# Synthesis of Nano-ZnO Composite Polystyrene Acrylic Emulsion and Its Application in Chinese Painting Pigments

Authors: Jian Liang; Ningning Sun
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

With the continuous development of coating technology and environmental protection concepts, coating has become an indispensable item in the field of architecture and industry. Styrene acrylic emulsion as a new type of waterborne paint has attracted much attention since its emergence. Its functional modification is the focus of research, but the research results have not been ideal. To further improve the performance of styrene acrylic emulsion, nano-ZnO composite polystyrene emulsion was synthesized by emulsion polymerization, and its properties were analyzed. Aiming at the problem that nanopigments are prone to agglomeration, corresponding solutions are proposed, and the stability of nano-coatings is preliminarily studied. The inherent culture and essence of traditional culture and art is the wealth of realizing the unique nationalization and internationalization of design works. There is a lot of artistic quintessence in traditional Chinese painting art that can be used for reference to visual communication design. Through in-depth understanding and learning of Chinese painting theory and techniques, designers’ aesthetic abilities and innovation abilities can be qualitatively improved. First of all, the emulsion polymerization was carried out by semicontinuous method. The composite polystyrene emulsion containing different content of nano-ZnO was successfully prepared, which was recorded as N, Z, Z15, Z25, and Z35, respectively. The properties of the emulsion were determined, and the solid content, monomer conversion, viscosity, water absorption, and bacteriostatic effect of the emulsion were determined. The experimental results show that the solid content of emulsion Z15 (nano-ZnO content is 15%) reaches the highest value of 43.5%. The content of monomer in the emulsion affects the solid content, but the higher the monomer content, the better the solid content. The highest monomer conversion of Z15 was 86.4% at 80°C. The monomer conversion increased with the increase of polymerization temperature and tended to be stable after reaching the highest value. In the absence of nano-ZnO, the viscosity of the emulsion is the highest, and the viscosity of the emulsion decreases with the increase of the content of nano-ZnO monomer. Z35 (when the content of nano-ZnO is 35%) is the highest, which is 18.91%. The water absorption increases with the increase of nano-ZnO content. The content of nano-ZnO in the emulsion increased, the MIC value became smaller, and the bacteriostatic effect became better and better. This indicates that nano-ZnO composite polystyrene emulsion has good monomer conversion, super water resistance, and bacteriostatic effect, but its viscosity is relatively poor.


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## Body

## 1. Introduction

### 1.1. Background Significance

Traditional coatings contain a large number of organic volatiles, which not only threaten health, but also cause irreversible and destructive pollution to the atmospheric environment. Waterborne coatings are widely used in the beautification and protection of building materials when they come into being. The emulsion is an important material that determines the properties of coatings. Styrene acrylic emulsion has the advantages of low pollution, low film forming temperature, and low price, but it is still not perfect in water resistance, corrosion resistance, and wear resistance [1]. These deficiencies limit the application of styrene acrylic emulsion, while nano-ZnO has good wear resistance and photocatalysis. Therefore, it is essential to modify styrene acrylic emulsion by nano-ZnO based on emulsion polymerization technology. As a part of traditional art in an efficient era that is impacted by multilevel cultural methods and influenced by Western painting art, the regional boundaries of traditional Chinese painting lines must go out of the boundary of East Asia and extend to the forefront of the world. However, the unique characteristics and exclusiveness of national culture are always born, especially in the historical environment dominated by Han culture in ancient China; this kind of embodiment is more obvious in culture. Chinese painting is an art developed in the pure Chinese culture, it is a typical representative of Chinese traditional art, and it is a self-contained system in the field of art in the world. Chinese painting includes three categories: landscape, flowers and birds, and characters. It depicts objects with unique lines, strokes, and colors, and by various means of expression such as hook effects, points, dyes, thick and light, dry and wet, and empty and solid. Chinese painting emphasizes “the creation of external teachers, the source of the heart,” through murals, barriers, scrolls, albums, fan, and other unique forms of painting and with the traditional mounting technology for the installation.


### 1.2. Related Work

Chen et al. tried to change the amount of twelve-alkylbenzene sulfonates (SDBS) continuously and successfully synthesized styrene acrylate emulsion particles with a diameter of about 240 nm by emulsion polymerization. Fullerene-modified styrene-acrylic emulsion microspheres are obtained by grafting polymer latex particles with amino groups of fullerenoic acids through amination [2]. Zhang et al. reported a combinatorial miniemulsion/emulsion polymerization method to prepare poly (styrene acrylic acid) paraffin encapsulated nanocapsules [3]. The waterborne polyurethane modified by acrylate/nano-zinc oxide (PUA/ZnO) was synthesized by Jiang et al. The UV resistance linearity of the treated fabrics was measured [4]. Gevorgyan et al. put the sol-gel on a sapphire substrate. The structure, morphology, and optical properties of the undoped nanocrystalline ZnO films were studied at 500°C and 700°C [5]. Both of them paid attention to the optical properties of nano-ZnO, but did not study its wear resistance in depth.


### 1.3. Innovative Points in This Article

Based on the related technology of emulsion polymerization, the nano-ZnO and styrene acrylic emulsion were polymerized by semicontinuous method, and a new nano-ZnO composite polystyrene emulsion was prepared. After the preparation, the solid content, monomer conversion, viscosity, water absorption, and antibacterial effect of the emulsion were tested. It was found that the emulsion had high solid content, high monomer conversion rate, good water resistance, and bacteriostatic effect, but was just passable in viscosity. Moreover, the experimental results showed that the amount of nano-ZnO in the emulsion would affect the performance of the emulsion. The solid content and monomer conversion rate were the best when the nano-ZnO content was 15%, and the water resistance and bacteriostatic effect were strengthened with the increase of the content of nano-ZnO, but the viscosity decreased with the increase of nano-ZnO content.


## 1.1. Background Significance

Traditional coatings contain a large number of organic volatiles, which not only threaten health, but also cause irreversible and destructive pollution to the atmospheric environment. Waterborne coatings are widely used in the beautification and protection of building materials when they come into being. The emulsion is an important material that determines the properties of coatings. Styrene acrylic emulsion has the advantages of low pollution, low film forming temperature, and low price, but it is still not perfect in water resistance, corrosion resistance, and wear resistance [1]. These deficiencies limit the application of styrene acrylic emulsion, while nano-ZnO has good wear resistance and photocatalysis. Therefore, it is essential to modify styrene acrylic emulsion by nano-ZnO based on emulsion polymerization technology. As a part of traditional art in an efficient era that is impacted by multilevel cultural methods and influenced by Western painting art, the regional boundaries of traditional Chinese painting lines must go out of the boundary of East Asia and extend to the forefront of the world. However, the unique characteristics and exclusiveness of national culture are always born, especially in the historical environment dominated by Han culture in ancient China; this kind of embodiment is more obvious in culture. Chinese painting is an art developed in the pure Chinese culture, it is a typical representative of Chinese traditional art, and it is a self-contained system in the field of art in the world. Chinese painting includes three categories: landscape, flowers and birds, and characters. It depicts objects with unique lines, strokes, and colors, and by various means of expression such as hook effects, points, dyes, thick and light, dry and wet, and empty and solid. Chinese painting emphasizes “the creation of external teachers, the source of the heart,” through murals, barriers, scrolls, albums, fan, and other unique forms of painting and with the traditional mounting technology for the installation.


## 1.2. Related Work

Chen et al. tried to change the amount of twelve-alkylbenzene sulfonates (SDBS) continuously and successfully synthesized styrene acrylate emulsion particles with a diameter of about 240 nm by emulsion polymerization. Fullerene-modified styrene-acrylic emulsion microspheres are obtained by grafting polymer latex particles with amino groups of fullerenoic acids through amination [2]. Zhang et al. reported a combinatorial miniemulsion/emulsion polymerization method to prepare poly (styrene acrylic acid) paraffin encapsulated nanocapsules [3]. The waterborne polyurethane modified by acrylate/nano-zinc oxide (PUA/ZnO) was synthesized by Jiang et al. The UV resistance linearity of the treated fabrics was measured [4]. Gevorgyan et al. put the sol-gel on a sapphire substrate. The structure, morphology, and optical properties of the undoped nanocrystalline ZnO films were studied at 500°C and 700°C [5]. Both of them paid attention to the optical properties of nano-ZnO, but did not study its wear resistance in depth.


## 1.3. Innovative Points in This Article

Based on the related technology of emulsion polymerization, the nano-ZnO and styrene acrylic emulsion were polymerized by semicontinuous method, and a new nano-ZnO composite polystyrene emulsion was prepared. After the preparation, the solid content, monomer conversion, viscosity, water absorption, and antibacterial effect of the emulsion were tested. It was found that the emulsion had high solid content, high monomer conversion rate, good water resistance, and bacteriostatic effect, but was just passable in viscosity. Moreover, the experimental results showed that the amount of nano-ZnO in the emulsion would affect the performance of the emulsion. The solid content and monomer conversion rate were the best when the nano-ZnO content was 15%, and the water resistance and bacteriostatic effect were strengthened with the increase of the content of nano-ZnO, but the viscosity decreased with the increase of nano-ZnO content.


## 2. Preparation Method of Nano-ZnO Composite Polystyrene Acrylate Emulsion

### 2.1. Preparation of Nano-ZnO

Nano-ZnO belongs to wide band gap semiconductor materials and new high-functional fine inorganic materials. It is soluble in strong acids and alkali, but difficult to dissolve in water. It has unique optical and chemical sensing properties, stable structure, and no pollution [6]. The crystal structure of nano-ZnO mainly includes tetragonal halite, wurtzite, and cubic sphalerite. The structure of wurtzite is the most stable under natural conditions. Due to its large specific surface area and strong surface activity, nano-ZnO is widely used in various fields, such as high activity photocatalyst, energy storage, nanosensor, sunscreen, etc. Its preparation methods are various, including liquid phase method, solid phase method, and gas phase method [7].


