Method for producing solid phase cellulose nanofiber composite and method for producing cellulose nanofiber composition using solid phase cellulose nanofiber composite

Abstract

To provide a method for producing a solid phase cellulose nanofiber composite having excellent dispersibility of a cellulose nanofiber in a dispersion medium and handleability.SOLUTION: There is provided a method for producing a solid phase cellulose nanofiber composite which comprises: a cellulose nanofiber preparation step of preparing a dispersion medium containing a cellulose nanofiber by dispersing a cellulose nanofiber in a dispersion medium; a preparation step of a dispersion containing a cellulose nanofiber and a cellulose derivative which is dispersion containing the cellulose nanofiber and the cellulose derivative by adding a cellulose derivative in a dispersion medium containing the cellulose nanofiber to dissolve at least a part of the cellulose derivative in the dispersion medium containing the cellulose nanofiber, followed by integrating the cellulose nanofiber and the cellulose derivative; and a drying step of subjecting the dispersion containing the cellulose nanofiber and the cellulose derivative to drying treatment.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a solid-phase cellulose nanofiber composite and a method for producing a cellulose nanofiber composition using a solid-phase cellulose nanofiber composite, and in particular to a method for producing a solid-phase cellulose nanofiber composite that also exhibits affinity for hydrophobic substances and a method for producing a cellulose nanofiber composition using a solid-phase cellulose nanofiber composite. [Background technology]

[0002] Nanocellulose is a cellulose fiber with a thickness on the order of nanometers. Nanocellulose is obtained, for example, by defibrating plant fibers such as pulp in an aqueous medium. Nanocellulose is classified into cellulose nanofibers, cellulose crystals, cellulose whiskers, bacterial cellulose, etc., depending on the structured cellulose of nanocellulose. Cellulose nanofibers are lightweight and have excellent strength, and therefore have attracted attention for use as a reinforcing material for thermoplastic resins, etc. (see, for example, Patent Document 1).

[0003] On the other hand, since cellulose nanofibers are hydrophilic, it is difficult to disperse them uniformly in organic solvents, and the range of application is limited. Thus, for example, cellulose nanofibers have been proposed that are made hydrophobic by reacting cellulose nanofibers in a water-containing state with vinyl organic acid and recovering the resulting reaction product, thereby improving the dispersibility in organic solvents (see, for example, Patent Document 2). Hereinafter, cellulose nanofibers that have been given desired properties such as hydrophobicity to naturally derived cellulose nanofibers obtained from plant fibers, etc., may be referred to as "modified cellulose nanofibers."

[0004] However, the modified cellulose nanofibers shown in Patent Document 2 require strict reaction conditions between cellulose nanofibers and vinyl organic acid, and the production process is complicated, so there is a need to improve production efficiency. Furthermore, in the modified cellulose nanofibers modified with vinyl organic acid shown in Patent Document 2, the molecular structure of the cellulose nanofiber skeleton itself changes depending on the degree of modification, so there is room for improvement in terms of improving the hydrophobicity of the modified cellulose nanofibers, and further, in terms of improving dispersibility in organic solvents. Therefore, the modified cellulose nanofibers shown in Patent Document 2 need to be improved in terms of obtaining a dispersion liquid with excellent dispersibility of cellulose nanofibers, and there is still a problem that the application range of cellulose nanofibers is limited.

[0005] Furthermore, as a technology for imparting hydrophobicity to cellulose nanofibers, it has been proposed to modify cellulose nanofibers to be hydrophobic with a small mass of modifying groups by binding two types of modifying groups to the surface of cellulose nanofibers: one selected for wettability, such as an aromatic group, and the other selected for steric repulsion and hydrophobicity, such as a polyalkylene glycol group. However, modified cellulose nanofibers produced using two types of modifying groups, such as an aromatic group and a polyalkylene glycol group, have a complex chemical structure, and there is still a need for improvement in terms of obtaining a dispersion with excellent dispersibility of cellulose nanofibers. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-11392 A [Patent Document 2] International Publication No. 2016 / 010016 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above circumstances, the present invention aims to provide a method for producing a solid-phase cellulose nanofiber composite that has excellent dispersibility of cellulose nanofibers in dispersion media such as organic solvents and excellent handleability in dispersion media such as organic solvents, and that can easily expand the range of application of cellulose nanofibers, and a method for producing a cellulose nanofiber composition using the solid-phase cellulose nanofiber composite. [Means for solving the problem]

[0008] The gist of the configuration of the present invention is as follows. [1] A cellulose nanofiber preparation step of preparing a cellulose nanofiber-containing dispersion medium in which cellulose nanofibers are dispersed; a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding a cellulose derivative to the cellulose nanofiber-containing dispersion medium and dissolving at least a portion of the cellulose derivative in the cellulose nanofiber-containing dispersion medium to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion; Including, A method for producing a solid-phase cellulose nanofiber composite. [2] A cellulose derivative preparation step of preparing a cellulose derivative-containing solution in which at least a portion of the cellulose derivative is dissolved in a dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers to the cellulose derivative-containing solution and dispersing the cellulose nanofibers in the cellulose derivative-containing solution to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers with the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion; Including, A method for producing a solid-phase cellulose nanofiber composite. [3] A dispersion medium preparation step of preparing a dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers and a cellulose derivative to the dispersion medium, dispersing the cellulose nanofibers in the dispersion medium and dissolving at least a portion of the cellulose derivative to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion; Including, A method for producing a solid-phase cellulose nanofiber composite. [4] A method for producing a solid-phase cellulose nanofiber composite according to any one of [1] to [3], in which the cellulose derivative is physically adsorbed and integrated onto the cellulose nanofiber. [5] A method for producing a solid-phase cellulose nanofiber composite according to any one of [1] to [3], wherein the drying treatment is freeze-drying. [6] A method for producing a solid-phase cellulose nanofiber composite described in any one of [1] to [3], comprising containing 5.0 parts by mass or more and 5,000 parts by mass or less of the cellulose derivative per 100 parts by mass of the cellulose nanofiber. [7] A method for producing a solid-phase cellulose nanofiber composite described in any one of [1] to [3], comprising containing 10 parts by mass or more and 2,000 parts by mass or less of the cellulose derivative per 100 parts by mass of the cellulose nanofiber. [8] A method for producing a solid-phase cellulose nanofiber composite described in any one of [1] to [3], wherein the standard deviation in a transmittance test for light with a wavelength of 400 nm measured every 2 seconds over a period of 180 seconds for the solid-phase cellulose nanofiber composite containing 10 parts by mass or more and 2,000 parts by mass or less of the cellulose derivative per 100 parts by mass of the cellulose nanofiber is 0.10 or less. [9] A method for producing a solid-phase cellulose nanofiber composite described in any one of [1] to [3], wherein the cellulose derivative comprises at least one selected from the group consisting of hydroxyalkyl cellulose and alkyl cellulose.

[10] A method for producing a solid-phase cellulose nanofiber composite according to any one of [1] to [3], wherein the cellulose derivative is hydroxyalkyl cellulose.

[11] The method for producing a solid-phase cellulose nanofiber composite according to

[10] , wherein the hydroxyalkyl cellulose is hydroxypropyl cellulose.

[12] A cellulose nanofiber preparation step of preparing a cellulose nanofiber-containing dispersion medium in which cellulose nanofibers are dispersed in a first dispersion medium; a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding a cellulose derivative to the cellulose nanofiber-containing dispersion medium and dissolving at least a portion of the cellulose derivative in the cellulose nanofiber-containing dispersion medium to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion to obtain a solid-phase cellulose nanofiber composite; A cellulose nanofiber composite adding step of adding the cellulose nanofiber composite in a solid phase to a second dispersion medium to prepare a cellulose nanofiber composite-containing dispersion; Including, A method for producing a cellulose nanofiber composition.

[13] A cellulose derivative preparation step of preparing a cellulose derivative-containing solution in which at least a portion of the cellulose derivative is dissolved in a first dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers to the cellulose derivative-containing solution and dispersing the cellulose nanofibers in the cellulose derivative-containing solution to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers with the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion to obtain a solid-phase cellulose nanofiber composite; A cellulose nanofiber composite adding step of adding the cellulose nanofiber composite in a solid phase to a second dispersion medium to prepare a cellulose nanofiber composite-containing dispersion; Including, A method for producing a cellulose nanofiber composition.

[14] A dispersion medium preparation step of preparing a first dispersion medium; a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers and a cellulose derivative to the first dispersion medium, dispersing the cellulose nanofibers in the first dispersion medium and dissolving at least a portion of the cellulose derivative to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion to obtain a solid-phase cellulose nanofiber composite; A cellulose nanofiber composite adding step of adding the cellulose nanofiber composite in a solid phase to a second dispersion medium to prepare a cellulose nanofiber composite-containing dispersion; Including, A method for producing a cellulose nanofiber composition.

