JP5918496B2 - Gel-like body and method for producing the same - Google Patents

Description

  The present invention relates to a highly elastic and highly heat-resistant gel-like material containing cellulose nanofibers and a liquid organic medium, and a method for producing the same.

  A gel material (gel-like body) is a soft material that has a polymer network that is three-dimensionally cross-linked and swells with water or an organic solvent inside the polymer network. Hydrogels and organic gels are called organogels. Gel materials have been used for daily necessities such as disposable diapers, contact lenses, superabsorbent resins, sustained-release agents, foods, cosmetics, etc., and in recent years, such as haps, drug delivery systems, and regenerative medical base materials. Applications are wide-ranging, such as medical materials, electronic materials such as lithium ion polymer batteries, shock absorbers and vibration-damping / sound-proofing materials. However, gel materials generally have low mechanical strength and are broken by a slight stress, so that they are not suitable for applications that require stable mechanical strength. Examples of the gel material suitable for the application requiring stable mechanical strength include a gel material having high elasticity and high heat resistance.

  Conventionally, polymer materials derived from petroleum, which is a finite resource, have been used extensively, but in recent years, technologies with low environmental impact have come into the spotlight, and in such a technical background, they exist in large quantities naturally. Attention has been focused on materials using cellulose fibers, which are biomass to be produced, and various improved techniques have been proposed in this regard. For example, Patent Document 1 discloses an invention related to cellulose fibers (cellulose nanofibers) having nano-sized fiber diameters, and discloses a dispersion liquid in which cellulose nanofibers are dispersed in water or a hydrophilic organic solvent. . Patent Document 1 describes that the cellulose nanofiber described in Patent Document 1 may be used as a gelling agent. However, a specific method for producing a gel material and its mechanical strength are described. Not.

  Patent Document 2 discloses a resin composition containing cellulose nanofibers and a resin as a resin composition that can form a dry film having high strength and can be used as an adhesive, paint, wax, or a raw material for producing them. Things are disclosed. However, Patent Document 2 does not disclose that an organic medium can be gelled using cellulose nanofibers.

  Patent Document 3 discloses a gel composition containing cellulose nanofibers and water. Patent Document 4 discloses an organogel comprising an organic solvent in a network polymer as an organogel that exhibits a behavior in which a frictional force decreases as the load increases in a certain load region.

  Patent Documents 1 and 3 refer to a gel-like body using cellulose nanofibers. Among these, the gel composition described in Patent Document 3 is a hydrogel containing a large amount of water, and even if the technique described in Patent Document 3 is used, cellulose nanofibers and a liquid organic medium are sufficiently obtained. It is difficult to obtain a gel containing. Further, the gel composition described in Patent Document 3 contains a large amount of water, and the electrostatic repulsion force (that is, the dissociation of carboxyl groups contained in the cellulose fiber described later), which is the main cause of the dispersibility of the cellulose nanofibers. Therefore, it is difficult to say that it is suitable for applications requiring stable mechanical strength.

  Moreover, since the gel-like composition of patent documents 1 and 3 contains many water as a preferable composition, it is difficult to maintain a fixed shape and physical property in air | atmosphere by the volatilization of the water | moisture content from a gel surface. Due to the above, it is difficult to say that practical problems have been improved due to heat resistance problems such as difficulty in use at a temperature above which water can exist as a liquid.

  In addition, as a gel material, a physical gel obtained by using various polymers (carboxymethylcellulose, sodium alginate, sodium polyacrylate, etc.) used as a thickener as a gelling agent, and a polymer in a solvent Chemical gels obtained by gelling the solvent by polymerizing or cross-linking are known, and physical gels are solated at high temperatures because the cross-linking points between polymers are not fixed. There is a problem in heat resistance, such as easy separation of solvent and polymer, and chemical gel is difficult to obtain reaction control and uniform gel during its production, and it becomes gel with low mechanical strength There is a fear.

  In addition, the organogel described in Patent Document 4 is obtained by gelling an organic solvent such as silicone oil mainly with a network polymer, and a polymer used as a gelling agent has been conventionally used such as polysiloxane. This polymer has problems in heat resistance and mechanical strength.

JP 2008-1728 A JP 2009-197122 A JP 2010-37348 A International Publication No. 2004/015012

  Therefore, the subject of this invention is providing the gel-like body which has high elasticity and high heat resistance, and its manufacturing method.

  As a result of various studies on novel gel-like bodies using cellulose nanofibers, the present inventors have found that a specific cellulose nanofiber obtained by the method described later and a liquid organic medium having a lower vapor pressure at 20 ° C. than water. It was found that the contained gel-like body has high elasticity and high heat resistance.

  The present invention has been made based on the above knowledge, and is a gel-like body containing cellulose nanofibers and a liquid organic medium, and the organic medium has a vapor pressure at 20 ° C. lower than that of water and a water content of 50. The problem is solved by providing a gel-like body having a mass% or less.

  The present invention is also a method for producing the gel-like body, comprising: mixing a cellulose nanofiber and an organic medium in a dispersion medium to obtain a gel precursor; and removing the dispersion medium from the gel precursor. The above-mentioned problems are solved by providing a method for producing a gel-like body.

  The gel-like body of the present invention is a gel-like body having high elasticity and high heat resistance, and as a gel material requiring mechanical strength and heat resistance, such as chemical, medical, electronic / electrical, architectural, pharmaceutical, agricultural, etc. Useful in the field. Moreover, the manufacturing method of the gel-like body of this invention can provide the gel-like body of this invention which has such a characteristic stably.

  The gel-like body of the present invention contains cellulose nanofibers and a liquid organic medium, and the organic medium has a vapor pressure at 20 ° C. lower than that of water and a water content of 50% by mass or less. The gel-like body of the present invention has high elasticity, high heat resistance, high mechanical strength, is flexible with respect to tension, bending and twisting, and has high resilience after deformation.

  The gel-like body of the present invention preferably has high heat resistance capable of maintaining certain gel physical properties in a wide temperature range. From this viewpoint, it is preferable that the temperature dependence of the elastic modulus is small. More specifically, the change rate of the elastic modulus (hereinafter also referred to as the temperature dependency change rate of the elastic modulus) in the temperature range of 25 to 110 ° C. is 0.5 to 5, particularly 0.7 to 4, particularly 0. It is preferably 9 to 1.5. The temperature-dependent change rate of the elastic modulus represents a change in the storage elastic modulus in the dynamic viscoelasticity of the gel-like body measured by the method described later. It means that there is little change, that is, heat resistance is high.

  Further, the gel-like body of the present invention preferably has high shape stability capable of maintaining the gel state over a long period of time, and from this viewpoint, it is preferable that the frequency dependence of the elastic modulus is small. . More specifically, the gel-like body of the present invention has an elastic modulus change rate (hereinafter also referred to as an elastic modulus frequency-dependent change rate) of 0.1 to 20, in a frequency range of 0.01 to 10 Hz. It is particularly preferably 0.5 to 10, particularly 0.8 to 5. The frequency-dependent change rate of the elastic modulus represents a change in the storage elastic modulus in the dynamic viscoelasticity of the gel-like body measured by the method described later. It means less change. The gel-like body of the present invention in which the frequency-dependent change rate of the elastic modulus is in such a range is difficult to be sol even when an external force is applied, and can maintain a highly elastic gel state for a long period of time.