#### 2.1.1. Liquid Phase Method

Sol-gel, hydrothermal, and homogeneous precipitation methods are all liquid phase methods. The basic principle is that one or more soluble metal salts are combined to form a solution, then a precipitant is added, and the metal ions are precipitated or crystallized. After heating and decomposition, the ultrafine powder can be prepared.The sol is an alternate suspension in the solvent. The gel is a substance formed by many substances and plays a fixed role. The preparation process generally includes sol preparation, spin coating, sol, and annealing. When the nano-ZnO was prepared by the sol-gel method, the soluble inorganic salts of Zn could be obtained by sol-gel and heat treatments[8]. The method is simple and easy to operate, which is suitable for mass production.The use of the hydrothermal methods requires the use of water as a solvent in a specific temperature and high-pressure environment, so that the chemical substances in the solution react in the reactor to produce dissolved products. The hydrothermal method has many advantages because of its high frequency. It can be used for materials with high temperature and low solubility, and for some crystals that will decompose before and after melting, which are easy to sublimate at high temperature or can maintain stability in special atmospheres. Moreover, the temperature is very constant during the growth process, and the resolved crystal has small thermal stress and uniform and high purity. However, the hydrothermal method also has some disadvantages, such as unstable reaction processes and certain risks.In the homogeneous precipitation method, intermediate reactants are needed to adjust the reaction rate and process. By controlling the concentration of precipitant in the solution, it can be increased evenly and slowly. Therefore, to avoid local uneven concentration, the precipitant is not added directly, but the intermediate reactant is added into the solution to form the precipitant. The intermediate reactant commonly used is a slow-release agent, and the most used slow-release agent is urea [9]. Compared with other precipitation methods, the homogeneous precipitation method can effectively control the precipitation process.


#### 2.1.2. Solid Phase Method

The solid-state method needs to grind the mixture of metal salts or metal oxides first, and then grind after the solid-state reaction of calcination. As a new type of solid-state method, mechanochemistry can be used to prepare nanomaterials. The preparation process can be said to be the process of mechanical alloying. The metal or alloy powder is impacted and collided for a long time in the high-energy ball mill, and the powder particles repeatedly produce cold welding and fracture, which reduces the size of the powder particles, and the atoms in the particles can be diffused, to obtain the powder.Mechanochemistry focuses on energy conversion, and its core theory is the mechanism of mechanical energy transforming chemical energy. The grinders used in mechanochemical methods are high-energy grinders with ultra-high energy density, which can be divided into ball mills and impact mills [10]. The preparation of nano-ZnO by the mechanochemical method has the advantages of simple process, low cost, fast speed, and easy industrialization.


#### 2.1.3. Gas Phase Method

The gas phase method needs to make the gas raw materials undergo physical or chemical reactions, and the reactants continuously condense and grow when they are cooled to form nanoparticles.Chemical vapor deposition (CVD) requires that raw materials containing Zn elements be put into the confined space in the form of gas, and then a thin film is formed on the surface of the substrate by gas phase reaction [11, 12]. Molecular beam epitaxy (MBE) is a new type of crystal growth technology in the vacuum evaporation process. Molecular beam epitaxy (MBE) projects a molecular beam onto a substrate to realize epitaxy. In an ultra-high vacuum environment, the reactants are heated to evaporate into a gaseous state and then condense on the substrate. In the magnetron sputtering method, ZnO is used as the target material, and Ar and O2 are mixed as reaction gases. The rapid and high-energy impact force of the gas in the coating process makes the target surface sputtered, thus forming nano-ZnO.


### 2.2. Modification of Styrene Acrylic Emulsion

Styrene acrylic emulsion is formed by the polymerization of acrylic monomers and styrene. It has the advantages of alkali resistance, water resistance, aging resistance, and scrubbing. It is widely used in adhesives and coatings. The coating made of styrene acrylic emulsion has strong adhesion and the transparent film makes it more beautiful. However, there are still deficiencies in antioxidant and expansibility, so it is necessary to modify its function to strengthen its performance. At present, the common modification methods for styrene acrylic emulsion are graphene modification, epoxy resin modification, organic fluorine modification, organic silicon modification, nanomaterial modification, and others [13].


#### 2.2.1. Modification of Graphene and Epoxy Resin

As a new material, graphene has excellent aging resistance, hydrophobicity, and shielding properties. If a small amount of graphene is added to the polymer, it can improve the properties of the material. Graphene-modified styrene acrylic emulsion is divided into two methods: physical mixing and in situ polymerization of [14]. A modified styrene acrylic emulsion coating was obtained after the physical mixing of graphene and carbon nanofiller. The prepared coating was coated on the glass plate by gap coating. The coating after drying had higher conductivity, hardness, energy storage modulus, and thermal stability, and the nanofiller did not lower the adhesion and glass transition temperature of the coating. Graphene oxide and styrene acrylic composites can be prepared by in situ polymerization. The graphene in the composite has better dispersion and stronger interface interaction, and the coating also has excellent water resistance and alkali resistance.Epoxy resin modification can enhance the corrosion resistance, light retention, and water resistance of styrene acrylic emulsion [15]. Through core/shell emulsion polymerization and composite emulsifier polymerization, epoxy resin-modified styrene acrylic emulsion can also improve the adhesion and hardness of coatings. The specific method of core/shell emulsion polymerization is to prepare water dispersions of high molecular weight solid epoxy prepolymer through a continuous solvent-free mechanical dispersion process and use it as the seed of emulsion polymerization to polymerize.


#### 2.2.2. Modification of Organofluorine and Organosilicon

Organic fluorine-modified polymers are widely used in building materials, electronic products, and furniture fields [16]. The styrene acrylic emulsion modified by organic fluorine is a new type of coating with excellent performance. It has good alkali resistance and light resistance. Such polymers have high bond energy and two molecules are tightly aligned on the carbon frame, which can effectively avoid the loss of carbon molecules, thus significantly improving the chemical properties of styrene acrylic emulsion. Emulsion polymerization is usually used to modify styrene acrylic emulsion when organic fluorine is used.The main chain of the organosilicon is Si–O–Si, and the side methyl groups are very regular, so it has good hydrophobicity and heat and cold resistance [17]. The modification of styrene acrylic emulsion by using silicone can fuse the advantages of both of them and improve the thermal viscosity and crisp problem of styrene acrylic emulsion after film forming. After the catalytic reaction, the seven-styrene three-siloxane was first modified with allyl methacrylate and then polymerized by styrene in situ polymerization. The surface roughness and water contact angle can be increased, thus having better water self-extinction.


#### 2.2.3. Modification of Nanomaterials

If nano-molecules are diffused into styrene acrylic emulsion, organic molecules and inorganic molecules can be polymerized by binding reaction or electrostatic reaction to maximize the advantages of both sides. Therefore, the performance of styrene acrylic emulsion can be improved effectively, so that it can be widely applied in many fields. Architectural coatings are often exposed to sunlight, alternating heat and cold, wind and rain, and other natural environments and are prone to fade, cracks, peeling, and other general problems. The oxidation reaction of ultraviolet radiation in the coating film often causes the problem of fading. The addition of nano-molecules can absorb or rebound ultraviolet radiation and provide a protective film to maximize the service life of the coating. Nanomaterials can also enhance the expansion of the outer membrane and prevent coating cracks caused by wall cracks.The modification of styrene acrylic emulsion by nanomaterials is the research direction of this article. The modification method will be described in detail in the experimental part.


### 2.3. Methods of Emulsion Polymerization

#### 2.3.1. Basic Principle of Emulsion Polymerization

Before emulsion polymerization, the system can have three different phase states: water phase, micelle phase, and oil phase. When a certain amount of emulsifier and a small amount of monomer are in the water phase state, the emulsifier and monomer will also form an aqueous phase after mixing with water [18]. The formation of micelle phase in the presence of emulsifier is due to the presence of some monomers in the micelles. The polymerization occurs in micellar ions, and the emulsion also exhibits a micellar phase. When most of the monomer ions are dispersed to form small droplets, there will be a protective layer of emulsifier on the surface. The emulsion will be the oil phase.Emulsion polymerization will undergo three stages, namely the growth stage, the constant speed stage, and the slow stage [19]. During the growth period, the primary free radical of emulsion polymerization is formed, and polymerization occurs in the compatibilized micelles. With the deepening of the degree of reaction, single body fluid drops continue to provide monomers for latex particles, so that the number of micelles decreases, thus increasing the number of latex particles and accelerating the polymerization rate. In the middle stage of polymerization, that is the constant rate period, the number of latex particles remains unchanged, and the rate of polymerization does not change. The volume of latex particles increases slowly, and the volume of single body fluid drops decreases slowly [20]. In the decreasing period of polymerization, the monomer is completely converted into polymer.


#### 2.3.2. Emulsion Polymerization Method

There are many methods and techniques for emulsion polymerization, such as core/shell emulsion polymerization, soap-free emulsion polymerization, etc.In the core/shell emulsion polymerization, there are two parts of the monomer in the latex particles, which are composed of core and shell. The structure of heterogeneous particles with different structural characteristics can be obtained by the different monomer proportion of the core part and shell part, and different emulsion properties can be formed [21]. The process of core/shell emulsion polymerization is as follows: the emulsion polymerization of the core part of the monomer is added to the shell part of the monomer. After the monomer emulsion polymerization of the shell part is completed, the heterogeneous latex particles of the core/shell structure can be obtained [22]. The preparation methods can be divided into batch method, semicontinuous method, and swelling method according to the way of adding shell monomer. The structure of latex particles prepared by different methods is also different. The latex particles prepared by batch method and swelling method have high content and good stability, while those prepared by semicontinuous method have stable size. The emulsion obtained by core/shell emulsion polymerization has many advantages, such as good anti-adhesion, good film formation, stable storage and use, and good mechanical properties.Emulsifier-free emulsion polymerization requires only a small amount of emulsifier or [23] without emulsifier in the polymerization process. In the process of polymerization, the effect of emulsifier on emulsifier-free emulsion is different from that of traditional emulsion polymerization, mainly because the formation mechanism of micelle particles is different and the stability conditions of the emulsion system are different. The residual emulsifier in traditional emulsion polymerization will reduce the water resistance and friction resistance of the emulsion, and the emulsifier content in soap-free emulsion is very little or even zero, which can reduce the influence of emulsifier on the properties of the emulsion. The widely used emulsifier-free emulsion polymerization methods include emulsifying copolymers, surfactants, acrylic monomers, and oligomers.


