JP2019189824A - Composite particle, manufacturing method of composite particle, and dry powder - Google Patents

Abstract

Disclosed are a new composite particle that is easy to handle and has biodegradability while maintaining the properties of cellulose nanofiber, a method for producing the composite particle, and a dry powder containing the composite particle.
A composite particle 5 according to an aspect of the present invention includes at least one kind of compound particle 3 having biodegradability and fine cellulose that covers at least a part of the surface of the compound particle 3 having biodegradability. The compound particles 3 having biodegradability and the finely divided cellulose 1 are in an indivisible state.

Description

  The present invention relates to composite particles of finely divided cellulose and a compound having biodegradability, a method for producing composite particles of finely divided cellulose and a compound having biodegradability, and a dry powder containing the composite particles.

In recent years, attempts have been actively made to refine cellulose fibers in wood so that at least one side of the structure is on the order of nanometers and to use them as novel functional materials.
For example, as disclosed in Patent Document 1, it is disclosed that fine cellulose fibers, that is, cellulose nanofibers (hereinafter also referred to as CNF) can be obtained by repeating mechanical processing using wood blender or grinder on wood cellulose. Yes. CNF obtained by this method has been reported to have a short axis diameter of 10 to 50 nm and a long axis diameter ranging from 1 μm to 10 mm. This CNF is 1/5 lighter than steel, has a strength five times higher, and has an enormous specific surface area of 250 m ² / g or more, so it is expected to be used as a resin reinforcing filler and adsorbent. ing.

  In addition, attempts have been actively made to produce CNF by chemically treating cellulose fibers in wood in advance so as to be easily refined, and then refining by a low energy mechanical treatment similar to a home mixer. Although the method of the said chemical treatment is not specifically limited, The method of introduce | transducing an anionic functional group into a cellulose fiber and making it easy to refine | miniaturize is preferable. By introducing an anionic functional group into the cellulose fiber, the solvent can easily enter between the cellulose microfibril structures due to the osmotic pressure effect, and the energy required for refining the cellulose raw material can be greatly reduced. The method for introducing the anionic functional group is not particularly limited. For example, Non-Patent Document 1 discloses a method for selectively subjecting the fine fiber surface of cellulose to a phosphoric esterification treatment using a phosphoric esterification treatment. ing. Patent Document 2 discloses a method for carrying out carboxymethylation by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a high-concentration alkaline aqueous solution. Alternatively, a carboxy group may be introduced by directly reacting a carboxylic anhydride compound such as maleic acid or phthalic acid gasified in an autoclave with cellulose.

  Also, a method for selectively oxidizing the surface of cellulose fine fibers using 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO), which is a relatively stable N-oxyl compound, as a catalyst. Has also been reported (see, for example, Patent Document 3). Oxidation reaction using TEMPO as a catalyst (TEMPO oxidation reaction) can be chemically modified in an environmentally friendly manner that proceeds in water, at room temperature, and at normal pressure. When applied to cellulose in wood, there is a reaction inside the crystal. Without proceeding, only the alcoholic primary carbon possessed by the cellulose molecular chain on the crystal surface can be selectively converted into a carboxy group.

  Cellulose single nanofibers (hereinafter also referred to as CSNF) dispersed in individual cellulose microfibril units in a solvent by the osmotic pressure effect accompanying ionization of carboxy groups selectively introduced on the crystal surface by TEMPO oxidation. Can be obtained). CSNF exhibits high dispersion stability derived from surface carboxy groups. Wood-derived CSNF obtained from wood by TEMPO oxidation reaction is a structure having a high aspect ratio with a minor axis diameter of around 3 nm and a major axis diameter ranging from several tens of nanometers to several micrometers, and its aqueous dispersion and molded article Has been reported to have high transparency. Patent Document 4 reports that a laminated film obtained by applying and drying a CSNF dispersion has gas barrier properties.

  Here, for the practical application of CNF, it is a problem that the solid content concentration of the obtained CNF dispersion is as low as about 0.1 to 5%. For example, when trying to transport a finely divided cellulose dispersion, it is equivalent to transporting a large amount of solvent, so that there is a problem that the transportation cost rises and the business property is remarkably impaired. In addition, when used as an additive for resin reinforcement, there are problems that the addition efficiency is deteriorated due to low solid content and that it is difficult to make a composite when water as a solvent is not compatible with the resin. Further, when handling in a water-containing state, the water-containing CNF dispersion may be spoiled, so measures such as refrigeration storage and antiseptic treatment are required, and the cost may increase.

However, if the solvent of the refined cellulose dispersion is simply removed by heat drying or the like, the refined cellulose will aggregate, keratinize or form a film, and it will be difficult to develop a stable function as an additive. End up. Furthermore, since the solid content concentration of CNF is low, a large amount of energy is applied to the solvent removal process itself by drying, which is a factor that impairs the business.
Thus, since handling itself of CNF in the state of a dispersion itself becomes a cause which impairs business property, providing the new handling mode which can handle CNF easily is desired strongly.
As exemplified above, various studies have been made on the development of highly functional members that impart new functionality to refined cellulose, including CNF or CSNF, which are carbon neutral materials.

  On the other hand, various microparticles and microcapsules have been put into practical use as functional materials in various fields. Usually, microparticles are microsize order particles formed from various polymers, and are used, for example, as fillers, spacers, abrasives, and the like. As a conventional method for producing a resin powder, for example, a method in which a monomer emulsified using a surfactant is polymerized and a resin mass is cooled to a low temperature of −50 to −180 ° C. Examples include a method of obtaining fine powder by mechanical pulverization and classification (Patent Document 5). However, the former, for example, causes foam troubles due to foaming in each step such as stirring operation, transfer, auxiliary agent addition, coating, etc., leading to a decrease in production efficiency, and wastewater load due to outflow of surfactants. It is a problem. In the latter case, for example, a long time is required for the pulverization / classification work, and there is a problem that the shape of the powder is not uniform. Further, by providing a microcapsule structure in which microparticles are used as a core substance and the particle surface is coated with a wall film, it has been attempted to impart and develop further functionality. Specifically, for example, by incorporating functional materials such as magnetic substances, pharmaceuticals, agricultural chemicals, fragrances, adhesives, enzymes, pigments, and dyes into a core substance, the functional properties are obtained by microencapsulation. It is possible to protect the material and control the release behavior. It is also possible to further add a functional material to the wall film itself covering the core substance. In recent years, there has been a strong demand for a powder having biodegradability, which is environmentally friendly and can be decomposed by natural microorganisms after use and eventually become water and carbon dioxide.

  Thus, it is highly desired to provide a new handling mode that can easily handle biodegradable microparticles.

JP 2010-216021 A International Publication No. 2014/088072 JP 2008-001728 A International Publication No. 2013/042654 JP 2001/288273 A

Noguchi Y, Homma I, Matsubara Y. Complete nanofibrillation of cellulose prepared by phosphorylation. Cellulose. 2017; 24: 1295.10.1007 / s10570-017-1191-3

  The present invention has been made in view of such circumstances. New composite particles that are easy to handle, have biodegradability while maintaining the properties of cellulose nanofibers, a method for producing the composite particles, and composites thereof The object is to provide a dry powder containing particles.

In order to solve the above problems, the present invention proposes the following means.
The composite particles according to one embodiment of the present invention include particles containing at least one type of biodegradable compound, and fine cellulose that covers at least part of the surface of the particles containing the biodegradable compound, The particles containing the biodegradable compound and the fine cellulose are in an indivisible state.

  The method for producing composite particles according to one aspect of the present invention includes a first step of obtaining a fine cellulose dispersion by defibrating a cellulose raw material in a solvent, and a biodegradable compound in the dispersion. A second step of covering at least a part of the surface of the droplet containing the liquid with the micronized cellulose and stabilizing the liquid droplet containing the biodegradable compound as an emulsion, and the biodegradable compound. In a state where at least a part of the surface of the droplet is covered with the fine cellulose, the droplet containing the biodegradable compound is solidified to form a polymer particle, whereby at least the surface of the polymer particle is A third step of covering a part with the finely divided cellulose and making the polymer particles and the finely divided cellulose indivisible.

  In the second step of the method for producing composite particles according to one embodiment of the present invention, a mixture of the biodegradable compound containing an initiator and a polymerizable monomer is added to the fine cellulose dispersion. A step of emulsifying, a step of adding the biodegradable compound dissolved in a solvent having low compatibility with the finely divided cellulose dispersion to the finely divided cellulose dispersion, and emulsifying Using any of the steps of adding the biodegradable compound that is solid at room temperature to the finely divided cellulose dispersion and heating it to the melting point or higher of the biodegradable compound to make it emulsify May be.

  The dry powder according to one embodiment of the present invention includes the composite particles described above, and has a solid content of 80% or more.

  According to one aspect of the present invention, new composite particles that are biodegradable and easy to handle while maintaining the properties of cellulose nanofibers, a method for producing the composite particles, and drying including the composite particles Powders can be provided.

