Preparation, surface modification and application

Preparation, surface modification and application of nano zinc oxide

nano zinc oxide is a new type of high-function fine inorganic product facing the 21st century. Its particle size is between 1 ~ 100 nm, also known as ultra-fine zinc oxide. Due to the refinement of particle size and the sharp increase of specific surface area, nano zinc oxide has the surface effect, small size effect and macro quantum tunneling effect that its bulk material does not have. Therefore, nano zinc oxide has incomparable special properties and new uses in magnetism, light, electricity, chemistry, physics, sensitivity and other aspects compared with general zinc oxide products. It shows a broad application prospect in the fields of rubber, coatings, inks, pigments and fillers, catalysts, high-end cosmetics and medicine. In this paper, the nano zinc oxide produced by our company will be introduced in detail from the aspects of preparation methods, performance characterization, surface modification and currently developed application fields

I. preparation of nano zinc oxide

the preparation methods of zinc oxide are divided into three categories: direct method (also known as American method), indirect method (also known as French method) and wet chemical method. At present, many commercial zinc oxide products are mostly direct or indirect products, with particle size of micron and small specific surface area. These properties greatly restrict their application fields and properties in products. Our company adopts the wet chemical method (NPP method) to prepare nano-sized ultra-fine active zinc oxide. Various zinc containing materials can be used as raw materials, zinc is leached by acid leaching, impurities in the raw materials are removed after many times of purification, then basic zinc carbonate is obtained by precipitation, and finally nano zinc oxide is obtained by calcination. Compared with the previous process technology for preparing nano ultra-fine zinc oxide, this new process has the following technical innovations:

1 Under equilibrium conditions, the principle of reaction kinetics is combined with enhanced heat transfer technology to quickly complete the calcination of basic zinc carbonate

2. Through the adjustment of process parameters, various types of nano zinc oxide products with different purity, particle size and color can be prepared

3. This process can use a variety of zinc containing materials as raw materials to convert them into high value-added products

4. A typical green chemical process belongs to an environment-friendly process

II. Performance characterization of nano zinc oxide

the outstanding feature of nano zinc oxide is that the product particles are nano-sized, and have the dual characteristics of nano materials and traditional zinc oxide at the same time. Compared with traditional zinc oxide products, it has large specific surface area and high chemical activity. The fineness, chemical purity and particle shape of the product can be adjusted according to needs. It also has photochemical effect and good UV shielding performance, and its UV shielding rate is as high as 98%; At the same time, it also has a series of unique properties, such as antibacterial, odor removal and enzyme prevention

the analysis and testing center of Tsinghua University analyzed the product with transmission electron microscope. The nano zinc oxide particles are spherical, with uniform particle size distribution, with an average particle size of 20-30 nm, and the particle sizes of all particles are below 50 nm. The BET specific surface area of nano zinc oxide powder is more than 35m2/g by ST-A surface and pore size tester. In addition, rod-shaped nano zinc oxide can also be produced by adjusting the preparation process parameters. This product has been tested and identified by the Institute of Microbiology, Chinese Academy of Sciences. The results show that adding 0.5%~1% nano zinc oxide to the rich bacterial culture medium can effectively inhibit the growth of E. coli, and the antibacterial rate is more than 99.9%

III. surface modification of nano zinc oxide

because nano zinc oxide has the characteristics of large specific surface area and large specific surface energy, it is easy to agglomerate itself; On the other hand, the surface polarity of nano zinc oxide is strong, and it is not easy to be evenly dispersed in organic media such as high-performance fibers and composites, biomedical materials, rare earth functional materials, which have advantages for our province, which greatly limits the play of its nano effect. Therefore, the dispersion and surface modification of nano zinc oxide powder become the necessary treatment means before the application of nano materials in the matrix

the so-called nano dispersion refers to the technology of using various principles, methods and means to reduce various forms of aggregates composed of dried nanoparticles into primary particles in a specific liquid medium (such as water) and make them stable and evenly distributed in the medium. The surface ratchet wrench change experimental machine of nano powder has been recognized by customers and the market. Surface modification is an expansion and extension based on nano dispersion technology, that is, according to the needs of applications, coating the surface of dispersed nanoparticles with a film of appropriate substances or dispersing nanoparticles in a soluble solid carrier. After surface modification, a series of surface properties such as adsorption, wetting and dispersion of nano dry powder will change. Generally, it can be automatically or easily dispersed in specific media, so it is very convenient to use. Generally speaking, there are three methods to modify nanoparticles: 1 The surface of the particles is uniformly coated with a film of other substances, so that the surface properties of the particles are changed; 2. Use charge transfer complexes (such as silane, titanate and other coupling agents, stearic acid, silicone, etc.) as surface modifiers to chemically adsorb or react on the surface of nanoparticles; 3. The surface of nanoparticles was modified by corona discharge, UV, plasma, radiation and other high-energy means

according to the requirements of different application fields, select appropriate surface modifiers or surface modification processes to modify the surface of nano zinc oxide, improve its surface properties, and increase the compatibility between nano particles and matrix, so as to be applied in various fields and improve the performance and technical indicators of products

IV. application of nano zinc oxide

our company has attached great importance to the research of its application technology development since the beginning of the preparation of nano zinc oxide. A series of important achievements have been made in the application technology of nano zinc oxide through the dedicated research of internal scientific researchers and the technical cooperation with relevant scientific research institutions. At present, the main application fields of the product are:

