Apparatus for producing cellulose fiber, method for producing cellulose fiber, and cellulose fiber

Abstract

The present invention relates to a production apparatus capable of producing cellulose fiber in which the orientation direction of cellulose nanofibers is aligned in one direction and tensile strength and toughness are enhanced, and a production method using said production apparatus. A production apparatus according to the present invention comprises a flow channel (11) through which a feedstock liquid containing cellulose nanofibers is flowed from the upstream side toward the downstream side, the apparatus being characterized in that: the flow channel (11) has an upstream part (12), which extends in a state in which the shape and cross-sectional area of cross sections perpendicular to the longitudinal direction are constant, a downstream part (13), which extends in a state in which the area of cross sections perpendicular to the longitudinal direction is smaller than that of the upstream side, and a contracting part (14), which connects the upstream part (12) and the downstream part (13) and in which the area of cross sections perpendicular to the longitudinal direction gradually decreases toward the downstream side; and at least the upstream part (12) has an electrode (17), which forms an electric field inside the flow channel (11).

Description

Cellulose fiber manufacturing apparatus, cellulose fiber manufacturing method and cellulose fiber

[0001] The present invention relates to a cellulose fiber manufacturing apparatus, a cellulose fiber manufacturing method using the same, and cellulose fibers. This application claims priority based on Japanese Patent Application No. 2023-137034, filed on August 25, 2023, the contents of which are incorporated herein by reference.

[0002] Cellulose nanofibers (CNF), which are wood fibers mechanically and chemically untangled to nano-order sizes, are highly crystalline ultrafine fibers with diameters of approximately 10 nm, and are being considered for use as next-generation biomass materials (see, for example, Patent Document 1).

[0003] By using these cellulose nanofibers and forming them into fibers with a uniform orientation, it is possible to obtain cellulose single fibers with tensile strength and toughness equal to or greater than that of glass fibers. For example, a method for obtaining cellulose single fibers is known in which a TEMPO-oxidized CNF solution obtained by chemically defibrating wood fibers with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) is poured out into fine fibers, and the resulting solution is coagulated using a coagulating solution such as hydrochloric acid.

[0004] Japanese Patent Application Publication No. 2023-113115 (A)

[0005] However, cellulose nanofibers have a strong tendency to diffuse due to Brownian motion, making it difficult to obtain cellulose fibers with a uniform orientation. Therefore, there has been a demand for cellulose nanofibers with a uniform orientation that have improved tensile strength and toughness.

[0006] The present invention has been proposed in light of the above-mentioned problems, and aims to provide a cellulose fiber manufacturing device capable of producing cellulose fibers with unidirectional orientation of cellulose nanofibers and improved tensile strength and toughness, and a cellulose fiber manufacturing method using the same.

[0007] To solve the above problems, the cellulose fiber production apparatus and cellulose fiber production method using the same according to one embodiment of the present invention propose the following means: (1) A cellulose fiber production apparatus according to aspect 1 of the present invention is characterized in that it includes a flow path through which a raw material liquid containing cellulose nanofibers flows from the upstream side to the downstream side, the flow path having an upstream section that extends with a constant cross-sectional shape and cross-sectional area perpendicular to the longitudinal direction, a downstream section that extends with a cross-sectional area perpendicular to the longitudinal direction that is smaller than that of the upstream section, and a constricted section that connects the upstream section and the downstream section and whose cross-sectional area perpendicular to the longitudinal direction gradually decreases toward the downstream side, and at least the upstream section has electrodes that form an electric field inside the flow path.

[0008] (2) Aspect 2 of the present invention is characterized in that, in the cellulose fiber production apparatus of aspect 1, the ratio of the cross-sectional area of ​​the upstream portion to the cross-sectional area of ​​the downstream portion is 1.5 or more.

[0009] (3) Aspect 3 of the present invention is characterized in that in the cellulose fiber manufacturing apparatus of aspect 1 or 2, the electrodes are formed in both the upstream portion and the downstream portion.

[0010] (4) Aspect 4 of the present invention is characterized in that in the cellulose fiber production apparatus according to any one of aspects 1 to 3, an alternating current is applied to the electrodes.

[0011] (5) Aspect 5 of the present invention is characterized in that, in the cellulose fiber manufacturing apparatus of any one of aspects 1 to 4, a dielectric layer is formed between the electrode and the inner surface of the flow path.

[0012] (6) Aspect 6 of the present invention is characterized in that, in the cellulose fiber production apparatus according to any one of aspects 1 to 5, the shape of a cross section perpendicular to the longitudinal direction of the flow channel is rectangular.

[0013] (7) Aspect 7 of the present invention is characterized in that, in the cellulose fiber manufacturing apparatus of any one of aspects 1 to 6, the inclination angle of the inner surface of the constriction section with respect to the central axis along the longitudinal direction of the flow path is in the range of 5° or more and 30° or less.

[0014] (8) Aspect 8 of the present invention is characterized in that, in the cellulose fiber manufacturing apparatus of any one of aspects 1 to 7, the total length of the flow path from the inlet to the outlet of the flow path is within a range of 50 to 500 mm, the length of the upstream section is within a range of 50 to 90% of the total length of the flow path, the length of the downstream section is within a range of 9 to 40% of the total length of the flow path, and the length of the constriction section is within a range of 1 to 10% of the total length of the flow path.