It is the schematic of the composite particle obtained by solidifying the O / W type pickering emulsion using CNF which concerns on embodiment of this invention, and the compound which has biodegradability inside an emulsion. 2 is a result of spectral transmission spectrum measurement of an aqueous dispersion of fine cellulose obtained in Example 1. FIG. It is the result of having performed steady-state viscoelasticity measurement using the rheometer with respect to the aqueous dispersion liquid of the refined cellulose obtained in Example 1. FIG. It is a figure (SEM image) which shows the result of having observed the composite particle obtained in Example 1 with the scanning electron microscope (SEM). It is a figure (SEM image) which shows the result of having observed the composite particle obtained in Example 1 with the scanning electron microscope (SEM) at high magnification.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the same reference numerals are given to portions corresponding to each other in the drawings to be described below, and description of the overlapping portions will be omitted as appropriate. In addition, the present embodiment exemplifies a configuration for embodying the technical idea of the present invention, and does not specify the material, shape, structure, arrangement, dimensions, and the like of each part as follows. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

<Refined cellulose / compound composite particles having biodegradability>
First, the refined cellulose / biodegradable compound particle composite particle 5 according to an embodiment of the present invention will be described. FIG. 1 shows an outline of an O / W-type pickering emulsion using cellulose nanofiber (hereinafter also referred to as CNF or cellulose) 1 and a composite particle 5 obtained by solidifying a compound having biodegradability inside the emulsion. FIG. The term “micronized cellulose” as used herein means fibrous cellulose having a number average minor axis diameter in the range of 1 nm to 1000 nm in terms of minor axis diameter. The term “biodegradable” as used herein means decomposing and disappearing in the earth environment such as soil and seawater. In general, polymers and the like are decomposed and disappeared by enzymes of microorganisms in soil and seawater, whereas they are decomposed and disappeared by physicochemical hydrolysis without requiring enzymes in vivo.

The composite particle 5 includes the compound particle 3 that is a particle containing at least one kind of biodegradable compound, and the surface of the biodegradable compound particle 3 is constituted by the refined cellulose 1. It is a composite particle in which the compound particles 3 having biodegradability and the refined cellulose 1 are in an inseparable state.
As shown in FIG. 1, O / W-type Pickering emulsion is obtained by adsorbing fine cellulose 1 on the interface of compound droplet 2 which is a droplet containing a biodegradable compound dispersed in dispersion 4. The composite particles 5 using the emulsion as a template are produced by solidifying the biodegradable compound in the emulsion while maintaining the stabilized state.

  “Inseparable” as used herein refers to, for example, an operation of purifying and washing the composite particles 5 by centrifuging the dispersion containing the composite particles 5 to remove the supernatant, and further adding a solvent and redispersing, or Even after repeated washing with a solvent by filtration washing using a membrane filter, the refined cellulose 1 and the biodegradable compound particles 3 are not separated, and the biodegradability by the refined cellulose 1 is not separated. This means that the covering state of the compound particles 3 having the above is maintained. The coating state can be confirmed, for example, by observing the surface of the composite particle 5 with a scanning electron microscope. Although the binding mechanism between the refined cellulose 1 and the biodegradable compound particles 3 in the composite particles 5 is not clear, an O / W emulsion in which the composite particles 5 are stabilized by the refined cellulose 1 is used as a template. Since the compound droplet 2 having biodegradability is solidified with the finely divided cellulose 1 in contact with the compound droplet 2 having biodegradability inside the emulsion, the composite particles obtained after solidification 5, it is expected that at least a part of the refined cellulose 1 present on the surface of the biodegradable compound particles 3 serving as the core is taken into the biodegradable compound particles 3. . For the above reasons, the micronized cellulose 1 is physically fixed to the compound particle 3 having biodegradability after solidification, and finally the compound particle 3 having biodegradability and the micronized cellulose 1 are inseparable. It is inferred that it will reach a new state.

Here, the O / W type emulsion is also referred to as oil-in-water type, and water is a continuous phase in which oil is dispersed as oil droplets (oil particles). .
In addition, since the composite particle 5 is produced using an O / W emulsion stabilized by the refined cellulose 1 as a template, the shape of the composite particle 5 is a true sphere derived from the O / W emulsion. is there. Specifically, the coating layer made of the finely divided cellulose 1 is formed on the surface of the true spherical biodegradable compound particles 3 with a relatively uniform thickness. The average thickness of the coating layer is obtained by, for example, scanning a scanning electron microscope after cutting the composite particle 5 fixed with an embedding resin with a microtome, and measuring the thickness of the coating layer in the cross-sectional image of the composite particle 5 in the image. It can be calculated by measuring 100 locations at random and taking an average value. Further, the composite particles 5 are characterized by being uniformly coated with a coating layer having a relatively uniform thickness. Specifically, the coefficient of variation of the above-described coating layer thickness value is 0.5 or less. Is more preferable and 0.4 or less is more preferable. When the variation coefficient of the thickness value of the coating layer containing the micronized cellulose 1 exceeds 0.5, for example, it may be difficult to collect the composite particles 5.

  Furthermore, it is preferable that the refined cellulose 1 has a fiber shape derived from a microfibril structure. Specifically, the refined cellulose 1 is fibrous, the number average minor axis diameter is 1 nm or more and 1000 nm or less, the number average major axis diameter is 50 nm or more, and the number average major axis diameter is the number average minor axis diameter. It is preferable that it is 5 times or more. Moreover, it is preferable that the crystal structure of the refined cellulose 1 is cellulose I type.

<Method for producing composite particles>
Next, the manufacturing method of the composite particle of this embodiment is demonstrated. In the method for producing composite particles according to the present embodiment, a cellulose raw material is defibrated in a solvent to obtain a dispersion 4 of fine cellulose 1 (first process), and in the dispersion 4 of fine cellulose 1 Covering at least a part of the surface of the compound droplet 2 having biodegradability with the micronized cellulose 1 and stabilizing the compound droplet 2 having biodegradability as an emulsion (second step); In a state where at least a part of the surface of the compound droplet 2 is covered with the fine cellulose 1, the compound droplet 2 having biodegradability is solidified to form the compound particle 3 having biodegradability. A step of covering at least a part of the surface of the decomposable compound particles 3 with the finely divided cellulose 1 and making the compound particles 3 having the biodegradability and the finely divided cellulose 1 inseparable (third step); Have That is a method of producing composite particles 5.

  The composite particles 5 obtained by the above production method are obtained as a dispersion in a solvent. Further, it is obtained as a dry solid by removing the solvent. The method for removing the solvent is not particularly limited, and for example, excess water can be removed by a centrifugal separation method or a filtration method, and further dried by heat in an oven to obtain a dry solid. At this time, the obtained dry solid does not form a film or an aggregate, but is obtained as a fine powder. The reason for this is not clear, but it is generally known that when the solvent is removed from the refined cellulose dispersion, the refined cellulose strongly aggregates and forms a film. On the other hand, in the case of the dispersion containing the composite particles 5, since the refined cellulose 1 is a true spherical composite particle fixed on the surface, the refined cellulose 1 does not aggregate even if the solvent is removed. It is thought that the dry solid is obtained as a fine powder because it only touches the points between the particles. Further, since there is no aggregation between the composite particles 5, it is easy to re-disperse the composite particles 5 obtained as a dry powder in the solvent again, and the fine particles bonded to the surface of the composite particles 5 after the re-dispersion. The dispersion stability derived from cellulose 1 is shown.

  The dry powder of the composite particles 5 is a dry solid characterized by containing almost no solvent and being redispersible in the solvent. Specifically, the solid content may be 80% or more. Further, it can be 90% or more, and can be 95% or more. Since the solvent can be almost removed, for example, favorable effects are obtained from the viewpoints of reducing transportation costs, preventing spoilage, improving the addition rate, and improving the kneading efficiency with the resin. In addition, when the solid content rate is increased to 80% or more by the drying treatment, the refined cellulose 1 easily absorbs moisture, so that moisture in the air may be adsorbed and the solid content rate may decrease with time. However, considering the technical idea of the present invention, which is characterized in that the composite particles 5 can be easily obtained as a dry powder and can be redispersed, the solid content ratio of the dry powder containing the composite particles 5 is 80%. A dry solid produced by the dry solid production method including the steps described above is defined as being included in the technical scope of the present invention.

