Heat resistance of fluororubber

Fluorine rubber is a type of rubber that contains fluorine atoms on the carbon atoms of the main or side chains. It has excellent high-temperature resistance, oxidation resistance, oil resistance, and chemical resistance, and is an indispensable high-temperature resistant elastomer material in modern industry. There are many varieties of fluororubber, at least 12 of which are classified according to their chemical composition as follows:

(1) Fluorinated olefin fluororubber

Vinylidene fluoride and trifluoroethylene copolymer, vinylidene fluoride and hexafluoropropene copolymer, vinylidene fluoride, tetrafluoroethylene and hexafluoropropene ternary copolymer, tetrafluoroethylene and propene copolymer, vinylidene fluoride and pentafluoropropene copolymer, vinylidene fluoride, tetrafluoroethylene and pentafluoropropene ternary copolymer

(2) Perfluoroether rubber

(3) Fluorinated phosphorus nitrile rubber

(4) Perfluoroalkyl triazine rubber

(5) Fluorosilicone rubber

In fluorine rubber, the heat resistance of perfluoroether rubber exceeds that of other fluorine rubbers, except for perfluorotriazine rubber. Because it has a perfluorinated structure, it has high heat resistance. Perfluoroether rubber still has working ability at 316 ℃, and can maintain good strength and elongation performance after thousands of hours in air at 260 ℃ and hundreds of hours at 288 ℃.

Heat resistance of silicone rubber

Silicone rubber is the rubber with the highest heat resistance rating among all rubbers. When silicone rubber undergoes thermal aging in air, it undergoes cross-linking, and its elongation at break decreases much more than its tensile strength. Silicone rubber has excellent resistance to dry hot air aging, but it is not resistant to damp heat aging. When there is excessive moisture in the air or sample, the vulcanizate will undergo strong degradation. After aging at 315 ℃ for 24 hours, the strength of the vulcanized rubber remained basically unchanged, but when the humidity was 180g/m2, the sample was damaged. In addition, silicone rubber can undergo strong degradation under airtight aging conditions with no air circulation, leading to deterioration in performance. The heat resistance of silicone rubber mainly depends on its molecular structure: methyl vinyl silicone rubber and methyl phenyl vinyl silicone rubber, with a maximum temperature of 250 ℃ for long-term use; However, the maximum temperature for long-term use of ethyl silicone rubber does not exceed 200 ℃. Among silicone rubber, borosilicate rubber has the best heat resistance. This silicone rubber can work for a long time at 350 ℃ and can be used for a short time at around 410 ℃.

Heat resistance of ethylene propylene rubber

Its heat resistance mainly depends on its unsaturation and the third monomer. The heat resistance of ethylene propylene diene rubber with low unsaturation is better than that of ethylene propylene diene rubber. The thermal aging behavior of the two in the air is completely different, with the degradation of ethylene propylene diene rubber being dominant, while the crosslinking of ethylene propylene diene rubber is dominant. As the content of the third monomer and propylene in EPDM rubber increases, its heat resistance decreases.

Heat resistance of butyl rubber

The heat resistance of resin cured butyl rubber mainly depends on its unsaturation, and the heat resistance increases with the increase of unsaturation. Mixing 15 to 20 parts by mass of chloroprene rubber or chlorosulfonated polyethylene in butyl rubber can improve its heat resistance. The general usage temperature of butyl rubber is not higher than 150 ℃, and only resin cured butyl rubber can work for a long time at 150 ℃ to 180 ℃. The heat resistance of chlorinated butyl rubber is related to the vulcanization system. Generally, chlorinated butyl rubber has a maximum temperature of 130 ℃ to 150 ℃ for long-term use, and 160 ℃ to 170 ℃ in the absence of air. Brominated butyl rubber has lower heat resistance than chlorinated butyl rubber.

Heat resistance of hydrogenated nitrile

Hydrogenated nitrile rubber (HNBR) has always been the most commonly used type of rubber in oil resistant rubber products, especially in sealing products, due to its good oil resistance and comprehensive performance. However, nitrile rubber belongs to the diene rubber category, with many double bonds on its molecular chain and high unsaturation, resulting in poor stability to heat and oxygen. The heat resistance of general nitrile rubber is not high, and the long-term use temperature is 100 ℃; Even using peroxide vulcanized nitrile rubber, its long-term use temperature can only be at 120 ℃, making it difficult to reach 150 ℃. The heat resistance of hydrogenated nitrile rubber can reach 175 ℃, which is superior to butyl rubber and ethylene propylene rubber, and is between acrylic rubber and fluororubber.

Heat resistance of acrylic rubber

Acrylate rubber is a rubber produced by copolymerization of ethyl acrylate or butyl acrylate with a small amount of 2-chloroethyl vinyl ether or acrylonitrile. Its heat resistance is higher than that of nitrile rubber and lower than that of fluorine rubber. The long-term (1000h) use temperature is 170 ℃, and the short-term (70h) use temperature can be increased to 200 ℃. During the thermal aging process, cross-linking reaction is usually dominant, resulting in an increase in tensile stress and hardness, and a decrease in tensile strength and elongation at break. However, some acrylic rubber undergoes degradation during thermal aging. Various types of acrylic rubber show little difference after aging at 150 ℃ for 70 hours. At 200 ℃, the vulcanizate based on Hycar401 ethyl acrylate rubber has the best heat resistance. The heat resistance of ethylene methyl acrylate rubber (trade name Varmc) developed by Dupont Company in the United States is second only to fluorine rubber and silicone rubber.

Heat resistance of chlorohydrin rubber

The molecular chain of chlorohydrin rubber is highly saturated, so it has good heat resistance. Its heat resistance is higher than that of nitrile rubber. In co chlorinated alcohol rubber (HCO), the heat resistance of the co chlorinated alcohol rubber decreases with the increase of ethylene oxide content. In the ternary copolymerization of epichlorohydrin, ethylene oxide, and allyl glycidyl ether, the heat resistance of the co chlorinated alcohol rubber increases with the increase of the weight of allyl glycidyl ether.