WO2020130701A2 - Composite particles of cellulose nanofibers and polymer, and method for preparing same - Google Patents

Abstract

Described in the present invention are composite particles in which cellulose nanofibers are non-consecutively coated on the surface of a polymer core particle. The composite particles can be prepared by means of an environment-friendly emulsion polymer polymerization reaction, and thus a composite material which is transparent and shows enhanced mechanical properties can be provided.

Description

Composite particles of cellulose nanofibers and polymers and manufacturing method thereof

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0167773 filed on December 21, 2018, and all content disclosed in the literature of the Korean patent application is incorporated as part of this specification.

The present invention relates to a composite particle capable of producing a high-strength transparent material and a method of manufacturing the same.

Polymethyl methacrylate (PMMA) and polystyrene (PS), which are mainly used as glass replacement materials, have excellent mechanical properties and high visibility of 92% visible light transmittance, making it possible for automobile windows and sunroofs, aquarium tanks, and ice hockey links. It is used in a wide variety of industries such as bleachers, eyeglass lenses. The use of such a glass substitute material can realize advantages such as reducing fuel consumption and raw material use by reducing the weight of materials, improving the working environment of industrial workers, and using flexible film materials.

Recently, as environmental problems have emerged worldwide, interest in eco-friendly composite materials has increased. For this reason, utilization of glass substitute materials is gradually widening, and higher mechanical properties are required, and thus, complex research using nano fillers within a range that does not interfere with visibility has been actively conducted.

Conventional composite material manufacturing methods have been using organic solvents or pre-treatment on the surface of nano-fillers to effectively disperse hydrophilic nano-fillers and hydrophobic polymers. This method requires very high energy and increases production costs due to complicated processes. And there are many problems, such as environmental problems due to the use of organic solvents.

As an example of various composite materials, Korean Patent Application No. 10-2015-0106317 discloses a method of manufacturing an emulsion having excellent dispersibility and stability using a picking emulsion. Specifically, a method of preparing a highly dispersed phase 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 has not disclosed how a transparent composite material can be produced.

In addition, Korean Patent Application No. 10-2017-7019015 discloses a method of manufacturing 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 hydrophobic particles use various acrylate polymers. However, the use of the emulsion is limited to cosmetic compositions applied to keratin, and a transparent composite material that can replace glass is not disclosed.

Therefore, there is a need for a method capable of manufacturing a transparent composite material in an environmentally friendly and simpler process.

Accordingly, the present invention is to provide a high-strength and high-transparent composite material that can be used as a glass substitute material and an emulsion capable of manufacturing the same.

In addition, the present invention is to provide a method for preparing the emulsion.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems that are not mentioned will be clearly understood by those skilled in the art from the following description. Will be able to.

In order to achieve the above technical problem, the present invention provides composite particles in which cellulose nanofibers are discontinuously coated on the surface of a polymer core particle.

According to one embodiment, the polymer may be a hydrophobic polymer.

According to a preferred embodiment, the polymer may be methacrylate-based.

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

According to a preferred embodiment, the cellulose nanofibers are 4 to 100 nm in diameter and 0.5 to 5 um in length.

According to a preferred embodiment, the weight ratio of the polymer core particles and the cellulose nanofibers is 100:1 to 20.

The composite particles may have an average size of 50 to 200 nm.

In addition, the composite particles may have a glass transition temperature of 120°C or higher.

According to another aspect of the present invention, an emulsion in which the composite particles are dispersed in water is provided.

The emulsion may have a zeta potential of -100 mV or more and -30 mV or less.

According to another aspect of the invention,

a) dispersing a monomer having a polymerizable functional group in a water phase, a polymerization initiator, and cellulose nanofibers to prepare a dispersion liquid;

b) The polymerization reaction is carried out while stirring and emulsifying the dispersion, and the monomer having the polymerizable functional group forms polymer core particles, so that the cellulose nanofibers are discontinuously coated on the surface of the polymer core particles to form polymer composite particles. Provided is a method for preparing a polymer composite particle comprising an emulsion formation step.

According to one embodiment, the step of b) may further include obtaining the polymer composite particles by freeze-drying the emulsion of the polymer composite particles.

