JP6853551B2 - Composite fiber and its manufacturing method, and adsorbent - Google Patents

Description

The present invention relates to a composite fiber, more specifically a chitosan fiber supporting a cellulose fiber, and a method for producing the same. It also relates to an adsorbent containing the composite fiber.

Conventionally, as chitosan fibers, chitosan is dissolved in an acidic aqueous solution, and the obtained chitosan solution is wet-spun from a nozzle in a basic coagulation solvent to form fibers (see Patent Document 1). Since such chitosan fibers are easily swollen by water, for example, an adsorbent using chitosan fibers as a carrier has a problem that the strength is easily lowered. In addition, the adsorbent using chitosan fiber has a derivative having an anionic group, an oxidate, an acidic compound, an isoelectric point on the acidic side of the physiological pH, or having a plurality of carboxyl groups. Adsorption ability to acidic proteins containing a large amount of amino acids is high, but adsorption to nitrogen-containing compounds and basic proteins having an isoelectric point on the basic side of the physiological pH or containing a large amount of amino acids having multiple amino groups. Since the ability is low, it is necessary to synthetically modify a ligand having an affinity or the like.

By the way, Patent Document 2 discloses an adsorbent for cesium in which the surface of a cellulose fiber is coated with chitosan. In this document, cellulose fibers are coated with chitosan by reacting an aldehyde group obtained by an oxidative cleavage reaction of cellulose with an oxidizing agent with an amino group of chitosan, and the cellulose fibers are coated or supported on the chitosan fibers. That is not stated.

Patent Document 3 discloses a composition for wound dressing comprising chitosan and cellulose oxide, and describes a chemical complex between an amine group of chitosan and a carboxylate group of cellulose oxide. There is. However, the oxidized cellulose does not have an I-type crystal structure because it is obtained by oxidizing regenerated cellulose such as rayon with an oxidizing agent such as dinitrogen tetraoxide or hydrogen peroxide. Further, Patent Document 3 describes a homogeneous mixture of chitosan and oxidized cellulose, and does not describe supporting cellulose fibers on chitosan fibers.

Japanese Unexamined Patent Publication No. 2001-031702 Japanese Unexamined Patent Publication No. 2015-169633 Special Table 2006-514843

In the embodiment of the present invention, by compounding a cellulose fiber having an I-type crystal structure with a chitosan fiber, swelling of the chitosan fiber due to water can be suppressed, and not only an acidic substance such as an acidic protein but also a nitrogen-containing compound can be suppressed. It is an object of the present invention to provide a composite fiber having an ability to adsorb basic substances such as chitosan and basic proteins.

In order to solve the above problems, the composite fiber according to the embodiment of the present invention is formed by supporting a cellulose fiber having an I-type crystal structure and an anionic functional group on the surface of the chitosan fiber.

The method for producing a composite fiber according to an embodiment of the present invention is a method for producing the composite fiber, which comprises a step of spinning an aqueous chitosan salt solution in a coagulating solution containing cellulose fibers and an alkali to obtain a composite fiber. ..

The adsorbent according to the embodiment of the present invention contains the above-mentioned composite fiber.

In the composite fiber according to the embodiment of the present invention, by supporting the cellulose fiber on the surface of the chitosan fiber, swelling due to water can be suppressed and the mechanical strength can be improved. Further, not only acidic substances such as acidic proteins but also basic substances such as nitrogen-containing compounds and basic proteins can be adsorbed by the amino group of chitosan fiber and the anionic functional group of cellulose fiber.

Further, according to the production method according to the embodiment of the present invention, it is possible to change the fiber diameter of the composite fiber by adjusting the concentrations of the cellulose fibers and the alkali in the coagulating liquid.

Graph showing the relationship between the TOCN concentration in the coagulation bath and the breaking strength of the composite fiber Graph showing the relationship between the TOCN concentration in the coagulation bath and the breaking elongation of the composite fiber Graph showing the relationship between the TOCN concentration in the coagulation bath and the swelling rate of the composite fiber

Hereinafter, preferred embodiments of the present invention will be described in detail.

The composite fiber according to the present embodiment includes a chitosan fiber (A) and a cellulose fiber (B) supported on the surface of the chitosan fiber.

[Chitosan fiber (A)]
Chitosan fiber is a fiber composed of chitosan, which is a cationic polysaccharide. Chitosan is a deacetylase of chitin, which is a natural polymer, and has an amino group formed by deacetylation. The chitosan fiber is not particularly limited, but may be obtained by wet spinning a chitosan solution, for example.

