Main properties of ethylene propylene diene monomer rubber

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The main properties of EPDM rubber: EPDM rubber is an extremely important raw material in the rubber products industry. EPDM can be further divided into binary EPDM, terpolymer EPDM, modified EPDM, and thermoplastic EPDM. Ethylene propylene diene monomer rubber (EPDM) has been widely used in the automotive sealing strip industry. In 2003, China’s consumption of synthetic rubber reached around 1.13 million tons, of which 20,400 tons were used for ethylene propylene diene monomer rubber, accounting for only 1.8% of the total synthetic rubber consumption. In recent years, the growth rate of global synthetic rubber production capacity has slowed down. Although the production and consumption of EPDM have seen some increase, the growth rate is not high, at around 3.8% per year on average. The growth in domestic consumption of EPDM is also modest; according to forecasts, the use of EPDM in automotive parts (excluding tire products) in 2004 will be only between 10,000 and 12,000 tons. However, EPDM has become the primary material in the production of rubber sealing strips for use in vehicles in China, and its development and application hold broad market prospects. The main properties of EPDM are as follows: 1. Low density and high fillability – EPDM is a rubber with a relatively low density, at 0.87. Furthermore, the ability to add large amounts of oil and fillers allows for reduced costs of rubber products, compensating for the high price of EPDM raw material. Moreover, in the case of EPDM with a high Mooney value, the physical and mechanical properties do not decline significantly even after high levels of filling are used. 2. Aging resistance: EPDM rubber possesses excellent resistance to weathering, ozone, heat, acids and alkalis, water vapor, color stability, electrical properties, oil absorption, and flowability at room temperature. EPDM products can be used for extended periods at 120°C, and can be used for short periods or intermittently at 150–200°C. Adding appropriate anti-aging agents can increase its operating temperature. Polyethylenepropylene rubber cross-linked with peroxides can be used under more severe conditions. EPDM can remain crack-free for over 150 hours under conditions of an ozone concentration of 50 pphm and a 30% strain. 3. Corrosion resistance: Due to the lack of polarity and low degree of unsaturation in EPDM, it exhibits good resistance to various polar chemicals such as alcohols, acids, bases, oxidizers, refrigerants, detergents, animal and vegetable oils, and waxes ； However, it has poor stability in aliphatic and aromatic solvents (such as gasoline, benzene, etc.) as well as mineral oils. Performance also declines under the long-term effect of concentrated acids. 4. Resistance to water vapor: EPDM exhibits excellent resistance to water vapor, and this property is even better than its heat resistance. In superheated steam at 230°C, there was no change in appearance after nearly 100 hours. Under the same conditions, fluororubber, silicone rubber, fluorosilicone rubber, butyl rubber, nitrile rubber, and natural rubber exhibit significant visual degradation after a shorter period of time. 5. Resistance to hot water: EPDM also exhibits good resistance to hot water, but this property is closely related to the vulcanization system used. EPDM using dithiodi**rine and TMTD as sulfurization systems showed very little change in its mechanical properties after being immersed in superheated water at 125°C for 15 months, with a volume expansion rate of only 0.3%. 6. Electrical properties: EPDM possesses excellent electrical insulation properties and corona resistance, with electrical performance that is superior to or comparable to that of SBR, chlorosulfonated polyethylene, polyethylene, and cross-linked polyethylene. 7. Elasticity: Due to the absence of polar substituents in the molecular structure of EPDM, its intermolecular cohesive energy is low, allowing the molecular chains to remain flexible over a wide range; this property is second only to that of natural rubber and cis-butadiene rubber, and it is maintained even at low temperatures. 8. Adhesiveness: Due to the lack of active groups in its molecular structure, EPDM has low cohesive energy; moreover, the rubber compound tends to frost over, resulting in poor self-adhesiveness and inter-adhesiveness. Ethylene Propylene Diene Monomer (EPDM). Chinese name: Ethylene Propylene Diene Monomer. Introduction to EPDM: EPDM is a terpolymer of ethylene, propylene, and a non-conjugated diene. Its commercial production began in 1963. The global consumption volume each year is 800,000 tons. The most prominent feature of EPDM is its excellent resistance to oxidation, ozone, and corrosion. Since EPDM belongs to the polyolefin family, it possesses excellent vulcanization properties. Of all rubbers, EPDM has the lowest specific gravity. It can absorb large amounts of filler and oil with little effect on its properties. Therefore, rubber compounds with low production costs can be manufactured. Molecular Structure and Properties: EPDM is a terpolymer of ethylene, propylene, and a non-conjugated diene. Dienes have a special structure, allowing only one of their double bonds to participate in copolymerization, with the unsaturated double bond serving primarily as a cross-linking site. The other unsaturated group will not become part of the polymer’s main chain; it will only serve as a side chain. The main polymer chains of EPDM are completely saturated. This property enables EPDM to resist heat, light, oxygen, and especially ozone. EPDM is essentially non-polar, resistant to polar solutions and chemicals, has a low water absorption rate, and exhibits excellent insulating properties. During the production of EPDM, its properties can be adjusted by changing the amounts of the three monomers, the ethylene-to-propylene ratio, the molecular weight and its distribution, as well as the vulcanization method. Selection of the third monomer for EPDM: Monomers of the third diene type are obtained through the copolymerization of ethylene and propylene, thereby introducing unsaturation into the polymer to enable vulcanization. The selection of the third monomer must meet the following requirements: at most two bonds – one that can be polymerized and one that can be vulcanized; the reaction should be similar to that of two basic monomers; random polymerization of the bonds should result in a uniform distribution; it should have sufficient volatility to allow for its removal from the polymer; and the vulcanization rate of the final polymer should be appropriate. The type and amount of dienes affect the properties of the polymer. In the production of EPDM, ENB and DCPD are primarily used. The most widely used type in EPDM is ENB, which cures much faster than DCPD products. Under the same polymerization conditions, the nature of the third monomer influences long-chain branching, in the following increasing order: EPM