method for producing a dried solid of cellulose nanofiber according to the above.
[4] The cellulose nanofiber obtained in the above (A) is a cellulose nanofiber having a degree of cation substitution per glucose unit of the cellulose of 0.02 to 0.50. Method for producing a dried solid of cellulose nanofibers.
[5] The cellulose nanofiber according to any one of [1] to [4], wherein the step (B) of shortening the fiber is a fiber shortening treatment using hydrogen peroxide. A method for producing a dried solid.
[6] A cellulose comprising a step of redispersing a dry solid of cellulose nanofiber obtained by the method according to any one of [1] to [5] in a solvent to obtain a cellulose nanofiber dispersion. A method for producing a nanofiber dispersion.

  According to the present invention, the viscosity, transparency and other properties of a CNF dispersion obtained by redispersing a CNF dry solid obtained by drying a stably dispersed CNF dispersion in water are compared with those of a CNF dispersion before drying. As a result, it is possible to provide a dry solid of CNF having characteristics (redispersibility) with little change.

  The dry solid of CNF obtained by the present invention is obtained by dispersing the solid in water to obtain wet CNF, and various properties such as solubility, dispersibility, sedimentation, and viscosity of wet CNF before drying. (Redispersibility).

  Although it is not clear why the dry solid matter of the CNF of the present invention exhibits excellent redispersibility, the formation of hydrogen bonds between fibers considered to be a factor that reduces the redispersibility as a result of CNF shortening treatment. It is speculated that the entanglement between fibers and fibers can be suppressed and controlled, so that the redispersibility of the dried solid can be significantly improved.

  In the present invention, the term “dry solid” refers to a dried state in which the water content is 20% by mass or less. The water content is preferably from 0 to 20% by mass, and more preferably from 0 to 15% by mass from the viewpoint of reducing transportation costs. At the time of drying, it may be dried to a water content of 0% (absolutely dry). For example, absolute drying can be performed by drying at 105 ° C. for 3 hours.

  Examples of the dried solid of cellulose nanofibers include those obtained by drying a dispersion liquid of cellulose nanofibers and those obtained by drying a liquid mixture of cellulose nanofibers and a water-soluble polymer. The latter is preferred from the viewpoint of redispersibility. Examples of the water-soluble polymer include cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, and starch. , Kudzu flour, positive starch, phosphorylated starch, corn starch, gum arabic, locust bean gum, gellan gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein dissolved product, peptone, polyvinyl alcohol , Polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, polymalic acid, polyglycer Resin, latex, rosin-based sizing agent, petroleum resin-based sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide / polyamine resin, polyethylene imine, polyamine, vegetable gum, polyethylene oxide, hydrophilic cross-linked polymer, polyacryl Acid salt, starch polyacrylic acid copolymer, tamarind gum, gellan gum, pectin, guar gum, colloidal silica and mixtures of one or more thereof. Among them, carboxymethylcellulose and its salts are preferably used from the viewpoint of compatibility.

  The dried solid material of the cellulose nanofiber is dehydrated and dried after adjusting the pH of the aqueous dispersion of the cellulose nanofiber or the mixture containing the cellulose nanofiber dispersion and the water-soluble polymer to 9 to 11, and then drying. Is preferred from the viewpoint of redispersibility. When the water-soluble polymer is mixed with the dispersion liquid of the cellulose nanofiber, the compounding amount of the water-soluble polymer is preferably 5 to 50% by weight based on the absolute dry solid content of the cellulose nanofiber. If it is less than 5% by weight, a sufficient redispersibility effect is not exhibited. On the other hand, if it exceeds 50% by weight, problems such as a decrease in viscosity characteristics and dispersion stability, which are characteristics of cellulose nanofibers, occur.

(Cellulose nanofiber)
In the present invention, CNF is a fine fiber having a fiber width of about 2 to 500 nm and an aspect ratio of 100 or more, and can be obtained by fibrillating a cellulose material such as pulp.

