Rubber is a highly elastic polymer material with reversible deformability. It remains elastic at room temperature, undergoes significant deformation under external force, and quickly returns to its original shape once the force is removed. This unique property makes rubber an indispensable basic material in modern industry.

Generally speaking, rubber can be divided into two major categories: Natural Rubber and Synthetic Rubber.

I. Natural Rubber

Natural rubber is primarily derived from the rubber tree (Hevea brasiliensis). Its basic chemical composition is cis-1,4-polyisoprene. It possesses excellent elasticity, high strength, good electrical insulation, and easy processability. However, its disadvantages include poor temperature resistance, susceptibility to aging, and poor oil resistance.

Natural rubber has a service temperature range of approximately –60°C to +80°C and is generally used in the manufacture of tires, hoses, conveyor belts, vibration-damping components, and more.

II. Synthetic Rubber

Synthetic rubber is produced by artificial synthesis, and different monomers can be polymerized to yield various types of rubber. Since Russian chemist Lebedev first synthesized sodium-butadiene rubber using metallic sodium as an initiator in 1910, the variety of synthetic rubbers has continued to expand, and their production volume now far exceeds that of natural rubber.

Synthetic rubbers are generally classified into general-purpose rubbers and specialty rubbers based on their applications and performance characteristics.

1. General-Purpose Rubbers

General-purpose rubbers are those that can partially or completely replace natural rubber in various applications. They are produced in large quantities and represent the main varieties of synthetic rubber.

Chloroprene Rubber (CR): A polymer produced by emulsion polymerization of chloroprene as the monomer. It offers excellent aging resistance, ozone resistance, flame retardancy, and better oil resistance than natural rubber. Its disadvantages are poor cold resistance and low electrical insulation properties. It is commonly used in cable sheathing, oil-resistant hoses, seals, and flame-resistant rubber products.

Ethylene-Propylene Rubber (EPDM): Synthesized from ethylene and propylene as the main raw materials, EPDM exhibits outstanding aging resistance, ozone resistance, and electrical insulation. It has good chemical stability and can be heavily extended with oils and carbon black to reduce costs. It is widely used in tire sidewalls, automotive parts, wire and cable jacketing, and high-voltage insulation materials.

Styrene-Butadiene Rubber (SBR): A copolymer of butadiene and styrene. It is the highest-volume general-purpose synthetic rubber. It offers superior abrasion resistance, aging resistance, and heat resistance compared to natural rubber, but has inferior elasticity and tear strength, poor processability—particularly poor self-adhesion and low green strength. It is mainly used as a substitute for natural rubber in tires, rubber sheets, hoses, rubber footwear, and other general-purpose products.

Polybutadiene Rubber (BR): A cis-structure rubber polymerized from butadiene. It exhibits exceptional cold resistance, abrasion resistance, and resilience, with low heat generation under dynamic loading. Its drawbacks include poor tear strength and low wet-grip performance. The vast majority is used in tire treads, as well as in conveyor belts and specialty cold-resistant products.

2. Specialty Rubbers

Specialty rubbers refer to those with exceptional properties—such as high-temperature resistance, oil resistance, ozone resistance, or high gas impermeability—that make them suitable for specialized applications. Although their production volumes are smaller, they are indispensable in certain fields.

Nitrile Rubber (NBR): A copolymer of butadiene and acrylonitrile. It exhibits excellent oil resistance, along with good abrasion resistance, heat resistance, and adhesive strength. Its drawback is low electrical insulation properties. It is mainly used in oil-resistant seals, oil hoses, gaskets, and can also be used in oil-resistant hoses, conveyor belts, rubber rollers, vacuum hoses, vibration-damping products, and textile components.

Silicone Rubber (MVQ): A specialty rubber whose backbone contains silicon and oxygen atoms. Its service temperature range spans from –100°C to 300°C, making it the best cold-resistant and heat-resistant rubber available. It also features excellent weatherability, ozone resistance, and electrical insulation. Its disadvantages are low strength and poor tear resistance. It is used in high- and low-temperature resistant products (hoses, seals, etc.) and high-temperature wire and cable insulation. Because it is non-toxic and odorless, it is also used in the food and medical industries.

Fluororubber (FKM): An organic elastomer copolymerized from fluorine-containing monomers, with heat resistance up to 300°C. It exhibits excellent resistance to heat, oils, oxidation, and chemicals. It is mainly used in the aerospace, chemical, petroleum, and automotive industries as sealing materials and media-resistant components.

Chlorosulfonated Polyethylene Rubber (CSM): An elastic polymer obtained by chlorination and sulfonation of polyethylene. It offers excellent resistance to oils, heat, oxidation, weathering, corrosion, and flame. Its disadvantages are poor tear resistance and poor processability. It is commonly used in corrosion-resistant pipes, conveyor belts, seals, and as anti-corrosion coatings for bridges, containers, and other structures.

Acrylate Rubber (ACM/AEM): A polymer of ethyl acrylate or butyl acrylate. It is renowned for its excellent high-temperature resistance, oil resistance, and weatherability, offering high cost-effectiveness and earning the nickname "automotive rubber." Its disadvantages include poor cold resistance, poor water resistance, poor resistance to steam and organic/inorganic acids and alkalis. It swells significantly in water-soluble fluids such as methanol, ethylene glycol, ketones, and esters. Additionally, it has poor elasticity, poor abrasion resistance, low electrical insulation, and poor processability. It is particularly suitable for various automotive oil seals (such as crankshaft seals and transmission seals) and is widely used in the automotive field.

Epichlorohydrin Rubber (CO/ECO): A polymer obtained by homopolymerization of epichlorohydrin or copolymerization of epichlorohydrin with ethylene oxide. It offers a balanced combination of oil resistance, heat resistance, cold resistance, and ozone resistance, and its gas impermeability is outstanding—three times that of butyl rubber. Its disadvantages include low mechanical strength, poor abrasion resistance, poor water resistance, and susceptibility to deformation under high temperature and pressure. It is commonly used in automotive fuel hoses, intake hoses, seals, diaphragms, and more.

Conclusion

The world of rubber is far richer than we might imagine. From the general-purpose performance of natural rubber, to the large-scale applications of general-purpose synthetic rubbers, to the irreplaceable role of specialty rubbers in harsh environments—each type of rubber has its own distinct "personality" and suitable application scenarios. Understanding these classifications helps in making more appropriate material choices in engineering design and everyday life.