KR20220074067A - Process for Preparing Composite Particles of Cellulose Nanofiber and Polymer - Google Patents

Abstract

The present invention describes a method for producing a polymer composite particle containing cellulose nanofibers by a Pickering emulsion. According to the present invention, the adsorption force of the cellulose nanofiber can be increased, so that the resulting composite particles have more mechanical properties. can be improved

Description

{Process for Preparing Composite Particles of Cellulose Nanofiber and Polymer}

The present invention relates to a method for preparing polymer composite particles using a Pickering emulsion.

Polymethyl methacrylate (PMMA) and polystyrene (PS), which are mainly used as substitutes for glass, not only have excellent mechanical properties, but also have high visibility of 92% of visible light transmittance. It is used in a wide variety of industrial fields, such as guard plates for grandstands and spectacle lenses. The use of such a glass substitute material can realize advantages such as reduction of fuel efficiency and raw material use of automobiles through weight reduction of materials, improvement of the working environment of industrial workers, and availability of flexible film materials.

Recently, as environmental problems have emerged around the world, interest in eco-friendly composite materials is increasing. For this reason, the utilization of glass substitutes is gradually expanding, and higher mechanical properties are required. Therefore, complex studies using nanopillars are actively conducted within a range that does not obstruct visibility.

Conventional composite material manufacturing methods have used an organic solvent to effectively disperse hydrophilic nanopillars and hydrophobic polymers or have performed pretreatment on the surface of nanopillars, but this method requires very high energy and increases production costs due to complicated processes There are many problems such as environmental problems and load caused by the use of organic solvents.

As an example of various composite materials, Korean Patent Application No. 10-2015-0106317 discloses a method for preparing an emulsion having excellent dispersibility and stability using a Pickering emulsion. Specifically, a method for preparing a highly dispersed emulsion using an ionic water-soluble polymer and silica particles, copper particles or polystyrene particles having an average particle diameter of 10 nm to 100 μm is disclosed. However, it does not disclose a method for manufacturing a transparent composite material.

In addition, Korean Patent Application No. 10-2017-7019015 discloses a method for preparing a stable emulsion by coating a plurality of hydrophobic particles on a hydrophilic core particle. The hydrophilic core particles include polysaccharides, specifically porous cellulose particles, and the hydrophobic particles use various acrylate polymers. However, the use of the emulsion is limited to a cosmetic composition applied to keratin, and a transparent composite material that can replace glass is not disclosed. Accordingly, the inventors of the present application proposed a method for manufacturing a transparent composite material in an environment-friendly and simpler process in Korean Patent Application No. 2018-0167773. As part of the present invention, the inventors of the present invention studied a method for further improving the mechanical properties and transparency of the composite material by facilitating the adsorption of cellulose during the preparation of the polymer composite material using the Pickering emulsion.

Accordingly, an object of the present invention is to provide a method capable of further improving the adsorption property of cellulose when manufacturing a composite material containing cellulose and a polymer.

In addition, an object of the present invention is to provide a composite material manufactured by the above method and having superior physical properties such as mechanical strength and transparency.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. will be able

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. will be able

In order to achieve the above technical object, the present invention provides a method for producing a polymer composite particle,

a) preparing an oil phase by mixing a monomer having a polymerizable functional group and a hydrophobic organic solvent;

b) preparing a suspension in which cellulose nanofibers are suspended in water;

c) preparing a dispersion by mixing the oil phase and the suspension and then stirring; and

d) after adding a polymerization initiator to the dispersion, a polymerization reaction proceeds while stirring to obtain an emulsion of the polymer composite particles.

According to an embodiment, the hydrophobic organic solvent may have an interfacial tension of 30-50 mN/m when in contact with water at 20°C.

According to an embodiment, the oil phase in which the monomer and the hydrophobic organic solvent are mixed may have an interfacial tension of 20 to 40 mN/m when in contact with water at 20°C.

According to an embodiment, in the oil phase in which the monomer and the hydrophobic organic solvent are mixed, the absolute value of the spreading coefficient (S) calculated by Equation 1 below may be 5 to 20.

[Equation 1]

S (O/W) = γ _ow (cosθ _w -1)

In Equation 1, S (O/W) represents the spreading coefficient of a system in which solid particles are dispersed in a solvent containing oil and water, and γ _ow represents the interfacial tension between oil and water (mN/m) , θ _w represents the contact angle between solid particles-water-oil.

