WO2022102671A1 - Titanium oxide-cellulose fiber composite material and method for producing same - Google Patents

Abstract

The present invention addresses the problem of providing a method which is for producing a titanium oxide-cellulose fiber composite material and is a low environmental load process, and by which a composite material having higher durability than conventional composite materials is obtained.　A method for producing a titanium oxide-cellulose fiber composite material according to the present invention comprises: (P1) preparing a cellulose fiber, and an aqueous solution containing ammonium fluorotitanate, boric acid, and water; and (P2, P3) precipitating titanium oxide on the surface of the cellulose fiber in the aqueous solution.

Description

Titanium oxide / cellulose fiber composite material and its manufacturing method Cross-reference to related applications

This application is based on Japanese Patent Application No. 2020-187264 filed on November 10, 2020, the contents of which are incorporated herein by reference.

The present invention relates to a titanium oxide / cellulose fiber composite material and a method for producing the same.

Nanocellulose obtained by nanoscaled cellulose, which has been used as paper and cotton, has new functions such as high strength, viscosity, and thermal stability, and is expected to be used in various applications such as food, packaging, and diaphragms. There is.

As an application example of nanocellulose, there is a composite material having a photocatalytic function by titanium oxide and cellulose fiber. In Patent Document 1, a polymer nanofiber sheet produced by an electrospinning method is alternately dipped in a positive electrolyte polymer aqueous solution in which TiO ₂ fine particles are dispersed and a negative electrolytic polymer aqueous solution in which TiO ₂ fine particles are dispersed. Thereby, the TiO ₂ fine particles fixed to the surface of each nanofiber constituting the sheet by the first charged polymer layer having a positive charge and the second charged polymer layer having a negative charge are fixed to the surface. Described is a nanofiber sheet having a laminated TiO ₂ fine particle coating layer formed by alternately laminating the TiO ₂ fine particles.

Non-Patent Document 1 has a TiO ₂ fine particle coating layer obtained by ultrasonically dispersing TiO ₂ fine particles and algae-derived cellulose in acetone and drying them in an environment of 70 ° C. using an oven. Fiber sheets are listed.

Japanese Unexamined Patent Publication No. 2005-264386

However, the conventional method for producing a composite material described above is a method of synthesizing a titanium oxide material having a photocatalytic function and then physically adsorbing the titanium oxide material to the cellulose material. Since the titanium oxide material is adsorbed to the cellulose material, the titanium oxide material is easily peeled off from the cellulose material. For this reason, conventional composite materials have low durability. Further, the synthesis of titanium oxide is carried out by a high temperature process such as 1000 ° C. at normal pressure or a high pressure process such as a hydrothermal synthesis method in which the pressure is higher than normal pressure. Therefore, the conventional method for manufacturing a composite material requires a large amount of energy and has a large environmental load. These things can be said not only when nanocellulose is used as the cellulose material, but also when cellulose fibers other than nanocellulose are used.

An object of the present invention is to provide a titanium oxide / cellulose fiber composite material which is more durable than a conventional composite material and has a photocatalytic function. Further, the present invention is a method for producing a titanium oxide / cellulose fiber composite material having a photocatalytic function, wherein a composite material having higher durability than a conventional composite material can be obtained, and titanium oxide / cellulose oxide is a low environmental load process. Another object is to provide a method for producing a fiber composite material.

According to the invention of claim 1, the titanium oxide / cellulose fiber composite material includes cellulose fiber and titanium oxide that covers at least a part of the surface of the cellulose fiber. Titanium oxide coats the surface of the cellulose fiber by being synthesized directly with respect to the surface of the cellulose fiber. According to this, since titanium oxide is synthesized directly on the surface of the cellulose fiber, it is possible to provide a titanium oxide-cellulose fiber composite material which is more durable than the conventional composite material and has a photocatalytic function. can.

According to the invention of claim 3, the titanium oxide / cellulose fiber composite material includes cellulose fiber and titanium oxide that covers at least a part of the surface of the cellulose fiber. The adsorption force of titanium oxide on the cellulose fiber is 4.4 N / 10 mm or more. According to this, since the adsorption force of titanium oxide to the cellulose fiber is 4.4 N / 10 mm or more, the titanium oxide / cellulose fiber composite material having higher durability than the conventional composite material and having a photocatalytic function is provided. be able to.

According to the invention of claim 7, the method for producing the titanium oxide / cellulose fiber composite material is a method of directly synthesizing titanium oxide on the surface of the cellulose fiber by the liquid phase precipitation method. According to this, titanium oxide is directly synthesized on the surface of the cellulose fiber. Furthermore, titanium oxide can be synthesized at low temperature and normal pressure by the liquid phase precipitation method, and the energy required for the synthesis of titanium oxide can be suppressed to a small value. Therefore, a composite material having higher durability than the conventional composite material can be obtained, and a method for producing a titanium oxide / cellulose fiber composite material, which is a low environmental load process, can be provided.