The average fiber diameter of the chitosan fiber is not particularly limited, and may be 1 to 1000 μm, 1 to 400 μm, or 1 to 200 μm. The average fiber diameter of chitosan fibers can be determined by the arithmetic mean of the fiber diameters of 20 fibers by observation with an optical microscope.

[Cellulose fiber (B)]
As the cellulose fiber, one having an I-type crystal structure and an anionic functional group is used.

The cellulose I-type crystal is a crystal form of natural cellulose, and by having the I-type crystal structure, the cellulose fiber can be made water-insoluble and the swelling of the composite fiber with respect to water can be suppressed. Further, since the cellulose fiber has an I-type crystal structure, the effect of improving the mechanical strength of the composite fiber with the chitosan fiber can be obtained.

The fact that the cellulose fibers have an I-type crystal structure means that, for example, in the diffraction profile obtained by wide-angle X-ray diffraction image measurement, there are two positions, 2θ = 14 ° to 17 ° and 2θ = 22 ° to 23 °. It can be identified by having a typical peak.

Examples of the anionic functional group contained in the cellulose fiber include at least one selected from the group consisting of a carboxyl group, a phosphoric acid group, a sulfonic acid group, a nitric acid group, a boric acid group, and a sulfate group. In the present specification, the carboxyl group is a concept including not only an acid type (-COOH) but also a salt type, that is, a carboxylic acid base (-COOX, where X is a cation forming a salt with a carboxylic acid). Similarly, the phosphate group, the sulfonic acid group, the nitric acid group, the boric acid group, and the sulfate group are concepts that include not only the acid type but also the salt type.

In one embodiment, the anionic functional group is preferably a carboxyl group. Examples of the cellulose fiber containing a carboxyl group include an oxidized cellulose fiber obtained by oxidizing the hydroxyl group of a glucose unit in a cellulose molecule and a carboxymethylated cellulose fiber obtained by carboxymethylating a hydroxyl group of a glucose unit in a cellulose molecule. Can be mentioned.

The amount of the anionic functional group in the cellulose fiber is not particularly limited, and may be, for example, 0.5 to 3.0 mmol / g or 1.5 to 2.0 mmol / g. For the amount of anionic functional groups, for example, in the case of a carboxyl group, 60 mL of a 0.5 to 1 mass% slurry is prepared from a cellulose sample whose dry mass has been precisely weighed, and the pH is adjusted to about 2 with a 0.1 mol / L hydrochloric acid aqueous solution. After setting the pH to 5.5, a 0.05 mol / L aqueous sodium hydroxide solution was added dropwise to measure the electrical conductivity, and the pH was continued until the pH reached about 11, and the neutralization step of the weak acid in which the change in electrical conductivity was gradual. From the amount of sodium hydroxide (V) consumed in, it can be calculated according to the following formula. The phosphoric acid group can also be measured by the same electrical conductivity measurement. Other anion groups may also be measured by a known method.
Anionic functional group amount (mmol / g) = V (mL) x [0.05 / cellulose sample mass (g)]

Since the cellulose fiber is supported on the surface of the chitosan fiber, it is preferable to use a cellulose fiber having an average fiber diameter smaller than that of the chitosan fiber. More specifically, as the cellulose fiber, for example, cellulose fine fiber (cellulose nanofiber) having an average fiber diameter of 3 nm or more and 500 nm or less may be used. The average fiber diameter of the cellulose fine fibers is more preferably 3 to 100 nm, still more preferably 3 to 30 nm.

Here, the average fiber diameter of the cellulose fine fibers can be measured as follows. That is, an aqueous dispersion of cellulose fine fibers having a solid content of 0.05 to 0.1% by mass is prepared, and the aqueous dispersion is cast on a hydrophilized carbon film-coated grid to be a permeation type. It is used as an observation sample of an electron microscope (TEM). When fibers having a large fiber diameter are included, a scanning electron microscope (SEM) image of the surface cast on the glass may be observed. Further, the observation sample may be negatively stained with, for example, 2% uranyl acetate. Then, observation is performed using an electron microscope image at a magnification of 5000 times, 10000 times, or 50,000 times depending on the size of the constituent fibers. At that time, an axis having an arbitrary vertical and horizontal image width is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect the axis. Then, after obtaining an observation image satisfying this condition, two random axes in each of the vertical and horizontal directions are drawn with respect to this image, and the fiber diameters of the fibers intersecting the axes are visually read. In this way, images of at least three non-overlapping surface portions are taken with an electron microscope and the value of the fiber diameter of the fibers intersecting each of the two axes is read (thus, at least 20 fibers × 2 × 3 = 120). Information on the fiber diameter of the book can be obtained). The arithmetic mean of the fiber diameters thus obtained is taken as the average fiber diameter.

