Cellulose nanofiber composition and method for producing the same

Abstract

To provide a composition capable of storing a cellulose nanofiber in a dry state in which a moisture content is reduced significantly, capable of re-dispersing the cellulose nanofiber easily to a rubber or resin after storage thereof when adding the cellulose nanofiber, and after dispersion or addition, easily removing an unnecessary component for facilitating use of the cellulose nanofiber.SOLUTION: There is provided a cellulose nanofiber composition including: a diol compound which is formed of diol, a diol derivative or both thereof; and water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a composition in which cellulose nanofibers can be easily redispersed.

Background Art

[0002] A new material called nanocellulose, in which the fibers constituting plant-derived cellulose materials are subdivided to a fiber diameter of less than about 1 μm, has attracted attention. Among these, materials mainly having a fiber diameter of about 3 to 100 nm have a large specific surface area and excellent properties as reinforcing fibers for resins, rubbers, etc. Such fine fibrous nanocellulose is called cellulose nanofiber (hereinafter abbreviated as "CNF"). To produce this CNF, cellulose materials such as pulp are finely defibrated in a liquid. However, even if the cellulose material itself is directly defibrated, a large amount of energy is required for defibrating because it is a strong material. Therefore, technologies for chemically modifying cellulose materials to make them easier to defibrate have been proposed. Such fine fibers obtained by chemically modifying cellulose and then defibrating it, as well as those obtained by regenerating it into cellulose, are collectively called CNF.

[0003] Normally, CNF is produced by being dispersed in water in the state of an aqueous suspension. When shipped in such a state, the volume and mass of water as the dispersion medium are much larger than the CNF itself, and the load during transportation is too high. Also, space is required for storage. Furthermore, it is difficult to use it in combination with hydrophobic resins while remaining in the aqueous suspension. Therefore, it is desirable to make a composition with as little water as possible.

[0004] However, if this aqueous suspension is once dried to reduce the water content until it becomes a solid state, there is a problem that the individual fibers of CNF strongly aggregate and cannot easily return to the original dispersed state even when water is added after drying.

[0005] In contrast, Patent Document 1 describes a technique for making a microfibrillated cellulose aqueous dispersion, manufactured according to the procedure described in Patent Document 2, easier to redisperse in water after drying by adding various polyhydroxy compounds, including carbohydrates such as sucrose, as additives that substantially inhibit hydrogen bonding between cellulose fibers in the cellulose.

[0006] Patent Document 3 describes a method for obtaining a dried product that is easily redispersible after drying, which involves adding a hydroxy acid, a hydroxy salt, glycerin, or a glycerin derivative as a redispersant to an aqueous dispersion of CNF.

[0007] Furthermore, Patent Document 4 describes a manufacturing method for adding a water-soluble polymer to an aqueous dispersion of CNF and drying it to obtain a solid product, in order to add CNF to a rubber composition while maintaining the dispersibility of CNF.

[0008] Furthermore, Patent Document 5 describes a polyurethane resin composition obtained by reacting a polyol composition, in which cellulose is micronized in a polyol, with a polyisocyanate in order to produce a polyurethane resin composition. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 59-189141 [Patent Document 2] U.S. Patent Publication No. 4374702 [Patent Document 3] Patent No. 6276740 [Patent Document 4] Re-listed 2017 / 061605 publication [Patent Document 5] Japanese Patent Publication No. 2013-194162 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, Patent Document 1 does not specifically describe the size of the microfibrillated cellulose, and on the lower left of page 2 of Patent Document 1, it is stated that Patent Document 2 should be referred to for the manufacturing procedure. According to Patent Document 2, from line 55 of the second column, it is stated that Orifice 3 needs to be small enough to apply sufficient shear force to the cellulose slurry, but it needs to be larger than the diameter of the fibers. In other words, the diameter of this Orifice 3 is roughly close to the diameter of the microfibrillated cellulose, and line 57 of the second column of Patent Document 2 states that the diameter is between 1 / 64″ and 1 / 4″. 1 / 64″ is equivalent to 0.40 mm. For this reason, the microfibrillated cellulose described in Patent Document 1 has a diameter that differs by more than three orders of magnitude from that of CNF, and as a result, its behavior, such as water retention and slurry viscosity, is completely different. Therefore, even a person skilled in the art cannot deduce from Patent Document 1 which polyhydroxy compounds are suitable for the redispersion of CNF.

[0011] Furthermore, the polyhydroxy compounds described in Patent Document 1, the redispersants described in Patent Document 3, and the water-soluble polymers described in Patent Document 4 have poor volatility, making them difficult to remove after use. They tend to remain in resins and rubbers, leading to problems such as poor compatibility with resins and rubbers, weakened effects such as reinforcement by CNF addition, and changes in the physical properties of resins and rubbers.

[0012] Furthermore, the technology described in Patent Document 5 physically refines cellulose in a polyol rather than water, making it difficult to sufficiently reduce the fiber diameter to that of cellulose nanofibers. In addition, the technology is performed in a non-aqueous environment both before and after dispersion, rather than by adding a polyol to disperse the CNF, and therefore the underlying environment differs from the technology of the present application, which disperses CNF in an aqueous suspension.

[0013] Therefore, the objective of this invention is to provide a CNF composition that allows CNF to be stored in a dry state with significantly reduced moisture content, can be easily redispersed when added to resins or rubbers after storage, and allows for easy removal of unwanted components after dispersion or addition, making it easy to use. [Means for solving the problem]

[0014] This invention solves the above problems with a CNF composition containing a diol compound consisting of a diol, a diol derivative, or both, water, and CNF.

