Porous cellulose particles and method for producing the same

Abstract

The present disclosure provides a porous cellulose particle containing chitosan having a predetermined opening on the surface and having a predetermined particle size, and a method for manufacturing the same. A porous cellulose particle, the porous cellulose particle contains unsubstituted cellulose and chitosan, and in a total of 100% by mass of the unsubstituted cellulose and the chitosan, the content rate of the chitosan is 20% by mass or less. In an image of observing the surface of the porous cellulose particle using a scanning electron microscope, pores having a diameter of 0.05 to 5 μm are observed, and the proportion of the porous cellulose particles having a particle size of 10 to 200 μm is 90% by mass or more.

Description

Technical Field

[0001] The present disclosure relates to a porous cellulose particle and a method for producing the same. Background Art

[0002] Polysaccharides and their derivatives represented by cellulose are used for various purposes. For example, in the case of their microporous bodies, they can themselves be adsorbents, and in addition, by performing certain chemical modifications on their surfaces, functions such as adsorption, separation, and catalysts can be imparted.

[0003] For example, various methods for producing matrices for separating biopolymers using cellulose, agarose, etc. have been disclosed, and their usefulness is also well known. Chemical modifications are performed to make the surfaces of cellulose and other polysaccharides functional. For example, when the -OH group of a sugar reacts with chloroacetic acid under alkaline conditions, carboxymethyl ether is formed, and when the -OH group of a sugar reacts with 1-chloro-2-(diethylamino)ethane, diethylaminoethyl ether is formed, which are used as weak ion exchangers, respectively. However, such chemical modifications not only increase the manufacturing cost but also require the use of harmful drugs, or may also have an adverse effect on the structure of the particles from the micro to the macro scale. Therefore, a simpler method for introducing functional groups is desired.

[0004] As one method for solving such problems, mixing polymers having functions that cellulose originally does not have is considered. In this sense, if chitosan having an anion exchange ability and containing an amino group that can serve as a foothold for bonding various atomic groups can be mixed, it can be expected to impart various functions to cellulose beads. Since cellulose and chitosan do not necessarily have a common solvent, there have been attempts to mix the powder of one with the solution of the other and form a shape (see Patent Documents 1 and 2). However, the shaped product thus obtained retains the characteristics of cellulose and chitosan as it is. Therefore, for example, when washed with an acidic aqueous solution, chitosan dissolves and precipitates.

[0005] In addition, for example, Patent Document 3 discloses the following: First, a predetermined amount of spray-dried chitosan is dissolved in N-methylmorpholine N-oxide (NMMO), and then cellulose is added to prepare a solution having a composition ratio of chitosan to cellulose of 0 / 100 to 5 / 95. The solution is dropped from a syringe in the form of droplets into water to solidify it. However, the beads are made to have a diameter of 2 to 3 mm, and under SEM observation of the freeze-dried sample, the surface is not open. Regarding the size of the bead diameters described in Patent Document 3 and the fact that the surface is not open, it is not suitable for processes such as chromatography that require the speed of substance movement, and in particular, it is actually not applicable to chromatography processes for treating high molecular weight samples such as proteins and nucleic acids.

[0006] Prior Art Documents

[0007] Non-patent literature

[0008] Non-patent literature 1: Carbohydrate Polymers, 150 (2016), Pages 216 - 226

[0009] Non-patent literature 2: Cellulose (2014) 21: 4405 - 4418

[0010] Non-patent literature 3: Carbohydrate Polymers, 54, (4) 2003, 425 - 43 Summary of the invention

[0011] Problems to be solved by the invention

[0012] The main object of the present disclosure is to provide a porous cellulose particle containing chitosan having a predetermined opening on the surface and having a predetermined particle size, and a method for manufacturing the same.

[0013] Technical solution

[0014] Relative to the prior art as described above, in the development of porous cellulose particles containing chitosan, the inventors of the present disclosure have focused on using an aqueous solution containing alkali hydroxide and urea as a solvent with low cost, safety, and low environmental load such as odor. However, chitosan, as a basic polymer, can be fully dissolved in acid, but is generally not easily dissolved in an alkaline aqueous solution. In fact, even when commercially available chitosan is added to an aqueous solution of alkali hydroxide and urea, it does not dissolve at all.

[0015] Therefore, the inventors of the present disclosure temporarily dissolved chitosan in a small amount of acid, then added an excessive amount of alkali hydroxide and urea and cooled it, thereby successfully dissolving it. The solution was mixed with a cellulose solution using the same solvent, thereby successfully obtaining porous cellulose particles. These porous cellulose particles are porous cellulose particles containing chitosan at the same time, and unexpectedly, even when these porous cellulose particles are immersed in an acidic aqueous solution, the dissolution and precipitation of chitosan are inhibited. Such porous cellulose particles can be an anion exchanger in an appropriate pH environment, can also be an adsorbent for metal ions, and can also be a carrier for chromatography. In addition, by modifying the amino group of chitosan, various functions can be further imparted.

[0016] The present disclosure has been completed through further repeated research based on these insights.

[0017] Item 1. A porous cellulose particle, comprising unsubstituted cellulose and chitosan,

[0018] In a total of 100% by mass of the unsubstituted cellulose and the chitosan, the content rate of the chitosan is 20% by mass or less.

[0019] In the image of observing the surface of the porous cellulose particles using a scanning electron microscope, pores with a diameter of 0.05 to 5 μm were observed.

[0020] The proportion of the porous cellulose particles with a particle size of 10 to 200 μm is 90% by mass or more.

