JP7170380B2 - Process for producing chemically modified pulp dry solids - Google Patents

Description

The present invention relates to a method for producing chemically modified pulp dry solids.

Chemically modified pulp is useful as a raw material for cellulose nanofibers (hereinafter also referred to as "CNF") and the like. Cellulose nanofibers are fine fibers with a fiber diameter of about 2 to several hundred nm, and are excellent in water-based dispersibility, so they are expected to be applied to fields such as foods, cosmetics, medical products, and paints. Specifically, it is expected to be applied to viscosity retention of paints, reinforcement of food raw material dough, retention of moisture, improvement of food stability, low-calorie additives, emulsion stabilization aids, and the like.

The chemically modified pulp can be obtained in a state of being dispersed in water, but it is preferable to use it as a dry product in consideration of transportation costs and the like. However, since hydrogen bonds are formed between cellulose fibers in chemically modified pulp dry solids, it is difficult to sufficiently defibrate the dry solids by adding water to the dry solids. Therefore, the CNF obtained in this manner has a problem of poor dispersibility in a dispersion medium as compared with CNF obtained without drying.

In order to solve this problem, a method of drying after reducing oxidized cellulose (Patent Document 1), a method of defibrating dried oxidized cellulose using hot water (Patent Document 2), and the like have been proposed. .

JP 2015-113376 JP 2015-134870

The method described in Patent Literature 1 requires a reduction treatment, which complicates the process. Moreover, the method described in Patent Document 2 requires hot water at the time of fibrillation, which similarly complicates the process. In view of such circumstances, an object of the present invention is to provide a chemically modified pulp dry solid that gives CNF having good dispersibility by a simpler method.

The above problems are solved by the present invention described below.
(1) A method for producing chemically modified pulp dry solids, which comprises the step of drying a mixture of chemically modified pulp obtained by chemically modifying a cellulose raw material and a liquid medium at 20 to 80°C.
(2) The production method according to (1), wherein the liquid medium is water or a mixed solvent of water and a water-soluble organic solvent.
(3) The production method according to (2), wherein the amount of the water-soluble organic solvent in the mixed solvent is 10% by mass or more.
(4) According to any one of (1) to (3), wherein the chemically modified pulp has a carboxyl group content of 0.6 to 3.0 mmol/g relative to the absolute dry mass of the cellulose nanofibers. Production method.
(5) The production method according to any one of (1) to (3), wherein the chemically modified pulp has a degree of carboxymethyl substitution per glucose unit of 0.01 to 0.50.
(6) The production method according to any one of (1) to (3), wherein the chemically modified pulp has a degree of cation substitution per glucose unit of 0.02 to 0.50.
(7) The production method according to any one of (1) to (6), wherein the water-soluble organic solvent is a lower alcohol.
(8) A method for producing a chemically modified pulp dispersion, comprising dispersing the dry solids of the chemically modified pulp obtained by the method according to any one of (1) to (7) above in a dispersion medium.
(9) A method for producing cellulose nanofibers, comprising defibrating the chemically modified pulp in the chemically modified pulp dispersion liquid according to (8) above.

INDUSTRIAL APPLICABILITY The present invention can provide chemically modified pulp dry solids that provide CNF with good dispersibility in a dispersion medium.

The present invention will be described in detail below. In the present invention, "X to Y" includes X and Y which are end values. Moreover, "X or Y" means either one or both of X and Y.

1. Method for Producing Chemically Modified Pulp Dry Solid Material Chemically modified pulp is pulp obtained by chemically modifying a cellulose raw material. Chemically modified pulp is a source of CNF and is different from CNF. Preferably, the chemically modified pulp has an average fiber diameter of 10 μm or more. The method for producing chemically modified pulp dry solids of the present invention includes a step of drying a mixture of chemically modified pulp obtained by chemically modifying a cellulose raw material and a liquid medium at 20 to 80°C.