[0015] The aforementioned diol compound is considered suitable due to the strong affinity between the hydroxyl groups it contains and CNF. A diol is a compound having two hydroxyl groups in its molecule. However, monools with only one hydroxyl group have a low boiling point and high volatility, causing them to evaporate during drying. Furthermore, even if a monool with a high boiling point is used, these monools are incompatible with water and therefore cannot be used as a dispersant for CNF. On the other hand, triols with three hydroxyl groups, such as glycerin, or compounds with even more hydroxyl groups, can ensure dispersibility, but their boiling point is too high, making it difficult to remove the composition after it has been added to resins or rubbers. In contrast to these, diols offer an excellent balance between volatility and compatibility with water. Diol derivatives are compounds obtained by modifying one or both of the two hydroxyl groups of a diol to impart functional groups, and the compatibility with resins and rubbers can be adjusted by these functional groups.

[0016] Even among diol compounds, those with large molecular weights tend to be difficult to remove by evaporation. Therefore, when selecting diol compounds for CNF composition production, factors such as volatility and compatibility with water, as well as a balance between redispersibility and removal performance after addition, are considered when adding them to resins or rubbers.

[0017] In addition, particularly when CNF is used as a reinforcing material in the production of polyurethane, the CNF composition containing the diol compound, water, and CNF can be used as it is, or the CNF composition can be redispersed with the diol compound and then used.

[0018] As the CNF composition according to this invention, a configuration in which the water content is 10% by mass or less and the mass mixing ratio of the CNF and the diol compound is 1:2 to 1:10 can be adopted.

[0019] As a specific method for producing the CNF composition, there is a procedure in which diol, a diol derivative, or both are added to a water suspension containing dispersed CNF, and then water is evaporated to obtain the CNF composition.

[0020] As a method of using such a CNF composition, for example, the CNF composition is compounded with a resin or rubber to produce a molded body of a resin or rubber containing CNF. The molded body can also be further heated to remove part or all of the contained diol compound.

[0021] Another method of using the CNF composition is to disperse CNF in a polyol, and then react the polyol containing the diol compound contained in the CNF composition with a polyisocyanate to produce polyurethane, thereby producing a cellulose nanofiber-containing polyurethane. Here, only the diol compound contained in the CNF composition may be used as the polyol, or a polyol compound may be additionally added. Alternatively, a urethane prepolymer obtained by reacting a separately prepared polyol with an excess of polyisocyanate is mixed with the CNF composition, and the isocyanate group in the urethane prepolymer is reacted with the diol compound contained in the CNF composition to chain-extend the urethane prepolymer and produce a polyurethane containing the CNF composition. The cellulose nanofiber-containing polyurethane thus obtained has improved strength compared to those not using the CNF composition.

Advantages of the Invention

[0022] The CNF composition containing the diol compound obtained by this invention can be easily returned to a dispersed state by adding water even after once reducing the water content to a solid state. It is also possible to disperse it in a polar solvent such as dimethylformamide other than water. On the other hand, without adding water to this CNF composition, it can also be directly added into a molten resin or a kneaded rubber masterbatch to easily disperse the CNF. Furthermore, after the diol compound disperses the CNF composition in a resin or rubber, it can be easily removed by evaporation by heating. After fully exerting the reinforcing effect, it can suppress the change in physical properties of the resin or rubber after addition. Also, instead of removing the diol compound, by using the diol compound as part of the polyurethane material while keeping the CNF dispersed, the CNF contained in the CNF composition can also be used as a material for improving the strength of polyurethane.

[0023] Furthermore, since the CNF composition is lighter and has a lower volume compared to a state where CNF is dispersed in a water suspension, the load during storage and transportation after manufacturing the CNF composition can be reduced.

Brief Description of Drawings

[0024] [Figure 1] Photograph of the CNF composition of Example 1 [Figure 2] Graph showing the measurement results of strain and stress in Experimental Example 2 [Figure 3] Graph showing the measurement results of strain and stress in Experimental Example 3

Modes for Carrying Out the Invention

[0025] Hereinafter, this invention will be described in detail. This invention is a CNF composition containing a diol compound composed of a diol, a diol derivative, or both, water, and CNF.

[0026] The CNF used in this invention may include not only CNF with no change in the molecular structure of cellulose, but also CNF in which a part of the molecular structure of cellulose has been chemically modified, and CNF that has been chemically modified and then regenerated into cellulose, and these may be included.

[0027] Examples of chemically modified cellulose include TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidized TEMPO-oxidized cellulose, carboxymethylated carboxymethyl cellulose, phosphate esterified cellulose, and alkali-treated cellulose to which carbon disulfide is added to form xantate groups (-OCSS). - M + Examples include xantate-modified cellulose, which incorporates cellulose compounds. Chemically modifying cellulose materials, such as pulp, makes it easier to form nanofibers than simply defibrating the cellulose material as is. CNF obtained by chemical modification and defibration is called "chemically modified CNF." Furthermore, among chemically modified celluloses, phosphate-esterified cellulose and xantate-modified cellulose can be regenerated back into cellulose. CNF obtained by regenerating chemically modified cellulose, returning its molecular structure to that of cellulose, is called "regenerated CNF."

[0028] In this invention, the term CNF refers not only to simply defibrated cellulose material, but also to the chemically modified CNF and regenerated CNF mentioned above. Furthermore, regenerated CNF may include not only those in which all hydroxyl groups that were initially modified into other functional groups such as xantate groups have been returned to their original hydroxyl groups, but also those in which some remain as other functional groups. In addition, these CNFs may be purified before use if necessary.