[0021] Item 2. The porous cellulose particles according to Item 1, wherein the solid content ratio of the porous cellulose particles in the water-containing state measured by the following method is 10% by mass or less. (Method for measuring the solid content ratio)

[0022] The porous cellulose particles in the state of having settled in pure water are left standing for one day or more in an environment of atmospheric pressure and a temperature of 25°C. Then, about 2 mL of the porous cellulose particles in the pure water is sucked up with a pipette and dispersed in 20 ml of a solution obtained by diluting a neutral detergent 1000-fold with pure water, and the porous cellulose particles are left standing for one day or more to settle. Then, the supernatant is removed by decantation, and about 1 / 3 of the remaining slurry is taken as one sample, dropped on three types of filter papers specified in JIS P 3801 [Filter paper (for chemical analysis)], left for 20 seconds, and after removing the remaining moisture, the mass of the block of the porous cellulose particles remaining on the filter paper is peeled off from the filter paper and weighed as the wet mass of the porous cellulose particles. Then, the porous cellulose particles are dried in an oven at 80°C for 2 hours and then weighed as the dry mass. These operations are performed on three samples, and the ratio of the dry mass to the wet mass is calculated respectively, and the average value of the three obtained values is used as the solid content ratio.

[0023] Item 3. A method for producing porous cellulose particles, comprising:

[0024] A mixed solution preparation step of preparing a mixed solution by mixing an unsubstituted cellulose solution and a chitosan solution; and

[0025] A step of bringing the mixed solution into contact with a coagulation solvent,

[0026] An aqueous solution containing alkali hydroxide and urea is used as the solvent of the mixed solution.

[0027] Item 4. The method for producing porous cellulose particles according to Item 3, further comprising: an acid washing step of the porous cellulose particles obtained in the step of bringing the mixed solution into contact with the coagulation solvent by acid washing.

[0028] Item 5. The method for producing porous cellulose particles according to Item 4, wherein in the porous cellulose particles after the pickling step, in the total of 100% by mass of the unsubstituted cellulose and the chitosan, the content of the chitosan is 1% by mass or more and 20% by mass or less.

[0029] Item 6. The method for producing porous cellulose particles according to any one of Items 3 to 5, wherein the mixed solution preparation step includes the following steps.

[0030] A step of dissolving chitosan in an aqueous acid-containing solution and further mixing alkali hydroxide and urea to obtain the chitosan solution.

[0031] A step of mixing unsubstituted cellulose, alkali hydroxide, urea, and water to obtain the unsubstituted cellulose solution.

[0032] A step of mixing the chitosan solution cooled to a temperature of -10°C or lower with the unsubstituted cellulose solution.

[0033] Advantages of the Invention

[0034] According to the present disclosure, it is possible to provide porous cellulose particles containing chitosan having a predetermined opening on the surface and having a predetermined particle size, and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is an image of the porous cellulose particles obtained in Example 1 observed by an optical microscope.

[0036] Figure 2 It is an image of the porous cellulose particles obtained in Example 1 observed by a scanning electron microscope.

[0037] Figure 3 It is an image of the porous cellulose particles obtained in Example 2 observed by an optical microscope. DETAILED DESCRIPTION

[0038] The porous cellulose particles of the present disclosure are characterized in that they contain unsubstituted cellulose and chitosan. In the total of 100% by mass of the unsubstituted cellulose and the chitosan, the content of the chitosan is 20% by mass or less. In an image of the surface of the porous cellulose particles observed by a scanning electron microscope, pores having a diameter of 0.05 to 5 μm are observed, and the proportion of the porous cellulose particles having a particle size of 10 to 200 μm is 90% by mass or more. The porous cellulose particles of the present disclosure are porous cellulose particles containing chitosan having a predetermined opening on the surface and having a predetermined particle size.

[0039] In addition, as described below, the porous cellulose particles of the present disclosure that exhibit such functionality can be appropriately produced by, for example, a method for producing porous cellulose particles that includes a mixed solution preparation step of preparing a mixed solution by mixing an unsubstituted cellulose solution and a chitosan solution, and uses an aqueous solution containing an alkali hydroxide and urea as a solvent for the mixed solution.

[0040] Hereinafter, the porous cellulose particles of the present disclosure and their production methods will be described in detail.

[0041] 1. Porous cellulose particles

[0042] The porous cellulose particles of the present disclosure contain unsubstituted cellulose (hereinafter sometimes simply referred to as "unsubstituted cellulose") and chitosan.

[0043] In the present disclosure, unsubstituted cellulose means that the hydroxyl groups of cellulose are substantially unsubstituted (i.e., not substituted cellulose), and for example, it is cellulose with a degree of substitution of hydroxyl groups of 0.05 or less. There is no particular limitation on the degree of polymerization of unsubstituted cellulose. For example, it is preferably 1000 or less. If the degree of polymerization is 1000 or less, the dispersibility / swelling property in the alkali aqueous solution described later becomes high, which is preferable. In addition, if the degree of polymerization of unsubstituted cellulose is 10 or more, the mechanical strength of the obtained porous cellulose particles becomes large, and thus it is preferable. The preferable range of the degree of polymerization of unsubstituted cellulose is about 10 to 1000.

[0044] In addition, in the present disclosure, chitosan means a β-1,4-dehydration condensation polymer of glucosamine. Chitin, which is taken out industrially as a component of the shell of crabs, is further subjected to alkali hydrolysis to hydrolyze the acetyl group, but generally sold chitosan more or less retains unreacted acetyl groups. Generally, a substance in which 60% or more of the acetylamino groups are converted to amino groups is called chitosan. Its acetyl group content and degree of polymerization have ranges, but in the present disclosure, there is no particular limitation as long as it is chitosan that can be mixed with porous cellulose. Among them, from the viewpoint of suppressing dissolution and precipitation from the porous cellulose particles, it is ideal that the number average degree of polymerization of chitosan is 10 or more. It should be noted that the upper limit of the number average degree of polymerization of chitosan is, for example, 500 or less, and as a preferable range, 50 to 300 can be cited.