#### 2.3.3. Advantages of Emulsion Polymerization

The reaction heat expelled in emulsion polymerization is very easy. The removal of reaction heat is not only related to the stability of the operation control, but also related to the safety of the production process. Water is the dispersant of the emulsion, and the latex particles are independent. The interaction between particles is small, the viscosity will be reduced, and the heat of the reaction will quickly diffuse out.The emulsion polymerization rate is fast and the molecular weight is high. In emulsion polymerization, the free radical chain is trapped in stable latex particles. The binding between latex particles is not very easy. Chain termination is almost impossible. Only the primary free radicals can be diffused into the latex for the water phase to terminate, so the average lifespan of the chain radical is greatly extended, which can produce high molecular weight polymers. However, in bulk and solution polymerization, on the one hand, to improve the molecular weight of the polymer, it is necessary to reduce the reaction temperature and the termination speed of free radicals, and reducing the reaction temperature also reduces the reaction speed. On the other hand, to improve the polymerization rate, the temperature should be increased to accelerate the decomposition of free radicals, increase the concentration of free radicals, and thus increase the chain termination speed, thus reducing the molecular weight of the polymer.The process of emulsion polymerization is safe and has environmental protection. The dispersed phase of emulsion polymerization is water, which is cheap and easy to obtain. It is also very safe to use. In this way, not only can the cost of raw materials be reduced, but also the cost of solvent recovery will be reduced due to the reduction of solvent use. The solvent will not have a negative impact on the environment, and because solvent is not flammable, it is very safe in the process of transportation and storage.Polymer particles can be prepared by emulsion polymerization. By selecting different monomers, adding different functional monomers, designing a precise ratio, and changing the false talk mode, latex particles with different particle size distribution, morphology, and performance can be prepared. These particles can meet different specific needs and have good mechanical properties. This is incomparable with other polymerization methods.


### 2.4. Nano-Chinese Painting Pigments

Because the particle size of the nanomaterial particles is in the nanometer range, the optical properties of the paper can be greatly improved, and its opacity is relatively high. For example, nano-alumina is used as nanopigment particles in coatings. Due to the small particle size of the particles and the narrow distribution range of particle size, it can ensure the purity of the color as a white material, thereby improving the performance of the coated paper. Whiteness improves the gloss of paper. In addition, some nanomaterials can also produce special optical effects. For example, when scattering occurs, the color of the coated paper will change with the change of people’s observation angle, so it can be used to produce special-purpose coatings. The application of nanopigment particles to coatings can improve the rheological properties of coatings. Nanopigments have special surface effects and quantum size effects, so they can control the particle size performance, pH value, and zeta potential of the coating, to obtain coatings with high concentration but low viscosity. In addition, the particles of nanopigments are extremely fine, which is very beneficial to the improvement of the stability of the coating and can greatly avoid the occurrence of precipitation, delamination, and other phenomena.The development of Chinese painting line has a long history, attaching great importance to the inheritance of national culture; the application of line in Chinese painting from the art of ancient times to today and its role and influence is self-evident. No matter the change of dynasties or the impact of modern and contemporary foreign painting ideas, no matter how many debates on the existence and form of line, but with its rich connotations, the seemingly weak line language can remain invincible. The atoms or molecules of the pigment are excited and the electrons transition from the ground state to the excited state. When the excited state is unstable, it jumps back to the ground state and emits a certain wavelength of light, thus showing a certain color. The color of the pigment mainly depends on the existing state of colored ions, that is the atomic or molecular structure of the pigment itself, while the coloring of matter is mainly caused by the transition of electrons between different energy levels and the absorption and scattering of light by ions.


## 2.1. Preparation of Nano-ZnO

Nano-ZnO belongs to wide band gap semiconductor materials and new high-functional fine inorganic materials. It is soluble in strong acids and alkali, but difficult to dissolve in water. It has unique optical and chemical sensing properties, stable structure, and no pollution [6]. The crystal structure of nano-ZnO mainly includes tetragonal halite, wurtzite, and cubic sphalerite. The structure of wurtzite is the most stable under natural conditions. Due to its large specific surface area and strong surface activity, nano-ZnO is widely used in various fields, such as high activity photocatalyst, energy storage, nanosensor, sunscreen, etc. Its preparation methods are various, including liquid phase method, solid phase method, and gas phase method [7].


### 2.1.1. Liquid Phase Method

Sol-gel, hydrothermal, and homogeneous precipitation methods are all liquid phase methods. The basic principle is that one or more soluble metal salts are combined to form a solution, then a precipitant is added, and the metal ions are precipitated or crystallized. After heating and decomposition, the ultrafine powder can be prepared.The sol is an alternate suspension in the solvent. The gel is a substance formed by many substances and plays a fixed role. The preparation process generally includes sol preparation, spin coating, sol, and annealing. When the nano-ZnO was prepared by the sol-gel method, the soluble inorganic salts of Zn could be obtained by sol-gel and heat treatments[8]. The method is simple and easy to operate, which is suitable for mass production.The use of the hydrothermal methods requires the use of water as a solvent in a specific temperature and high-pressure environment, so that the chemical substances in the solution react in the reactor to produce dissolved products. The hydrothermal method has many advantages because of its high frequency. It can be used for materials with high temperature and low solubility, and for some crystals that will decompose before and after melting, which are easy to sublimate at high temperature or can maintain stability in special atmospheres. Moreover, the temperature is very constant during the growth process, and the resolved crystal has small thermal stress and uniform and high purity. However, the hydrothermal method also has some disadvantages, such as unstable reaction processes and certain risks.In the homogeneous precipitation method, intermediate reactants are needed to adjust the reaction rate and process. By controlling the concentration of precipitant in the solution, it can be increased evenly and slowly. Therefore, to avoid local uneven concentration, the precipitant is not added directly, but the intermediate reactant is added into the solution to form the precipitant. The intermediate reactant commonly used is a slow-release agent, and the most used slow-release agent is urea [9]. Compared with other precipitation methods, the homogeneous precipitation method can effectively control the precipitation process.


### 2.1.2. Solid Phase Method

The solid-state method needs to grind the mixture of metal salts or metal oxides first, and then grind after the solid-state reaction of calcination. As a new type of solid-state method, mechanochemistry can be used to prepare nanomaterials. The preparation process can be said to be the process of mechanical alloying. The metal or alloy powder is impacted and collided for a long time in the high-energy ball mill, and the powder particles repeatedly produce cold welding and fracture, which reduces the size of the powder particles, and the atoms in the particles can be diffused, to obtain the powder.Mechanochemistry focuses on energy conversion, and its core theory is the mechanism of mechanical energy transforming chemical energy. The grinders used in mechanochemical methods are high-energy grinders with ultra-high energy density, which can be divided into ball mills and impact mills [10]. The preparation of nano-ZnO by the mechanochemical method has the advantages of simple process, low cost, fast speed, and easy industrialization.


### 2.1.3. Gas Phase Method

The gas phase method needs to make the gas raw materials undergo physical or chemical reactions, and the reactants continuously condense and grow when they are cooled to form nanoparticles.Chemical vapor deposition (CVD) requires that raw materials containing Zn elements be put into the confined space in the form of gas, and then a thin film is formed on the surface of the substrate by gas phase reaction [11, 12]. Molecular beam epitaxy (MBE) is a new type of crystal growth technology in the vacuum evaporation process. Molecular beam epitaxy (MBE) projects a molecular beam onto a substrate to realize epitaxy. In an ultra-high vacuum environment, the reactants are heated to evaporate into a gaseous state and then condense on the substrate. In the magnetron sputtering method, ZnO is used as the target material, and Ar and O2 are mixed as reaction gases. The rapid and high-energy impact force of the gas in the coating process makes the target surface sputtered, thus forming nano-ZnO.


## 2.1.1. Liquid Phase Method

Sol-gel, hydrothermal, and homogeneous precipitation methods are all liquid phase methods. The basic principle is that one or more soluble metal salts are combined to form a solution, then a precipitant is added, and the metal ions are precipitated or crystallized. After heating and decomposition, the ultrafine powder can be prepared.The sol is an alternate suspension in the solvent. The gel is a substance formed by many substances and plays a fixed role. The preparation process generally includes sol preparation, spin coating, sol, and annealing. When the nano-ZnO was prepared by the sol-gel method, the soluble inorganic salts of Zn could be obtained by sol-gel and heat treatments[8]. The method is simple and easy to operate, which is suitable for mass production.The use of the hydrothermal methods requires the use of water as a solvent in a specific temperature and high-pressure environment, so that the chemical substances in the solution react in the reactor to produce dissolved products. The hydrothermal method has many advantages because of its high frequency. It can be used for materials with high temperature and low solubility, and for some crystals that will decompose before and after melting, which are easy to sublimate at high temperature or can maintain stability in special atmospheres. Moreover, the temperature is very constant during the growth process, and the resolved crystal has small thermal stress and uniform and high purity. However, the hydrothermal method also has some disadvantages, such as unstable reaction processes and certain risks.In the homogeneous precipitation method, intermediate reactants are needed to adjust the reaction rate and process. By controlling the concentration of precipitant in the solution, it can be increased evenly and slowly. Therefore, to avoid local uneven concentration, the precipitant is not added directly, but the intermediate reactant is added into the solution to form the precipitant. The intermediate reactant commonly used is a slow-release agent, and the most used slow-release agent is urea [9]. Compared with other precipitation methods, the homogeneous precipitation method can effectively control the precipitation process.


## 2.1.2. Solid Phase Method

The solid-state method needs to grind the mixture of metal salts or metal oxides first, and then grind after the solid-state reaction of calcination. As a new type of solid-state method, mechanochemistry can be used to prepare nanomaterials. The preparation process can be said to be the process of mechanical alloying. The metal or alloy powder is impacted and collided for a long time in the high-energy ball mill, and the powder particles repeatedly produce cold welding and fracture, which reduces the size of the powder particles, and the atoms in the particles can be diffused, to obtain the powder.Mechanochemistry focuses on energy conversion, and its core theory is the mechanism of mechanical energy transforming chemical energy. The grinders used in mechanochemical methods are high-energy grinders with ultra-high energy density, which can be divided into ball mills and impact mills [10]. The preparation of nano-ZnO by the mechanochemical method has the advantages of simple process, low cost, fast speed, and easy industrialization.


## 2.1.3. Gas Phase Method

The gas phase method needs to make the gas raw materials undergo physical or chemical reactions, and the reactants continuously condense and grow when they are cooled to form nanoparticles.Chemical vapor deposition (CVD) requires that raw materials containing Zn elements be put into the confined space in the form of gas, and then a thin film is formed on the surface of the substrate by gas phase reaction [11, 12]. Molecular beam epitaxy (MBE) is a new type of crystal growth technology in the vacuum evaporation process. Molecular beam epitaxy (MBE) projects a molecular beam onto a substrate to realize epitaxy. In an ultra-high vacuum environment, the reactants are heated to evaporate into a gaseous state and then condense on the substrate. In the magnetron sputtering method, ZnO is used as the target material, and Ar and O2 are mixed as reaction gases. The rapid and high-energy impact force of the gas in the coating process makes the target surface sputtered, thus forming nano-ZnO.