Below, each process is demonstrated in detail.
(First step)
The first step is a step in which a cellulose raw material is defibrated in a solvent to obtain a fine cellulose dispersion. First, various cellulose raw materials are dispersed in a solvent to form a suspension. The concentration of the cellulose raw material in the suspension is preferably 0.1% or more and less than 10%. If the concentration of the cellulose raw material in the suspension is less than 0.1%, the solvent is excessive and the productivity tends to be impaired, which is not preferable. Further, if the concentration of the cellulose raw material in the suspension is 10% or more, the suspension is rapidly thickened along with the defibration of the cellulose raw material, and it tends to be difficult to perform a uniform defibrating process. . The solvent used for preparing the suspension preferably contains 50% or more of water. When the proportion of water in the suspension is less than 50%, the dispersion of the fine cellulose 1 tends to be inhibited in the step of defibrating the cellulose raw material described later in a solvent to obtain a fine cellulose dispersion. . Moreover, as a solvent contained other than water, a hydrophilic solvent is preferable. The hydrophilic solvent is not particularly limited, but for example, alcohols such as methanol, ethanol and isopropanol; and cyclic ethers such as tetrahydrofuran are preferable. If necessary, the pH of the suspension may be adjusted, for example, in order to increase the dispersibility of the cellulose and the refined cellulose 1 to be produced. Examples of the alkaline aqueous solution used for pH adjustment include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, And organic alkalis such as benzyltrimethylammonium hydroxide aqueous solution. A sodium hydroxide aqueous solution is preferable from the viewpoint of cost.

  Subsequently, the suspension is physically defibrated to refine the cellulose raw material. The method of physical fibrillation treatment is not particularly limited. For example, a high pressure homogenizer, an ultra high pressure homogenizer, a ball mill, a roll mill, a cutter mill, a planetary mill, a jet mill, an attritor, a grinder, a juicer mixer, a homomixer, and an ultrasonic homogenizer. , Nanogenizer, mechanical treatment such as underwater collision. By performing such a physical defibrating treatment, the cellulose in the suspension is refined, and a dispersion of cellulose (micronized cellulose) 1 that is refined until at least one side of its structure is on the order of nanometers. Can be obtained. Further, the number average minor axis diameter and the number average major axis diameter of the fine cellulose 1 obtained can be adjusted by the time and number of times of physical fibrillation treatment at this time.

As described above, a dispersion of cellulose 1 (a refined cellulose dispersion) that is refined until at least one side of the structure is on the order of nanometers is obtained. The obtained dispersion can be used as a stabilizer for an O / W emulsion, which will be described later, as it is or after being diluted, concentrated or the like.
Moreover, the refined cellulose dispersion may contain other components other than the components used for adjusting the pH and cellulose as long as the effects of the present invention are not impaired. The other components are not particularly limited, and can be appropriately selected from known additives depending on the use of the composite particle 5 and the like. Specifically, organometallic compounds such as alkoxysilanes or hydrolysates thereof, inorganic layered compounds, inorganic needle minerals, antifoaming agents, inorganic particles, organic particles, lubricants, antioxidants, antistatic agents, UV absorber, stabilizer, magnetic powder, alignment accelerator, plasticizer, crosslinking agent, magnetic substance, pharmaceutical, agricultural chemical, fragrance, adhesive, enzyme, pigment, dye, deodorant, metal, metal oxide, inorganic An oxide etc. are mentioned.

  Usually, since the refined cellulose 1 has a fiber shape derived from a microfibril structure, the refined cellulose 1 used in the production method of the present embodiment preferably has a fiber shape in the following range. That is, the shape of the refined cellulose 1 is preferably fibrous. Further, the fibrous refined cellulose 1 may have a number average minor axis diameter of 1 nm or more and 1000 nm or less, preferably 2 nm or more and 500 nm or less in terms of minor axis diameter. Here, if the number average minor axis diameter is less than 1 nm, a highly crystalline rigidly refined cellulose fiber structure cannot be obtained, and it is difficult to carry out the stabilization of the emulsion and the polymerization reaction using the emulsion as a template. Tend to be. On the other hand, if the number average minor axis diameter exceeds 1000 nm in the minor axis diameter, the size becomes too large to stabilize the emulsion, and therefore it tends to be difficult to control the size and shape of the resulting composite particles 5. is there. Further, the number average major axis diameter is not particularly limited, but is preferably 5 times or more the number average minor axis diameter. If the number average major axis diameter is less than 5 times the number average minor axis diameter, it is not preferable because it tends to be difficult to sufficiently control the size and shape of the composite particles 5.

In addition, the number average short axis diameter of the refined cellulose fiber is obtained, for example, by measuring the short axis diameter (minimum diameter) of 100 fibers by observation with a transmission electron microscope or atomic force microscope, and obtaining the average value. . On the other hand, the number average major axis diameter of the refined cellulose fiber is obtained as an average value by measuring the major axis diameter (maximum diameter) of 100 fibers by observation with a transmission electron microscope or atomic force microscope, for example. .
The type and crystal structure of cellulose that can be used as a raw material for the refined cellulose 1 are not particularly limited. Specifically, as a raw material comprising cellulose I-type crystals, for example, in addition to wood-based natural cellulose, non-wood-based natural cellulose such as cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, squirt cellulose, and valonia cellulose Can be used. Furthermore, the regenerated cellulose represented by the rayon fiber which consists of a cellulose II type crystal | crystallization, and a cupra fiber can also be used. From the viewpoint of easy material procurement, it is preferable to use wood-based natural cellulose as a raw material. The wood-based natural cellulose is not particularly limited, and for example, those generally used for producing cellulose nanofibers such as softwood pulp, hardwood pulp, and waste paper pulp can be used. Softwood pulp is preferred because it is easy to refine and refine.

Further, the refined cellulose raw material is preferably chemically modified. More specifically, an anionic functional group is preferably introduced on the crystal surface of the refined cellulose raw material. This is because the introduction of an anionic functional group on the surface of the cellulose crystal makes it easier for the solvent to enter between the cellulose crystals due to the osmotic pressure effect, and the refining of the cellulose raw material easily proceeds.
The type and introduction method of the anionic functional group introduced into the crystal surface of cellulose are not particularly limited, but a carboxy group or a phosphate group is preferable. In view of ease of selective introduction to the cellulose crystal surface, a carboxy group is more preferable.

  The method for introducing a carboxy group into the cellulose fiber surface is not particularly limited. Specifically, for example, carboxymethylation may be performed by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a high-concentration aqueous alkaline solution. Alternatively, a carboxy group may be introduced by directly reacting a carboxylic anhydride compound such as maleic acid or phthalic acid gasified in an autoclave with cellulose. Furthermore, a co-oxidant is used in the presence of N-oxyl compounds such as TEMPO, which has high selectivity to the oxidation of alcoholic primary carbon while maintaining the structure as much as possible under relatively mild conditions in water. The method used may be used. Oxidation using an N-oxyl compound is more preferred for the selectivity of the carboxy group introduction site and the reduction of environmental burden.

  Here, examples of the N-oxyl compound include TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical), 2,2,6,6-tetramethyl-4-hydroxypiperidine- 1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-acetamido-2, 2,6,6-tetramethylpiperidine-N-oxyl, and the like. Among them, TEMPO having high reactivity is preferable. The amount of the N-oxyl compound used is not particularly limited, and may be an amount as a catalyst. Usually, it is about 0.01-5.0 mass% with respect to solid content of the wood type natural cellulose to oxidize.

  Examples of the oxidation method using an N-oxyl compound include a method in which wood-based natural cellulose is dispersed in water and oxidized in the presence of the N-oxyl compound. At this time, it is preferable to use a co-oxidant together with the N-oxyl compound. In this case, in the reaction system, the N-oxyl compound is sequentially oxidized by a co-oxidant to produce an oxoammonium salt, and cellulose is oxidized by the oxoammonium salt. According to this oxidation treatment, the oxidation reaction proceeds smoothly even under mild conditions, and the introduction efficiency of the carboxy group is improved. When the oxidation treatment is performed under mild conditions, it is easy to maintain the crystal structure of cellulose.

As the co-oxidant, for example, it is possible to promote an oxidation reaction such as halogen, hypohalous acid, halous acid or perhalogen acid, or a salt thereof, halogen oxide, nitrogen oxide, peroxide or the like. Any oxidizing agent can be used if present. Sodium hypochlorite is preferred because of its availability and reactivity. The amount of the co-oxidant used is not particularly limited, and may be an amount that can promote the oxidation reaction. Usually, it is about 1-200 mass% with respect to solid content of the wood type natural cellulose to oxidize.
In addition to the N-oxyl compound and the co-oxidant, at least one compound selected from the group consisting of bromide and iodide may be further used in combination. Thereby, an oxidation reaction can be advanced smoothly and the introduction efficiency of a carboxy group can be improved. As such a compound, sodium bromide or lithium bromide is preferable, and sodium bromide is more preferable from the viewpoint of cost and stability. The amount of the compound used is not particularly limited, and may be an amount that can promote the oxidation reaction. Usually, it is about 1-50 mass% with respect to solid content of the wood type natural cellulose to oxidize.