[0045] In the porous cellulose particles of the present disclosure, in a total of 100% by mass of unsubstituted cellulose and chitosan, the content rate of chitosan is 20% by mass or less. In the present disclosure, the content rate of chitosan is set to 20% by mass, whereby porous cellulose particles having a predetermined opening on the surface and a predetermined particle size are obtained. Regarding the upper limit of the content rate of chitosan, it is preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 8% by mass or less. Regarding the lower limit, it is preferably 1% by mass or more, more preferably 2% by mass or more, and still more preferably 3% by mass or more. Examples of the preferred range include: about 1 to 20% by mass, about 1 to 15% by mass, about 1 to 10% by mass, about 1 to 8% by mass, about 2 to 20% by mass, about 2 to 15% by mass, about 2 to 10% by mass, about 2 to 8% by mass, about 3 to 20% by mass, about 3 to 15% by mass, about 3 to 10% by mass, and about 3 to 8% by mass. It should be noted that the chitosan content rate can be measured by performing elemental analysis based on calcination, which is usually carried out, after drying the porous cellulose washed with pure water or the like (the chitosan content rate can be converted by multiplying the nitrogen content value by 161 / 14).

[0046] The porous cellulose particles of the present disclosure are porous materials in which pores having a diameter of 0.05 to 5 μm are observed in an image of observing the surface using a scanning electron microscope. In addition, in the porous cellulose particles of the present disclosure, the proportion of porous cellulose particles having a particle size of 10 to 200 μm is 90% by mass or more. Examples of the upper limit of this proportion include: 95% by mass or less, 98% by mass or less, 99% by mass or less, 100% by mass or less, etc. When the porous cellulose particles of the present disclosure contain porous cellulose particles having a particle size other than 10 to 200 μm, the particle size of the porous cellulose particles of the present disclosure is also preferably in the range of about 1 to 600 μm.

[0047] One use of the porous cellulose particles of the present disclosure is as a carrier for bonding atomic groups with certain functions to the surface for selective separation and reaction. In most cases, their morphology is in the form of fine particles, which are used to fill columns for separation and purification by chromatography or dispersed in liquids for selective adsorption and selective reaction. For this purpose, it is necessary to enable the rapid diffusion or permeation of substances inside the carrier particles and between the inside and outside. Therefore, it is necessary to have a specified particle size and specified openings. Moreover, inside the porous cellulose particles, it is preferable to have a structure in which the ratio of the space is overwhelmingly larger than that of a solid (for example, a structure in which fibers are intertwined). Such a structure is manifested by making the solid content rate of the porous cellulose particles in the water-containing state a low-density gel of 10% by mass or less. That is, for such a structure, the appearance of the porous cellulose particles is solid particles, but spaces of 5 μm or less that are not visible to the naked eye account for about 90% by volume or more, and these pores or spaces are filled with a liquid (water in the case of a hydrogel). Regarding the lower limit of the solid content rate, for example, it is 1% by mass or more, preferably 3% by mass or more, and preferred ranges include 1 to 10% by mass and 3 to 10% by mass. The solid content rate of the porous cellulose particles in the water-containing state is measured by the following method.

[0048] (Measurement of solid content rate)

[0049] The porous cellulose particles in a state of having settled in pure water are left standing for one day or more (usually within three days) in an environment of atmospheric pressure and a temperature of 25°C. Then, about 2 mL of the porous cellulose particles in pure water is pipetted and dispersed in 20 mL of a solution obtained by diluting a neutral detergent (for example, the product name mama lemon manufactured by LION Corporation) 1000 times with pure water, and left standing for one day or more (usually within three days) to settle. Then, the supernatant is removed by decantation, and 1 / 3 of the remaining slurry is taken as one sample and dropped onto three types of filter papers (for example, No. 131 150 mm manufactured by ADVANTEC) corresponding to those specified in JIS P 3801 [Filter paper (for chemical analysis)]. After leaving it for 20 seconds and removing the remaining moisture, the mass of the porous cellulose particle mass remaining on the filter paper is peeled off from the filter paper and weighed to obtain the wet mass of the porous cellulose particles. Then, the porous cellulose particles are dried in an oven at 80°C for 2 hours to obtain the dry mass. These operations are performed on three samples, and the ratio of the dry mass to the wet mass is calculated respectively, and the average value of the three obtained values is taken as the solid content rate.

[0050] As described later, the porous cellulose particles of the present disclosure are preferably obtained in a state of being dispersed or impregnated in water. The porous cellulose particles of the present disclosure are in a water-containing state in water and form a hydrogel. In addition, the porous cellulose particles of the present disclosure can generally be stored in a water-wet state.

[0051] In the case of long-term storage in a water-wet state, preservatives such as alcohol and sodium azide are added to prevent spoilage. In addition, it can be dried in a state where glycerol, sugars, urea, etc. are added, and freeze-drying is preferably performed.

[0052] In addition, the porous cellulose particles of the present disclosure exhibit functions that the porous cellulose itself composed only of unsubstituted cellulose does not have. Therefore, for example, they can be preferably used in size exclusion chromatography. Moreover, this means that it is not necessary to perform it again, and it can also be used for chromatographic separation based on various modes other than size exclusion. These include ion exchange, hydrophobicity, affinity, and other modes.