  Further, the gel-like body of the present invention preferably has a gel state, and from this viewpoint, it is preferable that the loss tangent (tan δ) is small. The loss tangent is the tan value of the phase difference δ between the measured sine strain wave and the detected sine stress wave in the dynamic viscoelasticity of the gel-like body measured by the method described later. The physical meaning is the viscosity response / Elastic response ratio. The value of loss tangent is defined as loss elastic modulus / storage elastic modulus. If the value (tan δ value) is larger than 1, the viscous response is dominant, and if it is smaller than 1, the elastic response is dominant. About a gel, it means that it is a solid gel, so that a tan-delta value is small. More specifically, the gel-like body of the present invention preferably has a loss tangent of less than 0.6, particularly less than 0.1, especially less than 0.07. In general, the gel has a loss tangent of less than 1, and it is considered that the solvent is immobilized by a polymer (cellulose nanofiber in the present invention), but the loss is caused by an external force load (large strain or frequency range). Some have a tangent of 1 or more, that is, a fluidized sol state. The gel-like body of the present invention having a loss tangent (tan δ) within such a range has high elasticity, high heat resistance, high mechanical strength, flexibility against tension, bending, and twisting, and high resilience after deformation.

  From the same viewpoint, the gel-like body of the present invention preferably has a small loss tangent temperature change rate. More specifically, the F / E is defined as 0.1 to 5, particularly 0.4 to 2, especially 0.4, as defined by the loss tangent value (E) at 25 ° C. and the loss tangent value (F) at 110 ° C. It is preferable that it is 5-1.5. The loss tangent values E and F are measured by the following measurement method (ii). The gel-like body of the present invention in which the loss tangent change rate falls within such a range can maintain a highly elastic gel state regardless of temperature changes.

  The storage elastic modulus, loss elastic modulus and loss tangent are measured using, for example, a rotary rheometer (apparatus: MCR300, manufactured by PHYSICA). The measurement cell was a parallel plate with a diameter of 25 mm, and the sample thickness was 0.5 to 1 mm. In the measurement of the gel sample, a measurement control mode in which a force of about 1 N is applied to the sample through the cell surface in order to cope with the suppression of the slip between the measurement cell surface and the sample and the interface and the change of the sample thickness due to thermal expansion. Selected and used. Since the physical properties of the gel-like material of the present invention are unlikely to change due to evaporation of volatile components, the rheological measurement is performed in consideration of the characteristics of the gel-like material, and the rheological measurement is performed by controlling the temperature of dry nitrogen gas (liquid nitrogen is vaporized). Was carried out while flowing through the measurement cell section. In order to estimate the degree of evaporation of volatile components from the sample, the sample is mounted in a measurement cell that has been controlled to 25 ° C in advance, and the frequency-dependent change rate (frequency dependency) of the elastic modulus is first measured as follows. Measurement was carried out according to method (i), and then the temperature-dependent change rate (temperature dependence) of the elastic modulus was measured according to the following measurement method (ii). As the loss tangent, the measured value at 25 ° C. in the following measuring method (ii) was used.

Measurement method (i): Frequency-dependent change rate (frequency dependency) of elastic modulus is a storage elastic modulus at 0.01 Hz measured when the temperature is changed from 0.01 Hz to 100 Hz at a linear strain of 25 ° C. It is defined by D / C from (C) and the storage elastic modulus (D) at 10 Hz.
Measurement method (ii): The temperature-dependent change rate (temperature dependency) of the elastic modulus is measured when the temperature is increased from 25 ° C. to 110 ° C. at 2.5 ° C./min at a linear strain of 2 Hz. It is defined as B / A from the storage elastic modulus (A) at 100 ° C. and the storage elastic modulus (B) at 110 ° C. Note that the rate of change of the elastic modulus of the gel-like body that could not be measured up to 110 ° C. under the same conditions was greatly reduced in the temperature rising process.

The gel-like body of the present invention is preferably a highly elastic gel, and from this viewpoint, it is preferable that the value of the storage elastic modulus is large. More specifically, the storage elastic modulus at 25 ° C. measured by the measurement method (ii) is preferably 10 ² Pa or more, particularly 10 ³ Pa or more, and particularly preferably 10 ⁴ Pa or more. The gel-like body of the present invention having a storage elastic modulus in such a range can be used as a high-strength gel.

  In addition, the gel-like body of the present invention preferably has high heat resistance, in which the organic medium to be contained is not easily eluted by heating, and more specifically, the organic medium is measured by the following measurement method. The amount is preferably 50% by mass or less, particularly preferably 20% by mass or less, and particularly preferably 5% or less.

<Measurement method of elution amount of organic medium>
The gel-like body to be measured is heated by being left for 30 minutes in a thermostatic chamber set at a bath temperature of 105 ° C. This operation can be carried out, for example, by storing about 2 g of a gel-like body in a glass petri dish, putting the glass petri dish together with the glass petri dish in a constant temperature bath, and leaving it for 30 minutes. After 30 minutes, the glass petri dish is removed from the thermostat and left at room temperature until the temperature of the gel-like body reaches room temperature. Thereafter, the eluate (organic medium or the like) on the surface of the gel-like body is removed, the mass of the gel-like body is measured, and the measured value (mass B) is recorded. The removal of the eluate can be performed, for example, by allowing the paper to absorb the eluate on the surface of the gel-like body by sandwiching the gel-like body with paper (for example, Kimwipe made by Nippon Paper Crecia). Then, the elution amount of the organic medium is calculated from the mass B and the previously measured mass of the gel-like body before heating (mass A, about 2 g in the specific example) by the following formula.
Elution amount of organic medium (%) = {(AB) / A} × 100

  Further, the gel-like body of the present invention preferably has flexibility in addition to having high elasticity and high heat resistance. From such a viewpoint, it conforms to the standard of ASTM D 2240. The hardness measured by the method is preferably 20 degrees or less, particularly 0.1 to 15 degrees, particularly 1 to 10 degrees. The hardness is measured using a generally used rubber or plastic hardness meter (for example, a rubber hardness meter GS-709 A type, manufactured by Teclock Corporation).

  The gel-like body of the present invention contains cellulose nanofibers and a liquid organic medium as essential components. In the present invention, it is sufficient that these two components are contained in the gel-like body, and the containing form is not particularly limited, and an appropriate containing form is selected as long as the gel-like body can have predetermined physical properties. Can do. Each component will be described in detail below.

  The cellulose nanofiber used in the present invention functions as a gelling agent that gels a liquid organic medium, and exhibits various properties of the gel-like material of the present invention described above, particularly high elasticity and high heat resistance. Is an ingredient that plays an important role. The gel-like body of the present invention has a structure in which a liquid organic medium is held in a large number of minute spaces formed by a network of cellulose nanofibers, and is highly elastic and heat-resistant due to such a structure. It is thought that it is a highly gel-like body.