[0029] Furthermore, the CNF preferably contains fine fibers with a fiber diameter of 3 nm to 100 nm as its main component. Here, "main component" means that 50% or more of the present fibers fall within the above fiber diameter condition. However, fine fibers with fiber diameters outside the above range may be included as long as it does not interfere with the manufacture or use of the composition. The number average fiber diameter is preferably 20 nm or less. If the number average fiber diameter is too large, the surface area relative to the mass will be small, and the dispersion by the diol compound may not work well. The number average fiber diameter of the CNF is preferably 3 nm or more. The present invention can be implemented even with smaller numbers, but making it too fine requires a great deal of energy and is not very practical in terms of work efficiency.

[0030] A diol compound is used as a dispersant to disperse CNF in the CNF composition according to this invention. It is possible to obtain the CNF composition according to this invention even if a polar solvent other than the diol compound is included. However, care must be taken in selecting other polar solvents, as they may evaporate during drying or storage, increase the number of steps required for removal after use, or may not be removable. Therefore, it is preferable to have a low content of other polar solvents in the CNF composition.

[0031] The diol compound contained in the CNF composition according to this invention is a diol, a diol derivative, or both. Here, a diol is a compound having two hydroxyl groups in its molecule. A diol derivative is a compound in which one or both of the hydroxyl groups are modified to impart a functional group. Here, the modification method is, for example, etherification or etherification. Sterling reactions are one example. Specifically, this includes alkyl ethers of diols and alkyl esters of diols.

[0032] Examples of the aforementioned diol compounds include diols such as diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexylene glycol, and 3-methyl-1,3-butylene glycol, as well as diol derivatives such as dipropylene glycol monopropyl ether, diethylene glycol ethyl ether acetate, diethylene glycol monoethyl ether, tripropylene glycol methyl ether, and dipropylene glycol methyl ether acetate. These may be used individually or in combination. When CNF is added to resins or rubbers, an appropriate diol compound is selected based on its compatibility with those materials. Among these, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, dipropylene glycol monopropyl ether, diethylene glycol ethyl ether acetate, 1,4-butylene glycol, and 1,6-hexylene glycol are particularly preferred because they offer an excellent balance of residual rate after drying, evaporation performance after use, maintenance of dispersibility, and compatibility with resins and rubbers. Diol compounds that excel in these aspects include, for example, those in which the viscosity recovery rate after redispersion is 50% or more, and the residual rate of the diol compound after adding and mixing it with an aqueous suspension of CNF and then heating it at 105°C for 15 hours is 50% or less, which can be used as useful diol compounds.

[0033] In the CNF composition, the preferred mass mixing ratio of CNF to the diol compound is 1:2 to 1:10. Depending on the type of diol compound, if the amount of CNF is too high compared to 1:2, there will be insufficient diol compound to maintain dispersibility, and the CNF composition may not disperse well even if it is attempted to be redispersed in water or the diol compound. On the other hand, if the amount of diol compound is higher than 1:10, dispersion is possible, but further increasing the ratio of the diol compound will not contribute much to improving redispersibility, and evaporation after use may take a long time. In addition, even after removing the water, the mass of the CNF composition will remain high due to the mass of the diol compound, reducing the advantages of using the CNF composition.

[0034] The water content of the CNF composition is preferably 10% by mass or less, and more preferably 7% by mass or less. Since water increases the mass and volume of the CNF composition during storage and transportation, it is desirable to have as little water as possible.

[0035] The procedure for producing the CNF composition involves first adding the diol compound to an aqueous suspension of CNF and mixing it. This mixture is then dried to evaporate the water, reducing its water content and obtaining the CNF composition. While drying can be done at room temperature, heating is preferable to shorten the production time. The drying temperature is preferably 50°C or higher, and more preferably 60°C or higher. Below 50°C, the rate of water evaporation from the mixture is too slow, resulting in an excessively long production time for the CNF composition. On the other hand, a temperature of 110°C or lower is preferable, and more preferably 90°C or lower. Above 110°C, the diol compound also evaporates, making redispersion of the CNF difficult. Depending on the selection of the diol compound, the evaporation of the diol compound can also be suppressed by keeping the temperature below 90°C. Known drying methods such as hot air drying, spray drying, or vacuum drying can be used to obtain the CNF composition.

[0036] The CNF composition can be stored and transported with a significantly reduced water content compared to the aqueous suspension state after defibration of CNF. Because it is lightweight and has a small volume, the burden during transportation is reduced. The CNF composition can then be added directly to resins or rubber. Furthermore, by mixing in a polar solvent, the CNF can be redispersed and easily used as a redispersed CNF product. Since the CNF is suitably dispersed in this redispersed product, it can be suitably used as a thickener, moisture-retaining agent, or emulsifying stabilizer in cosmetics, paints, and other products.

[0037] Here, the polar solvent used to mix the CNF composition and redisperse the CNF can be water or other solvents such as dimethylformamide, dimethyl sulfoxide, or dimethylacetamide. However, when the diol compound is used as a polymer material, a polar solvent containing the diol compound may be used, or the diol compound itself may be used as the polar solvent.

[0038] Furthermore, the CNF composition can be directly added to thermoplastic resins, rubbers, polyurethanes, etc., to obtain the effects of CNF, such as improved strength. In addition, by using some of the compounds constituting the CNF composition as a material for a resin compound to produce a polymer and incorporating CNF into the polymer, the effects of CNF, such as improved strength, can also be obtained.

[0039] When the CNF composition is added to a thermoplastic resin such as a polyolefin, a resin molded product in which the CNF is suitably dispersed in the resin can be obtained by adding the CNF composition to the molten resin and kneading it. Examples of resins include polyolefins such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene, polyesters such as polyethylene terephthalate and polytrimethylene terephthalate, and polyamides such as nylon 6 and nylon 12. Alternatively, the CNF composition may be added to a heated and molten resin to produce a masterbatch, which may then be molded using a general method.