[0053] In addition, by using a cross-linking agent in the porous cellulose particles of the present disclosure and cross-linking cellulose or chitosan chains through covalent bonds, it can also be used as a separating agent with further improved strength.

[0054] An adsorbent can also be manufactured by immobilizing an affinity ligand on the porous cellulose particles of the present disclosure and the cross-linked porous cellulose medium. This adsorbent can also be used as a separating agent for affinity chromatography.

[0055] In the present disclosure, the method for manufacturing porous cellulose particles is not particularly limited as long as the porous cellulose particles of the present disclosure having the above-described configuration are obtained, and it can preferably be manufactured by the manufacturing method shown in the following "2. Method for manufacturing porous cellulose particles".

[0056] 2. Method for producing porous cellulose particles

[0057] The method for manufacturing porous cellulose particles of the present disclosure is characterized by including a mixed solution preparation step of preparing a mixed solution obtained by mixing an unsubstituted cellulose solution and a chitosan solution, and using an aqueous solution containing an alkali hydroxide and urea as a solvent for the mixed solution. Details of unsubstituted cellulose, chitosan, etc. are as described in the above "1. Porous cellulose particles" section.

[0058] (Mixed solution preparation step)

[0059] The mixed solution preparation step is a step of preparing a mixed solution in which an unsubstituted cellulose solution and a chitosan solution are mixed.

[0060] An unsubstituted cellulose solution is a solution prepared using a solvent capable of dissolving unsubstituted cellulose. In addition, a chitosan solution is a solution prepared using a solvent capable of dissolving chitosan. It is known that unsubstituted cellulose dissolves well in an aqueous alkali hydroxide solution and an alkali hydroxide-urea aqueous solution (for example, a urea-alkali hydroxide aqueous solution containing urea, thiourea, etc.). In contrast, chitosan, which has an amino group and is basic, is generally insoluble in such aqueous solutions. However, chitosan dissolves in water containing about an equal amount of acid, and when a specified amount of alkali hydroxide and urea are added thereto and the mixture is cooled while stirring (preferably to about -10°C to -15°C), then returned to room temperature and stirring is continued, a chitosan solution that is slightly thixotropic and almost homogeneous is obtained. By repeating this operation, a chitosan solution with gradually increasing homogeneity is obtained. Thus, in the present disclosure, as the solvent for the unsubstituted cellulose solution and the chitosan solution, an aqueous solution containing both alkali hydroxide and urea is preferably used, whereby the aqueous solution containing alkali hydroxide and urea can be used as the solvent for the mixed solution.

[0061] That is, preferably, in the method for producing porous cellulose particles of the present disclosure, the mixed solution preparation step includes: a step of dissolving chitosan in an acid-containing aqueous solution, further mixing alkali hydroxide and urea to obtain a chitosan solution; a step of mixing unsubstituted cellulose, alkali hydroxide, urea, and water to obtain the unsubstituted cellulose solution; and a step of mixing the chitosan solution cooled to a temperature of -10°C or lower (preferably about -10°C to -15°C) with the unsubstituted cellulose solution.

[0062] Specific examples of the aqueous solution containing alkali hydroxide and urea include an aqueous solution (urea-alkali hydroxide aqueous solution) containing 7 to 10% by mass of alkali hydroxide and 5 to 15% by mass of urea (thiourea may also be used. The same applies hereinafter). As the alkali hydroxide, lithium hydroxide and sodium hydroxide are preferred in terms of the good solubility of unsubstituted cellulose and chitosan, and sodium hydroxide is preferred from the viewpoint of raw material cost. In the solvent based on this aqueous alkali hydroxide solution, it is preferred to cool to around -10°C to -15°C while stirring the solute (unsubstituted cellulose, chitosan) and the solvent, then return to room temperature, and perform this operation one or more times to form a fluid solution. Furthermore, in the case where insolubles remain and have an adverse effect on the function of the final product, the insolubles can be removed by filtration or centrifugation.

[0063] An unsubstituted cellulose solution refers to a liquid containing unsubstituted cellulose, showing fluidity. When it comes into contact with a coagulation solvent in the form of a mixed solution mixed with a chitosan solution, the unsubstituted cellulose and chitosan solidify in a compatible state. It is acceptable that unsubstituted cellulose molecules are dispersed in the unsubstituted cellulose solution, or a part of the aggregates remain, or only fine fibrous substances are dispersed (sometimes called a dispersion). That is, in the method for manufacturing porous cellulose particles of the present disclosure, the unsubstituted cellulose solution refers to a liquid containing unsubstituted cellulose, which is a concept including a dispersion formed by dispersing unsubstituted cellulose in a liquid and a solution formed by dissolving unsubstituted cellulose in a liquid. In the method for manufacturing porous cellulose particles of the present disclosure, when preparing the unsubstituted cellulose solution, as long as the unsubstituted cellulose solution contains unsubstituted cellulose, regarding its form, it can be any of the dispersion / dissolution or their mixed states.

[0064] In addition, the same applies to the chitosan solution. The chitosan solution refers to a liquid containing chitosan, showing fluidity. When it comes into contact with a coagulation solvent in the form of a mixed solution mixed with an unsubstituted cellulose solution, the unsubstituted cellulose and chitosan solidify in a compatible state. It is acceptable that chitosan molecules are dispersed in the chitosan solution, or a part of the aggregates remain, or only fine fibrous substances are dispersed (sometimes called a dispersion). That is, in the method for manufacturing porous cellulose particles of the present disclosure, the chitosan solution refers to a liquid containing chitosan, which is a concept including a dispersion formed by dispersing chitosan in a liquid and a solution formed by dissolving chitosan in a liquid. In the method for manufacturing porous cellulose particles of the present disclosure, when preparing the chitosan solution, as long as the chitosan solution contains chitosan, regarding its form, it can be any of the dispersion / dissolution or their mixed states.