The composite material according to the present invention does not contain additives such as surfactants and stabilizers, and is manufactured through the formation of a picking emulsion using water as a solvent, so it is eco-friendly and the manufacturing process is simple. In addition, since the cellulose nanofiber having excellent specific strength serves as a reinforcing material, it has excellent transmittance to visible light and excellent mechanical properties. Therefore, it can be used in various fields by replacing glass or polymer resins used in fields requiring optical properties and mechanical properties.

1 shows the structure of cellulose.

2 is a view illustrating cellulose nanofibers (CNF) and cellulose nanocrystals (CNC).

Figure 3 schematically shows the PMMA / CNF composite particle manufacturing process according to Example 1.

4 is a result of measuring the Zeta potential of the emulsion prepared in Example 1.

5 is a scanning electron microscope (SEM) photograph of the PMMA/CNF composite particles prepared in Example 1.

6 is a result of differential scanning calorimetry of particles according to Example 1 (PMMA/CNF composite particles) and Comparative Example 1 (pure PMMA particles).

7 is a scanning electron microscope (SEM) photograph of the emulsion prepared in Example 2 (PEMA/CNF composite particles).

8A to 8D are scanning electron microscope (SEM) photographs of composite particles prepared by changing the CNF content in Example 3.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. The drawings are provided as an example 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, but 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 otherwise defined in the technical terms and scientific terms used herein, those skilled in the art to which the present invention pertains have the meanings commonly understood, and the following description and the accompanying drawings of the present invention Descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter are omitted.

The present invention relates to composite particles in which cellulose nanofibers are discontinuously coated on the surface of polymer core particles. Here, the term'discontinuous' means that cellulose nanofibers are evenly surrounded on the surface of the polymer core particles so that they do not stick or entangle with each other, and thus exist individually, thereby forming a stable and constant size oil-in-water picking emulsion.

Cellulose is a major component of the cell wall of plants, and is an organic compound that exists in large quantities after coal in nature. As shown in FIG. 1, cellulose is a polysaccharide in which β-D-glucose forms a polymer through β-glucoside bond (1-4 glucoside bond), and the chemical formula is (C ₆ H ₁₀ O ₅ ) _n . The repeating unit is cellobiose. It is a linear structure through 1-4 glucosidic bonds in which carbon 1 and carbon 4 of β-D-glucose are combined, and the glucose units alternately turn upside down. Due to this structure, hydrogen bonds are formed between hydroxyl groups of carbons 3 and 6 adjacent to parallel cellulose molecules and exist as linear chains.

As can be seen in FIG. 2, approximately 80 linear chains of these cellulose molecules gather to form cellulose microfibril, a functional unit in an organism. A number of cellulose molecules gather to form a fiber. The minimum unit is a micelle, which is about 0.05 nm in diameter and about 0.6 nm in length or more. The micelles form a crystal structure, and the connecting region between micelles and micelles is an amorphous region.

Cellulose possesses numerous hydrogen bonds, so crystallinity is formed and causes excellent mechanical strength. Due to the strong hydrogen bond, cellulose has almost no glass transition temperature or melting point, making it almost impossible to perform three-dimensional molding. In addition, since there are six hydroxyl groups per unit structure (cellobiose), they exhibit strong hydrophilic properties, but are not soluble in water due to hydrogen bonds. Therefore, there is a need for a nano-technology that can be complexed by minimizing and dispersing the size while maintaining the mechanical properties of cellulose.

Nanocellulose that can be obtained by nano-cellulose includes cellulose nanocrystals (CNC) and cellulose nanofibers (CNF).

CNF consists of nano-sized cellulose fibrils with a high aspect ratio, fibril widths of 5 to 20 nm, and lengths of typically several micrometers. It represents thixotropy, which is a characteristic of a viscous gel or liquid under normal conditions, but when shaken or shaken, it becomes less viscous. 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, which produces shorter (100-1000 nm) and higher crystalline and hard nanoparticles than CNF obtained through homogenization, microfluidization or grinding pathways, which produce cellulose It is called nanocrystal (CNC). As shown in Fig. 2, micelles forming the crystal region are the main components of the CNC.

According to an embodiment, the cellulose nanofibers have at least one of length and diameter, preferably less than 100 nm in diameter.