[0040] When the CNF composition is used by adding it to rubber, for example, natural rubber or common synthetic rubbers such as butadiene rubber, styrene-butadiene rubber, and isoprene rubber can be used as the rubber. However, since these rubbers tend to have low compatibility with diols, it is preferable to use the diol derivative, which has higher hydrophobicity than the diol compound, as the diol compound, as this makes it easier to redisperse the CNF in the rubber.

[0041] One example of using the diol compound contained in the CNF composition as a polymer material is to produce polyurethane by polyaddition reaction with polyisocyanate. In this case, after obtaining the CNF composition, the diol compound or other polyols that will be used as materials for the urethane reaction are added to the CNF composition to redisperse the CNF in these polyols and react with polyisocyanate to produce polyurethane. Alternatively, a urethane prepolymer obtained by reacting a polyol prepared separately with an excess of polyisocyanate may be mixed with the CNF composition to react the diol compound contained in the CNF composition with the isocyanate groups in the urethane prepolymer, thereby elongating the chain of the urethane prepolymer and producing polyurethane with redispersed CNF. This is preferable because it facilitates the urethane reaction with the CNF sufficiently dispersed. When a polyol containing the diol compound contained in the CNF composition is reacted with a polyisocyanate to produce polyurethane, the resulting polyurethane contains the CNF dispersed in the CNF composition (cellulose nanofiber-containing polyurethane), and its strength is improved compared to polyurethane without the CNF composition. Here, polyisocyanate is a compound having two or more isocyanate groups in its molecule, and examples include tolylene diisocyanate and diphenylmethane diisocyanate. These may be used individually or in combination.

[0042] Furthermore, the CNF composition can be added to resins, rubbers, etc., to fully exhibit the effects of CNF, such as strength improvement, and then the diol compound can be removed as needed. If there is a step of heating at a high temperature after addition, the diol compound will evaporate depending on the temperature and time. However, by proceeding with heating within a range that does not affect the appearance or physical properties of the resin or rubber, the content of the diol compound can be further reduced. For example, after heating at 105°C for 15 hours, the content of the diol compound remaining in the CNF composition (dispersant residue rate) is preferably 50% or less, more preferably 30% or less, and most preferably 10% or less.

[0043] The heating temperature and time for removing the diol compound by heating can be adjusted as appropriate depending on the diol compound. Depending on the diol compound, a temperature of 50°C or higher is preferable, and 60°C or higher facilitates evaporation for many diol compounds. On the other hand, if the temperature is too high, there is a risk of ignition, and the resin or other material that should remain after the diol compound has evaporated may be easily deformed. For this reason, it is preferable to use a temperature within a range where changes in the physical properties of the resin are acceptable. Depending on the resin, a temperature of 200°C or lower is preferable, 150°C or lower is more preferable, and 120°C or lower is usable for a wider range of resins. Furthermore, the evaporation time should be at least one hour, and more preferably five hours or more, because attempting to evaporate it for a short time requires high temperatures, which can easily deform the resin or other material. On the other hand, heating for too long is disadvantageous in terms of work efficiency and also makes the resin or other material more susceptible to deformation, so it is preferable to evaporate for no more than 48 hours, and more preferably for no more than 24 hours.

[0044] The redispersed CNF composition preferably has a viscosity restored to 50% or more of the original viscosity when compared to the original aqueous suspension of CNF, more preferably to 80% or more, and most preferably to 100%. This percentage of restoration is called the viscosity restoration rate. When the viscosity of the redispersed material is restored to 50% or more, it indicates that the CNF is dispersed appropriately without agglomerating.

[0045] Furthermore, for dispersion to obtain a redispersed product, general stirring devices such as rotary homogenizers, homomixers, and homodispersers can be used, and a sufficiently dispersed state can be achieved without using high-load stirring devices such as high-pressure homogenizers. [Examples]

[0046] The following are examples of specific embodiments of this invention. First, we will explain the manufacturing procedure for xantate-type CNF, which is a chemically modified CNF obtained by defibrating chemically modified cellulose. The following materials were used. Kraft pulp (manufactured by Nippon Paper Industries Co., Ltd.: NBKP, α-cellulose content: 90% by mass, average degree of polymerization of α-cellulose: 1000) will be referred to as "NBKP" below.

[0047] <Alkaline treatment> NBKP was weighed to obtain 100g of pulp solids (pulp solids are defined as the pulp after removing water; the same applies hereinafter). This was placed in a 3L beaker, 2500g of an 8.5% by mass sodium hydroxide aqueous solution was added, and the mixture was stirred at room temperature for 3 hours to perform alkaline treatment. The pulp after this alkaline treatment was separated into solid and liquid components using a centrifugal dehydrator (H-110A, manufactured by Kokusan Co., Ltd., with a 400-mesh filter cloth) to obtain dehydrated alkali cellulose. The sodium hydroxide content of this dehydrated alkali cellulose was 7.5% by mass, and the pulp solids content was 27.4% by mass.

[0048] <Xantate treatment> The dehydrated alkali cellulose prepared above was weighed to a pulp solid content of 100 g and placed in a round-bottom flask. 35 g of carbon disulfide (35% by mass relative to the pulp solid content) was added to this flask, and the sulfurization reaction was carried out at room temperature for 4.5 hours to perform xantate treatment and obtain xantate cellulose.