[0015] (9) A cellulose fiber manufacturing method according to aspect 9 of the present invention is a cellulose fiber manufacturing method using the cellulose fiber manufacturing apparatus according to any one of aspects 1 to 8, and is characterized by comprising at least a first orientation step in which the longitudinal direction of the cellulose nanofibers is oriented along the longitudinal direction of the flow path using an electric field formed by a current applied to the electrodes; a second orientation step in which the longitudinal direction of the cellulose nanofibers is oriented along the longitudinal direction of the flow path using an elongational flow field generated by the constriction section; and a coagulation step in which the raw material liquid that has undergone the first orientation step and the second orientation step is brought into contact with a coagulation liquid to coagulate, thereby obtaining cellulose fibers.

[0016] (10) Aspect 10 of the present invention is characterized in that, in the method for producing cellulose fibers of aspect 9, the raw material liquid further contains at least one of carbon nanotubes and metal nanoparticles in addition to the cellulose nanofibers.

[0017] (11) Aspect 11 of the present invention is the method for producing cellulose fibers according to aspect 9 or 10, characterized in that the coagulation liquid is a solution containing hydrochloric acid or polyvalent metal ions.

[0018] (12) Aspect 12 of the present invention is the method for producing cellulose fibers according to any one of aspects 9 to 11, wherein in the first orientation step, the voltage is 0.2 to 10 kV. ｐｐ A voltage in the range of is applied to the electrodes.

[0019] (13) Aspect 13 of the present invention is characterized in that, in the method for producing cellulose fibers according to any one of aspects 9 to 12, the flow rate of the raw material liquid flowing through the flow path is within the range of 10 to 500 mL / hour.

[0020] (14) Aspect 14 of the present invention is characterized in that, in the method for producing cellulose fibers according to any one of aspects 9 to 13, the concentration of the cellulose nanofibers contained in the raw material liquid is within the range of 0.03 to 3 mass%.

[0021] (15) A cellulose fiber according to aspect 15 of the present invention is a cellulose fiber containing silver nanoparticles, characterized in that the silver content is within the range of 1.0 to 10.0 mass %.

[0022] (16) Aspect 16 of the present invention is characterized in that the cellulose fiber of aspect 15 has an elastic modulus in the range of 4 to 40 GPa.

[0023] According to the present invention, it is possible to provide a cellulose fiber manufacturing apparatus capable of producing cellulose fibers in which the orientation direction of cellulose nanofibers is aligned in one direction and which have improved tensile strength and toughness, and a cellulose fiber manufacturing method using the same.

[0024] 1 is a schematic cross-sectional view showing a cellulose fiber manufacturing apparatus according to one embodiment of the present invention; 2 is a photograph showing a configuration actually produced using the cellulose fiber manufacturing apparatus according to this embodiment; 3 is an explanatory diagram showing the configuration of the cellulose fiber manufacturing apparatus used in the verification in the examples; 4 is an aqueous dispersion medium (concentration: 0.3% by mass, flow rate: 180 mL / hour) for CNF, and a 1 mol / L aqueous hydrochloric acid solution was used as the coagulant in the coagulation tank; and 5 is an explanatory diagram showing the cellulose fiber manufacturing conditions in the examples; 6 is an arrangement of electrodes in five locations on one side or three locations on the other side, and the applied voltage is in the absence of an electric field and an alternating electric field (5 kHz, 3 kV ｐｐ) is an explanatory diagram showing the configuration of a flow path (ratio of cross-sectional area of ​​the upstream portion to the cross-sectional area of ​​the downstream portion: 1.0, flow path cross section: 1 mm × 1 mm (rectangular)) of a cellulose fiber production apparatus used in verification in the examples. FIG. 1 is an explanatory diagram showing the configuration of a flow path (ratio of cross-sectional area of ​​the upstream portion to the cross-sectional area of ​​the downstream portion: 2.0, flow path cross section: 1 mm × 2 mm (rectangular)) of a cellulose fiber production apparatus used in verification in the examples. FIG. 2 is an explanatory diagram showing the configuration of a flow path (ratio of cross-sectional area of ​​the upstream portion to the cross-sectional area of ​​the downstream portion: 3.0, flow path cross section: 1 mm × 3 mm (rectangular)) of a cellulose fiber production apparatus used in verification in the examples. FIG. 3 is an SEM photograph of a cellulose fiber (sample) obtained in Comparative Example 1. FIG. 4 is an SEM photograph of a cellulose fiber (sample) obtained in Inventive Example 1. FIG. 5 is an SEM photograph of a cellulose fiber (sample) obtained in Inventive Example 2. FIG. 6 is a graph showing the tensile strength (UTS), elastic modulus (EM), and toughness (TN) of Comparative Example 1, and Inventive Examples 1 and 2. FIG. 7 is an SEM photograph of a cellulose single fiber carrying silver nanoparticles. 1 is a graph showing the tensile strength (UTS), modulus of elasticity (EM), and toughness (TN) of Comparative Examples 11 to 15 prepared without the application of an electric field. ｐｐ 1 is a graph showing the tensile strength (UTS), elastic modulus (EM), and toughness (TN) of Inventive Examples 11 to 15 prepared by the method described above. 2 is a photograph showing the evaluation of the antibacterial effect of the cellulose single fiber of Comparative Example 14. 3 is a photograph showing the evaluation of the antibacterial effect of the cellulose single fiber of Inventive Example 14. 4 is a graph showing the tensile strength (UTS), elastic modulus (EM), and toughness (TN) of Inventive Examples 11 to 15 and Comparative Example 16 (chemical fiber derived from a commercially available product).

