KR102206030B1 - Composite Particles of Cellulose Nanofiber and Polymer, and A Process for Preparing Same - Google Patents

Abstract

The present invention describes a composite particle in which cellulose nanofibers are discontinuously coated on the surface of a polymer core particle, and the composite particle can be prepared through an eco-friendly emulsion polymer polymerization reaction, and as a result, a composite particle having improved mechanical properties while being transparent Material can be provided.

Description

Composite Particles of Cellulose Nanofiber and Polymer, and A Process for Preparing Same}

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

Polymethyl methacrylate (PMMA) and polystyrene (PS), which are mainly used as glass substitutes, not only have excellent mechanical properties, but also have a high visibility of 92% visible light transmittance, which is why windows and sunroofs of automobiles, aquarium tanks, ice hockey rinks It is used in a wide variety of industries, such as guards for grandstands and eyeglass lenses. The use of such a glass substitute material can realize advantages such as reduction of fuel economy and the use of raw materials through weight reduction of materials, improvement of working environment for industrial workers, and availability of flexible film materials.

Recently, as environmental issues emerge around the world, interest in eco-friendly composite materials is increasing. For this reason, the utilization of glass substitutes is gradually becoming wider, and higher mechanical properties are required, and thus, complex studies using nano fillers are being actively conducted within a range that does not interfere with visibility.

Conventional methods of manufacturing composite materials have used organic solvents or pre-treatment on the nano-filler surface to effectively disperse hydrophilic nano-fillers and hydrophobic polymers.These methods require very high energy and increase production costs due to complex processes. There are many problems such as environmental problems and loads caused by the use of organic solvents.

As an example of various composite materials, Korean Patent Application No. 10-2015-0106317 discloses a method of preparing an emulsion having excellent dispersibility and stability by using a Pickering emulsion. Specifically, a method of 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 of preparing a stable emulsion by coating a plurality of hydrophobic particles on a hydrophilic core particle. The hydrophilic core particles contain polysaccharides, specifically porous cellulose particles, and the 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 with an eco-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, 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 of ordinary skill in the technical field to which the present invention belongs from the following description. I 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 an embodiment, the polymer may be a hydrophobic polymer.

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

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

According to a preferred embodiment, the mass 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, there is provided an emulsion in which the composite particles are dispersed in water.

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

According to another aspect of the present invention,

a) preparing a dispersion by dispersing a monomer having a polymerizable functional group, a polymerization initiator, and cellulose nanofibers in an aqueous phase;

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

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

Since 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 pickering emulsion using water as a solvent, it is eco-friendly and the manufacturing process is simple. In addition, since cellulose nanofibers having excellent specific strength serve as a reinforcing material, they have excellent transmittance to visible light and excellent mechanical properties. Therefore, it can be used in various fields by replacing glass or polymer resin used in fields requiring optical properties and mechanical properties.

1 shows the structure of cellulose.
2 is a schematic diagram illustrating cellulose nanofibers and cellulose nanocrystals.
3 schematically shows a process of manufacturing PMMA/CNF composite particles according to an embodiment.
4 is a measurement result of Zeta potential of the emulsion prepared in Example 1.
5 is an electron micrograph of the PMMA/CNF composite particles prepared in Example 1. FIG.
6 is a differential scanning calorie analysis result of particles according to Example 1 (PMMA/CNF composite particles) and Comparative Example 1 (pure PMMA particles).
7 is an electron micrograph of the emulsion prepared in Example 2 (PEMA/CNF composite particles).
8 is an electron micrograph of composite particles prepared by varying the CNF content in Example 3. FIG.

Hereinafter, embodiments of 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 the technical terms and scientific terms used herein, they have the meanings 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 composite particles in which cellulose nanofibers are discontinuously coated on the surface of a polymer core particle.

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

As can be seen in FIG. 2, about 80 linear chains of these cellulose molecules are collected to form cellulose microfibrils, which are functional units in living organisms. Many cellulose molecules gather to form a fiber, and the minimum unit is called a micelle, which is about 0.05 nm in diameter and about 0.6 nm in length. The micelles have a crystalline structure, and the connection site between the micelles and micelles is an amorphous region.