[0009] The cellulose nanofibers used in the method for producing a solid-phase cellulose nanofiber composite of the present invention are not modified cellulose nanofibers that have been given desired properties such as hydrophobicity (hereinafter, cellulose nanofibers that are not modified cellulose nanofibers may be simply referred to as "cellulose nanofibers"). In other words, the cellulose nanofibers used in the method for producing a solid-phase cellulose nanofiber composite of the present invention themselves have a hydrophilic chemical structure. The cellulose nanofibers are cellulose fibers with an average fiber diameter of less than 1.0 μm, that is, an average fiber diameter on the nano order.

[0010] Furthermore, the cellulose derivative used in the method for producing a solid-phase cellulose nanofiber composite of the present invention is integrated with the cellulose nanofibers, which have a hydrophilic chemical structure, in the obtained solid-phase cellulose nanofiber composite. Furthermore, by dispersing the solid-phase cellulose nanofiber composite in a dispersion such as an organic solvent, the hydroxyl groups of the cellulose derivative and the hydroxyl groups of the cellulose nanofibers interact with each other, resulting in a state in which the cellulose derivative is coordinated to the cellulose nanofibers.

[0011] In addition, in the above embodiment, "transmittance test of light with a wavelength of 400 nm measured every 2 seconds over a period of 180 seconds" refers to a test in which a dispersion of a solid-phase cellulose nanofiber composite in which 0.01 g to 2.0 g of cellulose derivative is integrated with 0.1 g of cellulose nanofiber is added to 20 ml of tetrahydrofuran (dispersion medium) so that the cellulose nanofiber is 0.1 g, and 2.0 ml of the dispersion is placed in a 4.5 ml container under conditions of 25°C and stirred at a rotation speed of 1000 rpm using a stirrer (stirring means) with a diameter of 9 mm and a height of 6.5 mm. The transmittance is measured at the center of the height of the dispersion of the cellulose nanofiber composite every 2 seconds over a period of 180 seconds from the start of stirring, and the average transmittance of the transmittance of each measurement time is calculated, and this test measures the transmittance of light with a wavelength of 400 nm over an optical path length of 1 cm. In addition, in the above embodiment, the "standard deviation in the transmittance test" refers to the average value of each standard deviation (n=3) obtained from one measurement of the average transmittance, that is, the standard deviation of the transmittance measured every 2 seconds over a period of 180 seconds from the start of stirring, calculated from three measurements of the average transmittance. Effect of the Invention

[0012] According to the method for producing a solid-phase cellulose nanofiber composite of the present invention, the method includes a cellulose nanofiber preparation step of preparing a cellulose nanofiber-containing dispersion medium in which cellulose nanofibers are dispersed, a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding a cellulose derivative to the cellulose nanofiber-containing dispersion medium and dissolving at least a portion of the cellulose derivative in the cellulose nanofiber-containing dispersion medium to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative, and a drying step of drying the cellulose nanofibers and cellulose derivative-containing dispersion, or includes a cellulose derivative preparation step of preparing a cellulose derivative-containing solution in which at least a portion of the cellulose derivative is dissolved in a dispersion medium, and a cellulose derivative preparation step of adding cellulose nanofibers to the cellulose derivative-containing solution and dispersing the cellulose nanofibers in the cellulose derivative-containing solution to integrate the cellulose nanofibers and the cellulose derivative. a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of preparing a cellulose nanofiber- and cellulose derivative-containing dispersion, which is a dispersion containing a cellulose nanofiber and a cellulose derivative, and integrating the cellulose nanofibers with the cellulose derivative, and a drying step of drying the cellulose nanofiber- and cellulose derivative-containing dispersion, or a dispersion medium preparation step of preparing a dispersion medium, adding cellulose nanofibers and a cellulose derivative to the dispersion medium, dispersing the cellulose nanofibers in the dispersion medium, and dissolving at least a portion of the cellulose derivative, to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion, which is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers with the cellulose derivative, and a drying step of drying the cellulose nanofiber- and cellulose derivative-containing dispersion, thereby achieving excellent dispersibility of cellulose nanofibers in a dispersion medium such as an organic solvent, andIt is possible to produce a solid-phase cellulose nanofiber composite that is easy to handle in a dispersion medium such as an organic solvent.

[0013] The solid-phase cellulose nanofiber composite obtained by the production method of the present invention has excellent dispersibility of cellulose nanofibers in a dispersion medium such as an organic solvent, even if the cellulose nanofibers are not modified cellulose nanofibers to which properties such as hydrophobicity have been imparted. Therefore, a cellulose nanofiber composition obtained by adding the solid-phase cellulose nanofiber composite obtained by the production method of the present invention to a dispersion medium has excellent dispersibility of cellulose nanofibers. From the above, according to the production method of the solid-phase cellulose nanofiber composite of the present invention, it is possible to obtain a solid-phase cellulose nanofiber composite that can easily and uniformly disperse cellulose nanofibers in hydrophobic substances to which the cellulose nanofibers are applied, and can easily expand the range of application of the cellulose nanofiber.

[0014] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, there is no need to modify the cellulose nanofibers to be hydrophobic in advance, and the skeleton of the cellulose nanofiber is maintained, so the properties of the cellulose nanofiber can be reliably imparted to the subject of application.

[0015] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, the cellulose derivative is physically adsorbed and integrated onto the cellulose nanofiber, thereby further reliably improving the dispersibility of the cellulose nanofiber, which is a component of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0016] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, the cellulose nanofibers and cellulose derivatives are freeze-dried, thereby further reliably improving the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0017] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, by containing 5.0 parts by mass or more and 5000 parts by mass or less of a cellulose derivative per 100 parts by mass of cellulose nanofibers, excellent dispersibility of the cellulose nanofibers, which are a component of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent can be reliably obtained. Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, by containing 10 parts by mass or more and 2000 parts by mass or less of a cellulose derivative per 100 parts by mass of cellulose nanofibers, excellent dispersibility of the cellulose nanofibers, which are a component of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent can be further reliably obtained.

[0018] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, the cellulose derivative contains at least one type selected from the group consisting of hydroxyalkyl cellulose and alkyl cellulose, thereby ensuring excellent dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0019] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, the cellulose derivative is hydroxyalkyl cellulose, which more reliably improves the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0020] Furthermore, according to the method for producing a solid-phase cellulose nanofiber composite of the present invention, the hydroxyalkyl cellulose is hydroxypropyl cellulose, which further reliably improves the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent. [Brief description of the drawings]

[0021] [Figure 1]Photographs showing the dispersibility of solid-phase cellulose nanofiber composites in Comparative Example 1 (left), Example 1 (center), and Example 2 (right). [Diagram 2] Photographs showing the dispersibility of solid-phase cellulose nanofiber composites in Comparative Example 1 (left), Example 3 (center), and Example 4 (right). [Diagram 3] Photographs showing the dispersibility of solid-phase cellulose nanofiber composites in Comparative Example 1 (left), Example 5 (center), and Example 6 (right). [Figure 4] Photographs showing the dispersibility of solid-phase cellulose nanofiber composites in Comparative Example 1 (left) and Example 7 (right). [Diagram 5] 1 is a photograph showing the dispersibility of cellulose nanofibers in Reference Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The method for producing a solid-phase cellulose nanofiber composite of the present invention will be described in detail below. First, a first embodiment of the method for producing a solid-phase cellulose nanofiber composite of the present invention will be described.

[0023] <First embodiment of the method for producing a solid-phase cellulose nanofiber composite> A first aspect of the method for producing a solid-phase cellulose nanofiber composite includes: (1) a cellulose nanofiber preparation step of preparing a cellulose nanofiber-containing dispersion medium in which cellulose nanofibers are dispersed; (2) a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding a cellulose derivative to the cellulose nanofiber-containing dispersion medium and dissolving at least a portion of the cellulose derivative in the cellulose nanofiber-containing dispersion medium to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; and (3) a drying step of drying the cellulose nanofiber- and cellulose derivative-containing dispersion. In the first embodiment, a cellulose derivative is added to a cellulose nanofiber-containing dispersion medium and the cellulose derivative is dissolved in the cellulose nanofiber-containing dispersion medium, for example, by causing the cellulose derivative to physically adsorb to the cellulose nanofiber in the dispersion medium due to intermolecular forces such as van der Waals forces and hydrogen bonds, thereby integrating the cellulose nanofiber and the cellulose derivative.The dispersion medium is then removed by a drying treatment, thereby further promoting the adsorption between the cellulose nanofiber and the cellulose derivative, and a solid-phase cellulose nanofiber composite is produced.

[0024] The solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite contains cellulose nanofibers and a cellulose derivative, and the cellulose nanofibers and the cellulose derivatives are integrated. The above-mentioned solid-phase cellulose nanofiber composite is a single material in which the cellulose nanofibers and the cellulose derivatives are integrated. For example, the solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite is a composite material in which the cellulose nanofibers and the cellulose derivatives are bonded by intermolecular forces such as van der Waals forces and hydrogen bonds. From the above, the solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite is not a mixture in which the solid-phase cellulose nanofibers and the solid-phase cellulose derivatives are simply mixed together.