[0025] Hereinafter, a cellulose fiber manufacturing apparatus and a cellulose fiber manufacturing method according to one embodiment of the present invention will be described with reference to the drawings. Note that the embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0026] In the following embodiments, cellulose nanofibers (CNF) refer to cellulose nanofibers (CNFs) obtained by defibrating plant materials, which consist of cellulose microfibrils (single nanofibers) consisting of crystalline, quasi-crystalline, and amorphous portions, or aggregates of longitudinally torn, tangled, or mesh-like structures, with a diameter of 2 to 100 nm, an aspect ratio of 10 or more, and a length of 200 μm or less. In the present specification, when A to B are used, both the end values ​​A and B of the numerical value are included, unless otherwise specified, and the range is from A to B.

[0027] (Cellulose fiber production apparatus) Figure 1 is a schematic cross-sectional view showing a cellulose fiber production apparatus according to one embodiment of the present invention. The cellulose fiber production apparatus 10 of this embodiment is equipped with a flow path 11 extending along a longitudinal direction L, which is a vertical direction. The flow path 11 constitutes a pipe through which a raw material liquid containing cellulose nanofibers flows from the upstream side (upper side or one side) to the downstream side (lower side or the other side) of the longitudinal direction L. The cross section of this flow path 11 perpendicular to the longitudinal direction L is rectangular.

[0028] If the cross section perpendicular to the longitudinal direction L of the flow channel 11 is rectangular, for example, when the raw material solution in which the orientation direction of the cellulose nanofibers has been aligned is flowed from the lower end of the flow channel 11 into a liquid bath containing a coagulation liquid (coagulation tank 21) (coagulation step), strong surface tension acts on the corners of the rectangle, making it possible to obtain cellulose fibers with a cross section that is closer to a perfect circle. When injecting this raw material solution, the raw material solution may be flowed into a liquid bath containing a coagulation liquid (coagulation tank 21) (coagulation step), or the solution containing the coagulation liquid may be injected from the side of the flow channel.

[0029] In this embodiment, the flow path 11 is made of a dielectric material, such as an acrylic resin material, with a long hole formed therein to serve as the flow path 11. By making the cross section of the flow path 11 perpendicular to the longitudinal direction L rectangular, for example, when the raw material liquid in which the orientation direction of the cellulose nanofibers is aligned is flowed from the lower end of the flow path 11 into a liquid tank containing a coagulation liquid (coagulation process), strong surface tension acts on the corners of the rectangle, making it possible to obtain cellulose fibers with a cross section that is closer to a perfect circle.

[0030] Furthermore, when the cross-sectional shape of the flow path 11 perpendicular to the longitudinal direction L is rectangular, it can be formed from stacked plate-shaped members, as described below (see Figure 2), which makes it easier to manufacture the cellulose fiber manufacturing apparatus 10 compared to when the cross-sectional shape of the flow path is circular or the like.

[0031] The cross-sectional shape of the flow channel 11 perpendicular to the longitudinal direction L may be a rectangle with rounded corners. The cross-sectional shape of the flow channel perpendicular to the longitudinal direction L is not limited to a rectangle as in this embodiment, and may be, for example, a perfect circle, an ellipse, a hexagon, a polygon, or the like. Any cross-sectional shape may be used as long as the raw material liquid flowing from the upstream side to the downstream side does not generate significant turbulence inside the flow channel.

[0032] The flow path 11 is composed of an upstream section 12 (first region), a downstream section 13 (second region), and a throttle section 14 (third region) connecting the upstream section 12 and the downstream section 13. A coagulation liquid injection pipe 15 is connected to the downstream section 13. Note that the coagulation liquid injection pipe 15 may not be connected to the flow path of the downstream section 13, and a coagulation liquid tank storing the coagulation liquid may be provided at the end of the downstream section 13. A supply pipe 16 that supplies the raw material liquid into the flow path 11 may be connected to the upper end of the upstream section 12.

[0033] The upstream section 12 has a rectangular cross section perpendicular to the longitudinal direction L and extends along the longitudinal direction L with a constant cross-sectional area. The downstream section 13 has a rectangular cross section perpendicular to the longitudinal direction L and extends along the longitudinal direction L with a smaller cross-sectional area than the upstream section 12.

[0034] In this embodiment, the rectangular cross-sectional shape of the downstream section 13 is such that one pair of opposing sides of the rectangular cross-sectional shape of the upstream section 12 are shorter in length and the other pair of sides are the same in length, thereby making the cross-sectional area of ​​the downstream section 13 smaller than the cross-sectional area of ​​the upstream section 12. Alternatively, the rectangular cross-sectional shape of the downstream section may be such that both pairs of opposing sides constituting the rectangular cross section of the upstream section are shorter in length.