(1) Preparation of Mixture of Chemically Modified Pulp and Liquid Medium In the present invention, first, a mixture of chemically modified pulp obtained by chemically modifying a cellulose raw material and a liquid medium is prepared. The mixture may be a simple mixture of the chemically modified pulp and the liquid medium, or may be a dispersion liquid in which the chemically modified pulp is dispersed in the liquid medium. It is more preferable to acidify the chemically modified pulp before preparing the mixture. By acidifying the pulp, it is possible to improve workability in washing and dehydrating chemicals used for chemical modification contained in the chemically modified pulp. In the present invention, acidification means dispersing chemically modified pulp in water to form an aqueous dispersion, and using an acid such as a mineral acid to adjust the pH of the dispersion (water) to preferably 5 or less, more preferably 3 or less. Say things. A chemically modified pulp that has been acidified by a conventional method can be isolated and used to prepare the mixture. Even if the chemically modified pulp treated in this way is subjected to filtration and washing again, the pH of the aqueous dispersion does not become 5 or more.

(1-1) Cellulose raw materials Cellulose raw materials are known to originate from plants, animals (such as sea squirts), algae, microorganisms (such as acetobacter), and microbial products. Either can be used in the invention. Plant-derived materials include, for example, wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp ( LUKP), bleached hardwood kraft pulp (LBKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.). In the present invention, plant- or microorganism-derived cellulose fibers are preferred, and plant-derived cellulose fibers are more preferred. Cellulose feedstocks are chemically modified as described below.

(1-2) Chemical denaturation [Carboxymethylation]
Carboxymethylated cellulose can be used as chemically modified pulp. As the cellulose, the above-mentioned cellulose raw material carboxymethylated by a known method can be used, but a commercially available product may also be used. The following method can be cited as an example of the method for producing such carboxymethylated cellulose. First, the cellulose raw material is used as a starting raw material, and a solvent and a mercerizing agent are mixed. performs mercerization processing. As a solvent, 3 to 20 times by mass of water or lower alcohol, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, or a combination thereof is used. can. When a lower alcohol is mixed, the mixing ratio is 60 to 95% by mass. As the mercerizing agent, an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, can be used in an amount of 0.5 to 20 times the moles of the anhydroglucose residue of the starting material.

Then, a carboxymethylating agent is added at 0.05 to 10.0 mol per glucose residue, 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. The etherification reaction is carried out for ~4 hours to give carboxymethylated cellulose. As described above, the degree of carboxymethyl substitution per glucose unit is preferably 0.01 to 0.50, more preferably 0.02 to 0.50. If the number of substituents is less than 0.01, sufficient nano-fibrillation may not be possible. On the other hand, when the number of carboxymethyl substituents per glucose unit is greater than 0.50, the nanofibers may not be formed due to swelling or dissolution.

[Carboxylation]
Carboxylated (oxidized) cellulose (also referred to as “oxidized cellulose”) can be used as the chemically modified pulp. Carboxylated cellulose can be obtained by carboxylating (oxidizing) the aforementioned cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.6 to 3.0 mmol/g, more preferably 1.0 to 2.0 mmol/g, relative to the absolute dry mass of CNF.

As an example of a 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 bromides, iodides or mixtures thereof. A method can be mentioned. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface, resulting in a cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or carboxylate group (-COO- ⁾ on the surface. can be obtained. Although the concentration of cellulose during the reaction is not particularly limited, it is preferably 5% by mass or less.

An N-oxyl compound means a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it promotes the desired oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivatives (eg 4-hydroxy TEMPO).

The amount of the N-oxyl compound to be used is not particularly limited as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, it is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, even more preferably 0.05 to 0.5 mmol, relative to 1 g of absolute dry cellulose. Also, it 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 be dissociated and ionized in water. Also, iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide to be used can be selected within a range capable of promoting the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, even more preferably 0.5 to 5 mmol, relative to 1 g of absolute dry cellulose.