According to the invention of claim 8, the method for producing the titanium oxide / cellulose fiber composite material is to prepare an aqueous solution containing titanium fluoride ammonium fluoride, boric acid and water, cellulose fiber (P1), and an aqueous solution. Among them, the precipitation of titanium oxide on the surface of the cellulose fiber (P2, P3) is included. According to this, titanium oxide is directly synthesized on the surface of the cellulose fiber. Furthermore, titanium oxide can be synthesized at low temperature and normal pressure by the liquid phase precipitation method, and the energy required for the synthesis of titanium oxide can be suppressed to a small value. Therefore, a composite material having higher durability than the conventional composite material can be obtained, and a method for producing a titanium oxide / cellulose fiber composite material, which is a low environmental load process, can be provided.

It is a figure which showed the cellulose fiber schematically. It is a figure which shows schematically the titanium oxide-cellulose fiber composite material which comprises a cellulose fiber and titanium oxide which covers at least a part of the surface of the cellulose fiber. It is a figure which showed the example of the synthesis procedure of the titanium oxide / nanocellulose fiber composite material. It is a figure which showed schematically the mechanism which TiO ₂ is synthesized on the surface of a cellulose fiber. It is an SEM image of the nanocellulose fiber derived from a broad-leaved tree. It is a figure which showed the XRD pattern of the nanocellulose fiber derived from a broad-leaved tree, and the XRD pattern of a titanium oxide / nanocellulose fiber composite material which has a nanocellulose fiber derived from a broad-leaved tree and anatase type titanium oxide nanoparticles. It is a figure which showed the Raman spectrum of each of the titanium oxide / nanocellulose fiber composite material derived from broad-leaved tree, derived from coniferous tree, or chemical pulp. It is an SEM image of the titanium oxide / nanocellulose fiber composite material derived from hardwood. FIG. 5A is an enlarged view of titanium oxide covering the titanium oxide / nanocellulose fiber of FIG. 5A. 6 is an SEM image of a titanium oxide / nanocellulose fiber composite material derived from a hardwood of Example 1 before being subjected to ultrasonic waves. It is an SEM image of the titanium oxide / nanocellulose fiber composite material derived from the hardwood of Example 1 after being subjected to ultrasonic waves. 6 is an SEM image of the TiO ₂ / nanocellulose fiber composite material of Comparative Example 1 before being subjected to ultrasonic waves. It is an SEM image of the TiO ₂ / nanocellulose fiber composite material of Comparative Example 1 after being subjected to ultrasonic waves. It is an SEM image of the nanocellulose fiber / titanium oxide composite material derived from the coniferous tree of Example 2. 6 is an SEM image of a titanium oxide / nanocellulose fiber composite material derived from seaweed in Non-Patent Document 1. FIG. 7A is an enlarged view of a part of FIG. 7A. It is an SEM image of the titanium oxide / nanocellulose fiber composite material derived from the chemical pulp of Example 3. A part of FIG. 9A is enlarged. It is a figure which showed the photocatalytic effect for each of the nanocellulose fiber, the titanium oxide / nanocellulose fiber composite material of chemical pulp, and the titanium oxide / nanocellulose fiber composite material derived from coniferous tree. It is an SEM image of cotton as a cellulose fiber. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Example 4. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Example 4. It is a schematic diagram which shows the state of the peeling test. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Example 4 before the peeling test. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Example 4 after the peeling test using the first tape. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Example 4 before the peeling test using the second tape. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Comparative Example 2 before the peeling test. 6 is an SEM image of the TiO ₂ / cellulose fiber composite material of Comparative Example 2 after the peeling test using the first tape. It is an SEM image of the TiO ₂ / cellulose fiber composite material of Comparative Example 2 before the peeling test using the second tape.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

As shown in FIG. 1B, the titanium oxide / cellulose fiber composite material 2 according to the embodiment of the present invention includes the cellulose fiber 1 shown in FIG. 1A and the titanium oxide nano-titanium oxide that covers at least a part of the surface of the cellulose fiber 1. The particle 3 is provided.

The cellulose fiber 1 is not particularly limited as long as the cellulose has a fiber shape. From the viewpoint of increasing the effective area of the photocatalyst, it is preferable to use nanocellulose fiber having a large specific surface area as the cellulose fiber 1. Nanocellulose fiber is a general term for cellulose having a diameter of 1 nm or more and 100 nm or less. Nanocellulose fibers are obtained by finely loosening cellulose fibers that are the source of plant origin, etc., using various physical and chemical methods. Nanocellulose fibers are characterized by having a large surface area (specific surface area) per unit mass (120-150 m ² / g), a low coefficient of thermal expansion, and transparency as compared with cellulose fibers.

The titanium oxide nanoparticles 3 have a photocatalytic function. The titanium oxide nanoparticles 3 are particles having a spherical outer shape. Sphere shapes include spheres, ellipsoids, and similar shapes. The particle size of the particles is 90 nm or more and 400 nm or less. The titanium oxide nanoparticles 3 have a plurality of protrusions. The shape of each of the plurality of protrusions is a cone shape having a width of 20 nm or more and 40 nm or less and a length of 20 nm or more and 60 nm or less. The titanium oxide that covers the surface of the cellulose fiber 1 is not limited to the shape of the particles, and may be in the shape of a plate.