Cellulose has a number of hydrogen bonds, resulting in crystallinity and excellent mechanical strength. Due to strong hydrogen bonding, cellulose has no glass transition temperature or melting point, making 3D molding process almost impossible. In addition, since there are 6 hydroxyl groups per unit structure (cellobiose), it shows strong hydrophilicity, but it does not dissolve in water due to hydrogen bonding by them. Therefore, there is a need for a nanotechnology capable of minimizing and dispersing the size while maintaining the mechanical properties of cellulose.

There are cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) as nano cellulose obtained by nano-izing cellulose.

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

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

According to a preferred embodiment, the cellulose nanofibers have a diameter of 4 to 100 nm and a length of 0.5 to 5 um. Preferably, it may be 4 to 50 nm in diameter, 0.5 to 3 um in length, or 5 to 20 nm in diameter, and 0.5 to 2 um in length.

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

In the present invention, cellulose nanofibers (CNF) at the nanometer level were used so as not to affect the visibility of the final product, and cellulose nanofibers (CNF) and a transparent polymer material (for example, methacrylate-based ) In the polymerization and emulsification step, control of the particle size, stability, and dispersibility were maintained. In complexing cellulose nanofibers (CNF) and transparent polymer materials, the process is very simple and eco-friendly, and high dispersibility can be exhibited by modifying the CNF surface or using only pure water without the use of any solvent.

Emulsion is a system in which oil droplets are dispersed in water or water droplets are dispersed in oil.In particular, High Internal Phase Emulsion (HIPE) is a system in which the volume of dispersed droplets is more than 74% by volume of the total emulsion. Refers to an emulsion system. These highly dispersed emulsions have a very high volume-to-volume specific surface area compared to ordinary emulsions, so they can be usefully utilized, and various porous materials can be produced by using a highly dispersed emulsion as a template. It can be used in overall fields of industry such as adsorbents and catalyst supports.

The emulsion according to an embodiment may be an oil-in-water type pickering emulsion in which an oil phase is a dispersed phase and a 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 period of time. When the oil layer and the water layer are mixed to form an oil phase as a dispersed phase and an aqueous phase as a continuous phase, the polymer monomers dispersed in the water phase cause depletion pressure so that CNF is well adsorbed on the surface (interface) of the oil droplets. 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. In addition, according to the present invention, when CNF is dispersed in a polymer matrix, the method is simple and eco-friendly because an aqueous solution and a hydrophobic monomer are stabilized with CNF by using only water in a continuous phase without using an organic solvent.

Specifically, the present invention

a) preparing a dispersion by dispersing a monomer having a polymerizable functional group, a polymerization initiator, and cellulose nanofibers in an aqueous phase;

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

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

According to an embodiment, the polymerization reaction may be performed for 5 to 20 hours at a temperature of 50 to 100 °C.

The advantages of the method for manufacturing composite particles according to the present invention can be largely seen 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, physical properties are deteriorated 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 Pickering emulsion according to the present invention have excellent emulsion stability and have stronger mechanical strength due to the absence of surfactants. It is possible to manufacture polymer composites.

Second, the emulsion formation method according to the present invention uses water as a solvent. In general, a solution casting method using an organic solvent is used as a method to disperse nano fillers and polymers and form a complex. When using an organic solvent, 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 emulsification process to stabilize the emulsion and the polymerization reaction to properly control the molecular weight of the emulsion particles are simultaneously carried out, each process is not separated and is performed in-situ. Therefore, it is very simple compared to the existing 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 less than about -30 mV, the solution system is stable and no aggregation is formed. If the absolute value of the zeta potential is less than 30mV, the electrostatic repulsion between the particles decreases, and the formed particles may re-aggregate.

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

According to an embodiment, the mass ratio of the polymer core particles and the cellulose nanofibers may be 100: 1 to 20, and preferably 100: 5 to 15. If the mass ratio of the cellulose nanofibers is too high, the overall agitation is not performed smoothly due to an increase in the viscosity of the dispersion itself, so that the CNF particles are difficult to be adsorbed on 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 amount of input by adjusting the aspect ratio of CNF in order to obtain the greatest mechanical property improvement effect within the range in which the optical properties are maintained. The aspect ratio of CNF may be adjusted in the range of 5 to 1250, and preferably may be 25 to 400.

The composite particles prepared 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 particle 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 particle 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 a problem in the formability. If it is too low, the physical properties may be poor.