(Cellulose raw material)
In the present invention, as a cellulose raw material, plants (for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood Bleached Kraft Pulp (LUKP), Hardwood Bleached Kraft Pulp (LBKP), Softwood Unbleached Sulfite Pulp (NUSP), Softwood Bleached Sulfite Pulp (NBSP) Thermomechanical Pulp (TMP), Recycled Pulp, Used Paper, etc. Ascidians), algae, microorganisms (for example, acetic acid bacteria (Acetobacter)), those derived from microbial products, etc. are known, and any of them can be used in the present invention. Preferably, cellulose fibers derived from plants or microorganisms And more preferably a plant-derived cellulose fiber.

(Carboxymethylation)
In the present invention, when carboxymethylated cellulose is used as the chemically modified cellulose, the carboxymethylated cellulose may be obtained by carboxymethylating the above-mentioned cellulose raw material by a known method, using a commercially available product. Is also good. In any case, it is preferable that the degree of carboxymethyl group substitution per anhydroglucose unit of cellulose is 0.01 to 0.50. An example of a method for producing such carboxymethylated cellulose includes the following method. Cellulose is used as the starting material, and 3 to 20 times by weight of water and / or lower alcohol as a solvent, specifically, water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary A single medium such as butanol or a mixed medium of two or more kinds is used. The mixing ratio of the lower alcohol when the lower alcohol is mixed is 60 to 95% by weight. As the mercerizing agent, 0.5 to 20 moles of alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, is used in an amount of 0.5 to 20 moles per anhydroglucose residue of the starting material. The bottoming raw material, a solvent and a mercerizing agent are mixed, and a mercerization treatment is performed at a reaction temperature of 0 to 70 ° C, preferably 10 to 60 ° C, and a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added in a molar amount of 0.05 to 10.0 times per glucose residue, and the reaction temperature is 30 to 90 ° C, preferably 40 to 80 ° C, and the reaction time is 30 minutes to 10 hours, preferably 1 hour. Perform etherification reaction for ~ 4 hours.

(Carboxylation)
In the present invention, when a carboxylated (oxidized) cellulose is used as the chemically modified cellulose, the carboxylated cellulose (also referred to as oxidized cellulose) can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material by a known method. it can. Although not particularly limited, at the time of carboxylation, the amount of the carboxyl group is adjusted to be 0.6 to 3.0 mmol / g with respect to the absolute dry weight of the anion-modified cellulose nanofiber. And more preferably adjusted to be 1.0 mmol / g to 2.0 mmol / g. 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 or a mixture thereof. Methods can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and the cellulose fiber having an aldehyde group and a carboxyl group (—COOH) or a carboxylate group (—COO—) on the surface. Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by weight or less.

  An N-oxyl compound refers to a compound that can generate a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes a 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 cellulose as a raw material. For example, the amount is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and still more preferably 0.05 to 0.5 mmol, based on 1 g of absolutely dried cellulose. Further, the amount is preferably about 0.1 to 4 mmol / L with respect to the reaction system.

  Bromides are compounds containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Further, iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and still more preferably 0.5 to 5 mmol, based on 1 g of absolutely dried cellulose.

  As the oxidizing agent, known agents can be used. For example, halogen, hypohalous acid, halogenous acid, perhalic acid or salts thereof, halogen oxide, peroxide and the like can be used. Among them, sodium hypochlorite which is inexpensive and has a low environmental load is preferable. The appropriate amount of the oxidizing agent is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, based on 1 g of absolutely dried cellulose. . Further, for example, 1 to 40 mol is preferable for 1 mol of the N-oxyl compound.

  In the step of oxidizing cellulose, the reaction can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40 ° C, and may be room temperature of about 15 to 30 ° C. Since a carboxyl group is generated in the cellulose as the reaction proceeds, a decrease in the pH of the reaction solution is observed. In order for the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. Water is preferred as the reaction medium because of its easy handling and little side reaction.

  The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of the oxidation, and is usually 0.5 to 6 hours, for example, about 0.5 to 4 hours.