The nanocellulose fiber composite material can be synthesized by the typical synthesis procedure shown in FIG. 2A. In step P1, ammonium titanium fluoride ((NH ₄ ) ₂ TiF ₆ ) and boric acid (H ₃ BO ₃ ) are mixed in equal volumes to prepare a mixed solution. The molar concentration ratio is ammonium titanium fluoride: boric acid = 0.1: 0.3. The molar concentration ratio is not limited to this. The molar concentration ratio of ammonium titanium fluoride: boric acid is preferably 0.05 to 0.2: 0.05 to 0.3 from the viewpoint of obtaining anatase-type titanium oxide having excellent crystallinity and a high photocatalytic effect. , 0.1: 0.1 to 0.1: 0.3 are more preferable.

As described above, in step P1, an aqueous solution containing ammonium titanium fluoride, boric acid and water is prepared. Further, in step P1, a nanocellulose fiber dispersion solution in which nanocellulose fibers are dispersed in water is prepared.

In step P2, the nanocellulose fiber dispersion solution is added to the prepared mixed solution. For example, the nanocellulose fiber dispersion solution to be added is, for example, 20 mL. The concentration of the cellulose fiber is preferably 0.02 to 0.2% by mass from the viewpoint of the dispersibility of the cellulose fiber.

In step P3, the mixture containing the nanocellulose fibers according to step P2 is stirred at a heating temperature of, for example, 60 ° C. for 3 hours. From the viewpoint of synthesizing highly crystalline anatase titanium oxide with good reproducibility, the heating temperature is preferably 45 to 75 ° C. The stirring time is preferably 3 hours from the viewpoint of obtaining uniform nano-sized TiO ₂ crystals. Steps P2 and P3 deposit titanium oxide on the surface of the nanocellulose fiber in an aqueous solution. That is, titanium oxide is directly synthesized on the surface of the nanocellulose fiber by the liquid phase precipitation method.

In step P4, following step P3, stirring is performed at room temperature for 24 hours. As a result, the TIO ₂ / nanocellulose fiber composite material and the titanium oxide particles in the aqueous solution are separated. By the process up to step P4, the TiO ₂ / nanocellulose fiber composite material is synthesized. Then, in step P5, the _TiO2 / nanocellulose fiber composite material is washed with water.

Since the liquid phase precipitation method (LPD synthesis method) is used as in the above step, synthesis at low temperature and normal pressure is possible. The low temperature is a temperature equal to or lower than the boiling point of water. In this way, the energy required for the synthesis of titanium oxide can be kept small. Therefore, the method for producing the titanium oxide / nanocellulose fiber composite material of the present embodiment is a low environmental load process.

In step P2, not only the nanocellulose fiber but also other cellulose fibers may be used. As the cellulose fiber, cotton, mechanical pulp or the like can be used. Further, in step P2, cellulose fibers such as cotton and mechanical pulp may be immersed in the prepared mixed solution. On the other hand, from the viewpoint of increasing the effective area of the photocatalyst, the cellulose fiber used is preferably nanocellulose fiber having a large specific surface area.

In step P3, it is not necessary to heat the mixed solution containing the nanocellulose fiber. Even in this case, titanium oxide can be deposited on the surface of the nanocellulose fiber, although it takes longer than in the case of heating. However, from the viewpoint of enhancing the photocatalytic function, it is preferable to heat in step P3.

The mechanism by which TiO ₂ is synthesized on the surface of the cellulose fiber is presumed as follows. As shown in FIG. 2B, the hydroxyl group on the surface of the cellulose fiber and the water in the solution cause hydrolysis of titanium fluoride ion. That is, the fluorine atom in the titanium fluoride ion is replaced with the oxygen atom in the hydroxyl group and the oxygen atom in the water molecule on the surface of the cellulose fiber by the ligand exchange reaction. At this time, the generated fluorine ions are consumed by the reaction with boric acid. As a result, it is presumed that the titanium oxide precipitation reaction proceeds and titanium oxide nucleation and nanostructure formation are formed on the cellulose surface. In the synthesized TiO ₂ and the cellulose fiber, it is presumed that the Ti atom of TiO ₂ and the O atom of the cellulose fiber are covalently bonded.

As described above, titanium oxide coats the surface of the cellulose fiber by being directly synthesized with respect to the surface of the cellulose fiber. According to this, titanium oxide is chemically bonded to the surface of the cellulose fiber by being directly synthesized with respect to the surface of the cellulose fiber. Therefore, it is possible to provide a titanium oxide / cellulose fiber composite material which is more durable than the conventional composite material and has a photocatalytic function.

(Manufacturing and evaluation of TiO ₂ / nanocellulose fiber composite material of Examples 1 to 3 and Comparative Example 1)
Titanium fluoride ammonium fluoride (manufactured by Fujifilm Wako Junyaku Co., Ltd., first-class reagent), boric acid (manufactured by Fujifilm Wako Junyaku Co., Ltd., special reagent grade), and nanocellulose fiber derived from broadleaf tree as a nanocellulose fiber dispersion solution. _A washed nanocellulose fiber composite derived from broadleaf tree was obtained using a dispersed nanocellulose fiber dispersion solution (manufactured by Daio Paper Co., Ltd., nanocellulose fiber concentration: 15.57% by mass) according to FIG. 2 (manufactured by Daio Paper Co., Ltd., nanocellulose fiber concentration: 15.57% by mass). Example 1, it may be simply referred to as "a reagent derived from a broad _- leaved tree and a nanocellulose fiber composite material").

