A brief analysis of the application methods of cold resistance of fluorosilicone rubber
Fluorosilicone rubber is a polymer with a main chain formed by silicon-oxygen bonds and a trifluoroalkyl group on the guilium chain. Its polymerization method is similar to that of dimethyl silicone rubber, using cyclic siloxane to open the ring. Made by polymerization. The heat resistance and chemical resistance of fluorosilicone rubber are not as good as other fluorine rubbers, but because its main chain contains silicon-oxygen bonds and the side groups contain fluorine atoms, it has the advantages of both, so it can be used at -60°C It is used in a very wide temperature range of -200°C, has excellent fuel oil resistance, and has little swelling to methanol, but its disadvantage is that its physical and mechanical properties are worse than other fluororubbers.
In summary, the introduction of Si-O bonds, double bonds into the main chain, or the introduction of ether bonds into the side chains of molecules can improve the flexibility of macromolecules, thereby improving the cold resistance of fluorine rubber while retaining the properties of fluorine rubber. It has original characteristics, but its high price greatly limits its application and promotion. Therefore, while modifying the molecular chain to prepare new fluororubbers, it is also necessary to improve the cold resistance of a series of original lower-priced fluororubbers.
Rubber combined use
The combined use of fluorine rubber with some general rubber and special rubber can improve the shortcomings of fluorine rubber such as low elasticity, poor cold resistance, and high price, and obtain materials with excellent performance and low cost. Due to the structural characteristics of fluororubber, it is difficult to select a co-vulcanization system, and the unique characteristics of fluororubber will be partially reduced after combined use. Therefore, research on combined use is not extensive at home and abroad. Among them, fluororubber can improve The main combination systems for cold resistance are as follows.
Fluorine rubber/fluoroether rubber combined use
In order to improve the low-temperature performance of fluorine rubber, fluoroether rubber has been synthesized abroad in the early 1970s. Its low-temperature performance is significantly improved compared to fluorine rubber. For example, the Tg of VitonGLT fluoroether rubber is about 14°C lower than that of fluorine rubber F246, but Its price is higher. Beijing Aeronautical Materials Research Institute developed fluororubber FX-13 using rubber combined technology and a small amount of fluoroether rubber, which improved the cold resistance of fluororubber. Its brittleness temperature can reach -45°C, and its other physical and mechanical properties are excellent. The combined use of fluoroether rubber not only effectively improves the cold resistance of fluorocarbon rubber, but its price is also significantly lower than that of fluoroether rubber.
Fluorine rubber/ethylene propylene rubber combined use
Both ethylene-propylene rubber and ethylene-propylene diene rubber can be modified together with fluororubber, and the most researched one is the modification of tetrapropylene fluororubber. Compared with PTFE, ethylene-propylene rubber also has many excellent properties such as extremely high chemical stability, heat resistance, weather resistance, water resistance, water vapor resistance, chemical resistance, etc. However, its typical feature is that its resistance to polar media is relatively low. Good and excellent low temperature performance. Tetrapropylene fluoroelastomer is equivalent to a copolymer of fluorine substituted products of ethylene molecules and propylene. Therefore, the similarity in composition and structure between the two provides a basis for compatibility for their combined use. According to the data, the use of PTFE and binary or EPDM rubber can improve the cold resistance and elasticity of PTFE, improve processing performance and reduce material costs. However, due to the large difference in polarity between the two, rational solution to the co-vulcanization of the blend is the key to successful combination.
Combination of fluorine rubber/cis isoprene rubber
The combination of cis-1,4-polyisoprene and fluorine rubber with different structures can be used to produce rubber seals. In this type of combined rubber, as the ratio of fluorine rubber and isoprene rubber changes, the combined rubber can show different properties. When the fluororubber content is less than 50 parts, isoprene rubber is a continuous phase, and the combined rubber has good cold resistance, but its oil resistance is poor. This shortcoming can be improved by using appropriate vulcanization methods (such as dynamic vulcanization methods) . Using the dynamic vulcanization method, the oil resistance and cold resistance of the combined glue can be reasonably controlled.
Fluorine rubber/silicone rubber combined use
Silicone rubber refers to a type of linear polymer whose main molecular chain is -Si-O- bond, and the side groups are organic groups (mainly methyl). It is a polymer elasticity with both inorganic and organic properties. body.