According to an embodiment, in step a), the monomer and the organic solvent may be mixed in a volume ratio of 0.5:1 to 1:0.5.

According to an embodiment, the organic solvent may be at least one selected from the group consisting of chlorobenzene, dichlorobenzene, xylene and d-limonene.

According to one embodiment, the content of the cellulose nanofibers in the suspension in step b) may be 0.01 to 1% by weight.

According to an embodiment, the dispersion may be prepared by mixing the oil phase and the suspension in a volume ratio of 1:1 to 1:50 in step c).

According to an embodiment, the monomer having a polymerizable functional group may include at least one selected from the group consisting of acrylic acid, methacrylic acid, and acrylic acid ester.

According to one embodiment, the polymer composite particles may be one in which the monomer having the polymerizable functional group forms a polymer core particle, and cellulose nanofibers are discontinuously coated on the surface of the polymer core particle.

According to an embodiment, the cellulose nanofiber may have at least one of a length and a diameter of 100 nm or less, and an aspect ratio of 5 to 1250.

According to an embodiment, the cellulose nanofiber may have a diameter of 4 to 100 nm and a length of 0.5 to 5 um.

According to one embodiment, the weight ratio of the polymer monomer to the cellulose nanofiber may be 100: 1 to 20.

According to one embodiment, the average size of the polymer composite particles may be 50 ~ 200nm.

In addition, the present invention is a method for adsorbing oil by adding particles to a dispersion in which oil and water, which have a lower interfacial tension than water, are mixed. provides a way to do it.

The present invention relates to a method for manufacturing a composite material of cellulose and a polymer, wherein additives such as surfactants and stabilizers are not used, and in manufacturing the composite material through the formation of a Pickering emulsion using water as a solvent, an appropriate solvent is added. By improving the adsorption property of cellulose through a simple process, the film produced using the resulting composite material has improved permeability, mechanical properties, and thermal stability. The process according to the present invention is simple because only a solvent is added, and it does not require an additional process such as surface modification and does not change the surface properties of cellulose, so that the original physicochemical properties of cellulose can be maintained.

1 and 2 show the stability of the emulsions prepared in Example 1 and Comparative Example 1.
3 and 4 are SEM photographs showing the structures of the composite particles prepared in Example 2 and Comparative Example 2.
5 is a SEM photograph showing the structure of the composite particles prepared in Examples 3 and 4.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. The drawings are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention.

In addition, unless there are other definitions in technical and scientific terms used herein, it has the meaning commonly understood by those of ordinary skill in the art to which this invention belongs, and in the following description and accompanying drawings, Descriptions of known functions and configurations that may unnecessarily obscure the subject matter will be omitted.

The present invention relates to a method for manufacturing a composite particle in which cellulose nanofibers are continuously or discontinuously coated on the surface of a polymer core particle.

Cellulose is the main component of the cell wall of plants, and it is an organic compound that exists in large quantities in nature after coal. Cellulose is a polysaccharide in which β-D-glucose is polymerized through β-glucosidic bonds (1-4 glucosidic bonds), and the chemical formula is (C ₆ H ₁₀ O ₅ ) _n . The repeating unit is cellobiose. It forms a linear structure through a 1-4 glucosidic bond in which carbons 1 and 4 of β-D-glucose are bonded, and the glucose units are alternately inverted. Due to this structure, a hydrogen bond is formed between the hydroxyl groups of adjacent carbons 3 and 6 of parallel cellulose molecules, so that they exist as a linear chain.

About 80 linear chains of these cellulose molecules gather to form cellulose microfibrils, which are functional units in living organisms. A large number of cellulose molecules are gathered to form a fiber, and the smallest unit is a micelle, with a diameter of about 0.05 nm and a length of about 0.6 nm or more. The micelle has a crystalline structure, and the connection site between the micelle and the micelle is an amorphous region.

Cellulose possesses numerous hydrogen bonds, resulting in crystallinity and excellent mechanical strength. Due to strong hydrogen bonding, cellulose has no glass transition temperature or melting point, making it almost impossible to process three-dimensionally. In addition, there are 6 hydroxyl groups per unit structure (cellobiose), so it has strong hydrophilicity, but is not soluble in water due to hydrogen bonding by these groups. Therefore, there is a need for a nanotechnology that can be combined by minimizing and dispersing the size while maintaining the mechanical properties of cellulose.