A nanocellulose fiber washed with a nanocellulose fiber dispersion solution (manufactured by Daio Paper Co., Ltd., nanocellulose fiber concentration: 3.5% by mass) in which nanocellulose fiber derived from coniferous tree is dispersed instead of nanocellulose fiber derived from broadleaf tree. A derived _TiO2 / nanocellulose fiber composite was obtained (Example 2, may be simply referred to as “a conifer-derived _TiO2 / nanocellulose fiber composite material”).

Chemistry washed using a nanocellulose fiber dispersion solution (manufactured by Daio Paper Co., Ltd., nanocellulose fiber concentration: 2.9% by mass) in which nanocellulose fibers of chemical pulp are dispersed instead of nanocellulose fibers derived from broadleaf trees. A TiO ₂ -nanocellulose fiber composite of pulp was obtained (Example 3, may be simply referred to as "TiO ₂ -nanocellulose fiber composite material of chemical pulp").

From the SEM image of FIG. 3A, it was found that the nanocellulose fibers derived from hardwood are as follows. Fibrous cellulose has a form in which each is entangled and aggregated. For example, when compared with a scale of 1 μm, it can be seen that the diameter of one bundle is 50 nm or less. Since the sample of the SEM image is a dry-prepared nanocellulose fiber, it is an aggregate as shown in the figure, but it is considered that each fiber is isolated and dispersed in the aqueous dispersion.

Further, from the XRD pattern of FIG. 3B, a peak of anatase-type titanium oxide nanoparticles (sometimes referred to as "TIO ₂ A") was detected after LPD (liquid phase precipitation method) synthesis. As a result, it was found that anatase-type titanium oxide nanoparticles were precipitated on the surface of _TiO2 / nanocellulose fibers derived from broad-leaved trees, and at least a part of the surface was covered with anatase-type titanium oxide nanoparticles. The measurement conditions and equipment for the Raman spectrum were as follows. The device used was an NRS-3300 micro-Raman spectroscope (RAMAN) manufactured by JASCO Corporation. The excitation laser wavelength was 532 nm and the spectrum acquisition time was 60 seconds.

As shown in the Raman spectrum of FIG. 4, TiO ₂ / nanocellulose fiber composite material derived from broadleaf tree (Example 1), TiO ₂ / nanocellulose fiber composite material derived from coniferous tree (Example 2), TiO ₂ of chemical pulp. -A peak of anatase-type titanium oxide was detected in each of the nanocellulose fiber composite materials (Example 3). The anatase _- type titanium oxide (TiO 2A) peaks are those found at 170 cm ^-1 and 400-650 cm ^-1 . The measurement conditions and equipment for the Raman spectrum were as follows. The device used was an NRS-3300 micro-Raman spectroscope (RAMAN) manufactured by JASCO Corporation. The excitation laser wavelength was 532 nm and the spectrum acquisition time was 60 seconds.

As shown in FIG. 5A, in the TiO ₂ / nanocellulose fiber composite material 12 derived from broadleaf tree, the nanocellulose fiber aggregate fiber 16, the nanocellulose fiber 17 in which the TiO ₂ layer is loosely bonded, and the TiO ₂ are bonded at high density. -Contains nanocellulose fiber composite material 13. Further, as shown in FIG. 5B, the anatase-type titanium oxide nanoparticles 13a had a spherical shape close to the shape of a sphere or an ellipsoid, and an uneven shape was observed on the surface thereof. In other words, the anatase-type titanium oxide nanoparticles 13a have protrusions on the outside thereof. It was also observed that a plurality of anatase-type titanium oxide nanoparticles such as anatase-type titanium oxide nanoparticles 13a gather to form a small aggregate, and a plurality of the small aggregates gather on nanocellulose to form an aggregate. did it. For example, when compared with a scale of 1 μm, it was found that the particle size of the anatase-type titanium oxide nanoparticles 13a was 100 to 400 nm. The particle size here is the maximum width of the particles.

The durability of anatase-type titanium oxide nanoparticles such as anatase-type titanium oxide nanoparticles 23 was investigated for the hardwood-derived _TiO2 -nanocellulose fiber composite material 22 shown in FIG. 6A as follows. The dio ₂ / nanocellulose fiber composite material 22 derived from hardwood was immersed in water and ultrasonically applied at 40 KHz and 300 W for 5 hours (ultrasonic device: SHARP, UT-304F). Nevertheless, as shown in FIG. 6B, anatase-type titanium oxide nanoparticles and anatase-type titanium oxide nanoparticles after being subjected to ultrasonic waves, such as anatase-type titanium oxide nanoparticles 23a of the _TiO2 / nanocellulose fiber composite material 22a derived from broadleaf trees. Even if the anatase-type titanium oxide nanoparticles 23 before applying ultrasonic waves like the particles 23 are compared, no change can be observed between them, and the durability of the anatase-type titanium oxide nanoparticles such as the anatase-type titanium oxide nanoparticles 23 cannot be observed. I was able to confirm the sex. Compared with a scale of, for example, 1 μm, the particle size of the spherical anatase-type titanium oxide nanoparticles 23 is 100 nm at the smallest and 400 nm at the maximum. The size of the protrusions is several tens of nm for any anatase-type titanium oxide nanoparticles 23.