  Further, the oxidation reaction may be performed 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 of the oxidized cellulose can be reduced without being inhibited by the salt produced as a by-product in the first-stage reaction. Can be well oxidized.

As another example of the carboxylation (oxidation) method, there can be mentioned a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, at least the hydroxyl groups at the 2- and 6-positions of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. The ozone concentration in the gas containing ozone is preferably from 50 to 250 g / m3, and more preferably from 50 to 220 g / m3. The amount of ozone added to the cellulose raw material is preferably 0.1 to 30 parts by weight, more preferably 5 to 30 parts by weight, when the solid content of the cellulose raw material is 100 parts by weight. The ozone treatment temperature is 0
To 50 ° C, more preferably 20 to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 to 360 minutes, preferably about 30 to 360 minutes. When the conditions of the ozone treatment are within these ranges, the cellulose can be prevented from being excessively oxidized and decomposed, and the yield of oxidized cellulose is improved. After the ozone treatment, an additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the re-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, these oxidizing agents may be dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the additional oxidation treatment may be performed by immersing the cellulose raw material in the solution.

  The amount of the carboxyl group of the oxidized cellulose can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent and the reaction time.

(Cationization)
In the present invention, when carboxylated (oxidized) cellulose is used as the chemically modified cellulose, cationization such as glycidyltrimethylammonium chloride, 3-chloro-2hydroxypropyltrialkylammonium hydrate or its halohydrin type is used as the above-mentioned cellulose raw material. A cation-modified cellulose can be obtained by reacting the agent with an alkali metal hydroxide (such as sodium hydroxide or potassium hydroxide) as a catalyst in the presence of water and / or an alcohol having 1 to 4 carbon atoms. . In this method, the degree of cation substitution per glucose unit of the obtained cation-modified cellulose is controlled by controlling the amount of the cationizing agent to be reacted and the composition ratio of water and / or an alcohol having 1 to 4 carbon atoms. Can be adjusted.

  The cation-modified cellulose preferably has a degree of cation substitution per glucose unit of 0.02 to 0.50. By introducing a cation substituent into cellulose, the celluloses repel each other electrically. For this reason, the cellulose into which the cation substituent is introduced can be easily nano-defibrated. If the degree of cation substitution per glucose unit is less than 0.02, nanofibrillation cannot be sufficiently performed. On the other hand, if the degree of cation substitution per glucose unit is greater than 0.50, the swelling or dissolution may result in the inability to obtain a nanofiber. In order to perform defibration efficiently, it is preferable that the oxidized cellulosic material obtained above is washed.

(Esterification)
In the present invention, when a cellulose into which a phosphate group is introduced is used as the chemically modified cellulose, the compound having a phosphate group as the cellulose raw material includes phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, and phosphoric acid. Trisodium, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid Triammonium, ammonium pyrophosphate, ammonium metaphosphate and the like. These can be used alone or in combination of two or more to introduce a phosphate group. The ratio of the compound having a phosphate group to the cellulose raw material is preferably 0.1 to 500 parts by weight, more preferably 1 to 400 parts by weight, in terms of the amount of phosphorus element, relative to 100 parts by weight of the solid content of the cellulose raw material. Part by weight, more preferably 2 to 200 parts by weight.

(Defibrillation)
In the present invention, the device for defibrating is not particularly limited, but a high-speed rotation type, a colloid mill type, a high pressure type, a roll mill type, applying a strong shearing force to the aqueous dispersion using an apparatus such as an ultrasonic type. Is preferred. In particular, for efficient defibration, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer capable of applying a pressure of 50 MPa or more to the aqueous dispersion and applying a strong shearing force. The pressure is more preferably at least 100 MPa, even more preferably at least 140 MPa. In addition, prior to the defibration / dispersion treatment with a high-pressure homogenizer, the above-mentioned CNF can be subjected to a pretreatment, if necessary, using a known mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer. It is. The average fiber diameter of the cellulose nanofiber after defibration is preferably from 2 to 500 nm, and particularly preferably from 3 to 150 nm from the viewpoint of improving redispersion.