[0049] <Measurement of Xantate Replacement Degree> The average degree of xantate substitution in the xantate-modified cellulose was measured by the Bredee method and found to be 0.312. This degree of xantate substitution represents the degree to which xantate groups are introduced per glucose unit of cellulose. The Bredee method was performed as follows: 1.5 g of xantate-modified cellulose was weighed into a 100 mL beaker, and 40 mL of saturated ammonium chloride aqueous solution (5°C) was added. The sample was thoroughly mixed while crushing it with a glass rod, and after standing for 15 minutes, it was filtered through GFP filter paper (GS-25, ADVANTEC) and thoroughly washed with saturated ammonium chloride aqueous solution. The sample, along with the GFP filter paper, was placed in a 500 mL tall beaker, and 50 mL of 0.5 M sodium hydroxide aqueous solution (5°C) was added and stirred. After standing for 15 minutes, it was neutralized with 1.5 M acetic acid aqueous solution. Phenolphthalein indicator was used as the indicator. After neutralization, 250 mL of distilled water was added and thoroughly stirred. Then, 10 mL of 1.5 M acetic acid aqueous solution and 10 mL of 0.05 mol / L iodine aqueous solution were added using a volumetric pipette. This solution was titrated with 0.05 mol / L sodium thiosulfate aqueous solution. A 1% starch aqueous solution indicator was used as the indicator. The degree of xantate substitution was calculated from the titration volume of sodium thiosulfate aqueous solution and the cellulose content in the sample using the following formula (1). The cellulose content in xantate cellulose was determined by dispersing xantate cellulose with water, regenerating it with hydrochloric acid, filtering the regenerated cellulose, washing it thoroughly, and then drying it completely before measuring the mass of only the cellulose.

[0050] Degree of xantate substitution = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration volume (mL)) ÷ 1000 ÷ (cellulose content in sample (g) / 162.1) ... (1)

[0051] <Fibrillation treatment> The xanthated cellulose produced by the above xanthation treatment was weighed into a 5-L beaker to a pulp solid content of 100 g, and distilled water was added and dispersed so that the pulp solid content concentration was 5% by mass. While centrifuging using the centrifuge, distilled water was added and thoroughly washed to remove impurities, alkali, unreacted carbon disulfide, etc. All of the washed xanthated cellulose was recovered, and distilled water was added to make 20 kg of an aqueous suspension having a cellulose concentration (hereinafter referred to as "cellulose concentration") of 0.5% by mass contained in the xanthated cellulose. This aqueous suspension was passed through a high-pressure homogenizer (manufactured by Sanwa Engineering Co., Ltd., model H20) five times at a flow rate of 2.5 L / min and a pressure of 40 MPa for defibration treatment to obtain xanthated CNF.

[0052] <Degree of defibration of CNF> Distilled water was added to the aqueous suspension of the xanthated CNF (cellulose concentration 0.5% by mass) to dilute the cellulose concentration to 0.1% by mass. This diluted aqueous suspension was centrifuged at 12,000 G for 10 minutes using a centrifuge (manufactured by Beckman Coulter, Avanti J-25I) to precipitate undefibrated matter. The supernatant was separated and transferred to an Erlenmeyer flask, and distilled water was added to the precipitated undefibrated matter and centrifuged again to wash the undefibrated matter. The undefibrated matter was transferred to a crucible and dried to a constant weight, and the mass of the undefibrated matter was measured. The production rate of nanofibers generated from the following formula (2) based on the mass of the undefibrated matter and the cellulose content in the xanthated cellulose was determined to be 99.0% by mass.

[0053] Production rate of nanofibers (% by mass) = (cellulose content in xanthated cellulose - mass of undefibrated matter) ÷ (cellulose content in xanthated cellulose) × 100......(2)

[0054] <Measurement of fiber diameter of CNF> An aqueous suspension of xanthated CNF diluted to a cellulose concentration of 0.1% by mass with water was placed in a centrifuge tube, and centrifuged at 12,000 G for 10 minutes using the centrifuge, and the centrifuged supernatant was recovered. This centrifuged supernatant was further diluted and then stained, and dried on a support film to obtain a dried specimen. Trans A transmission electron microscope (TEM: manufactured by JEOL Ltd., JEM-1400) was used for observation at an acceleration voltage of 120 kV. Fifty nanofibers were selected from the 50,000-fold magnified images obtained by observation, and the fiber diameters were measured. When the average value was calculated, the fiber diameters were from 3.0 nm to 7.4 nm, and the number-average fiber diameter was 6.1 nm.

[0055] <Regeneration treatment and redispersion treatment> To 16.4 kg of the aqueous suspension of zanthated CNF (cellulose concentration: 0.5% by mass) obtained by the above procedure, 360 ml of 1M sulfuric acid aqueous solution (sulfuric acid amount: 4.4 mmol / g-cellulose content) was added, and the mixture was stirred with an agitator for 1 hour to conduct a regeneration treatment. After the treatment was completed, it was neutralized to pH 7 with 1M sodium hydroxide aqueous solution to obtain a regenerated CNF aqueous suspension. When the average degree of zanthate substitution was measured, it was less than 0.001, which is the lower limit of measurement. It was confirmed that the zanthate groups were almost completely detached and returned to hydroxyl groups by the acid treatment.

[0056] The aqueous suspension of the regenerated CNF obtained above was centrifugally dehydrated using the centrifuge, and distilled water was added to wash it sufficiently. All of the washed regenerated CNF was recovered, and distilled water was added to obtain an 8 kg aqueous suspension with a CNF concentration of 1.0% by mass. This aqueous suspension was redispersed by passing it through the high-pressure homogenizer three times at a flow rate of 2.5 L / min and a pressure of 40 MPa. After the treatment, when the average fiber diameter of the redispersion of the regenerated CNF was calculated, the fiber diameters were from 3.0 nm to 7.4 nm, and the number-average fiber diameter was 6.0 nm.