## 2.2. Modification of Styrene Acrylic Emulsion

Styrene acrylic emulsion is formed by the polymerization of acrylic monomers and styrene. It has the advantages of alkali resistance, water resistance, aging resistance, and scrubbing. It is widely used in adhesives and coatings. The coating made of styrene acrylic emulsion has strong adhesion and the transparent film makes it more beautiful. However, there are still deficiencies in antioxidant and expansibility, so it is necessary to modify its function to strengthen its performance. At present, the common modification methods for styrene acrylic emulsion are graphene modification, epoxy resin modification, organic fluorine modification, organic silicon modification, nanomaterial modification, and others [13].


### 2.2.1. Modification of Graphene and Epoxy Resin

As a new material, graphene has excellent aging resistance, hydrophobicity, and shielding properties. If a small amount of graphene is added to the polymer, it can improve the properties of the material. Graphene-modified styrene acrylic emulsion is divided into two methods: physical mixing and in situ polymerization of [14]. A modified styrene acrylic emulsion coating was obtained after the physical mixing of graphene and carbon nanofiller. The prepared coating was coated on the glass plate by gap coating. The coating after drying had higher conductivity, hardness, energy storage modulus, and thermal stability, and the nanofiller did not lower the adhesion and glass transition temperature of the coating. Graphene oxide and styrene acrylic composites can be prepared by in situ polymerization. The graphene in the composite has better dispersion and stronger interface interaction, and the coating also has excellent water resistance and alkali resistance.Epoxy resin modification can enhance the corrosion resistance, light retention, and water resistance of styrene acrylic emulsion [15]. Through core/shell emulsion polymerization and composite emulsifier polymerization, epoxy resin-modified styrene acrylic emulsion can also improve the adhesion and hardness of coatings. The specific method of core/shell emulsion polymerization is to prepare water dispersions of high molecular weight solid epoxy prepolymer through a continuous solvent-free mechanical dispersion process and use it as the seed of emulsion polymerization to polymerize.


### 2.2.2. Modification of Organofluorine and Organosilicon

Organic fluorine-modified polymers are widely used in building materials, electronic products, and furniture fields [16]. The styrene acrylic emulsion modified by organic fluorine is a new type of coating with excellent performance. It has good alkali resistance and light resistance. Such polymers have high bond energy and two molecules are tightly aligned on the carbon frame, which can effectively avoid the loss of carbon molecules, thus significantly improving the chemical properties of styrene acrylic emulsion. Emulsion polymerization is usually used to modify styrene acrylic emulsion when organic fluorine is used.The main chain of the organosilicon is Si–O–Si, and the side methyl groups are very regular, so it has good hydrophobicity and heat and cold resistance [17]. The modification of styrene acrylic emulsion by using silicone can fuse the advantages of both of them and improve the thermal viscosity and crisp problem of styrene acrylic emulsion after film forming. After the catalytic reaction, the seven-styrene three-siloxane was first modified with allyl methacrylate and then polymerized by styrene in situ polymerization. The surface roughness and water contact angle can be increased, thus having better water self-extinction.


### 2.2.3. Modification of Nanomaterials

If nano-molecules are diffused into styrene acrylic emulsion, organic molecules and inorganic molecules can be polymerized by binding reaction or electrostatic reaction to maximize the advantages of both sides. Therefore, the performance of styrene acrylic emulsion can be improved effectively, so that it can be widely applied in many fields. Architectural coatings are often exposed to sunlight, alternating heat and cold, wind and rain, and other natural environments and are prone to fade, cracks, peeling, and other general problems. The oxidation reaction of ultraviolet radiation in the coating film often causes the problem of fading. The addition of nano-molecules can absorb or rebound ultraviolet radiation and provide a protective film to maximize the service life of the coating. Nanomaterials can also enhance the expansion of the outer membrane and prevent coating cracks caused by wall cracks.The modification of styrene acrylic emulsion by nanomaterials is the research direction of this article. The modification method will be described in detail in the experimental part.


## 2.2.1. Modification of Graphene and Epoxy Resin

As a new material, graphene has excellent aging resistance, hydrophobicity, and shielding properties. If a small amount of graphene is added to the polymer, it can improve the properties of the material. Graphene-modified styrene acrylic emulsion is divided into two methods: physical mixing and in situ polymerization of [14]. A modified styrene acrylic emulsion coating was obtained after the physical mixing of graphene and carbon nanofiller. The prepared coating was coated on the glass plate by gap coating. The coating after drying had higher conductivity, hardness, energy storage modulus, and thermal stability, and the nanofiller did not lower the adhesion and glass transition temperature of the coating. Graphene oxide and styrene acrylic composites can be prepared by in situ polymerization. The graphene in the composite has better dispersion and stronger interface interaction, and the coating also has excellent water resistance and alkali resistance.Epoxy resin modification can enhance the corrosion resistance, light retention, and water resistance of styrene acrylic emulsion [15]. Through core/shell emulsion polymerization and composite emulsifier polymerization, epoxy resin-modified styrene acrylic emulsion can also improve the adhesion and hardness of coatings. The specific method of core/shell emulsion polymerization is to prepare water dispersions of high molecular weight solid epoxy prepolymer through a continuous solvent-free mechanical dispersion process and use it as the seed of emulsion polymerization to polymerize.


## 2.2.2. Modification of Organofluorine and Organosilicon

Organic fluorine-modified polymers are widely used in building materials, electronic products, and furniture fields [16]. The styrene acrylic emulsion modified by organic fluorine is a new type of coating with excellent performance. It has good alkali resistance and light resistance. Such polymers have high bond energy and two molecules are tightly aligned on the carbon frame, which can effectively avoid the loss of carbon molecules, thus significantly improving the chemical properties of styrene acrylic emulsion. Emulsion polymerization is usually used to modify styrene acrylic emulsion when organic fluorine is used.The main chain of the organosilicon is Si–O–Si, and the side methyl groups are very regular, so it has good hydrophobicity and heat and cold resistance [17]. The modification of styrene acrylic emulsion by using silicone can fuse the advantages of both of them and improve the thermal viscosity and crisp problem of styrene acrylic emulsion after film forming. After the catalytic reaction, the seven-styrene three-siloxane was first modified with allyl methacrylate and then polymerized by styrene in situ polymerization. The surface roughness and water contact angle can be increased, thus having better water self-extinction.


## 2.2.3. Modification of Nanomaterials

If nano-molecules are diffused into styrene acrylic emulsion, organic molecules and inorganic molecules can be polymerized by binding reaction or electrostatic reaction to maximize the advantages of both sides. Therefore, the performance of styrene acrylic emulsion can be improved effectively, so that it can be widely applied in many fields. Architectural coatings are often exposed to sunlight, alternating heat and cold, wind and rain, and other natural environments and are prone to fade, cracks, peeling, and other general problems. The oxidation reaction of ultraviolet radiation in the coating film often causes the problem of fading. The addition of nano-molecules can absorb or rebound ultraviolet radiation and provide a protective film to maximize the service life of the coating. Nanomaterials can also enhance the expansion of the outer membrane and prevent coating cracks caused by wall cracks.The modification of styrene acrylic emulsion by nanomaterials is the research direction of this article. The modification method will be described in detail in the experimental part.


## 2.3. Methods of Emulsion Polymerization

### 2.3.1. Basic Principle of Emulsion Polymerization

Before emulsion polymerization, the system can have three different phase states: water phase, micelle phase, and oil phase. When a certain amount of emulsifier and a small amount of monomer are in the water phase state, the emulsifier and monomer will also form an aqueous phase after mixing with water [18]. The formation of micelle phase in the presence of emulsifier is due to the presence of some monomers in the micelles. The polymerization occurs in micellar ions, and the emulsion also exhibits a micellar phase. When most of the monomer ions are dispersed to form small droplets, there will be a protective layer of emulsifier on the surface. The emulsion will be the oil phase.Emulsion polymerization will undergo three stages, namely the growth stage, the constant speed stage, and the slow stage [19]. During the growth period, the primary free radical of emulsion polymerization is formed, and polymerization occurs in the compatibilized micelles. With the deepening of the degree of reaction, single body fluid drops continue to provide monomers for latex particles, so that the number of micelles decreases, thus increasing the number of latex particles and accelerating the polymerization rate. In the middle stage of polymerization, that is the constant rate period, the number of latex particles remains unchanged, and the rate of polymerization does not change. The volume of latex particles increases slowly, and the volume of single body fluid drops decreases slowly [20]. In the decreasing period of polymerization, the monomer is completely converted into polymer.


### 2.3.2. Emulsion Polymerization Method

There are many methods and techniques for emulsion polymerization, such as core/shell emulsion polymerization, soap-free emulsion polymerization, etc.In the core/shell emulsion polymerization, there are two parts of the monomer in the latex particles, which are composed of core and shell. The structure of heterogeneous particles with different structural characteristics can be obtained by the different monomer proportion of the core part and shell part, and different emulsion properties can be formed [21]. The process of core/shell emulsion polymerization is as follows: the emulsion polymerization of the core part of the monomer is added to the shell part of the monomer. After the monomer emulsion polymerization of the shell part is completed, the heterogeneous latex particles of the core/shell structure can be obtained [22]. The preparation methods can be divided into batch method, semicontinuous method, and swelling method according to the way of adding shell monomer. The structure of latex particles prepared by different methods is also different. The latex particles prepared by batch method and swelling method have high content and good stability, while those prepared by semicontinuous method have stable size. The emulsion obtained by core/shell emulsion polymerization has many advantages, such as good anti-adhesion, good film formation, stable storage and use, and good mechanical properties.Emulsifier-free emulsion polymerization requires only a small amount of emulsifier or [23] without emulsifier in the polymerization process. In the process of polymerization, the effect of emulsifier on emulsifier-free emulsion is different from that of traditional emulsion polymerization, mainly because the formation mechanism of micelle particles is different and the stability conditions of the emulsion system are different. The residual emulsifier in traditional emulsion polymerization will reduce the water resistance and friction resistance of the emulsion, and the emulsifier content in soap-free emulsion is very little or even zero, which can reduce the influence of emulsifier on the properties of the emulsion. The widely used emulsifier-free emulsion polymerization methods include emulsifying copolymers, surfactants, acrylic monomers, and oligomers.


