JP2018048218A - Method for producing cellulose nanofiber concentrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily concentrate cellulose nanofibers. SOLUTION: In the presence of a concentration aid (A) capable of giving a cloud point or a thermal gelation point to the aqueous dispersion by addition to the cellulose nanofiber aqueous dispersion, 1) a cellulose nanofiber aqueous dispersion. To generate aggregates containing cellulose nanofibers by raising the temperature to a temperature above the cloud point or thermal gelation point, and 2) to raise the liquid containing the obtained aggregates to a temperature above the cloud point or thermal gelation point. A method for producing a cellulose nanofiber concentrate, which comprises a step of filtering with. [Selection diagram] None

Description

  Embodiments of the present invention relate to a method for producing a cellulose nanofiber concentrate.

  In recent years, cellulose nanofiber obtained by refining cellulose fiber, particularly cellulose fiber (pulp) derived from wood by various methods, has attracted attention because of its excellent characteristics and recyclability. Cellulose nanofibers are produced in the state of an aqueous dispersion with a low solid content, but the yield and the drainage are insufficient, and the distribution cost is low when the product form is an aqueous dispersion with a low solid content. There is a problem of becoming higher. Further, when the product form is a gel, there is a problem that a trouble occurs in the product transfer and the handling property at the time of handling is poor. These problems are major issues that should be solved when developing cellulose nanofibers in the future and developing applications in a wide range of fields.

  As a means to solve these problems, technical studies have been made to produce cellulose nanofibers with a higher solid content, or to concentrate and achieve high solid differentiation after production with a low solid content. In addition, the technology that can be used commercially at low cost is limited. In addition, the technology for re-dispersing and using cellulose nanofiber concentrate is also limited.

  In Patent Document 1, in order to concentrate a cellulose nanofiber aqueous dispersion, a low concentration cellulose nanofiber aqueous dispersion is concentrated in the presence of a polyoxyalkylene compound of HLB 8-18 to obtain a high concentration cellulose nanofiber aqueous solution. It is disclosed to obtain a dispersion. However, there is a problem in terms of redispersibility of the concentrate.

JP2015-117340A

  An object of the embodiment of the present invention is to provide a method for producing a cellulose nanofiber concentrate, in which cellulose nanofibers can be easily highly solidified, that is, concentrated.

  The method for producing a cellulose nanofiber concentrate according to an embodiment of the present invention includes a concentration aid (A) that can add a cloud point or a thermal gelation point to an aqueous dispersion by adding the cellulose nanofiber aqueous dispersion. 1) a step of raising the temperature of the aqueous dispersion of cellulose nanofibers to a temperature equal to or higher than the cloud point or the thermal gelation point to produce an aggregate containing cellulose nanofibers, and 2) the obtained aggregate And a step of filtering the liquid to be contained at a temperature equal to or higher than the cloud point or the thermal gelation point.

  In the method for redispersing cellulose nanofibers according to an embodiment of the present invention, the cellulose nanofiber concentrate obtained by the above method is used as at least one dispersion medium selected from the group consisting of water, an organic solvent, and a resin. Re-dispersed.

  In the production method according to the embodiment of the present invention, the cellulose nanofiber aqueous dispersion can be efficiently concentrated to obtain a cellulose nanofiber concentrate.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the present embodiment, the cellulose nanofiber refers to a fine fiber having a fiber diameter of nanometer level obtained by defibrating a cellulose-based raw material. The cellulose nanofibers preferably have an average fiber length of 50 nm to 5000 nm, more preferably 0.1 to 5 μm, and an average fiber diameter of 1 nm to 1000 nm, more preferably 2 to 300 nm. 2 to 150 nm may be used.

  Here, the average fiber diameter is a number average fiber diameter measured as follows. That is, an aqueous dispersion of cellulose nanofibers having a solid content of 0.05 to 0.1% by mass was prepared, and the dispersion was cast on a carbon film-coated grid that had been subjected to a hydrophilization treatment. Using a microscope (TEM) or a scanning electron microscope (SEM), observation with an electron microscope image is performed at a magnification of 5000 times, 10000 times, or 50000 times depending on the size of the constituent fibers. At that time, an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect the axis. Random shafts are drawn two by two for each image, and the fiber diameter of the fibers crossing the shaft is visually read. In this way, images of at least three non-overlapping surface portions are taken with an electron microscope, and the fiber diameter values of the fibers intersecting with each of the two axes are read (thus, at least 20 × 2 × 3 = 120). Information on the fiber diameter of the book is obtained). The number average fiber diameter is calculated from the fiber diameter data thus obtained.

  Examples of cellulosic materials include wood-derived kraft pulp or sulfite pulp, powdered cellulose obtained by pulverizing them with a high-pressure homogenizer or mill, or microcrystalline cellulose powder obtained by purifying them by chemical treatment such as acid hydrolysis. . In addition, plant-derived cellulosic materials such as kenaf, hemp, rice, bacus, and bamboo can also be used. In addition, the cellulose-based material is obtained by refining these cellulose-based materials with a dispersing device such as a high-speed rotating type, a colloid mill type, a high-pressure type, a roll mill type, or an ultrasonic type, preferably a wet high-pressure or ultra-high-pressure homogenizer. It can also be used. Here, the powdered cellulose is rod-like particles made of microcrystalline or crystalline cellulose obtained by removing a non-crystalline portion of wood pulp by acid hydrolysis, and then pulverizing and sieving.

  The cellulosic material is a concept including not only cellulose but also anion-modified cellulose. Anion-modified cellulose refers to a cellulose-based raw material into which an anionic group (carboxyl group, carboxymethyl group, phosphate group, etc.) has been introduced. Therefore, specific examples of cellulose nanofibers include carboxylated cellulose nanofibers introduced with carboxyl groups, carboxymethylated cellulose nanofibers introduced with carboxymethyl groups, and phosphorylated cellulose nanofibers introduced with phosphate groups It is. Here, the anionic group such as carboxyl group, carboxymethyl group, and phosphoric acid group is not only an acid type, but also an alkali metal salt such as a sodium salt, an alkaline earth metal salt such as a calcium salt, or a salt type. The acid type and the salt type may be mixed.