Due to the particularity of its molecular structure, compared with other rubbers, silicone rubber has excellent heat resistance, elasticity, cold resistance, excellent mold release, electrical properties, air permeability, thermal conductivity, waterproofness and good temperature stability sex. By using silicone rubber and fluororubber together, you can obtain a compound rubber that has the characteristics of both, which can significantly improve the shortcomings of fluororubber's poor cold resistance and elasticity. For example, the JSR-JENIXF series of fluororubber/silicone rubber compounds developed by Japan Synthetic Rubber Company It has excellent heat resistance, cold resistance, oil resistance, water resistance and steam resistance, and the price is relatively low.
Add appropriate plasticizer
Plasticizer is the compounding agent that has the greatest impact on cold resistance in the formula design of cold-resistant rubber products, besides raw rubber. Research shows that adding plasticizers can increase the flexibility of rubber molecular chains, thereby improving the cold resistance of vulcanized rubber. Generally, adding a plasticizer with a lower freezing point can reduce the glass transition temperature of the vulcanized rubber; conversely, if the plasticizer has a higher freezing point temperature, the glass transition temperature of the vulcanized rubber can be increased. From the perspective of improving the cold resistance of vulcanized rubber, the selection of plasticizer must fully estimate the impact of the plasticizer on the glass transition temperature.
The type and amount of plasticizer are determined by the type of rubber and the cold resistance index of the product. Adding appropriate plasticizers to polar rubber with poor cold resistance reduces the interaction between polar rubber molecules through the interaction between the polar groups of the plasticizer and the polar groups in the polar rubber molecular chain. The force makes the molecular chain segments easy to move, so that better low-temperature performance can be obtained. However, for fluorine rubber, due to its highly stable molecular structure, ordinary plasticizers will not work on it. Moreover, the plasticizer will evaporate during the second-stage vulcanization process at 200-250°C, so it can be used The types of plasticizers in fluorine rubber are extremely limited: one is to use a low molecular weight fluorine-containing olefin copolymer, that is, fluorine wax, as a plasticizer for fluorine rubber. For example, in the combined system of isoprene rubber and fluororubber, if the pre-prepared low molecular plasticizer ΦNA (prepared by the mechanical degradation of isoprene rubber and fluororubber in a reactor with a special structure) is added, the combined use can be significantly improved. The cold resistance of glue. The other is to use fluorinated acid esters, such as fluorinated adipate, as plasticizers for fluorine rubber. Because this plasticizer contains fluorine in its molecular structure, it has good affinity with fluorine rubber, so it can improve the dispersion of compounding agents and the processing performance of rubber. However, its biggest advantage is in the physical and mechanical properties of vulcanized rubber. Without significant impact on performance, the cold resistance of fluororubber can be significantly improved, allowing fluororubber products to be used at temperatures of -50°C.
Choose the appropriate vulcanization system
The vulcanization systems used in fluorine rubber can currently be roughly divided into three categories: amines, phenols and organic peroxides. According to reports, for the F246 series of fluorine rubber produced by Sanaifu Company, when a single vulcanizing agent is used as the vulcanization system, whether amine, phenol or peroxide vulcanizing agents are used, the low-temperature performance of the fluorine rubber will be affected. It's not very obvious and the difference isn't huge. The effects of different fluororubber varieties and different vulcanization systems, as well as the use of different vulcanization methods on the cold resistance of fluororubber, remain to be further studied.
Choose the right filler
Generally speaking, adding fillers will not significantly change the glass transition temperature of rubber. The impact of fillers on the cold resistance of rubber depends on the structure formed after the interaction between fillers and rubber. Different physical adsorption bonds and strong chemical adsorption bonds will be formed between activated carbon black particles and rubber molecules, and a raw rubber adsorption layer (interface layer) will be formed on the surface of the carbon black particles. The performance of this interface layer is similar to that of glassy raw rubber. The properties are very similar, which limits the movement of the molecular chain, increases the glass transition temperature of the adsorbed raw rubber, and hinders the change of chain segment configuration. Therefore, you cannot expect to add fillers to improve the cold resistance of fluororubber.
Research on the cold resistance of existing fluororubber varieties and the development of new fluororubber with excellent cold resistance are of great significance for broadening the application fields of fluororubber and promoting the development of domestic sealing industry.
Fluorosilicone compound for transformers