[0025] According to the first aspect of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite having excellent dispersibility of cellulose nanofibers in a dispersion medium such as an organic solvent and excellent handleability in a dispersion medium such as an organic solvent can be produced by the simple production steps (1) to (3) above. According to the first aspect of the method for producing a solid-phase cellulose nanofiber composite, even if the cellulose nanofiber is not modified to have properties such as hydrophobicity, the dispersibility of the cellulose nanofiber in a dispersion medium such as an organic solvent is excellent. Therefore, the cellulose nanofiber composition obtained by adding the solid-phase cellulose nanofiber composite obtained by the first aspect of the method for producing a solid-phase cellulose nanofiber composite to a dispersion medium has excellent dispersibility of the cellulose nanofiber. From the above, according to the first aspect of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite can be obtained that can easily and uniformly disperse the cellulose nanofiber in the hydrophobic substance to which it is applied, and can easily expand the range of application of the cellulose nanofiber.

[0026] Furthermore, according to the first aspect of the method for producing a solid-phase cellulose nanofiber composite, there is no need to modify the cellulose nanofibers to be hydrophobic in advance, and therefore the skeleton of the cellulose nanofiber is maintained, so that the properties of the cellulose nanofiber can be reliably imparted to the subject of application.

[0027] (1) Cellulose nanofiber preparation process This is a step of preparing a cellulose nanofiber-containing dispersion medium by dispersing cellulose nanofibers in a dispersion medium (first dispersion medium). As the dispersion medium in which the cellulose nanofibers are dispersed, water is preferable, pure water is preferable, and ultrapure water is particularly preferable.

[0028] The cellulose nanofibers used in the method for producing a solid-phase cellulose nanofiber composite of the present invention are not modified cellulose nanofibers that have been given desired properties such as hydrophobicity, but are hydrophilic cellulose nanofibers that have not been modified. Therefore, when dispersing cellulose nanofibers in a dispersion medium, it is not necessary to modify the cellulose nanofibers to give them desired properties such as hydrophobicity. In addition, dried cellulose nanofibers may be used as the cellulose nanofibers as necessary. In this case, the cellulose nanofibers are dried before being added to the dispersion medium (i.e., dried cellulose nanofibers). The drying conditions are not particularly limited, and examples include air drying, natural drying, and freeze drying.

[0029] Examples of cellulose nanofibers include cellulose derived from natural products. For example, examples of cellulose nanofibers include nanofibers obtained by subjecting a cellulose precursor derived from a natural product, which is the raw material, to a defibration treatment. Examples of cellulose precursors, which are the raw material for cellulose nanofibers, include plant fibers such as pulp. The method for defibrating the cellulose precursor is not particularly limited, and examples of the method include defibration treatment using a mixer, a high-speed homogenizer, an ultrasonic homogenizer, a low-pressure homogenizer, a high-pressure homogenizer, a high-speed rotating mixer, a grinder, freeze grinding, a media mill, a ball mill, etc.

[0030] The cellulose nanofibers obtained by subjecting a cellulose precursor to a defibration treatment to form nanofibers are obtained, for example, as a cellulose nanofiber aqueous dispersion in which the cellulose nanofibers are dispersed in water. The cellulose nanofiber aqueous dispersion obtained by subjecting a defibration treatment may be used as a cellulose nanofiber-containing dispersion medium, or a dispersion medium may be added to the cellulose nanofiber aqueous dispersion obtained by subjecting a defibration treatment to use as a cellulose nanofiber-containing dispersion medium. Furthermore, cellulose nanofibers can be obtained by carrying out a drying step in which the cellulose nanofiber aqueous dispersion is dried to remove moisture.

[0031] The cellulose nanofibers have an average fiber diameter of less than 1.0 μm. As long as the cellulose nanofiber has an average fiber diameter of less than 1.0 μm, the size of the cellulose is not particularly limited, but from the viewpoint of expanding the range of application of the cellulose nanofibers, the average fiber diameter is preferably 4 nm or more and 100 nm or less, and particularly preferably 10 nm or more and 50 nm or less. The average fiber length of the cellulose nanofibers is not particularly limited, but from the viewpoint of expanding the range of application of the cellulose nanofibers, the average fiber diameter is preferably 20 μm or more and 200 μm or less, and particularly preferably 50 μm or more and 150 μm or less. The average fiber diameter and the average fiber length of the cellulose nanofibers can be measured, for example, by a scanning probe microscope or a nitrogen adsorption method for the average fiber diameter, and by an electron microscope (transmission electron microscope (TEM), scanning electron microscope (SEM)) or a scanning probe microscope for the average fiber length.

[0032] The content of cellulose nanofibers in the cellulose nanofiber-containing dispersion medium is not particularly limited and can be appropriately selected depending on the dispersion state of the cellulose nanofibers in the cellulose nanofiber-containing dispersion medium. However, the lower limit of the content of cellulose nanofibers in the cellulose nanofiber-containing dispersion medium is preferably 0.5 parts by mass, more preferably 1.0 parts by mass, and particularly preferably 2.0 parts by mass, relative to 100 parts by mass of the dispersion medium, from the viewpoint of improving the production efficiency of a solid-phase cellulose nanofiber composite. On the other hand, the upper limit of the content of cellulose nanofibers in the cellulose nanofiber-containing dispersion medium is preferably 30 parts by mass, more preferably 20 parts by mass, and particularly preferably 10 parts by mass, from the viewpoint of smooth stirring of the cellulose nanofiber-containing dispersion medium and facilitating dissolution of the cellulose derivative described below.

[0033] (2) Cellulose nanofiber and cellulose derivative-containing dispersion preparation process A cellulose derivative is added to the cellulose nanofiber-containing dispersion medium obtained in the step (1), and at least a part of the cellulose derivative added is dissolved in the cellulose nanofiber-containing dispersion medium to prepare a dispersion containing the cellulose nanofiber and the cellulose derivative, and the cellulose nanofiber and the cellulose derivative are integrated. Examples of the cellulose derivative include solid-phase cellulose derivatives such as powders. The cellulose derivative is a component different from the cellulose nanofiber in that it is a compound obtained by chemically modifying cellulose. The cellulose derivative is in a state of being dissolved in the dispersion medium in the cellulose nanofiber and the cellulose derivative-containing dispersion. It is considered that the cellulose derivative is dissolved in the dispersion medium in the cellulose nanofiber and the cellulose derivative-containing dispersion, and the hydroxyl group of the cellulose derivative interacts with the hydroxyl group of the cellulose nanofiber, and the cellulose derivative is coordinated to the cellulose nanofiber, thereby integrating the cellulose nanofiber and the cellulose derivative. In addition, the cellulose nanofiber and the cellulose derivative both have a cellulose skeleton, and therefore have similar molecular structures. Therefore, it is considered that the cellulose nanofiber has a high affinity with the cellulose derivative, and therefore the cellulose derivative is easily coordinated to the cellulose nanofiber. It is believed that the cellulose derivative is coordinated to the cellulose nanofibers, which allows the surfactant properties of the cellulose derivative to be exerted, and thus the cellulose nanofibers have excellent dispersibility in the cellulose nanofiber and cellulose derivative-containing dispersion.

[0034] Moreover, since cellulose derivatives are biocompatible materials, their safety for the human body can be ensured, and since forest resources such as thinned wood can be utilized, the environmental burden can be reduced.

[0035] The cellulose derivative is not particularly limited as long as it is a derivative obtained by chemically reacting at least a portion of the hydroxyl groups of cellulose, and examples thereof include hydroxyalkyl cellulose, alkyl cellulose, carboxyalkyl cellulose, hydroxyalkyl alkyl cellulose, etc. Among these, hydroxyalkyl cellulose and alkyl cellulose are preferred because they can reliably obtain excellent dispersibility of cellulose nanofibers, which are a component of the solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent, and hydroxyalkyl cellulose is particularly preferred because they can more reliably improve the dispersibility of cellulose nanofibers, which are a component of the solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent. As the cellulose derivative, for example, hydroxyalkyl cellulose and alkyl cellulose may be used in combination, or either one may be used alone.

[0036] Examples of hydroxyalkyl cellulose include hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose, hydroxypentyl cellulose, and hydroxyhexyl cellulose. These compounds may be used alone or in combination of two or more. Among these, hydroxyethyl cellulose and hydroxypropyl cellulose are preferred, and hydroxypropyl cellulose is particularly preferred, in that they further reliably improve the dispersibility of cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent.

[0037] Examples of alkyl cellulose include methyl cellulose, ethyl cellulose, propyl cellulose, butyl cellulose, pentyl cellulose, and hexyl cellulose. These compounds may be used alone or in combination of two or more. Among these, methyl cellulose and ethyl cellulose are preferred, and ethyl cellulose is particularly preferred, since they can more reliably obtain excellent dispersibility of cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0038] Examples of the carboxyalkyl cellulose include carboxymethyl cellulose, carboxyethyl cellulose, carboxypropyl cellulose, carboxybutyl cellulose, carboxypentyl cellulose, and carboxyhexyl cellulose.