### 2.3.3. Advantages of Emulsion Polymerization

The reaction heat expelled in emulsion polymerization is very easy. The removal of reaction heat is not only related to the stability of the operation control, but also related to the safety of the production process. Water is the dispersant of the emulsion, and the latex particles are independent. The interaction between particles is small, the viscosity will be reduced, and the heat of the reaction will quickly diffuse out.The emulsion polymerization rate is fast and the molecular weight is high. In emulsion polymerization, the free radical chain is trapped in stable latex particles. The binding between latex particles is not very easy. Chain termination is almost impossible. Only the primary free radicals can be diffused into the latex for the water phase to terminate, so the average lifespan of the chain radical is greatly extended, which can produce high molecular weight polymers. However, in bulk and solution polymerization, on the one hand, to improve the molecular weight of the polymer, it is necessary to reduce the reaction temperature and the termination speed of free radicals, and reducing the reaction temperature also reduces the reaction speed. On the other hand, to improve the polymerization rate, the temperature should be increased to accelerate the decomposition of free radicals, increase the concentration of free radicals, and thus increase the chain termination speed, thus reducing the molecular weight of the polymer.The process of emulsion polymerization is safe and has environmental protection. The dispersed phase of emulsion polymerization is water, which is cheap and easy to obtain. It is also very safe to use. In this way, not only can the cost of raw materials be reduced, but also the cost of solvent recovery will be reduced due to the reduction of solvent use. The solvent will not have a negative impact on the environment, and because solvent is not flammable, it is very safe in the process of transportation and storage.Polymer particles can be prepared by emulsion polymerization. By selecting different monomers, adding different functional monomers, designing a precise ratio, and changing the false talk mode, latex particles with different particle size distribution, morphology, and performance can be prepared. These particles can meet different specific needs and have good mechanical properties. This is incomparable with other polymerization methods.


## 2.3.1. Basic Principle of Emulsion Polymerization

Before emulsion polymerization, the system can have three different phase states: water phase, micelle phase, and oil phase. When a certain amount of emulsifier and a small amount of monomer are in the water phase state, the emulsifier and monomer will also form an aqueous phase after mixing with water [18]. The formation of micelle phase in the presence of emulsifier is due to the presence of some monomers in the micelles. The polymerization occurs in micellar ions, and the emulsion also exhibits a micellar phase. When most of the monomer ions are dispersed to form small droplets, there will be a protective layer of emulsifier on the surface. The emulsion will be the oil phase.Emulsion polymerization will undergo three stages, namely the growth stage, the constant speed stage, and the slow stage [19]. During the growth period, the primary free radical of emulsion polymerization is formed, and polymerization occurs in the compatibilized micelles. With the deepening of the degree of reaction, single body fluid drops continue to provide monomers for latex particles, so that the number of micelles decreases, thus increasing the number of latex particles and accelerating the polymerization rate. In the middle stage of polymerization, that is the constant rate period, the number of latex particles remains unchanged, and the rate of polymerization does not change. The volume of latex particles increases slowly, and the volume of single body fluid drops decreases slowly [20]. In the decreasing period of polymerization, the monomer is completely converted into polymer.


## 2.3.2. Emulsion Polymerization Method

There are many methods and techniques for emulsion polymerization, such as core/shell emulsion polymerization, soap-free emulsion polymerization, etc.In the core/shell emulsion polymerization, there are two parts of the monomer in the latex particles, which are composed of core and shell. The structure of heterogeneous particles with different structural characteristics can be obtained by the different monomer proportion of the core part and shell part, and different emulsion properties can be formed [21]. The process of core/shell emulsion polymerization is as follows: the emulsion polymerization of the core part of the monomer is added to the shell part of the monomer. After the monomer emulsion polymerization of the shell part is completed, the heterogeneous latex particles of the core/shell structure can be obtained [22]. The preparation methods can be divided into batch method, semicontinuous method, and swelling method according to the way of adding shell monomer. The structure of latex particles prepared by different methods is also different. The latex particles prepared by batch method and swelling method have high content and good stability, while those prepared by semicontinuous method have stable size. The emulsion obtained by core/shell emulsion polymerization has many advantages, such as good anti-adhesion, good film formation, stable storage and use, and good mechanical properties.Emulsifier-free emulsion polymerization requires only a small amount of emulsifier or [23] without emulsifier in the polymerization process. In the process of polymerization, the effect of emulsifier on emulsifier-free emulsion is different from that of traditional emulsion polymerization, mainly because the formation mechanism of micelle particles is different and the stability conditions of the emulsion system are different. The residual emulsifier in traditional emulsion polymerization will reduce the water resistance and friction resistance of the emulsion, and the emulsifier content in soap-free emulsion is very little or even zero, which can reduce the influence of emulsifier on the properties of the emulsion. The widely used emulsifier-free emulsion polymerization methods include emulsifying copolymers, surfactants, acrylic monomers, and oligomers.


## 2.3.3. Advantages of Emulsion Polymerization

The reaction heat expelled in emulsion polymerization is very easy. The removal of reaction heat is not only related to the stability of the operation control, but also related to the safety of the production process. Water is the dispersant of the emulsion, and the latex particles are independent. The interaction between particles is small, the viscosity will be reduced, and the heat of the reaction will quickly diffuse out.The emulsion polymerization rate is fast and the molecular weight is high. In emulsion polymerization, the free radical chain is trapped in stable latex particles. The binding between latex particles is not very easy. Chain termination is almost impossible. Only the primary free radicals can be diffused into the latex for the water phase to terminate, so the average lifespan of the chain radical is greatly extended, which can produce high molecular weight polymers. However, in bulk and solution polymerization, on the one hand, to improve the molecular weight of the polymer, it is necessary to reduce the reaction temperature and the termination speed of free radicals, and reducing the reaction temperature also reduces the reaction speed. On the other hand, to improve the polymerization rate, the temperature should be increased to accelerate the decomposition of free radicals, increase the concentration of free radicals, and thus increase the chain termination speed, thus reducing the molecular weight of the polymer.The process of emulsion polymerization is safe and has environmental protection. The dispersed phase of emulsion polymerization is water, which is cheap and easy to obtain. It is also very safe to use. In this way, not only can the cost of raw materials be reduced, but also the cost of solvent recovery will be reduced due to the reduction of solvent use. The solvent will not have a negative impact on the environment, and because solvent is not flammable, it is very safe in the process of transportation and storage.Polymer particles can be prepared by emulsion polymerization. By selecting different monomers, adding different functional monomers, designing a precise ratio, and changing the false talk mode, latex particles with different particle size distribution, morphology, and performance can be prepared. These particles can meet different specific needs and have good mechanical properties. This is incomparable with other polymerization methods.


## 2.4. Nano-Chinese Painting Pigments

Because the particle size of the nanomaterial particles is in the nanometer range, the optical properties of the paper can be greatly improved, and its opacity is relatively high. For example, nano-alumina is used as nanopigment particles in coatings. Due to the small particle size of the particles and the narrow distribution range of particle size, it can ensure the purity of the color as a white material, thereby improving the performance of the coated paper. Whiteness improves the gloss of paper. In addition, some nanomaterials can also produce special optical effects. For example, when scattering occurs, the color of the coated paper will change with the change of people’s observation angle, so it can be used to produce special-purpose coatings. The application of nanopigment particles to coatings can improve the rheological properties of coatings. Nanopigments have special surface effects and quantum size effects, so they can control the particle size performance, pH value, and zeta potential of the coating, to obtain coatings with high concentration but low viscosity. In addition, the particles of nanopigments are extremely fine, which is very beneficial to the improvement of the stability of the coating and can greatly avoid the occurrence of precipitation, delamination, and other phenomena.The development of Chinese painting line has a long history, attaching great importance to the inheritance of national culture; the application of line in Chinese painting from the art of ancient times to today and its role and influence is self-evident. No matter the change of dynasties or the impact of modern and contemporary foreign painting ideas, no matter how many debates on the existence and form of line, but with its rich connotations, the seemingly weak line language can remain invincible. The atoms or molecules of the pigment are excited and the electrons transition from the ground state to the excited state. When the excited state is unstable, it jumps back to the ground state and emits a certain wavelength of light, thus showing a certain color. The color of the pigment mainly depends on the existing state of colored ions, that is the atomic or molecular structure of the pigment itself, while the coloring of matter is mainly caused by the transition of electrons between different energy levels and the absorption and scattering of light by ions.


## 3. Synthesis Experiments of Nano-ZnO Composite Polystyrene Acrylate Emulsion

### 3.1. Preparation of Nano-ZnO Composite Polystyrene Acrylate Emulsion

#### 3.1.1. Experimental Materials and Equipment

The experimental materials include nano-ZnO with an average particle size of 18 nm, analytically pure styrene, butyl acrylate, acrylic acid, potassium persulfate, chemically pure sodium bicarbonate, cetyltrimethyl ammonium chloride, distilled water, PBS solution,Escherichia coli, ethanol, and nutrient agar powder.The experimental equipment includes electronic balance, digital display, top-mounted strong electronic stirrer, centrifuge, vacuum drying oven, glass instrument, air dryer, digital viscometer, laser particle size tester, electron microscope, rod coating coater, thermogravimetric analyzer, micro-moisture analyzer, high-pressure steam sterilization pot, and water bath oscillator.


#### 3.1.2. Emulsion Polymerization Process

Emulsion polymerization was carried out by semicontinuous method. Distilled water, monomer, and microemulsifier were added into the beaker, stirred for 30 min until there was no delamination, and the preemulsion was prepared for standby. The initiator and buffer were mixed into an aqueous solution for standby.First, the styrene acrylic emulsion without nano-ZnO was prepared. 20% of the pre-emulsion and 20% water solution were added to the flask. A certain amount of distilled water was put into the agitator. The water bath heated up to 70°C and the speed was 125 r/min, stirring until the emulsion had no reflux. The remaining pre-emulsion and aqueous solution were added, which needs to be added slowly. The water bath temperature was adjusted to 75°C for 2 h and waited for polymerization. After polymerization, the emulsion was labeled as N.When preparing styrene acrylic emulsion containing nano-ZnO, it is necessary to weigh a certain amount of nano-ZnO particles first, add distilled water and a small amount of acrylic acid, and stir for 15 min in the electronic mixer, so that it can be completely dispersed in water. The content of nano-ZnO is controlled at 5%, 15%, 25%, and 35%, respectively. In addition to the pre-emulsion and aqueous solution, the solution containing nano-ZnO particles was added. The subsequent operation was the same as above. Finally, the waiting time of polymerization was adjusted to 3 h. After polymerization, the emulsions were labeled Z, Z15, Z25, and Z35, respectively.