There are cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) for nanocellulose that can be obtained by nanoizing cellulose.

CNF is composed of nano-sized cellulose fibrils with high aspect ratio. Fibrils have a width of 5-20 nm, a length of usually several micrometers, and exhibit thixotropy, which is characteristic of a viscous gel or liquid under normal conditions, but loses its viscosity when shaken or shaken. Fibrils are separated from cellulose-containing raw materials through high-pressure, high-temperature and high-speed impact homogenization, grinding or microfluidization.

Nanocellulose can also be obtained from natural fibers by acid hydrolysis, producing highly crystalline and hard nanoparticles with shorter lengths (100-1000 nm) than CNFs obtained through homogenization, microfluidization or grinding routes They are called nanocrystals (CNC). The micelle constituting the crystal region is the main component of CNC.

In the present invention, nanometer-level cellulose nanofibers (CNF) were used so as not to affect the visibility of the final product, and cellulose nanofibers (CNF) and transparent polymer materials (e.g., methacrylate-based ) to control the particle size and maintain stability and dispersibility in the polymerization emulsification step. In compositing cellulose nanofiber (CNF) and transparent polymer material, it provides an effective method to improve the adsorption property of CNF in the process of using only water as a reaction solvent without modifying the CNF surface.

Since nanocellulose has an excellent ability to make an emulsion of a hydrophobic component (oil) in water, it is possible to form stable oil droplets by adsorbing nanocellulose to the surface of oil droplets. An emulsion stabilized with only particles such as CNF without using a surfactant is called a Pickering emulsion, and the Pickering emulsion is used in various industries such as oil recovery, drug delivery, and composite particle manufacturing. In order to form a stable emulsion, the adsorption performance of nanocellulose at the interface between water and oil is very important.

Also, although nanocellulose has an excellent ability to stabilize a hydrophobic component in water as an emulsion, it cannot form a Pickering emulsion for all hydrophobic components. For example, it is known that CNF is difficult to adsorb to components with low interfacial tension, such as Octanol or methyl decanoate. In order to enable adsorption in a system where nanocellulose adsorption is poor, studies have been conducted to change the wettability of the nanocellulose surface through surface modification. For example, a method of increasing the stability of the Pickering emulsion by changing the surface of the nanocellulose to a positive charge using glycidyl trimethylammonium chloride is known. Also known is a method to change the surface properties by enclosing the cellulose nanocrystal surface with methyl cellulose. As such, most approaches enable Pickering emulsions by altering the wettability by modifying the surface of the nanocellulose. However, these methods require an additional process because a pretreatment process for surface modification of nanocellulose is added. Because the surface properties of the nanocellulose are changed, the dispersibility in water may be affected, and the physicochemical properties of the nanocellulose may be changed due to the change in the surface properties.

The present invention relates to a method for facilitating the adsorption of nanocellulose in the production of a polymer composite material by a Pickering emulsion.

An emulsion is a system in which oil droplets are dispersed in water or water droplets are dispersed in oil. It refers to the emulsion system. This highly dispersed emulsion has a very high volume-to-volume specific surface area compared to normal emulsions, so it can be usefully used, and it is possible to manufacture various porous materials using the highly dispersed emulsion as a template, so that filters, sensors, It can be used in general fields of industry, such as adsorbents and catalyst supports.

The emulsion formed according to the method of the present invention is a Pickering emulsion of an oil-in-water type in which an oil phase (hereinafter, also referred to as an 'oil phase') is a dispersed phase and a water phase is a continuous phase. (Oil-in-water type pickering emulsion).

In this way, by having the oil phase as the dispersed phase, it is possible to obtain a very stable emulsion in which phase separation does not easily occur even after a long period of time. When the oil layer and water layer are mixed to form a dispersed oil phase and a continuous water phase, the polymer monomer dispersed in the aqueous phase causes depletion pressure so that CNF is well adsorbed on the surface (interface) of the oil drop. This is because by lowering the interfacial tension, phase separation due to the interfacial tension can be suppressed.

In the Pickering emulsion formation method, since the size of the formed emulsion has a specific size in a thermodynamic equilibrium state, it is possible to form a small and uniform emulsion at the level of 100 nm.