The reaction temperature of the oxidation reaction is preferably 4 ° C. or higher and 80 ° C. or lower, and more preferably 10 ° C. or higher and 70 ° C. or lower. When the reaction temperature of the oxidation reaction is less than 4 ° C., the reactivity of the reagent tends to decrease and the reaction time tends to be long. When the reaction temperature of the oxidation reaction exceeds 80 ° C., the side reaction is promoted to lower the molecular weight of the cellulose as a sample, and the highly crystalline rigid finely divided cellulose fiber structure is collapsed, and the stabilizer for the O / W emulsion. Tends to be difficult to use.
The reaction time for the oxidation treatment can be appropriately set in consideration of the reaction temperature, the desired amount of carboxy group, and the like, and is not particularly limited, but is usually about 10 minutes to 5 hours.

  The pH of the reaction system during the oxidation reaction is not particularly limited, but is preferably 9 to 11. When the pH is 9 or more, the reaction can be efficiently carried out. If the pH exceeds 11, side reactions may proceed, and the decomposition of cellulose as a sample may be accelerated. Further, in the oxidation treatment, as the oxidation proceeds, the pH in the system decreases due to the formation of a carboxy group. Therefore, it is preferable to maintain the pH of the reaction system at 9 to 11 during the oxidation treatment. Examples of a method for maintaining the pH of the reaction system at 9 to 11 include a method of adding an alkaline aqueous solution in accordance with a decrease in pH.

Examples of the alkaline aqueous solution include sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and benzyltrimethylammonium hydroxide. An organic alkali such as an aqueous solution may be mentioned. A sodium hydroxide aqueous solution is preferable from the viewpoint of cost.
The oxidation reaction with the N-oxyl compound can be stopped, for example, by adding alcohol to the reaction system. At this time, the pH of the reaction system is preferably maintained within the above range. As the alcohol to be added, for example, a low molecular weight alcohol such as methanol, ethanol, propanol or the like is preferable in order to quickly terminate the reaction, and ethanol is particularly preferable from the viewpoint of safety of by-products generated by the reaction.

The reaction solution after the oxidation treatment may be directly subjected to a refinement process, but in order to remove a catalyst such as an N-oxyl compound, impurities, etc., the oxidized cellulose contained in the reaction solution is recovered and washed with a washing solution. It is preferable. The collection of the oxidized cellulose can be carried out by a known method such as filtration using a glass filter or a nylon mesh having a pore diameter of 20 μm. As a cleaning liquid used for cleaning oxidized cellulose, pure water is preferable.
When the obtained TEMPO-oxidized cellulose is defibrated, cellulose single nanofibers (CSNF) having a uniform fiber width of about 3 nm are obtained. When CSNF is used as a raw material for the refined cellulose 1 of the composite particles 5, the particle size of the obtained O / W emulsion tends to be uniform due to its uniform structure.

  As described above, the CSNF used in the present embodiment can be obtained by the step of oxidizing the cellulose raw material and the step of refining it into a dispersion liquid. Moreover, as content of the carboxy group introduce | transduced into CSNF, 0.1 mmol / g or more and 5.0 mmol / g or less are preferable, and 0.5 mmol / g or more and 2.0 mmol / g or less are more preferable. Here, when the amount of carboxy group is less than 0.1 mmol / g, the solvent invasion action due to the osmotic pressure effect does not work between the cellulose microfibrils, so that it tends to be difficult to make the cellulose finely dispersed uniformly. is there. In addition, if the amount of carboxy group exceeds 5.0 mmol / g, cellulose microfibrils are reduced in molecular weight due to side reaction accompanying chemical treatment, so that a highly crystalline rigid micronized cellulose fiber structure cannot be taken. It tends to be difficult to use as a stabilizer for / W type emulsion.

(Second step)
In the second step, at least a part of the surface of the biodegradable compound droplet 2 in the dispersion 4 of the micronized cellulose 1 is coated with the micronized cellulose 1 to form the biodegradable compound droplet 2. It is a process of stabilizing as an emulsion.
Specifically, a biodegradable compound is added to the refined cellulose dispersion obtained in the first step, and the biodegradable compound is further dispersed as droplets in the refined cellulose dispersion. In this step, at least a part of the surface of the decomposable compound droplet 2 is coated with the refined cellulose 1 to produce an O / W emulsion stabilized by the refined cellulose 1.

  As a method for preparing an O / W type emulsion, for example, a method of adding a mixture of a biodegradable compound containing an initiator and a polymerizable monomer to a finely divided cellulose dispersion and emulsifying the same, biodegradability can be achieved. A method of emulsifying a compound obtained by dissolving a compound with a solvent having low compatibility with the fine cellulose dispersion into the fine cellulose dispersion, and having a biodegradability that is solid at room temperature in the fine cellulose dispersion There is a method in which a compound is added and heated to the melting point or higher of the biodegradable compound to melt and emulsify. In any method, the compound having biodegradability is preferably one that is not compatible with the fine cellulose dispersion. When there is compatibility, it becomes difficult to form droplets of a compound having biodegradability in the finely divided cellulose dispersion, and it tends to be difficult to obtain a composite.

A biodegradable compound that can be used in a method of emulsification by adding a mixture of a biodegradable compound containing an initiator and a polymerizable monomer to a finely divided cellulose dispersion is a resin that does not dissolve in water. Can be used without limitation, specifically, cellulose acetate derivatives such as cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polysaccharides such as chitin and chitosan, polylactic acid, lactic acid and others Polylactic acid such as copolymer of hydroxycarboxylic acid, dibasic polyester such as polybutylene succinate, polyethylene succinate, polybutylene adipate, polycaprolactone, copolymer of caprolactone and hydroxycarboxylic acid, etc. Polycaprolactones, polyhydroxy Polyhydroxybutyrates such as tyrates, copolymers of polyhydroxybutyrate and hydroxycarboxylic acids, aliphatic polyesters such as polyhydroxybutyric acid, copolymers of polyhydroxybutyric acid and other hydroxycarboxylic acids, polyamino acids , Natural resins such as polyester polycarbonate and rosin. Moreover, these can be used 1 type or in combination of 2 or more types.
The biodegradable compound described above is preferably soluble in a polymerizable monomer described later.

Next, the polymerizable monomer that can be used in the second step will be described.
The type of polymerizable monomer that can be used in the second step is a polymer monomer that has a polymerizable functional group in its structure, is liquid at room temperature, and is completely compatible with water. There is no particular limitation as long as it does not melt and can form a polymer (polymer) by a polymerization reaction. The polymerizable monomer has at least one polymerizable functional group. A polymerizable monomer having one polymerizable functional group is also referred to as a monofunctional monomer. A polymerizable monomer having two or more polymerizable functional groups is also referred to as a polyfunctional monomer. Although it does not specifically limit as a kind of polymerizable monomer, For example, a (meth) acrylic-type monomer, a vinyl-type monomer, etc. are mentioned. It is also possible to use a polymerizable monomer having a cyclic ether structure such as an epoxy group or an oxetane structure (for example, ε-caprolactone, etc.).
Note that the notation “(meth) acrylate” includes both “acrylate” and “methacrylate”.

  Examples of monofunctional (meth) acrylic monomers include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl. (Meth) acrylate, t-butyl (meth) acrylate, glycidyl (meth) acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isobornyl ( (Meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate, benzyl (Meth) acrylate, 2-ethoxyethyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, ethyl carbitol (meth) acrylate, phosphoric acid (meth) acrylate, ethylene oxide modified phosphoric acid (meth) acrylate, phenoxy (meta) ) Acrylate, ethylene oxide modified phenoxy (meth) acrylate, propylene oxide modified phenoxy (meth) acrylate, nonylphenol (meth) acrylate, ethylene oxide modified nonylphenol (meth) acrylate, propylene oxide modified nonylphenol (meth) acrylate, methoxydiethylene glycol (meth) Acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate 2- (meth) acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl hydrogen phthalate, 2- (meth) acryloyloxypropyl hydrogen Phthalate, 2- (meth) acryloyloxypropyl hexahydrohydrogen phthalate, 2- (meth) acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth) acrylate, trifluoroethyl (meth) acrylate, tetrafluoropropyl (meth) acrylate , Hexafluoropropyl (meth) acrylate, octafluoropropyl (meth) acrylate, octafluoropropyl (meth) acrylate, 2 -Adamantane derivatives mono (meth) acrylates such as adamantyl acrylate having a monovalent mono (meth) acrylate derived from adamantane and adamantanediol.

  Examples of the bifunctional (meth) acrylic monomer include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, butanediol di (meth) acrylate, hexanediol di (meth) acrylate, and nonanediol di (meth) ) Acrylate, ethoxylated hexanediol di (meth) acrylate, propoxylated hexanediol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (Meth) acrylate, neopentyl glycol di (meth) acrylate, ethoxylated neopentyl glycol di (meth) acrylate, tripropylene glycol Di (meth) acrylate, di (meth) acrylate, such as hydroxypivalic acid neopentyl glycol di (meth) acrylate.

