Xu Yongxian, a native of Sixian County, Anhui Province, now lives in Jiangmen City, Guangdong Province (EMBA of Jinan University)
Director of research on new silicon and fluorine materials and equipment industry in Guangdong (Heshan)
Secretary general, Dawan District Society for silicofluoroerganic materials
General manager of Shenzhen kejunchi Technology Co., Ltd
General manager of Jiangmen kejunchi new materials Co., Ltd
General manager of Guangdong Guolian Chemical Technology Information Center
Platinum catalyst industry benchmark - kejunchi
In the past 25 years, only one thing kejunchi has done is the research and development of platinum catalyst and sulfurizer. Unity and persistence are the soul of kejunchi company.
Nano-SiO2 is one of the most promising nano materials for industrial application. It has a wide range of applications, almost all of which are used in the original SiO2 powder industry. Nano silica has the advantages of small particle size, large specific surface area, good biocompatibility, and has the surface interface effect, small size effect, quantum size effect and so on. As a filler, it does not change the technological process, but only replaces the coarse-grained SiO2. The performance indexes of its products will be greatly improved, and the application of Nano-SiO2 is far more than that. However, the surface energy of Nano-SiO2 is high, which is in the state of thermodynamic instability. It is very easy to aggregate into a group, and it is not easy to fully mix with organic matters. At the same time, the surface of SiO2 is hydrophilic and oil repellent, which is difficult to evenly disperse in organic media, and the bonding force between the nano-SiO2 and organic matrix is poor, which is easy to cause interface defects and reduce the performance of composite materials. Figure 1 Schematic diagram of silica nanoparticles
In order to solve the problem of dispersion and compatibility of nano silica with organic matrix, it is necessary to modify its surface, weaken the polarity of silica surface, reduce the energy state of silica surface, and improve the compatibility between nano silica and organic matrix. Method 1: heat treatment method heat treatment can reduce the adsorption water on the surface of Nano-SiO2. This is because high temperature heating will promote the dehydration reaction of the hydrogen bond associated consecutive silicon hydroxyl to form a stable bond, resulting in the reduction of adsorption water. Although this method is economical and simple, the combination effect of nano silica and organics can not be improved by heat treatment. Therefore, the actual heat treatment process is usually to add zinc compounds at 200-400 ℃ for heat treatment, or to use silane and transition metal ions to treat nano silica before heat treatment.
Chemical modification methods the chemical methods of surface modification of nano silica can be divided into inorganic modification and organic modification. Inorganic modification usually uses titanium dioxide to cover nano silicon dioxide, while organic modification is the main method of nano silicon dioxide surface modification. (1) Among the coupling agent modification methods, silane coupling agent is the most widely used one. It can be condensed with hydroxyl groups on the surface of nano silica to form silica oxygen bond. When the coupling agent is used to modify the surface of nano silica, the coupling agent needs to be hydrolyzed before it can react with nano silica. However, the hydrolysate will self condense, which hinders the reaction between the hydrolysate and the hydroxyl group on the surface of silica, to a certain extent, reduces the coupling efficiency, and makes the surface modification of nano silica incomplete. (2) In order to change the surface wettability of silica, the alcohol ester modified method is to react aliphatic alcohol with hydroxyl groups on the surface of nano silica under high temperature and high pressure. Compared with the silane coupling agent method, the alcohol ester method has the advantages of low price, easy synthesis and structure control. However, the modification effect is affected by the alkyl chain length of alcohol, and it needs to be carried out at high temperature and high pressure, which requires high reaction conditions. (3) Polymer grafting modification can effectively improve the hydrophobicity of the particles and the interface affinity of the particles in the nanocomposites by grafting the polymer onto the surface of nano silica in a specific way. The long chain structure of the grafted polymer can produce chain entanglement with the matrix polymer, which makes the modification more uniform and compact. At the same time, different grafting monomers and grafting conditions can be selected according to the needs, which makes the modification more diverse and controllable. According to different grafting methods, nano