Ethylene-propylene rubber

About Ethylene propylene rubber

Ethylene-propylene rubber has developed very rapidly since the 1960s and is the fastest growing category of synthetic rubber. Its output and consumption both rank third among synthetic rubber varieties in the world.

Depending on the number of comonomers, ethylene-propylene rubber is divided into binary ethylene-propylene rubber and ethylene-propylene diene monomer (EPDM). These two types of rubber are collectively called ethylene-propylene rubber. Ethylene propylene rubber is a copolymer of ethylene and propylene. Since its molecular chain does not contain cross-linkable double bonds, it cannot be vulcanized, which limits its application.

Among the grades of ethylene-propylene rubber, binary ethylene-propylene rubber only accounts for about 10% of the total. EPDM rubber is copolymerized from ethylene, propylene and a small amount of non-conjugated diene as monomers. Since the double bond used for cross-linking on the EPDM rubber molecular chain is located on the side chain, this double bond provides a reaction point for vulcanization without affecting the main chain of saturated hydrocarbons (does not contain double bonds). It has been widely used and accounts for about 90% of ethylene-propylene rubber grades.

Ethylene-propylene rubber is synthesized using a coordination copolymerization mechanism, using a vanadium-aluminum complex initiator. On the main chain of the copolymer molecule, the ethylene and propylene monomers are arranged randomly, and pure ethylene segments or pure propylene segments are lost. The regularity makes the copolymer very flexible and can be used as an elastomer.

Typical high elasticity and good comprehensive performance binary, EPDM rubber, the ethylene content is 45%-70% (mole fraction). Studies have shown that the length of the ethylene segment ‹CH2-CH2›X , when Industrially common ethylene-propylene rubber has an ethylene content of 45%-70%. Tg=-50°C The melting point of ethylene-propylene rubber is mainly reflected in the melting point of the ethylene segment, and the temperature range of different varieties can be as wide as 70 -120°C.It is generally believed that only by controlling the ethylene content at around 60% can we obtain better processing performance and vulcanized rubber performance. When the propylene content is higher, the low-temperature properties of ethylene-propylene rubber are improved. When the ethylene content is high, it is easy to extrude, the extrusion surface is smooth, and the extruded parts are not easily deformed after being parked.

Ethylene-propylene rubber is a binary or ternary copolymer, and its performance is related to factors such as the type and amount of comonomers, the copolymer composition and its structural unit sequence distribution, molecular weight and distribution, and other factors. The structural composition of ethylene-propylene rubber depends largely on the reactivity rate of ethylene and propylene, which is closely related to the structure of the initiator and the polymerization temperature.

EPDM

The weight average molecular weight of ethylene propylene rubber is 200,000-400,000, the number average molecular weight is 40,000-200,000, the viscosity average molecular weight is 100,000-400,000, and the molecular weight distribution index is generally 2-5, mostly around 3, and the highest 8-9. Closely related to Mooney viscosity value. As the Mooney viscosity value increases, the filling amount can also increase, and the tensile strength and resilience of the vulcanized ethylene-propylene rubber increase, but the processing performance can become worse. EPDM rubber with a bimodal molecular weight distribution has been developed. Improved physical and mechanical properties, good stiffness after extrusion, and good fluidity.

In the electrical and electronics industry, ethylene-propylene rubber is mainly used for its excellent electrical insulation, weather resistance and corrosion resistance. For example, ethylene-propylene rubber is used to produce cables, and submarine cables use EPDM instead of PVC/NBR to make the insulation layer of cables. Improves the insulation performance and service life of the cable. Ethylene-propylene rubber is also widely used in transformer insulation pads and electronic insulation sheaths.