(Short fiber processing)
The above CNF is subjected to a short fiber treatment. In this step, an auxiliary agent is used. The auxiliary agent is not particularly limited, but is preferably an oxidizing agent or a reducing agent. As the oxidizing agent or the reducing agent, those having activity in an alkaline region can be used. Examples of the oxidizing agent include oxygen, ozone, hydrogen peroxide, hypochlorite, and the like, and one or more of these may be used in combination. Examples of the reducing agent include sodium borohydride, hydrosulfite, sulfite, and the like, and one or more of these may be used in combination. From the viewpoint of reaction efficiency, hydrogen peroxide is preferable. When hydrogen peroxide is used, its addition amount is preferably 0.01 to 10% by weight, but more preferably 0.1 to 5% by weight, based on the absolutely dried CNF. Preferably, it is 0.2 to 2% by weight.

Further, the short fiber treatment of the CNF may be performed under alkaline conditions. In this case, the pH of the system in the fiber shortening treatment reaction is preferably from 8 to 14, more preferably from 9 to 13, and even more preferably from 9 to 11. As the alkali to be used, an alkali metal hydroxide, specifically, sodium hydroxide, potassium hydroxide, or the like may be used as long as it is water-soluble. From the viewpoint of production cost, sodium hydroxide is most suitable.
The temperature of the above-mentioned CNF shortening treatment is preferably from 40 to 100C, more preferably from 50 to 100C, even more preferably from 60 to 90C. The reaction time is preferably 0.5 hours or more, more preferably 1 to 24 hours, and even more preferably 1.5 to 12 hours. The concentration of CNF in the system is preferably 1 to 20% by weight, more preferably 1 to 15% by weight, and still more preferably 1 to 10% by weight.

(Production method)
The dry solid substance of CNF of the present invention can be obtained by dehydrating and drying an aqueous suspension of CNF. In addition, by adjusting the pH of the aqueous suspension to 9 to 11, a dried solid of cellulose nanofibers having better redispersibility can be obtained.

(Drying method)
In the method of the present invention, the dehydration / drying method may be any conventionally known method, and examples thereof include spray drying, pressing, air drying, hot air drying, and vacuum drying. Examples of the drying apparatus specifically used in the method of the present invention are as follows. That is, continuous tunnel dryers, band dryers, vertical dryers, vertical turbo dryers, multistage disk dryers, through-air dryers, rotary dryers, flash dryers, spray dryers, spray dryers , Cylindrical drying device, drum drying device, screw conveyor drying device, rotary drying device with heating tube, vibration transport drying device, batch type box type drying device, through-air drying device, vacuum box type drying device, stirring drying device, etc. Can be used alone or in combination of two or more. Among them, the use of a drum drying device is preferable from the viewpoint of energy efficiency because heat energy is directly supplied to the object to be dried uniformly. In addition, in order to increase the efficiency of the drying process, it is common practice to perform pre-concentration treatment on the cellulose nanofibers containing water before drying so that the water content is reduced as much as possible. Is an obstacle. On the other hand, by forming a thin film on the drum using a blade or a die and drying it, the drying process can be performed more efficiently, uniformly and in a short time. Further, the drum drying device is preferable in that the dried product can be recovered immediately without applying excessive heat.
(Redispersion process)
The dried solid of cellulose nanofibers obtained according to the present invention can be made into a cellulose nanofiber dispersion by redispersing (nanodispersing) in a solvent. The apparatus for redispersing (nanodispersing) the dried solid in a solvent is not particularly limited, but can be dispersed by a disperser such as a homomixer. The dispersion medium is most preferably water, and the solid content concentration in the dispersion medium is not particularly limited, but is preferably about 0.1 to 10% by mass, and more preferably about 1 to 5% by mass.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