[0035] The constricted section 14 has a rectangular funnel shape in which the cross-sectional area perpendicular to the longitudinal direction L gradually decreases from the upstream side connected to the upstream section 12 toward the downstream side connected to the downstream section 13. The constricted section 14 gradually narrows the cross-sectional area of ​​the upstream section 12 to the smaller cross-sectional area of ​​the downstream section 13.

[0036] In this embodiment, the throttle section 14 narrows the cross-sectional area of ​​the flow path 11 so that the ratio (S1 / S2) of the cross-sectional area S1 of the upstream section 12 to the cross-sectional area S2 of the downstream section 13 is 1.5 or more. More preferably, the cross-sectional area ratio of the downstream section 13 to the upstream section 12 is 3.0 or more.

[0037] If the cross-sectional area ratio of the downstream section 13 to the upstream section 12 is less than 1.5, there is a concern that the effect of controlling the orientation of cellulose nanofibers by forming an elongational flow field, which will be described later, will be reduced. Also, if the cross-sectional area ratio of the downstream section 13 to the upstream section 12 is greater than 5.0, there is a concern that turbulence will occur due to a significant change in flow velocity caused by a sudden decrease in cross-sectional area.

[0038] In the present embodiment, the constriction section 14 has two opposing surfaces constituting the inner surface of the constriction section 14 that are inclined surfaces 14a, so that the length of one pair of opposing sides of the flow path 11, which has a rectangular cross section, is shortened and the length of the other pair of sides is the same.

[0039] It is preferable that the inclination angle θ of such an inclined surface 14a with respect to the central axis Cp along the longitudinal direction L of the flow channel 11 is in the range of 5° or more and 30° or less. If the inclination angle θ exceeds 30° and approaches a right angle, vortexes are more likely to occur near the constricted section 14, which may disrupt the orientation of the cellulose nanofibers. Furthermore, if the inclination angle θ is less than 5°, there is a concern that the effect of controlling the orientation of the cellulose nanofibers may be reduced. By setting the inclination angle θ within the above range, it is possible to prevent the raw material liquid from stagnating in the constricted section 14 or the flow of the raw material liquid from becoming unstable, thereby disrupting the orientation.

[0040] A plurality of electrodes 17 are formed in the flow channel 11 to form an electric field within the flow channel through which the raw material liquid flows. These electrodes 17 need only be formed in at least the upstream section 12, and preferably also in the downstream section 13. In this embodiment, the electrodes 17 are formed in both the upstream section 12 and the downstream section 13. It is also possible to form an electrode 17 in the constricted section 14. These electrodes 17 provide the effect of controlling the orientation of cellulose nanofibers by forming an electric field, as described below.

[0041] In this embodiment, the electrode 17 is made of a metal foil, for example, copper tape, and is formed on the outer surface of the material forming the flow channel 11. As a result, if a dielectric, for example, an acrylic resin material, is used as the material forming the flow channel 11, a dielectric layer serving as the material forming the flow channel 11 is disposed between the electrode 17 and the inner surface of the flow channel 11 that comes into contact with the raw material liquid. If a dielectric layer is disposed between the inner surface of the flow channel 11 and the electrode 17, it is possible to suppress the outflow of ions or impurities from the electrode to the fluid flowing within the flow channel 11. It is also possible to provide an electrode that forms an electric field on the inner surface of the flow channel 11, and cover the exposed electrode with a dielectric layer such as a resin film.

[0042] In this embodiment, an AC power supply (not shown) is connected to the electrode 17, and an AC electric field is formed in the flow channel 11. Note that a DC power supply may be connected to the electrode 17, and a DC electric field may be formed in the flow channel 11.

[0043] 2 is a photograph showing an actual configuration of the cellulose fiber production apparatus of this embodiment. For example, the cellulose fiber production apparatus 10 is composed of five stacked plate-shaped members A to E made of acrylic resin. Of these, member C, located in the middle, has a long groove formed to form the flow path 11. The width of this long groove is made different between the upper and lower parts, and a portion where the groove width is narrowed is formed between them, thereby forming the upstream section 12, downstream section 13, and constricted section 14 that make up the flow path 11.

[0044] Furthermore, copper tape constituting the electrode 17 is attached in a ladder shape to members B and D, which sandwich member C from both sides. By forming such copper tape on the outer surfaces of members B and D, members B and D themselves function as dielectric layers disposed between the copper tape (electrode 17) and the long groove (flow path 11) of member A. By integrating these members B, C, and D with screws and nuts so that they are sandwiched between members A and E from both sides, the cellulose fiber production apparatus 10 of this embodiment can be formed.

[0045] The above embodiment has been described assuming that the manufacturing apparatus 10 is used in an upright position, but the manner in which the manufacturing apparatus 10 is placed during use is not particularly limited. The manufacturing apparatus 10 may be used in a position parallel to a horizontal placement surface. The manufacturing apparatus 10 may also be used in a position inclined relative to a horizontal placement surface.