  Examples of the trifunctional or higher functional (meth) acrylic monomer include trimethylolpropane tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tri (meth) acrylate, and tris 2-hydroxy. Ethyl isocyanurate tri (meth) acrylate, tri (meth) acrylate such as glycerin tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol tri (meth) acrylate, ditrimethylolpropane tri (meth) acrylate, etc. Trifunctional (meth) acrylate compounds, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, dipentaerythritol tetra Trifunctional or more polyfunctional (meth) such as (meth) acrylate, dipentaerythritol penta (meth) acrylate, ditrimethylolpropane penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane hexa (meth) acrylate Examples thereof include acrylate compounds and polyfunctional (meth) acrylate compounds in which a part of these (meth) acrylates is substituted with an alkyl group or ε-caprolactone.

As the monofunctional vinyl monomer, for example, a liquid that is not compatible with water at room temperature, such as vinyl ether, vinyl ester, and aromatic vinyl, particularly styrene and styrene monomers, is preferable.
Among the monofunctional vinyl monomers, as (meth) acrylate, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Lauryl (meth) acrylate, alkyl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofur Furyl (meth) acrylate, allyl (meth) acrylate, diethylaminoethyl (meth) acrylate, trifluoroethyl (meth) acrylate, heptafluorodecyl (meth) acrylate Over DOO, dicyclopentenyl (meth) acrylate, dicyclopentenyl oxyethyl (meth) acrylate, tricyclodecanyl (meth) acrylate.

Examples of monofunctional aromatic vinyl monomers include styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, ethyl styrene, isopropenyl toluene, isobutyl toluene, tert-butyl styrene. Vinyl naphthalene, vinyl biphenyl, 1,1-diphenylethylene, and the like.
As a polyfunctional vinyl-type monomer, the polyfunctional group which has unsaturated bonds, such as divinylbenzene, is mentioned, for example. A liquid that is incompatible with water at room temperature is preferred.

  For example, specific examples of the polyfunctional vinyl monomer include (1) divinyls such as divinylbenzene, 1,2,4-trivinylbenzene, 1,3,5-trivinylbenzene, and (2) ethylene glycol. Dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexamethylene glycol dimethacrylate, neopentyl glycol dimethacrylate Dimethacrylates such as methacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis (4-methacryloxydiethoxyphenyl) propane, (3) Trimethacrylates such as limethylolpropane trimethacrylate, triethylolethane trimethacrylate, (4) ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, 1,3-dipropylene glycol diacrylate, 1,4-dibutylene glycol diacrylate, 1,6-hexylene glycol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, 2,2-bis (4-acryloxypropoxyphenyl) Diacrylates such as propane and 2,2-bis (4-acryloxydiethoxyphenyl) propane, (5) Trimethylo Triacrylates such as propane triacrylate and triethylolethane triacrylate, (6) Tetraacrylates such as tetramethylolmethane tetraacrylate, (7) Other examples include tetramethylene bis (ethyl fumarate), hexamethylene bis (acrylamide) ), Triallyl cyanurate, and triallyl isocyanurate.

For example, specific functional styrenic monomers include divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene, divinylxylene, divinylbiphenyl, bis (vinylphenyl) methane, bis (vinylphenyl) ethane, and bis (vinyl). Phenyl) propane, bis (vinylphenyl) butane and the like.
In addition to these, it is possible to use polyether resins, polyester resins, polyurethane resins, epoxy resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol polyene resins, etc. having at least one polymerizable functional group. The material is not particularly limited.
The said polymerizable monomer may be used independently and may be used in combination of 2 or more type.

The mixing ratio of the biodegradable compound and the polymerizable monomer is within the range of 10/90 to 85/15, preferably 15/85 to the weight ratio of the biodegradable compound / polymerizable monomer. It is within the range of 70/30. When the amount of the biodegradable compound is lower than 10, the biodegradability is weak, and when the amount of the polymerizable monomer is lower than 15, it tends to be difficult to form a polymer.
Further, the polymerization monomer may contain a polymerization initiator in advance. Examples of general polymerization initiators include radical initiators such as organic peroxides and azo polymerization initiators.
Examples of the organic peroxide include peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxycarbonate, and peroxyester.
Examples of the azo polymerization initiator include ADVN and AIBN.

  For example, 2,2-azobis (isobutyronitrile) (AIBN), 2,2-azobis (2-methylbutyronitrile) (AMBN), 2,2-azobis (2,4-dimethylvaleronitrile) (ADVN) 1,1-azobis (1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2-azobisisobutyrate (MAIB), 4,4-azobis (4-cyanovaleric acid) (ACVA), 1, 1-azobis (1-acetoxy-1-phenylethane), 2,2-azobis (2-methylbutyramide), 2,2-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2- Azobis (2-methylamidinopropane) dihydrochloride, 2,2-azobis [2- (2-imidazolin-2-yl) propane], 2,2-azobis [2-methyl-N- (2-hi Loxyethyl) propionamide], 2,2-azobis (2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2-azobis (N-butyl-2-methylpropionamide), 2 , 2-azobis (N-cyclohexyl-2-methylpropionamide) and the like.

If a polymerizable monomer that contains a polymerization initiator in advance is used in the second step, polymerizable monomer droplets (biodegradable compound droplets) inside the emulsion particles when an O / W emulsion is formed. Since a polymerization initiator is contained in 2, the polymerization reaction easily proceeds when the monomer inside the emulsion is polymerized in the third step described later.
The weight ratio of the polymerizable monomer and the polymerization initiator that can be used in the second step is not particularly limited, but the polymerization initiator is usually 0.1 parts by mass or more with respect to 100 parts by mass of the polymerizable monomer. preferable. If the polymerizable monomer is less than 0.1 part by mass, the polymerization reaction does not proceed sufficiently and the yield of the composite particles 5 tends to decrease, such being undesirable.

  A compound having biodegradability is dissolved in a solvent having low compatibility with the fine cellulose dispersion and added to the fine cellulose dispersion to be emulsified. Compounds. Moreover, as a solvent which melt | dissolves the compound which has biodegradability, the solvent with low compatibility to a refined cellulose dispersion liquid is preferable. When the solubility in water is high, the solvent easily dissolves from the biodegradable compound phase into the aqueous phase, and thus emulsification tends to be difficult. When there is no solubility in water, the solvent cannot move from the compound phase, so that it tends to be extremely difficult to obtain composite particles. Moreover, it is preferable that the solvent which melt | dissolves the compound which has biodegradability has a boiling point of 90 degrees C or less. When the boiling point is higher than 90 ° C., the fine cellulose dispersion liquid evaporates before the solvent that dissolves the biodegradable compound, and it tends to be extremely difficult to obtain composite particles. Specific examples of the solvent for dissolving the biodegradable compound include dichloromethane, chloroform, 1,2-dichloroethane, benzene and the like.

  As a method that can be used for a method of adding a biodegradable compound that is solid at room temperature to a finely divided cellulose dispersion and heating it to a melting point of the compound having biodegradability to melt and emulsify it at room temperature, It is a solid that dissolves when heated and has a melting point of 40 ° C. or higher and 90 ° C. or lower. When the melting point of the biodegradable compound is less than 40 ° C., it is difficult to solidify at room temperature, and it tends to be extremely difficult to obtain a composite. In addition, when the melting point of the biodegradable compound is 90 ° C. or higher, the water that is the solvent of the finely divided cellulose dispersion that is heated together evaporates rather than the biodegradable compound is dissolved. There is a tendency that it becomes difficult. Therefore, the biodegradable compounds that can be used in the present embodiment are specifically pentaerythritol tetrastearate, pentaerythritol distearate, pentaerythritol tristearate, stearyl stearate, stearic acid stearate, stearic acid Stearyl, myristyl myristate, cetyl palmitate, ethylene glycol distearate, behenyl alcohol, microcrystalline wax, paraffin wax, hydrocarbon wax, fatty acid alkyl ester, polyol fatty acid ester, mixture of fatty acid ester and wax, mixture of fatty acid ester, glycerin mono Palmitate (/ stearic acid monoglyceride), glycerin mono distearate (/ glycerin stearate), glycerin Noaceto monostearate (/ glycerin fatty acid ester), succinic acid aliphatic monoglyceride (/ glycerin fatty acid ester), citric acid saturated aliphatic monoglyceride, sorbitan monostearate, sorbitan fatty acid ester, sorbitan tribehenate, propylene glycol monobehenate (/ Propylene glycol fatty acid ester), stearate of pentaerythritol polymer of adipic acid, pentaerythritol tetrastearate, dipentaerythritol hexastearate, stearyl citrate, pentaerythritol fatty acid ester, glycerin fatty acid ester, ultralight rosin, rosin-containing diol , Ultra-light rosin metal salt, hydrogenated petroleum resin, rosin ester, hydrogenated rosin ester, special rosin ester, novolat , Crystalline polyalphaolefin, polyalkylene glycol, polyalkylene glycol ester, polyoxyalkylene ether, and the like.