[0065] In addition, the same applies to the mixed solution. The mixed solution refers to a liquid containing unsubstituted cellulose and chitosan, showing fluidity. When the mixed solution comes into contact with a coagulation solvent, the unsubstituted cellulose and chitosan solidify in a compatible state. It is acceptable that unsubstituted cellulose molecules and chitosan molecules are dispersed in the mixed solution, or a part of the aggregates remain, or only fine fibrous substances are dispersed (sometimes called a dispersion). That is, in the method for manufacturing porous cellulose particles of the present disclosure, the mixed solution refers to a liquid containing unsubstituted cellulose and chitosan, which is a concept including a dispersion formed by dispersing unsubstituted cellulose or chitosan in a liquid and a solution formed by dissolving unsubstituted cellulose or chitosan in a liquid. In the method for manufacturing porous cellulose particles of the present disclosure, regarding the forms of the unsubstituted cellulose and chitosan in the mixed solution, they can be any of the dispersion / dissolution or their mixed states respectively.

[0066] Hereinafter, taking the case where the solvent is an aqueous solution of urea - alkali hydroxide as an example, the preparation method of the cellulose solution will be specifically described. Regarding the chitosan solution, chitosan can also be used as the solute, and the chitosan solution can be prepared in the same way. However, as described above, regarding the chitosan solution, ideally, chitosan is dissolved in an aqueous solution containing an acid, and then alkali hydroxide and urea are further mixed to obtain the chitosan solution. The acidic component of the aqueous solution containing an acid can be any acidic component such as hydrogen chloride, acetic acid, formic acid, nitric acid, trifluoroacetic acid, etc. In the next step, to completely neutralize this acid, an excessive amount of alkali hydroxide is required. Therefore, the amount of the acid is set to be equal to or less than the equivalent amount relative to the amino group of chitosan, and preferably set to the minimum amount required to dissolve chitosan.

[0067] The alkali contained in the aqueous solution of alkali hydroxide is preferably lithium hydroxide, sodium hydroxide, potassium hydroxide, or quaternary ammonium base. Considering product safety, price, and good dissolution or dispersion, sodium hydroxide is most preferred.

[0068] The alkali concentration of the alkali aqueous solution is not particularly limited. Except for the part consumed by neutralization with the acid, it is preferably 3 to 20% by mass. If the alkali concentration is within this range, the dispersibility / swelling property and solubility of unsubstituted cellulose in the alkali aqueous solution become high, so it is preferred. The more preferred alkali concentration is 5 to 15% by mass, and further preferably 6 to 10% by mass.

[0069] Urea is further added to the above alkali aqueous solution. The concentration of urea is preferably 10 to 15% by mass. When adding three components (cellulose, alkali hydroxide, urea) to water, the addition order is appropriately selected to optimize the dissolution state of cellulose. By cooling the slurry obtained in this way under the conditions described below, a transparent unsubstituted cellulose solution can be obtained compared to just after adding all the components.

[0070] As described above, if the degree of polymerization of unsubstituted cellulose is 1000 or less, the dispersibility / swelling property in the alkali aqueous solution is preferably high. In addition, as an example of unsubstituted cellulose with improved solubility, dissolving pulp can also be cited.

[0071] Regarding the mixing conditions of the alkali aqueous solution and unsubstituted cellulose, there is no particular limitation as long as an unsubstituted cellulose solution can be obtained. For example, unsubstituted cellulose can be added to the alkali aqueous solution, or the alkali aqueous solution can be added to unsubstituted cellulose. In the case of preparing a chitosan solution, regarding the mixing conditions of the alkali aqueous solution and the aqueous solution in which chitosan is dissolved in an aqueous solution containing an acid, there is no particular limitation as long as a chitosan solution can be obtained. The aqueous solution in which chitosan is dissolved in an aqueous solution containing an acid can be added to the alkali aqueous solution, or the alkali aqueous solution can be added to the aqueous solution in which chitosan is dissolved in an aqueous solution containing an acid.

[0072] Unsubstituted cellulose can be suspended in water before mixing with the alkali aqueous solution.

[0073] In addition, the concentration of the unsubstituted cellulose in the unsubstituted cellulose solution is not particularly limited as long as it is appropriately set so as to be the content rate in the mixed solution described later. For example, it can be about 1 to 10% by mass. In addition, the concentration of the chitosan in the chitosan solution is not particularly limited as long as it is appropriately set so as to be the content rate in the mixed solution described later. For example, it can be about 1 to 10% by mass.

[0074] There is no particular limitation on the temperature when preparing the unsubstituted cellulose solution. For example, the unsubstituted cellulose and the aqueous alkali solution containing urea are mixed at room temperature, cooled to a low temperature while stirring, and then returned to a temperature that is easy to operate, thereby appropriately forming the unsubstituted cellulose solution. As the temperature when cooling to a low temperature, for example, it can be from 0°C to -30°C, preferably about -5°C to -15°C. The same applies to the temperature when preparing the chitosan solution.

[0075] The mixed solution is prepared by mixing the unsubstituted cellulose solution and the chitosan solution. The mixing ratio of the unsubstituted cellulose solution and the chitosan solution is adjusted so as to be the content rate in the mixed solution described later. When mixing the unsubstituted cellulose solution and the chitosan solution, it is preferably stirred sufficiently so that the unsubstituted cellulose solution and the chitosan solution are mixed into a single-phase mixed solution.