  The content of cellulose nanofibers in the gel-like body of the present invention can be arbitrarily set within a range that can have predetermined properties, but imparts the properties of high elasticity and high heat resistance to the gel-like body. In addition, from the viewpoint of achieving both flexibility and transparency of the gel-like body, 0.1 to 90% by mass is preferable, particularly 1 to 50% by mass, and particularly 2 to 20% by mass is preferable. In particular, by using cellulose nanofibers (cellulose nanofibers having an average fiber diameter and a carboxyl group content in a specific range) described below, even if the cellulose nanofiber content is as small as 0.1% by mass, A highly elastic and heat-resistant gel is obtained. The transparency of the gel-like body is mainly derived from the transparency of the liquid organic medium itself, and cellulose nanofibers have a high organic medium when a highly transparent liquid organic medium is used. Realizes high elasticity and high heat resistance without losing transparency. From such a viewpoint, it is preferable that the transmittance of the gel-like body is 70 to 100%, particularly 80 to 100%, particularly 90 to 100%. The transmittance can be evaluated by measuring the transmittance at a wavelength of 660 nm using an ultraviolet-visible spectral hardness meter (for example, an ultraviolet-visible spectral hardness meter U-3310, manufactured by Shimadzu Corporation). When a liquid organic medium having a low transmittance is used, the transmittance of the gel-like body may be out of such a range.

  The cellulose nanofibers used in the present invention preferably have an average fiber diameter of 200 nm or less, more preferably 50 nm or less, and particularly preferably 10 to 1 nm. The average fiber diameter is measured by the following measuring method.

<Measurement method of average fiber diameter>
Water is added to 0.0001% by mass of cellulose fibers at a solid content concentration to prepare a dispersion, and the dispersion is dropped onto mica (mica) and dried, and an atomic force microscope ( NanoNaVi IIe, SPA400, manufactured by SII Nano Technology, Inc., and the probe uses SI-DF40Al manufactured by the same company), and the fiber height of the cellulose fiber in the observed sample is measured. In a microscopic image in which cellulose fibers can be confirmed, five or more cellulose fibers are extracted, and the average fiber diameter is calculated from the fiber heights. In general, the smallest unit of cellulose nanofibers prepared from higher plants is a 36 × 36 molecular chain packed in a substantially square shape. Therefore, the height that can be analyzed by the atomic force microscope image is regarded as the fiber diameter. be able to.

  The cellulose nanofiber used in the present invention has an average aspect ratio (fiber length / fiber diameter) of preferably 10 to 1000, more preferably 10 to 500, and particularly preferably 100 to 350. By using cellulose nanofibers having an average aspect ratio in such a range as a material for the gel-like body of the present invention, the gel-like body containing the cellulose nanofibers obtained by the method described later and a liquid organic medium is small. Even with the content of the cellulose nanofiber, high elasticity and heat resistance are exhibited. The average aspect ratio is measured by the following measurement method.

<Measuring method of average aspect ratio>
The average aspect ratio is calculated from the viscosity of a dispersion liquid prepared by adding water to cellulose fibers (mass concentration of cellulose fibers: 0.005 to 0.04 mass%). The viscosity of the dispersion is measured at 20 ° C. using a rheometer (MCR, DG42 (double cylinder), manufactured by PHYSICA). From the relationship between the mass concentration of the cellulose fibers in the dispersion and the specific viscosity of the dispersion with respect to water, the aspect ratio of the cellulose fibers is calculated by the following formula (1) to obtain the average aspect ratio. The following formula (1) is obtained from The Theory of Polymer Dynamics, M .; DOI and D.D. F. EDWARDS, CLARENDON PRESS · OXFORD, 1986 , P312 viscosity rigid-rod molecules according to equation (8.138), the relationship wherein the ^{Lb 2 × ρ = M / N} A, L is the fiber length, b is fiber width (The cross section of the cellulose fiber is a square), ρ is the concentration of the cellulose fiber (kg / m ³ ), M is the molecular weight, and N _A is the Avogadro number. In the viscosity formula (8.138), rigid rod-like molecules = cellulose fibers. In the following formula (1), η _SP is the specific viscosity, π is the circumference ratio, ln is the natural logarithm, P is the aspect ratio (L / b), γ = 0.8, ρ _S is the density of the dispersion medium ( kg / m ³ ), ρ ₀ represents the density of cellulose crystals (kg / m ³ ), and C represents the mass concentration of cellulose (C = ρ / ρ _S ).

  The cellulose nanofiber used in the present invention has a carboxyl group from the viewpoint of the cellulose nanofiber stably having a fine fiber diameter of an average fiber diameter of 200 nm or less and various physical properties of the gel-like material of the present invention. The content (carboxyl group content of cellulose constituting the cellulose nanofiber) is preferably 0.1 to 3 mmol / g, particularly 0.4 to 1.8 mmol / g, especially 0.6 to 1.5 mmol. / G is preferable. The carboxyl group content is measured by the following measuring method.

<Measurement method of carboxyl group content>
Take a cellulose fiber with a dry mass of 0.5 g in a 100 ml beaker, add ion-exchanged water to make a total of 55 ml, add 5 ml of 0.01 M sodium chloride aqueous solution to prepare a dispersion, and until the cellulose fibers are sufficiently dispersed The dispersion is stirred. 0.1M hydrochloric acid is added to this dispersion to adjust the pH to 2.5-3, and 0.05M sodium hydroxide aqueous solution is waited for using an automatic titrator (AUT-50, manufactured by Toa DKK Co., Ltd.). The solution is dropped into the dispersion under the condition of 60 seconds, and the conductivity and pH values are measured every minute, and the measurement is continued until the pH is about 11, thereby obtaining an conductivity curve. From this conductivity curve, the sodium hydroxide titration amount is obtained, and the carboxyl group content of the cellulose fiber is calculated by the following formula.
Carboxyl group content (mmol / g) = sodium hydroxide titration × sodium hydroxide aqueous solution concentration (0.05 M) / mass of cellulose fiber (0.5 g)

  In particular, the carboxyl group content is an important factor in stably obtaining cellulose nanofibers having a fine fiber diameter of preferably an average fiber diameter of preferably 200 nm or less. That is, in the process of biosynthesis of natural cellulose, usually, nanofibers called microfibrils are first formed, and these are bundled to form a higher-order solid structure. Cellulose nanofibers used in the present invention As will be described later, this is obtained by using this in principle, in order to weaken the hydrogen bond between the surfaces, which is the driving force of the strong cohesive force between microfibrils in the naturally-derived cellulose solid raw material. , Part of which is obtained by oxidation and conversion to a carboxyl group. Therefore, the larger the total amount of carboxyl groups present in the cellulose (carboxyl group content), the smaller the fiber diameter, the more stable it can exist, and the electrical repulsive force is generated in water. As a result, the tendency of the microfibrils to break apart without maintaining aggregation is increased, and the dispersion stability of the nanofibers is further increased. When the carboxyl group content is less than 0.1 mmol / g, it is difficult to obtain nanofibers having a fine fiber diameter of 200 nm or less, and dispersion stability in a polar solvent such as water may be reduced. is there.

  However, the cellulose nanofiber used in the present invention does not require the carboxyl group content to be in the range of 0.1 to 3 mmol / g. For example, the carboxyl group content is 0.1 to 3 mmol / g for the purpose of improving the affinity between cellulose nanofibers and other gel-like constituents (liquid organic medium, dispersion medium, etc.). Cellulose nanofibers may be chemically modified, and a part of carboxyl groups present in the cellulose may be derivatized to other modified groups. The modified cellulose nanofiber obtained by such chemical modification treatment may include those having a carboxyl group content outside the range of 0.1 to 3 mmol / g. Even fibers are preferably used in the present invention.