#### 3.1.3. Culture of Bacteria

First LB culture medium was prepared for standby; 12 g of peptone, 6 g of yeast powder, and 8 g of sodium chloride were added in a conical flask; nutrients and distilled water were added to ensure the volume reaches 1 L; and then solid medium was prepared and to that 20 g of agar powder was added on the basis of the above formula. The pH value of both of them needs to be adjusted to 7.0, and then the culture medium is put into the sterilization pot for high-temperature sterilization. The temperature is 120°C and the time is controlled at 30 min.The strains were resuscitated and passaged. On the sterile operating table, the freeze-drying bacteria tube was opened, and to that the culture medium was added and blown repeatedly to dissolve it. The strain was inoculated into LB medium and cultured in an incubator for 24 h at 35°C. The first-generation culture was taken out of the inoculation ring and then inoculated on agar medium for further cultivation. The passage time was once every 2 months. The subcultured strains were stored in the refrigerator for future use.For the preparation of bacterial suspension, a few cultivatedEscherichia coli and Staphylococcus aureus were taken from the inoculation ring and put them into the incubator for cultivation. The temperature was 37°C for 12 to 24 hours. 2 ml of it was added into 8 ml of sterile sodium chloride and mixed. After continuous dilution, the inoculum solution with the concentration of 1 × 105 CFU/ml was selected as the standard.Then the styrene acrylic emulsion was treated and sterilized. The emulsion was dried in a beaker and processed into a diameter of 5-mm wafer. It was irradiated for 30 min and sterilized under an ultraviolet lamp.


### 3.2. Testing of Emulsion Properties

#### 3.2.1. Determination of Solid Content and Monomer Conversion

The nano-ZnO polymerized styrene acrylic emulsion (1 g emulsion with different ZnO content) needs to be sampled. It was dried in a glass dish. The calculation formula of solid content is as follows:(1)W=G1−vG2−v×100%,where G1 is the total quality of glass dishes and drying film, G2 is the total quality of glass dishes and emulsion, V is the quality of glass dishes, and the unit is g.The monomer conversion rate of nano-ZnO polymerized styrene acrylic emulsion was determined. The monomer conversion rate was calculated as follows:(2)Q=W+PK,where W is the solid content of the emulsion calculated in the previous step, P is the rate of the emulsion polymerization, and K is the theoretical solid content of the emulsion. The rate of emulsion polymerization is the ratio of the dry weight of emulsion polymerized flocs to the theoretical total amount of emulsion.


#### 3.2.2. Viscosity and Water Absorption

The viscosity of the emulsion was measured by a digital viscometer. The temperature was 28°C, and the rotor number 3 was selected with a rotational speed of 25 r/min.A certain amount of emulsion was drawn on the glass plate, placed into a drying oven, and dried to a constant temperature. After weighing, it was immersed in distilled water for 24 hours, and the water on the surface of the glass plate was absorbed by filter paper and then weighed. The calculation formula of water absorption is as follows:(3)Z=C−XX−C0,where C is the mass of the glass plate after immersion, X is the total mass of the glass plate and dry film, and C0 is the weight of the glass plate.


#### 3.2.3. Determination of Antibacterial Properties

The minimum inhibitory concentration (MIC) of the two emulsions was determined by the broth dilution method. First, the bacterial suspension was prepared with bacterial liquid and LB liquid medium for standby, and the concentration of bacterial liquid was controlled at about 1 × 105 CFU/ml. Then the bacterial suspension was diluted with PBS solution by double dilution method. Adding the dilute bacteria suspension into the two emulsions, put them in the incubator, incubated for 12 to 24 h at 37°C, and compared the two sets of emulsions. The minimum antibacterial solution in all clarification tubes is MIC.


### 3.3. Pigment Stability Test

Once the final coating has been prepared, 100 mL was added to a 100 mL plunger measuring cylinder and dried for 24 hours at 60°C. Then, the coating was removed and cooled to about 25°C. The stability of the paint was analyzed by measuring the amount of clear water that precipitates above the paint.


## 3.1. Preparation of Nano-ZnO Composite Polystyrene Acrylate Emulsion

### 3.1.1. Experimental Materials and Equipment

The experimental materials include nano-ZnO with an average particle size of 18 nm, analytically pure styrene, butyl acrylate, acrylic acid, potassium persulfate, chemically pure sodium bicarbonate, cetyltrimethyl ammonium chloride, distilled water, PBS solution,Escherichia coli, ethanol, and nutrient agar powder.The experimental equipment includes electronic balance, digital display, top-mounted strong electronic stirrer, centrifuge, vacuum drying oven, glass instrument, air dryer, digital viscometer, laser particle size tester, electron microscope, rod coating coater, thermogravimetric analyzer, micro-moisture analyzer, high-pressure steam sterilization pot, and water bath oscillator.


### 3.1.2. Emulsion Polymerization Process

Emulsion polymerization was carried out by semicontinuous method. Distilled water, monomer, and microemulsifier were added into the beaker, stirred for 30 min until there was no delamination, and the preemulsion was prepared for standby. The initiator and buffer were mixed into an aqueous solution for standby.First, the styrene acrylic emulsion without nano-ZnO was prepared. 20% of the pre-emulsion and 20% water solution were added to the flask. A certain amount of distilled water was put into the agitator. The water bath heated up to 70°C and the speed was 125 r/min, stirring until the emulsion had no reflux. The remaining pre-emulsion and aqueous solution were added, which needs to be added slowly. The water bath temperature was adjusted to 75°C for 2 h and waited for polymerization. After polymerization, the emulsion was labeled as N.When preparing styrene acrylic emulsion containing nano-ZnO, it is necessary to weigh a certain amount of nano-ZnO particles first, add distilled water and a small amount of acrylic acid, and stir for 15 min in the electronic mixer, so that it can be completely dispersed in water. The content of nano-ZnO is controlled at 5%, 15%, 25%, and 35%, respectively. In addition to the pre-emulsion and aqueous solution, the solution containing nano-ZnO particles was added. The subsequent operation was the same as above. Finally, the waiting time of polymerization was adjusted to 3 h. After polymerization, the emulsions were labeled Z, Z15, Z25, and Z35, respectively.


### 3.1.3. Culture of Bacteria

First LB culture medium was prepared for standby; 12 g of peptone, 6 g of yeast powder, and 8 g of sodium chloride were added in a conical flask; nutrients and distilled water were added to ensure the volume reaches 1 L; and then solid medium was prepared and to that 20 g of agar powder was added on the basis of the above formula. The pH value of both of them needs to be adjusted to 7.0, and then the culture medium is put into the sterilization pot for high-temperature sterilization. The temperature is 120°C and the time is controlled at 30 min.The strains were resuscitated and passaged. On the sterile operating table, the freeze-drying bacteria tube was opened, and to that the culture medium was added and blown repeatedly to dissolve it. The strain was inoculated into LB medium and cultured in an incubator for 24 h at 35°C. The first-generation culture was taken out of the inoculation ring and then inoculated on agar medium for further cultivation. The passage time was once every 2 months. The subcultured strains were stored in the refrigerator for future use.For the preparation of bacterial suspension, a few cultivatedEscherichia coli and Staphylococcus aureus were taken from the inoculation ring and put them into the incubator for cultivation. The temperature was 37°C for 12 to 24 hours. 2 ml of it was added into 8 ml of sterile sodium chloride and mixed. After continuous dilution, the inoculum solution with the concentration of 1 × 105 CFU/ml was selected as the standard.Then the styrene acrylic emulsion was treated and sterilized. The emulsion was dried in a beaker and processed into a diameter of 5-mm wafer. It was irradiated for 30 min and sterilized under an ultraviolet lamp.


## 3.1.1. Experimental Materials and Equipment

The experimental materials include nano-ZnO with an average particle size of 18 nm, analytically pure styrene, butyl acrylate, acrylic acid, potassium persulfate, chemically pure sodium bicarbonate, cetyltrimethyl ammonium chloride, distilled water, PBS solution,Escherichia coli, ethanol, and nutrient agar powder.The experimental equipment includes electronic balance, digital display, top-mounted strong electronic stirrer, centrifuge, vacuum drying oven, glass instrument, air dryer, digital viscometer, laser particle size tester, electron microscope, rod coating coater, thermogravimetric analyzer, micro-moisture analyzer, high-pressure steam sterilization pot, and water bath oscillator.


## 3.1.2. Emulsion Polymerization Process

Emulsion polymerization was carried out by semicontinuous method. Distilled water, monomer, and microemulsifier were added into the beaker, stirred for 30 min until there was no delamination, and the preemulsion was prepared for standby. The initiator and buffer were mixed into an aqueous solution for standby.First, the styrene acrylic emulsion without nano-ZnO was prepared. 20% of the pre-emulsion and 20% water solution were added to the flask. A certain amount of distilled water was put into the agitator. The water bath heated up to 70°C and the speed was 125 r/min, stirring until the emulsion had no reflux. The remaining pre-emulsion and aqueous solution were added, which needs to be added slowly. The water bath temperature was adjusted to 75°C for 2 h and waited for polymerization. After polymerization, the emulsion was labeled as N.When preparing styrene acrylic emulsion containing nano-ZnO, it is necessary to weigh a certain amount of nano-ZnO particles first, add distilled water and a small amount of acrylic acid, and stir for 15 min in the electronic mixer, so that it can be completely dispersed in water. The content of nano-ZnO is controlled at 5%, 15%, 25%, and 35%, respectively. In addition to the pre-emulsion and aqueous solution, the solution containing nano-ZnO particles was added. The subsequent operation was the same as above. Finally, the waiting time of polymerization was adjusted to 3 h. After polymerization, the emulsions were labeled Z, Z15, Z25, and Z35, respectively.


## 3.1.3. Culture of Bacteria

First LB culture medium was prepared for standby; 12 g of peptone, 6 g of yeast powder, and 8 g of sodium chloride were added in a conical flask; nutrients and distilled water were added to ensure the volume reaches 1 L; and then solid medium was prepared and to that 20 g of agar powder was added on the basis of the above formula. The pH value of both of them needs to be adjusted to 7.0, and then the culture medium is put into the sterilization pot for high-temperature sterilization. The temperature is 120°C and the time is controlled at 30 min.The strains were resuscitated and passaged. On the sterile operating table, the freeze-drying bacteria tube was opened, and to that the culture medium was added and blown repeatedly to dissolve it. The strain was inoculated into LB medium and cultured in an incubator for 24 h at 35°C. The first-generation culture was taken out of the inoculation ring and then inoculated on agar medium for further cultivation. The passage time was once every 2 months. The subcultured strains were stored in the refrigerator for future use.For the preparation of bacterial suspension, a few cultivatedEscherichia coli and Staphylococcus aureus were taken from the inoculation ring and put them into the incubator for cultivation. The temperature was 37°C for 12 to 24 hours. 2 ml of it was added into 8 ml of sterile sodium chloride and mixed. After continuous dilution, the inoculum solution with the concentration of 1 × 105 CFU/ml was selected as the standard.Then the styrene acrylic emulsion was treated and sterilized. The emulsion was dried in a beaker and processed into a diameter of 5-mm wafer. It was irradiated for 30 min and sterilized under an ultraviolet lamp.