[0046] (Method for producing cellulose fibers) A method for producing cellulose fibers according to this embodiment using the cellulose fiber production apparatus configured as described above will now be described. When producing cellulose fibers using the cellulose fiber production apparatus 10 configured as shown in Figure 1, first, a raw material liquid is prepared. The raw material liquid may be any liquid containing cellulose nanofibers.

[0047] In this embodiment, to produce the raw material solution, first, natural cellulose made from plant materials (woody materials, etc.) is dispersed in water, and a catalytic amount of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) is added to the dispersion and the pH is adjusted to 10 to 11. After that, an aqueous solution of sodium hypochlorite is added at room temperature and the mixture is stirred to dissolve the cellulose, thereby obtaining TEMPO-oxidized cellulose fibers.

[0048] Because these TEMPO-oxidized cellulose fibers made from natural cellulose maintain their original fiber shape, they can be easily cleaned and purified by filtration, and can be squeezed and stored or transported at a high solids content. By diluting and dispersing these TEMPO-oxidized cellulose fibers in water to a solids concentration of 0.1 to 2%, and then subjecting them to a defibration process using a mixer or similar, a transparent, highly viscous gel-like liquid containing dispersed cellulose nanofibers is obtained. The cellulose nanofibers contained in this liquid are in a state of random longitudinal orientation.

[0049] Next, the raw material liquid Q is introduced into the flow path 11 from a supply pipe 16 connected to the upstream portion 12 of the flow path 11 of the cellulose fiber production apparatus 10. The raw material liquid Q flows down inside the flow path 11 from the upstream side to the downstream side of the flow path 11. The flow of the raw material liquid Q may be a natural flow due to its own weight, or a pressurized flow using a pump or the like.

[0050] The flow rate of the raw material liquid Q flowing through the flow path 11 may be in the range of 10 to 500 mL / hour or less, or in the range of 50 to 400 mL / hour or less, or in the range of 100 to 300 mL / hour or less.

[0051] When an alternating current is applied to the electrode 17 formed in the upstream section 12, the longitudinal direction of the cellulose nanofibers introduced into the flow path 11 begins to align and become oriented in the longitudinal direction L of the flow path 11 due to the action of an alternating current electric field formed inside the flow path 11. Note that the alternating current used to form this electric field may be applied at different power values ​​(current, voltage) to the electrode 17 formed in the upstream section 12 and the electrode 17 formed in the downstream section 13.

[0052] Then, the raw material liquid Q that flows from the upstream section 12 into the constricted section 14 is aligned so that the longitudinal direction of each cellulose nanofiber approaches the longitudinal direction L of the flow channel 11 even more due to the action of an elongational flow field formed by the flow channel constriction, in which the cross-sectional area of ​​the flow channel 11 gradually decreases downstream (second orientation step). Here, an elongational flow field is a flow field in which the fluid is stretched into elongated shapes by an elongational flow, and in such an elongational flow field, elongated particles are oriented in the direction of the fluid flow due to the elongational flow effect and shear flow effect.

[0053] Then, the raw material liquid Q flows from the constriction section 14 into the downstream section with a smaller cross-sectional area, and the orientation direction of the cellulose nanofibers is further aligned in the longitudinal direction L of the flow path 11 by the action of the alternating electric field formed by the electrode 17 formed in the downstream section 13, and near the lower end of the downstream section 13, most of the cellulose nanofibers are oriented along the longitudinal direction L of the flow path 11.

[0054] In the first and second alignment steps, the voltage applied to the electrode 17 is 0.5 to 10.0 kV. ｐｐ and 1.0 to 8.0 kV ｐｐ and may be in the range of 2.0 to 6.0 kV. ｐｐ may be in the range of

[0055] The raw material liquid Q containing cellulose nanofibers oriented along the longitudinal direction L is then coagulated into cellulose fibers F with a fiber diameter approximately equal to the width of the downstream section 13 by, for example, a coagulation liquid S injected into the flow path 11 through a coagulation liquid injection pipe 15 connected to the downstream section 13 (coagulation step). For example, dilute hydrochloric acid or a solution containing polyvalent metal ions can be used as the coagulation liquid S, which promotes hydrogen bonding and allows the cellulose nanofibers to aggregate into a fibrous form.

[0056] Alternatively, the coagulation liquid injection pipe 15 may not be connected to the flow path of the downstream section 13, and a coagulation liquid tank storing coagulation liquid may be provided at the end of the downstream section 13. In this case, the raw material liquid Q, in which the orientation direction of the cellulose nanofibers is aligned with the longitudinal direction L of the flow path 11 and flows out from the end of the downstream section 13, immediately comes into contact with the coagulation liquid after flowing out and is coagulated as cellulose fibers F with a fiber diameter approximately equal to the width of the flow path of the downstream section 13 (coagulation process).

[0057] The first orientation step, the second orientation step, and the solidification step may be performed at room temperature (for example, 18 to 25°C). The first orientation step, the second orientation step, and the solidification step may be performed at a constant temperature, or may be performed at different temperatures depending on the step. The solidification step may be performed within a temperature range of 10 to 50°C.

