Synthetic rubber is a man-made material classified as an elastomer, a polymer with high elasticity that returns to its original shape after deformation. These polymers are synthesized in controlled environments, typically using monomers derived from petroleum byproducts. Synthetic rubber was developed to create materials with tailored properties that exceed the performance limitations of natural rubber in demanding applications. Precise control over the chemical structure during polymerization allows manufacturers to engineer products with targeted resistance to heat, chemicals, and mechanical stress, making them indispensable across modern industry.
Major Categories of Synthetic Rubber
The diversity of synthetic rubber is rooted in the specific monomers used during polymerization.
Styrene-Butadiene Rubber (SBR) is widely produced, formed by the copolymerization of styrene and 1,3-butadiene. This cost-effective material offers good abrasion resistance, making it a common choice for tire treads and high-wear applications.
Nitrile Rubber (NBR), or acrylonitrile-butadiene rubber, is a copolymer of butadiene and acrylonitrile. The percentage of acrylonitrile content controls the material’s resistance to hydrocarbon fluids and oils.
Polychloroprene, commonly known as Neoprene, is synthesized from the monomer chloroprene and was one of the earliest successful synthetic rubbers developed.
Ethylene Propylene Diene Monomer (EPDM) combines ethylene, propylene, and a diene component, resulting in a chemically saturated backbone structure. This structure provides environmental stability, while the diene allows for curing.
Butyl Rubber is produced by the copolymerization of isobutylene with a small amount of isoprene. This structure gives it extremely low permeability to gases, a highly valued property in certain applications.
Mechanical Strength and Flexibility
The mechanical performance of synthetic rubber describes its reaction to physical forces like pulling, tearing, and compression. Tensile strength, the maximum stress a material can withstand before breaking, varies widely among synthetic elastomers. For example, highly engineered synthetic polyisoprene can achieve tensile strengths comparable to natural rubber, sometimes exceeding 25 megapascals (MPa) after vulcanization.
Abrasion resistance measures how well the material resists wear caused by friction, a property often enhanced in compounds like SBR through reinforcing fillers such as carbon black. Vulcanization establishes chemical cross-links between polymer chains, providing elasticity and the ability to stretch without permanent deformation. Synthetic rubber can be engineered for a wide range of resilience, which is the material’s ability to absorb energy and quickly return to its original shape.
Compression set measures the material’s ability to recover its original thickness after sustained compressive load and temperature. Elastomers with a low compression set, such as silicone or fluorocarbon rubber, are used for sealing applications like gaskets and O-rings, where maintaining a tight seal is essential. The specific monomers and cross-linking density determine if the material is highly resilient (like polybutadiene) or possesses strong vibration-dampening qualities (like butyl rubber).
Resistance to Heat, Chemicals, and Environment
Synthetic rubber is engineered for chemical stability and environmental durability to withstand harsh operating conditions. Resistance to oils and solvents is a key property; Nitrile Rubber (NBR) is a classic example, where acrylonitrile groups provide a barrier against hydrocarbon fluids and greases. For extreme chemical environments involving aggressive fuels or strong acids, highly fluorinated elastomers, such as FKM (Fluoroelastomer), are used due to their nearly inert polymer backbone.
The thermal stability of synthetic rubbers spans a broad spectrum. Specialized silicone rubbers can operate continuously above 200°C, while silicone and fluorosilicone elastomers maintain flexibility down to approximately -50°C, preventing embrittlement. Conversely, materials like Hydrogenated Nitrile Rubber (HNBR) tolerate continuous temperatures up to 150°C in high-heat automotive applications.
Synthetic versions offer targeted resistance against environmental degradation from ozone and ultraviolet (UV) radiation. Ethylene Propylene Diene Monomer (EPDM) is highly stable against weathering and ozone exposure due to the absence of double bonds in its main polymer chain, making it ideal for outdoor seals and roofing membranes. Neoprene (polychloroprene) also possesses inherent flame-retardant properties, making it suitable for electrical cable jacketing and construction applications where fire safety is a concern.
How Synthetic Rubber Compares to Natural Rubber
Synthetic rubber provides property customization unattainable with natural rubber, which is derived from the Hevea brasiliensis tree. While natural rubber is valued for its exceptional tensile strength, elasticity, and high resilience, its molecular structure contains double bonds. This makes it susceptible to degradation from ozone, UV light, and petroleum-based oils and solvents.
Synthetic elastomers, as manufactured polymers, offer predictable and consistent quality. They excel in specialized resistance profiles, such as the oil resistance of NBR or the thermal stability of silicone rubber. The low gas permeability of butyl rubber, for example, is a property unmatched by natural rubber, making it the standard for tire inner tubes.
Natural rubber exhibits less heat buildup under dynamic stress, a benefit in large, high-performance tires that experience significant flexing. However, synthetic options are more resistant to aging and oxidation, contributing to a longer service life in industrial and outdoor settings. The choice between the two materials is driven by specific performance requirements, balancing the mechanical strength of natural rubber with the specialized environmental resistance of its synthetic counterparts.