What Is Nanoparticle Zinc Oxide?

Nano-sized zinc oxide (ZnO) has a particle size between 1-100 nm and is a high-end high-function fine inorganic product that exhibits many special properties, such as non-migratory, fluorescent, piezoelectric, absorption and scattering Utilizing its wonderful properties in light, electricity, magnetism, sensitivity, etc., it can manufacture gas sensors, phosphors, rheostats, ultraviolet shielding materials, image recording materials, piezoelectric materials, varistor, high-efficiency catalysts, magnetic properties, etc. Materials and plastic films. Microscopic changes Many people can't see the excellent characteristics of nanomaterials. Through practice, nano zinc oxide is now more and more widely used in various fields such as rubber with its excellent characteristics.

Nano zinc oxide

Nano-sized zinc oxide (ZnO) has a particle size between 1-100 nm and is a high-end high-function fine inorganic product that exhibits many special properties, such as non-migratory, fluorescent, piezoelectric, absorption and scattering Ultraviolet power, etc., using its wonderful properties in light, electricity, magnetism, sensitivity, etc., can make gas sensors, phosphors, rheostats,

Zinc oxide is an electronic structure of a semiconductor catalyst. Under light irradiation, when a photon with a certain energy or a photon exceeding the semiconductor band gap energy Eg is incident on a semiconductor, an electron is excited from the valence band VB to the conduction band CB. And left a hole. The excited state conduction band electrons and valence band holes can be recombined to eliminate the input energy and heat. The electrons are captured on the surface state of the material. The valence electrons transition to the conduction band. Snatches to make hydroxyl groups become free radicals, as a strong oxidant to complete the degradation of organic matter (or chlorine), killing bacteria and viruses.

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 commercially available zinc oxides are mostly direct or indirect products, the particle size is micron, and the specific surface area is small. These properties greatly restrict their application fields and their performance in products.

Nano-zinc oxide uses 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. After multiple purifications, impurities in the raw materials are removed and then precipitated. Basic zinc carbonate, final baking, etc. to obtain nano zinc oxide. Compared with the previous technology for preparing nano-scale ultrafine zinc oxide, the new process has the following technological innovations:

1. Combining the principle of reaction kinetics with enhanced heat transfer technology under equilibrium conditions to quickly complete the baking 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. Typical green chemical process belongs to environmentally friendly process.

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

Tsinghua University Analytical and Testing Center analyzed the product using transmission electron microscopy. The nano zinc oxide particles are spherical and have a uniform particle size distribution, with an average particle size of 20-30 nanometers, and all particles have a particle size below 50 nanometers. Tested by specific surface and pore size analyzer, the BET specific surface area of nanometer zinc oxide powder is above 35m2 / g. In addition, by adjusting the preparation process parameters, rod-shaped nano zinc oxide can also be produced. This product has been tested and identified by the Institute of Microbiology, Chinese Academy of Sciences, and the results show that the addition of 0.5% to 1% of nano-sized zinc oxide in the rich bacterial culture medium can effectively inhibit the growth of E. coli with a bacteriostatic rate of more than 99.9%.

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Metal oxide powders such as zinc oxide, titanium dioxide, silicon dioxide, aluminum oxide, and magnesium oxide. When these powders are made into nanoscale, the size of the particles is equal to or smaller than the light wave, and the conduction band is caused by the size effect. And the interval of the valence band is increased, so the light absorption is significantly enhanced. Various powders have different differences in the shielding and reflection efficiency of light. Comparing zinc oxide and titanium dioxide, when the wavelength is less than 350 nanometers (UVB), the shielding efficiency of the two is similar, but at 350 to 400 nm (UVA), the shielding efficiency of zinc oxide is significantly higher than that of titanium dioxide. At the same time, the refractive index of zinc oxide (n = 1.9) is smaller than that of titanium dioxide (n = 2.6), and the diffuse reflectance to light is low, which makes the fiber more transparent and facilitates textile dyeing.

Effect of different specific surface area on rubber properties

The core index of nano zinc oxide is specific surface area. Products with different specific surface areas greatly affect the performance of rubber products. The following is the experimental data of a large tire factory load bias tire application.

There is a correlation between the physical properties and performance of rubber compounds and the specific surface area of the materials. From the point of view of the tensile strength of the rubber compound, the nanometer zinc oxide can obviously increase the fixed tensile strength of the rubber compound without substantially reducing the elongation. With the increase of the specific surface area of the material, this trend is obvious. But it is more obvious that the abrasion reduction of the rubber compound decreases and the compression fatigue temperature rise decreases. From this, it can be seen that when the specific surface area of the nano-sized zinc oxide reaches more than 80m2 / g, it can show the comprehensive performance that excellent ordinary zinc oxide does not have. Although the nano-zinc oxide with a specific surface area below 80m2 / g is also superior in general performance compared to ordinary zinc oxide, the gap is still more obvious than that above 80m2 / g.