  Examples of chemical modification treatment for the carboxyl group of cellulose nanofiber include alkyl groups (methyl group, ethyl group, propyl group, 2-propyl group, butyl group, 2-butyl group, tert-butyl group, pentyl group, hexyl group). , Heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, myristyl group, palmityl group, stearyl group, and the like). In addition, a cellulose nanofiber derivative may be obtained by chemically modifying the hydroxyl group on the surface of the cellulose nanofiber. Examples of chemical modification treatment for the hydroxyl group of cellulose nanofiber include acyl groups (acetyl group, acryloyl group, methacryloyl group, propionyl group, propioyl group, butyryl group, 2-butyryl group, pentanoyl group, hexanoyl group, heptanoyl group, octanoyl group) Group, nonanoyl group, decanoyl group, undecanoyl group, dodecanoyl group, myristoyl group, palmitoyl group, stearoyl group, pivaloyl group, benzoyl group, naphthoyl group, nicotinoyl group, isonicotinoyl group, furoyl group, cinnamoyl group), isocyanate group (2 -Methacryloyloxyethyl isocyanoyl group), alkyl group (methyl group, ethyl group, propyl group, 2-propyl group, butyl group, 2-butyl group, tert-butyl group, pentyl group, hexyl group, Ptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, myristyl group, palmityl group, stearyl group, etc.), oxirane group, oxetane group, thiirane group, thietane group, etc. Can be mentioned. Cellulose nanofiber derivatives obtained by such various chemical modification treatments are modified in the organic medium and dispersion medium used for the gel-like body due to the change in hydrophilicity / hydrophobicity of unmodified cellulose nanofibers. May be arbitrarily selected as necessary.

  The cellulose nanofiber used in the present invention can be produced, for example, by the following method. That is, the cellulose nanofiber used in the present invention can be obtained by a production method including an oxidation reaction step in which a natural cellulose fiber is oxidized to obtain a reactant fiber, and a refinement step in which the reactant fiber is refined. Each step will be described in detail below.

  In the oxidation reaction step, first, a slurry in which natural cellulose fibers are dispersed in water is prepared. The slurry is obtained by adding about 10 to 1000 times (mass basis) of water to the natural cellulose fiber (absolute dry basis) as a raw material, and processing with a mixer or the like. Examples of natural cellulose fibers include wood pulp such as softwood pulp and hardwood pulp; cotton pulp such as cotton linter and cotton lint; non-wood pulp such as straw pulp and bagasse pulp; bacterial cellulose and the like. These 1 type can be used individually or in combination of 2 or more types. The natural cellulose fiber may be subjected to a treatment for increasing the surface area such as beating.

  Next, a natural fiber is oxidized in water using an N-oxyl compound as an oxidation catalyst to obtain a reactant fiber. Examples of N-oxyl compounds that can be used as an oxidation catalyst for cellulose include 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (hereinafter also referred to as TEMPO), 4-acetamide-TEMPO, 4-carboxy-TEMPO, 4-phosphonooxy-TEMPO, etc. can be used. A catalytic amount is sufficient for the addition of these N-oxyl compounds, and is usually in a range of 0.1 to 10% by mass with respect to natural cellulose fibers (absolute dry basis) used as a raw material.

  In the oxidation treatment of the natural cellulose fiber, cooxidation with an oxidizing agent (for example, hypohalous acid or a salt thereof, hypohalous acid or a salt thereof, perhalogenic acid or a salt thereof, hydrogen peroxide, a perorganic acid, etc.) An agent (for example, an alkali metal bromide such as sodium bromide) is used in combination. As the oxidizing agent, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are particularly preferable. The amount of the oxidizing agent used is usually in the range of about 1 to 100% by mass with respect to the natural cellulose fiber (absolute dry standard) used as a raw material. Moreover, the usage-amount of a co-oxidant is the range used as about 1-30 mass% normally with respect to the natural cellulose fiber (absolute dry reference | standard) used as a raw material.

  Moreover, in the oxidation treatment of the natural cellulose fiber, the pH of the reaction solution (the slurry) is preferably maintained in the range of 9 to 12 from the viewpoint of allowing the oxidation reaction to proceed efficiently. The temperature of the oxidation treatment (the temperature of the slurry) is arbitrary at 1 to 50 ° C., but the reaction is possible at room temperature, and no temperature control is required. The reaction time is preferably 1 to 240 minutes.

  After the oxidation reaction step, a purification step is performed before the miniaturization step to remove impurities other than reactant fibers and water contained in the slurry, such as unreacted oxidant and various by-products. At this stage, the reaction product fibers are usually not dispersed evenly to the nanofiber unit. Therefore, in the purification process, for example, a purification method in which water washing and filtration are repeated can be performed, and the purification apparatus used in that case is not particularly limited. The purified oxidized cellulose fiber (or cellulose nanofiber intermediate) thus obtained is usually sent to the next step (miniaturization step) in the state of being impregnated with an appropriate amount of water, but if necessary, dried. A treated fiber or powder may be used.

  In the refinement step, the reaction product fibers that have undergone the purification step are dispersed in a solvent such as water, and the refinement process is performed. By passing through this refinement | miniaturization process, the cellulose nanofiber which has an average fiber diameter and an average aspect ratio in the said range, respectively is obtained.

  In the above-mentioned micronization treatment, the solvent as the dispersion medium is usually preferably water, but water-soluble organic solvents (alcohols, ethers, ketones, etc.) may be used in addition to water depending on the purpose. These mixtures can also be suitably used. Examples of the disperser used in the miniaturization process include a disaggregator, a beater, a low pressure homogenizer, a high pressure homogenizer, a grinder, a cutter mill, a ball mill, a jet mill, a short shaft extruder, a twin screw extruder, and an ultrasonic stirrer. A home juicer mixer or the like can be used. The solid content concentration of the oxidized cellulose fiber in the refining treatment is preferably 50% by mass or less. When the solid content concentration exceeds 50% by mass, it is not preferable because extremely high energy is required for dispersion.

  As the form of the cellulose nanofibers obtained after the above-mentioned micronization step, the solids concentration is adjusted as required (sustainedly colorless transparent or opaque liquid), or the dried powder (however, cellulose It is also a powder form in which nanofibers are aggregated and does not mean cellulose particles). In the case of a suspension, only water may be used as a dispersion medium, and a mixed solvent of water and other organic solvents (for example, alcohols such as ethanol), surfactants, acids, bases, etc. May be used.

  By such oxidation treatment and refinement treatment of natural cellulose fibers, the hydroxyl group at the C6 position of the cellulose constituent unit is selectively oxidized to a carboxyl group via an aldehyde group, and preferably the average fiber diameter is 200 nm or less. Finely divided highly crystalline cellulose fibers can be obtained. This highly crystalline cellulose fiber has a cellulose I-type crystal structure. This means that the cellulose nanofiber used in the present invention is a fiber obtained by surface-oxidizing and refining a naturally-derived cellulose solid raw material having an I-type crystal structure. In other words, natural cellulose fibers have a high-order solid structure in which fine fibers called microfibrils produced in the process of biosynthesis are bundled to form a high-order solid structure. The cellulose nanofibers can be obtained by weakening the hydrogen bond) by introducing the aldehyde group or carboxyl group by the oxidation treatment, and further through the refinement treatment. Then, by adjusting the conditions of the oxidation treatment, the carboxyl group content is increased or decreased within a predetermined range, the polarity is changed, or the electrostatic repulsion of the carboxyl group or the refinement treatment is performed on the cellulose fiber. The average fiber diameter, average fiber length, average aspect ratio, etc. can be controlled.