According to a preferred embodiment, the cellulose nanofibers have a diameter of 4 nm or more or 5 nm or more, 100 nm, or less, or 50 nm or less or 20 nm or less, and a length of 0.5 um or more and 5 um or less or 3 um or less or 2 um or less.

Cellulose nanofibers are more effective in stabilizing the interface when they have amphiphilic surface properties through surface treatment. It can have the amphiphilic surface properties of the hydrophobic surface and the hydrophilic end of the cellulose chain, and the amphiphilic property can effectively stabilize the oil/water interface. Therefore, the property of amphiphilic surface particles has great potential as an emulsion stabilizer. Unlike surfactant molecules, particles have a high adsorption energy, so they can be irreversibly adsorbed at the liquid-liquid interface to form a more stable emulsion system, thereby providing great diversity in material processing.

The present invention used cellulose nanofibers (CNF) at the nanometer level so as not to affect the visibility of the final product, and cellulose nanofibers (CNF) and transparent polymer materials (e.g., methacrylate based) through a pickering emulsion method ) In the polymerization emulsification step, the particle size was controlled, and stability and dispersibility were maintained. In the composite of cellulose nanofibers (CNF) and transparent polymer materials, the process is very simple, eco-friendly, and high dispersibility by using only pure water without modifying the CNF surface or using a special solvent.

Emulsion is a system in which oil droplets are dispersed in water or water droplets are dispersed in oil. In particular, in High Internal Phase Emulsion (HIPE), the volume of dispersed droplets is about 74% by volume of the total emulsion. It refers to the above emulsion system. These high dispersion phase emulsions have a very high volume to specific surface area compared to ordinary emulsions, and thus can be usefully utilized.The high dispersion phase emulsion can be used as a template to produce various porous materials. It can be used in all areas of the industry, such as adsorbents and catalyst supports.

The emulsion according to an embodiment may be an oil-in-water type pickering emulsion in which the oil phase is a dispersed phase, and the water phase is a continuous phase. have. Thus, by having the oil phase as a dispersed phase, it is possible to obtain a very stable emulsion in which phase separation does not easily occur even after a long time has elapsed. When the oil layer and the water layer are mixed to form a dispersed phase oil phase and a continuous phase aqueous 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 droplets. This is because the phase separation by interfacial tension can be suppressed by lowering the interfacial tension.

In the method of forming the picking emulsion, 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 having a level of 100 nm. In addition, according to the present invention, when dispersing CNF in a polymer matrix, an emulsion is prepared by stabilizing an aqueous solution and a hydrophobic monomer with CNF using only a continuous phase without using an organic solvent, so the method is simple and eco-friendly.

Specifically, the present invention

a) dispersing a monomer having a polymerizable functional group in a water phase, a polymerization initiator, and cellulose nanofibers to prepare a dispersion liquid;

b) The polymerization reaction is carried out while stirring and emulsifying the dispersion, and the monomer having the polymerizable functional group forms polymer core particles, so that the cellulose nanofibers are discontinuously coated on the surface of the polymer core particles to form polymer composite particles. It provides a method for producing a polymer composite particle comprising an emulsion forming step.

According to one embodiment, the step of b) may further include obtaining the polymer composite particles by freeze-drying the emulsion of the polymer composite particles.

According to one embodiment, the polymerization reaction may be carried out for 5 to 20 hours at a temperature of 50 ~ 100 ℃.

Advantages of the method for manufacturing a composite particle according to the present invention can be largely viewed in three ways.

First, the emulsion formation method according to the present invention does not use a surfactant. When the emulsion resin particles are synthesized using a surfactant, a decrease in physical properties is caused by the surfactant remaining in the particles. Unlike the general method of using a surfactant for the stability of the synthesized emulsion, the polymer particles synthesized through the picking emulsion according to the present invention have excellent emulsion stability and no surfactant exists, so CNF/ It is possible to manufacture polymer composites.

Second, in the emulsion formation method according to the present invention, water is used as a solvent. In general, a solution casting method using an organic solvent is used to disperse the nano-pillar and the polymer and form a complex. When an organic solvent is used, there is an environmental load in the process, and toxicity when the solvent remains in the complex. It has the potential to continuously adversely affect the human body.

Third, the emulsion formation process is very simple. Since the emulsion process for stabilizing the emulsion and the polymerization reaction for appropriately controlling the molecular weight of the emulsion particles are simultaneously carried out, each process is not separated and is made of in-situ. Therefore, it is very simple compared to the conventional method.