  Examples of carboxylated cellulose nanofibers include TEMPO oxidized cellulose. TEMPO-oxidized cellulose refers to cellulose single nano particles obtained by oxidizing natural cellulose such as pulp with TEMPO (abbreviation for 2,2,6,6-tetramethylpiperidinyl-1-oxyl), which is a water-soluble stable nitroxyl radical. It is a fiber. TEMPO-oxidized cellulose is a cellulose fiber having a number average fiber diameter of 2 to 150 nm, and is a fine cellulose fiber in which the hydroxyl group at the C6 position of the glucose unit in the cellulose molecule is selectively oxidized and modified to a carboxyl group.

  TEMPO-oxidized cellulose is prepared by dispersing natural cellulose and TEMPO in water, adding a co-oxidant such as sodium hypochlorite, and then performing a reduction reaction as necessary, followed by purification. Then, it can be manufactured by defibrating treatment. Defibration treatment is performed using a powerful and beating-capable device such as a homomixer, high-pressure homogenizer, ultrasonic dispersion processor, beater, disc type refiner, conical type refiner, double disc type refiner, and grinder under high-speed rotation. Can be done.

  Carboxymethylated cellulose nanofibers are those obtained by carboxymethylating the hydroxyl groups of glucose units constituting cellulose. For example, carboxymethylated cellulose nanofibers can be obtained by defibrating cellulose with carboxymethyl groups prepared as follows. it can. Cellulosic raw materials are used as bottoming raw materials, and 3 to 20 times by mass lower alcohol, specifically, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, tertiary butanol, etc. alone, or A mixed medium of two or more kinds and water is used as a solvent. The mixing ratio of the lower alcohol in the mixed medium is 60 to 95% by mass. A bottoming raw material, a solvent, and a mercerizing agent, using 0.5 to 20 moles of alkali metal hydroxide per glucose residue of the bottoming raw material, specifically sodium hydroxide or potassium hydroxide as a mercerizing agent And a mercerization treatment is performed at a reaction temperature of 0 to 70 ° C. and a reaction time of 15 minutes to 8 hours. Thereafter, monochloroacetic acid or sodium monochloroacetate (carboxymethylating agent) is added in an amount of 0.05 to 10.0 times mol per glucose residue, and the etherification reaction is performed at a reaction temperature of 30 to 90 ° C. and a reaction time of 30 minutes to 10 hours. By performing the step, cellulose having a carboxymethyl group introduced can be obtained. After the etherification reaction, nanofibers of carboxymethylated cellulose can be obtained by performing a defibrating treatment similar to that of TEMPO-oxidized cellulose.

  Phosphorylated cellulose nanofibers can be produced, for example, by the following method. Examples include a method of mixing phosphoric acid or a phosphoric acid derivative powder or an aqueous solution with a dry or wet cellulose raw material, a method of adding an aqueous solution of phosphoric acid or a phosphoric acid derivative to a dispersion of a cellulose raw material, and the like. Examples of phosphoric acid or phosphoric acid derivatives include at least one compound selected from oxo acids, polyoxo acids or derivatives thereof containing a phosphorus atom. Thereby, the compound or salt thereof containing a phosphate group at the hydroxyl group of the glucose unit constituting cellulose undergoes a dehydration reaction to form a phosphate ester, and the phosphate group or salt thereof is introduced. Cellulose fibers introduced with phosphoric acid groups become cellulose nanofibers by performing the same defibrating treatment as TEMPO oxidized cellulose.

  The cellulose nanofiber aqueous dispersion means a dispersion of cellulose nanofibers in an aqueous medium containing water as an essential component. Further, the component may contain a preservative, a pH adjuster and the like.

  As an aqueous medium, in addition to water, lower alcohol (methanol, ethanol, propanol and isopropanol (IPA), etc.), acetone, methyl ethyl ketone, glycol or an ether derivative thereof (ethylene glycol, propylene glycol, diethylene glycol, methyl cellosolve, ethyl cellosolve, propyl) Water such as cellosolve, isopropyl cellosolve, dimethyl cellosolve, diethyl cellosolve, methyl carbitol, ethyl carbitol, propyl carbitol, butyl carbitol), glycerin, tetrahydrofuran, N-methylpyrrolidone, N, N-dimethylformamide, dimethyl sulfoxide, etc. A miscible organic solvent is mentioned. These may be used alone or in combination of two or more. As the aqueous medium, water or a mixed solution of water and a water-miscible organic solvent is preferable. The water-miscible organic solvent means an organic solvent that is dissolved in 50 g or more in 1 L of ion-exchanged water at 25 ° C.

  The amount of cellulose nanofibers contained in the aqueous cellulose nanofiber dispersion is not particularly limited. For example, with respect to the total amount of the aqueous dispersion of cellulose nanofibers, the content of cellulose nanofibers may be 0.01 to 30% by mass, 0.1 to 10% by mass, or 0.1 to 3% by mass Good.

  The method for producing a cellulose nanofiber concentrate according to this embodiment is characterized by a method of concentrating, that is, increasing the concentration of the cellulose nanofiber aqueous dispersion produced as described above. The preparation process is not particularly limited.

  In the present embodiment, the cellulose nanofiber aqueous dispersion is concentrated in the presence of a specific concentration aid (A), and 1) the temperature of the cellulose nanofiber aqueous dispersion is raised to a temperature equal to or higher than the cloud point or the thermal gelation point. And a step of producing an aggregate containing cellulose nanofibers (hereinafter, step 1) and 2) a step of filtering the liquid containing the obtained aggregate at a temperature equal to or higher than the cloud point or the thermal gelation point (hereinafter, step) 2). Thus, the cellulose nanofiber can be made highly concentrated easily by producing the aggregate containing the cellulose nanofiber using the concentration aid (A) and filtering in that state. That is, the concentration aid (A) exhibits high freeness when producing the cellulose nanofiber concentrate, and can efficiently produce the cellulose nanofiber concentrate. This concentration method is simple and low-cost, and can be applied to commercial production in that it can be manufactured using general-purpose equipment, and has a great industrial utility value. Moreover, the cellulose nanofiber concentrate obtained by this embodiment can be easily redispersed in water and / or an organic solvent. Moreover, it is also possible to mix | blend with resin as a filler.