The average aspect ratio of the cellulose fine fibers is not particularly limited, and may be, for example, 10 to 1000, 50 or more, 100 or more, 800 or less, or 500 or less.

Here, the average aspect ratio of the cellulose fine fibers can be measured as follows. That is, the average fiber diameter is calculated according to the method described above, the average fiber length of the cellulose fine fibers is calculated from the same observation image, and the average aspect ratio is calculated according to the following formula using these values.
Average aspect ratio = average fiber length (nm) / average fiber diameter (nm)

Cellulose fine fibers are obtained by performing a defibration treatment. The defibration treatment may be carried out after the anionic functional group is introduced, or may be carried out before the introduction. As the defibration treatment, for example, a homomixer under high-speed rotation, a high-pressure homogenizer, an ultrasonic disperser, a beater, a disc-type refiner, a conical-type refiner, a double-disc type refiner, a grinder, or the like is used to water cellulose fibers. This can be done by treating the dispersion, and an aqueous dispersion of cellulose fine fibers can be obtained.

Examples of the cellulose fine fiber according to a preferred embodiment include oxidized cellulose fine fiber in which the hydroxyl group at the C6 position of the glucose unit in the cellulose molecule is selectively oxidized and modified to a carboxyl group. Oxidized cellulose fine fibers are obtained by oxidizing natural cellulose such as wood pulp with a cooxidant in the presence of an N-oxyl compound and defibrating (refining) the fibers. As the N-oxyl compound, a compound having a nitroxy radical generally used as an oxidation catalyst is used, for example, a piperidine nitroxyoxy radical, and particularly 2,2,6,6-tetramethylpiperidinooxy radical (TEMPO). ) Or 4-acetamide-TEMPO is preferred. Cellulose fine fibers oxidized by TEMPO are generally called TEMPO oxidized cellulose nanofibers (TOCN), and can also be used in this embodiment. The cellulose oxide fine fibers may have an aldehyde group or a ketone group together with the carboxyl group, but preferably do not have substantially no aldehyde group and a ketone group.

[Composite fiber]
The composite fiber according to the present embodiment is formed by supporting the cellulose fiber on the surface of the chitosan fiber.

The term "support according to the present embodiment" refers to a state in which the cellulose fibers do not fall off or scatter on the surface of the chitosan fibers and adhere to or cover the whole or a part, or a state in which the pores or the inside are impregnated. Including, more specifically, a state of being chemically, physically or electrically bound, adsorbed or immobilized, and the like.

The ratio of chitosan fiber to cellulose fiber in the composite fiber is not particularly limited. For example, the cellulose fiber may be 0.001 to 50 parts by mass, 0.001 to 20 parts by mass, or 0.001 to 10 parts by mass with respect to 100 parts by mass of chitosan fiber.

The average fiber diameter of the composite fiber is preferably 10 to 1200 μm, more preferably 20 to 500 μm, and even more preferably 50 to 300 μm. The average fiber diameter of the composite fiber can be determined by the arithmetic mean of the fiber diameters of 20 fibers by observing with an optical microscope.

[Manufacturing method of composite fiber]
The method for producing a composite fiber according to an embodiment includes the following steps.
(1) A step of spinning an aqueous chitosan salt solution in a coagulating solution containing cellulose fibers and an alkali to obtain composite fibers, and
(2) A step of immersing the obtained composite fiber in alcohol and then drying it.

Specifically, chitosan is dissolved in an acidic aqueous solution to prepare a chitosan salt aqueous solution (chitosan, which is a cationic polymer, forms a salt in combination with an acid). A chitosan salt aqueous solution is used as a spinning stock solution (dope solution) and is discharged by applying pressure from a nozzle to perform wet spinning in a basic coagulating solution containing an alkali. At that time, in the present embodiment, the cellulose fibers are dispersed together with the alkali in the coagulating liquid. As a result, with the coagulation of chitosan, the electrostatic interaction between the cellulose fibers and chitosan in the coagulating liquid (specifically, the interaction between the anionic functional group of the cellulose fibers and the protonated amino group of chitosan) causes An ion complex is formed, and a complex in which cellulose fibers are supported on the surface of chitosan fibers is obtained.