[0057] <Production procedure of CNF composition> Next, the production of the CNF composition will be described. The following diols or diol derivatives were used as the diol compound. ·Diethylene glycol (diol: manufactured by Nacalai Tesque, Inc.: diethylene glycol)·Triethylene glycol (diol: manufactured by Nacalai Tesque, Inc.: triethylene glycol) ·Dipropylene glycol (diol: manufactured by Nacalai Tesque, Inc.: dipropylene glycol) Tripropylene glycol (diol: manufactured by Nacalai Tesque Co., Ltd.: tripropylene glycol) • 1,3-Butylene glycol (diol: manufactured by Kanto Chemical Co., Ltd.: 1,3-butanediol) ) • 1,4-Butylene glycol (diol: manufactured by Kanto Chemical Co., Ltd.: 1,4-butanediol) ) • 1,6-Hexylene glycol (diol: manufactured by Tokyo Chemical Industry Co., Ltd.: 1,6-Hexanediol) • Dipropylene glycol monopropyl ether (diol derivative: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.: dipropylene glycol monopropyl ether) • Diethylene glycol ethyl ether acetate (diol derivative: manufactured by Tokyo Chemical Industry Co., Ltd.: diethylene glycol monoethyl ether acetate) • Glycerin (polyols other than diols: manufactured by Nacalai Tesque Co., Ltd.: glycerin) • Diglycerol (polyol other than diol: manufactured by Nacalai Tesque Co., Ltd.: diglycerol)

[0058] (Examples 1-7) Diol compounds, as shown in Table 1, were added to a regenerated CNF aqueous suspension in an amount 10 times that of the regenerated CNF. 30 g of the mixture, with a CNF concentration of 0.7% by mass and a diol compound concentration of 7.0% by mass, was dried for each diol compound at 60°C using a hot air dryer for the specified time shown in Table 1 to obtain the CNF composition. A photograph of the CNF composition of Example 1 is shown in Figure 1.

[0059] <Method for calculating the remaining percentage of dispersant> In each example, approximately 0.2 to 0.4 g of the CNF composition sample was taken, 6 ml of methanol was added, and the mixture was dispersed for 5 minutes at 8000 rpm using a rotary homogenizer (AM-7, manufactured by Nippon Seiki Seisakusho Co., Ltd.). After dispersion, methanol was added to a total volume of 25 ml, and the content of the diol compound, which is the dispersant, was measured by gas chromatography. The dispersant retention rate was calculated from the content of the dispersant relative to the total mass of the CNF composition. In addition, the residual water content was calculated by subtracting the mass of the dispersant and CNF from the total mass of the CNF composition, and the post-drying water content relative to the total CNF composition was calculated. These results are shown in Tables 1 to 3. The gas chromatography analysis conditions were as follows: the instrument used was a Shimadzu GC-17A, and the column was an Agilent HP-WAX 25m (inner diameter 0.32 μm). The temperature conditions were 250°C for injection and 250°C for the detector. An FID detector was used, and the column heating conditions were t=0 (40°C), t=0.5 (40°C), t=20.5 (240°C), and t=24.5 (240°C).

[0060] <Method for calculating viscosity recovery rate> To each of the CNF compositions, water was added to the same amount as before drying, and the mixture was dispersed using the rotary homogenizer at 8000 rpm for 15 minutes to obtain a redispersed mixture with a CNF concentration of 0.7% by mass. This redispersed mixture was measured using an E-type viscometer manufactured by Toki Sangyo Co., Ltd. at 20°C and a rotation speed of 1 rpm (shear rate = 3.8 s). -1 Viscosity measurements were performed, and the viscosity recovery rate was determined by comparing it with the viscosity of the original CNF aqueous suspension. For example, the viscosity of the original CNF aqueous suspension in Example 1 was 448 mPa·s, while the viscosity of the redispersed material was exactly the same, 448 mPa·s, and the viscosity recovery rate was calculated to be 100%. Similarly, the results obtained in other examples, reference examples, and comparative examples are shown in Tables 1 to 4.

[0061] [Table 1]

[0062] The CNF compositions of Examples 1-9, dried at 60°C, retained more than 80% of the diol compound acting as a dispersant, and all showed high viscosity restoration rates in the redispersed materials.

[0063] (Reference examples 1~7) Using the same procedure as in Examples 1-7, mixtures with a CNF concentration of 0.7% by mass and a diol compound concentration of 7.0% by mass were prepared. These mixtures were then heated at 105°C for 15 hours, and the results are presented as Reference Examples 1-7. The dispersant retention rate and viscosity recovery rate are shown in Table 2. In Reference Example 1, the retention rate of the diol compound, which acts as a dispersant, remained at approximately 30%, while in the other Reference Examples, the diol compound almost completely evaporated. This confirmed that these dispersants can be easily removed by heating after using the CNF composition.

[0064] [Table 2]

[0065] (Consideration) From these results, it was confirmed that CNF compositions exhibiting a desirable viscosity recovery rate of 50% or more preferably contain at least 50% by mass of the diol compound acting as a dispersant. In all cases where no dispersant remained, the viscosity recovery rate was significantly low or redispersion was impossible.

[0066] (Comparative Examples 1 and 2) Table 3 shows the results of Comparative Examples 1 and 2, in which glycerin with 3 hydroxyl groups in the molecule and diglycerol with 4 hydroxyl groups were used as dispersants. While these showed favorable values ​​in terms of dispersant retention rate and viscosity recovery rate when dried at 60°C, a large amount of dispersant remained even after heating at 105°C for 15 hours, confirming that removal of the dispersant was difficult.

[0067] [Table 3]

[0068] <Investigation of the effect of diol addition ratio> (Examples 8a to 8d) Water suspensions of 30 g each were prepared such that the CNF concentration was 0.7% by mass and the content of triethylene glycol as the diol compound was 7.0% by mass (Example 8a), 3.5% by mass (Example 8b), 1.4% by mass (Example 8c), and 0.7% by mass (Example 8d), respectively, and the viscosities were measured. Next, each water suspension was dried at 60 °C using a hot air dryer until the water content became 10% by mass or less. After drying, water was added to adjust the total mass to 30 g each, and the mixtures were mixed at 8000 rpm for 15 minutes using the rotary homogenizer to obtain redispersions. The viscosities of the respective redispersions were measured, and the viscosity recovery rates were calculated. The results are shown in Table 4.