  As the concentration aid (A), a water-soluble compound capable of giving the aqueous dispersion a cloud point or a thermal gelation point by addition to the cellulose nanofiber aqueous dispersion is used. Here, the concentration aid that can give the clouding point to the cellulose nanofiber aqueous dispersion is called the concentration aid (A1) having a cloud point, and the concentration aid that can give the thermal gelation point. , Referred to as a concentration aid (A2) having a thermal gelation point.

  As the concentration aid (A), it is preferable to use at least one selected from the group consisting of a compound having a polyoxyalkylene chain in the molecule, an alkylcellulose, and a hydroxyalkylalkylcellulose. Among these, the compound having a polyoxyalkylene chain in the molecule is a concentration aid (A1) having a cloud point, and the alkylcellulose and the hydroxyalkylalkylcellulose are concentration aids (A2) having a thermal gelation point. It is.

  Here, the cloud point is a temperature at which the concentration aid (A1) starts to insolubilize from the solution when the temperature of the solution containing the concentration aid (A1) is raised (“Chemical Dictionary”, ( Tokyo Chemistry Dojin, published in 1994).

  As a compound having a polyoxyalkylene chain in the molecule, which is a concentration aid (A1) having a cloud point, for example, a polyoxyethylene polyoxypropylene block polymer, a polyoxyalkylene alkyl ether, a polyoxyalkylene alkyl phenyl ether, Nonionic surfactants such as polyoxyalkylene styrenated phenyl ethers and polyoxyalkylene sorbitan fatty acid esters may be mentioned.

  The polyoxyalkylene chain is preferably a ring-opening polymer of one or more alkyne oxides selected from the group consisting of ethylene oxide, propylene oxide, and butylene oxide. More preferably, the polyoxyalkylene chain is a ring-opening polymer of ethylene oxide alone or a ring-opening polymer in which ethylene oxide is combined with propylene oxide and / or butylene oxide. The average number of added moles of alkylene oxide (oxyalkylene group) is not particularly limited, but is preferably 20 to 300 moles, and more preferably 30 to 100 moles.

  Examples of the polyoxyethylene polyoxypropylene block polymer include copolymers of 5 to 200 mol of ethylene oxide and 5 to 200 mol of propylene oxide. Examples of the polyoxyethylene polyoxypropylene block polymer that can be suitably used include “Epan” series manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

  Examples of the polyoxyalkylene alkyl ether include an alkylene oxide adduct of an alcohol having an alkyl group having 6 to 22 carbon atoms, such as polyoxyethylene lauryl ether (for example, “DKS NL” series, Daiichi Kogyo Seiyaku Co., Ltd.). ), Polyoxyethylene tridecyl ether (for example, “Neugen TDS” series), polyoxyalkylene lauryl ether (for example, “Neugen LP” series, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene tridecyl ether (for example, , "Neugen TDX" series, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), polyoxyalkylene branched decyl ether (for example, "Neugen XL" series, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and the like.

  As the polyoxyalkylene alkyl phenyl ether, for example, polyoxyethylene nonyl phenyl ether (for example, “Nonipol series” manufactured by Sanyo Chemical Industries, Ltd.) can be preferably used. Here, 7-10 may be sufficient as carbon number of an alkyl group.

  As the polyoxyalkylene styrenated phenyl ether, for example, polyoxyethylene styrenated phenyl ether (for example, “Neugen EA-137”, “Neugen EA-157”, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) can be preferably used. .

  As polyoxyalkylene sorbitan fatty acid ester, for example, polyoxyethylene sorbitan fatty acid ester (for example, “Sorgen TW” series, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) can be preferably used.

The thermal gelation point is a temperature at which a solution exhibiting thermal gel properties by containing a concentration aid (A2) starts gelation by heating (“temperature associated with thermoreversible gelation of cellulose ether aqueous solution− viscosity behavior "(polymer Collected papers, vol.38, pp.133-137, 1981 years) reference. is" thickening start temperature _{T 2} "in the same document). The thermal gel property is a property (thermo-reversible gelation) in which a solution containing the concentration aid (A2) gels by heating and is restored to the original aqueous solution by cooling.

  Examples of the alkyl cellulose that is the concentration aid (A2) having a thermal gelation point include methyl cellulose (for example, “Metroses SM” series, manufactured by Shin-Etsu Chemical Co., Ltd.). For example, hydroxypropyl methylcellulose (for example, “Metroze SH” series, manufactured by Shin-Etsu Chemical Co., Ltd.) can be mentioned. These are, for example, water-soluble cellulose ethers obtained by treating cellulose with sodium hydroxide and then reacting with an etherifying agent such as methyl chloride or propylene oxide. Here, methylcellulose is one in which a part of hydrogen atoms of a hydroxyl group of cellulose is substituted with a methyl group. Examples of hydroxypropylmethylcellulose include those obtained by substituting a part of hydrogen atoms of the hydroxyl group of cellulose with a methyl group or a hydroxypropyl group.

  In step 1, the concentration aid (A) is added to and mixed with the cellulose nanofiber aqueous dispersion to prepare a concentration assistant-containing cellulose nanofiber aqueous dispersion, and the resulting aqueous dispersion is heated. The temperature may be raised to a temperature equal to or higher than the cloud point or the thermal gelation point of the aqueous dispersion.

  Although the usage-amount of a concentration adjuvant (A) is not specifically limited, 0.01-50 mass% is preferable with respect to the whole quantity of a concentration assistant containing cellulose nanofiber aqueous dispersion, More preferably, it is 0.05-20. It is mass%, More preferably, it is 0.05-5 mass%.