[0058] The cellulose fiber F obtained in this manner has an orientation rate, which is the proportion of cellulose nanofibers oriented in the longitudinal direction of the total cellulose nanofibers contained therein, of 90% or more. The cellulose fiber F obtained by the cellulose fiber production method of this embodiment has higher tensile strength and excellent toughness compared to cellulose fibers having a lower orientation rate of cellulose nanofibers. In addition, the cellulose fiber F has a high elastic modulus and is easy to process, and woven fabrics using such cellulose fiber can be easily formed.

[0059] In this embodiment, a solution containing cellulose nanofibers is used as the raw material liquid, but it is also preferable to use a raw material liquid that further contains carbon nanotubes and metal nanoparticles in addition to cellulose nanofibers.

[0060] For example, when cellulose fibers are formed using a raw material solution containing carbon nanotubes in addition to cellulose nanofibers, electrically conductive cellulose fibers having a structure in which carbon nanotubes are wrapped around the cellulose nanofibers are obtained.

[0061] Conventionally, a problem with conductive cellulose fibers has been that there is a trade-off between conductivity and tensile strength. However, by using the cellulose fiber manufacturing method of this embodiment, it is possible to control the orientation of the raw material liquid containing cellulose nanofibers and carbon nanotubes, and to realize carbon nanotube-containing cellulose fibers with high conductivity and high tensile strength.

[0062] Furthermore, when cellulose fibers are formed using a raw material solution containing, in addition to cellulose nanofibers, metal nanoparticles, such as silver nanoparticles, it is possible to obtain electrically conductive cellulose fibers with a structure in which silver nanoparticles are attached to the cellulose nanofibers. By supporting silver nanoparticles on the cellulose fibers in this way, it is also possible to impart antibacterial properties to the cellulose fibers.

[0063] The average particle size of the nanoparticles (including carbon nanotubes) supported on the cellulose fibers may be 1 to 1000 nm, 10 to 1000 nm, or 100 to 500 nm.

[0064] The average diameter of the cellulose fibers may be 10 to 500 μm, 20 to 400 μm, or 50 to 200 μm.

[0065] The average length of the cellulose fibers may be 1 to 10 m, 1 to 100 cmμm, or 1 to 10 cm.

[0066] The silver content in the cellulose fibers carrying silver nanoparticles may be in the range of 1.0 to 10.0 mass%, may be in the range of 2.0 to 9.0 mass%, or may be in the range of 3.0 to 8.0 mass%.

[0067] The elastic modulus of the cellulose fibers may be in the range of 3 to 40 GPa, may be in the range of 4 to 8 GPa, or may be in the range of 4 to 7 GPa.

[0068] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims.

[0069] Below, cellulose fibers were actually produced and their properties were examined. (Example 1) Figure 3 shows the configuration of the cellulose fiber production apparatus used for the verification and the production conditions. As shown in Figure 4, in Comparative Example 1, a flow path was formed in which the cross-sectional area ratio of the upstream portion to the downstream portion was 1.0, i.e., no constricted portion was formed. In addition, in Inventive Example 1, a flow path was formed in which the cross-sectional area ratio of the upstream portion to the downstream portion was 1.5. Furthermore, in Inventive Example 2, a flow path was formed in which the cross-sectional area ratio of the upstream portion to the downstream portion was 3.0.

[0070] Cellulose fibers were produced using a cellulose fiber production apparatus having each of these flow paths. SEM photographs of the cellulose fibers (samples) obtained in Comparative Example 1 and Invention Examples 1 and 2 are shown in FIG.

[0071] The tensile strength (UTS), modulus of elasticity (EM), and toughness (TN) of the cellulose fibers of each sample were then measured. The results are shown in the graph in FIG. 6. According to the results shown in FIG. 6, the cellulose fiber of Inventive Example 1 had a tensile strength (UTS) that was approximately 15% higher than that of the cellulose fiber of Comparative Example 1, and the cellulose fiber of Inventive Example 2 had a tensile strength (UTS) that was approximately 42% higher than that of the cellulose fiber of Comparative Example 1. Furthermore, the cellulose fiber of Inventive Example 2 had a modulus of elasticity (EM) that was approximately 28% higher than that of the cellulose fiber of Comparative Example 1. Furthermore, the cellulose fiber of Inventive Example 2 had a toughness (TN) that was approximately 15% higher than that of the cellulose fiber of Comparative Example 1.

[0072] As described above, it has been confirmed that the cellulose fiber manufacturing method using the cellulose fiber manufacturing apparatus of this embodiment can produce cellulose fibers with excellent tensile strength, elastic modulus, and toughness by controlling orientation using an electric field and by controlling orientation using an elongational flow field formed by the squeezing section.

[0073] Example 2 Cellulose fibers carrying silver nanoparticles were prepared by the method described below, and their antibacterial properties were evaluated.