Moreover, the functional component may be contained in the compound which has biodegradability. Specific examples include magnetic materials, pharmaceuticals, agricultural chemicals, fragrances, adhesives, enzymes, pigments, dyes, deodorants, metals, metal oxides, and inorganic oxides. When a functional component is included in the biodegradable compound in advance, the above-mentioned functional component can be contained inside the particle when it is formed as the composite particle 5, and the function can be expressed depending on the application. It becomes.
The weight ratio of the finely divided cellulose dispersion that can be used in the second step, the biodegradable compound, and the mixture of the biodegradable compound and the polymerizable monomer is not particularly limited, but is 100 mass of fine cellulose fiber. The amount of the biodegradable compound and the mixture of the biodegradable compound and the polymerizable monomer is preferably 1 part by mass or more and 50 parts by mass or less with respect to parts. When the amount of the biodegradable compound and the mixed solution of the biodegradable compound and additive is less than 1 part by mass, the yield of the composite particles 5 tends to decrease, such being undesirable. Further, when the amount of the biodegradable compound and the mixture of the biodegradable compound and the polymerizable monomer exceeds 50 parts by mass, the compound droplet 2 having biodegradability can be uniformly coated with the fine cellulose 1. This tends to be difficult and is not preferable.

Although it does not specifically limit as a method of producing O / W type | mold emulsion, A general emulsification process, for example, various homogenizer processes and a mechanical stirring process can be used, Specifically, a high pressure homogenizer, an ultrahigh pressure homogenizer, a universal homogenizer, Examples include mechanical processing such as a ball mill, roll mill, cutter mill, planetary mill, jet mill, attritor, grinder, juicer mixer, homomixer, ultrasonic homogenizer, nanogenizer, underwater collision, and paint shaker. A plurality of mechanical processes may be used in combination.
For example, when an ultrasonic homogenizer is used, a polymerizable monomer is added to the fine cellulose dispersion obtained in the first step to form a mixed solvent, and the ultrasonic homogenizer is inserted into the mixed solvent for ultrasonic treatment. carry out. The processing conditions of the ultrasonic homogenizer are not particularly limited. For example, the frequency is generally 20 kHz or higher, and the output is generally 10 W / cm ² or higher. The processing time is not particularly limited, but is usually about 10 seconds to 1 hour.

  By the ultrasonic treatment, the compound droplet 2 having biodegradability is dispersed in the fine cellulose dispersion and the emulsion progresses, and further the liquid of the compound droplet 2 having biodegradability and the fine cellulose dispersion is obtained. By selectively adsorbing the refined cellulose 1 at the / liquid interface, the compound droplet 2 having biodegradability is coated with the refined cellulose 1 to form a stable structure as an O / W emulsion. Thus, an emulsion in which a solid substance is adsorbed and stabilized at the liquid / liquid interface is academically called a “Pickering emulsion”. As described above, the mechanism by which the pickering emulsion is formed by the refined cellulose fiber is not clear, but cellulose has a hydrophilic site derived from a hydroxyl group and a hydrophobic site derived from a hydrocarbon group in its molecular structure. Therefore, it is considered that it is adsorbed on the liquid / liquid interface between the hydrophobic monomer and the hydrophilic solvent due to the amphiphilicity.

The O / W type emulsion structure can be confirmed, for example, by observation with an optical microscope. The particle size of the O / W emulsion is not particularly limited, but is usually about 0.1 μm to 1000 μm.
In the O / W type emulsion structure, the thickness of the fine cellulose layer (coating layer) formed on the surface layer of the biodegradable compound droplet 2 is not particularly limited, but is usually about 3 nm to 1000 nm. The thickness of the fine cellulose layer can be measured using, for example, a cryo TEM.

(Third step)
The third step is a step of solidifying the compound droplet 2 having biodegradability to obtain composite particles 5 in which the compound particles 3 having biodegradability are coated with the refined cellulose 1. More specifically, the third step is a compound containing a compound having biodegradability in a state in which at least a part of the surface of the compound droplet 2 containing the compound having biodegradability is covered with the finely divided cellulose 1. By solidifying the droplets 2 into compound particles 3 having biodegradability, at least a part of the surface of the compound particles 3 having biodegradability is covered with the fine cellulose 1, and the compound particles having biodegradability are covered. 3 is a process of bringing the finely divided cellulose 1 into an indivisible state.
In the second step, when using a method of adding a mixture of a biodegradable compound containing an initiator and a polymerizable monomer to the finely divided cellulose dispersion and emulsifying it, biodegradable compound and polymerizability are used. The method for polymerizing the monomer is not particularly limited, and can be appropriately selected depending on the type of polymerizable monomer used and the type of polymerization initiator. Examples of a method for polymerizing the aforementioned biodegradable compound and polymerizable monomer include suspension polymerization.

  The specific suspension polymerization method is also not particularly limited, and can be carried out using a known method. For example, the O / W emulsion prepared by the second step and stabilized by coating the compound droplet 2 containing the biodegradable compound containing the polymerization initiator and the polymerizable monomer with the fine cellulose 1 is stirred. It can be carried out by heating while heating. The stirring method is not particularly limited, and a known method can be used. Specifically, a disper or a stirring bar can be used. Further, only heat treatment may be performed without stirring. The temperature condition during heating can be appropriately set depending on the type of the polymerizable monomer and the type of the polymerization initiator, but is preferably 20 degrees or more and 90 degrees or less. If the temperature during heating is less than 20 degrees, the polymerization reaction rate tends to decrease, which is not preferable. If it exceeds 90 degrees, the fine cellulose dispersion tends to evaporate. The time for the polymerization reaction can be appropriately set depending on the type of the polymerizable monomer and the type of the polymerization initiator, but is usually about 1 to 24 hours. Further, the polymerization reaction may be carried out by ultraviolet irradiation treatment which is a kind of electromagnetic waves. In addition to electromagnetic waves, particle beams such as electron beams may be used.

  In the second step, when using a method in which a compound having biodegradability is dissolved in a solvent having low compatibility with the fine cellulose dispersion and added to the fine cellulose dispersion to emulsify, the emulsion is heated, By volatilizing the solvent in which the compound having decomposability is dissolved, the compound having biodegradability can be solidified. The temperature condition at the time of heating can be appropriately set depending on the type of solvent to be dissolved, but is preferably from the boiling point of the solvent to 90 ° C. If the temperature at the time of heating is less than the boiling point of the solvent, the solvent will slowly move to the aqueous phase, and if it exceeds 90 degrees, the fine cellulose dispersion tends to evaporate.

When using a method of adding a biodegradable compound that is solid at room temperature to the finely divided cellulose dispersion in the second step and heating it to the melting point of the compound having biodegradability to melt and emulsify the emulsion, Is cooled to below the melting point of the biodegradable compound, the biodegradable compound can be solidified.
Through the above-described steps, it is possible to produce true spherical composite particles 5 in which biodegradable compound particles 3 are coated with micronized cellulose 1.

The state immediately after the completion of the solidification reaction is a state in which a large amount of water and free fine cellulose 1 that does not contribute to the formation of the coating layer of the composite particles 5 are mixed in the dispersion of the composite particles 5. Yes. Therefore, it is necessary to collect and purify the produced composite particles 5, and as a recovery and purification method, washing by centrifugation or filtration washing is preferable. As a washing method by centrifugation, a known method can be used. Specifically, the operation of sedimenting the composite particles 5 by centrifugation to remove the supernatant and redispersing in a water / methanol mixed solvent is repeated. In addition, the composite solvent 5 can be recovered by removing the residual solvent from the sediment obtained by centrifugation. A known method can also be used for filtration and washing. For example, a PTFE membrane filter having a pore size of 0.1 μm is repeatedly subjected to suction filtration with water and methanol, and finally the residual solvent is further removed from the paste remaining on the membrane filter. Thus, the composite particles 5 can be recovered.
The method for removing the residual solvent is not particularly limited, and for example, it can be carried out by air drying or heat drying in an oven. The dried solid material containing the composite particles 5 obtained in this way is not a film or an aggregate as described above, but is obtained as a fine powder.

(Effect of embodiment)
The composite particle 5 according to the present embodiment is a novel composite particle derived from the refined cellulose 1 on the surface of the composite particle 5 and having good biocompatibility and good dispersion stability that does not aggregate even in a solvent.
Moreover, the dry solid substance containing the composite particle 5 which concerns on this embodiment is obtained as a fine powder, and there is no aggregation of particles. For this reason, it is easy to re-disperse the composite particles 5 obtained as a dry powder in the solvent again, and the dispersion derived from the coating layer of the fine cellulose 1 bonded to the surface of the composite particles 5 after the re-dispersion. Shows stability.
Moreover, according to the manufacturing method of the composite particle 5 which concerns on this embodiment, the load to an environment is low and the manufacturing method of the novel composite particle 5 which can be provided by a simple method can be provided.