silica modified by polymer grafting can be divided into "grafting to" and "grafting from". "Grafting to" method generally refers to covalently connecting the end functionalized polymer to the surface of nano silica. The "grafting from" rule is to use a large number of hydroxyl groups on the surface of nano-SiO2, first introduce the active points that can initiate polymerization, such as cations, anions or free radicals, into the surface of nano-SiO2, and then initiate the polymerization of surrounding monomers on the particle surface, so that the polymer grows on the surface of Nano-SiO2. The "grafting from" method introduced the polymer by in-situ grafting the prepolymer chain segment, and the steric hindrance did not limit the grafting growth of monomers with smaller active initiation sites, so it had higher grafting efficiency. However, in the process of composite with the material, the long chain polymer connected on the surface of Nano-SiO2 may entangle and reunite the adjacent SiO2, which is not conducive to its further dispersion in the polymer matrix. (4) In situ chemical modification can effectively reduce the agglomeration of nano-SiO2, but there is also the problem of agglomeration before modification. Therefore, it can be considered to complete the modification in the preparation process of nano silica to obtain the surface functionalized silica particles. Huang Fen et al. Used sol gel method to produce organosilicon modified nano silica particles in situ, and prepared TH1178-2 corona free solventless insulating paint with epoxy polyester. Compared with the direct doping nano silica, the modified nano silica particles in situ were dispersed more evenly without obvious agglomeration phenomenon, and the corona resistance of the prepared corona resistant varnish was better. Electrical and mechanical properties are better.
Application of Nano-SiO2 1: application researchers in ceramics add appropriate nano-SiO2 to ceramic products, which not only greatly reduces the brittleness of ceramic products, but also improves the toughness by several times or even dozens of times, and obviously improves the finish. Moreover, ceramics are fired at a lower temperature, thus improving the quality of ceramic products by several grades. The application of conventional SiO2 in the field of plastics as a reinforcing agent can improve the performance of plastics. The function of Nano-SiO2 is not only reinforcing, but also has many new properties. This is mainly to use nano-SiO2 for light transmission and small particle size, which can make plastics more compact. The addition of nano SiO2 in polystyrene plastic film can improve its transparency, strength and toughness, and its waterproof and anti-aging properties are also improved. The performance indexes of Nano-SiO2 modified PVC waterproof roll can reach or exceed EPDM waterproof roll. Application of Nano-SiO2 in the field of rubber new rubber not only has superior mechanical properties, but also can be designed according to the needs of new rubber with special. The nano-SiO2 in this new material not only has the function of reinforcing, but also has some functional characteristics that the conventional rubber does not have. In addition, the color tire can be produced by using nano-SiO2 modified tire side rubber. The application of Nano-SiO2 in coatings has strong UV and IR reflection characteristics. Therefore, it can form a shielding effect on the coating when added to the coating, so as to achieve the purpose of anti ultraviolet aging and thermal aging, and at the same time, increase the thermal insulation of the coating. In addition, nano-SiO2 also has a three-dimensional network structure, with a large specific surface area, showing great activity. It can form a network structure when the paint is dry, which not only increases the strength and finish of the paint, but also keeps the color of the paint unchanged for a long time. 5. In the field of textile, the composite powder with the proper ratio of nano-SiO2 and nano-TiO2 is an important additive of anti ultraviolet radiation fiber. The chemical fiber obtained by mixing nano-SiO2 and nano-TiO2 into the chemical fiber has the function of deodorization and air purification. Other applications in agriculture, the use of Nano-SiO2 to produce agricultural seed treatment agent, can make vegetables (cabbage, tomato, cucumber) cotton, corn, wheat increase yield, early maturity. In addition, nano-SiO2 has high surface energy and adsorption properties, good stability and biocompatibility, and can be used as a new sensor. The sunscreen modified by nano-SiO2 can shield up to 99% UV light, which has completely replaced the organic UV absorbers used in sunscreen. In addition, it also has important applications in electronic assembly materials, sealants, adhesives, functional fibers, catalysts and catalyst carriers, wood and environmental adsorption.