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

Oxidation of cellulose allows the reaction to 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 carboxyl groups are generated in the cellulose as the reaction progresses, the pH of the reaction solution decreases. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8-12, preferably about 10-11. Water is preferable as the reaction medium because it is easy to handle and less likely to cause side reactions.

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

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

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

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

[Cationization]
As the chemically modified cellulose, cellulose obtained by further cationizing the carboxylated cellulose can be used. The cation-modified cellulose is obtained by adding a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrate or its halohydrin type to the carboxylated cellulose raw material, and an alkali hydroxide as a catalyst. It can be obtained by reacting a metal (sodium hydroxide, potassium hydroxide, etc.) in the presence of water or an alcohol having 1 to 4 carbon atoms.

Preferably, the degree of cation substitution per glucose unit is between 0.02 and 0.50. By introducing cationic substituents into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which cationic substituents have been introduced can be easily nano-fibrillated. If the degree of cation substitution per glucose unit is less than 0.02, sufficient nanofibrillation cannot be achieved. On the other hand, if the degree of cation substitution per glucose unit is greater than 0.50, the nanofibers may not be obtained due to swelling or dissolution. In order to defibrate efficiently, the cation-modified cellulosic raw material obtained above is preferably washed. The degree of cation substitution can be adjusted by adjusting the amount of the cationizing agent to be reacted and the composition ratio of water or alcohol having 1 to 4 carbon atoms.

[Esterification]
Esterified cellulose can be used as the chemically modified cellulose. The cellulose can be obtained by a method of mixing a powder or an aqueous solution of the phosphoric acid compound A with the cellulosic raw material described above, or a method of adding an aqueous solution of the phosphoric acid compound A to a slurry of the cellulosic raw material.

Phosphoric acid compound A includes phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among these, compounds having a phosphate group are preferred because they are low in cost, easy to handle, and can improve defibration efficiency by introducing a phosphate group into the cellulose of pulp fibers. Compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, phosphorus Tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. These can be used singly or in combination of two or more. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, phosphoric acid, from the viewpoint of high efficiency of introduction of phosphate group, easy fibrillation in the fibrillation process described below, and easy industrial application is more preferred. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Further, it is preferable to use the phosphoric acid-based compound A in the form of an aqueous solution, since the uniformity of the reaction is enhanced and the efficiency of introduction of the phosphoric acid group is enhanced. The pH of the aqueous solution of the phosphoric acid-based compound A is preferably 7 or less because the efficiency of introducing phosphate groups is high, but from the viewpoint of suppressing hydrolysis of pulp fibers, the pH is preferably 3 to 7.

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

At this time, in addition to the cellulose raw material and the phosphoric acid-based compound A, a powder or an aqueous solution of a compound B other than these may be mixed. The compound B is not particularly limited, but a basic nitrogen-containing compound is preferable. "Basic" herein is defined as the pink-red color of the aqueous solution in the presence of the phenolphthalein indicator or the pH of the aqueous solution being greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as the effect of the present invention is exhibited, but a compound having an amino group is preferable. Examples include, but are not limited to, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, urea is preferable because it is inexpensive and easy to handle. The amount of compound B added is preferably 2 to 1,000 parts by mass, more preferably 100 to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. Although the reaction time is not particularly limited, it is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the esterification reaction conditions are within these ranges, cellulose can be prevented from being excessively esterified and easily dissolved, and the yield of phosphate-esterified cellulose is improved. After dehydrating the obtained phosphate-esterified cellulose suspension, it is preferable to heat-treat at 100 to 170° C. from the viewpoint of suppressing hydrolysis of cellulose. Furthermore, it is preferable to heat at 130° C. or less, preferably 110° C. or less while water is contained in the heat treatment, and heat at 100 to 170° C. after removing the water.