The present inventor produced the _TiO2 / nanocellulose fiber composite material of Comparative Example 1 with reference to the production method described in Non-Patent Document 1. Specifically, anatase-type titanium oxide (Evonik (Degussa) P25) is added to distilled water, and ultrasonic treatment is performed for 15 minutes using an ultrasonic device (SHARP, UT-304F) to disperse anatase-type titanium oxide. I let you. Nanocellulose (manufactured by Daio Paper Co., Ltd., nanocellulose fiber concentration: 15.57% by mass) was added thereto, subjected to ultrasonic treatment for 1 hour, allowed to stand at room temperature for 1 minute, and the supernatant titanium oxide was removed and precipitated. The material was dried at room temperature for 48 hours or more to obtain a TiO ₂ / nanocellulose fiber composite material. As shown in FIG. 6C, in the TiO ₂ / nanocellulose fiber composite material of Comparative Example 1, titanium oxide nanoparticles are attached to the surface of the fibers, but the individual fibers are covered with the titanium oxide nanoparticles. It wasn't.

Furthermore, the present inventor investigated the durability of anatase-type titanium oxide nanoparticles in the _TiO2 / nanocellulose fiber composite material of Comparative Example 1 by a durability test by ultrasonic cleaning treatment. The ultrasonic apparatus and treatment conditions used are the same as the durability test for the above-mentioned hardwood _- derived TIM2 / nanocellulose fiber composite material 22 except that the treatment time is 1 hour.

The coverage of the titanium oxide nanoparticles before applying the ultrasonic wave shown in FIG. 6C was 77.6%. On the other hand, the coverage of the titanium oxide nanoparticles after applying the ultrasonic wave shown in FIG. 6D was 66.7%. In the composite material after the ultrasonic wave was applied, the titanium oxide nanoparticles were reduced as compared with the composite material before the ultrasonic wave was applied. As described above, it was confirmed that the titanium oxide nanoparticles had low durability in the _TiO2 / nanocellulose fiber composite material of Comparative Example 1.

Compared with the TiO ₂ / nanocellulose fiber composite material of Comparative Example 1 in which titanium oxide nanoparticles are physically adsorbed to the nanocellulose fiber, the durability of the _TiO2 / nanocellulose fiber composite material of Example 1 is high. From this, it is presumed that in the _TiO2 / nanocellulose fiber composite material of Example 1, the titanium oxide nanoparticles are chemically adsorbed, that is, chemically bonded to the nanocellulose fiber.

As shown in FIG. 7A, the TiO ₂ / nanocellulose fiber composite material 32 derived from the coniferous tree comprises anatase-type titanium oxide nanoparticles such as anatase-type titanium oxide nanoparticles 33, and anatase-type such as anatase-type titanium oxide nanoparticles 33. Titanium oxide nanoparticles covered the surface of nanocellulose fibers derived from coniferous trees. For example, the particle size of the anatase-type titanium oxide nanoparticles 33 was 100-300 nm as compared with the scale of 1 μm.

On the other hand, the _TiO2 / nanocellulose fiber composite material 36 shown in FIG. 7B was as follows. The _TiO2 / nanocellulose fiber composite material 36 in Non-Patent Document 1 contains titanium oxide nanoparticles 35 aggregated on the surface of cellulose. In addition, there are some places where the cellulose surface is exposed.

Comparing FIGS. 7A and 7B, the following was found. In the _TiO2 / nanocellulose fiber composite material 36 reported in Non-Patent Document 1, the cellulose surface is partially exposed and aggregated titanium oxide nanoparticles are adhered to the composite material 36. On the other hand, in the _TiO2 / nanocellulose fiber composite material 32 derived from coniferous trees, the cellulose surface is completely covered with titanium oxide nanoparticles, and no aggregates are observed.

The following can be observed from the enlarged view shown in FIG. 8 for the anatase-type titanium oxide nanoparticles such as the anatase-type titanium oxide nanoparticles 33 in FIG. 7A. The anatase-type titanium oxide nanoparticles 33a covering the surface of the nanocellulose fiber derived from coniferous trees were composed of aggregates of needle-shaped crystals, and no part where the cellulose was exposed was found. Comparing the anatase-type titanium oxide nanoparticles 33a with a scale of, for example, 1 μm, it can be seen that the width of the protrusions is several tens of nm.

As shown in FIG. 9A, the TiO ₂ / nanocellulose fiber composite material 42 of the chemical pulp comprises anatase titanium oxide nanoparticles such as anatase-type titanium oxide nanoparticles 43 and anatase-type oxidation such as anatase-type titanium oxide nanoparticles 43. The titanium nanoparticles covered the surface of the nanocellulose fibers of the chemical pulp. The outer shape of the anatase-type titanium oxide nanoparticles 43 was spherical. For example, the particle size of the anatase-type titanium oxide nanoparticles 43 was about 100 nm as compared with the scale of 1 μm.