[0076] In the mixed solution, in 100% by mass in total of the chitosan and the unsubstituted cellulose, the content rate of the chitosan is preferably 20% by mass or less. By setting the content rate of the chitosan in the mixed solution to 20% by mass, porous cellulose particles having a specified particle size and a specified opening are appropriately obtained. From the viewpoint of more appropriately exhibiting these characteristics, the content rate of the chitosan in the mixed solution is preferably 15% by mass or less, more preferably 10% by mass or less, further preferably 8% by mass or less. Regarding the lower limit, it is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more. As the preferred range, the following can be cited: about 1 to 20% by mass, about 1 to 15% by mass, about 1 to 10% by mass, about 1 to 8% by mass, about 2 to 20% by mass, about 2 to 15% by mass, about 2 to 10% by mass, about 2 to 8% by mass, about 3 to 20% by mass, about 3 to 15% by mass, about 3 to 10% by mass, about 3 to 8% by mass.

[0077] In addition, the total concentration of chitosan and unsubstituted cellulose in the mixed solution is preferably 1 to 10% by mass. If it is 1% by mass or more, the mechanical strength of the obtained porous cellulose particles becomes large, so it is preferred. If it is 10% by mass or less, the viscosity of the mixed solution is low, and for example, it is easy to spray from a spray nozzle so as to have the above-mentioned specified particle size, so it is preferred. As the total concentration in the mixed solution, 2 to 6% by mass is more preferably cited, and 3 to 5% by mass is further preferably cited. It should be noted that the total concentration in the mixed solution does not include components that are not completely dissolved / dispersed / swelled and are not made uniform.

[0078] (Coagulation step)

[0079] In the method for producing porous cellulose particles of the present disclosure, after the mixed solution preparation step, a coagulation step of bringing the mixed solution into contact with a coagulation solvent is performed. By bringing the mixed solution into contact with the coagulation solvent, the unsubstituted cellulose solution and chitosan in the mixed solution are coagulated in a compatible state to obtain porous cellulose particles.

[0080] The specific form of the contact with the coagulation solvent mentioned here is not particularly limited, and known methods can be used. In the coagulation step, a representative method for obtaining porous cellulose particles has the following method: in a liquid with a high viscosity that does not mix with the mixed solution (such as liquid paraffin, fluorolube, etc.), if necessary, the mixed solution is stirred and dispersed together with an appropriate dispersant, and while stirring, the obtained dispersion liquid and a coagulation solvent (a solvent that precipitates unsubstituted cellulose and chitosan by mixing with the dispersion liquid) are gradually added.

[0081] In addition, a sprayer, a nozzle, etc. can also be used to form the mixed solution into droplets in a gas, and the droplets are dropped into the coagulation solvent. That is, in the case of preparing porous cellulose particles by this method, the coagulation step can adopt the following step: after forming the mixed solution into minute droplets in a gas, the minute droplets are absorbed into the coagulation solvent. In addition, the mixed solution can be extruded into a line and added to the coagulation solvent, and after coagulating it, it is cut or broken to form amorphous particles.

[0082] The coagulation solvent is not particularly limited as long as it is a solvent that precipitates unsubstituted cellulose and chitosan from the mixed solution, and examples thereof include organic solvents such as methanol, ethanol, and acetone, water, water in which salts such as sodium chloride are dissolved, and water containing an acid in the case where the mixed solution contains an alkali hydroxide.

[0083] The obtained particles can also be directly washed and utilized. However, for the purpose of avoiding the dissolution and precipitation of unnecessary components during use, it is ideal to wash with an acidic aqueous solution at least once or more. That is, in the present disclosure, it may further include: an acid washing step of the porous cellulose particles obtained in the step of bringing the mixed solution into contact with the coagulation solvent by acid washing. In the method for producing porous cellulose particles of the present disclosure, after the acid washing step, the porous cellulose particles having a chitosan content of 1% by mass or more and 20% by mass or less can also be appropriately produced. It should be noted that after the acid washing step, the preferred chitosan content in the porous cellulose particles is the same as the value described in the column of "1. Porous cellulose particles". The acid washing conditions are as follows: at room temperature (25 °C), 3 g of porous cellulose particles in the form of a water-containing filter cake after allowing water to flow naturally from a sieve are subjected to the following operations: washed three times with 10 mL of hydrochloric acid (0.1 N HCl) (each washing takes about 1 hour), washed once with 5 mL of water (each washing takes about 1 hour), washed once with a liquid obtained by dissolving 0.2 g of potassium carbonate in 5 mL of water (each washing takes about 1 hour), and washed twice with 10 mL of water (each washing takes about 1 hour). It should be noted that if such an operation is performed, it is not surprising that all of the acid-soluble chitosan is washed out. However, it can be said that in the porous cellulose particles of the present disclosure, chitosan and cellulose have almost the same skeleton and are partially embedded in the aggregates of cellulose molecules, so that the dissolution and precipitation of chitosan are inhibited even when washed with an acidic aqueous solution.

[0084] In the case of long-term storage in a water-wet state, preservatives such as alcohol and sodium azide are added to prevent spoilage. In addition, it can be dried in a state where glycerol, sugars, urea, etc. are added, and freeze-drying is preferably performed.

[0085] Examples

[0086] Hereinafter, examples and comparative examples will be shown to explain the present disclosure in detail. However, each component and their combinations in each example are examples, and within the scope not departing from the gist of the present disclosure, additional components, omissions, substitutions, and other changes can be appropriately made. The present disclosure is not limited to the examples, but only to the claims.