<Production of carboxylated (TEMPO oxidation) CNF dispersion>
5 g of bleached unbeaten kraft pulp (whiteness 85%) derived from conifers was added to 500 ml of an aqueous solution in which 39 mg of TEMPO (Sigma Aldrich) and 514 g of sodium bromide were dissolved, and the mixture was stirred until the pulp was uniformly dispersed. . An aqueous sodium hypochlorite solution was added to the reaction system to a concentration of 5.5 mmol / g, and an oxidation reaction was started. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by sequentially adding a 3M aqueous sodium hydroxide 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 through a glass filter to separate pulp, and the pulp was sufficiently washed with water to obtain oxidized pulp (hereinafter, also referred to as carboxylated cellulose, carboxylated pulp, and TEMPO oxidized pulp). At this time, the pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g.

  Thereafter, the TEMPO oxidized pulp was adjusted to 1.0% (w / v) with water and treated five times with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a TEMPO oxidized CNF dispersion having an average fiber diameter of 4 nm. .

<Method for measuring carboxyl group content>
60 ml of a 0.5% by weight carboxylated cellulose slurry (aqueous dispersion) was prepared, and a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. The electrical conductivity was measured until the value became, and the amount of sodium hydroxide consumed in the neutralization step of the weak acid having a slow change in electrical conductivity (a) was calculated using the following formula: the amount of carboxyl groups [mmol / g carboxylated cellulose] = a [ml] × 0.05 / mass of carboxylated cellulose [g].

<Production of carboxymethylated CNF dispersion>
200 g of pulp (NBKP (softwood bleached kraft pulp), manufactured by Nippon Paper Industries) and 111 g of sodium hydroxide by dry weight were added to a stirrer capable of mixing pulp, and the pulp solid content was 20% (w / v). ) Was added. Then, after stirring at 30 ° C. for 30 minutes, 216 g (in terms of active ingredient) of sodium monochloroacetate was added. After stirring for 30 minutes, the temperature was raised to 70 ° C., and the mixture was stirred for 1 hour. Thereafter, the reaction product was taken out, neutralized and washed to obtain a carboxymethylated pulp having a carboxymethyl substitution degree of 0.25 per glucose unit. Thereafter, the carboxymethylated pulp is made 1% solids with water, and is fibrillated by treating it with a high-pressure homogenizer at 20 ° C. and a pressure of 150 MPa five times to obtain a carboxymethylated CNF dispersion having an average fiber diameter of 11 nm. Was.

(Method of measuring carboxymethyl substitution degree per glucose unit)
About 2.0 g of carboxymethylated cellulose fiber (absolutely dried) was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol nitrate was added, and the mixture was shaken for 3 hours to convert the carboxymethylcellulose salt (CM cellulose) into hydrogenated CM cellulose. 1.5 to 2.0 g of hydrogenated CM-modified cellulose (absolutely dried) was precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. The hydrogenated CM cellulose was wet with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Excess NaOH was back titrated with 0.1 N H2SO4 using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) was calculated by the following equation:
A = [(100 × F ′ − (0.1N H 2 SO 4) (mL) × F) × 0.1] / (absolute dry weight of hydrogenated CM cellulose (g))
DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required for neutralization of 1 g of hydrogenated CM cellulose
F ': Factor of 0.1N H2SO4 F: Factor of 0.1N NaOH

<Production of cationized CNF dispersion>
200 g of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) and 24 g of sodium hydroxide by dry weight were added to a stirrer capable of stirring pulp, and water was added so that the pulp solid concentration became 15% by weight. Was added. Thereafter, the mixture was stirred at 30 ° C. for 30 minutes and then heated to 70 ° C., and 190 g (in terms of active ingredient) of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added as a cationizing agent. After the reaction for 1 hour, the reaction product was taken out, neutralized and washed to obtain a cation-modified cellulose having a degree of cation substitution of 0.04 per glucose unit. Thereafter, the cation-modified cellulose is adjusted to a solid concentration of 1% (w / v) with water, and treated five times with a high-pressure homogenizer at 20 ° C. and a pressure of 140 MPa to give a cellulose nanofiber dispersion derived from cation-modified cellulose having an average fiber diameter of 15 nm. I got

