What Is Ethylene Propylene Rubber?

Ethylene-propylene rubber is a synthetic rubber with ethylene and propylene as the main monomers. Depending on the composition of the monomers in the molecular chain, there are two types of ethylene-propylene rubber and three-component ethylene-propylene rubber. The former is a copolymer of ethylene and propylene. Expressed as EPM, the latter is a copolymer of ethylene, propylene, and a small amount of a non-conjugated diene tertiary monomer, expressed as EPDM. Both are collectively referred to as ethylene propylene rubber, or ethylene propylene rubber (EPR). Widely used in automotive parts, waterproofing materials for construction, wire and cable jackets, heat-resistant rubber hoses, tapes, automotive seals, lubricant additives and other products.

Chinese name: Ethylene propylene rubber
English name: Ethylene propylene rubber

nickname: EPR
Belong to: Synthetic rubber

Brief introduction of ethylene propylene rubber

Ethylene-propylene rubber is a copolymer of ethylene and propylene-based monomers. According to the composition of the monomer units in the rubber molecular chain, there are two types of ethylene-propylene rubber and ethylene-propylene rubber. The former is a copolymer of ethylene and propylene, represented by EPM; the latter is a copolymer of ethylene, propylene, and a small amount of a non-conjugated diene third monomer, represented by EPDM. The two are collectively referred to as ethylene propylene rubber [ EPR]. Since the ethylene-propylene rubber does not contain double bonds and cannot be vulcanized with sulfur, its application is limited. It only accounts for about 15% to 20% of the total number of ethylene-propylene rubber brands. The chain contains diolefins, so it can not only be vulcanized with sulfur, but also maintain the various characteristics of ethylene-propylene rubber, thus becoming the main variety of ethylene-propylene rubber and widely used, accounting for 80% of the ethylene-propylene rubber trade brands. % To 85%.

Ethylene-propylene rubber has a main chain composed of chemically stable saturated hydrocarbons, so it has excellent aging resistance such as ozone, heat resistance, and weather resistance. It has good chemical resistance, electrical insulation properties, impact elasticity, low temperature performance, and low density. With high filling properties, hot water resistance and water vapor resistance, it can be widely used in automotive parts, waterproof materials for construction, wire and cable jackets, heat resistant hoses, tapes, automotive seals, and lubricant modification.

In the 1850s, Nata and Montecatini (Italy) used ethylene and propylene as raw materials and adopted a Ziegler-Natta type catalytic system (that is, an organometallic compound and a transition metal halide) for coordination copolymerization. First, they were successfully synthesized. A fully saturated ethylene-propylene-diene rubber with excellent ozone resistance and heat resistance. In 1961, the United States Exxon company built the world's first ethylene-propylene rubber solution polymerization industrial production device. ENB began to be used as the third monomer in industrial production in 1968. In 1971, the United States and Italy jointly developed the suspension ethylene-propylene rubber synthesis technology and realized industrialization. At the end of 1996, UCC (United Carbide) Company of the United States built a 91 kt / a large-scale gas-phase ethylene-propylene rubber industrial unit in Seadrift, Texas, and completed and put into operation in November 1998, marking the production of ethylene-propylene rubber Breakthroughs have been made in technology. In addition, the United States DuPont company completed a 91kt / a solution polymerization metallocene ethylene-propylene rubber plant in 1997; the same year, Japan's Mitsui Corporation completed a 30kt / a solution polymerization metallocene ethylene-propylene rubber plant. The metallocene catalyst successfully synthesized ethylene-propylene rubber, marking the Acrylic rubber has entered a new stage of development. In addition to the above countries, there are currently countries such as Germany, Canada, France, Russia, South Korea, and China that can produce ethylene-propylene rubber.

Molecular Structure

Chemical structure of ethylene-propylene rubber

Ethylene-propylene rubber is copolymerized with mono-olefin ethylene and propylene to form binary ethylene-propylene rubber; ethylene, propylene and a small amount of non-conjugated diene are used as monomers to obtain ternary ethylene-propylene rubber. On the main chain of ethylene-propylene rubber, the ethylene and propylene monomers are randomly arranged, losing the regularity of the polyethylene or polypropylene structure, thus becoming an elastomer. Since the diethylene-propylene rubber diene is located on the side chain, the three Ethylene-propylene rubber not only can be vulcanized with sulfur, but also maintains the various characteristics of ethylene-propylene rubber.

The third monomer commonly used in industrially produced EPDM rubber is ethylidene norbornene (ENB), dicyclopentadiene (DCPD), and 1,4-hexadiene (HD). The third monomer technology has new developments, and 1,7-octadiene, 6,10-dimethyl-1,5,9-undecene, 3,7-dimethyl-1 have been developed abroad. As the third monomer of ethylene-propylene-diene rubber, 1,6-octadiene, 5,7-dimethyl-1,6-octadiene, 7-methyl-1,6-octadiene, etc. The performance of EPR rubber has been improved.