[0039] Hydroxyalkyl alkyl cellulose is a cellulose having hydroxyalkyl and alkyl. Examples of hydroxyalkyl alkyl cellulose include cellulose having hydroxymethyl and alkyl such as hydroxymethyl methyl cellulose, hydroxymethyl ethyl cellulose, hydroxymethyl propyl cellulose, hydroxymethyl butyl cellulose, etc.; cellulose having hydroxyethyl and alkyl such as hydroxyethyl methyl cellulose, hydroxyethyl ethyl cellulose, hydroxyethyl propyl cellulose, hydroxyethyl butyl cellulose, etc.; cellulose having hydroxypropyl and alkyl such as hydroxypropyl methyl cellulose, hydroxypropyl ethyl cellulose, hydroxypropyl propyl cellulose, hydroxypropyl butyl cellulose, etc.; cellulose having hydroxybutyl and alkyl such as hydroxybutyl methyl cellulose, hydroxybutyl ethyl cellulose, hydroxybutyl propyl cellulose, hydroxybutyl butyl cellulose, etc.

[0040] An example of a method for preparing a dispersion containing cellulose nanofibers and a cellulose derivative is a method in which a predetermined amount of cellulose derivative is added to a cellulose nanofiber-containing dispersion medium, and the mixture is stirred under predetermined stirring conditions to dissolve the cellulose derivative in the cellulose nanofiber-containing dispersion medium. The stirring conditions can be appropriately selected depending on the molecular weight and amount of the cellulose derivative, the size of the stirring vessel, the type of stirrer, etc., and are not particularly limited. For example, the stirring temperature is 10°C to 60°C, the stirring time is 1 minute to 120 minutes, and the stirring speed is 600 rpm to 1350 rpm. The stirring time and stirring speed can be set appropriately depending on the type of stirrer, the size of the stirring vessel, the molecular weight and amount of the cellulose derivative, etc. The stirring means is not particularly limited, and examples thereof include a stirrer, a stirring blade, etc.

[0041] The amount of cellulose derivative added to a cellulose nanofiber-containing dispersion medium is not particularly limited, but the lower limit is preferably 5.0 parts by mass per 100 parts by mass of cellulose nanofiber, from the viewpoint of ensuring excellent dispersibility of cellulose nanofibers, which are components of a solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent, and more preferably 10 parts by mass, from the viewpoint of even more ensuring excellent dispersibility of cellulose nanofibers, which are components of a solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent, and still more preferably 100 parts by mass, and particularly preferably 200 parts by mass, from the viewpoint of further improving the dispersibility of cellulose nanofibers, which are components of a solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent. On the other hand, the upper limit of the amount of cellulose derivative added is preferably 5,000 parts by mass per 100 parts by mass of cellulose nanofiber, in order to reliably impart the properties of cellulose nanofiber to the application target while reliably obtaining excellent dispersibility of the cellulose nanofiber, which is a component of the solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent, and is more preferably 4,000 parts by mass, even more preferably 3,000 parts by mass, and particularly preferably 2,000 parts by mass, in order to further reliably obtain excellent dispersibility of the cellulose nanofiber, which is a component of the solid-phase cellulose nanofiber composite in a dispersion medium such as an organic solvent.

[0042] (3) Drying process A solid-phase cellulose nanofiber composite can be obtained by carrying out a drying step in which the cellulose nanofiber- and cellulose derivative-containing dispersion obtained in step (2) is subjected to a drying treatment to remove the dispersion medium. In the solid-phase cellulose nanofiber composite, for example, the cellulose derivative is physically adsorbed to the cellulose nanofiber, thereby integrating the cellulose nanofiber and the cellulose derivative. Specifically, for example, the cellulose derivative, which is in a chain form along the surface of the cellulose nanofiber, is physically adsorbed to the cellulose nanofiber, thereby integrating the cellulose nanofiber and the cellulose derivative.

[0043] The method of drying treatment is not particularly limited, and examples thereof include air drying, natural drying, heat drying, freeze drying, etc. Among these, freeze drying is preferred because it further reliably improves the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0044] From the above, the solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite may be, for example, a form in which the cellulose nanofiber and the cellulose derivative are integrated and dried, such as a form in which the cellulose nanofiber and the cellulose derivative are integrated and freeze-dried. Thus, for example, the cellulose nanofiber and the cellulose derivative are freeze-dried, so that the cellulose derivative, which is in a chain form along the surface of the cellulose nanofiber, is physically adsorbed to the cellulose nanofiber. From the above, the shape of the solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite may be, for example, cotton-like.

[0045] The solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite may, for example, have at least a portion of the cellulose derivative wrapped around the cellulose nanofiber. Specifically, for example, the cellulose derivative may have at least a partial region physically adsorbed to the cellulose nanofiber while wrapped around the surface of the cellulose nanofiber. The solid-phase cellulose nanofiber composite obtained by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite may, for example, have the entire cellulose derivative physically adsorbed to the cellulose nanofiber, or the end of the cellulose derivative physically adsorbed to the cellulose nanofiber. From the viewpoint of physical adsorption to the cellulose nanofiber, the cellulose derivative is preferably a chain-like cellulose derivative.

[0046] In the above solid-phase cellulose nanofiber composite, the cellulose nanofibers and the cellulose derivative are integrated together, which suppresses aggregation of the cellulose nanofibers, and therefore when added to a dispersion medium such as an organic solvent, the cellulose nanofibers have excellent dispersibility in the dispersion medium. In particular, in the above solid-phase cellulose nanofiber composite, the cellulose derivative is physically adsorbed to the cellulose nanofibers and integrated together, which further reliably improves the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent. In particular, in the above solid-phase cellulose nanofiber composite, the cellulose nanofibers and the cellulose derivative are integrated together in a freeze-dried state, which further reliably suppresses aggregation of the cellulose nanofibers, and therefore further reliably improves the dispersibility of the cellulose nanofibers in a dispersion medium such as an organic solvent.

[0047] Furthermore, the solid-phase cellulose nanofiber composite has handleability in organic solvents because aggregation of the cellulose nanofibers is suppressed by integrating the cellulose nanofibers with the cellulose derivative. That is, the solid-phase cellulose nanofiber composite has excellent dispersibility in a dispersion medium such as an organic solvent even if it is not a modified cellulose nanofiber that has been given properties such as hydrophobicity, and therefore a composition with excellent dispersibility of the cellulose nanofibers can be easily obtained by adding it to a dispersion medium.

[0048] <Second embodiment of the method for producing a solid-phase cellulose nanofiber composite> A second aspect of the method for producing a solid-phase cellulose nanofiber composite includes (1) a cellulose derivative preparation step of preparing a cellulose derivative-containing solution in which at least a part of the cellulose derivative is dissolved in a dispersion medium, (2) a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers to the cellulose derivative-containing solution and dispersing the cellulose nanofibers in the cellulose derivative-containing solution to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative, and (3) a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion. In the second aspect, by adding cellulose nanofibers to the cellulose derivative-containing solution to disperse the cellulose nanofibers in the cellulose derivative-containing solution, for example, the cellulose derivatives are physically adsorbed to the cellulose nanofibers by intermolecular forces such as van der Waals forces and hydrogen bonds in the dispersion medium to integrate the cellulose nanofibers and the cellulose derivatives, and then a drying process is performed to remove the dispersion medium, thereby further promoting the adsorption of the cellulose nanofibers and the cellulose derivative to produce a solid-phase cellulose nanofiber composite. Therefore, the second embodiment differs from the first embodiment in that the order in which the cellulose nanofibers and the cellulose derivative are added to the dispersion medium is different, but in other respects it is similar to the first embodiment described above.

[0049] In the cellulose derivative preparation step, a method for dissolving the cellulose derivative in a dispersion medium (first dispersion medium) includes, for example, a method of adding the cellulose derivative to the dispersion medium and stirring under predetermined stirring conditions. The stirring conditions can be appropriately selected depending on the molecular weight and amount of the cellulose derivative, the size of the stirring vessel, the type of stirrer, etc., and are not particularly limited, but include, for example, a stirring temperature of 10°C to 60°C, a stirring time of 1 minute to 120 minutes, and a stirring speed of 600 rpm to 1350 rpm. The stirring time and stirring speed can be set appropriately depending on the type of stirrer, the size of the stirring vessel, the molecular weight and amount of the cellulose derivative, etc. In addition, the stirring means is not particularly limited, and examples thereof include a stirrer, a stirring blade, etc.