(Measurement method of cation substitution degree per glucose unit)
The degree of substitution of the cationic group was calculated by the following equation after drying the sample (cationically modified cellulose) and measuring the nitrogen content with a total nitrogen analyzer TN-10 (Mitsubishi Chemical). The term “degree of substitution” as used herein indicates an average value of the number of moles of the substituent per mole of the anhydrous glucose unit.
Degree of cation substitution = (162 × N) / (1−151.6 × N)
N: Nitrogen content

(Example 1)
A 0.5% by weight aqueous dispersion of the carboxylated CNF (average fiber length: 2.78 μm, aspect ratio: 150) was heated to 80 ° C. While stirring with a propeller blade at a speed of 600 rpm, 0.2% by weight of hydrogen peroxide based on the absolute dry weight of CNF was added, and the mixture was stirred for 2 hours to shorten the fiber. This aqueous dispersion was subjected to a vapor pressure of 0.5 MPa. G, dried with a drum drier D0303 (Katsuragi Kogyo) having a drum rotation speed of 2 rpm to obtain a dry solid of carboxylated CNF having a water content of 5% by weight.

  Next, water was added to the dry solid obtained above so as to form a 1% by weight aqueous suspension, and the mixture was stirred for 60 minutes using a TK homomixer (6,000 rpm) to redisperse the carboxylated CNF. An aqueous suspension was obtained.

<Method of measuring average fiber diameter, average fiber length, and aspect ratio of CNF>
The average fiber diameter and average fiber length of CNF were analyzed for 200 randomly selected fibers using a field emission scanning electron microscope (FE-SEM). The aspect ratio was calculated by the following equation:
Aspect ratio = average fiber length / average fiber diameter.

<Measurement of B-type viscosity>
The B-type viscosity of CNF (solid content 1.0%, 25 ° C.) was measured. The measurement conditions for the B-type viscosity were 60 rpm for 3 minutes.

<Measurement of transparency>
The transparency (transmittance of light at 660 nm) of the CNF dispersion (solid content: 0.1%) was measured using a UV spectrophotometer U-3000 (Hitachi High-Tech).

<Evaluation of restoration rate>
The B-type viscosity and the restoration rate of the transparency were calculated by the following equations.
Restoration rate (%) = (viscosity or transparency after redispersion) / (viscosity or transparency before drying) × 100

(Example 2)
The procedure was performed in the same manner as in Example 1 except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 0.02% by weight.

(Example 3)
The procedure was performed in the same manner as in Example 1 except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 8% by weight.

(Example 4)
The procedure was performed in the same manner as in Example 1 except that the processing temperature in the shortening treatment was changed from 80 ° C to 50 ° C.

(Example 5)
The procedure was performed in the same manner as in Example 1 except that the processing temperature in the shortening treatment was changed from 80 ° C to 90 ° C.

(Example 6)
The procedure was performed in the same manner as in Example 1 except that the treatment time in the fiber shortening treatment was changed from 2 hours to 0.75 hours.

(Example 7)
The procedure was performed in the same manner as in Example 1 except that the pH in the shortening treatment was changed from 7 to 9.

(Example 8)
A 0.5% by weight aqueous dispersion of the carboxymethylated CNF (average fiber length: 1.45 μm, aspect ratio: 110) was heated to 80 ° C. While stirring with a propeller blade at a speed of 600 rpm, 0.2% by weight of hydrogen peroxide based on the absolute dry weight of CNF was added, and the mixture was stirred for 2 hours to shorten the fiber. This aqueous dispersion was subjected to a vapor pressure of 0.5 MPa. G, dried with a drum drier D0303 (Katsuragi Kogyo) having a drum rotation speed of 2 rpm to obtain a dried solid of carboxymethylated CNF having a water content of 5% by weight. Next, water was added to the above-obtained dry solid so as to form a 1% by weight aqueous suspension, and the mixture was stirred for 60 minutes using a TK homomixer (6,000 rpm) to regenerate carboxymethylated CNF. A dispersed aqueous suspension was obtained.

