Introduction to special rubber materials -- Ethylene propylene rubber series

Introduction:
Ethylene propylene rubber [Ethylene Propylene Diene Monomer, EP (D) M; formerly called EPR in China] is a copolymer rubber molecular chain synthesized with ethylene and propylene as the basic monomers. According to the composition of monomer units, there are two types of EPDM and EPDM rubber. Ethylene propylene diene is a copolymer of ethylene and propylene, represented by EPM; Ethylene propylene diene monomer (EPDM) is a copolymer of ethylene, propylene and a small amount of non conjugated Diene third monomer, expressed in EPDM, and both are collectively referred to as Ethylene propylene rubber EP (D) M.
Most EPDM rubber on the market has only two third monomers: ethylenenenenebb norbornene (ENB) and Dicyclopentadiene (DCPD). ENB-EPDM has a fast sulfur content and high production efficiency. Although the sulfur content in DCPD-EPDM is relatively slow, the peroxide vulcanization rate is relatively fast.
The biggest difference between Ethylene propylene rubber and other general rubbers is that the Degree of unsaturation degree of the molecular chain is low. Taking EPDM and NR as examples, there are approximately 250 double bonds per 1000 carbon atoms on the NR molecular chain; However, the number of double bonds per 1000 carbon atoms on the EPDM molecular chain is only about 10. On the one hand, the chemical stability of EPDM is much better than that of NR. This is because during the vulcanization process, there will be many double bonds on the molecular chain of NR that are not used for sulfur cross-linking, and it is easy to be affected by external factors to cause the fracture and destruction of Chemical bond, which is also the main reason for the poor ozone resistance and weather resistance of NR. On the other hand, the vulcanization of EPDM is more difficult and slower than that of NR, and the required promotion dose for EPDM vulcanization is also higher than that of NR.
Because the main chain of Ethylene propylene rubber is composed of chemically stable saturated hydrocarbons, and only contains unsaturated double bonds in the side chain, it has excellent ozone resistance, heat resistance, aging resistance, good chemical resistance, electrical insulation, impact elasticity, low temperature performance, low density and high filling, hot water resistance and water vapor resistance. It can be widely used in automotive parts, building waterproof materials, wire and cable sheaths, heat resistant hose, tape Automotive seals and other products. As EPDM rubber diene is located on the side chain, it can not only use sulfur, but also maintain various characteristics of Ethylene propylene rubber, thus becoming the main variety of Ethylene propylene rubber and widely used, accounting for about 90% of Ethylene propylene rubber brand names. However, since the molecular chain of binary Ethylene propylene rubber does not contain double bonds, it cannot be vulcanized with sulfur, and can only be vulcanized with peroxide and other compounds that can produce free radical crosslinking, or radiation vulcanization, which limits its application, accounting for only about 10% of the total number of Ethylene propylene rubber brand names.

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