  The aqueous dispersion obtained by diluting the cellulose nanofibers thus obtained to a solid content of 1% by mass preferably has a light transmittance of 40% or more, more preferably from the viewpoint of obtaining a highly elastic gel. 60% or more, more preferably 80% or more. The transmittance of the cellulose nanofiber aqueous dispersion can be measured by the same method as the method for measuring the transmittance of the gel-like material described above.

  The gel-like body of the present invention contains a liquid organic medium as an essential component in addition to cellulose nanofibers. It can be said that the gel-like body of the present invention is a physical gel using the cellulose nanofiber as a gelling agent. Although the gel-like body of the present invention is a physical gel, it does not have the problem of heat resistance unlike the conventional physical gel, and has the features of high elasticity and high heat resistance as described above. .

  The liquid organic medium used in the present invention is characterized by having a vapor pressure at 20 ° C. lower than that of water, and is an organic liquid in the temperature range (usually 1 to 150 ° C.) in which the gel-like material of the present invention is used. Any substance can be used without particular limitation, and may be a hydrophilic organic medium or a hydrophobic organic medium. In particular, in addition to imparting the properties of high elasticity and high heat resistance to the gel-like material of the present invention, the liquid organic medium is a hydrophilic organic medium from the viewpoint of achieving both flexibility and transparency of the gel-like material. Is preferred.

  In the gel-like body of the present invention, the liquid organic medium preferably has a vapor pressure at 20 ° C. lower than that of water. When the vapor pressure (mmHg, 20 ° C.) of a liquid organic medium at 20 ° C. is P1, and the vapor pressure of water at 20 ° C. (17.5 mmHg, 20 ° C.) is Pw, P1 / Pw is preferably 0.001. It is -0.9, More preferably, it is 0.001-0.5. By having P1 / Pw within such a range, a highly heat-resistant gel-like body that can maintain its shape and physical properties even at high temperatures (above the boiling point of water) can be obtained.

  The liquid organic medium used in the present invention may be hydrophilic or hydrophobic. Examples of the liquid hydrophilic organic medium include alcohols such as glycerin, 2-butanol, 2-methyl-1-propanol glycerin, 1-pentanol, ethylene glycol, propylene glycol, and polyethylene glycol, ethylene carbonate, propylene carbonate, Esters such as methyl diglycol succinate, amides such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, polyoxides such as polyethylene glycol and polymethylene oxide, and ionic liquids such as 1-ethyl-3-methylimidazolium ethyl sulfate , Dimethyl sulfoxide, acetonitrile, propionitrile and the like. Examples of liquid hydrophobic organic media include silicone oils such as polydimethylsiloxane, higher fatty acids such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, oleic acid, stearin, octyl alcohol, decyl alcohol, and lauryl. Alcohols, higher alcohols such as myristyl alcohol and stearic alcohol, hydrocarbon oils such as liquid paraffin, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin Fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, alkylamine, quaternary ammonia Surfactants such as salt, alkyl sulfate ester, polyoxyethylene alkyl ether sulfate, alkylbenzene sulfonate, ester oil, light oil, kerosene, crude oil, salad oil, soybean oil, castor oil, triglyceride, polyisoprene, fluorine Examples include modified oils. In the present invention, one of these liquid organic media can be used alone or in combination of two or more.

  Liquid organic media particularly preferably used in the present invention are glycerin, glycerin derivatives (for example, glyceryl monostearate, glyceryl monooleate, glyceryl tri-2-ethylhexanoate, glyceryl monocaprylate, glyceryl tricaprylate and tri (capryl). Glycerin fatty acid esters such as acid / capric acid glycerin and polyglycerin), ethylene glycol, propylene glycol, polyethylene glycol (PEG), ethylene carbonate (EC), propylene carbonate (PC), dimethyl sulfoxide (DMSO) Succinic acid methyltriglycol diester, ionic liquid (above, liquid hydrophilic organic medium), silicone oil, liquid paraffin (above, liquid hydrophobic organic medium)By using one or more of these as the liquid organic medium, the physical properties of the gel-like body of the present invention are more preferable.

  The content of the liquid organic medium in the gel-like body of the present invention can be arbitrarily set as long as it can have a predetermined property, but imparts the properties of high elasticity and high heat resistance to the gel-like body. In addition, from the viewpoint of achieving both flexibility and transparency of the gel-like body, the content is preferably 10 to 99.9% by mass, particularly preferably 50 to 98% by mass, and particularly preferably 70 to 97% by mass. The content of the liquid organic medium uses the difference in the thermal decomposition temperature of the components in the gel-like body by, for example, thermogravimetric analysis in addition to the method of calculating from the charged amount of each component in the gel-like body manufacturing method described later And a method of calculating from a change in weight using a difference in solubility and volatility in various solvents.

  The gel-like body of the present invention may contain water within a range that does not adversely affect physical properties, but the water content is 50% by mass or less, preferably 25% by mass or less, more preferably 15% by mass or less. It is. In general, gels containing a large amount of water whose water content exceeds 50% by mass have a large change in shape and physical properties due to volatilization of water, so it is difficult to maintain a certain shape and physical properties in the atmosphere. In the invention, from such a viewpoint, the moisture content of the gel-like body is set to 50% by mass or less. In addition, the cellulose nanofiber, which is an essential component of the gel-like material of the present invention, is caused by its electrostatic repulsion (that is, a negative charge due to dissociation of carboxyl groups), and is particularly a sol-state dispersion having high fluidity in water. However, such a sol state can be effectively prevented by setting the water content of the gel-like body to 50% by mass or less. Adjusting the moisture content of the gel-like body within the above range is effective in obtaining a gel-like body having high elasticity and high heat resistance.

  When the gel-like material of the present invention further contains a dispersion medium in addition to the cellulose nanofibers and the liquid organic medium, the vapor pressure of the liquid organic medium at 20 ° C. is the vapor pressure of the dispersion medium at 20 ° C. The pressure is preferably smaller than the pressure. The dispersion medium is a liquid other than the liquid organic medium described above, and may be any liquid that can substantially disperse or dissolve the cellulose nanofiber and the organic medium, and includes water. In particular, when the gel-like material of the present invention is produced by a production method (a production method having a dispersion medium volatilization step) to be described later, the liquid organic medium is a vapor at 20 ° C. than the dispersion medium used in combination. A thing with a small pressure is preferable. When the vapor pressure (mmHg, 20 ° C) at 20 ° C of the liquid organic medium is P1, and the vapor pressure (mmHg, 20 ° C) at 20 ° C of the dispersion medium is P2, P1 / P2 is preferably 0.001 to 0.001. 0.9, more preferably 0.001 to 0.5. For example, when the dispersion medium is water, the vapor pressure is lower than water at 20 ° C., and the liquid organic medium preferably used in the present invention includes glycerin, glycerin derivatives, ethylene glycol, propylene glycol, polyethylene glycol (PEG), Examples thereof include ethylene carbonate (EC), propylene carbonate (PC), dimethyl sulfoxide (DMSO), succinic acid methyl triglycol diester, ionic liquid, silicone oil, and liquid paraffin.