Specifically, the present invention

a) preparing an oil phase by mixing a monomer having a polymerizable functional group and a hydrophobic organic solvent;

b) preparing a suspension in which cellulose nanofibers are suspended in water;

c) preparing a dispersion by mixing the oil phase and the suspension and then stirring; and

d) after adding a polymerization initiator to the dispersion, a polymerization reaction proceeds while stirring to obtain an emulsion of the polymer composite particles.

The present inventors have found that the adsorption performance of cellulose nanofibers is significantly improved by mixing a monomer having a low interfacial tension and an organic solvent having an appropriate interfacial tension and then contacting the cellulose nanofibers suspended in water.

The degree of interfacial adsorption of cellulose nanofibers can be confirmed from a spreading coefficient (hereinafter referred to as 'S'). The spreading coefficient can be finally calculated by the experimentally measured contact angle and interfacial tension by Equation 1 below. it means.

[Equation 1]

S (O/W) = γ _ow (cosθ _w -1)

In Equation 1, S(O/W) represents the spreading coefficient of a system in which solid particles are dispersed in a solvent containing oil and water, and γ _ow represents the interfacial tension between oil and water (mN/m) , θ _w represents the contact angle between solid particles-water-oil.

The contact angle can be measured by forming a solid particle film (eg, a CNF film) on a Si wafer at room temperature, and then dropping water on the solid particle film in an oil-filled environment.

Theoretically, if the value of the spreading coefficient ( S ) is positive, the solid particles can be wetted on only one side, and if it is negative, the solid particles are partially wetted on both phases. That is, when the spreading coefficient is positive, it is difficult to form a Pickering emulsion. On the other hand, if the spread coefficient is negative, both phases can be wetted and the Pickering emulsion is well formed. On the other hand, it is difficult to form a Pickering emulsion because the closer to 0, the boundary value, the more difficult it is for the particles to wet both phases. That is, the larger the absolute value of the spreading coefficient is, the more negative the number is, the more advantageous it is to form a Pickering emulsion.

Table 1 below shows the contact angle, interfacial tension, and spreading coefficient values for several oil components.

The contact angle (θ _w ) was performed using MATLAB and a CCD camera at 20 °C, and is the average of the values measured at three different locations. About 1 mL of CNF suspension (1% w/w) was cast on a Si wafer and left to dry at ambient conditions. The CNF film of the Si wafer was placed in a glass cuvette filled with the oil to be measured, and 3 μL of water was dropped on the CNF film, and the water contact angle was measured with MATLAB and a CCD camera.

The oil-water interfacial tension ( γ _ow ) was measured by the pendant drop method, and the unit is mN/m. The shape of the oil drop hanging on the tip of the needle (22 gauge, Hamilton) was photographed at 20℃ using a CCD camera (WAT-902H Ultimate, Watec). The shape of the droplet was tracked using MATLAB and analyzed to calculate the interfacial tension. Each value is the average of the values measured at three different locations on the sample.

The unit of the spreading coefficient (S) is mN/m, and was calculated by Equation 1 above.

According to the results in Table 1, the spread coefficient of MMA (methyl methacrylate) is -2.2 mN/m, which is significantly smaller in absolute value compared to other oils known to have relatively good cellulose adsorption. From this, it can be seen that cellulose adsorption is not good in the system using MMA.

In this way, in order to improve the adsorption performance of the monomer component, which is poorly adsorbed to cellulose (the absolute value of the spreading coefficient is small), by mixing the hydrophobic organic solvent with a certain high interfacial tension, the oil is mixed with the monomer and the hydrophobic organic solvent. The phase may be such that the absolute value of the spreading coefficient (mN/m) calculated by Equation 1 is 5 to 20.

In this case, the monomer having a polymerizable functional group may have an interfacial tension of 10 mN/m or more and 20 mN/m or less, or 15 mN/m or less when in contact with water at 20°C. The absolute value of the spreading coefficient of the monomer may be less than 5.

In addition, the hydrophobic organic solvent may have an interfacial tension of 30-50 mN/m or 30-40 mN/m when in contact with water at 20°C. Also, the absolute value of the spreading coefficient may be 20 to 30.

The oil phase in which the monomer and the hydrophobic organic solvent are mixed has an interfacial tension of 20-40 mN/m or 20-30 mN/m when in contact with water at 20°C, and the absolute value of the spreading coefficient is 5-20 or 10-15. have.