The following can be observed from the enlarged view shown in FIG. 9B for the anatase-type titanium oxide nanoparticles such as the anatase-type titanium oxide nanoparticles 43. Titanium oxide nanoparticles are composed of aggregates of smaller titanium oxide needle-like crystals. The single titanium oxide nanoparticles were an aggregate of crystals that grew radially from the surface of the nanocellulose fiber. In other words, the anatase-type titanium oxide nanoparticles 43a had a spherical outer shape and had protrusions. Comparing the anatase-type titanium oxide nanoparticles 43a to a scale of, for example, 1 μm, the protrusions were 60 nm long and 25 nm wide.

Photocatalytic effect on nanocellulose fiber (Comparative Example 1, cellulose only), _TiO2 / nanocellulose fiber composite material derived from coniferous tree (Example 2) and _TiO2 / nanocellulose fiber of chemical pulp (Example 3). Evaluation was performed. The evaluation of the photocatalytic effect was performed as follows. An aqueous solution of methylene blue (200 mM) was applied to the above sample and dried. Then, the absorbance of the methylene blue dye was measured for 80 seconds while irradiating with ultraviolet light. The measurement conditions and equipment for evaluating the photocatalytic effect were as follows. The measuring device was set up using a homemade ultraviolet laser light source. A He-Cd laser (wavelength 325 nm, 5 mW) manufactured by Kinmon Konami Co., Ltd. was used as an ultraviolet light source. A red laser (wavelength 650 nm) was used to measure the absorbance, and the light intensity transmitted through the sample was detected by a photodetector.

As shown in FIG. 10, nanocellulose fiber (cellulose only) did not show a photocatalytic effect, but both the TiO ₂ / nanocellulose fiber composite material of chemical pulp and the _TiO2 / nanocellulose fiber composite material derived from coniferous trees were photocatalyst. The effect was shown. That is, in the TiO ₂ / nanocellulose fiber composite material of chemical pulp, the concentration of the dye standardized at the initial concentration was reduced by the ultraviolet irradiation time of 10 sec. In addition, in the conifer-derived _TiO2 / nanocellulose fiber composite material, the concentration of the dye standardized at the initial concentration decreased until the ultraviolet irradiation time was up to 80 sec, and the decrease in the dye concentration was particularly large when the ultraviolet irradiation time was up to 20 sec. rice field. The TiO ₂ / nanocellulose fiber composite material derived from coniferous trees has a greater photocatalytic effect than the _TiO2 / nanocellulose fiber composite material of chemical pulp.

(Manufacturing and Evaluation of TIO ₂ / Cellulose Fiber Composite Material of Example 4 and Comparative Example 2)
Instead of the nanocellulose fiber dispersion solution of Example 1, the present inventor used a cloth obtained by cutting bleached small-width cotton (100% cotton) into 50 mm squares as cellulose fibers. FIG. 11 is an SEM image of this cellulose fiber. The diameter of this cellulose fiber is micro size. This cellulose fiber was immersed in a mixed solution, and each step P3, P4, P5 was carried out under the same synthetic conditions as in Example 1 to obtain a _TiO2 / cellulose fiber composite material of Example 4.

12A and 12B are SEM images of the TiO ₂ / cellulose fiber composite material of Example 4. It is presumed that the titanium oxide that coats the cellulose fiber does not show the boundary of particles at the place where the coverage is 100%, and forms a flat plate-like aggregate. Titanium oxide that coats the cellulose fiber is a particle having a spherical outer shape in a place where the coverage is not 100%. The particle size of the particles is 100 nm or more and 400 nm or less. Although not shown in FIGS. 12A, 12B, the particles have a plurality of protrusions. The shape of each of the plurality of protrusions is a cone shape having a width of 30 nm or more and 40 nm or less and a length of 40 nm or more and 60 nm or less.

Further, the present inventor produced the _TiO2 / cellulose fiber composite material of Comparative Example 2 with reference to the production method described in Non-Patent Document 1. Specifically, anatase-type titanium oxide (Evonik (Degussa) P25) is added to distilled water, and ultrasonic treatment is performed for 15 minutes using an ultrasonic device (SHARP, UT-304F) to disperse anatase-type titanium oxide. I let you. A cloth of the same type as that used in Example 4 was immersed therein as a cellulose fiber, and ultrasonic treatment was performed for 1 hour. Then, it was dried at room temperature for 48 hours to obtain the TiO ₂ / cellulose fiber composite material of Comparative Example 2. The _TiO2 / cellulose fiber composite material of Comparative Example 2 was obtained by physically adsorbing titanium oxide nanoparticles to the cellulose fiber.

Then, the durability test of the titanium oxide nanoparticles by the peeling test was performed on each of the TiO ₂ / cellulose fiber composite material of Example 4 and the TiO ₂ / cellulose fiber composite material of Comparative Example 2. In the peeling test, each _TiO2 / cellulose fiber composite material was fixed to a glass substrate with double-sided tape, and the following two different types of tapes (that is, the first and second tapes) were used as test tapes. The first tape is product name: NITOMS masking tape (manufactured by NITOMS), product number: J8102, adhesive strength: 2.06N / 10 mm. The second tape is a cloth adhesive tape manufactured by TRUSCO, product number: GNT-50, adhesive strength: 4.4 N / 10 mm.