The emulsion prepared by the method according to the present invention may have a zeta potential of -100 mV or more and -30 mV or less. When the zeta potential is about -30 mV or less, the system of the solution is stable and does not form aggregation. If the absolute value of the zeta potential is less than 30 mV, the electrostatic repulsive force between the particles may drop and the formed particles may re-aggregate. Preferably, the zeka potential may be -90 mV or more, -80 mV or more, -40 mV or less, -50 mV or less, -60 mV or less, or -70 mV or less.

In the present invention, the polymer capable of forming a picking emulsion through interaction with CNF is preferably a monomer of a hydrophobic polymer, and may be, for example, a methacrylate-based polymer. The monomer capable of forming the methacrylate-based polymer may be, but is not limited to, methyl methacrylate, ethyl methacrylate, phenyl methacrylate, 2-hydropropyl methacrylate, and the like.

According to a preferred embodiment, the weight ratio of cellulose nanofibers to 100 parts by weight of polymer core particles is 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more, and 20 parts by weight or less , 15 parts by weight or less, 12 parts by weight or less, 10 parts by weight or less, or 8 parts by weight or less.

The weight ratio of the core of the polymer and the cellulose nanofibers can be adjusted by the weight ratio of the monomer and cellulose nanofibers used for pickering polymerization. When the weight ratio of cellulose nanofibers is too high, overall stirring is not smoothly performed due to an increase in the viscosity of the dispersion itself, and thus it is difficult for CNF particles to be adsorbed on the polymer core particles, and optical properties are deteriorated due to overlap between CNF particles. On the other hand, if it is too low, the effect of improving mechanical properties may be negligible. Therefore, it may be important to increase the input amount by adjusting the aspect ratio of CNF in order to obtain the effect of improving the maximum mechanical properties within a range in which optical properties are maintained.

The aspect ratio of CNF can be adjusted in the range of 5 to 1250, preferably 10 or more, 15 or more, 20 or more or 25 or more, 1000 or less, 900 or less, 800 or less, 700 or less, 600 or less, 500 or less or 400 or less Can.

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.

Further, the composite particles may have a glass transition temperature of 120°C or higher or 125°C or higher, and may be 180°C or lower, 170°C or lower, 160°C or lower, 150°C or lower, or 140°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 with moldability, and if it is too low, the properties may be poor.

The composite particles according to the present invention are expected to be applicable to various fields requiring visible light transmission and mechanical strength because they have better physical properties when compared to pure PMMA particles.

Hereinafter, a manufacturing method according to the present invention will be described in more detail through examples. However, the following examples are only one reference for explaining 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 the additive not specifically described in the specification may be weight%.

<Example 1>

An emulsion of composite particles was prepared by a process as shown in FIG. 3. Specifically, 0.3 parts by weight of the radical initiator AIBN was dissolved in 100 parts by weight of methyl methacrylate. In 45 ml of water, 4 ml of methyl methacrylate (MMA) in which the initiator was dissolved and cellulose nanofibers (about 10 nm in diameter and about 1 µm in length) were mixed at a weight ratio of 10:1, followed by stirring at 1500 rpm. Emulsification and polymerization were carried out together for 8 hours at 70°C under stirring to prepare an emulsion of composite particles in which CNF was discontinuously coated on polymethylmethacrylate core particles.

The result of measuring the Zeta potential through the dynamic light scattering measurement method for the emulsion obtained in Example 1 is shown in FIG. 4. Zeta potential was measured at -78.6 mV. It can be confirmed from the results of FIG. 4 that a picking emulsion in which monomers of hydrophilic cellulose nanofibers and hydrophobic polymers are well dispersed is formed.

5 is an electron microscope photograph of the PMMA/CNF composite particles prepared in Example 1. From FIG. 5, it is possible to observe a form in which CNFs individually surround nanoscale PMMA particles. PMMA particles form nano-sized particles at about 100-300 nm.

6 is a result of differential scanning calorimetry of the PMMA/CNF composition prepared in Example 1. The glass transition temperature could be measured by thermal analysis. The Tg of the PMMA/CNF composition was about 129°C at the point where the inflection point was generated, which was 10°C higher than the Tg 119°C of pure PMMA. It can be seen that the mechanical properties were improved through the increased Tg.