Table 2 below shows the contact angle, interfacial tension, and spreading coefficient when the components listed in Table 1 are mixed with MMA in a volume ratio of 1:1.

From the results of Tables 1 and 2, it can be seen that, when chlorobenzene having interfacial tension and spreading coefficient within a predetermined range was mixed with a monomer, the absolute value of the spreading coefficient increased rapidly. As will be described in Examples below, the present inventors confirmed through experiments that adsorption of cellulose was effectively achieved when the absolute value of the spreading coefficient was large.

According to a preferred embodiment of the present invention, the monomer having a polymerizable functional group may include at least one selected from the group consisting of acrylic acid, methacrylic acid, and acrylic acid ester. For example, it may be methacrylate-based. The monomer capable of forming the methacrylate-based polymer may be methyl methacrylate, ethyl methacrylate, phenyl methacrylate, 2-hydropropyl methacrylate, or the like, but is not limited thereto.

In addition, the organic solvent may be at least one selected from the group consisting of chlorobenzene, dichlorobenzene, xylene and d-limonene.

According to a preferred embodiment of the present invention, in step a), the monomer and the organic solvent are mixed in a volume ratio of 0.5:1 to 1:0.5, or 0.8:1 to 1:0.8 by volume. Most preferably, it may be mixed in a volume ratio of 1:1. If the content of either the monomer or the organic solvent is too large or too small, the effect of improving the adsorption performance of the cellulose nanofibers may be insignificant.

In addition, the content of the cellulose nanofibers in the suspension in step b) may be 0.01 to 1% by weight or 0.05 to 0.5% by weight. If the content of cellulose nanofibers is too small, the effect of improving the physical properties of the composite material by the addition of cellulose nanofibers is insignificant. Conversely, if the content is too large, CNF may not be adsorbed into the polymer composite material particles and remaining CNF may remain.

In addition, the dispersion may be prepared by mixing the oil phase and the suspension in a volume ratio of 1:1 to 1:50 in step c). It is preferable that the volume ratio of the oil phase and the suspension is greater than the volume of the oil phase. For example, the volume ratio of the oil phase and the suspension may be 1:5 or more, 1:10 or more, 1:15 or more, or 1:20 or more.

According to an aspect of the present invention, the method may further include drying the emulsion of the polymer composite particles to obtain the polymer composite particles.

The polymer composite material prepared by the method according to the present invention may be in the form of a particle in which a monomer having a polymerizable functional group forms a polymer core particle, and cellulose nanofibers are discontinuously coated on the surface of the polymer core particle.

According to one embodiment, the mass ratio of the polymer core particles to the cellulose nanofibers may be 100: 1 to 20, preferably 100: 5 to 15. If the mass ratio of cellulose nanofibers is too high, overall stirring is not performed smoothly due to an increase in the viscosity of the dispersion itself, so it is difficult for the CNF particles to be adsorbed to the polymer core particles, and the optical properties are deteriorated due to the overlap between the CNF particles. On the other hand, if it is too low, the effect of improving mechanical properties may be insignificant. Therefore, it may be important to increase the input amount by controlling the aspect ratio of CNF in order to obtain the maximum mechanical property improvement effect within the range in which the optical properties are maintained.

According to a preferred embodiment, at least one of a length and a diameter of the cellulose nanofiber is 100 nm or less.

According to a preferred embodiment, the cellulose nanofiber has a diameter of 4 to 100 nm and a length of 0.5 to 5 um. Preferably, the diameter may be 4-50 nm, length 0.5-3um, or diameter 5-20nm, length 0.5-2um. The aspect ratio of the cellulose nanofibers can be adjusted in the range of 5 to 1250, preferably 25 to 400.

The composite particles produced by the method according to the present invention may have an average size of 50 to 200 nm, preferably 80 nm or more or 90 nm or more, and 150 nm or less or 120 nm or less.

In addition, the composite particles may have a glass transition temperature of 120°C or higher or 125°C or higher, and 180°C or lower or 150°C or lower. The glass transition temperature of the composite particles can be said to be a measure of mechanical properties, and the higher the glass transition temperature, the better the mechanical properties, but there may be problems in formability.