Effect of Nanometer Zinc Oxide on Vulcanization Properties of Rubber Compound

Nano-zinc oxide has a greater impact on the vulcanization characteristics of the rubber compound. Due to the high specific surface activity, the crosslinking density of the rubber compound is increased, which is reflected in the increase in the large torque MH of the vulcanization curve and also in the increase of the 300% set strength on. In addition, the vulcanization curve tends to shift back in time as a whole, and both ts2 and t90 are delayed compared to ordinary zinc oxide. This delay effect varies with the degree of the formulation system, and the specific mechanism remains to be explored.

Effect on rubber material machine performance

Nano-zinc oxide is very obvious to improve the overall performance of the rubber material machine. In terms of tensile strength, 300% fixed tensile strength is increased by about 10%, and the elongation at break can be basically maintained. It has obvious advantages in reducing abrasion loss and improving abrasion resistance. The reduction in abrasion loss is more than 10%. This is due to the small size effect of nanomaterials to reinforce the rubber. This reinforcement is completely different from carbon black. Reinforcing, its elongation at break and elasticity are not reduced, which is technically ideal.

Effect on heat generation performance of rubber compounds

The temperature rise of compression fatigue of ordinary rubber is 48 , which reduces the heat generation by 25%, which is very obvious. This is very important for dynamic rubber products such as tires. This is due to the small size effect of nano-materials that reinforce the rubber and reduce the deformation of the rubber. Although carbon black reinforced rubber compound can also reduce the deformation of the rubber compound, its elasticity is reduced, and the hysteresis loss is increased, which leads to a sharp increase in heat generation. The nano zinc oxide reinforcement avoids the above disadvantages, so its heat generation is significantly reduced.

Nano-zinc oxide has a higher elastic modulus and lower hysteresis loss. This trend becomes more apparent as the specific surface area of the material increases. This is in good agreement with the results of the heat generation test and provides a longer service life for dynamic products such as tires. Got very good help. It should also be pointed out that this feature of nano zinc oxide is also reflected in the tire carcass rubber, but it is not as significant as the tread rubber. This is similar to the carcass formula itself, which has high elasticity, low hysteresis, low heat generation, and low carbon black filling It is related to the low structure. The reduction of heat generation in the carcass formula is about 10%.

Effect on rubber aging performance

The tensile strength and elongation at break of nano-zinc oxide compounds after hot air aging are significantly better than ordinary compounds, which may increase the cross-linking network density with the small size effect of nano-zinc oxide, and increase the The molecular material realizes the binding at the molecular level. At present, many rubber miscellaneous parts factories, especially the seals industry, welcome and attach great importance to the characteristics of nanometer zinc oxide.

For products such as tires that are dynamically used, the degradation of material properties due to thermal oxygen aging in use will eventually lead to product damage. Increasing the performance retention rate of materials under aging conditions, and ultimately delaying such damage, will extend the service life of products very important.

Impact on actual use of tires

The following is a set of data from tire factory applications of nanometer zinc oxide indoor mileage tests and actual road tests. The formula using nano zinc oxide is tire crown rubber, shoulder rubber, cushion rubber and outer rubber.

We know that zinc oxide, as an indispensable auxiliary for vulcanization systems, has a high filling amount, generally about 5 parts. Due to the large proportion of zinc oxide and the large filling amount, its effect on the rubber density is very large. The more dynamic products such as tires, the larger the weight, the greater the heat generation and rolling resistance, which are detrimental to the product's service life and energy consumption. Especially in modern society, people have raised high levels of product safety and environmental protection. Requirements. Recent analysis data of famous foreign brand tires show that the amount of zinc oxide used is far lower than the domestic average level, generally about 1.5-2 parts. However, in the past, this was not possible in China due to the backwardness of materials. Now the appearance of large-scale surface nanometer zinc oxide can be completely reduced to this level, which basically fills this gap. In addition, the reduction in use has a greater impact on the cost of the formula, making it possible to reduce costs through reduction in use.

The following is a set of data from two large tire factories that use nano zinc oxide for weight reduction in beveled tire tire formulations.

After 50% reduction of nano-zinc oxide, it has little change compared with non-reduction in terms of elongation performance, heat generation, aging, etc., and it is much better than ordinary zinc oxide. It is superior to reduction of wear reduction. The unreduced nano zinc oxide is far superior to the unreduced ordinary zinc oxide, and the mechanism of this needs to be explored. In terms of density, the density of the reduced nano-zinc oxide is significantly reduced. This greatly reduces the cost, reduces the overall weight of the product, and improves the performance. Therefore, it is recommended to reduce the use of nano-zinc oxide. The amount used is about 50% of ordinary zinc oxide, which depends on the formulation system of each plant. This reduced use is not only a cost requirement, but also a performance requirement.

National Standard of the People's Republic of China GB / T 19589-2004. ^[1]

At present, some breakthroughs have been made in the preparation technology of nano zinc oxide, and several industrialized manufacturers have been formed in China. However, the surface modification technology and application technology of nano-zinc oxide have not been fully matured, and the development of its application field has been greatly restricted, which has restricted the formation and development of the industry. Although we have made great progress in the application of nano zinc oxide in recent years, compared with the application level of developed countries and the potential application prospects of nano zinc oxide, much work remains to be done. How to overcome the bottleneck of nano zinc oxide surface treatment technology and accelerate its wide application in various fields has become an urgent problem faced by many nano zinc oxide manufacturers.