  When the concentration aid (A) is added to and mixed with the cellulose nanofiber aqueous dispersion, a dispersion treatment using a dispersing device such as a homomixer may be performed, and the concentration aid (A ) Can be dissolved. At that time, an aqueous medium such as water may be further added together with the concentration aid (A) to adjust the concentration of the cellulose nanofibers.

  The aqueous dispersion of cellulose nanofibers containing the concentration assistant can raise aggregates containing the cellulose nanofibers by raising the temperature to a temperature equal to or higher than the cloud point or the thermal gelation point. Here, the rate of temperature rise is not particularly limited, but is preferably 0.5 to 10 ° C./min, and more preferably 1 to 5 ° C./min. The temperature to be raised is not particularly limited as long as it is equal to or higher than the cloud point or the thermal gelation point, but it is preferably 1 to 30 ° C higher than the cloud point or the thermal gelation point, more preferably The temperature is 5 to 20 ° C higher.

  In one embodiment, while the concentration aid-containing cellulose nanofiber aqueous dispersion is heated at the predetermined temperature increase rate, the cloud point exceeds the cloud point at which it begins to insolubilize or exceeds the thermal gel point at which it begins to gel. Or it is preferable to heat to the said predetermined temperature higher than a thermal gelation point. When raising the temperature, it is preferable not to stir or to stir gently so that aggregates are easily formed.

  The aggregate produced in this manner contains an aqueous medium and a concentration aid (A) together with cellulose nanofibers. The aggregate is formed in a state in which a part of the aqueous medium contained in the concentration aid-containing cellulose nanofiber aqueous dispersion is incorporated and separated from the remaining aqueous medium.

  In step 1, in addition to the concentration aid (A), an adjustment aid (B) having a function of increasing or decreasing the cloud point or the thermal gelation point may be used. That is, the clouding point or the thermal gelation point can be increased or decreased by including the preparation aid (B) in the concentration aid-containing cellulose nanofiber aqueous dispersion.

  The adjustment aid (B) having such a function includes (B1) at least one selected from the group consisting of sulfate ion, halide ion, carbonate ion, phosphate ion, acetate ion, and lactate ion as a component. And / or (B2) at least one compound selected from the group consisting of compounds represented by the following general formulas (1) to (5) is preferably used.

_{C n H 2n + 1 -OH (} 1)
_{C p H 2p + 1 -CO-} C q H 2q + 1 (2)
_{C s H 2s + 1 -COO-} C t H 2t + 1 (3)
C _u H _{2u + 1} O- (AO) _v -C _w H _{2w + 1} (4)
R (OH) _m (5)
In the formula, n is an integer of 1 to 9, p and q are each independently an integer of 1 to 9, s is an integer of 0 to 9, t is an integer of 1 to 4, u and w are each independently 0 to 9 , V is an integer of 1 to 3, AO is an oxyalkylene group having 2 to 4 carbon atoms, R is a hydrocarbon group having 3 to 10 carbon atoms, m is 3 or 4, and a plurality of AOs in one molecule Each may be the same or different.

  Examples of the preparation aid (B1) that includes sulfate ion as a component include sulfates such as sodium sulfate, lithium sulfate, potassium sulfate, and ammonium sulfate. Examples of the salt containing a halide ion as a component include sodium chloride, potassium chloride, aluminum chloride, calcium chloride, lithium chloride, and ammonium chloride. Examples of the salt containing carbonate ions include carbonates such as sodium bicarbonate, sodium carbonate, ammonium carbonate, and potassium carbonate. Examples of the salt having phosphate ion as a component include phosphates such as sodium phosphate, potassium phosphate, and ammonium phosphate. Examples of the salt containing acetate ion as a component include acetates such as sodium acetate, lithium acetate, and potassium acetate. Examples of the salt containing lactate ion as a component include lactates such as sodium lactate, potassium lactate, calcium lactate, magnesium lactate, and ammonium lactate. Any of these may be used alone or in combination of two or more.

  For the preparation aid (B2), n in the formula (1) is more preferably an integer of 1 to 4. Examples of the compound represented by the formula (1) include alcohols such as methanol, ethanol, propanol, isopropanol, and butanol. More preferably, p and q in the formula (2) are each independently an integer of 1 to 3. Examples of the compound represented by the formula (2) include ketones such as acetone and methyl ethyl ketone. S in Formula (3) is more preferably an integer of 1 to 3, and t is more preferably an integer of 1 to 3. Examples of the compound represented by the formula (3) include fatty acid esters such as methyl acetate and ethyl acetate. More preferably, u and w in the formula (4) are each independently an integer of 0 to 4, and v is more preferably 1 or 2. AO is more preferably an oxyalkylene group having 2 or 3 carbon atoms. Examples of the compound represented by the formula (4) include ethylene glycol, propylene glycol, diethylene glycol, methyl cellosolve, ethyl cellosolve, propyl cellosolve, isopropyl cellosolve, dimethyl cellosolve, diethyl cellosolve, methyl carbitol, ethyl carbitol, and propyl carbitol. Examples include glycols such as tol and butyl carbitol or ether derivatives thereof. R in Formula (5) is more preferably a hydrocarbon group having 3 to 6 carbon atoms, and m is more preferably 3. As a compound represented by Formula (5), polyhydric alcohols, such as glycerol, are mentioned, for example. These can be used alone or in combination of two or more. Moreover, you may use combining any at least 1 sort (s) of any preparation adjuvant (B1), and at least 1 sort (s) of any preparation adjuvant (B2).

  Although the usage-amount of a preparation adjuvant (B) is not specifically limited, 0.1-50 mass% is preferable with respect to the whole quantity of the concentration adjuvant containing cellulose nanofiber aqueous dispersion containing a preparation assistant (B), More preferably, it is 1-20 mass%.

  In step 2, the liquid containing the aggregate obtained in step 1 is filtered at a temperature equal to or higher than its cloud point or thermal gelation point. That is, using a liquid in which the aggregate and the aqueous medium are separated, a filtration operation is performed while maintaining the temperature above the cloud point or the thermal gelation point so that the state of the aggregate can be maintained. Separate the media.