In order to prepare a polymer composite material reinforced with cellulose using the Pickering emulsion, the reinforcing material must be able to easily adsorb to the interface between water and monomer. An organic solvent having predetermined interfacial tension and spreading coefficient characteristics was mixed with the monomer. In this way, since cellulose is more easily adsorbed, when the resulting polymer composite particles are thermocompression-bonded by hot press, etc., the manufactured composite film has the same characteristics as the composite film in which the reinforcing material is individually dispersed, and stress when an external force is applied. By smoothly dispersing it, excellent mechanical properties can be maintained. In addition, since a polymer composite material with excellent visible light transmittance can be manufactured according to the type of polymer monomer, it is expected to be applicable to various fields requiring transmittance and mechanical strength.

Hereinafter, the manufacturing method according to the present invention will be described in more detail through Examples. However, the following examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms. In addition, the unit of additives not specifically described in the specification may be weight %.

<Example 1>

An oil phase was prepared in which methyl methacrylate and chlorobenzene were mixed at 1:1 v/v. Cellulose nanofibers (diameter about 13 nm, length about 445 nm) were diluted in water to a concentration of 1 g/L, and then a suspension was prepared in which ultrasonic waves were applied and dispersed. All water used in this example was deionized (Milli-Q, Merck-Millipore, 18.2 MΩ·cm). The oil phase and the cellulose nanofiber suspension were mixed at 1:25 v/v (CNF input amount 2.5% w/w) and then emulsified through a homogenizer to prepare an emulsion.

<Comparative Example 1>

An emulsion was prepared in the same manner as in Example 1, except that chlorobenzene was not mixed.

The results of comparing the stability of the emulsion of Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2 . The stability of the emulsion was observed by the change in the size of the emulsion over time. The emulsion of Example 1 in which chlorobenzene was added showed high stability up to 7 days, but in the case of Comparative Example 1 in which chlorobenzene was not added, 1 day stability was shown.

<Example 2>

To the emulsion prepared in Example 1, potassium persulfate (KPS) was added as an initiator (1% w/w based on MMA), and polymerization was performed in a water bath at 70° C. for 8 hours. After completion of the reaction, the mixture was centrifuged and washed with water and methanol to remove the remaining monomers and initiators. The resulting PMMA/CNF composite particles were dried under vacuum conditions at 25° C. for 12 hours to obtain polymer composite particles having a particle diameter of about 100 nm.

<Comparative Example 2>

Polymer composite particles were prepared in the same manner as in Example 2, except that the emulsion of Comparative Example 1 was used.

3 and 4 are scanning electron microscope (SEM) pictures of the PMMA/CNF composite particles prepared in Example 2 and Comparative Example 2 (S-4800, Hitachi at 10 kV). FIG. 3 is a photograph of particles obtained 5 hours after initiation of polymerization, and FIG. 4 is a photograph of particles obtained after 8 hours. It can be observed that the particle (b) of Example 2 is more reliably adsorbed to the cellulose nanofiber compared to the particle (a) of Comparative Example 2.

<Example 3>

Polymer composite particles were prepared by reacting for 5 hours in the same manner as in Example 2, except that 1,2-dichlorobenzene was used as an organic solvent mixed with MMA.

<Example 4>

Polymer composite particles were prepared by reacting for 5 hours in the same manner as in Example 2, except that the organic solvent mixed with MMA was xylene.

5 is an SEM photograph of the composite particles obtained in Examples 3 and 4. 5A is the composite particle of Example 3, and b is the composite particle of Example 4. In both examples, it can be confirmed that the cellulose nanofibers are well adsorbed to the surface.

<Example 5>

Polymer composite particles were prepared in the same manner as in Example 2, except that the CNF input amount was changed to 7% w/w.

<Comparative Example 3>

A polymer composite particle was prepared in the same manner as in Comparative Example 2, except that the CNF input amount was changed to 7% w/w.

<Comparative Example 4>

Commercially purchased PMMA (Sigma Aldrich, product name-445746, molecular weight (Mw) 350,000 g/mol) was used.

<Example 6>

Composite films (thickness 200 μm) were prepared by pressing the polymer composite particles obtained in Examples 2 and 5 and Comparative Examples 2 to 4 at 160° C. and 20 MPa for 1 minute. Table 3 shows the results of measuring the mechanical properties (Young's modulus) of the composite film.

