Nitrile rubber (NBR) is a random copolymer obtained by emulsion polymerization of two monomers of acrylonitrile and butadiene. Because of its good oil resistance, chemical reagent resistance, and heat resistance, it is widely used in all kinds of rubber oil resistant products. It is widely used in fields with special application requirements, such as oil-resistant seals, oil pipes, oil tank linings, printing rubber compounds, insulating backing plates, and high hardness rubber products.
Reinforcing and plasticizing system of nitrile rubber
Nitrile rubber can only be used after being reinforced. Carbon black is the most commonly used reinforcing filler. Compared with carbon black with large particle size, fine particle carbon black can effectively improve the strength and hardness, but the operability is not good. Therefore, carbon black can be used to obtain rubber materials with different application requirements; Silica is commonly used in light-colored products, but it has the problems of poor dispersion and easy agglomeration; In addition, the cost can be reduced and the processing performance can be improved by filling inorganic reinforcing agents such as calcium carbonate and talc powder. The increase of filler is beneficial to the improvement of oil resistance.
Nitrile rubber belongs to polar rubber. The selection of ester plasticizer is not only easy to be compatible, with but also helpful to improve its cold resistance. When used in an oil environment, polyester plasticizers with large molecular weight are usually used to reduce extraction and other problems.
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Protective system of nitrile rubber
The protective system can improve the aging resistance of rubber materials and prolong the service life of products. It is generally divided into physical protective agents and chemical protective agents. Because NBR macromolecular chain contains double bonds with high activity, it is easy to age in use . In the oil environment, on the one hand, it isolates oxygen and delays the occurrence of aging. On the other hand, the oxidizing substances contained in the oil will reduce the service performance of rubber. Guo Yongji and others believe that the performance decline process of nitrile rubber after oil immersion can be divided into three steps: initial adsorption, oil diffusion, and final oil leakage. The research shows that irregular small cracks appear on the rubber surface after oil aging; Tang Liwen found that the methane produced by antioxidant RD in the aging process is the main reason for the decline of insulation performance of transformer oil. Therefore, the material exchange a nd the formation of harmful substances during the aging process of hot oil are important reasons for the decline of NBR seal performance. Therefore, to improve the aging resistance of NBR in the oil-resistant formula, measures can be taken to increase the dosage of antioxidants or use reactive antioxidants.
Overview of acrylate rubber
Acrylate rubber (ACM) is a kind of rubber obtained by emulsion polymerization of alkyl acrylate (mainly ethyl ester, butyl ester) and a small amount of cross-linked monomer. Because of its excellent aging resistance and oil resistance, it is widely used in all kinds of high-temperature-resistant products in contact with oil. With the rapid dev development of the automobile industry in the half-century try, the continuous improvement of engine power and the miniaturization of hydraulic systems make heat accumulation serious. Moreover, with the restrictions on energy conservation and environmental protection, there are more and more components of various additives in oil products. It is difficult for traditional NBR seals to meet the increasingly stringent performance requirements, ACM is also increasingly used in key parts of engines and transmission devices with heat and oil resistance requirements, so it has won the reputation of “automobile rubber”. With the development of the polyme rization process and coordination system, ACM has been widely used in oil resistance and high-temperature resistance in more and more industries, even in the aerospace industry.
Mechanism of unsaturated acrylate reinforced rubber
Unsaturated metal salts will self polymerize under the initiation of peroxide, and some particles can be grafted onto the rubber molecular chain to participate in the cross-linking network of rubber. Metal cations will also form ionic bonds with carboxylate ions through electrostatic interaction through “bridging “. Under the action of external force, the ionic bond can slip and relax like a sulfur cross-linking bond. Due to higher bond energy, the strength of rubber material has been greatly improved, and the compression deformation and other properties of products will be improved accordingly. Through experiments and summarizing the previous research results, Lu Yonglai proposed that the self polymerization of nanoparticles is one of the reasons why CDMA can effectively strengthen rubber. In addition, the properties of vulcanizate will be affected by comprehensive factors such as crosslinking structure, the interaction between nanoparticles and rubber macromolecular chains, and crossl inking type. Nanoparticles in vulcanizate will be affected by physical adsorption and grafting to produce a chemical combinations.
Unsaturated metal salts have an excellent reinforcing effect on HNBR and EPDM, especially in improving the hardness without damaging the original rebound performance of rubber. They have high application value in rubber. Unsaturated metal salt/rubber composites can be added through the in-situ generation and direct addition. The in-situ generation method refers to adding monomers that can generate unsaturated metal salt in the mixing process, and “in-situ” reinforcing particles are generated in the rubber matrix at high temperatures and high speeds. It is difficult to realize industrial production because monomers are volatile at high temperatures, harmful to human health, and corrode equipment; The commercial unsaturated metal salt can be directly added to the rubber by mixing, so it is more convenient and fast.
Due to its low strength and poor tear performance, the application range of acrylate rubber has been greatly limited. The chemical modification method is not suitable for large-scale production, while the traditional carbon black reinforcement method is a common method in industrial production. Because the unsaturated metal salt and ACM belong to acrylic compounds with good compatibility, we use MMG to partially replace carbon black and form the structure of polymethylmethacrylate magnesium network acrylate rubber interpenetrating network, to improve the physical and mechanical properties and oil resistance of acrylate rubber.
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