The obtained composite is immersed in an alcohol bath, stretched and dried to obtain a composite fiber in which cellulose fibers are supported on the surface of chitosan fibers.

The concentration of chitosan in the chitosan salt aqueous solution is not particularly limited as long as the chitosan fiber can be spun, and may be, for example, 0.1 to 10% by mass or 1 to 5% by mass.

As the coagulation liquid, a basic aqueous solution containing an alkali can be used, and as the solvent, water alone may be used, or an alcohol such as methanol or ethanol, or a water-miscible organic solvent such as acetone may be used together with water. The alkali is not particularly limited, _{and examples thereof include inorganic substances such as NaOH, KOH, NH 4} OH, NaOHCO ₃ , Ca (OH) ₂ , CaCl (OH), and MgCl (OH), and water-soluble amine compounds. .. The concentration of alkali in the coagulation liquid is preferably 0.01 to 40% by mass, more preferably 0.5 to 20% by mass, and may be 0.5 to 10% by mass.

The concentration of cellulose fibers in the coagulation liquid is preferably 0.001 to 0.4% by mass, more preferably 0.005 to 0.3% by mass, and even 0.005 to 0.1% by mass. Good.

Examples of the alcohol to be immersed after spinning include methanol and ethanol. The composite fibers are washed by immersing them in an alcohol bath, which may be done until the composite fibers are neutral (ie, pH 7).

[Action effect]
According to the present embodiment, a composite fiber in which the cellulose fiber is supported on the surface of the chitosan fiber can be obtained by forming an ion complex of the cationic chitosan fiber and the anionic cellulose fiber. By supporting the cellulose fibers in this way, the swelling of the chitosan fibers with respect to water can be suppressed due to the type I crystal structure of the cellulose fibers, and the mechanical strength can be improved. Further, since the mechanical properties can be improved by making the composite fiber, the composite fiber can be wound and braided.

Further, the fiber diameter of the composite fiber can be changed by adjusting the concentrations of the cellulose fibers and the alkali in the coagulating liquid.

Further, since the composite fiber contains chitosan fiber and chitosan itself has antibacterial activity, it is possible to suppress the generation of mold and putrefaction as compared with the case of the cellulose fiber alone.

In addition, chitosan is a cationic compound containing an amino group, and is a derivative having an anionic group such as a carboxylic acid, a phosphoric acid, or a sulfonic acid, or an oxygen acid salt such as a sulfate ester, a phosphoric acid ester, or a borate ester. Or, because the isoelectric point is on the acidic side of the physiological pH, or an acidic protein containing many amino acids having multiple carboxyl groups, and an anionic derivative, an oxidate, or an acidic protein to form an ionic bond. Has a high adsorption capacity. However, since chitosan is a cationic compound, nitrogen-containing compounds, other cationic compounds, amino acids whose isoelectric point is on the basic side of the physiological pH, or amino acids having a plurality of amino groups can be used. Ionic bonds are unlikely to occur with basic proteins containing a large amount. Therefore, when chitosan is used as an adsorbent, there is a problem that the adsorption ability is low due to the ionicity, isoelectric point and electric charge of the adsorbed substance.

On the other hand, the composite fiber according to the present embodiment has an amphoteric functional group derived from both natural polymers not used for forming the ion complex (that is, a cationic amino group of the chitosan fiber and an anionic group of the cellulose fiber). It has a functional group). Therefore, not only acidic substances such as derivatives having anionic groups, oxidates, and acidic proteins having an isoelectric point on the acidic side of the physiological pH or containing many amino acids having a plurality of carboxyl groups. , Nitrogen-containing compounds and basic substances such as basic proteins whose isoelectric point is on the acidic side of the physiological pH or which contains many amino acids having multiple amino groups can also be adsorbed and are physiologically active substances. It can be used as an adsorbent for nitrogen-containing compounds.

Here, the physiological pH according to the present embodiment refers to a pH in a relatively narrow range that usually occurs in human body fluids, generally in the range of 7.0 to 7.5.