CNF input chlorobenzene composite particles Young's modulus (GPa) initial dose
(% w/w) adsorption amount
(% w/w) 2.5 2.4 O Example 2 1.70±0.14 1.2 X Comparative Example 2 1.51±0.06 7 6.2 O Example 5 2.04±0.10 1.2 X Comparative Example 3 1.52±0.10 0 0 X Comparative Example 4 1.22±0.06

Young's modulus was measured with a universal tensioning machine (UTM) (DBCM-20, BONSHIN) equipped with a 200N load cell. A specimen measuring 3 Х 30 mm (width Х length) was measured at a strain rate of 0.01 min ^-1 through a motor (RKE543AC, Oriental motor) controlled by a software program. A minimum of 5 specimens were measured for each sample.

As can be seen from the above results, the composite film using the composite particles prepared by the method according to the present invention has improved strength by about 70% compared to the composite film of Comparative Example 3 in which cellulose nanofibers are not used at all, and chlorobenzene is It can be confirmed that the composite film of Comparative Example 2, which is not used, exhibits significantly superior strength.

From the above, the composite particles manufactured according to the present invention can be used only when transparency and mechanical properties are secured, that is, glass windows, sunroofs, aquarium partitions, ice hockey rink guard plates, lenses, etc. , for example, is expected to be widely used in transparent electrodes, films, coatings, adhesives, headlamps, and electronic component materials.

In addition, the method according to the present invention adjusts interfacial tension through a solvent mixing method when a system requiring particle adsorption such as oil recovery or encapsulation is required, as well as in the case of forming a composite material. adsorption can be facilitated.

Claims (15)

a) preparing an oil phase by mixing a monomer having a polymerizable functional group and a hydrophobic organic solvent;
b) preparing a suspension in which cellulose nanofibers are suspended in water;
c) preparing a dispersion by mixing the oil phase and the suspension and then stirring; and
d) after adding a polymerization initiator to the dispersion, the polymerization reaction proceeds while stirring to obtain an emulsion of the polymer composite particles. According to claim 1,
The hydrophobic organic solvent has an interfacial tension of 30-50 mN/m when in contact with water at 20°C. The method of claim 1,
The method for preparing polymer composite particles, wherein the oil phase in which the monomer and the hydrophobic organic solvent are mixed has an interfacial tension of 20 to 40 mN/m when in contact with water at 20°C. According to claim 1,
In the oil phase in which the monomer and the hydrophobic organic solvent are mixed, the absolute value of the spreading coefficient ( S ) calculated by Equation 1 below is 5 to 20.
[Equation 1]
S (O/W) = γ _ow (cosθ _w -1)
In Equation 1, S(O/W) represents the spreading coefficient of a system in which solid particles are dispersed in a solvent containing oil and water, and γ _ow represents the interfacial tension between oil and water (mN/m) , θ _w represents the contact angle between solid particles-water-oil. According to claim 1,
In step a), the monomer and the organic solvent are mixed in a volume ratio of 0.5: 1 to 1: 0.5. The method of claim 1,
The organic solvent is at least one selected from the group consisting of chlorobenzene, dichlorobenzene, xylene and d-limonene. The method of claim 1,
In step b), the content of the cellulose nanofibers in the suspension is 0.01 to 1% by weight of the method for producing a polymer composite particle. According to claim 1,
In step c), the oil phase and the suspension are mixed in a volume ratio of 1:1 to 1:50 to prepare the dispersion. The method of claim 1,
The method for producing a polymer composite particle wherein the monomer having the polymerizable functional group comprises at least one selected from the group consisting of acrylic acid, methacrylic acid and acrylic acid ester. The method of claim 1,
The polymer composite particle is a method for producing a polymer composite particle in which the monomer having the polymerizable functional group forms a polymer core particle, and cellulose nanofibers are discontinuously coated on the surface of the polymer core particle. The method of claim 1,
The cellulose nanofiber has at least one of a length and a diameter of 100 nm or less, and an aspect ratio of 5 to 1250. According to claim 1,
The cellulose nanofibers have a diameter of 4 to 100 nm, and a length of 0.5 to 5 um. According to claim 1,
The weight ratio of the polymer monomer to the cellulose nanofiber is 100: 1 to 20 composite particles. According to claim 1,
A method for producing a polymer composite particle having an average size of 50 to 200 nm of the polymer composite particle. A method of adsorbing oil by adding particles to a dispersion in which oil and water having an interfacial tension lower than that of water are mixed.

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