[0087] <Example 1>

[0088] (Preparation of chitosan solution)

[0089] 0.87 g of chitosan (chitosan manufactured by Wako Pure Chemical Industries, Ltd., 100) was dispersed in 13.84 g of water. 6.25 g of hydrochloric acid (1N HCl) was added thereto and stirred to obtain a transparent, highly viscous liquid. Then, when a liquid obtained by dissolving 2.39 g of sodium hydroxide in 2.06 g of water was added dropwise thereto, a precipitate formed, causing turbidity and loss of fluidity. When 6.42 g of urea was added thereto and stirred, the transparency slightly increased. This liquid was cooled on dry ice until partial white crystallization occurred, then returned to room temperature and stirred. When this operation was repeated three times, a substantially transparent and thixotropic liquid was obtained.

[0090] (Preparation of unsubstituted cellulose solution)

[0091] In a flask, 70.35 g of sodium hydroxide was dissolved in 808.05 g of water. After cooling to room temperature, 42.11 g of powdered cellulose (unsubstituted cellulose, Asahi Kasei CEOLUS PH101) was dispersed therein with stirring. After further adding 120.05 g of urea and dissolving it, it was cooled to -15°C with stirring over about 1 hour, and then warmed to room temperature using a water bath to obtain an almost transparent solution. Note that the moisture content of the powdered cellulose was 4.25% by mass. Therefore, the total solvent system was 1000.24 g, the unsubstituted cellulose was 40.32 g, the external ratio (external division) of the unsubstituted cellulose concentration was 4.0% by mass, and the internal ratio (internal division) of the unsubstituted cellulose concentration was 3.85% by mass.

[0092] (Preparation of mixed solution)

[0093] When 90 g of the prepared unsubstituted cellulose solution and 10 g of the chitosan solution were mixed and stirred, a uniformly mixed solution was obtained.

[0094] (Atomization)

[0095] The obtained mixed solution was sprayed to form a mist and absorbed in methanol to obtain fine powders in a suspended state. Acetic acid was added to make the methanol solution neutral, and the fine powders were filtered out and washed repeatedly with water to obtain porous cellulose particles (fine particles) containing chitosan.

[0096] (Pickling)

[0097] The obtained porous cellulose particles in a state of being appropriately dispersed in water were placed in a 20-μm sieve, and the water was allowed to flow down naturally. 3 g of the cellulose particles in the form of a water-containing filter cake remaining on the sieve were taken, washed three times with 10 mL of hydrochloric acid (0.1 N HCl) (about 1 hour for one washing), and washed twice with a liquid prepared by dissolving 0.2 g of potassium carbonate in 5 mL of water and then adding 5 mL of water. After drying the samples before and after acid washing, elemental analysis was carried out. As a result, in terms of the N content, the sample before acid washing was 0.53 mass%, and after acid washing was 0.52 mass%. If the N content of 0.52 mass% is converted to the chitosan content, it is 6.0 mass%. The mixing ratio of chitosan and unsubstituted cellulose in the stock solution was 7.3 mass% of chitosan. Therefore, about 80% of the chitosan used as a raw material was contained in the porous cellulose particles. It should be noted that the elemental analysis was carried out using a JM10 Micro Corder manufactured by J-Science Lab Co., Ltd.

[0098] (Optical microscope observation)

[0099] The obtained porous cellulose particles were washed with 50 mL of pure water containing sodium bicarbonate for 1 hr, rinsed twice with pure water, passed through a 200-μm sieve in water, thereby removing a small amount of lumps, and further passed through a 10-μm sieve to remove small particles smaller than that, and the particle size of the porous cellulose particles was adjusted to the range of 10 - 200 μm. The obtained particles were observed by transmitted light in water using an optical microscope. The product was approximately spherical, mainly particles with a diameter of 10 - 100 μm ( Figure 1 image).

[0100] (SEM observation)

[0101] A small amount of the obtained porous cellulose particles were dispersed in water, dropped into a metal container cooled with liquid nitrogen and frozen, and then freeze-dried under vacuum. After platinum was evaporated onto the obtained powder, when observed using a scanning electron microscope (HITACHI SU5000) (acceleration voltage 3 kV), a porous structure with fine pores in the range of 0.05 - 5 μm opening on the surface was confirmed. The images observed at each magnification (250 times, 1200 times, 20,000 times, and 100,000 times) are shown in Figure 2 .

[0102] (Solid component content rate)

[0103] The solid content of the porous cellulose particles in the water-containing state obtained in Example 1 was measured by the following method, and the solid content was 5.3% by mass. The porous cellulose particles in the state of being precipitated in pure water were left to stand for one day under atmospheric pressure and a temperature of 25°C. Then, about 2 mL of the porous cellulose particles in pure water were taken with a pipette, dispersed in 20 ml of a solution obtained by diluting a neutral detergent (trade name mama lemon manufactured by Lion Corporation) 1000 times with pure water, and left to stand for one day to allow the particles to settle. Then, the supernatant was removed by decantation, and 1 / 3 of the remaining slurry was used as a sample, and dripped on three types of filter paper (No. 131 150 mm manufactured by ADVANTEC) specified in JIS P3801 [Filter Paper (for Chemical Analysis)], and left for 20 seconds. After removing the remaining water, the block of porous cellulose particles remaining on the filter paper was peeled off from the filter paper and weighed to obtain the wet mass of the porous cellulose particles. Next, the porous cellulose particles were dried in an oven at 80° C. for 2 hours to obtain a dry mass. These operations were performed for three samples, and the ratio of the dry mass to the wet mass was calculated. The average of the three values ​​obtained was taken as the solid content.

[0104] <Example 2>

[0105] 9.5 parts by mass of the unsubstituted cellulose solution prepared in the same manner as in Example 1 and 0.5 parts by mass of the chitosan solution were mixed, and a portion of the mixture was added with a spoon while about 200 mL of methanol was being vigorously stirred, whereby a bulk precipitate was generated.