  As described above, the gel-like body of the present invention may contain only cellulose nanofibers and a liquid organic medium, but may further contain a dispersion medium in addition to these. As the dispersion medium, water is usually used. However, a dispersion medium other than water, such as a water-insoluble organic solvent, a water-soluble organic solvent, or the like, may be used as long as it does not adversely affect the production of the gel-like body and the gel properties. A mixed medium of water and water can be used. The specific dispersion medium to be used may be appropriately determined according to the solubility and dispersibility of the cellulose nanofiber and the liquid organic medium. Moreover, when manufacturing the gel-like body of the present invention by a manufacturing method (a manufacturing method having a dispersion medium removing step) described later, the gel-like body of the present invention is obtained by volatilizing the dispersion medium. The dispersion medium preferably has a higher vapor pressure at 20 ° C. than the liquid organic medium used in combination. The relationship between the vapor pressures at 20 ° C. of both is as described above.

  Examples of the dispersion medium other than water used in the present invention include water-insoluble organic solvents such as toluene, chloroform, ethyl acetate, hexane, benzene, methylene chloride, diethyl ether, xylene, phenol, and pyridine; ethanol, methanol, isopropanol, Water-soluble organic solvents such as t-butyl alcohol, acetone, N-methyl-2-pyrrolidone, tetrahydrofuran, and acetonitrile can be used, and one of these can be used alone or two or more can be used in combination.

  When the gel-like body of the present invention contains a dispersion medium other than water, the content of the dispersion medium other than water in the gel-like body is preferably 50% by mass from the viewpoint of the strength and heat resistance of the gel-like body. Hereinafter, it is more preferably 25% by mass or less, particularly preferably 15% by mass or less. If the content of the dispersion medium other than water is too large, the fluidity of the gel-like body is increased and the state becomes close to a sol, which is not preferable.

  In addition to the cellulose nanofibers and the liquid organic medium and dispersion medium described above, the gel-like body of the present invention may further include various polymers other than cellulose nanofibers, cross-linking agents, clay minerals, colorants, antistatic agents, as necessary. Various functional agents such as an agent, a fragrance component, an electrolyte, a physiologically active component, and an inorganic powder may be included. The content (total content) of these functional agents in the gel-like body of the present invention is usually about 0.01 to 30% by mass.

  The gel-like body of the present invention can be produced, for example, as follows. The production method of the present embodiment is a method for producing a gel-like body containing three components of cellulose nanofibers, an organic medium and a dispersion medium as essential components. (I) Cellulose nanofibers and an organic medium are dispersed in the dispersion medium. Mixing to obtain a gel precursor, and (ii) removing the dispersion medium from the gel precursor.

  In the step (i), the three components of cellulose nanofiber, organic medium and dispersion medium may be mixed. As a specific mixing method, for example, 1) nanofiber in which cellulose nanofiber is dispersed in the dispersion medium Prepare a fiber dispersion and prepare a liquid organic medium separately (if necessary, also dissolve the organic medium in the dispersion medium) and mix these two liquids. 2) Dry Examples thereof include a method in which cellulose nanofibers such as fibers or powders and an organic medium are added or mixed simultaneously or sequentially into a dispersion medium. Any dispersion medium may be used as long as it can substantially disperse or dissolve the cellulose nanofibers and the organic medium. Particularly, the dispersion medium can be appropriately selected from those described above. Considering the fact that cellulose nanofibers tend to disperse in water-soluble organic media including water, especially due to the presence of carboxyl groups on the surface of cellulose, hydrophilic organic media including water as a dispersion medium. Is preferred. In addition, what is necessary is just to mix these with a cellulose nanofiber, an organic medium, and a dispersion medium in the process of said (i), when making the gel-like body of this invention contain the said various functional agents.

  The organic medium used in the step (i) may be one that dissolves in a dispersion medium at a molecular level (for example, the water-soluble organic medium) or one that is dispersed in a dispersion medium in an emulsion state (emulsified organic medium). Medium). As the emulsified organic medium, those in which the hydrophobic organic medium is an emulsion dispersoid are particularly preferable. Specifically, silicone oil such as polydimethylsiloxane, caprylic acid, capric acid, lauric acid, myristic acid, Higher fatty acids such as palmitic acid, oleic acid, stearin, higher alcohols such as octyl alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, stearic alcohol, hydrocarbon oils such as liquid paraffin, polyoxyethylene alkyl ether, polyoxyalkylene derivatives, Sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene Surfactants such as alkylamines, alkylalkanolamides, alkylamines, quaternary ammonium salts, alkyl sulfate esters, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfonates, ester oils, light oils, kerosene, crude oils, salad oils , Soybean oil, castor oil, triglyceride, polyisoprene, fluorine-modified oil, etc., which are emulsified by addition or modification of surfactants, are preferably used. In that case, water is usually used as the dispersion medium for the emulsion. It is done.

  The cellulose nanofiber concentration in the gel precursor obtained in the step (i) is 0.05 to 30% by mass, particularly 0.1 to 10% by mass, regardless of the type of dispersion medium. It is preferable from the viewpoint of uniformly dispersing the nanofiber and the organic medium and from the viewpoint of reducing the energy load required for removing the dispersion medium (drying of the gel precursor) in the step (ii). From the same viewpoint, the concentration of the organic medium in the gel precursor is preferably 0.1 to 90% by mass, particularly preferably 0.2 to 80% by mass. Further, since the gel precursor is formed into a desired form and then dried into the gel-like body of the present invention as described later in the step (ii), such a step is smoothly advanced. From the viewpoint, it is preferable to have a certain degree of fluidity. When each component is in the above range, a gel precursor having an appropriate fluidity and excellent moldability can be obtained.

  In the step (ii), the dispersion medium is removed from the gel precursor obtained in the step (i) to gel the gel precursor to obtain the gel-like body of the present invention. The method for removing the dispersion medium is not particularly limited, but is mainly performed by drying the gel precursor (volatilization of the dispersion medium). The gel precursor may be dried by natural drying in which the gel precursor is allowed to stand at room temperature, or by a known drying method such as heat drying, vacuum drying, freeze drying, or spray drying. Spray drying is performed by ejecting the gel precursor from a nozzle to form fine droplets, and then heating and drying the droplets in convection air. In particular, when natural drying or heat drying is used, from the viewpoint of drying efficiency, the gel precursor may be cast (cast) and then formed into a film or sheet and then dried. preferable.

  By removing the dispersion medium from the gel precursor, regardless of the type of removal method, a gel-like body having high elasticity and high heat resistance and hardly undergoing structural change against strong stress or thermal load can be obtained. The reason is that the cellulose nanofibers are uniformly arranged in the organic medium without agglomeration during the drying process due to the electrostatic repulsion of the carboxyl groups of the cellulose nanofibers, thereby forming a network of cellulose nanofibers. This is probably because a structure in which an organic medium is held is formed in a large number of minute spaces. In addition, the cellulose nanofibers obtained by the above-described method have high crystallinity, and in the organic medium, the above-described electrostatic repulsion force is weakened, and the bonds between nanofibers (so-called cross-linking points) are fixed. This is considered to be a factor for obtaining a gel-like body that hardly undergoes structural change against strong stress or thermal load.