Moreover, according to the dry solid containing the composite of the refined cellulose 1 according to the present embodiment, the dry solid can be provided in a form that can be redispersed in a solvent.
Further, according to the composite particles 5 according to the present embodiment, since the solvent can be almost removed, the transportation cost is reduced, the risk of corruption is reduced, the addition efficiency as an additive is improved, and the kneading into the hydrophobic resin is performed. The effect of improving efficiency can be expected.
As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included. In addition, the constituent elements shown in the first embodiment and the modifications described above can be combined as appropriate.

[Example]
EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, the technical scope of this invention is not limited to these Examples. In each of the following examples, “%” indicates mass% (w / w%) unless otherwise specified.

<Example 1>
(First step: step of obtaining a cellulose nanofiber dispersion)
(TEMPO oxidation of wood cellulose)
70 g of softwood kraft pulp was suspended in 3500 g of distilled water, and a solution of 0.7 g of TEMPO and 7 g of sodium bromide dissolved in 350 g of distilled water was added and cooled to 20 ° C. 450 g of sodium hypochlorite aqueous solution having a concentration of 2 mol / L and a density of 1.15 g / mL was added dropwise thereto to initiate an oxidation reaction. The temperature in the system was always kept at 20 ° C., and the decrease in pH during the reaction was kept at pH 10 by adding a 0.5N aqueous sodium hydroxide solution. When the total amount of sodium hydroxide added reached 3.50 mmol / g based on the weight of cellulose, about 100 mL of ethanol was added to stop the reaction. Thereafter, filtration and washing with distilled water were repeated using a glass filter to obtain oxidized pulp.

(Measurement of carboxy group content in oxidized pulp)
Oxidized pulp and re-oxidized pulp obtained by the TEMPO oxidation were weighed in an amount of 0.1 g by solid content, dispersed in water at a concentration of 1%, and hydrochloric acid was added to adjust the pH to 2.5. Thereafter, the amount of carboxy groups (mmol / g) was determined by conductivity titration using a 0.5 M aqueous sodium hydroxide solution. The result was 1.6 mmol / g.

(Oxidized pulp defibration treatment)
1 g of oxidized pulp obtained by the above TEMPO oxidation was dispersed in 99 g of distilled water and refined with a juicer mixer for 30 minutes to obtain a CSNF aqueous dispersion having a CSNF concentration of 1%. FIG. 2 shows the result of measuring the spectral transmission spectrum using a spectrophotometer (manufactured by Shimadzu Corporation, “UV-3600”) after placing the CSNF dispersion in a quartz cell having an optical path length of 1 cm. As is clear from FIG. 2, the CSNF aqueous dispersion showed high transparency. The number average minor axis diameter of CSNF contained in the CSNF aqueous dispersion was 3 nm, and the number average major axis diameter was 1110 nm. Furthermore, the result of having performed steady-state viscoelasticity measurement using the rheometer is shown in FIG. As apparent from FIG. 3, the CSNF dispersion showed thixotropic properties.

(2nd process: The process of producing O / W type emulsion)
Next, 1 g of cellulose acetate butyrate (trade name CAB-551-0.2 or less, also referred to as CAB), which is a biodegradable compound, and 9 g of divinylbenzene (hereinafter also referred to as DVB), which is a polymerizable monomer. On the other hand, 1 g of 2,2-azobis-2,4-dimethylvaleronitrile (hereinafter also referred to as ADVN), which is a polymerization initiator, was dissolved. When the total amount of the CAB / DVB / ADVN mixed solution was added to 40 g of the CSNF dispersion having a CSNF concentration of 1%, the CAB / DVB / ADVN mixed solution and the CSNF dispersion were separated into two layers in a highly transparent state.
Next, an ultrasonic homogenizer shaft was inserted from the upper surface of the mixed liquid in the state where the two layers were separated, and an ultrasonic homogenizer treatment was performed for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W. The appearance of the mixed solution after the ultrasonic homogenizer treatment was like a cloudy emulsion. When a drop of the mixture is dropped on a slide glass, sealed with a cover glass, and observed with an optical microscope, countless emulsion droplets of about 1 to several μm are formed and dispersed and stabilized as an O / W emulsion. Was confirmed.

(3rd process: The process of obtaining the composite particle 5 coat | covered with CNF by polymerization reaction)
The O / W emulsion dispersion was used in a 70 ° C. hot water bath using a water bath and treated for 8 hours while stirring with a stirrer to carry out a polymerization reaction. After the treatment for 8 hours, the dispersion was cooled to room temperature. There was no change in the appearance of the dispersion before and after the polymerization reaction. The obtained dispersion was treated with a centrifugal force of 75,000 g (g is gravitational acceleration) for 5 minutes to obtain a sediment. The supernatant was removed by decantation, and the precipitate was collected, and further washed repeatedly with pure water and methanol using a PTFE membrane filter having a pore size of 0.1 μm. The purified / recovered material thus obtained was redispersed at a concentration of 1%, and the particle size was evaluated using a particle size distribution meter (NANOTRAC UPA-EX150, Nikkiso Co., Ltd.). The average particle size was 2.1 μm. Next, the purified / recovered product was air-dried and further subjected to vacuum drying treatment at room temperature of 25 ° C. for 24 hours to obtain a fine dry powder (composite particle 5).

(Shape observation with a scanning electron microscope)
The results of observing the obtained dry powder with a scanning electron microscope are shown in FIGS. As is clear from FIG. 4, an infinite number of true spherical composite particles 5 derived from the shape of the emulsion droplets were formed by carrying out the polymerization reaction using the O / W emulsion droplets as a template. confirmed. Further, as shown in FIG. 5, it was confirmed that the surface was uniformly coated with CNF having a width of several nm. In addition, since the surface of the composite particle 5 is uniformly and uniformly coated with the refined cellulose 1 in spite of repeated cleaning by filtration cleaning, in the composite particle 5 of the present embodiment, the monomer ( The compound particles 3) and the CNF that is the refined cellulose 1 may be bonded to each other, indicating that the compound particles 3 and the refined cellulose 1 are in an indivisible state.

(Evaluation of redispersibility)
When the dry powder of the composite particles 5 was added to pure water at a concentration of 1% and redispersed with a stirrer, it was easily redispersed and no aggregation was observed. Further, when the particle size was evaluated using a particle size distribution meter, the average particle size was 2.1 μm as before the drying, and no signal indicating aggregation was present in the data of the particle size distribution meter.
From the above, it was shown that the composite particle 5 was obtained as a powder without being formed into a film by drying even though the surface was coated with CNF, and the redispersibility was also good. .

<Example 2>
In Example 1, polybutylene succinate (trade name BioPBS, Mitsubishi Chemical, hereinafter referred to as PBS) was used instead of CBA, and diethylene glycol diacrylate (trade name FA-222A, Hitachi Chemical, hereinafter FA-) was used instead of DVB. The composite particles 5 according to Example 2 were produced under the same conditions as in Example 1 except that each of them was also used.
<Example 3>
In Example 1, instead of TEMPO oxidation, a C-merified CNF dispersion obtained by performing carboxymethylation (hereinafter also referred to as CM) treatment according to Patent Document 2 listed as the prior art document was used. Under the same conditions as in Example 1, composite particles 5 according to Example 3 were produced, and various evaluations were similarly performed.
<Example 4>
Example 1 is the same as Example 1 except that instead of TEMPO oxidation, a phosphate esterified CNF dispersion obtained by performing a phosphate esterification treatment according to Non-Patent Document 1 listed as the prior art document is used. The composite particles 5 according to Example 4 were produced under the same conditions, and various evaluations were performed in the same manner.

<Example 5>
As a biodegradable compound, 6 g of polylactic acid (trade name Terramac TE4000, hereinafter referred to as PLA) was dissolved in 4 g of dichloromethane (boiling point: 39.6 ° C.). The total amount of the polylactic acid / dichloromethane mixed solution was added to 40 g of the CSNF dispersion used in Example 1.
Next, the mixture was subjected to ultrasonic homogenizer treatment for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W in the same manner as in Example 1 to obtain an O / W emulsion dispersion.
Next, the O / W type emulsion dispersion was supplied into a 70 ° C. hot water bath using a water bath and treated for 8 hours while stirring with a stirrer to volatilize dichloromethane. After the treatment for 8 hours, the dispersion was treated in the same manner as in Example 1 to obtain a dry powder (composite particle 5) according to Example 5.
<Example 6>
In Example 5, polycaprolactone (trade name TONE, UCC, hereinafter also referred to as PCL) was used instead of polylactic acid, and chloroform was used instead of dichloromethane. 6 was produced, and various evaluations were performed in the same manner.