[0050] In addition, in the cellulose nanofiber and cellulose derivative-containing dispersion preparation process, an example of a method for adding and dispersing cellulose nanofibers in a cellulose derivative-containing solution is to add cellulose nanofibers to a cellulose derivative-containing solution and stir under a predetermined stirring condition. The stirring conditions can be appropriately selected depending on the molecular weight and amount of cellulose nanofibers, the size of the stirring vessel, the type of stirrer, etc., and are not particularly limited, but examples include a stirring temperature of 10°C to 60°C, a stirring time of 1 minute to 120 minutes, and a stirring speed of 600 rpm to 1350 rpm. Appropriate conditions can be set for the stirring time and stirring speed depending on the type of stirrer, the size of the stirring vessel, the molecular weight and amount of cellulose nanofibers, etc. In addition, the stirring means is not particularly limited, and examples include a stirrer, a stirring blade, etc.

[0051] In the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated can be obtained, similarly to the first embodiment. For example, in the second embodiment, the cellulose nanofibers and cellulose derivatives are integrated by physically adsorbing the cellulose derivatives to the cellulose nanofibers, similarly to the first embodiment. Specifically, for example, the cellulose nanofibers and cellulose derivatives are integrated by physically adsorbing the cellulose derivatives that are chain-like along the surface of the cellulose nanofibers to the cellulose nanofibers.

[0052] In the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, as in the first embodiment, the method of drying is not particularly limited and examples include air drying, natural drying, heat drying, freeze drying, etc. Among these, freeze drying is preferred since it further reliably improves the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0053] From the above, the solid-phase cellulose nanofiber composite obtained in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite can be, as in the first embodiment, for example, an embodiment in which the cellulose nanofiber and the cellulose derivative are integrated and dried, such as an embodiment in which the cellulose nanofiber and the cellulose derivative are integrated and freeze-dried. Thus, for example, an embodiment in which the cellulose nanofiber and the cellulose derivative are freeze-dried, such that the cellulose derivative, which is in a chain form along the surface of the cellulose nanofiber, is physically adsorbed to the cellulose nanofiber. From the above, the shape of the solid-phase cellulose nanofiber composite obtained in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite can be, as in the first embodiment, for example, cotton-like.

[0054] The solid-phase cellulose nanofiber composite obtained by the second embodiment of the method for producing a solid-phase cellulose nanofiber composite may, as in the first embodiment, have at least a portion of the cellulose derivative wrapped around the cellulose nanofiber. Specifically, the solid-phase cellulose nanofiber composite may have at least a portion of the cellulose derivative wrapped around the surface of the cellulose nanofiber and physically adsorbed to the cellulose nanofiber. The solid-phase cellulose nanofiber composite obtained by the second embodiment of the method for producing a solid-phase cellulose nanofiber composite may have at least a portion of the cellulose derivative wrapped around the surface of the cellulose nanofiber and physically adsorbed to the cellulose nanofiber at its end. From the viewpoint of physically adsorbing to the cellulose nanofiber, the cellulose derivative is preferably a chain-like cellulose derivative.

[0055] The solid-phase cellulose nanofiber composite obtained in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, like the first embodiment, contains cellulose nanofibers and a cellulose derivative, and is a single material in which the cellulose nanofibers and the cellulose derivatives are integrated. For example, the solid-phase cellulose nanofiber composite obtained in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite is a composite material in which the cellulose nanofibers and the cellulose derivatives are bonded by intermolecular forces such as van der Waals forces and hydrogen bonds. From the above, like the first embodiment, the solid-phase cellulose nanofiber composite obtained in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite is not a mixture in which the solid-phase cellulose nanofibers and the solid-phase cellulose derivatives are simply mixed together.

[0056] In the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite having excellent dispersibility of cellulose nanofibers in a dispersion medium such as an organic solvent and excellent handleability in a dispersion medium such as an organic solvent can be produced by the simple production steps (1) to (3) above. In the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, the cellulose nanofiber is excellent in dispersibility in a dispersion medium such as an organic solvent even if the cellulose nanofiber is not modified to have properties such as hydrophobicity. Therefore, the cellulose nanofiber composition obtained by adding the solid-phase cellulose nanofiber composite to a dispersion medium has excellent dispersibility of cellulose nanofibers. From the above, in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite can be obtained that can easily and uniformly disperse cellulose nanofibers in hydrophobic substances to which the cellulose nanofibers are to be applied, and can easily expand the range of application of the cellulose nanofibers.

[0057] Furthermore, in the second embodiment of the method for producing a solid-phase cellulose nanofiber composite, there is no need to modify the cellulose nanofibers to be hydrophobic in advance, and the skeleton of the cellulose nanofiber is maintained, so the properties of the cellulose nanofiber can be reliably imparted to the subject of application.

[0058] <Third aspect of the method for producing a solid-phase cellulose nanofiber composite> A third aspect of the method for producing a solid-phase cellulose nanofiber composite includes (1) a dispersion medium preparation step of preparing a dispersion medium, (2) a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers and a cellulose derivative to the dispersion medium, dispersing the cellulose nanofibers in the dispersion medium and dissolving at least a portion of the cellulose derivative to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative, and (3) a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion. In the third aspect, the cellulose nanofibers and the cellulose derivative are added to the dispersion medium, and while dissolving the cellulose derivative in the dispersion medium, the cellulose nanofibers are dispersed in the dispersion medium, and the cellulose derivative is physically adsorbed to the cellulose nanofibers by intermolecular forces such as van der Waals forces and hydrogen bonds in the dispersion medium to integrate the cellulose nanofibers and the cellulose derivative, and then the dispersion medium is removed by a drying process to further promote the adsorption of the cellulose nanofibers and the cellulose derivative, thereby producing a solid-phase cellulose nanofiber composite. Therefore, the third embodiment differs from the first embodiment in that the cellulose nanofibers and the cellulose derivative are added to the dispersion medium at the same time, but in other respects is similar to the first embodiment described above.

[0059] In the cellulose nanofiber and cellulose derivative-containing dispersion preparation process, the cellulose nanofiber and cellulose derivative are added to a dispersion medium (first dispersion medium) to dissolve the cellulose derivative in the dispersion medium and disperse the cellulose nanofiber in the dispersion medium. For example, the cellulose nanofiber and cellulose derivative are added to the dispersion medium and stirred under predetermined stirring conditions. The stirring conditions can be appropriately selected depending on the molecular weight and amount of the cellulose nanofiber and cellulose derivative, the size of the stirring vessel, the type of stirrer, etc., and are not particularly limited. For example, the stirring temperature is 10°C to 60°C, the stirring time is 1 minute to 120 minutes, and the stirring speed is 600 rpm to 1350 rpm. The stirring time and stirring speed can be set appropriately depending on the type of stirrer, the size of the stirring vessel, the molecular weight and amount of the cellulose nanofiber and cellulose derivative, etc. The stirring means is not particularly limited, and examples thereof include a stirrer, a stirring blade, etc.

[0060] In the third embodiment of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated can be obtained, similarly to the first and second embodiments. For example, in the third embodiment, the cellulose nanofibers and cellulose derivatives are integrated by physically adsorbing the cellulose derivatives to the cellulose nanofibers, similarly to the first and second embodiments. Specifically, for example, the cellulose nanofibers and cellulose derivatives are integrated by physically adsorbing the cellulose derivatives that are chain-like along the surface of the cellulose nanofibers to the cellulose nanofibers.

[0061] In the third aspect of the method for producing a solid-phase cellulose nanofiber composite, as in the first and second aspects, the method of drying is not particularly limited and examples include air drying, natural drying, heat drying, freeze drying, etc. Among these, freeze drying is preferred since it further reliably improves the dispersibility of the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in a dispersion medium such as an organic solvent.

[0062] From the above, the solid-phase cellulose nanofiber composite obtained in the third embodiment of the method for producing a solid-phase cellulose nanofiber composite can be, as in the first and second embodiments, for example, an embodiment in which the cellulose nanofiber and the cellulose derivative are integrated and dried, such as an embodiment in which the cellulose nanofiber and the cellulose derivative are integrated and freeze-dried. Therefore, for example, an embodiment in which the cellulose nanofiber and the cellulose derivative are freeze-dried, such that the cellulose derivative, which is in a chain form along the surface of the cellulose nanofiber, is physically adsorbed to the cellulose nanofiber. From the above, the shape of the solid-phase cellulose nanofiber composite obtained in the third embodiment of the method for producing a solid-phase cellulose nanofiber composite can be, as in the first and second embodiments, for example, a cotton-like shape.

[0063] The solid-phase cellulose nanofiber composite obtained by the third embodiment of the method for producing a solid-phase cellulose nanofiber composite may, as in the first and second embodiments, have at least a portion of the cellulose derivative wrapped around the cellulose nanofiber. Specifically, the solid-phase cellulose nanofiber composite may have at least a portion of the cellulose derivative wrapped around the surface of the cellulose nanofiber and physically adsorbed to the cellulose nanofiber. The solid-phase cellulose nanofiber composite obtained by the third embodiment of the method for producing a solid-phase cellulose nanofiber composite may have at least a portion of the cellulose derivative wrapped around the surface of the cellulose nanofiber and physically adsorbed to the cellulose nanofiber at its end. From the viewpoint of physically adsorbing to the cellulose nanofiber, the cellulose derivative is preferably a chain-like cellulose derivative.