  In the present invention, as a method for removing the dispersion medium, a method other than the above-described drying of the gel precursor can be used. For example, a dialysis method (removing only the dispersion medium using an osmotic pressure difference) or a precipitation method ( The gel precursor can be poured into a poor solvent for gelation), or a dehydrating agent such as molecular sieves can be used.

  In the step (ii), how much the dispersion medium is removed from the gel precursor is arbitrarily determined within a range in which the finally obtained gel-like body obtains predetermined physical properties (high elasticity, high heat resistance, etc.). You can choose. As described above, the content of the dispersion medium such as water in the gel-like material of the present invention is preferably 50% by mass or less from the viewpoint of various physical properties, and the content of the dispersion medium is reduced to 0 by completely removing the dispersion medium. It is good also as mass%. Therefore, it is preferable to appropriately adjust the removal amount of the dispersion medium from the gel precursor so as to achieve the content of the dispersion medium.

  The form of the gel-like body of the present invention is not particularly limited, and may be, for example, a three-dimensional shape, a film shape or a sheet shape, or a powder shape or a granular shape. The form of the gel-like body can be adjusted by appropriately selecting a method for removing the dispersion medium from the gel precursor in the manufacturing method described above. For example, the gel precursor is cast (cast) and dried. Thus, a film-like or sheet-like gel can be obtained, and a powder or granular gel can be obtained by using spray drying. Moreover, a three-dimensional gel-like body can also be manufactured by pouring a gel precursor into the mold | die of arbitrary shapes and drying.

  The gel-like body of the present invention can be manufactured by a manufacturing method other than the above-described manufacturing method (manufacturing method having a dispersion medium removing step). For example, dripping in which a cellulose nanofiber dispersion is dropped into an organic medium. It can also be produced by a method or a method of impregnating and injecting an organic medium into an airgel in which cellulose nanofibers prepared in advance are arranged in a network.

  As described above, by using cellulose nanofibers as an essential component (gelator) of a gel-like body, it is possible to achieve a very high gelation rate in the method for producing the gel-like body. That is, since a network network of cellulose nanofibers is formed widely and uniformly in an organic medium, a large amount of organic medium can be gelled even with a small amount of cellulose nanofiber used (content). Become.

  The gel-like body of the present invention obtained as described above has high elasticity and high heat resistance, high mechanical strength, flexibility against tension, bending and twisting, and high resilience after deformation. Have In particular, the gel-like body of the present invention has high shape stability and heat resistance, so that it can be used for daily necessities, specifically medical materials such as patches and regenerative medical base materials; electronic materials such as gel electrolytes for secondary batteries; It can be applied to cosmetics such as lipsticks; sustained release base materials for fragrances and cleaning agents; shock absorbers, etc., and is suitably used in a wide range of fields such as chemistry, medicine, electronics / electricity, architecture, pharmacy and agriculture. For example, a haptic agent using a gel sheet containing glycerin is currently used as an adhesive patch, and the gel-like material is used as a haptic agent by sticking the gel-like material of the present invention to the affected area. In addition, the gel precursor of the present invention can be directly formed on the affected area by applying the gel precursor according to the production method of the present invention to the affected area such as the skin and drying it. .

  In addition to the mechanical properties, the gel-like material of the present invention is characterized in that a liquid organic solvent can be retained at a high concentration. For example, by encapsulating a functional agent having a high affinity for water in the gel-like body of the present invention, it promotes the distribution and movement of the functional agent from the organic medium to the highly water-containing surface such as skin and internal organs, and has a high sustained release property. It can also be set as the base material which has.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to such examples. Hereinafter, unless otherwise specified, “%” means “mass%”. Examples 4 and 5 are reference examples.

[Method for producing oxidized cellulose fiber]
Soft cellulose bleached kraft pulp (Fletcher Challenge Canada, CSF 650 ml) is used as the raw natural cellulose fiber, TEMPO (ALDRICH, Free radical, 98%) is used as the oxidation catalyst, and sodium hypochlorite (Japanese) Kobunyaku Kogyo Co., Ltd., Cl: 5%) was used, and sodium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a co-oxidant. 9900 g of ion-exchanged water is added to 100 g of natural cellulose fibers and sufficiently stirred to obtain a slurry. In the slurry, TEMPO is 1.25% by mass of pulp, sodium bromide is 12.5% by mass of pulp, hypochlorite. 28.4% by mass of sodium acid to pulp was added in this order, and the pH of the slurry was maintained at 10.5 by adding 0.5 M sodium hydroxide dropwise using a pH stud, and the temperature was 20 to 0. The natural cellulose fiber was oxidized at 0 ° C. The dropping of sodium hydroxide was stopped after an oxidation time of 120 minutes, and the natural cellulose fiber after the oxidation treatment was sufficiently washed with ion-exchanged water and dehydrated. Thus, an oxidized cellulose fiber having a carboxyl group content of 1.2 mmol / g was obtained.

[Method for producing cellulose nanofiber]
Oxidized cellulose fiber 10 g (converted to solid content) obtained in [Oxidized cellulose fiber production method] and 990 g of ion-exchanged water were mixed for 120 minutes with a mixer (Vita-mix-Blender ABSOLUTE, manufactured by Osaka Chemikel Co., Ltd.). Stirring was performed (that is, the fine processing time was 120 minutes). Thus, an aqueous dispersion (solid content concentration: 1.0% by mass) of cellulose nanofibers having an average fiber diameter of 4 nm and a carboxyl group content of 1.2 mmol / g was obtained.

[Example 1]
The cellulose nanofiber (abbreviation: CSNF) obtained in the above [Method for producing cellulose nanofiber] is used as a gelling agent, glycerin (manufactured by Wako Pure Chemical Industries, Ltd.) is used as a liquid organic medium, and the dispersion medium is used. Using ion-exchanged water, a gel-like body was produced by a method according to the above-described method for producing a gel-like body (a production method having a dispersion medium removing step). More specifically, 32 parts by mass of glycerin is added to 100 parts by mass of the aqueous dispersion of cellulose nanofiber (solid content concentration: 1.0% by mass), and the mixture is stirred with a magnetic stirrer for 30 minutes to obtain a gel. A precursor was prepared. By pouring 12.4 g of this gel precursor into a petri dish made of polystyrene (φ80 mm) and holding it in a room temperature environment for 2 weeks, a predetermined amount of ion-exchanged water in the gel precursor is volatilized to perform a drying treatment, The gel precursor was gelled. The gel-like body thus obtained was referred to as Example 1. The gel-like body of Example 1 was a transparent gel that could maintain its sheet-like (film-like) form even when picked with tweezers.

[Example 2]
In Example 1, a gel-like body was obtained in the same manner as in Example 1 except that the amount of glycerin added was 19 parts by mass and the amount of the gel precursor poured into the petri dish was 18.4 g. 2. The gel-like body of Example 2 was a transparent gel that could maintain its sheet-like (film-like) form even when picked with tweezers.