## 3.2. Testing of Emulsion Properties

### 3.2.1. Determination of Solid Content and Monomer Conversion

The nano-ZnO polymerized styrene acrylic emulsion (1 g emulsion with different ZnO content) needs to be sampled. It was dried in a glass dish. The calculation formula of solid content is as follows:(1)W=G1−vG2−v×100%,where G1 is the total quality of glass dishes and drying film, G2 is the total quality of glass dishes and emulsion, V is the quality of glass dishes, and the unit is g.The monomer conversion rate of nano-ZnO polymerized styrene acrylic emulsion was determined. The monomer conversion rate was calculated as follows:(2)Q=W+PK,where W is the solid content of the emulsion calculated in the previous step, P is the rate of the emulsion polymerization, and K is the theoretical solid content of the emulsion. The rate of emulsion polymerization is the ratio of the dry weight of emulsion polymerized flocs to the theoretical total amount of emulsion.


### 3.2.2. Viscosity and Water Absorption

The viscosity of the emulsion was measured by a digital viscometer. The temperature was 28°C, and the rotor number 3 was selected with a rotational speed of 25 r/min.A certain amount of emulsion was drawn on the glass plate, placed into a drying oven, and dried to a constant temperature. After weighing, it was immersed in distilled water for 24 hours, and the water on the surface of the glass plate was absorbed by filter paper and then weighed. The calculation formula of water absorption is as follows:(3)Z=C−XX−C0,where C is the mass of the glass plate after immersion, X is the total mass of the glass plate and dry film, and C0 is the weight of the glass plate.


### 3.2.3. Determination of Antibacterial Properties

The minimum inhibitory concentration (MIC) of the two emulsions was determined by the broth dilution method. First, the bacterial suspension was prepared with bacterial liquid and LB liquid medium for standby, and the concentration of bacterial liquid was controlled at about 1 × 105 CFU/ml. Then the bacterial suspension was diluted with PBS solution by double dilution method. Adding the dilute bacteria suspension into the two emulsions, put them in the incubator, incubated for 12 to 24 h at 37°C, and compared the two sets of emulsions. The minimum antibacterial solution in all clarification tubes is MIC.


## 3.2.1. Determination of Solid Content and Monomer Conversion

The nano-ZnO polymerized styrene acrylic emulsion (1 g emulsion with different ZnO content) needs to be sampled. It was dried in a glass dish. The calculation formula of solid content is as follows:(1)W=G1−vG2−v×100%,where G1 is the total quality of glass dishes and drying film, G2 is the total quality of glass dishes and emulsion, V is the quality of glass dishes, and the unit is g.The monomer conversion rate of nano-ZnO polymerized styrene acrylic emulsion was determined. The monomer conversion rate was calculated as follows:(2)Q=W+PK,where W is the solid content of the emulsion calculated in the previous step, P is the rate of the emulsion polymerization, and K is the theoretical solid content of the emulsion. The rate of emulsion polymerization is the ratio of the dry weight of emulsion polymerized flocs to the theoretical total amount of emulsion.


## 3.2.2. Viscosity and Water Absorption

The viscosity of the emulsion was measured by a digital viscometer. The temperature was 28°C, and the rotor number 3 was selected with a rotational speed of 25 r/min.A certain amount of emulsion was drawn on the glass plate, placed into a drying oven, and dried to a constant temperature. After weighing, it was immersed in distilled water for 24 hours, and the water on the surface of the glass plate was absorbed by filter paper and then weighed. The calculation formula of water absorption is as follows:(3)Z=C−XX−C0,where C is the mass of the glass plate after immersion, X is the total mass of the glass plate and dry film, and C0 is the weight of the glass plate.


## 3.2.3. Determination of Antibacterial Properties

The minimum inhibitory concentration (MIC) of the two emulsions was determined by the broth dilution method. First, the bacterial suspension was prepared with bacterial liquid and LB liquid medium for standby, and the concentration of bacterial liquid was controlled at about 1 × 105 CFU/ml. Then the bacterial suspension was diluted with PBS solution by double dilution method. Adding the dilute bacteria suspension into the two emulsions, put them in the incubator, incubated for 12 to 24 h at 37°C, and compared the two sets of emulsions. The minimum antibacterial solution in all clarification tubes is MIC.


## 3.3. Pigment Stability Test

Once the final coating has been prepared, 100 mL was added to a 100 mL plunger measuring cylinder and dried for 24 hours at 60°C. Then, the coating was removed and cooled to about 25°C. The stability of the paint was analyzed by measuring the amount of clear water that precipitates above the paint.


## 4. Discussion on Functionality of Nano-ZnO Composite Polystyrene Emulsion

### 4.1. Comparison of Solid Content and Monomer Conversion of Emulsion

#### 4.1.1. Effect of Monomer Content on the Solid Content of Emulsion

In the determination of the solid content of emulsion, the solid content of styrene, acrylic emulsion N without nano-ZnO, and styrene acrylate emulsion containing different content of nano-ZnO, Z, Z15, Z25, and Z35 were compared, to explore the effect of monomer content on the solid content of emulsion. The results are shown in Figure1.Figure 1
Solid content of emulsion.As shown in Figure1, the solid content of styrene acrylic emulsion without nano-ZnO is 36.9%, and the solid content of nano-ZnO polymerized styrene acrylic emulsion will change due to the different content of nano-ZnO. When the content of nano-ZnO is 15%, the solid content of emulsion reaches the highest, which is 43.5%. When the content of nano-ZnO is 35%, the solid content of emulsion is the lowest, only 35.4%. This indicates that the content of monomer in the emulsion affects the solid content, but the higher the monomer content is, the better the monomer content is.


#### 4.1.2. Effect of Reaction Temperature on Monomer Conversion

After measuring the solid content of nano-ZnO polymerized styrene acrylic emulsion, the monomer conversion rate was calculated according to the formula, and the monomer conversion rate of nano-ZnO polymerized styrene acrylic emulsion at different temperatures was analyzed. The results are shown in Figure2.Figure 2
Monomer conversion rate.As shown in Figure2, no matter which kind of emulsion, the monomer conversion rate will gradually increase with the increase of polymerization temperature and will reach a plateau after reaching the maximum value. The monomer conversion rate of the polymerized styrene acrylic emulsion with nano-ZnO content of 15% is 86.4% at the temperature of 80°C. When the temperature is 60°C, the monomer conversion of all emulsion is the lowest, and as the temperature rises, the monomer conversion rate also rises and reaches the peak value at 80°C. When the temperature increases, the monomer conversion rate does not continue to increase, but tends to be stable. It may be because higher reaction temperature will accelerate the formation of free radicals, thus increasing the polymerization active point and improving the monomer conversion. However, when the temperature is too high, the heat cannot be dispersed in time, and the local temperature is too high to control the reaction. Therefore, in the polymerization reaction, the temperature should be controlled at 75–80°C, not too high.


### 4.2. Comparison of Viscosity and Water Absorption

#### 4.2.1. Viscosity

The viscosity of the emulsion directly affects the stability and film formation effect of the emulsion. The increase of viscosity will improve the stability of storage. In the process of film forming, the viscosity should be appropriate. Too little viscosity will result in poor leveling, while too much viscosity will result in sagging. Solid content, particle size, and type of monomer affect the viscosity of the emulsion. The effect of nano-ZnO content on the viscosity of the emulsion was investigated. The analysis data are given in Table1.Table 1
Changes in viscosity of emulsions.
Emulsion typeZZ15Z25Z35Viscosity (m Pa∙s)163978459As shown in Table1, the viscosity of the emulsion decreases with the increase of the content of nano-ZnO monomer. When there is no nano-ZnO in the emulsion, that is ordinary styrene acrylic emulsion, the viscosity is 163 m Pa s, the highest value. When the content of nano-ZnO in styrene acrylic emulsion reaches 35%, the viscosity decreases to 59 m Pa s.


#### 4.2.2. Water Absorption

When styrene acrylic emulsion is used as paint, its water absorption is an important index for testing the performance of the coating, especially the external wall of the building, which needs to be washed by rainwater, and its water resistance requirement is even higher. In this study, different types of emulsions were coated, respectively, and the water absorption rate after the formation of the film was tested. The results are given in Figure3.Figure 3
Water absorption of film.As shown in Figure3, when the styrene acrylic emulsion does not contain nano-ZnO, the water absorption of the film is 6.21%. With the increasing content of nano-ZnO in styrene acrylic emulsion, the water absorption rate is increasing. When the content of nano-ZnO is 35%, the water absorption rate reaches 18.91%. This is because the hydroxyl group after hydrolysis of nano-ZnO increases the water absorption of the film. The more nano-ZnO content is, the more residual hydroxyl is, so the water absorption will be higher and higher.


### 4.3. Comparison of Antibacterial Ability

The value of MIC represents the quality of antibacterial effect. The smaller the MIC value, the better the antibacterial effect. A total of 5 kinds of emulsion samples were determined by MIC, and the antibacterial activity of different emulsions againstEscherichia coli and Staphylococcus aureus was compared. The results are given in Figure 4.Figure 4
Bacteriostatic effect.As shown in Figure4, the styrene acrylic emulsion itself has a good inhibitory effect on Escherichia coli and Staphylococcus aureus. Even without adding nano-ZnO to polymerize, its MIC can reach 12 and 4 ppm, respectively, especially for Staphylococcus aureus. With the increasing content of nano-ZnO in the emulsion, the inhibition effect on the two kinds of bacteria is also getting better and better, and the MIC value is smaller and smaller. When the content of nano-ZnO reached 35%, the MIC value of the styrene acrylic emulsion against Escherichia coli and Staphylococcus aureus was as low as 4 ppm and 1 ppm, respectively.


## 4.1. Comparison of Solid Content and Monomer Conversion of Emulsion

### 4.1.1. Effect of Monomer Content on the Solid Content of Emulsion

In the determination of the solid content of emulsion, the solid content of styrene, acrylic emulsion N without nano-ZnO, and styrene acrylate emulsion containing different content of nano-ZnO, Z, Z15, Z25, and Z35 were compared, to explore the effect of monomer content on the solid content of emulsion. The results are shown in Figure1.Figure 1
Solid content of emulsion.As shown in Figure1, the solid content of styrene acrylic emulsion without nano-ZnO is 36.9%, and the solid content of nano-ZnO polymerized styrene acrylic emulsion will change due to the different content of nano-ZnO. When the content of nano-ZnO is 15%, the solid content of emulsion reaches the highest, which is 43.5%. When the content of nano-ZnO is 35%, the solid content of emulsion is the lowest, only 35.4%. This indicates that the content of monomer in the emulsion affects the solid content, but the higher the monomer content is, the better the monomer content is.