1 In the rubber industry, especially in the production of transparent rubber products, nano zinc oxide is an excellent vulcanizing activator. Because nano zinc oxide can be combined with rubber molecules at the molecular level, it can improve the properties of rubber and the properties of finished products. Taking radial tire and other rubber products as an example, the use of nano zinc oxide can significantly improve the thermal conductivity, wear resistance, tear resistance, tensile strength and other indicators of the product, and its dosage can be saved by%, greatly reducing the product cost; In terms of processing technology, it can prolong the scorch time of rubber, which is very beneficial to the processing technology. Nano zinc oxide is used in rubber shoes, rain boots, rubber gloves and other labor protection products, which can greatly prolong the service life of products and improve their appearance and color. When it is used in transparent or colored rubber products, it has an irreplaceable role of traditional active agents such as carbon black. Nano zinc oxide is used in products such as air tight sealant and gasket, which also plays a good role in improving the wear resistance and sealing effect of products. At present, our nano zinc oxide has been well applied in many large tire and rubber products enterprises in China

2. With the improvement of people's requirements for the color, film performance, environmental protection and other aspects of paint, the application of nano materials in the paint industry has attracted more and more attention. At present, the varieties of nano materials used in coatings include nano titanium dioxide, nano silicon dioxide, nano zinc oxide, nano calcium carbonate, etc. among them, nano titanium dioxide and nano silicon dioxide limit their application scope and quantity due to their expensive price. The performance of nano calcium carbonate is relatively single, and it plays a small role in improving the mildew resistance and UV aging resistance of coatings, Therefore, nano zinc oxide occupies a greater advantage in the application of coatings because of its excellent cost performance. Nano zinc oxide has new properties and uses that general zinc oxide can't match. It can make the coating have the effects of shielding ultraviolet rays, absorbing infrared rays, sterilization and mildew prevention. Therefore, it can be widely used in lotion coatings for internal and external walls of buildings and other coatings. At the same time, its thickening effect also helps to improve the stability of pigment dispersion. Through the joint development with relevant scientific research institutions, our company successfully applied nano zinc oxide to water-based coatings to produce nano zinc oxide modified coatings. The tests show that the traditional mechanical properties of the modified coatings, such as stain resistance, artificial aging resistance, water and alkali resistance, scrub resistance, hardness and adhesion, have been greatly improved. In addition, the antibacterial and anti mildew properties of nano zinc oxide modified coatings are also under further study

3. There are two ways for chemical fiber textile nanomaterials to be applied in chemical fiber textiles: one is to add nanoparticles directly to the initial reaction solution of chemical fibers, and use conventional polymerization to synthesize functional fibers, so that nanoparticles are evenly distributed in the fiber; Another method is to prepare nano particles as a kind of finishing agent into the finishing liquid of fabric, and make the nano particles adsorb on the surface of fiber by dip rolling, or use a certain adhesive to coat the nano particles on the surface of fabric to form a functional coating, so as to improve the wearing performance of fabric. Jilin chemical fiber group compounded the surface modified nano zinc oxide of our company into the spinning solution of viscose fiber to synthesize viscose fiber containing nano zinc oxide particles. After spinning and weaving, the anti UV fabric with nano zinc oxide was obtained. Compared with the ordinary fabric without nano zinc oxide, the UPF value (UV shielding coefficient) of the anti UV fabric was twice that of the control fabric. Our products can significantly improve the UV and antibacterial functions of viscose fiber and synthetic fiber products, and are used in the production of UV resistant fabrics, antibacterial fabrics, sunshades and other products. The UV resistant nano colloid developed by our company has been tried on the sunshade by Hangzhou paradise umbrella group Co., Ltd. the test of the Chinese Academy of Metrology shows that the UPF value (UV shielding coefficient) is 50, and its performance index has reached the Australian standard, exceeding the EU standard

4. Due to the destruction of the earth's ozone layer, sunscreen cosmetics lead to the continuous increase of ultraviolet radiation to the earth's biosphere, and the harm caused by excessive ultraviolet radiation to human health is increasing. In order to resist the damage of excessive ultraviolet radiation to human skin, people have developed a variety of sunscreens to protect the skin. Because most organic sunscreens have high activity, irritating to the skin, easy to decompose after ultraviolet radiation, and the sunscreen effect is not long, people have developed inorganic sunscreens, such as nano titanium dioxide, nano zinc oxide, etc. The study found that the protection function of nano zinc oxide against UV is stronger than that of traditional nano titanium dioxide, and it has good protection effect against UV-A and UV-B. therefore, the application of nano zinc oxide in the field of cosmetics has developed rapidly. Our company uses a special surface treatment technology to produce nano zinc oxide sunscreen, which can effectively absorb solar ultraviolet rays, especially to protect human body from UV-A and UV-B. Most traditional sunscreens can work on UV-B, but they can't effectively resist UV-A with longer wavelength. UV-A is increasingly considered to be related to premature skin aging and skin cancer. The average particle size of zinc oxide of our company is less than 50 nm. It can most effectively resist UV-A and UV-B. it is a broad-spectrum anti UV agent, non-toxic and harmless. It is worthy of the name and fatigue to metal rubber