As shown in FIG. 13, the tape 101 was fixed to the roller 102, and the tape 101 was brought into contact with the sample 103 and moved horizontally to perform a peeling test. 14A, 14B and 14C show SEM images of the _TiO2 / cellulose fiber composite material of Example 4 before and after the test. 15A, 15B and 15C show SEM images of the _TiO2 / cellulose fiber composite material of Comparative Example 2 before and after the test. 14A and 15A are SEM images before the peeling test. 14B and 15B are SEM images after the first tape is peeled off. 14C and 15C are SEM images after the second tape is peeled off.

The present inventor obtained the area of the particle portion in each SEM image using the Bi-modal Fit algorithm, and calculated the coverage of the particles. The software used in this calculation is Igor Pro (Version: 8.04, WaveMetrics). Table 1 shows the values of the coverage before and after the test.

If the difference between the average value of the coverage before peeling and the average value of the coverage after peeling is within the error range based on the 95% confidence interval of the normal distribution, it is judged that the stripping has not occurred. Can be done.

As shown in Table 1, in Example 4, the difference between the average value of the coverage before peeling and the average value of the coverage after peeling is 2.6% in the first tape, and the second It was 2.4% on tape. These are in the range of 3.51% (ie, 1.95 × SE) or less. SE is the sample standard error. Therefore, in Example 4, it can be determined that the titanium oxide nanoparticles have not been desorbed after the peeling test in either the first tape or the second tape. From this, it can be seen that in the TiO ₂ / cellulose fiber composite material of Example 4, the adsorption force of the titanium oxide nanoparticles on the cellulose fiber is 4.4 N / 10 mm or more.

On the other hand, in Comparative Example 2, the standard error before the peeling test was large, and the coverage was not normally distributed. That is, the titanium oxide nanoparticles were non-uniformly attached. Since the error in the average value of the coverage after peeling off the first tape and the second tape was reduced, it is inferred that the aggregate of large-sized titanium oxide nanoparticles was desorbed. From this, it can be seen that in the TiO ₂ / cellulose fiber composite material of Comparative Example 2, the adsorption force of the titanium oxide nanoparticles on the cellulose fiber is smaller than 2.06 N / 10 mm.

From the above, the TiO ₂ / cellulose fiber composite material obtained by the production method of the present invention has higher durability than the TiO ₂ / cellulose fiber composite material obtained by physical adsorption of titanium oxide particles. have understood.

In addition, the present inventor conducted an antibacterial property test on each of the TiO ₂ / cellulose fiber composite material of Example 4 and the cellulose fiber of Comparative Example 3 in accordance with JIS R 1702: 2020. The cellulose fiber of Comparative Example 3 is the same type of cloth as the cloth used in Example 4 without the composite of titanium oxide. In the antibacterial test, the test product was inoculated with bacteria and then irradiated with light to detect the number of bacteria. In addition, the number of bacteria in each test product after washing was detected. The test strain, irradiance, test bacterial solution intake, and washing method in the antibacterial test are as follows.

・ Test bacterial strain: Yellow coccus ・ Irradiance: 0.10 mW / cm ^2.8 hours ・ Test bacterial solution intake: 0.2 mL [Use test bacterial solution to which 0.05% of surfactant (Tween80) is added]
-Washing method: (one company) Textile Evaluation Technology Council "Washing method for SEK mark textile products" -Standard washing method

Table 2 shows the antibacterial test results of the cellulose fiber of Comparative Example 3.

As shown in Table 2, the viable cell count after light irradiation and the viable cell count in the dark were increased as compared with the viable cell count immediately after inoculation.

Table 3 shows the antibacterial test results of the TiO ₂ / cellulose fiber composite material of Example 4.

The viable cell count immediately after inoculation of the TiO ₂ / cellulose fiber composite material of Example 4 is the same as the viable cell count immediately after inoculation of the cellulose fiber of Comparative Example 3. As shown in Table 3, the common logarithmic value of the viable cell count after light irradiation of 0 times of washing decreased from the common logarithmic value of 4.4 immediately after inoculation to 1.3. From this, it was confirmed that it had a photocatalytic antibacterial effect. Furthermore, the viable cell count after light irradiation after repeated washing 10 times was the same as the usual logarithmic value of the viable cell count after light irradiation 0 times of washing. From this, it was confirmed that the photocatalytic antibacterial effect was maintained.

In addition, the regular logarithmic value of the viable cell count in the dark place after no washing was reduced from 4.4 to 1.3 of the viable cell count immediately after inoculation. From this, it was confirmed that the TiO ₂ / cellulose fiber composite material of Example 4 has antibacterial properties even without irradiation with light. Furthermore, the viable cell count in the dark after repeated washing 10 times was 2.8, which was lower than the usual logarithmic value 4.4 of the viable cell count immediately after inoculation. From this, it was confirmed that the antibacterial effect was maintained even without irradiation with light.

In addition, the present inventor conducted an anti-virus performance evaluation test using a virus for each of the TiO ₂ / cellulose fiber composite material of Example 4 and the cellulose fiber of Comparative Example 3 in accordance with JIS R 1706: 2020 and ISO 18184. gone. In this evaluation test, the test product was inoculated with the virus and then irradiated with light to detect the number of viruses. The test conditions are as follows.