[0069] [Table 4]

[0070] From the above results, it was confirmed that when the addition amount of the diol compound was 2 times or more with respect to CNF, the viscosity recovery rate showed good results of 50% or more.

[0071] [Resin kneading of CNF composition] (Experimental Example 1) A water suspension of 32 g containing 0.5% by mass of recycled CNF and 5.0% by mass of dipropylene glycol (DPG) as the diol compound was prepared. This water suspension was dried at 60 °C for 12 hours using a hot air dryer to obtain a CNF composition with a dried weight of 1.83 g.

[0072] 1.83 g of this CNF composition and 15 g of polypropylene resin (Wintech WFX4M manufactured by Nippon Polypropylene Co., Ltd.) were kneaded at 180 °C for 5 minutes using a bench-top small kneader (DSM Xplore MC15M manufactured by Xplore Instruments) to obtain a kneaded resin. The DPG content before kneading was 9.5% by mass.

[0073] A portion (112.6 mg) was taken from the kneaded resin and immersed in 1.5 mL of toluene, and left standing at 80 °C for 2 hours to dissolve the polypropylene resin. This solution was dropped into a vial containing 5 mL of methanol to dissolve DPG in methanol, and then further methanol was added to make up to 10 mL. Next, this methanol solution was subjected to gas chromatographic analysis to quantify the dissolved DPG. The analysis conditions of the gas chromatograph were the same as those in the above "Method for Calculating Dispersant Residual Ratio". As a result, the content of DPG contained in the kneaded resin was 1.3% by mass, which was sufficiently reduced from 9.5% by mass before kneading. Thus, it was confirmed that when the CNF composition was introduced into the heat-melted resin, the amount of the diol compound used for maintaining the dispersibility of CNF evaporated during kneading and the amount remaining in the resin was small.

[0074] <Rubber Kneading of CNF Composition> (Experimental Example 2) 300 g of a masterbatch prepared by drying natural rubber latex (manufactured by Rejtex Co., Ltd., HA NR LATEX, solid content 60% by mass, ammonia 0.7% by mass) was kneaded using a two-roll mill heated to 50 °C (a mixing roll machine manufactured by Nippon Roll Manufacturing Co., Ltd., φ200 mm × L500 mm). Next, 1.5 g of stearic acid (manufactured by Nacalai Tesque, Inc.) and 18 g of zinc oxide (manufactured by Nacalai Tesque, Inc.) were added and kneaded to obtain a kneaded product. Next, 90.32 g of a CNF composition (15.0 g of CNF, 75.0 g of diethylene glycol ethyl ether acetate, 0.32 g of moisture) prepared by mixing and drying diethylene glycol ethyl ether acetate as a diol compound and recycled CNF was added to the above kneaded product and further kneaded. Then, 10.5 g of sulfur (manufactured by Nacalai Tesque, Inc.) and 2.1 g of a vulcanization accelerator (Suncel NS-G manufactured by Sanshin Chemical Industry Co., Ltd.) were added and mixed to produce a compound sheet with a thickness of 2 mm or more.

[0075] Using the obtained compound sheet, the 90% vulcanization time (Tc90) was measured with a vulcanization determination machine (manufactured by Orientec Co., Ltd., Curemeter V type, measurement temperature 150 °C, measurement time 20 minutes). At this time, Tc90 was 6 minutes. This compound sheet was placed in a mold, Based on the measured Tc90 value, a vulcanized rubber sheet with a thickness of 2 mm was obtained by compression molding at 150 °C for 6 minutes. As described above, it was confirmed that a rubber sheet can be produced by adding the CNF composition to the rubber.

[0076] From the obtained rubber sheet, a dumbbell-shaped No. 3 test piece specified in JIS K 6251 was punched out. For this test piece, a tensile test (grip width: 50 mm, speed: 500 mm / min, conforming to JIS K6251) was performed using a tensile testing machine (Precision Universal Testing Machine AG-1000D manufactured by Shimadzu Corporation). Also, among the above procedures, a rubber sheet prepared by the same procedure except that only diethylene glycol ethyl ether acetate not containing regenerated CNF was added instead of the CNF composition was used as a blank.

[0077] The results of the tensile tests of this test piece and the blank are shown in Figure 2 and Table 5. As a result, the rubber sheet to which regenerated CNF was added had a 68.8% increase in stress (M30%) at 30% elongation (= strain), a 46.2% increase at 100% elongation (M100%), and a 26.8% increase at 300% elongation (M300%) compared to the blank. From this, it was confirmed that the strength of the rubber sheet was improved by the dispersed regenerated CNF.

[0078]

Table 5

[0079] <Synthesis of Polyurethane with CNF Composition> (Experimental Example 3) 1,4-butylene glycol was used as the diol compound and added in an amount 10 times that of the regenerated CNF to prepare a regenerated CNF aqueous suspension with a CNF concentration of 0.8% by mass and a diol concentration of 8.0% by mass. 200 g of this regenerated CNF aqueous suspension was dried in a hot air dryer at 60°C for 18 hours to obtain a CNF composition (regenerated CNF: 9.3% by mass, 1,4-butylene glycol: 86.8% by mass, water content: 4.0%).

[0080] To 10.8 g of this CNF composition, 89.2 g of polytetramethylene glycol (PTMG), a polyol that serves as a material for the urethane reaction, was added, and the mixture was dispersed using a rotary homogenizer (AM-7) at 10,000 rpm for 10 minutes to obtain a regenerated CNF polyol dispersion (regenerated CNF: 1.0% by mass, 1,4-butylene glycol: 9.4% by mass, PTMG: 89.1% by mass, water content 0.5%).