In the composite fiber according to the present embodiment, as an adsorbent having antibacterial activity and its carrier, for example, water purification in drinking water and aquaculture of adult and juvenile fish, biomolecule purification and separation material, ammonia and the like. It can be used as a material for removing physiologically active substances, proteins, bacteria, viruses, organic substances, and inorganic substances that are harmful to the human body. The form of the adsorbent is not particularly limited, and for example, a form such as a filter, a braided mesh, a filter cloth, a net-like filter medium, a membrane, or a material obtained by cutting or crushing a composite fiber into pellets or particles can be used. Examples thereof include a form in which a column is filled and used as column chromatography.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[Preparation of composite fiber 1]
10 g of chitosan (FM-80, manufactured by Koyo Chemical Co., Ltd.) and 240 mL of 1 mass% acetic acid were mixed for 6 hours at 130 rpm to prepare a 4 mass% chitosan acetate aqueous solution. The obtained chitosan salt aqueous solution was injected into the column, and a spinning nozzle was attached to the tip of the column. The spinning nozzle has 30 spinning holes with a diameter of 0.2 mm.

A spinning nozzle is placed in a coagulation bath in which TOCN is added to a NaOH aqueous solution so as to have the concentration shown in Table 1 below, and the column containing the chitosan salt aqueous solution is pressurized at 0.03 MPa to extrude the chitosan salt aqueous solution into the coagulation bath. By coagulation, a composite fiber in which TOCN was carried on the chitosan fiber was obtained. The obtained composite fiber was subsequently immersed in a methanol bath for washing, then stretched with a stretching roller, wound with a winding roll, and then dried. This produced a composite fiber. Here, the length of the coagulation bath is 100 cm, the length of the methanol bath is 50 cm, the take-up speed of the stretching roller is 6.4 m / min on the upstream side, 7.0 m / min on the downstream side, and the stretching ratio is 1. .1 times. Further, the drying was carried out by air drying, and the equilibrium moisture content was about 13% by mass.

As TOCN, "Leocrysta I-2SP" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (TEMPO oxidized cellulose nanofiber having cellulose type I crystal structure, number average fiber diameter = 4 nm, average aspect ratio = 280, amount of anionic functional groups (Amount of carboxyl group) = 1.9 mmol / g) was used.

The obtained composite fiber was observed with an optical microscope, and the average fiber diameter was obtained from the arithmetic mean of the fiber diameters of 20 fibers. The results are shown in Table 1. When the NaOH concentration in the coagulation bath was fixed and compared, it was confirmed that the fiber diameter increased as the TOCN concentration increased (however, it was saturated at about 0.0075% by mass). .. From this, it can be seen that the higher the concentration of TOCN in the coagulation bath, the larger the amount of TOCN supported, and the higher the TOCN ratio, the more composite fibers can be obtained.

[Preparation of composite fiber 2]
The NaOH concentration and the TOCN concentration in the coagulation bath were changed as shown in Table 2 below, and the composite fibers were produced in the same manner as in the above [Preparation of composite fibers 1]. The obtained composite fiber was observed with an optical microscope, and the average fiber diameter was obtained from the arithmetic mean of the fiber diameters of 20 fibers.

The results are shown in Table 2. When the TOCN concentration of the coagulation bath was fixed and compared, it was confirmed that the fiber diameter increased as the NaOH concentration increased (however, it was saturated at about 4% by mass). From this, it can be seen that the higher the concentration of NaOH in the coagulation bath, the larger the amount of TOCN supported, and the higher the TOCN ratio, the more composite fibers can be obtained.

[Mechanical properties of composite fibers]
The breaking strength and breaking elongation were measured as the mechanical properties of the composite fibers obtained in Comparative Example 1 and Examples 1, 3 and 4. Specifically, 20 dried fibers were bundled into one bundle, and the breaking strength and breaking elongation were measured by a tabletop universal material testing machine (manufactured by A & D Co., Ltd.).

The results are shown in Table 3 and FIGS. Comparative Example 1 is a fiber composed only of chitosan spun with a coagulation liquid containing no TOCN, and Examples 1, 3 and 4 have TOCN concentrations of 0.001, 0.0075 and 0. It is a composite fiber obtained by setting it to 01% by mass. The composite fiber of this example had a higher tensile strength than the chitosan single fiber of Comparative Example 1, and increased as the TOCN concentration increased. In particular, in Example 4 in which the TOCN concentration was 0.01% by mass, the breaking strength was increased by about 40% and the breaking elongation was increased more than twice as compared with Comparative Example 1 which was a chitosan single fiber. As described above, it was found that the composite fiber in which the cellulose fiber is supported on the surface of the chitosan fiber exhibits excellent fiber physical characteristics.

[Evaluation of adsorbability of protein and ammonia in composite fibers]
The composite fibers obtained in Comparative Example 1 and Examples 1, 3 and 4 were evaluated for their adsorption rates to the acidic protein bovine serum albumin (BSA), the basic protein cytochrome c, and ammonia.