[0064] The solid-phase cellulose nanofiber composite obtained in the third embodiment of the method for producing a solid-phase cellulose nanofiber composite contains cellulose nanofibers and a cellulose derivative, as in the first and second embodiments, and is a single material in which the cellulose nanofibers and the cellulose derivatives are integrated. For example, the solid-phase cellulose nanofiber composite obtained in the third embodiment of the method for producing a solid-phase cellulose nanofiber composite is a composite material in which the cellulose nanofibers and the cellulose derivatives are bonded by intermolecular forces such as van der Waals forces and hydrogen bonds. From the above, the solid-phase cellulose nanofiber composite obtained in the third embodiment of the method for producing a solid-phase cellulose nanofiber composite is not a mixture in which the solid-phase cellulose nanofibers and the solid-phase cellulose derivatives are simply mixed, as in the first and second embodiments.

[0065] In the third aspect of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite having excellent dispersibility of cellulose nanofibers in a dispersion medium such as an organic solvent and excellent handleability in a dispersion medium such as an organic solvent can be produced by the simple production steps (1) to (3) above. In the third aspect of the method for producing a solid-phase cellulose nanofiber composite, the cellulose nanofiber is excellent in dispersibility in a dispersion medium such as an organic solvent even if the cellulose nanofiber is not modified to have properties such as hydrophobicity. Therefore, the cellulose nanofiber composition obtained by adding the solid-phase cellulose nanofiber composite to a dispersion medium has excellent dispersibility of cellulose nanofibers. From the above, in the third aspect of the method for producing a solid-phase cellulose nanofiber composite, a solid-phase cellulose nanofiber composite can be obtained that can easily and uniformly disperse cellulose nanofibers in hydrophobic substances to which the cellulose nanofibers are to be applied, and can easily expand the range of application of the cellulose nanofibers.

[0066] Furthermore, in the third embodiment of the method for producing a solid-phase cellulose nanofiber composite, there is no need to modify the cellulose nanofibers to be hydrophobic in advance, and the skeleton of the cellulose nanofiber is maintained, so the properties of the cellulose nanofiber can be reliably imparted to the subject of application.

[0067] The dispersion characteristics of the solid-phase cellulose nanofiber composite in the dispersion medium can be confirmed by measuring the standard deviation of the transmittance test of light with a wavelength of 400 nm measured every 2 seconds over 180 seconds for a composition obtained by dispersing the solid-phase cellulose nanofiber composite obtained by the above-mentioned method for producing a solid-phase cellulose nanofiber composite of the present invention in a dispersion medium. In a composition obtained by dispersing a solid-phase cellulose nanofiber composite in a dispersion medium, the lower the dispersibility of the cellulose nanofibers, and therefore the more easily the cellulose nanofibers are in a state of aggregation, the lower the uniform dispersion of the cellulose nanofibers in the composition, and therefore the higher the standard deviation of the transmittance test of light with a wavelength of 400 nm measured every 2 seconds over 180 seconds. On the other hand, in a composition obtained by dispersing a solid-phase cellulose nanofiber composite in a dispersion medium, the lower the aggregation state of the cellulose nanofibers and the more uniform the dispersion of the cellulose nanofibers is, and therefore the higher the dispersion stability of the cellulose nanofibers is, and therefore the lower the standard deviation of the transmittance test of light with a wavelength of 400 nm measured every 2 seconds over 180 seconds.

[0068] The standard deviation in a transmittance test of light with a wavelength of 400 nm measured every 2 seconds over a period of 180 seconds for a composition obtained by dispersing in a dispersion medium a solid-phase cellulose nanofiber composite containing 10 parts by mass or more and 2,000 parts by mass or less of cellulose derivative per 100 parts by mass of cellulose nanofiber is preferably 0.10 or less, and more preferably 0.05 or less, in order to ensure that the solid-phase cellulose nanofiber composite has excellent dispersibility, and is even more preferably 0.02 or less, and particularly preferably 0.01 or less, in order to ensure that the solid-phase cellulose nanofiber composite has even better dispersibility.

[0069] In addition, the dispersion characteristics of the solid-phase cellulose nanofiber composite can be confirmed by measuring the transmittance of the composition obtained by dispersing the solid-phase cellulose nanofiber composite in a dispersion medium in a transmittance test of light with a wavelength of 400 nm measured every 2 seconds over 180 seconds. In a composition obtained by dispersing a solid-phase cellulose nanofiber composite in a dispersion medium, the lower the dispersibility of the cellulose nanofibers, and therefore the more easily the cellulose nanofibers are in a state of aggregation, the lower the uniform dispersion of the cellulose nanofibers in the composition, and therefore the higher the transmittance in the transmittance test of light with a wavelength of 400 nm measured every 2 seconds over 180 seconds. On the other hand, in a composition obtained by dispersing a solid-phase cellulose nanofiber composite in a dispersion medium, the lower the aggregation state of the cellulose nanofibers and the more uniform the dispersion of the cellulose nanofibers, and therefore the higher the dispersion stability of the cellulose nanofibers, and therefore the lower the transmittance in the transmittance test of light with a wavelength of 400 nm measured every 2 seconds over 180 seconds.

[0070] The above-mentioned "transmittance" refers to an average transmittance calculated from the transmittance at each measurement time, which is measured every 2 seconds for 180 seconds from the start of stirring in a transmittance test for light with a wavelength of 400 nm, measured every 2 seconds for 180 seconds. Also, the "average transmittance" refers to the average of three average transmittance measurements.

[0071] The average transmittance of a composition obtained by dispersing in a dispersion medium a solid-phase cellulose nanofiber composite containing 10 to 2000 parts by mass of a cellulose derivative relative to 100 parts by mass of cellulose nanofibers, measured every 2 seconds over a period of 180 seconds, is preferably 0.50% or less, more preferably 0.40% or less, because the solid-phase cellulose nanofiber composite is reliably provided with excellent dispersibility, and particularly preferably 0.30% or less, because the solid-phase cellulose nanofiber composite is reliably provided with even more excellent dispersibility. The lower limit of the average transmittance is, for example, 0.10%.

[0072] <Method for producing a cellulose nanofiber composition using a solid-phase cellulose nanofiber composite> The method for producing a cellulose nanofiber composition using a solid-phase cellulose nanofiber composite includes a step of obtaining a solid-phase cellulose nanofiber composite by any one of the above-mentioned production methods of the first to third aspects, and a cellulose nanofiber composite adding step of adding the solid-phase cellulose nanofiber composite to a dispersion medium (second dispersion medium) to prepare a cellulose nanofiber composite-containing dispersion. By the above steps, a cellulose nanofiber composition in which the solid-phase cellulose nanofiber composite is dispersed in the dispersion medium can be obtained.

[0073] The second dispersion medium used as a component of the cellulose nanofiber composition functions as a medium for dispersing the cellulose nanofibers, which are components of the solid-phase cellulose nanofiber composite, in the cellulose nanofiber composition, and also functions as a medium for dissolving the cellulose derivative, which is a component of the solid-phase cellulose nanofiber composite. In the cellulose nanofiber composition, the cellulose derivative is dissolved in the dispersion medium, and the cellulose nanofibers are dispersed in the dispersion medium, resulting in a state in which the cellulose derivative is coordinated to the cellulose nanofibers, and the cellulose nanofibers have excellent dispersibility in the cellulose nanofiber composition.

[0074] The second dispersion medium may be an organic solvent. Examples of the organic solvent include alcohols having 1 to 5 carbon atoms, such as tetrahydrofuran, acetone, ethanol, and propanol, cyclohexanol, propylene glycol, cyclohexanone, dioxane, cellosolve, butyl cellosolve, glacial acetic acid, formic acid, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, methylene chloride, chloroform, a mixture of benzene:methanol (1:1 (volume ratio)), a mixture of toluene:ethanol (3:2 (volume ratio)), and a mixture of glycerin:water (3:7 (volume ratio)). The second dispersion medium may be water. Any of these various dispersion media may be used alone, or two or more of them may be used in combination. The second dispersion liquid may be a solution in which organic solvents compatible with water are mixed at any ratio.

[0075] The amount of the second dispersion medium used is not particularly limited, and can be selected depending on the conditions of use of the solid-phase cellulose nanofiber composite.

[0076] <Cellulose nanofiber molded products> After forming the cellulose nanofiber composition obtained as described above into a predetermined shape, the second dispersion medium is removed from the cellulose nanofiber composition by drying or the like to obtain a cellulose nanofiber molded article of a predetermined shape. In the cellulose nanofiber composition obtained as described above, the aggregation state of the cellulose nanofibers is reduced and the cellulose nanofibers are uniformly dispersed, so that the cellulose nanofiber molded article obtained by removing the second dispersion medium from the cellulose nanofiber composition has a uniform distribution of the cellulose nanofibers and a smooth surface. Furthermore, the cellulose nanofiber composition obtained as described above has appropriate fluidity in addition to excellent dispersibility of the cellulose nanofibers, so that a film-like molded article can be easily obtained. EXAMPLES

[0077] Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as they do not depart from the spirit of the present invention.