[0081] 5.0 g of the above-mentioned regenerated CNF polyol dispersion was mixed with 45 ml of dimethylformamide (DMF) and dispersed using the aforementioned rotary homogenizer at 3000 rpm for 5 minutes to obtain a DMF dispersion. This DMF dispersion was then placed in a centrifuge tube and centrifuged at 1100 G for 10 minutes using the aforementioned centrifuge. After removing the supernatant from the centrifuged material, 50 ml of DMF was added to the precipitate and centrifuged again. After removing the supernatant from this second centrifugation, the precipitate was washed by adding a solvent and centrifuging again, first with acetone as the solvent, and then with distilled water as the solvent. This precipitate was then measured for weight as the undispersed material in the regenerated CNF polyol dispersion after drying at 105°C for 8 hours using a hot air dryer. The ratio of undispersed material to the amount of raw CNF was calculated. The result was 11%, confirming that 89% of the regenerated CNF was uniformly dispersed in the regenerated CNF polyol dispersion.

[0082] To 96.3 g of the above-mentioned recycled CNF polyol dispersion, 0.5 g of 1,4-butylene glycol was added so that the mass ratio of PTMG to 1,4-butylene glycol was 9:1, and the mixture was stirred at 80°C for 30 minutes using a three-one motor. To this mixture, 57.2 g of diphenylmethane diisocyanate was added and stirred for 5 minutes, then transferred to a preheated stainless steel tray and reacted at 110°C for 24 hours using a hot air dryer to obtain 136 g of synthetic polyurethane with dispersed recycled CNF.

[0083] The obtained synthetic polyurethane was melted at 220°C for 10 minutes using a tabletop test press machine SA-302 manufactured by Tester Industries Co., Ltd., and then processed into a 300 μm thick film by applying a pressure of 7 MPa and hot pressing for 5 minutes. Test specimens punched out from this film into dumbbell-shaped No. 8 pieces as specified in JIS K 7311 were subjected to tensile tests under the conditions of a measurement length of 25 mm and a tensile speed of 100 mm / min. On the other hand, the blank film without recycled CNF was prepared from synthetic polyurethane with the same amounts of PTMG and 1,4-butylene glycol, except that recycled CNF aqueous dispersion was not used.

[0084] The results of tensile tests on this specimen and blank are shown in Figure 3 and Table 6. Compared to the blank, the polyurethane with added recycled CNF showed a 9.7% improvement in stress (M100%) at 100% elongation (strain). Furthermore, the stress (M200%) at 200% elongation (strain) showed a 9.8% improvement. This confirms that the strength of synthetic polyurethane is improved by dispersed recycled CNF.

[0085] [Table 6]

Claims

1. A regenerated cellulose nanofiber aqueous suspension containing regenerated cellulose nanofibers having a number-average fiber diameter of 3 nm to 20 nm is given a diol compound consisting of a diol, a diol derivative, or both as a dispersant, and then a portion of the water is evaporated to obtain a regenerated cellulose nanofiber composition in which the remaining amount of the diol compound is 50% by mass or more. A method for producing a regenerated cellulose nanofiber composition, wherein the regenerated cellulose nanofiber, when redispersed, exhibits a viscosity recovery rate of 50% or more compared to an aqueous suspension of the original cellulose nanofiber.

2. The method for producing regenerated cellulose nanofibers according to claim 1, wherein the regenerated cellulose nanofibers are obtained by regenerating xantate-modified cellulose nanofibers to a degree of xantate substitution of less than 0.

001.

3. A method for producing a molded resin or rubber product containing regenerated cellulose nanofibers, comprising mixing a regenerated cellulose nanofiber composition containing a diol compound comprising a diol, a diol derivative, or both thereof, water, and regenerated cellulose nanofibers having a number-average fiber diameter of 3 nm to 20 nm, wherein the regenerated cellulose nanofiber composition, when redispersed, exhibits a viscosity recovery rate of 50% or more compared to an aqueous suspension of the original cellulose nanofibers, with molten resin or kneaded rubber.

4. A method for producing a molded resin or rubber article, comprising heating a molded resin or rubber article produced by the method described in claim 3 to remove part or all of the diol compound.

5. A method for producing polyurethane containing regenerated cellulose nanofibers, comprising: mixing a regenerated cellulose nanofiber composition containing a diol compound comprising a diol, a diol derivative, or both thereof, water, and regenerated cellulose nanofibers having a number-average fiber diameter of 3 nm to 20 nm, wherein the regenerated cellulose nanofiber composition, when redispersed, has a viscosity recovery rate of 50% or more compared to an aqueous suspension of the original cellulose nanofibers, with a polyol; dispersing the regenerated cellulose nanofibers in the polyol; and then reacting the polyol containing the diol compound contained in the regenerated cellulose nanofiber composition with a polyisocyanate to produce polyurethane.

6. A urethane prepolymer is obtained by reacting a polyol with an excess of polyisocyanate. The aforementioned urethane prepolymer, A regenerated cellulose nanofiber composition comprising a diol, a diol derivative, or both thereof, water, and regenerated cellulose nanofibers having a number-average fiber diameter of 3 nm to 20 nm, wherein when redispersed, the viscosity recovery rate compared to the original aqueous suspension of cellulose nanofibers is 50% or more. Mix them together, A method for producing a polyurethane containing regenerated cellulose nanofibers, comprising reacting isocyanate groups in the urethane prepolymer with the diol compound contained in the regenerated cellulose nanofiber composition to produce a polyurethane in which the urethane prepolymer's chains have been elongated.

Images