Around 1945, a series of silane coupling agents with typical structures were developed by companies such as United Carbon (UC) and Dow Corning; in 1955, UC company first proposed amino-containing silane coupling agents; from 1959 A series of modified amino silane coupling agents began to appear one after another; in the early 1960s, peroxy-containing silane coupling agents appeared, and in the late 1960s, silane coupling agents with diazo and azide structures appeared. In recent decades, with the development of glass fiber reinforced plastics, the research and development of various coupling agents has been promoted. The synthesis and application of modified aminosilane coupling agent, peroxysilane coupling agent and azidosilane coupling agent are the main achievements of this period.
my country began to develop silane coupling agents in the mid-1960s. First, the Institute of Chemistry, Chinese Academy of Sciences began to develop functional group silane coupling agents, and Nanjing University also began to develop functional group silane coupling agents. This article only describes the application of silane coupling agent in composite materials.
The application of silane coupling agent as surface modifier in metal anticorrosion pretreatment is its best application. In order to obtain a good anti-corrosion coating combined with the metal substrate, it is necessary to select a suitable coating system, formulate a reasonable coating process, and carry out strict surface pretreatment. There are currently 2 methods for surface pretreatment:
①The plasma polymerization method is used to deposit a layer of organic thin film on the metal surface, but the high cost of this method limits its popularization and application;
②Using an aqueous solution of organic silane coupling agent to deposit a thin layer of organic silane film on the metal surface. Since the silane coupling agent can form trihydroxy silanols after hydrolysis, the alcoholic hydroxyl groups can react with each other to form a cross-linked dense network hydrophobic film, because the surface of this film has organic functional groups that can react with the resin. Therefore, the adhesion of the paint film will be greatly improved, and the ability of anti-corrosion, anti-friction and impact resistance will also be improved.
In plastic research and production, a large number of inexpensive inorganic fillers (or reinforcing agents) are usually used. This not only increases the quality of the plastic and reduces the cost of the product, but also improves certain properties of the plastic product. However, due to the significant differences in chemical structure and physical form between inorganic fillers and organic polymers, the lack of affinity between the two often affects the mechanical properties and molding processability of plastic products. Through the chemical reaction or physical coating of the coupling agent and the inorganic filler, the surface of the filler is changed from hydrophilic to lipophilic, so as to achieve a close bond with the polymer and improve the strength, adhesion, electrical properties, hydrophobicity of the material. The performance and anti-aging performance are significantly improved.
Some people have used various silane coupling agents to treat the glass fiber surface. The results show that the coupling agent containing amino group has better surface treatment effect on glass fiber than the coupling agent without amino group, because the amino group of the coupling agent and additives And the amino group in the matrix has affinity, and together with the auxiliary agent for cross-linking, the interface of the composite material has good adhesion, but there is no such function without the amino group; the amino group can also interact with the grafted The acid anhydride functional group reacts to generate chemical bonds across the interface, which improves the bonding strength of the interface and improves the overall performance of the composite material.
The coupling agent has 2 groups with different properties. The inorganic-philic group can react with chemical groups on the surface of inorganic substances (such as glass, fly ash and other silicon-containing materials) to form strong chemical bonds; It can react with organic molecules or physically entangle, so that the interface between organic and inorganic materials can be chemically bonded, and the bonding strength can be greatly improved. But can the coupling agent "couple" 2 inorganic materials? Ma Yiping first made a useful attempt, painting marble with silane coupling agent, then smearing cement paste, and carrying out macroscopic mechanical properties test, measured the split The tensile strength is increased by 57% to 84%. Some people apply silane coupling agent solution on the surface of mortar and granite respectively, and then renew the mortar. The results show that the tensile strength can be increased by 38% and 23% respectively compared with that without coupling agent. Lots of chemical bonds.
The latest development of the role of coupling agents With the rapid development of high-performance and highly functional materials, coupling agents have entered a wider field of application. Therefore, silane coupling agent has become one of the indispensable auxiliaries in the silicone industry, composite material industry and polymer industry. At present, new products of silane coupling agents with different types and different characteristics have come out, enriching the family of silane coupling agents. US "Rubber and Plastics News" reports: Cromptonosi has developed a new silane coupling agent NXT. According to the company, the coupling agent has brought a major breakthrough in compounding technology for silica tire compounds.
The new generation of NXT silane coupling agent is a replacement product of the existing coupling agent. Filled in silica tread rubber, it can reduce the viscosity of the rubber compound, reduce the number of mixing stages, improve the processing performance of the rubber compound, and promote the dispersion of the reinforcing agent. Improve the dynamic mechanical properties of the compound. In addition, this coupling agent improves the aging resistance of the silica tread compound, prolongs the storage time of the compound, and reduces the content of volatile organic compounds in the finished tire. NXT coupling agent has been successfully developed for 7 years, but it was officially launched on the market on September 10, 2002. Due to the low fuel consumption, good traction, slip resistance and wear resistance of silica car tires, the annual sales growth rate of silica tires has reached more than 10%.
Therefore, the use of 100% silica tire tread compounds put forward new requirements for compounding technology. The main disadvantage of processing silica tire tread compounds is the need to repeatedly cool the compound in several stages of mixing, which increases the overall cost of the tire. When using Cromptonosi's NXT silane coupling agent, the tread compound can be prepared by a ~-stage mixing process. One-stage tread compound improves dynamic mechanical properties. The structure of the silane coupling agent is modified by the German Digosa Company, so that the modified silane coupling agent can be applied to the composite material to obtain better effect, and it has a better use in some aspects. The thiocyanopropyl triethoxysilane prepared by the company (Germany Digosa, trade name Si-264) is a kind of coupling agent for rubber, which is more efficient than the silane coupling agent bis-[3-(triethyl) Oxysilyl) propyl]-tetrasulfide (trade name Si-69 from Digosa, Germany) has more stable performance, and its advantage is that it is not easy to scorch the rubber. Silane coupling agent Si-264 is suitable for vulcanized rubber compound. It has multifunctional functions. It can also be used as reinforcing agent, coupling agent and plasticizer for processing, which can significantly improve the physical and processing properties of fillers.