  The temperature at the time of filtration will not be specifically limited if it is more than the cloud point or the thermal gelation point of the liquid containing an aggregate. For example, the liquid temperature of the liquid containing aggregates is preferably a temperature that is 1 to 30 ° C. higher than the cloud point or the thermal gelation point, and more preferably 5 to 20 ° C. higher.

  Any filtration device may be used as long as the temperature of the liquid containing the aggregate can be filtered while maintaining the temperature above the cloud point or the gel point. For example, a membrane filter with a heat retaining function can be used.

  The aggregate which is a residue separated from the filtrate in step 2 becomes a non-aggregated state at a temperature lower than the cloud point or the gel point, and has a higher concentration than the original cellulose nanofiber aqueous dispersion. It becomes the formed cellulose nanofiber aqueous dispersion. That is, a cellulose nanofiber concentrate is obtained.

  Here, the cellulose nanofiber concentrate is a highly concentrated cellulose nanofiber-containing material (that is, the content of the cellulose nanofiber is increased with respect to the aqueous dispersion of cellulose nanofibers to be processed in Step 1 above). ). Specifically, the cellulose nanofiber concentrate may have a higher concentration than the concentration aid-containing cellulose nanofiber aqueous dispersion that performs the temperature raising treatment, more preferably, the concentration aid (A) and The concentration of the aqueous dispersion of cellulose nanofibers before the addition of the aqueous medium for adjusting the concentration is increased.

  The property of the cellulose nanofiber concentrate is not particularly limited, and may be an aqueous dispersion, may be in the above-mentioned aggregate state, and may be in a dried body state described later. Moreover, the quantity of the cellulose nanofiber contained in a cellulose nanofiber concentrate is not specifically limited, For example, 2.0-100 mass% may be sufficient with respect to the whole quantity of a cellulose nanofiber concentrate, and 3.0-80 The mass% may be 4.0 to 50 mass%. Moreover, 1-50 mass% may be sufficient as the quantity of the concentration adjuvant (A) contained in a cellulose nanofiber concentrate with respect to the quantity of a cellulose nanofiber, and 2-25 mass% may be sufficient as it.

  In the method for producing a cellulose nanofiber concentrate according to the present embodiment, the aggregate separated from the filtrate in the filtration step of Step 2 above, or the aggregate is set to a temperature lower than the cloud point or the thermal gelation point. The aqueous dispersion obtained in (1) may further include a step of reducing moisture by dehydration and / or drying (hereinafter, step 3).

  Examples of dehydration in step 3 include centrifugation.

  Examples of the drying in step 3 include heat drying, air drying, microwave drying, and infrared drying. The drying temperature is not particularly limited, and may be 80 to 140 ° C. or 100 to 120 ° C., for example, in the case of heat drying. Also, the drying time is not particularly limited, and may be, for example, 1 to 3,000 minutes or 5 to 180 minutes.

  In the present embodiment, the cellulose nanofiber concentrate obtained by the above method may be redispersed in at least one dispersion medium selected from the group consisting of water, an organic solvent, and a resin. The redispersion method is not particularly limited, and the cellulose nanofiber concentrate is added to at least one dispersion medium selected from the group consisting of water, an organic solvent, and a resin, for example, a high-speed rotation type, a colloid mill type, Cellulose nanofibers can be dispersed in a dispersion medium by carrying out dispersion treatment using a high-pressure type, roll mill type, ultrasonic type, or other dispersing device. Preferably, a wet high pressure or ultrahigh pressure homogenizer is used as the dispersing device.

  The organic solvent as a dispersion medium used for redispersion can be appropriately selected according to the use of the cellulose nanofiber, and is not particularly limited. For example, lower alcohols (methanol, ethanol, propanol and isopropanol (IPA ), Etc.), acetone, methyl ethyl ketone, glycol or ether derivatives thereof (ethylene glycol, propylene glycol, diethylene glycol, methyl cellosolve, ethyl cellosolve, propyl cellosolve, isopropyl cellosolve, dimethyl cellosolve, diethyl cellosolve, methyl carbitol, ethyl carbitol, propyl carbi Tol, butyl carbitol, etc.), glycerin, tetrahydrofuran, N-methylpyrrolidone, N, N-dimethylformamide, dimethylsulfo Water-miscible organic solvent such as Sid the like. These may be used alone or in combination of two or more.

  Examples of the resin as a dispersion medium used for redispersion include a water-soluble resin such as polyvinyl alcohol (PVA), polyethylene glycol, sodium polyacrylate, and polyvinyl pyrrolidone, and a resin that dissolves in the organic solvent such as polyvinyl butyral. Is preferred. When using a resin together with water and / or an organic solvent as a dispersion medium to be redispersed, cellulose nanofiber / resin in which cellulose nanofibers are dispersed in the resin by drying the obtained cellulose nanofiber dispersion after redispersion A composite may be made.

  As the dispersion medium to be redispersed, water or a mixed liquid of water and another dispersion medium is preferable. Further, the concentration of the cellulose nanofiber after redispersion can be appropriately set according to the use of the cellulose nanofiber, and is not particularly limited, but may be 0.01 to 30% by mass, for example, 0.1 -10 mass% may be sufficient.

  In addition, the use of the cellulose nanofiber concentrate according to the present embodiment is not particularly limited. For example, the cellulose nanofiber concentrate may be used as a thickener, a gelling agent, a shape-retaining agent, etc. It can be used for various other purposes.

  Hereinafter, although an Example demonstrates further in detail, this invention is not limited to these. In addition, the measuring method of a cloud point and a heat | fever gelation point is as follows.

  Place the sample solution in a test tube up to a height of 50 mm so that the lower end of the thermometer is 15 mm above the bottom of the test tube and place the test tube in a beaker containing approximately 5 ° C. water. While stirring the sample solution, warm the beaker at a heating rate of 1 ° C. per minute and gently stir. The temperature at which the sample solution becomes cloudy rapidly is taken as the cloud point of the sample solution. The thermal gelation point is also measured by the same method.