[0078] <Production of solid-phase cellulose nanofiber composite> Example 1 A solid-phase cellulose nanofiber composite was produced by the first embodiment of the method for producing a solid-phase cellulose nanofiber composite. That is, 0.01 g of powdered hydroxypropyl cellulose (cellulose derivative) (mass ratio of cellulose nanofiber:hydroxypropyl cellulose = 1:0.1) was added to a cellulose nanofiber aqueous dispersion (cellulose nanofiber-containing dispersion medium, 0.1 g of cellulose nanofiber, average fiber length 100 μm, average fiber diameter 30 to 40 nm, Mori Machinery Corporation's "CellFim C-100 (water content about 95 mass%)") and stirred until the hydroxypropyl cellulose was dissolved, to prepare a cellulose nanofiber and cellulose derivative-containing aqueous dispersion. The obtained cellulose nanofiber and cellulose derivative-containing aqueous dispersion was frozen with liquid nitrogen and then dried to prepare a solid-phase cellulose nanofiber composite.

[0079] Example 2 A solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated was produced in the same manner as in Example 1, except that 0.05 g of powdered hydroxypropyl cellulose (cellulose derivative) was added (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:0.5).

[0080] Example 3 A solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated was produced in the same manner as in Example 1, except that 0.1 g of powdered hydroxypropyl cellulose (cellulose derivative) was added (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:1).

[0081] Example 4 A solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated was produced in the same manner as in Example 1, except that 0.3 g of powdered hydroxypropyl cellulose (cellulose derivative) was added (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:3).

[0082] Example 5 A solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated was produced in the same manner as in Example 1, except that 0.5 g of powdered hydroxypropyl cellulose (cellulose derivative) was added (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:5).

[0083] Example 6 A solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated was produced in the same manner as in Example 1, except that 1.0 g of powdered hydroxypropyl cellulose (cellulose derivative) was added (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:10).

[0084] Example 7 A solid-phase cellulose nanofiber composite in which cellulose nanofibers and cellulose derivatives are integrated was produced in the same manner as in Example 1, except that 2.0 g of powdered hydroxypropyl cellulose (cellulose derivative) was added (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:20).

[0085] Comparative Example 1 Solid-phase cellulose nanofibers were produced in the same manner as in Example 1, except that hydroxypropyl cellulose (a cellulose derivative) was not added.

[0086] <Evaluation items> (1) Handling of solid-phase cellulose nanofiber composites 20 ml of tetrahydrofuran was placed in a transparent test container, and while stirring with a stirrer at a rotation speed of 1000 rpm, the solid-phase cellulose nanofiber composites obtained by the manufacturing methods of Examples 1 to 7 and the solid-phase cellulose nanofibers obtained by the manufacturing method of Comparative Example 1 were added to the tetrahydrofuran so that the amount of cellulose nanofibers was 0.1 g. The time required from the addition of the solid-phase cellulose nanofiber composite until the cellulose nanofiber composite was uniformly dispersed was measured and evaluated as follows, with △ or higher being considered as passing. It was visually determined that the cellulose nanofiber composite was uniformly dispersed in tetrahydrofuran. ◎: The cellulose nanofiber composite was uniformly dispersed within 1.0 hour. ○: The cellulose nanofiber composite was uniformly dispersed within more than 1.0 hours and less than 2.0 hours. △: The cellulose nanofiber composite was uniformly dispersed within more than 2.0 hours and within 5.0 hours. ×: The cellulose nanofiber composite is not uniformly dispersed within 5.0 hours.

[0087] As a reference example 1 in which the cellulose nanofibers and the cellulose derivatives were not integrated, a cellulose nanofiber aqueous dispersion (average fiber length 100 μm, average fiber diameter 30-40 nm, "CellFim C-100 (water content approximately 95% by mass)" manufactured by Mori Machinery Corporation) was frozen in liquid nitrogen and then dried to remove water from the cellulose nanofiber aqueous dispersion to obtain solid-phase cellulose nanofibers. 0.05 g of hydroxypropyl cellulose and 0.1 g of the solid-phase cellulose nanofibers obtained as described above (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:0.5) were added to 20 ml of tetrahydrofuran, and the time required for the solid-phase cellulose nanofibers to be uniformly dispersed was measured while stirring at a rotation speed of 1000 rpm using a stirrer.

[0088] In addition, as Reference Example 2 in which the cellulose nanofibers and cellulose derivatives were not integrated, 0.5 g of hydroxypropyl cellulose and 0.1 g of the solid-phase cellulose nanofibers obtained as described above (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:5) were added to 20 ml of tetrahydrofuran, and the time required for the solid-phase cellulose nanofibers to be uniformly dispersed was measured while stirring at a rotation speed of 1000 rpm using a stirrer.

[0089] In addition, as Reference Example 3 in which the cellulose nanofibers and cellulose derivatives were not integrated, 1.0 g of hydroxypropyl cellulose and 0.1 g of the solid-phase cellulose nanofibers obtained as described above (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:10) were added to 20 ml of tetrahydrofuran, and the time required for the solid-phase cellulose nanofibers to be uniformly dispersed was measured while stirring at a rotation speed of 1000 rpm using a stirrer.

[0090] (2) Dispersibility of cellulose nanofiber composite in the solid phase 20 ml of tetrahydrofuran was added to a transparent test container, and then the solid-phase cellulose nanofiber composites obtained by the manufacturing methods of Examples 1 to 7 and the solid-phase cellulose nanofibers obtained by the manufacturing method of Comparative Example 1 were added to tetrahydrofuran so that the amount of cellulose nanofiber was 0.1 g, and the mixture was stirred at a rotation speed of 1000 rpm using a stirrer for 24 hours to prepare dispersion 1. Then, 0.5 ml of dispersion 1 was taken in a transparent test container, and 6 ml of tetrahydrofuran was added to prepare dispersion 2 for dispersibility evaluation, and the dispersion state of the cellulose nanofibers was visually observed and evaluated as follows, with ○ or higher being considered a pass. ◎: The dispersion state of cellulose nanofibers is excellent. ◯: Some aggregation of cellulose nanofibers is observed, but the dispersion is good. ×: Most of the cellulose nanofibers are in an aggregated state, and no dispersibility of the cellulose nanofibers is observed.

[0091] In addition, as Reference Example 4 in which the cellulose nanofibers and the cellulose derivatives are not integrated, a cellulose nanofiber aqueous dispersion (average fiber length 100 μm, average fiber diameter 30-40 nm, "CellFim C-100 (water content about 95 mass%)" manufactured by Mori Machinery Co., Ltd.) was dried to remove water from the cellulose nanofiber aqueous dispersion to obtain solid-phase cellulose nanofibers, and 0.1 g of hydroxypropyl cellulose and 0.1 g of the solid-phase cellulose nanofibers obtained as described above (mass ratio of cellulose nanofibers: hydroxypropyl cellulose = 1:1) were added to 20 ml of tetrahydrofuran, and the mixture was stirred at a rotation speed of 1000 rpm for 24 hours to prepare a cellulose nanofiber composition, which is a dispersion of cellulose nanofibers. 0.5 ml of this cellulose nanofiber composition was taken in a transparent test container, and 6 ml of tetrahydrofuran was added to prepare dispersion 2 for dispersibility evaluation.

[0092] (3) Transmittance of light with a wavelength of 400 nm 20 ml of tetrahydrofuran was added to a transparent test container, and the solid-phase cellulose nanofiber composites obtained by the manufacturing methods of Examples 1 to 7 and the solid-phase cellulose nanofibers obtained by the manufacturing method of Comparative Example 1 were added to tetrahydrofuran so that the amount of cellulose nanofibers was 0.1 g. Dispersion 3 was prepared by stirring for 24 hours at a rotation speed of 1000 rpm using a stirrer with a diameter of 9 mm and a height of 6.5 mm under the condition of 25°C. Light with a wavelength of 400 nm was irradiated to the center of the height direction of dispersion 3 during stirring with an optical path length of 1 cm, and the transmittance of light with a wavelength of 400 nm was measured from the radiant intensity (I0) of the incident light and the radiant intensity (I) of the light transmitted through the cellulose nanofiber composition. The measured value of the transmittance was calculated as the average value (average transmittance) of the transmittances measured every 2 seconds for 180 seconds from the start of stirring. This was repeated three times, and the average value of the average transmittance (n=3) obtained was taken as the transmittance of light with a wavelength of 400 nm.

[0093] (4) Standard deviation of transmittance The standard deviation was calculated for one average transmittance measurement taken every two seconds for 180 seconds, and the standard deviation of the transmittance was calculated from the average value of each standard deviation obtained from the three average transmittance measurements.