[0074] Tollens reagent (Ag(NH)) was used to prepare silver nanoparticles. ３ ) ２Five types of samples were prepared: a sample consisting of only cellulose nanofiber dispersion DS (concentration: 0.3% by mass) (hereinafter referred to as "raw material solution S11"), a sample in which CNF and Tollens reagent were mixed at a mixing ratio of 4.9:0.1 (hereinafter referred to as "raw material solution S12"), a sample in which CNF and Tollens reagent were mixed at a mixing ratio of 4.7:0.3 (hereinafter referred to as "raw material solution S13"), a sample in which CNF and Tollens reagent were mixed at a mixing ratio of 4.5:0.35 (hereinafter referred to as "raw material solution S14"), and a sample in which CNF and Tollens reagent were mixed at a mixing ratio of 4.3:0.7 (hereinafter referred to as "raw material solution S15").

[0075] Using raw material solutions S11 to S15 as raw material solutions, cellulose fibers were produced in the same manner as in Example 1, unless otherwise specified. The following conditions were used for producing cellulose fibers in Example 2: Cross-sectional area ratio of the upstream portion to the downstream portion: 3.0 Flow rate: 180 mL / hour Applied voltage: 0 kV ｐｐ (When not applied) / 5kV ｐｐ (When voltage is applied) Electrodes: 5 (3 ground electrodes, 2 voltage application electrodes) Coagulant: 1 mol / L HCl aqueous solution

[0076] The cellulose fibers produced from the raw material solutions S11 to S15 without applying voltage to the electrodes were designated as Comparative Examples 11 to 15, respectively. The cellulose fibers produced from the raw material solutions S11 to S15 with applying voltage to the electrodes were designated as Invention Examples 11 to 15, respectively.

[0077] Figure 7 shows an SEM photograph of the cellulose fibers of Example 2. The surface of the short cellulose fibers of Examples 1 and 2 had streaky irregularities, and the CNFs were bundled and oriented in the axial direction. Furthermore, silver nanoparticles of 200 to 700 nm were distributed almost uniformly inside the fibers.

[0078] The tensile strength (UTS), elastic modulus (EM), and toughness (TN) of the cellulose fibers of Comparative Examples 11 to 15, which were conducted without applying voltage to the electrode 17, and of Inventive Examples 11 to 15, which were conducted with applying voltage to the electrode 17, were measured. The results are shown in graphs in Figures 8 and 9, respectively. The results shown in Figures 8 and 9 show that the cellulose fibers of Inventive Examples 11 to 15 had significantly higher or at least equivalent tensile strength (UTS), elastic modulus (EM), and toughness (TN) than the cellulose fibers of Comparative Examples 11 to 15.

[0079] In Example 15 of the present invention, the difference between Comparative Example 15 and Comparative Example 15 was greatest depending on whether or not an electric field was applied to the electrode 17. In the cellulose fibers of Comparative Example 15, which had the highest amount of Tollens reagent added, the presence of excess silver nanoparticles impaired the affinity between CNFs, and it is thought that sufficiently oriented cellulose fibers could not be produced without an electric field. On the other hand, when the same raw material solution S15 was applied to the electrode 17 at 5 kV, ｐｐ In the case of Example 15 of the present invention, in which cellulose fibers were produced using the electrode with a voltage of 100 V, the tensile strength (UTS), elastic modulus (EM) and toughness (TN) were significantly increased.

[0080] This is thought to be because the negative effect of the added silver nanoparticles on the orientation of the cellulose fibers was more effectively counteracted by the application of an electric field.

[0081] In a comparison between Comparative Examples 11 to 14 and Inventive Examples 11 to 14, the cellulose fibers of Inventive Examples 11 to 14 subjected to an electric field exhibited high tensile strength (UTS), elastic modulus (EM), and toughness (TN), although not as high as in the comparison between Comparative Example 15 and Inventive Example 15.

[0082] 10 and 11 are photographs showing the evaluation of the antibacterial effects of the cellulose single fibers of Comparative Example 14 and Inventive Example 14.

[0083] The antibacterial test used Bacillus subtilis (natto), a gram-positive bacterium. The cellulose single fibers of Comparative Example 14 and Inventive Example 14 were each inoculated into a test bacterium solution (30 mL of Tryptic Soy Agar ICR) and cultured with shaking in an incubator at 37°C for 24 hours. The culture solution was then diluted, poured into an agar medium, and cultured statically in an incubator at 37°C for 24 hours.

[0084] A comparison of Figures 10 and 11 shows that antibacterial activity could be imparted to cellulose fibers carrying silver nanoparticles.

[0085] 12 is a graph showing the tensile strength (UTS), elastic modulus (EM), and toughness (TN) of Inventive Examples 11 to 15 and Comparative Example 16 (commercially available chemical fibers). The data for Inventive Examples 11 to 15 in FIG. 12 is the same as that shown in FIG. 9, but the scale of the vertical axis has been changed for comparison with Comparative Example 16, so the bar graph profiles appear significantly different.

[0086] The chemical fiber of Comparative Example 16 was prepared from commercially available drainage stockings (material: polyester, polyurethane, heat resistance temperature: 100°C, cold resistance temperature: -30°C).