[Examples 1-8, Comparative Examples 1-3]
Concentration aid (A) and water described in Table 1 were added to a 2% by mass aqueous dispersion of TEMPO-oxidized cellulose nanofiber (Reocrystallase I-2SP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and homomixer (TK). Concentrated auxiliary agent-containing TEMPO-oxidized cellulose nanofiber aqueous dispersions having the concentrations shown in Table 1 were prepared by processing at 8000 rpm for 10 minutes using.

  5 g of the sample liquid is heated at a temperature rising rate of 1 ° C. per minute to a temperature of 15 ° C. or more of the cloud point or the thermal gelation point of each sample liquid, and then the cloud point or the thermal gel of the sample liquid. The cellulose nanofiber concentrate which concerns on Examples 1-8 was obtained by filtering with the membrane filter heated to the temperature of 15 degreeC or more of crystallization temperature. The heating and filtration temperature are as shown in Table 1. As a filter of the filter, an omnipore membrane filter (diameter 47 mm, material PTFE) was used. At this time, the time from when the sample was put into the filter until the liquid stopped moving under the filter of the filter was measured, and was defined as the filtration time.

  Further, as Comparative Examples 1 and 2, a TEMPO oxidized cellulose nanofiber 0.3 mass% and 0.15 mass% aqueous dispersion was prepared in the same manner as above except that the concentration aid (A) was not added, and filtered. To make a blank. As Comparative Example 3, evaluation was performed in the same manner as in Example 1 except that filtration was performed without heating above the cloud point.

  The evaluation of filterability in Table 1 was evaluated by comparing the filtration times in Examples 1 to 7 and Comparative Example 3 with Comparative Example 1 as blank and Example 8 with Comparative Example 2 as blank. The filtration time of each example was shortened to 1/3 or less with respect to the blank filtration time, ◎, which was shortened to more than 1/3 and 2/3 or less, and ○, which was shortened to more than 2/3 Moreover, the thing whose filtration time became longer than the blank was set as x.

  Further, in the evaluation of the concentration, the solid content of the residue in each example and comparative example is the solid content of the TEMPO oxidized cellulose nanofiber aqueous dispersion used for sample preparation, that is, the product solid concentration before dilution 2 The degree of concentration with respect to mass% was evaluated. However, in Examples 1 to 8 and Comparative Example 3, in order to subtract the concentration aid (A) in the residue, the following calculation formula (*) is used for the solid content of the residue in each example. The solid content of the TEMPO oxidized cellulose nanofiber was calculated and evaluated. The calculation formula (*) is a simple calculation based on the solid content of the TEMPO oxidized cellulose nanofiber alone, depending on the ratio of the solid content of the residue in each example and the TEMPO oxidized cellulose nanofiber and the concentration aid (A) in the sample solution. Is calculated.

Formula (*): D = E × {F / (F + G)}
D: Solid content (mass%) of TEMPO oxidized cellulose nanofiber
E: Solid content of residue (% by mass)
F: TEMPO oxidized cellulose nanofiber amount (% by mass)
G: Concentration auxiliary (A) addition amount (% by mass)

  The evaluation of the degree of concentration in Table 1 is based on the solid content of the TEMPO oxidized cellulose nanofiber aqueous dispersion used in the sample preparation, that is, the solid concentration of the product before dilution. Those that were 4 times or more of a certain 2% by mass were rated ◎, those that were 1.5 times or more and less than 4 times ○, and those that were less than 1.5 times ×.

The concentration aid (A) in Table 1 is as follows.
Epan 740: Polyoxyethylene polyoxypropylene block polymer manufactured by Daiichi Kogyo Seiyaku Co., Ltd. DKS NL-60: Polyoxyethylene (6EO) lauryl ether manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Neugen LP-100: Daiichi Polyoxyethylene polyoxypropylene lauryl ether / Metrose SM4000 manufactured by Kogyo Seiyaku Co., Ltd .: Methylcellulose Metroze 65SH4000 manufactured by Shin-Etsu Chemical Co., Ltd .: Hydroxypropyl methylcellulose manufactured by Shin-Etsu Chemical Co., Ltd.

[Examples 9 to 16]
A TEMPO-oxidized cellulose nanofiber aqueous dispersion with the concentration aid (A) and the adjustment aid (B) added at the concentrations shown in Table 2 was prepared and used as a sample solution. Here, Epan 740 manufactured by Daiichi Kogyo Seiyaku Co., Ltd., which is a polyoxyethylene polyoxypropylene block polymer, is used as the concentration aid (A), and 2 mass% water of TEMPO oxidized cellulose nanofiber is used as the TEMPO oxidized cellulose nanofiber. Dispersion liquid (Reocrysta I-2SP, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used. After confirming that the sample solution was heated to a temperature of 15 ° C. or higher of the cloud point, the sample solution was similarly filtered with a membrane filter kept at a temperature of 15 ° C. or higher of the cloud point of the sample solution. The heating and filtration temperature are as shown in Table 2. At this time, the time from when the sample was put into the filter until the liquid stopped moving under the filter of the filter was measured, and was defined as the filtration time. Moreover, the solid content of the filtration residue was measured.

  The filterability evaluation in Table 2 was evaluated by comparing with the filtration time of Comparative Example 2. For comparison, Example 8 in Table 1 is also shown. Examples where the filtration time of the example could be shortened to 1/3 or less of the filtration time of Comparative Example 2, and those where the filtration time could be shortened to more than 1/3 to 2/3 or less Δ, and those in which the filtration time was longer than Comparative Example 2 were marked with ×.

  Further, in the evaluation of the concentration, the solid content of the residue in each example and comparative example is the solid content of the TEMPO oxidized cellulose nanofiber aqueous dispersion used for sample preparation, that is, the product solid concentration before dilution 2 The degree of concentration with respect to mass% was evaluated. However, in Examples 8 to 16, in order to subtract the concentration aid (A) in the residue, the TEMPO oxidized cellulose nanoparticle in the residue was obtained using the above formula (*) for the solid content of the residue in each Example. The solid content of the fiber was calculated and evaluated. The evaluation of the concentration in Table 2 is the same as the evaluation method for the concentration in Table 1.