[0094] The evaluation results are shown in Table 1 below. FIG. 1 is a photograph showing the dispersibility of the solid-phase cellulose nanofiber composites in Comparative Example 1 (left), Example 1 (center), and Example 2 (right). FIG. 2 is a photograph showing the dispersibility of the solid-phase cellulose nanofiber composites in Comparative Example 1 (left), Example 3 (center), and Example 4 (right). FIG. 3 is a photograph showing the dispersibility of the solid-phase cellulose nanofiber composites in Comparative Example 1 (left), Example 5 (center), and Example 6 (right). FIG. 4 is a photograph showing the dispersibility of the solid-phase cellulose nanofiber composites in Comparative Example 1 (left) and Example 7 (right). FIG. 5 is a photograph showing the dispersibility of the cellulose nanofibers in Reference Example 4.

[0095] [Table 1]

[0096] 1 to 4, the cellulose nanofiber composites in the solid phase in which the cellulose nanofibers and the cellulose derivatives are integrated, obtained by the manufacturing method of Examples 1 to 7, were rated as "◎" for handleability and quickly dispersed uniformly in the dispersion medium, so that they had handleability in the dispersion medium, and were rated as "○" or better, showing excellent dispersibility in the dispersion medium. In particular, in Examples 2 to 7, in which the mass ratio of cellulose nanofibers:hydroxypropyl cellulose was in the range of 1:0.5 to 20, the dispersibility was rated as "◎", and dispersibility in the dispersion medium was further improved.

[0097] Moreover, in the solid-phase cellulose nanofiber composites in which the cellulose nanofibers and the cellulose derivatives are integrated, obtained by the manufacturing method of Examples 1 to 7, the standard deviation of the transmittance test was 0.10 or less, and the uniform dispersion in the dispersion medium was excellent. In particular, in Examples 4 to 7, in which the mass ratio of cellulose nanofiber:hydroxypropyl cellulose was in the range of 1:3 to 20, the standard deviation of the transmittance test was 0.01 or less, and the uniform dispersion in the dispersion medium was further improved. Furthermore, in the solid-phase cellulose nanofiber composites in which the cellulose nanofibers and the cellulose derivatives are integrated, obtained by the manufacturing method of Examples 1 to 7, the transmittance of light with a wavelength of 400 nm was 0.3% or less, and the uniform dispersion in the dispersion medium was excellent.

[0098] Also, from Table 1, the solid-phase cellulose nanofiber composite in which the cellulose nanofiber and the cellulose derivative are integrated (mass ratio of cellulose nanofiber:hydroxypropyl cellulose = 1:0.5) obtained by the manufacturing method of Example 2 has further improved handleability compared to Reference Example 1 in which the cellulose nanofiber and the cellulose derivative are not integrated (mass ratio of cellulose nanofiber:hydroxypropyl cellulose = 1:0.5). Also, the solid-phase cellulose nanofiber composite in which the cellulose nanofiber and the cellulose derivative are integrated (mass ratio of cellulose nanofiber:hydroxypropyl cellulose = 1:5) obtained by the manufacturing method of Example 5 has further improved handleability compared to Reference Example 2 in which the cellulose nanofiber and the cellulose derivative are not integrated (mass ratio of cellulose nanofiber:hydroxypropyl cellulose = 1:5). Furthermore, the solid-phase cellulose nanofiber composite in which the cellulose nanofibers and cellulose derivatives are integrated (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:10) obtained by the manufacturing method of Example 6 had further improved handleability compared to Reference Example 3 in which the cellulose nanofibers and cellulose derivatives were not integrated (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:10).

[0099] Furthermore, as can be seen from Figures 2 and 5, the solid-phase cellulose nanofiber composite obtained by the manufacturing method of Example 3 (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:1) had improved uniform dispersion in the dispersion medium compared to Reference Example 4 (mass ratio of cellulose nanofibers:hydroxypropyl cellulose = 1:1), in which the cellulose nanofibers and cellulose derivatives were not integrated.

[0100] 1 to 4, the solid-phase cellulose nanofibers obtained by the manufacturing method of Comparative Example 1, in which no cellulose derivative was added, could not be dispersed uniformly in the dispersion medium quickly, did not have handleability in the dispersion medium, and did not achieve dispersibility in the dispersion medium. Furthermore, in Comparative Example 1, the standard deviation of the transmittance test was 2.1, and the transmittance of light with a wavelength of 400 nm was 1.536%, and uniform dispersibility in the dispersion medium was not achieved. [Industrial Applicability]

[0101] The method for producing a solid-phase cellulose nanofiber composite of the present invention can obtain a solid-phase cellulose nanofiber composite that has excellent dispersibility of cellulose nanofibers in a dispersion medium and also has excellent handleability in the dispersion medium, allowing the range of application of cellulose nanofibers to be easily expanded, and therefore can be used in a wide range of fields, such as the field of resin compositions that are used as materials for molded articles.

Claims

1. A cellulose nanofiber preparation step of preparing a cellulose nanofiber-containing dispersion medium in which cellulose nanofibers are dispersed; a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding a cellulose derivative to the cellulose nanofiber-containing dispersion medium and dissolving at least a portion of the cellulose derivative in the cellulose nanofiber-containing dispersion medium to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion; Including, A method for producing a solid-phase cellulose nanofiber composite.

2. a cellulose derivative preparation step of preparing a cellulose derivative-containing solution in which at least a part of the cellulose derivative is dissolved in a dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers to the cellulose derivative-containing solution and dispersing the cellulose nanofibers in the cellulose derivative-containing solution to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers with the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion; Including, A method for producing a solid-phase cellulose nanofiber composite.

3. A dispersion medium preparation step of preparing a dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers and a cellulose derivative to the dispersion medium, dispersing the cellulose nanofibers in the dispersion medium and dissolving at least a portion of the cellulose derivative to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion; Including, A method for producing a solid-phase cellulose nanofiber composite.

4. The method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the cellulose derivative is physically adsorbed and integrated with the cellulose nanofiber.

5. The method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the drying treatment is freeze-drying.

6. The method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the cellulose derivative is contained in an amount of 5.0 parts by mass or more and 5,000 parts by mass or less per 100 parts by mass of the cellulose nanofiber.

7. The method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the cellulose derivative is contained in an amount of 10 parts by mass or more and 2,000 parts by mass or less per 100 parts by mass of the cellulose nanofiber.

8. A method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the standard deviation in a transmittance test of light with a wavelength of 400 nm measured every 2 seconds over a period of 180 seconds for the solid-phase cellulose nanofiber composite containing 10 parts by mass or more and 2,000 parts by mass or less of the cellulose derivative per 100 parts by mass of the cellulose nanofiber is 0.10 or less.

9. The method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the cellulose derivative comprises at least one selected from the group consisting of hydroxyalkyl cellulose and alkyl cellulose.

10. The method for producing a solid-phase cellulose nanofiber composite according to any one of claims 1 to 3, wherein the cellulose derivative is a hydroxyalkyl cellulose.

11. The method for producing a solid-phase cellulose nanofiber composite according to claim 10, wherein the hydroxyalkyl cellulose is hydroxypropyl cellulose.

12. A cellulose nanofiber preparation step of preparing a cellulose nanofiber-containing dispersion medium in which cellulose nanofibers are dispersed in a first dispersion medium; a cellulose nanofiber- and cellulose derivative-containing dispersion preparation step of adding a cellulose derivative to the cellulose nanofiber-containing dispersion medium and dissolving at least a portion of the cellulose derivative in the cellulose nanofiber-containing dispersion medium to prepare a cellulose nanofiber- and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion to obtain a solid-phase cellulose nanofiber composite; A cellulose nanofiber composite adding step of adding the cellulose nanofiber composite in a solid phase to a second dispersion medium to prepare a cellulose nanofiber composite-containing dispersion; Including, A method for producing a cellulose nanofiber composition.

13. A cellulose derivative preparation step of preparing a cellulose derivative-containing solution by dissolving at least a part of the cellulose derivative in a first dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers to the cellulose derivative-containing solution and dispersing the cellulose nanofibers in the cellulose derivative-containing solution to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers with the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion to obtain a solid-phase cellulose nanofiber composite; A cellulose nanofiber composite adding step of adding the cellulose nanofiber composite in a solid phase to a second dispersion medium to prepare a cellulose nanofiber composite-containing dispersion; Including, A method for producing a cellulose nanofiber composition.

14. a dispersion medium preparation step of preparing a first dispersion medium; a cellulose nanofiber and cellulose derivative-containing dispersion preparation step of adding cellulose nanofibers and a cellulose derivative to the first dispersion medium, dispersing the cellulose nanofibers in the first dispersion medium and dissolving at least a portion of the cellulose derivative to prepare a cellulose nanofiber and cellulose derivative-containing dispersion that is a dispersion containing the cellulose nanofibers and the cellulose derivative, and integrating the cellulose nanofibers and the cellulose derivative; a drying step of drying the cellulose nanofiber and cellulose derivative-containing dispersion to obtain a solid-phase cellulose nanofiber composite; A cellulose nanofiber composite adding step of adding the cellulose nanofiber composite in a solid phase to a second dispersion medium to prepare a cellulose nanofiber composite-containing dispersion; Including, A method for producing a cellulose nanofiber composition.

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