-Test product size: 50 mm x 50 mm
・ Number of n: n = 1
-Test phage: Influenza A virus (H3N2) A / Hong Kong / 8/68 strain (influenza A virus, ATCC VR-1679) Host cell: MDCK cell (ATCC CCL-34)
・ Preliminary irradiation conditions: Ultraviolet light (FL20S / BLB) 1.0 mW / cm ² , 24 hours ・ Sterilization of test product: Germicidal lamp irradiation ・ Light source type: Black light fluorescent lamp FL20S / BLB
・ Irradiation conditions: dark place and ultraviolet light 0.1 mW / cm ² , irradiation time 0, 8 hours ・ Illuminance meter: UV integrated photometer (C9536-01 and H9958, Hamamatsu Photonics)
・ Adhesive film: Polypropylene film (VF-10, KOKUYO), 40 mm × 40 mm
・ Moisturizing glass: borosilicate glass ・ Concentration of inoculated virus solution: 3.2 × 10 ⁶ pfu / ml
・ Inoculation amount: 0.2 ml / sample

Table 4 shows the test results.

“<2.0 × 10 ² ” in Table 4 indicates that the value is lower than the detection limit. In the TiO ₂ / cellulose fiber composite material of Example 4, the virus infectivity after light irradiation was lower than the detection limit. From this, it was confirmed that the _TiO2 -cellulose fiber composite material of Example 4 had a photocatalytic antiviral effect.

Further, in the TiO ₂ / cellulose fiber composite material of Example 4, the virus infectivity titer after 8 hours in the dark was lower than the detection limit. From this, it was confirmed that the _TiO2 / cellulose fiber composite material of Example 4 had an antiviral effect even without irradiation with light.

As described above, the _TiO2 / cellulose fiber composite material of Example 4 has an antibacterial effect and an antiviral effect even without irradiation with light. It is considered that this is because the titanium oxide that coats the surface of the cellulose fiber is spherical particles, and the plurality of protrusions of these particles are present.

The titanium oxide / cellulose fiber composite material according to the present invention can be applied as a package or wall material having an environmental purification / antibacterial function, a household mask, a medical mask, or the like.

1: Cellulose fiber 2: Titanium oxide-cellulose fiber composite material 3: Titanium oxide (TiO ₂ ) nanoparticles 12, 22: _TiO2 / nanocellulose fiber composite material derived from broadleaf trees 13, 13a, 23, 23a, 33, 33a, 43, 43a: Anatase-type titanium oxide nanoparticles 16: Nanocellulose fiber aggregated fiber 17: Nanocellulose fiber 32: _TiO2 / nanocellulose fiber composite material derived from coniferous tree 35: Titanium oxide nanoparticles 36: TiO reported in Non-Patent Document 1. _2. Nanocellulose fiber composite material 42: TiO of chemical pulp _2. Nanocellulose fiber composite material

Claims (8)

1. Titanium oxide / cellulose fiber composite material
   Cellulose fiber and
   Titanium oxide, which covers at least a part of the surface of the cellulose fiber, is provided.
   The titanium oxide is a titanium oxide / cellulose fiber composite material that covers the surface of the cellulose fiber by being directly synthesized with respect to the surface of the cellulose fiber.
2. The titanium oxide / cellulose fiber composite material according to claim 1, wherein the synthesis is a synthesis by a liquid phase precipitation method using an aqueous solution containing ammonium titanium fluoride, boric acid and water.
3. Titanium oxide / cellulose fiber composite material
   Cellulose fiber and
   Titanium oxide, which covers at least a part of the surface of the cellulose fiber, is provided.
   A titanium oxide / cellulose fiber composite material having an adsorption force of titanium oxide on the cellulose fiber of 4.4 N / 10 mm or more.
4. The titanium oxide is a particle having a spherical outer shape and has a spherical shape.
   The particle size of the particles is 90 nm or more and 400 nm or less.
   The particles have a plurality of protrusions and have a plurality of protrusions.
   The titanium oxide / cellulose fiber composite according to any one of claims 1 to 3, wherein each of the plurality of protrusions has a cone shape having a width of 20 nm or more and 40 nm or less and a length of 20 nm or more and 60 nm or less. material.
5. The titanium oxide / cellulose fiber composite material according to any one of claims 1 to 4, wherein the cellulose fiber is a nanocellulose fiber having a diameter of 1 nm or more and 100 nm or less.
6. The titanium oxide / cellulose fiber composite material according to any one of claims 1 to 5, wherein the titanium oxide is an anatase type.
7. A method for manufacturing a titanium oxide / cellulose fiber composite material that directly synthesizes titanium oxide on the surface of cellulose fiber by the liquid phase precipitation method.
8. A method for manufacturing a titanium oxide / cellulose fiber composite material.
   Preparing an aqueous solution containing ammonium titanium fluoride, boric acid and water, and cellulose fiber (P1),
   A method for producing a titanium oxide / cellulose fiber composite material, which comprises precipitating titanium oxide on the surface of the cellulose fiber in the aqueous solution (P2, P3).

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