What is the chemical structure of Fluoroelastomer?
Fluoroelastomers are a class of synthetic rubbers known for their outstanding resistance to heat, chemicals, and fuels. As a trusted supplier of fluoroelastomers, I am often asked about the chemical structure of these remarkable materials. Understanding the chemical structure is crucial as it directly influences the physical and chemical properties of fluoroelastomers, making them suitable for a wide range of applications.
Basic Chemical Composition
Fluoroelastomers are based on polymers that contain fluorine atoms. The presence of fluorine is what gives fluoroelastomers their unique properties. The most common monomers used in the synthesis of fluoroelastomers are vinylidene fluoride (VDF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), and perfluoromethyl vinyl ether (PMVE).
Vinylidene fluoride (VDF) has the chemical formula CH₂=CF₂. It is a key monomer in many fluoroelastomers because it provides flexibility and reactivity. When polymerized, the double - bond in VDF breaks, and the monomers link together to form a polymer chain. The hydrogen atoms on the VDF monomer can also participate in certain chemical reactions during the vulcanization process.
Hexafluoropropylene (HFP), with the formula CF₃CF=CF₂, is another important monomer. It is used to introduce branching and irregularity into the polymer chain. This helps to lower the glass - transition temperature (Tg) of the fluoroelastomer, making it more flexible at lower temperatures. The presence of the trifluoromethyl group (-CF₃) in HFP also contributes to the chemical resistance of the fluoroelastomer.
Tetrafluoroethylene (TFE), CF₂=CF₂, is a highly fluorinated monomer. When incorporated into the polymer chain, it increases the chemical and thermal stability of the fluoroelastomer. TFE - based segments in the polymer are very resistant to oxidation, hydrolysis, and attack by most chemicals.
Perfluoromethyl vinyl ether (PMVE), CF₂=CFOCF₃, is often used in high - performance fluoroelastomers. It imparts excellent low - temperature flexibility and chemical resistance. The ether linkage in PMVE provides some degree of internal rotation, which helps to maintain the mobility of the polymer chains at low temperatures.
Polymer Structures
There are different types of polymer structures in fluoroelastomers, mainly classified into copolymers and terpolymers.
Copolymers
The most common copolymer is the VDF - HFP copolymer. In this copolymer, the VDF and HFP monomers are randomly arranged along the polymer chain. The ratio of VDF to HFP can vary, which affects the properties of the fluoroelastomer. A higher VDF content generally results in better mechanical properties and lower cost, but may reduce the chemical resistance and low - temperature flexibility. Conversely, a higher HFP content improves the low - temperature performance and chemical resistance but may increase the cost.
Terpolymers
Terpolymers are made by polymerizing three different monomers. For example, the VDF - HFP - TFE terpolymer combines the advantages of all three monomers. The VDF provides flexibility and reactivity, HFP introduces branching and low - temperature flexibility, and TFE enhances the chemical and thermal stability. Another important terpolymer is the VDF - TFE - PMVE terpolymer, which offers excellent low - temperature performance, chemical resistance, and compression set resistance.
Cross - Linking Structures
To transform the raw fluoroelastomer polymer into a useful rubber material, a cross - linking or vulcanization process is required. There are two main types of vulcanization methods for fluoroelastomers: bisphenol vulcanization and peroxy vulcanization.
Bisphenol Vulcanization
In bisphenol vulcanization, a bisphenol compound is used as the cross - linking agent. The bisphenol reacts with the fluoropolymer chains in the presence of a curing agent, usually a quaternary ammonium or phosphonium salt. During the vulcanization process, the bisphenol forms covalent bonds between the polymer chains, creating a three - dimensional network structure. This network structure gives the fluoroelastomer its elasticity, strength, and resistance to deformation. The Bisphenol Vulcanized Fluororubber Raw Rubber produced by this method has good compression set resistance and mechanical properties, and is suitable for a wide range of applications, such as seals and gaskets in automotive and industrial equipment.
Peroxy Vulcanization
Peroxy vulcanization uses organic peroxides as the cross - linking agents. The peroxide decomposes at elevated temperatures to generate free radicals. These free radicals abstract hydrogen atoms from the fluoropolymer chains, creating polymer radicals. The polymer radicals then react with each other to form cross - links between the chains. Peroxy - vulcanized fluoroelastomers have excellent chemical resistance, especially to amines and hot water. They also have better high - temperature performance and lower compression set compared to bisphenol - vulcanized fluoroelastomers. Our Peroxy Vulcanized Fluororubber Raw Rubber is widely used in applications where high - performance sealing is required, such as in aerospace and chemical processing industries.
Influence of Chemical Structure on Properties
The chemical structure of fluoroelastomers has a profound impact on their properties.
Thermal Resistance
The high fluorine content and the stable carbon - fluorine (C - F) bonds in fluoroelastomers contribute to their excellent thermal resistance. The C - F bond is very strong, with a high bond energy, which makes it difficult to break at high temperatures. The presence of TFE in the polymer structure further enhances the thermal stability. Fluoroelastomers can typically withstand continuous use at temperatures up to 200 - 300°C, depending on the specific formulation.
Chemical Resistance
The fluorine atoms in fluoroelastomers create a protective shield around the polymer chains. This shield repels most chemicals, preventing them from attacking the polymer. The highly fluorinated segments, such as those derived from TFE and HFP, are particularly resistant to acids, bases, solvents, and fuels. The cross - linking structure also plays a role in chemical resistance. A well - cross - linked fluoroelastomer has a more compact structure, which further reduces the penetration of chemicals.
Mechanical Properties
The mechanical properties of fluoroelastomers, such as hardness, tensile strength, and elongation at break, are influenced by the polymer structure and cross - linking density. The flexibility of the polymer chains, determined by the monomer composition (e.g., the presence of HFP or PMVE for low - temperature flexibility), affects the elongation at break. The cross - linking density affects the hardness and tensile strength. A higher cross - linking density generally results in higher hardness and tensile strength but lower elongation at break.
Applications Based on Chemical Structure
Due to their unique chemical structure and properties, fluoroelastomers are widely used in various industries.
In the automotive industry, fluoroelastomers are used for seals, gaskets, and O - rings in engines, transmissions, and fuel systems. Their excellent thermal and chemical resistance make them suitable for withstanding the high temperatures and harsh chemicals in these applications.
In the aerospace industry, fluoroelastomers are used in aircraft engines, hydraulic systems, and fuel lines. Their high - temperature performance and resistance to aviation fuels and hydraulic fluids are essential for ensuring the safety and reliability of aircraft.
In the chemical processing industry, fluoroelastomers are used in pumps, valves, and pipes to handle corrosive chemicals. Their chemical resistance allows them to maintain their integrity in contact with strong acids, bases, and solvents.
Conclusion
As a supplier of fluoroelastomers, I understand the importance of the chemical structure in determining the properties and applications of these materials. The unique combination of fluorinated monomers and cross - linking methods gives fluoroelastomers their outstanding thermal, chemical, and mechanical properties. Whether you need Bisphenol Vulcanized Fluororubber Raw Rubber for general - purpose applications or Peroxy Vulcanized Fluororubber Raw Rubber for high - performance applications, we can provide you with the right product. If you are interested in purchasing fluoroelastomers for your specific application, please feel free to contact us for further discussion and procurement negotiation.
References
- "Fluoroelastomers" in Kirk - Othmer Encyclopedia of Chemical Technology.
- Moore, D. R. "Rubber Technology", Chapman & Hall, 1995.
- Wypych, G. "Handbook of Polymeric Materials and Their Suppliers", ChemTec Publishing, 2004.