(1) BSA Adsorption Test 25 mL of phosphate buffered saline (PBS) of 50 mg of composite fiber and 214 mg / L bovine serum albumin (BSA) was stirred in a closed container for 60 minutes at 25 ° C. and 195 rpm. The stirred solution is filtered, the absorbance of the filtrate at 280 nm is measured with a visible / ultraviolet spectrophotometer, and the filtrate is obtained by measuring separately and using a calibration curve showing the relationship between the amount of BSA in PBS and the absorbance. BSA amount (mg / L) was calculated. The amount of BSA adsorbed on the composite fiber (%) was calculated by subtracting the amount of BSA in the filtrate (mg / L) from the initial amount of BSA (mg / L) and dividing by the initial amount of BSA (mg / L). Notated by ratio. The results are shown in Table 4 below.

(2) Adsorption test of cytochrome c 25 mL of phosphate buffered saline (PBS) of 50 mg of composite fiber and 1.256 μg / mL of cytochrome c was stirred in a closed container for 60 minutes at 25 ° C. and 195 rpm. The stirred solution is filtered, the absorbance at 409 nm of the filtrate is measured by a visible / ultraviolet spectrophotometer, and the filtrate is measured by a calibration curve showing the relationship between the amount of cytochrome c in PBS and the absorbance. The amount of cytochrome c (mg / L) in the solution was calculated. The amount of cytochrome c adsorbed on the composite fiber (%) is obtained by subtracting the amount of cytochrome c in the filtrate (mg / L) from the initial amount of cytochrome c (mg / L) and the initial amount of cytochrome c (mg / L). ) Divided by the ratio. The results are shown in Table 4 below.

(3) Ammonia adsorption test 50 mg of composite fiber and 100 mL of an aqueous ammonia solution of 9.7 mg / L were stirred in a closed container for 60 minutes at 25 ° C. and 195 rpm. The stirred solution was filtered, and the filtrate was titrated with 0.01 mol / L hydrochloric acid to quantify the amount of ammonia (mg / L) in the filtrate. The amount of ammonia adsorbed on the composite fiber (%) was calculated by subtracting the amount of ammonia in the filtrate (mg / L) from the initial amount of ammonia (mg / L) and dividing by the initial amount of ammonia (mg / L). Marked by ratio. The results are shown in Table 4 below.

As shown in Table 4, in the case of the composite fiber according to the example, the adsorption effect by the functional groups (carbocyclyl group and amino group) derived from both natural polymers that were not used for forming the ion complex was observed. The adsorption effect increased as the concentration of TOCN in the coagulation bath increased when the composite fiber was prepared.

[Swelling degree of composite fiber]
The swelling rate with respect to water was measured for the composite fibers obtained in Comparative Example 1 and Examples 1, 3 and 4. The swelling rate was evaluated by measuring the weight increase rate when immersed in water. The test method is as follows.
(1) The composite fiber was dried under reduced pressure at room temperature for 24 hours, and the initial weight was measured to obtain Wd.
(2) The sample of (1) above was immersed in distilled water for 1 or 5 days, the water on the surface of the sample was wiped off, and the weight was measured to obtain Ww.
(3) The weight increase rate (swelling rate) was calculated by the following formula.
Swelling rate (%) = (Ww-Wd) / Wd × 100

The results are shown in Table 5 and FIG. 3 below, and it was found that the higher the degree of TOCN compounding, the more the degree of swelling with water can be suppressed.

Although some 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 implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments, omissions, replacements, changes, etc. thereof are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and the equivalent scope thereof.

Claims (6)

A composite fiber in which a cellulose fiber having an I-type crystal structure and an anionic functional group is supported on the surface of the chitosan fiber. The composite fiber according to claim 1, wherein the average fiber diameter is 10 μm or more and 1200 μm or less. The method for producing a composite fiber according to claim 1 or 2.
A method for producing a composite fiber, which comprises a step of spinning an aqueous chitosan salt solution in a coagulating solution containing a cellulose fiber and an alkali to obtain a composite fiber. The method for producing a composite fiber according to claim 3, wherein the concentration of the cellulose fiber in the coagulating liquid is 0.001% by mass or more and 0.4% by mass or less. The method for producing a composite fiber according to claim 3 or 4, wherein the concentration of alkali in the coagulating liquid is 0.01% by mass or more and 40% by mass or less. An adsorbent containing the composite fiber according to claim 1 or 2.

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