<Example 7>
As a biodegradable compound, 10 g of stearic acid (melting point: 69.6 ° C.) was added to 40 g of the CSNF dispersion used in Example 1.
Next, the mixture was heated to 80 ° C. using a water bath to melt the stearic acid, and then subjected to ultrasonic homogenizer treatment for 3 minutes under the conditions of a frequency of 24 kHz and an output of 400 W as in Example 1. And an O / W emulsion dispersion was obtained.
Next, the O / W emulsion dispersion was cooled to room temperature.
Finally, the dispersion was treated in the same manner as in Example 1 to obtain a dry powder (composite particle 5) according to Example 7.
<Example 8>
In Example 7, paraffin wax (trade name: paraffin wax 135 ° F., melting point: 57.2 ° C., Sankei Sangyo, hereinafter also referred to as paraffin) was used instead of stearic acid. The composite particles 5 according to Example 8 were produced under the same conditions, and various evaluations were performed in the same manner.

<Comparative Example 1>
Production of composite particles according to Comparative Example 1 was attempted under the same conditions as in Example 1 except that pure water was used instead of the CSNF dispersion in Example 1.
<Comparative example 2>
Production of composite particles according to Comparative Example 2 was attempted under the same conditions as in Example 1 except that an aqueous solution of carboxymethyl cellulose (hereinafter also referred to as CMC) was used instead of the CSNF dispersion in Example 1.

<Comparative Example 3>
A composite according to Comparative Example 3 under the same conditions as in Example 1 except that a dispersion obtained by dispersing commercially available polylactic acid fine particles (trade name Trepearl PLA, Toray) at a concentration of 1% was used instead of the composite particles of the present invention. Attempts were made to produce particles.
<Comparative example 4>
Production of composite particles according to Comparative Example 4 was attempted under the same conditions as in Example 5 except that xylene (boiling point 144 ° C.) was used instead of dichloromethane in Example 5.

<Comparative Example 5>
Production of composite particles according to Comparative Example 5 was attempted under the same conditions as in Example 7 except that oleic acid (melting point: 13.4 ° C.) was used instead of stearic acid in Example 7.
<Comparative Example 6>
Comparison was made under the same conditions as in Example 7 except that amide wax (trade name ITOHWAX-J630, melting point: 135 ° C., Sankei Sangyo, hereinafter referred to as ITOWAX) was used instead of stearic acid in Example 7. An attempt was made to produce composite particles according to Example 6.

  The evaluation results using the above examples and comparative examples are collectively shown in Table 1 below.

  In Table 1, the emulsion stabilizer is an additive used to stabilize the O / W emulsion in the second step, and corresponds to, for example, the refined cellulose 1 in the present embodiment. To do.

〔Evaluation criteria〕
In Table 1, the possibility of the second step was determined as follows.
○: Formation of an O / W emulsion is possible ×: Formation of an O / W emulsion is impossible Further, whether or not the third step is possible was determined as follows.
○: True spherical particles obtained as the emulsion template in the third step were obtained. ×: The above particles were not obtained. Redispersibility was determined as follows.
○: The obtained composite particles were dispersed in the solvent (water) without agglomeration. X: Aggregated without being dispersed.

  The biodegradability was evaluated based on JIS standard "JIS K6950: 2000 Plastic-Determination of aerobic ultimate biodegradability in aqueous culture-Method by measurement of oxygen consumption using closed respirometer". The composite particles 5 and activated sludge are added to an inorganic salt medium so as to be 100 mg / L and 30 mg / L, respectively, the amount of oxygen consumed is measured, and the oxygen consumption biochemical oxygen demand (BOD; chemical substance or organic substance is The mass concentration of dissolved oxygen consumed by aerobic biooxidation in water under specific conditions was calculated.

As a control, an inorganic salt medium not containing the composite particles 5 was used. The amount of oxygen (theoretical oxygen demand, ThOD) required for converting all of the composite particles 5 into water and carbon dioxide was calculated from the polymer composition formula. The degree of biodegradation was calculated as the biochemical oxygen demand relative to the theoretical oxygen demand (biodegradation = BOD / ThOD × 100). Biodegradability was determined according to the following criteria.
A: The biodegradation degree after 28 days from the start of the test was 80% or more.
X: The degree of biodegradation after 28 days from the start of the test was less than 80%.

In addition, the hatched notation in each cell in the comparative example of Table 1 indicates that the process cannot be performed during each process, and the subsequent process is not performed.
As is clear from the evaluation results of Examples 1 to 8 in Table 1, the type of refined cellulose 1 (TEMPO oxidized CNF, CCM CNF, phosphate esterified CNF), or the type and polymerization of a biodegradable compound It was confirmed that the composite particles 5 having biodegradability could be produced regardless of the type of the functional monomer, and that the problems in the present invention were successfully solved.
On the other hand, in Comparative Example 1, it was impossible to perform the second step. Specifically, even when the ultrasonic homogenizer treatment was performed, the monomer layer and the CNF dispersion layer remained separated from each other, making it impossible to produce an O / W emulsion.

  Further, in Comparative Example 2, it was possible to form an O / W type emulsion in the second step. It is considered that this was because the CMC exhibited amphiphilic properties similar to the refined cellulose and thus functioned as an emulsion stabilizer. However, when the polymerization reaction was carried out in the subsequent third step, the emulsion collapsed and composite particles using the O / W emulsion as a template could not be obtained. The reason for this is not clear, but since CMC is water-soluble, it is highly likely that it is fragile as a coating layer for maintaining the emulsion shape even during the polymerization reaction, and the emulsion collapsed during the polymerization reaction. Conceivable.

Further, in Comparative Example 3, commercially available PLA fine particles not coated with CNF were used in a similar configuration, but it was not possible to observe a state where fine cellulose was coated on the surface of the fine particles by SEM shape observation. .
Moreover, in Comparative Example 4, it was possible to form an O / W emulsion in the second step. However, in removing the xylene in the third step, since the water used for the CNF dispersion cannot be made higher than the boiling point of xylene, the biodegradable compound droplet 2 can be solidified. The composite particles could not be obtained.

Moreover, in Comparative Example 5, it was possible to form an O / W emulsion in the second step. However, even when cooled to room temperature in the third step, oleic acid did not solidify, the compound droplet 2 having biodegradability could not be solidified, and composite particles could not be obtained.
Moreover, in Comparative Example 6, since it cannot be made higher than the boiling point of water used in the CNF dispersion in the second step and ITOWAX cannot be melted, an O / W emulsion is formed. I couldn't.

  The composite particles of the present invention have favorable effects from the viewpoint of industrial implementation, such as the addition efficiency as an additive, the kneading efficiency with the resin, and also contribute to cost reduction from the viewpoint of improving transport efficiency and preventing spoilage. It is done. Further, since the compound having biodegradability, which is a feature of the composite particles of the present invention, is included, and CNF covering the compound is also a biodegradable material, it is an environmentally friendly material. In addition, this composite particle makes use of the characteristics of finely divided cellulose on the particle surface and the polymer contained therein, thereby allowing coloring materials, adsorbents, cosmetic pigments, sustained-release materials, deodorants, antibacterial medical parts, personal care products For antibacterial products, packaging materials, dye-sensitized solar cells, photoelectric conversion materials, photothermal conversion materials, heat shielding materials, optical filters, Raman enhancement elements, image display elements, magnetic powders, catalyst carriers, drug delivery systems, etc. Can be applied.

1 Cellulose nanofiber (refined cellulose)
2 Biodegradable compound droplets (polymerizable monomer droplets)
3 Compound particles having biodegradability 4 Dispersion liquid 5 Composite particles

Claims (4)

  Having particles containing at least one kind of biodegradable compound and finely divided cellulose covering at least a part of the surface of the particles containing the biodegradable compound, and having the biodegradability A composite particle comprising particles containing a compound and the finely divided cellulose in an indivisible state. A first step in which a cellulose raw material is defibrated in a solvent to obtain a finely divided cellulose dispersion;
Secondly, at least a part of the surface of the droplet containing the biodegradable compound in the dispersion is covered with the fine cellulose, and the droplet containing the biodegradable compound is stabilized as an emulsion. Process,
In a state where at least a part of the surface of the droplet containing the biodegradable compound is covered with the fine cellulose, the droplet containing the biodegradable compound is solidified to form polymer particles. And a third step of covering at least a part of the surface of the polymer particles with the refined cellulose and making the polymer particles and the refined cellulose indivisible. Manufacturing method. In the second step,
A step of adding a mixture of the biodegradable compound containing an initiator and a polymerizable monomer to the finely divided cellulose dispersion to emulsify, and dispersing the biodegradable compound into the fine cellulose A step of adding a solution dissolved in a solvent having low compatibility with the liquid to the fine cellulose dispersion and emulsifying the fine cellulose dispersion; and the biodegradability of the fine cellulose dispersion that is solid at room temperature The method for producing composite particles according to claim 2, wherein any one of the steps of adding a compound and heating to a melting point of the compound having biodegradability to melt and emulsify is used.   A dry powder comprising the composite particles according to claim 1 and having a solid content of 80% or more.