The degree of phosphate group substitution per glucose unit of the phosphated cellulose is preferably 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses electrically repel each other. Therefore, cellulose into which a phosphate group has been introduced can be easily nano-fibrillated. If the degree of phosphate group substitution per glucose unit is less than 0.001, sufficient nano-fibrillation cannot be achieved. On the other hand, if the degree of phosphate group substitution per glucose unit is greater than 0.40, the nanofibers may not be obtained due to swelling or dissolution. In order to perform defibration efficiently, it is preferable that the obtained phosphoric esterified cellulose-based raw material is washed by washing with cold water after boiling.

(1-3) Liquid Medium The liquid medium is preferably water, a water-soluble organic solvent, or a mixed solvent thereof. Considering the dispersibility of the chemically modified pulp, the liquid medium is preferably water or a mixed solvent of water and a water-soluble organic solvent. When the liquid medium is water, the aqueous dispersion of the chemically modified pulp prepared as described above can be directly subjected to drying. Alternatively, the water dispersion may be dried, filtered, or the like to obtain a concentrated water dispersion.

When the liquid medium is used as the mixed solvent, a water-soluble organic solvent is added to the aqueous dispersion of the chemically modified pulp prepared as described above or the aqueous dispersion of the acidified chemically modified pulp, or A part may be replaced with a water-soluble organic solvent. The substitution is performed by removing water from the chemically modified pulp aqueous dispersion by drying or filtering to obtain a concentrated aqueous dispersion or a chemically modified pulp wet cake, to which a water-soluble organic solvent is added. can be prepared by The amount of the liquid medium is preferably such that the concentration of the chemically modified pulp in the mixture is 10 to 40% by mass, more preferably 20 to 30% by mass.

A water-soluble organic solvent is an organic solvent that dissolves in water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, Dimethylsulfoxide, acetonitrile, and combinations thereof. Among them, lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol, and 2-propanol are preferred, and from the viewpoint of safety and availability, methanol and ethanol are more preferred, and ethanol is even more preferred. The amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. Although the upper limit of the amount is not limited, it is preferably 95% by mass or less, more preferably 90% by mass or less. Moreover, the liquid medium may contain a water-insoluble organic solvent to the extent that the effects of the invention are not impaired.

(2) Drying In this step, the mixture is dried at a relatively low temperature of 20 to 80° C. to obtain a dry solid of chemically modified pulp. Drying may be carried out in a known manner. If the drying temperature is high, the cellulose will be colored or damaged, and if the drying temperature is low, the production efficiency will decrease. Therefore, the drying temperature is preferably 20-70°C, more preferably 30-60°C. Drying is preferably carried out at sub-atmospheric pressure.

Examples of drying methods include known methods such as spray drying, pressing, air drying, hot air drying, and vacuum drying. In the present invention, continuous tunnel dryers, band dryers, vertical dryers, vertical turbo dryers, multi-stage disk dryers, through-air dryers, rotary dryers, flash dryers, spray dryer dryers, atomization Drying equipment, cylindrical drying equipment, drum drying equipment, screw conveyor drying equipment, rotary drying equipment with heating tubes, vibration transport drying equipment, etc., batch type box drying equipment, ventilation drying equipment, vacuum box drying equipment, or stirring drying equipment Devices and the like can be used alone or in combination. Prior to drying, the amount of liquid medium in the mixture may be reduced as described above. Means for reducing the amount of liquid medium are not limited, but include separation means such as filtration.

2. Chemically Modified Pulp Dry Solids The dry solids refer to those in an absolutely dry state (0% by mass of liquid medium) or those in a wet state in which the amount of liquid medium is 20% by mass or less. From the viewpoint of reducing transportation costs, the amount of the liquid medium is preferably 0 to 20% by mass, more preferably 0 to 15% by mass.