### 4.1.2. Effect of Reaction Temperature on Monomer Conversion

After measuring the solid content of nano-ZnO polymerized styrene acrylic emulsion, the monomer conversion rate was calculated according to the formula, and the monomer conversion rate of nano-ZnO polymerized styrene acrylic emulsion at different temperatures was analyzed. The results are shown in Figure2.Figure 2
Monomer conversion rate.As shown in Figure2, no matter which kind of emulsion, the monomer conversion rate will gradually increase with the increase of polymerization temperature and will reach a plateau after reaching the maximum value. The monomer conversion rate of the polymerized styrene acrylic emulsion with nano-ZnO content of 15% is 86.4% at the temperature of 80°C. When the temperature is 60°C, the monomer conversion of all emulsion is the lowest, and as the temperature rises, the monomer conversion rate also rises and reaches the peak value at 80°C. When the temperature increases, the monomer conversion rate does not continue to increase, but tends to be stable. It may be because higher reaction temperature will accelerate the formation of free radicals, thus increasing the polymerization active point and improving the monomer conversion. However, when the temperature is too high, the heat cannot be dispersed in time, and the local temperature is too high to control the reaction. Therefore, in the polymerization reaction, the temperature should be controlled at 75–80°C, not too high.


## 4.1.1. Effect of Monomer Content on the Solid Content of Emulsion

In the determination of the solid content of emulsion, the solid content of styrene, acrylic emulsion N without nano-ZnO, and styrene acrylate emulsion containing different content of nano-ZnO, Z, Z15, Z25, and Z35 were compared, to explore the effect of monomer content on the solid content of emulsion. The results are shown in Figure1.Figure 1
Solid content of emulsion.As shown in Figure1, the solid content of styrene acrylic emulsion without nano-ZnO is 36.9%, and the solid content of nano-ZnO polymerized styrene acrylic emulsion will change due to the different content of nano-ZnO. When the content of nano-ZnO is 15%, the solid content of emulsion reaches the highest, which is 43.5%. When the content of nano-ZnO is 35%, the solid content of emulsion is the lowest, only 35.4%. This indicates that the content of monomer in the emulsion affects the solid content, but the higher the monomer content is, the better the monomer content is.


## 4.1.2. Effect of Reaction Temperature on Monomer Conversion

After measuring the solid content of nano-ZnO polymerized styrene acrylic emulsion, the monomer conversion rate was calculated according to the formula, and the monomer conversion rate of nano-ZnO polymerized styrene acrylic emulsion at different temperatures was analyzed. The results are shown in Figure2.Figure 2
Monomer conversion rate.As shown in Figure2, no matter which kind of emulsion, the monomer conversion rate will gradually increase with the increase of polymerization temperature and will reach a plateau after reaching the maximum value. The monomer conversion rate of the polymerized styrene acrylic emulsion with nano-ZnO content of 15% is 86.4% at the temperature of 80°C. When the temperature is 60°C, the monomer conversion of all emulsion is the lowest, and as the temperature rises, the monomer conversion rate also rises and reaches the peak value at 80°C. When the temperature increases, the monomer conversion rate does not continue to increase, but tends to be stable. It may be because higher reaction temperature will accelerate the formation of free radicals, thus increasing the polymerization active point and improving the monomer conversion. However, when the temperature is too high, the heat cannot be dispersed in time, and the local temperature is too high to control the reaction. Therefore, in the polymerization reaction, the temperature should be controlled at 75–80°C, not too high.


## 4.2. Comparison of Viscosity and Water Absorption

### 4.2.1. Viscosity

The viscosity of the emulsion directly affects the stability and film formation effect of the emulsion. The increase of viscosity will improve the stability of storage. In the process of film forming, the viscosity should be appropriate. Too little viscosity will result in poor leveling, while too much viscosity will result in sagging. Solid content, particle size, and type of monomer affect the viscosity of the emulsion. The effect of nano-ZnO content on the viscosity of the emulsion was investigated. The analysis data are given in Table1.Table 1
Changes in viscosity of emulsions.
Emulsion typeZZ15Z25Z35Viscosity (m Pa∙s)163978459As shown in Table1, the viscosity of the emulsion decreases with the increase of the content of nano-ZnO monomer. When there is no nano-ZnO in the emulsion, that is ordinary styrene acrylic emulsion, the viscosity is 163 m Pa s, the highest value. When the content of nano-ZnO in styrene acrylic emulsion reaches 35%, the viscosity decreases to 59 m Pa s.


### 4.2.2. Water Absorption

When styrene acrylic emulsion is used as paint, its water absorption is an important index for testing the performance of the coating, especially the external wall of the building, which needs to be washed by rainwater, and its water resistance requirement is even higher. In this study, different types of emulsions were coated, respectively, and the water absorption rate after the formation of the film was tested. The results are given in Figure3.Figure 3
Water absorption of film.As shown in Figure3, when the styrene acrylic emulsion does not contain nano-ZnO, the water absorption of the film is 6.21%. With the increasing content of nano-ZnO in styrene acrylic emulsion, the water absorption rate is increasing. When the content of nano-ZnO is 35%, the water absorption rate reaches 18.91%. This is because the hydroxyl group after hydrolysis of nano-ZnO increases the water absorption of the film. The more nano-ZnO content is, the more residual hydroxyl is, so the water absorption will be higher and higher.


## 4.2.1. Viscosity

The viscosity of the emulsion directly affects the stability and film formation effect of the emulsion. The increase of viscosity will improve the stability of storage. In the process of film forming, the viscosity should be appropriate. Too little viscosity will result in poor leveling, while too much viscosity will result in sagging. Solid content, particle size, and type of monomer affect the viscosity of the emulsion. The effect of nano-ZnO content on the viscosity of the emulsion was investigated. The analysis data are given in Table1.Table 1
Changes in viscosity of emulsions.
Emulsion typeZZ15Z25Z35Viscosity (m Pa∙s)163978459As shown in Table1, the viscosity of the emulsion decreases with the increase of the content of nano-ZnO monomer. When there is no nano-ZnO in the emulsion, that is ordinary styrene acrylic emulsion, the viscosity is 163 m Pa s, the highest value. When the content of nano-ZnO in styrene acrylic emulsion reaches 35%, the viscosity decreases to 59 m Pa s.


## 4.2.2. Water Absorption

When styrene acrylic emulsion is used as paint, its water absorption is an important index for testing the performance of the coating, especially the external wall of the building, which needs to be washed by rainwater, and its water resistance requirement is even higher. In this study, different types of emulsions were coated, respectively, and the water absorption rate after the formation of the film was tested. The results are given in Figure3.Figure 3
Water absorption of film.As shown in Figure3, when the styrene acrylic emulsion does not contain nano-ZnO, the water absorption of the film is 6.21%. With the increasing content of nano-ZnO in styrene acrylic emulsion, the water absorption rate is increasing. When the content of nano-ZnO is 35%, the water absorption rate reaches 18.91%. This is because the hydroxyl group after hydrolysis of nano-ZnO increases the water absorption of the film. The more nano-ZnO content is, the more residual hydroxyl is, so the water absorption will be higher and higher.


## 4.3. Comparison of Antibacterial Ability

The value of MIC represents the quality of antibacterial effect. The smaller the MIC value, the better the antibacterial effect. A total of 5 kinds of emulsion samples were determined by MIC, and the antibacterial activity of different emulsions againstEscherichia coli and Staphylococcus aureus was compared. The results are given in Figure 4.Figure 4
Bacteriostatic effect.As shown in Figure4, the styrene acrylic emulsion itself has a good inhibitory effect on Escherichia coli and Staphylococcus aureus. Even without adding nano-ZnO to polymerize, its MIC can reach 12 and 4 ppm, respectively, especially for Staphylococcus aureus. With the increasing content of nano-ZnO in the emulsion, the inhibition effect on the two kinds of bacteria is also getting better and better, and the MIC value is smaller and smaller. When the content of nano-ZnO reached 35%, the MIC value of the styrene acrylic emulsion against Escherichia coli and Staphylococcus aureus was as low as 4 ppm and 1 ppm, respectively.


## 5. Conclusions

Styrene acrylic emulsion has the advantages of alkali resistance, waterproof, antiaging, and scrubbing. It is widely used in adhesives and coatings. However, there are still some shortcomings, so it is necessary to modify the function to enhance the performance. At present, the common modification methods for styrene acrylic emulsion are graphene modification, organic fluorine modification, organic silicon modification, and nanomaterial modification.In this study, nano-ZnO and styrene acrylic emulsion were used as raw materials to prepare nano-ZnO composite polystyrene emulsion by emulsion polymerization. A series of experiments were carried out to study the effect of nano-ZnO content on the properties of the emulsion. The experimental results show that the emulsion has high solid content and monomer conversion rate, good water resistance, and bacteriostatic effect, but the viscosity of the emulsion has not been strengthened. In this experiment, a variety of dispersion methods were used to disperse the nanopigments: first, the method of high-speed grinding and dispersion was used, and then the surfactant was added to coat the particles. At the same time, ultrasonic dispersion was used during the dispersion, and a suitable dispersant was added to disperse the nanopigments. Trying to make the nanocoating evenly dispersed, the better the dispersion stability, the better its special properties can be exerted. The unique aesthetic consciousness, thinking method, aesthetic ideology, and philosophical concepts of Chinese painting form China’s unique artistic system, which carries the lofty wisdom of the ancient Chinese people, representing the cultural history of China’s past years. Today’s Chinese painting art is constantly developing forward. No matter what means of expression are adopted in the picture, it has not weakened the traditional artistic language of Chinese painting, but makes the picture expression form of Chinese painting more diversified, which also proves that Chinese painting is constantly absorbing and learning from foreign culture and art in the process of the development of the times, which is in constant exploration, research, and innovation. On the road to innovating Chinese painting, it is necessary to carry forward and develop Chinese traditional culture and art.Due to limited time and knowledge, the adhesion, hardness, and UV resistance of the nano-ZnO composite polystyrene emulsion were neglected. Moreover, there will be some deficiencies in the viscosity of the final emulsion products. These problems will be further improved in the next step.



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*Source: 5019050-2022-07-30.xml*