Exploration and research report of NR molecular chains
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2022-09-22 14:02
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The biggest difference between ethylene propylene rubber and other general-purpose rubbers is the low unsaturation of the molecular chains. Taking EPDM and NR as examples, there are about 250 double bonds per 1000 carbon atoms on the NR molecular chain. However, the number of double bonds per 1000 carbon atoms in the EPDM molecular chain is only about 10. This leads to the fact that the chemical stability of EPDM is much superior to that of NR, because in the process of vulcanization, there will be many double bonds on the NR molecular chain that are not used by sulfur cross-linking, which is easy to be broken and damaged by external factors, which is also the main reason for the poor ozone and weather resistance of NR. On the other hand, the vulcanization of EPDM is more difficult and slower than that of NR, and the amount of boosting dose required for vulcanization of EPDM is also higher than that of NR.
Because the main chain is composed of chemically stable saturated hydrocarbons, ethylene propylene rubber only contains unsaturated double bonds in the side chain, so it has excellent ozone resistance, heat resistance, aging resistance, good chemical resistance, electrical insulation performance, impact elasticity, low temperature performance, low density and high filling, hot water resistance and water vapor resistance, etc., can be widely used in automotive parts, waterproof materials for construction, wire and cable sheaths, heat-resistant hoses, tapes, automotive seals and other products. Because EPDM diene is located on the side chain, it can not only be used for sulfur and sulfur, but also maintains various characteristics of EPDM rubber, so that it has become the main variety of EPDM rubber and has been widely used, accounting for about 90% of the EPDM brand name. However, due to the fact that the molecular chain does not contain double bonds, dibasic ethylene propylene rubber cannot be sulfurized with sulfur, and can only be vulcanized with compounds such as peroxide that can produce free radical cross-linking, or radiation vulcanization, which limits its application, accounting for only about 10% of the total number of EPDM brands.
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