Conventionally, when a dispersion liquid in which dried chemically modified pulp is re-dispersed in a dispersion medium is defibrated, nano-fibrillation can be achieved to some extent and a CNF dispersion can be obtained, but the nano-fibrillation is not sufficient. There was a problem that foreign matter remained. However, according to the present invention, it is possible to obtain a CNF dispersion containing almost no foreign matter, that is, having good dispersibility even if the dispersion is re-dispersed. The reason for this is not limited, but by drying the chemically modified pulp at a relatively low temperature of 20 to 80° C., the generation of hydrogen bonds between fibers, which is considered to be a factor in reducing the electrical repulsion suitable for fibrillation, and It is presumed that this is because entanglement between fibers can be suppressed. When the liquid medium contains a water-soluble organic solvent, the formation of hydrogen bonds can be suppressed more effectively, so the effect becomes even more pronounced.

The device for re-dispersing the dry solid matter in the dispersion medium to obtain a dispersion liquid is not particularly limited, but a dispersing machine such as a homomixer can be used. As the dispersion medium used for redispersion, water, the water-soluble organic solvent, and a mixed solvent thereof can be used, and water is most preferable. The solid content concentration in the re-dispersed dispersion is not particularly limited, but is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass. Cellulose nanofibers (CNF) can be produced by defibrating the redispersion liquid. Defibrillation can be performed using a known device such as a high-pressure homogenizer.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.
<Production of aqueous dispersion of carboxylated (TEMPO-oxidized) pulp>
5 g (absolute dry) of bleached unbeaten kraft pulp (85% whiteness) derived from softwood was added to 500 mL of an aqueous solution containing 39 mg of TEMPO (Sigma Aldrich) and 514 mg of sodium bromide, and stirred until the pulp was uniformly dispersed. . An aqueous sodium hypochlorite solution was added to the reaction system so as to have a concentration of 5.5 mmol/g to initiate an oxidation reaction. The pH in the system decreased during the reaction, but was adjusted to pH 10 by successively adding 3M sodium hydroxide aqueous solution. The reaction was terminated when the sodium hypochlorite was consumed and the pH in the system stopped changing. The mixture after the reaction is acidified with hydrochloric acid, filtered through a glass filter to separate the pulp, and the pulp is thoroughly washed with water to obtain oxidized pulp (hereinafter referred to as "carboxylated cellulose", "carboxylated pulp" or sometimes referred to as "TEMPO oxidized pulp") was obtained. 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.

<Method for measuring carboxyl group content>
60 mL of a 0.5% by mass slurry (aqueous dispersion) of carboxylated cellulose was prepared, and 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. It was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization step of the weak acid, in which the change in electrical conductivity is gradual: carboxyl group amount [mmol/ g carboxylated cellulose]=a [mL]×0.05/mass of carboxylated cellulose [g].

<Production of aqueous dispersion of carboxymethylated pulp>
Add 200 g of dry mass of pulp (NBKP (conifer bleached kraft pulp), manufactured by Nippon Paper Industries Co., Ltd.) and 111 g of sodium hydroxide to a stirrer that can mix pulp, and the pulp solid content is 20% by mass. I added water to make it. Then, after stirring at 30° C. for 30 minutes, 216 g of sodium monochloroacetate (converted to active ingredient) was added. After stirring for 30 minutes, the temperature was raised to 70° C. and the mixture was stirred for 1 hour. Thereafter, the reactant was taken out, neutralized, acidified with hydrochloric acid, and washed to obtain a carboxymethylated pulp having a degree of carboxymethyl substitution of 0.25 per glucose unit.

<Method for measuring degree of carboxymethyl substitution per glucose unit>
About 2.0 g of carboxymethylated cellulose fiber (absolute dry) was precisely weighed and put into a 300 mL conical flask with a common stopper. 100 mL of a liquid prepared by adding 10 mL of special grade concentrated nitric acid to 90 mL of methanol was added and shaken for 3 hours to convert carboxymethylated cellulose salt (CM cellulose) into hydrogenated CM cellulose. 1.5 to 2.0 g of hydrogenated CM cellulose (absolute dry) was accurately weighed and put into a 300 mL conical flask equipped with a common stopper. Hydrogenated CM-cellulose was wetted 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. Excess NaOH was back _- titrated with 0.1N _H2SO4 using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) was calculated by the following formula:
A=[(100×F′−(0.1N H ₂ SO ₄ ) (mL)×F)×0.1]/(absolute dry weight of hydrogen-type CM cellulose (g))
DS = 0.162 x A/(1 - 0.058 x A)
A: Amount of 1N NaOH (mL) required to neutralize 1 g of hydrogenated CM-cellulose
F: Factor of _{0.1N H2SO4} F': Factor of 0.1N NaOH