[0106] Next, it was stirred using a high-speed stirrer with a blade-shaped rotating wing to obtain a slurry containing fine powder. The slurry was neutralized in a large excess of dry ice, washed thoroughly with water, further washed twice with methanol, air-dried, and then vacuum-dried (80 °C). Furthermore, for approximately 1 mL of this precipitate portion, it was washed for 30 minutes each with a liquid obtained by diluting 10 mL of hydrochloric acid (1N HCl) in 55 mL of water and a liquid obtained by diluting 5 mL of hydrochloric acid in 50 mL of water, washed with 50 mL of pure water for 5 minutes, washed with 50 mL of pure water containing 100 mg of sodium bicarbonate for 1 hr, rinsed twice with pure water, rinsed twice with 20 mL of methanol, and then air-dried and vacuum-dried (80 °C). The porous cellulose particles before and after acid washing were each dried and dehydrated, and elemental analysis was performed. As a result, the nitrogen contents were 0.37 mass% and 0.28 mass% respectively. If the nitrogen content of 0.28% in the solid component after acid washing is converted to chitosan content, it is 3.2 mass%. If the total amount of chitosan originally mixed (4.42 mass% of the total mass of cellulose and chitosan) remained, the nitrogen content was estimated to be 0.38 mass%. Thus, the porous cellulose particles 1 before acid washing retained almost the total amount of chitosan, and the porous cellulose particles 2 after acid washing retained approximately 74 mass% of chitosan.

[0107] (Optical microscope observation)

[0108] The obtained porous cellulose particles were washed with 50 mL of pure water containing sodium bicarbonate for 1 hr and rinsed twice with pure water. The obtained material was passed through a 200 μm sieve in water to remove a small amount of lumps. Further, a 10 μm sieve was used to remove small particles smaller than that, and the particle size of the porous cellulose particles was adjusted to the range of 10 - 200 μm. The obtained particles were observed by transmitted light in water using an optical microscope. The product was amorphous, mainly particles with a major axis of approximately 30 μm. ( Figure 3 image)(SEM observation)

[0109] Regarding the obtained porous cellulose particles, when observed using a scanning electron microscope in the same manner as in Example 1, a porous structure with pores in the range of 0.05 - 5 μm was confirmed to be open on the surface.

[0110] (Solid component content rate)

[0111] For the porous cellulose particles obtained in Example 2, when impregnated with water by the same method as in Example 1, the solid component content rate was 4.9 mass%.

Claims

1. A porous cellulose particle, the porous cellulose particle comprising unsubstituted cellulose and chitosan, In a total of 100% by mass of the unsubstituted cellulose and the chitosan, the content of the chitosan is 3% by mass or more and 8% by mass or less, In an image of observing the surface of the porous cellulose particle using a scanning electron microscope, pores with a diameter of 0.05 to 5 μm are observed, The proportion of the porous cellulose particles with a particle size of 10 to 200 μm is 90% by mass or more, The particle size of the porous cellulose particle is in the range of 1 to 600 μm.

2. The porous cellulose particle according to claim 1, wherein, The solid content ratio of the porous cellulose particles in the water-containing state measured by the following method is 10% by mass or less. The method for measuring the solid content ratio is as follows: The porous cellulose particles in the state of having settled in pure water are left standing for one day or more in an environment of atmospheric pressure and a temperature of 25°C. Then, 2 mL of the porous cellulose particles in the pure water is pipetted and dispersed in 20 mL of a solution obtained by diluting a neutral detergent 1000-fold with pure water. The porous cellulose particles are left standing for one day or more to settle, and then the supernatant is removed by decantation. One-third of the amount of the remaining slurry is taken as a sample and dropped onto three types of filter papers specified in JIS P3801 [Filter Paper (for Chemical Analysis)]. After leaving it for 20 seconds and removing the remaining moisture, the mass of the block of the porous cellulose particles remaining on the filter paper is peeled off from the filter paper and weighed as the wet mass of the porous cellulose particles. Then, the porous cellulose particles are dried in an oven at 80°C for 2 hours and then weighed as the dry mass. These operations are performed on three samples, and the ratio of the dry mass to the wet mass is calculated for each. The average value of the three obtained values is taken as the solid content ratio.

3. A method for manufacturing the porous cellulose particle according to claim 1 or 2, the manufacturing method comprising: A mixed solution preparation step of preparing a mixed solution by mixing an unsubstituted cellulose solution and a chitosan solution; and A step of bringing the mixed solution into contact with a coagulation solvent, An aqueous solution containing alkali hydroxide and urea is used as the solvent of the mixed solution.

4. The method for manufacturing the porous cellulose particle according to claim 3, wherein, The manufacturing method further includes a pickling step for the porous cellulose particles obtained in the step of bringing the mixed solution into contact with the coagulation solvent by pickling with an acid.

5. The method for manufacturing the porous cellulose particle according to claim 4, wherein, In the porous cellulose particles after the pickling step, the content ratio of chitosan is 3% by mass or more and 8% by mass or less in a total of 100% by mass of the unsubstituted cellulose and chitosan.

6. The method for manufacturing the porous cellulose particle according to any one of claims 3 to 5, wherein, The mixed solution preparation step includes the following steps: A step of dissolving chitosan in an aqueous solution containing an acid and further mixing an alkali hydroxide and urea to obtain the chitosan solution; A step of mixing unsubstituted cellulose, an alkali hydroxide, urea, and water to obtain the unsubstituted cellulose solution; and A step of mixing the chitosan solution cooled to a temperature of -10°C or lower with the unsubstituted cellulose solution.

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