Example 3
In Example 1, a gel-like body was obtained in the same manner as in Example 1 except that the amount of glycerin added was 4 parts by mass and the amount of the gel precursor poured into the petri dish was 40 g. did. The gel-like body of Example 3 was a transparent gel that could maintain its sheet-like (film-like) form even when picked with tweezers.

Example 4
In Example 1, a gel was obtained in the same manner as in Example 1 except that dimethyl sulfoxide (DMSO, manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of glycerin. The gel-like body of Example 4 was a transparent gel capable of maintaining its sheet-like (film-like) form even when picked with tweezers.

Example 5
A gel-like body was obtained in the same manner as in Example 1 except that polyethylene glycol (PEG 400 manufactured by Wako Pure Chemical Industries, Ltd.) was used in place of glycerin. The gel-like body of Example 5 was a transparent gel that could maintain its sheet-like (film-like) form even when picked with tweezers.

Example 6
In Example 1, a gel was obtained in the same manner as in Example 1 except that 1-ethyl-3-methylimidazolium ethyl sulfate (manufactured by Sigma Aldrich), which is an ionic liquid, was used instead of glycerin. Was taken as Example 6. The gel-like body of Example 6 was a transparent gel that could maintain its sheet-like (film-like) form even when picked with tweezers.

[Comparative Example 1]
1 g of carboxymethylcellulose (abbreviation: CMC, trade name: HE1500F, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added to 99 g of ion-exchanged water and stirred to obtain a CMC aqueous solution having a solid content concentration of 1% by mass. In Example 1, a gel-like body was obtained in the same manner as in Example 2 except that the CMC aqueous solution was used in place of the aqueous dispersion of cellulose nanofibers. The gel-like body of Comparative Example 1 was a transparent gel having a viscosity (fluidity) that cannot be picked with tweezers.

[Comparative Example 2]
50 g of oxidized cellulose fiber (in terms of solid content) obtained in the above [Method for producing oxidized cellulose fiber] and 950 g of ion-exchanged water are mixed, and a high-pressure homogenizer (Starburst Lab HJP-25005, manufactured by Sugino Machine Co., Ltd.) is used. A refinement treatment was performed once at 245 MPa, and thus an aqueous dispersion of cellulose nanofibers having a carboxyl group content of 1.2 mmol / g (solid content concentration 5.0 mass%) was obtained. 33 parts by mass of glycerin was added to 67 parts by mass of the aqueous dispersion of cellulose nanofibers and stirred well to obtain a gel precursor, and this gel precursor (not subjected to the dispersion medium removal step) was used as Comparative Example 2. . The gel-like body of Comparative Example 2 was a translucent gel having a viscosity (fluidity) that cannot be picked with tweezers.

[Evaluation]
For the samples of Examples and Comparative Examples (gel bodies), the storage elastic modulus, loss elastic modulus, and elution amount of the organic medium were measured under the respective conditions by the above method, and the elastic modulus change rate (temperature dependence, Frequency dependence) and loss tangent were calculated, and the water content of the gel (the content of water as a dispersion medium) was measured and the cellulose nanofiber content was calculated by the following method. These results are shown in Table 1 below.

<Measurement method of moisture content and calculation method of cellulose nanofiber content>
The gel-like body was heated at 105 ° C. for 40 minutes using a moisture meter (halogen moisture meter HR83, manufactured by METTLER TOLEDO), and its moisture content was evaluated. Moreover, the cellulose nanofiber content in a gel-like body was computed from this moisture content.

As apparent from Table 1, Examples 1 to 6 using cellulose nanofibers as a gelling agent with a moisture content of 50% by mass or less have a rate of change in elastic modulus (temperature dependence) of 0.7 to 4. The range and the rate of change in elastic modulus (frequency dependency) were in the range of 0.8 to 5, and the gel-like body was highly elastic and highly heat resistant. On the other hand, in Comparative Example 1 in which cellulose nanofibers were not contained and CMC was used as a gelling agent, in the above-described viscoelasticity measurement, the gel-like body was solated at a temperature of about 80 ° C., and measurement was not possible (the rate of change in elastic modulus was 0). ), It was a gel-like body with low heat resistance, and the rate of change in elastic modulus with frequency was as large as 14. Particularly, in Example 1 in which the content of the gelling agent is almost the same as that of Comparative Example 1, all of the elastic modulus change rate, loss tangent, and storage elastic modulus are included in the above-described preferred ranges. Compared with conventional gelling agents such as CMC, it can be seen that cellulose nanofibers are useful for obtaining a gel-like body having high elasticity and high heat resistance. .

Further, Comparative Example 2 having a water content of more than 50% by mass uses cellulose nanofibers as a gelling agent. Therefore, the rate of change in elastic modulus (frequency dependence) is small due to its network structure, but 100 Above ℃, the elastic modulus increased rapidly with the water phase transition. Therefore, Comparative Example 2 was a gel-like body having a large elastic modulus change rate (temperature dependency) of 7.5 and low heat resistance.

  In Examples 1 to 3, glycerin was used as the liquid organic medium, and the content (gelator content) of the cellulose nanofiber was changed. Although it becomes the largest, the loss tangent was in the range (less than 0.07) in Examples 1 and 2. In Examples 1 and 4 to 6, although the types of liquid organic media are different from each other, since good results were obtained, various liquids were obtained by using cellulose nanofiber as a gelling agent. It can be seen that the organic medium can be made into a gel-like body having high elasticity and high heat resistance.

Claims (7)

A gel-like body containing cellulose nanofibers and a liquid organic medium, the organic medium having a lower vapor pressure at 20 ° C. than water, a water content of 50% by mass or less , and a temperature in the range of 25 to 110 ° C. The rate of change of elastic modulus is 0.9 to 1.5,
A gel-like body in which the organic medium is at least one selected from the group consisting of glycerin, glycerin derivatives and ionic liquids .   The gel-like body according to claim 1, wherein the elastic modulus has a rate of change of 0.1 to 20 in a frequency range of 0.01 to 10 Hz. The gel-like body according to claim 1 or 2 , wherein a loss tangent under conditions of a temperature of 25 ° C and a frequency of 2 Hz is less than 0.6. The gelled body according to any one of claims 1 to 3 , wherein the elution amount of the organic medium measured by the following measurement method is 20% by mass or less.
Measuring method of elution amount of organic medium: After heating the gel-like body to be measured in a thermostat set at 105 ° C. for 30 minutes, the gel-like body is taken out from the thermostat and the temperature of the gel-like body Leave at room temperature until the temperature reaches room temperature (25 ° C.). Then, after removing the eluate on the surface of the gel-like body, the mass of the gel-like body is measured, and the measured value (mass B) and the pre-measured mass (mass A) of the gel-like body are measured. ) And the elution amount of the organic medium is calculated by the following formula.
Elution amount of organic medium (%) = {(AB) / A} × 100 Content of the said cellulose nanofiber is 2-20 mass%, The gel-like body in any one of Claims 1-4 . The gel-like body according to any one of claims 1 to 5 , wherein the organic medium is a hydrophilic organic medium. It is a manufacturing method of the gel-like object in any one of Claims 1-6 , Comprising: Cellulose nanofiber and an organic medium are mixed in a dispersion medium, a gel precursor is obtained, and from the gel precursor, the gel precursor is obtained. The manufacturing method of the gel-like body which has the process of removing a dispersion medium.