[Example 17]
As Example 17, instead of TEMPO-oxidized cellulose nanofibers, concentration was carried out in the same manner as in Example 1 except that carboxymethylated cellulose nanofibers having a substitution degree of 0.05 produced using coniferous pulp by the following method were used. When the concentration test was carried out using Epan 740 as the auxiliary agent (A), the same results as those obtained in Example 1 were obtained, which showed good filterability and concentration.

160 g of a mixed solvent of 112 g of isopropyl alcohol (IPA) and 48 g of water is added to 20 g of softwood pulp (LBKP) pulverized by a home mixer, and then 8.8 g of sodium hydroxide is added, followed by stirring and mixing. Stir at 60 ° C. for 60 minutes. Next, the temperature of the reaction solution was raised to 70 ° C., and 12 g (in terms of active ingredient) of sodium monochloroacetate was added. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain anion-modified cellulose fibers having a substitution degree of 0.05 per glucose unit. Thereafter, the anion-modified cellulose fiber is made to have a solid content concentration of 2% by mass, and treated with a high-pressure homogenizer at a pressure of 140 MPa five times to obtain sodium carboxylate derived from a carboxymethyl group (—CH ₂ COONa) as an anionic group. An aqueous dispersion of cellulose nanofibers was obtained. The obtained carboxylmethylated cellulose nanofibers had a number average fiber diameter of 25 nm and an anionic group (carboxyl group) amount of 0.30 mmol / g.

[Example 18]
As Example 18, instead of TEMPO-oxidized cellulose nanofibers, Epane was added to the concentration aid (A) in the same manner as in Example 1 except that phosphorylated cellulose nanofibers prepared using softwood pulp were used by the following method. When a concentration test was performed using 740, the results showing good filterability and concentration were obtained in the same manner as the results obtained in Example 1.

  10.14 g of sodium dihydrogen phosphate dihydrate and 1.79 g of disodium hydrogen phosphate are dissolved in 19.27 g of water, and an aqueous solution of a phosphoric acid compound (hereinafter referred to as “phosphorylation reagent A”) is obtained. Obtained. The pH of this phosphorylating reagent A was 4.73 at 25 ° C.

  Add water to the conifer bleached kraft pulp to a concentration of 4% by mass, and use a double disk refiner to create an irregular CSF (JIS P8121-2 (Canada standard filtered water, except that the plain weaving is 80 mesh and the amount of pulp collected is 0.3 g) Beating to 250 ml and length average fiber length of 0.68 mm, to obtain a pulp slurry. 3 g of the obtained pulp slurry was collected at an absolutely dry mass, diluted to 0.3% by mass with ion-exchanged water, and then dehydrated by a papermaking method to obtain a pulp sheet. The obtained pulp sheet had a moisture content of 90% and a thickness of 200 μm.

  This pulp sheet was immersed in 31.2 g of the phosphorylating reagent A (80.2 parts by mass as phosphorus element amount with respect to 100 parts by mass of dry pulp), and 2 hours with a 170 ° C. air blow dryer (Yamato Scientific Co., Ltd. DKM400). Half-heat treatment was performed to introduce a phosphorus oxoacid group into cellulose. Next, 500 ml of ion-exchanged water was added to the cellulose into which the phosphorus oxo acid group had been introduced, and after stirring and washing, filtration and dehydration were performed to obtain a dehydrated sheet. The obtained dehydrated sheet was diluted with 300 ml of ion-exchanged water, and 5 ml of 1N sodium hydroxide aqueous solution was added little by little while stirring to obtain a pulp slurry having a pH of 12 to 13. Then, this pulp slurry was dehydrated and washed by adding 500 ml of ion exchange water. This dehydration washing was further repeated twice to obtain a dehydrated sheet of cellulose containing phosphooxo acid.

  Ion exchange water was added to the dehydrated sheet of phosphooxoacid-introduced cellulose obtained after washing and dehydration, and the mixture was stirred to make a 2.0 mass% slurry. This slurry was defibrated for 30 minutes under a condition of 21500 rpm using a defibrating apparatus (Cleamix-2.2S manufactured by MTechnic Co., Ltd.) to obtain a phosphorylated cellulose nanofiber slurry.

[Evaluation of redispersibility]
The concentrates obtained in the above Examples 1 to 5, 17 and 18 were dried at 105 ° C. for 3 hours and added to the dispersion medium so that the solid content was 0.3% by mass, and an ultrasonic homogenizer (Sonic The product was redispersed by treating with VC-505), manufactured by the company. Table 3 shows the evaluation of dispersibility. The dispersibility was visually evaluated by the presence or absence of the Tyndall phenomenon with respect to what was left after redispersion treatment, and the Tyndall phenomenon was confirmed after being allowed to stand for 24 hours. ◯ (good), △ (possible) when the Tyndall phenomenon was confirmed after standing for 3 hours, and X (not possible) when the Tyndall phenomenon was confirmed only immediately after.

  As shown in Table 3, the TEMPO-oxidized cellulose nanofiber concentrate of Comparative Example 1 obtained by concentrating the sample solution without using a concentration aid was based on either water, isopropanol (IPA) or ethylene glycol. However, redispersibility was insufficient, and redispersibility was particularly poor for IPA. On the other hand, when Epan 740 was used as the concentration aid (A), it was possible to redisperse in water and IPA, and in particular, redispersibility with respect to ethylene glycol could be improved. Moreover, when DKS NL-60 was used for the concentration aid (A), redispersion into IPA and ethylene glycol was possible, and in particular, redispersibility with respect to water could be improved. When Neugen LP-100 was used as the concentration aid (A), the redispersibility with respect to IPA could be improved, and the redispersibility with respect to water could be improved particularly well. Further, when Metro's SM-4000 was used as the concentration aid (A), the redispersibility with respect to IPA and ethylene glycol could be improved. Furthermore, when Metrolose 65SH-4000 was used as the concentration aid (A), redispersion into IPA and ethylene glycol was possible, and in particular, redispersibility with respect to water could be improved.