(Example 9)
Example 8 was carried out in the same manner as in Example 8 , except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 0.02% by weight.

(Example 10)
Example 8 was carried out in the same manner as in Example 8 , except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 8% by weight.

(Example 11)
Example 8 was carried out in the same manner as in Example 8 , except that the treatment temperature in the shortening treatment was changed from 80 ° C to 50 ° C.

(Example 12)
Example 8 was carried out in the same manner as in Example 8 , except that the processing temperature in the shortening treatment was changed from 80 ° C to 90 ° C.

(Example 13)
Example 8 was carried out in the same manner as in Example 8 , except that the treatment time in the fiber shortening treatment was changed from 2 hours to 0.75 hours.

(Example 14)
Example 8 was carried out in the same manner as in Example 8 , except that the pH in the shortening treatment was changed from 7 to 9.

(Example 15)
A 0.5% by weight aqueous dispersion of the above-mentioned cationized CNF (average fiber length: 2.18 μm, aspect ratio: 180) was heated to 80 ° C. While stirring with a propeller blade at a speed of 600 rpm, 0.2% by weight of hydrogen peroxide based on the absolute dry weight of CNF was added, and the mixture was stirred for 2 hours to shorten the fiber. This aqueous dispersion was subjected to a vapor pressure of 0.5 MPa. G, dried with a drum drier D0303 (Katsuragi Kogyo) having a drum rotation speed of 2 rpm to obtain a dried solid of carboxymethylated CNF having a water content of 5% by weight. Next, water was added to the above-obtained dry solid so as to form a 1% by weight aqueous suspension, and the mixture was stirred for 60 minutes using a TK homomixer (6,000 rpm) to regenerate carboxymethylated CNF. A dispersed aqueous suspension was obtained.

(Example 16)
Example 15 was carried out in the same manner as in Example 15 except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 0.02% by weight.

(Example 17)
Example 15 was carried out in the same manner as in Example 15 except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 8% by weight.

(Example 18)
Example 15 was carried out in the same manner as in Example 15 except that the processing temperature in the shortening treatment was changed from 80 ° C to 50 ° C.

(Example 19)
Example 15 was carried out in the same manner as in Example 15 , except that the treatment temperature in the shortening treatment was changed from 80 ° C to 90 ° C.

(Example 20)
Example 15 was carried out in the same manner as in Example 15 , except that the treatment time in the fiber shortening treatment was changed from 2 hours to 0.75 hours.

(Example 21)
The same procedure as in Example 15 was carried out except that the pH in the shortening treatment was changed from 7 to 9.

(Comparative Example 1)
The operation was performed in the same manner as in Example 1 except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 0% by weight.

(Comparative Example 2)
The procedure was performed in the same manner as in Example 1 except that the processing temperature in the shortening treatment was changed from 80 ° C. to 30 ° C.

(Comparative Example 3)
The procedure was performed in the same manner as in Example 1 except that the treatment time in the fiber shortening treatment was changed from 2 hours to 0.25 hours.

(Comparative Example 4)
5 g of bleached unbeaten kraft pulp (whiteness 85%) derived from conifers was added to 500 ml of an aqueous solution in which 39 mg of TEMPO (Sigma Aldrich) and 514 g of sodium bromide were dissolved, and the mixture was stirred until the pulp was uniformly dispersed. . An aqueous sodium hypochlorite solution was added to the reaction system to a concentration of 5.5.0 mmol / g, and an oxidation reaction was started. During the reaction, the pH in the system decreased, but the pH was adjusted to 10 by sequentially adding a 3M aqueous sodium hydroxide 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 through a glass filter to separate the pulp, and the pulp was sufficiently washed with water to obtain a carboxylated pulp. At this time, the pulp yield was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g. The average fiber length of the obtained carboxylated pulp was 1.86 mm.