[0087] The obtained chemical fiber had an average diameter of 45.7 μm, an average tensile strength (UTS) of 457.7 MPa, an average modulus of elasticity (EM) of 3.7 GPa, an average strain at break of 0.31, and an average toughness (TN) of 100.8 MJ / m ３ The cellulose fibers of Inventions 11 to 15 exhibited lower values ​​(1 / 5 to 1 / 50) of the tensile strength (UTS) and toughness (TN) of Comparative Example 16, which is a chemical fiber. On the other hand, the cellulose fibers of Inventions 11 to 15 exhibited values ​​equivalent to or higher than the chemical fiber of Comparative Example 16 in terms of modulus of elasticity. In particular, the cellulose fibers of Examples 12 to 15, which carried silver nanoparticles, exhibited a modulus of elasticity that was 40% or more higher than that of Comparative Example 16.

[0088] The cellulose fiber production apparatus and cellulose fiber production method of the present invention contribute to the production of cellulose fibers with improved tensile strength, elastic modulus, and toughness by unidirectionally aligning cellulose nanofibers with a simple configuration, and therefore have industrial applicability.

[0089] DESCRIPTION OF SYMBOLS 10 Cellulose fiber manufacturing apparatus 11 Flow path 12 Upstream section 13 Downstream section 14 Throttle section 15 Coagulation liquid injection pipe 16 Supply pipe 17 Electrode (copper electrode) 21 Coagulation tank 22 Amplifier 23 Transmitter 31 Syringe pump 32 Rectangular flow path 33 Acrylic 34 Polystyrene plate (t=0.2 mm) 35 Ground electrode 36 High voltage electrode DS Cellulose nanofiber dispersion (raw material liquid)

Claims

1. A cellulose fiber production device comprising a flow path for flowing a raw material liquid containing cellulose nanofibers from the upstream side to the downstream side, the flow path having an upstream section that extends with a constant cross-sectional shape and cross-sectional area perpendicular to the longitudinal direction, a downstream section that extends with a smaller cross-sectional area perpendicular to the longitudinal direction than the upstream side, and a constriction section that connects the upstream section and the downstream section and whose cross-sectional area perpendicular to the longitudinal direction gradually decreases towards the downstream side, and at least the upstream section has electrodes that form an electric field inside the flow path.

2. The cellulose fiber manufacturing apparatus according to claim 1, characterized in that the ratio of the cross-sectional area of ​​the upstream portion to the cross-sectional area of ​​the downstream portion is 1.5 or more.

3. The cellulose fiber manufacturing apparatus according to claim 1 or 2, characterized in that the electrodes are formed in both the upstream portion and the downstream portion.

4. An apparatus for producing cellulose fiber as described in claim 1 or 2, characterized in that an alternating current is applied to the electrodes.

5. The cellulose fiber manufacturing apparatus according to claim 1 or 2, characterized in that a dielectric layer is formed between the electrodes and the inner surface of the flow path.

6. A cellulose fiber manufacturing apparatus as described in claim 1 or 2, characterized in that the cross-sectional shape of the flow path perpendicular to the longitudinal direction is rectangular.

7. A cellulose fiber manufacturing apparatus as described in claim 1 or 2, characterized in that the inclination angle of the inner surface of the constriction section with respect to the central axis along the longitudinal direction of the flow path is in the range of 5° or more and 30° or less.

8. A cellulose fiber manufacturing apparatus as described in claim 1 or 2, characterized in that the total length of the flow path from the inlet to the outlet is within the range of 50 to 500 mm, the length of the upstream portion is within the range of 50 to 90% of the total length of the flow path, the length of the downstream portion is within the range of 9 to 40% of the total length of the flow path, and the length of the constriction portion is within the range of 1 to 10% of the total length of the flow path.

9. A method for producing cellulose fibers using the cellulose fiber production apparatus described in claim 1 or 2, comprising at least a first orientation step in which an electric field formed by a current applied to the electrodes is used to orient the longitudinal direction of the cellulose nanofibers so that they align with the longitudinal direction of the flow path; a second orientation step in which an elongational flow field generated by the constriction section is used to orient the longitudinal direction of the cellulose nanofibers so that they align with the longitudinal direction of the flow path; and a coagulation step in which the raw material liquid that has undergone the first orientation step and the second orientation step is brought into contact with a coagulation liquid to coagulate it, thereby obtaining the cellulose fibers.

10. The method for producing cellulose fibers as described in claim 9, characterized in that the raw material liquid contains, in addition to the cellulose nanofibers, at least one of carbon nanotubes and metal nanoparticles.

11. The method for producing cellulose fiber according to claim 9, characterized in that the coagulation liquid is a solution containing hydrochloric acid or polyvalent metal ions.

12. In the first orientation process, 0.2 to 10 kV ｐｐ 10. The method of claim 9, wherein a voltage in the range of is applied to the electrodes.

13. The method for producing cellulose fibers according to claim 9, characterized in that the flow rate of the raw material liquid flowing through the flow path is within the range of 10 to 500 mL / hour.

14. A method for producing cellulose fibers as described in claim 9, characterized in that the concentration of the cellulose nanofibers contained in the raw material liquid is within the range of 0.03 to 3 mass%.

15. A cellulose fiber containing silver nanoparticles, the silver content being within the range of 1.0 to 10.0 mass %.

16. The cellulose fiber according to claim 15, characterized in that the elastic modulus is within the range of 4 to 40 GPa.

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