  Further, low-substituted carboxymethyl cellulose nanofibers can be redispersed in water and IPA by using Epan 740 as a concentration aid (A), and particularly improve redispersibility with respect to ethylene glycol. I was able to. The phosphorylated cellulose nanofibers can be redispersed in water and IPA by using Epan 740 as the concentration aid (A), and in particular, the redispersibility can be improved with respect to ethylene glycol.

  As described above, when the concentration method according to this embodiment is used, a concentrate composed of cellulose nanofibers and a concentration aid can be obtained with a high solid content. That is, since the manufacturing method of this embodiment can concentrate a cellulose nanofiber easily, improvement of manufacturing efficiency and reduction of energy cost can be expected. Moreover, the cellulose nanofiber concentrate obtained by this embodiment can be redispersed in a solvent.

[Evaluation of redispersibility in resin]
0.19 g of the filtration residue obtained in Example 1 was measured in a 100 mL beaker, 30 mL of pure water was added, and the mixture was stirred for 5 minutes with an ultrasonic homogenizer (VC-505, manufactured by Sonic Corporation) to obtain a redispersion. This re-dispersed liquid was dissolved in pure water so that the solid content was 10% by mass, and 1 g of the prepared PVA solution had a solid content of TEMPO-oxidized cellulose nanofibers of 5% by mass relative to the PVA solid content. It added so that it might become 005g. After sufficiently stirring the mixed solution, it was cast into a petri dish and dried to prepare a TEMPO-oxidized cellulose nanofiber / PVA composite membrane.

  Further, a TEMPO oxidized cellulose nanofiber / PVA composite membrane was prepared in the same manner as in Example 19 except that the filtration residue obtained in Comparative Example 1 was used. Furthermore, a PVA membrane was prepared in the same manner as in Example 19 and Comparative Example 4 except that the TEMPO-oxidized cellulose nanofiber redispersion liquid was not added, and was designated as Comparative Example 5.

About the obtained composite film, the redispersibility of the cellulose nanofiber in the resin was evaluated. The evaluation was performed by visually observing the obtained composite membrane, and examining the presence or absence of coarse materials in which the cellulose nanofibers remained without being redispersed. The evaluation criteria are described below.
◯: No coarse material is confirmed in the composite film, and there is uniformity equivalent to that of the PVA film (Comparative Example 5).
X: Coarse material can be confirmed in the composite film, and there is no uniformity compared to the PVA film (Comparative Example 5).

  As shown in Table 4, the cellulose nanofiber concentrate of Comparative Example 1 obtained by concentrating the sample solution without using a concentration aid has insufficient redispersibility with respect to water or PVA, and PVA When a composite film was prepared, a coarse product was produced. On the other hand, when Epan 740 was used as the concentration aid (A), redispersibility was good with respect to water or PVA, and no coarse product was produced when a composite membrane with PVA was prepared.

  As described above, a concentrate composed of cellulose nanofibers and a concentration aid obtained by using the concentration method according to this embodiment can be easily redispersed in the resin. That is, the production method of the present embodiment is useful in the composite of cellulose nanofiber and resin.

Claims (7)

  In the presence of a concentration aid (A) that can give the aqueous dispersion a cloud point or a thermal gelation point by addition to the cellulose nanofiber aqueous dispersion, 1) A step of raising the temperature to a temperature equal to or higher than the thermal gelation point to form an aggregate containing cellulose nanofibers, and 2) a step of filtering the liquid containing the obtained aggregate at a temperature equal to or higher than the cloud point or the thermal gelation point. And a method for producing a cellulose nanofiber concentrate.   The production method according to claim 1, wherein the concentration aid (A) is at least one selected from the group consisting of a compound having a polyoxyalkylene chain in the molecule, an alkyl cellulose, and a hydroxyalkylalkyl cellulose.   The manufacturing method of Claim 1 or 2 which uses the adjustment adjuvant (B) which has the function to raise or reduce a cloud point or a heat | fever gelation point in addition to the said concentration adjuvant (A). The adjustment aid (B) is a salt comprising at least one selected from the group consisting of sulfate ion, halide ion, carbonate ion, phosphate ion, acetate ion and lactate ion, and / or the following general The manufacturing method of any one of Claims 1-3 which is at least 1 sort (s) of compound chosen from the group which consists of a compound represented by Formula (1)-(5).
_{C n H 2n + 1 -OH (} 1)
_{C p H 2p + 1 -CO-} C q H 2q + 1 (2)
_{C s H 2s + 1 -COO-} C t H 2t + 1 (3)
C _u H _{2u + 1} O- (AO) _v -C _w H _{2w + 1} (4)
R (OH) _m (5)
In the formula, n is an integer of 1 to 9, p and q are each independently an integer of 1 to 9, s is an integer of 0 to 9, t is an integer of 1 to 4, u and w are each independently 0 to 9 , V is an integer of 1 to 3, AO is an oxyalkylene group having 2 to 4 carbon atoms, R is a hydrocarbon group having 3 to 10 carbon atoms, m is 3 or 4, and a plurality of AOs in one molecule Each may be the same or different.   The manufacturing method in any one of Claims 1-4 which makes the liquid temperature of the liquid containing an aggregate 1-30 degreeC higher than a cloud point or a heat | fever gelation point in the said process to filter.   Aggregates separated from the filtrate in the filtration step, or an aqueous dispersion obtained by bringing the aggregates to a temperature lower than the cloud point or the thermal gelation point, are dehydrated and / or dried to remove moisture. The manufacturing method of any one of Claims 1-5 which further includes the process to reduce.   The cellulose nanofiber obtained by redispersing the cellulose nanofiber concentrate obtained by the method according to claim 1 in at least one dispersion medium selected from the group consisting of water, an organic solvent, and a resin. Redistribution method.