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

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

<Example 1>

0.3 parts by weight of the radical initiator AIBN was dissolved in 100 parts by weight of methyl methacrylate. 4 ml of methyl methacrylate in which an initiator is dissolved in 45 ml of water and cellulose nanofibers (about 10 nm in diameter and about 1 μm in length) were mixed at a mass ratio of 10:1, and then stirred at 1500 rpm. Under stirring, the emulsification process and the polymerization reaction were carried out at 70° C. for 8 hours together to prepare an emulsion of composite particles in which CNF was discontinuously coated on the polymethyl methacrylate core particles.

Figure 4 shows the results of measuring the Zeta potential through the dynamic light scattering method for the emulsion obtained in Example 1. Zeta potential was measured to be -78.6 mV. Therefore, it can be seen from the results of FIG. 4 that a pickering emulsion in which a hydrophilic cellulose nanofiber and a hydrophobic polymer monomer are well dispersed was formed.

5 is an electron micrograph of the PMMA/CNF composite particles prepared in Example 1. FIG. From FIG. 5, nano-scale PMMA particles can be observed in a form surrounded by CNF. The PMMA molecule has a size of about 100 to 300 nm, and can form nano-sized particles.

6 is a result of differential scanning calorimetry analysis of the PMMA/CNF composition prepared in Example 1. The glass transition temperature could be measured through thermal analysis. At the inflection point, the Tg of the PMMA/CNF composition was about 129°C, which was 10°C higher than that of pure PMMA at 119°C. It can be seen that mechanical properties are 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 mass of CNF was changed to 2, 4, 6, and 8 parts by weight relative to 100 parts by weight of MMA. 8 is This is an electron micrograph of the emulsion prepared in this way.

PMMA particles having a certain size (150 nm) were formed up to the CNF ratio of 6 wt%. However, as it fell below 4wt%, the amount of CNF surrounding the PMMA particles was significantly reduced, and PMMA particles having a large particle size were formed. This is because the amount of CNF surrounding the oil droplet surface decreased, and the interface was 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>

PMMA ( Sigma Aldrich , product name-445746, molecular weight (Mw) 350,000 g/mol) 20 g is dissolved in 100 ml acetone, and cellulose nanofibers are mixed at 10 parts by weight (mass ratio 10:1) to 100 parts by weight of PMMA. A solution dispersed through ultra-sonication at °C for about 1 hour was prepared. Then, through a solution casting method, it was slowly evaporated in a glass Petri dish at 50°C to obtain a composite composition.

This method has a disadvantage in that it uses a fairly large amount of solvent (about 500 wt%) and requires an additional process and time because it requires a separate evaporation process (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 finally made film, it was difficult to make a transparent film due to the black optical properties that originate from the carbon atoms of the 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 prepared 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 guards, lenses, etc. , For example, it is expected to be used for transparent electrodes, films, coatings, adhesives, headlamps, and electronic component materials.

Claims (12)

Composite particles in which non-surface-treated cellulose nanofibers are individually and discontinuously coated on the surface of a polymer core particle. The method of claim 1,
The composite particle of the polymer is a hydrophobic polymer. The method of claim 1,
The polymer is a methacrylate-based composite particles. The method of claim 1,
The cellulose nanofibers are composite particles having at least one of a length and a diameter of 100 nm or less, and an aspect ratio of 5 to 1250. The method of claim 1,
The cellulose nanofibers are composite particles of 4 to 100 nm in diameter and 0.5 to 5 um in length. The method of claim 1,
A composite particle having a mass ratio of the polymer core particle and the cellulose nanofibers of 100: 1 to 20. The method of claim 1,
Composite particles with an average size of 50 to 200 nm. The method of claim 1,
Composite particles with a glass transition temperature of 120℃ or higher. An emulsion in which the composite particles of any one of claims 1 to 8 are dispersed in water. The method of claim 9,
An emulsion with a zeta potential of -100 mV or more and -30mV or less. a) preparing a dispersion by dispersing a monomer having a polymerizable functional group in an aqueous phase, a polymerization initiator, and cellulose nanofibers without surface treatment;
b) The dispersion is stirred and emulsified while a polymerization reaction is carried out, so that the monomer having the polymerizable functional group forms the polymer core particles, and the cellulose nanofibers are discontinuously coated on the surface of the polymer core particles, A method for producing a polymer composite particle according to any one of claims 1 to 8, comprising the step of forming an emulsion. The method of claim 11,
The method for producing polymer composite particles further comprising the step of obtaining polymer composite particles by lyophilizing the emulsion of the polymer composite particles in step b).

Images