<Example 2>

An emulsion of composite particles was prepared in the same manner as in Example 1, except that ethyl methacrylate was used instead of Methyl methacrylate. 7 is an electron micrograph of the prepared emulsion.

<Example 3>

An emulsion of composite particles was prepared in the same manner as in Example 1, except that the CNF mass was changed to 2, 4, 6, and 8 parts by weight based on 100 parts by weight of the MMA in which the initiator was dissolved. 8A to 8D It is an electron microscope photograph of the prepared emulsion.

PMMA particles of a certain size (150 nm) were formed until the proportion of CNF was 6 wt%. However, as the proportion of CNF dropped below 4 wt%, the amount of CNF surrounding PMMA particles was significantly reduced, resulting in the formation of PMMA particles with large particle sizes. This is because as the amount of CNF surrounding the surface of the remains decreases, the interface is relatively unstable, resulting in the formation of large PMMA particles.

<Comparative Example 1>

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

<Comparative Example 2>

Dissolve 20 g of PMMA ( Sigma Aldrich , product name-445746, molecular weight Mw 350,000 g/mol) in 100 ml acetone, mix cellulose nanofibers with 100 parts by weight of PMMA to 10 parts by weight (weight ratio 10:1), and then at 50°C 1 Dispersed solution was prepared through ultra-sonication for about an hour. Thereafter, the mixture was evaporated slowly in a glass petri dish at 50°C through a solution casting method to obtain a composite composition.

This method has the disadvantage that it uses a fairly large amount of solvent of about 500 wt% and requires a separate evaporation process, which requires additional processing and time (KIZILTAS, Esra Erbas, et al., Preparation and characterization of transparent PMMA-cellulose-based nanocomposites,　Carbohydrate polymers, 2015, 127: 381-389).

<Comparative Example 3>

An emulsion was prepared in the same manner as in Example 1, except that graphene oxide was used instead of CNF. In the case of the final film, it was difficult to make a transparent film due to the optical properties of black originating from the carbon atom of graphene particles. (GUDARZI, Mohsen Moazzami; SHARIF, Farhad, Self assembly of graphene oxide at the liquid-liquid interface: A new route to the fabrication of graphene based composites.Soft Matter, 2011, 7.7: 3432-3440).

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 bleachers, lenses, and other alternatives to glass or existing transparent plastic materials , For example, it is expected to be used for transparent electrodes, films, coating materials, adhesives, headlamps, and electronic component materials.

Claims (12)

1. Composite particles in which cellulose nanofibers are discontinuously coated on the surface of polymer core particles.
2. According to claim 1,

   Composite particles of the polymer is a hydrophobic polymer.
3. According to claim 1,

   The polymer is a methacrylate-based composite particle.
4. According to claim 1,

   The cellulose nanofibers are composite particles having at least one of length and diameter of 100 nm or less, and an aspect ratio of 5 to 1250.
5. According to claim 1,

   The cellulose nanofibers are composite particles having a diameter of 4 to 100 nm and a length of 0.5 to 5 um.
6. According to claim 1,

   Composite particles having a weight ratio of polymer core particles and cellulose nanofibers of 100:1 to 20.
7. According to claim 1,

   Composite particles with an average size of 50 to 200 nm.
8. According to claim 1,

   Composite particles with a glass transition temperature of 120℃ or higher.
9. An emulsion in which the composite particles of claim 1 are dispersed in water.
10. The method of claim 9,

    An emulsion with a zeta potential of -100 mV or more and -30 mV or less.
11. a) dispersing a monomer having a polymerizable functional group in a water phase, a polymerization initiator, and cellulose nanofibers to prepare a dispersion liquid;

    b) The polymerization reaction is carried out while stirring and emulsifying the dispersion, and the monomer having the polymerizable functional group forms polymer core particles, so that the cellulose nanofibers are discontinuously coated on the surface of the polymer core particles to form polymer composite particles. Method for producing polymer composite particles comprising the step of forming an emulsion.
12. The method of claim 11,

    Method of manufacturing a polymer composite particle further comprising the step of obtaining the polymer composite particle by freeze-drying the emulsion of the polymer composite particle of step b).

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