<Production of aqueous dispersion of cationized pulp>
200 g of pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) in dry mass and 24 g of sodium hydroxide in dry mass are added to a stirrer capable of stirring pulp, and water is added so that the pulp solid concentration becomes 15% by mass. added. Then, after stirring at 30° C. for 30 minutes, the temperature was raised to 70° C., and 190 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (converted to active ingredient) was added as a cationizing agent. After reacting for 1 hour, the reactant was taken out, neutralized and washed to obtain a cationically modified cellulose having a degree of cation substitution per glucose unit of 0.04.

<Method for measuring degree of cation substitution per glucose unit>
The degree of substitution of cationic groups was calculated by the following formula after drying a sample (cationically modified cellulose) and measuring the nitrogen content with a total nitrogen analyzer TN-10 (manufactured by Mitsubishi Chemical Corporation). The degree of substitution here means the average number of moles of substituents per mole of anhydroglucose unit.
Cation substitution degree = (162 × N) / (1-151.6 × N)
N: nitrogen content

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

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

<Measurement of transparency>
The transparency (660 nm light transmittance) of the CNF aqueous dispersion (solid content 1.0% by mass) was measured using a UV spectrophotometer U-3000 (manufactured by Hitachi High-Tech).

[Reference example 1]
Water was added to the carboxylated pulp to prepare an aqueous dispersion with a solid content concentration of 1.0% by mass, neutralized with sodium hydroxide, and then treated twice with a high pressure homogenizer (20 ° C., 150 MPa) to obtain carboxyl An aqueous CNF dispersion derived from oxidized pulp (average fiber diameter: 4 nm, aspect ratio: 150) was obtained.

[Reference example 2]
Water is added to the carboxymethylated pulp to prepare an aqueous dispersion with a solid content concentration of 1.0% by mass, neutralized with sodium hydroxide, and then treated twice with a high pressure homogenizer (20 ° C., 150 MPa), An aqueous CNF dispersion derived from carboxymethylated pulp (average fiber length: 12 nm, aspect ratio: 130) was obtained.

[Reference example 3]
Water was added to the cationized pulp to prepare an aqueous dispersion with a solid content concentration of 1.0% by mass, neutralized with sodium hydroxide, and then treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to An aqueous CNF dispersion (average fiber length: 20 nm, aspect ratio: 110) derived from oxidized pulp was obtained.

[Example 1]
A dispersion having a solid concentration of 1.0% by weight was prepared by dispersing the carboxylated pulp in 50 mL of a liquid medium. However, the composition of the liquid medium was water:ethanol=25% by mass:75% by mass. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel and drying it with a blower dryer at 50 ° C. until the mass became constant. A dry solid was obtained.

Next, water was added to the dry solid of the carboxylated pulp thus obtained to obtain an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxylated pulp (average fiber diameter: 4 nm, aspect ratio: 150). got

[Example 2]
A mixed solvent dispersion of carboxylated pulp (solid concentration: 1.0% by mass) was obtained in the same manner as in Example 1, except that the composition of the liquid medium was water:ethanol=10% by mass:90% by mass. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, and this was dried in a blower dryer at 50 ° C. until the mass became constant. A dry solid was obtained.