<Method of measuring average fiber length of carboxylated pulp>
It measured based on ISO16065-2.

  The obtained carboxylated pulp was prepared in a 5% (w / v) aqueous dispersion, and 1% (w / v) hydrogen peroxide was added to the dispersion to the carboxylated pulp, and 1M hydroxylation was performed. The pH was adjusted to 12 with sodium. This aqueous dispersion was heated at 80 ° C. for 2 hours to shorten the carboxylated pulp, followed by sufficient washing with water and dehydration.

  The carboxylated pulp subjected to the shortening treatment is adjusted to 1.0% (w / v) with water, and treated with a high-pressure homogenizer (20 ° C., 150 MPa) five times to prepare a carboxylated (TEMPO-oxidized) CNF dispersion. Obtained.

(Comparative Example 5)
Example 8 was carried out in the same manner as in Example 8 , except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 0% by weight.

(Comparative Example 6)
Example 8 was carried out in the same manner as in Example 8 , except that the processing temperature in the shortening treatment was changed from 80 ° C to 30 ° C.

(Comparative Example 7)
Example 8 was carried out in the same manner as in Example 8 , except that the treatment time in the fiber shortening treatment was changed from 2 hours to 0.25 hours.

(Comparative Example 8)
Example 15 was carried out in the same manner as in Example 15 except that the amount of hydrogen peroxide added in the shortening treatment was changed from 0.2% by weight to 0% by weight.

(Comparative Example 9)
Example 15 was carried out in the same manner as in Example 15 except that the treatment temperature in the shortening treatment was changed from 80 ° C to 30 ° C.

(Comparative Example 10)
Example 15 was carried out in the same manner as in Example 15, except that the treatment time in the fiber shortening treatment was changed from 2 hours to 0.25 hours.

Claims (5)

(A) a step of fibrillating the cellulose raw material to obtain a cellulose nanofiber having an average fiber diameter of 2 to 15 nm;
(B) a step of shortening the cellulose nanofiber obtained in (A) to an average fiber length of 0.2 to 1.0 μm; and (C) a cellulose nanofiber obtained in (B). The step of drying
The method of manufacturing a dry solids including cellulose nanofibers,
The cellulose nanofiber obtained in (A) above has a cellulose carboxymethyl substitution degree per glucose unit of the cellulose of 0.01 to 0.50 or a cation substitution degree per glucose unit of the cellulose of 0.1 to 0.50. The above production method, which is a cellulose nanofiber of 02 to 0.50 . Method of manufacturing steps of fiber shortening of the (B) is a fiber shortening treatment with hydrogen peroxide, dry solids of the cellulose nanofiber according to claim 1. (A) a step of fibrillating the cellulose raw material to obtain a cellulose nanofiber having an average fiber diameter of 2 to 15 nm;
(B) a step of shortening the cellulose nanofiber obtained in (A) so that the average fiber length becomes 0.2 to 1.0 μm;
(C) a step of drying the cellulose nanofiber obtained in (B), and
(D) a step of redispersing the dried solid of the cellulose nanofiber obtained in (C) in a solvent to obtain a cellulose nanofiber dispersion;
A method for producing a cellulose nanofiber dispersion, comprising:   The method for producing a cellulose nanofiber dispersion according to claim 3, wherein the step (B) of shortening the fiber is a fiber shortening treatment using hydrogen peroxide. The cellulose nanofiber obtained in (A) is a cellulose nanofiber having a carboxyl group content of 0.6 mmol / g to 3.0 mmol / g based on the absolute dry weight of the cellulose nanofiber, and a glucose unit of the cellulose. The cellulose nanofiber having a degree of carboxymethyl substitution per unit weight of 0.01 to 0.50 or a cellulose nanofiber having a degree of cation substitution per glucose unit of the cellulose of 0.02 to 0.50. 3. The method for producing a cellulose nanofiber dispersion according to item 1.