Next, water was added to the dry solid of the carboxylated pulp thus obtained to obtain an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxylated pulp (average fiber diameter: 4 nm, aspect ratio: 150). got

[Example 3]
A dry solid of carboxylated pulp having a solid concentration of 95% by mass was obtained in the same manner as in Example 1, except that the drying temperature was 30°C. Next, water was added to the dry solid of the carboxylated pulp to form an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxylated pulp (average fiber diameter: 4 nm, aspect ratio: 150). got

[Example 4]
A dry solid of carboxylated pulp having a solid content concentration of 97% by mass was obtained in the same manner as in Example 1, except that methanol was used instead of ethanol. Next, water was added to the dry solid of the carboxylated pulp to obtain an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxylated pulp (average fiber diameter: 4 nm, aspect ratio: 150). got

[Example 5]
A dispersion having a solid concentration of 1.0% by mass was prepared by dispersing the carboxymethylated pulp in 50 mL of a dispersion medium. The composition of the liquid medium was water:ethanol=25% by mass:75% by mass. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel and drying it with a blower dryer at 50 ° C. until the mass became constant. Carboxylmethylated pulp with a solid content concentration of 96% by mass of dry solid was obtained.

Next, water was added to the dry solid matter of the carboxymethylated pulp thus obtained to obtain an aqueous dispersion having a solid content concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxymethylated pulp (average fiber length 12 nm, aspect ratio: 130). got

[Example 6]
A carboxymethylated pulp dispersion (solid concentration: 1.0% by mass) was obtained in the same manner as in Example 5, except that the composition of the liquid medium was water:ethanol=10% by mass:90% by mass. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, and dried in a blower dryer at 50 ° C. until the mass became constant, and the carboxymethylated pulp with a solid content concentration of 98% by mass was dried. A solid was obtained.

Next, water was added to the dry solid matter of the carboxymethylated pulp thus obtained to obtain an aqueous dispersion having a solid content concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxymethylated pulp (average fiber length 12 nm, aspect ratio: 130). got

[Example 7]
A dispersion having a solid concentration of 1.0% by mass was prepared by dispersing cationized pulp in 50 mL of a dispersion medium. However, the composition of the liquid medium was water:ethanol=25% by mass:75% by mass. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, and dried in a blower dryer at 50 ° C. until the mass became constant. got stuff

Next, water was added to the dry solid of the cationized pulp thus obtained to obtain an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to produce a CNF aqueous dispersion derived from cationized pulp (average fiber length 20 nm, aspect ratio: 110). Obtained.

[Example 8]
A dispersion of cationized pulp (solid concentration: 1.0% by mass) was obtained in the same manner as in Example 7, except that the composition of the liquid medium was water:ethanol=10% by mass:90% by mass. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, and dried in a blower dryer at 50 ° C. until the mass became constant. got stuff

Next, water was added to the dry solid of the cationized pulp thus obtained to obtain an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to produce a CNF aqueous dispersion derived from cationized pulp (average fiber length 20 nm, aspect ratio: 110). Obtained.

[Comparative Example 1]
An aqueous dispersion having a solid concentration of 1.0% by mass was prepared by dispersing carboxylated pulp in 50 mL of water. A wet cake-like mixture was prepared by reducing the amount of water using a Buchner funnel and dried in a blower dryer at 105 ° C. for 3 hours to a constant weight to obtain a dry solid of carboxylated pulp with a solid content concentration of 95% by mass. rice field.

Next, water was added to the solid matter of the carboxylated pulp thus obtained to obtain an aqueous dispersion having a solid content concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxylated pulp (average fiber diameter: 4 nm, aspect ratio: 150). got

[Example 9]
An aqueous dispersion having a solid concentration of 1.0% by mass was prepared by dispersing carboxylated pulp in 50 mL of water. A wet cake-like mixture was prepared by reducing the amount of water using a Buchner funnel and dried in a blower dryer at 50 ° C. until the mass became constant to obtain a dried carboxylated pulp with a solid content concentration of 94% by mass. rice field.

Next, water was added to the dried carboxylated pulp thus obtained to form an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxylated pulp (average fiber diameter: 4 nm, aspect ratio: 150). got

[Example 10]
50 mL of a carboxymethylated pulp aqueous dispersion having a solid content concentration of 1.0% by mass, in which carboxymethylated pulp was dispersed in 50 mL of water, was obtained. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, and dried with a blower dryer at 50 ° C. until the mass became constant, and the carboxymethylated pulp with a solid content concentration of 94% by mass was dried. got stuff

Next, water was added to the dried carboxymethylated pulp thus obtained to form an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain a CNF aqueous dispersion derived from carboxymethylated pulp (average fiber length 12 nm, aspect ratio: 130). got

[Example 11]
50 mL of a cationized pulp aqueous dispersion having a solid content concentration of 1.0% by mass, in which the cationized pulp was dispersed in 50 mL of water, was obtained. A wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, and dried with a blower dryer at 50 ° C. until the mass became constant. got

Next, water was added to the dried cationized pulp thus obtained to obtain an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it is treated twice with a high-pressure homogenizer (20 ° C., 150 MPa) to produce a CNF aqueous dispersion derived from cationized pulp (average fiber length 20 nm, aspect ratio: 110). Obtained.

[Comparative Example 2]
A dispersion having a solid concentration of 1.0% by mass was prepared by dispersing NBKP (bleached softwood kraft pulp, manufactured by Nippon Paper Industries Co., Ltd.) in 50 mL of a dispersion medium. However, the composition of the liquid medium was water:ethanol=25% by mass:75% by mass. A concentrated wet cake-like mixture was prepared by reducing the amount of liquid medium using a Buchner funnel, dried with a blower dryer at 50 ° C. for 3 hours to a constant weight, and a dry solid of NBKP with a solid content concentration of 96% by mass was obtained. .

Next, water was added to the dry solid of NBKP obtained in this manner to form an aqueous dispersion having a solid concentration of 1.0% by mass, and the dispersion was stirred for 60 minutes using a disper (1,000 rpm). After neutralizing the aqueous dispersion with sodium hydroxide, it was treated five times with a high-pressure homogenizer (20 ° C., 150 MPa) to obtain an NBKP-derived CNF aqueous dispersion (average fiber length 630 nm, aspect ratio: 30). . These results are shown in Table 1.

It is clear that the CNF obtained from the dry solids of the chemically modified pulp of the present invention has the same physical properties as the CNF obtained from the chemically modified pulp dispersion without drying.

Claims (8)

A step of drying a mixture of a chemically modified pulp obtained by chemically modifying a cellulose raw material and a mixed solvent of water and a water-soluble organic solvent at 20 to 80 ° C.,
the chemical modification is carboxylation, carboxymethylation, cationization, or esterification;
The amount of the water-soluble organic solvent in the mixed solvent is 50 to 95% by mass,
A method for producing chemically modified pulp dry solids. 2. The production method according to claim 1, wherein the amount of the water-soluble organic solvent in the mixed solvent is 70% by mass or more. The production method according to claim 1 or 2, wherein the chemically modified pulp has a carboxyl group content of 0.6 to 3.0 mmol/g relative to the absolute dry mass of the chemically modified pulp. The production method according to claim 1 or 2, wherein the chemically modified pulp has a degree of carboxymethyl substitution per glucose unit of 0.01 to 0.50. The production method according to claim 1 or 2, wherein the chemically modified pulp has a degree of cation substitution per glucose unit of 0.02 to 0.50. The production method according to any one of claims 1 to 5, wherein the water-soluble organic solvent is a lower alcohol. A method for producing a chemically modified pulp dispersion, comprising dispersing the dry solids of the chemically modified pulp obtained by the production method according to any one of claims 1 to 6 in a dispersion medium. A method for producing cellulose nanofibers, comprising defibrating the chemically modified pulp in the chemically modified pulp dispersion obtained by the production method according to claim 7.