The type and content of the third monomer in the EPDM rubber have a direct effect on the vulcanization speed and the properties of the vulcanized rubber. Among them, dicyclopentadiene (DCPD) is the third monomer. Although the price is low, this EPDM rubber has a slow vulcanization speed and is difficult to use with high unsaturated diene rubbers. Ethylene (ENB), 6,10-dimethyl-1,5,9-undecanetriene and other third monomers are fast curing speeds of ethylene-propylene rubber, the former has become the main varieties of ethylene-propylene rubber . The third monomer content is expressed by the iodine value. The iodine value of the EPDM rubber is generally 6-30, and most of them are about 15. When the iodine value is 6-10, the vulcanization speed is slow and it is difficult to use it with high unsaturated rubber; when the iodine value is 25-30, it is an ultra-high speed vulcanization type. It can be used in combination with high unsaturated diene rubber in any proportion. Therefore, when EPDM rubber is used in combination with other rubbers, care should be taken to select an appropriate EPDM rubber variety.

The type of the third monomer contained in EPDM rubber is known. When carbon black is filled, the vulcanization rate of the vulcanization system is as follows from fast to slow: 1. Sulfur vulcanization system: ethylidene norbornene, 1,4 -Hexadiene, dicyclopentadiene; 2. peroxide curing system: fluorene dicyclopentadiene, fluorene ethylidene norbornene, 1,4-hexadiene.

EPDM rubber containing ethylidene norbornene as the third monomer is selected, and its vulcanized rubber has higher heat resistance and tensile strength and less compression set; while it contains dicyclopentadiene (DCPD) Ethylene-propylene-diene rubber as the third monomer, lower cost, higher ozone resistance, and odorous products; ethylene-propylene-diene rubber containing 1,4-hexadiene is not easy to scorch, and will compress and permanently deform after vulcanization Smaller.

In the polymer molecular structure of ethylene-propylene rubber, the ethylene / propylene content ratio has a direct effect on the performance and processability of ethylene-propylene rubber raw and compound rubbers. In application, 2-3 kinds of ethylene-propylene rubber with different ethylene / propylene content ratio can be used together to meet different performance requirements. It is generally believed that the ethylene content is controlled at about 60% in order to obtain better processability and vulcanizate properties; when the propylene content is higher, the low-temperature performance of ethylene-propylene rubber is improved; when the ethylene content is higher, it is easy to squeeze out The exit surface is smooth, and the extruded part is not easy to deform after parking.

Ethylene propylene rubber has a weight average molecular weight of 200,000 to 400,000, a number average molecular weight of 50,000 to 150,000, and a viscosity average molecular weight of 100,000 to 300,000. The weight average molecular weight is closely related to Mooney viscosity. Ethylene-propylene rubber Mooney viscosity value [ML (1 + 4) 100 ] is 25-90, and there are many varieties of high Mooney value 105-110. With the increase of the Mooney value, the filling amount can also be improved, but the processability becomes worse; the tensile strength and resilience of the ethylene-propylene rubber after vulcanization are improved. The molecular weight distribution index of ethylene-propylene rubber is generally 3-5, and most of them are around 3. Ethylene-propylene rubber with a wide molecular weight distribution has good kneadability and calenderability in an open mill. Ethylene-propylene-diene rubber with a bimodal distribution of molecular weight has been developed, that is, a narrower peak appears in the low-molecular weight portion and the extremely low-molecular-weight portion is reduced. This type of ethylene-propylene rubber improves both physical and mechanical properties. Have good stiffness after extrusion, and ensure good fluidity and foaming rate.

Ethylene-propylene rubber production method

Ethylene-propylene rubber production technologies mainly include solution polymerization, suspension polymerization and gas phase polymerization ^[3] .

Solution polymerization is a homogeneous reaction in a solvent that can dissolve both the product and the monomer and the catalyst system. Usually, a linear alkane is used as a solvent (such as n-hexane). At present, the solution polymerization method is the main production method of ethylene-propylene rubber, which is adopted by most foreign manufacturers. Industrialized solution polymerization mainly includes two types of low temperature solution polymerization of Ziegler-Natta series catalysts and high temperature solution polymerization technology of metallocene series catalysts. The vanadium catalyst system solution process has the largest output of ethylene-propylene rubber, the most product grades, and strong market adaptability. Its output accounts for about 80% of the world's ethylene-propylene rubber production.

The advantages of the Ziegler-Natta solution polymerization method are mature technology, stable operation, more product grades, uniform quality, less ash content, and wide application range. The disadvantage is that because the polymerization reaction is performed in a solvent, the mass and heat transfer is limited. The polymer mass concentration is generally controlled at 6% to 9%, the highest is only 11% to 14%, and the polymerization efficiency is low; in addition, due to the use of solvents. Need to be recycled and refined. Long production process. More equipment. Construction investment and operating costs are high.

Suspension polymerization does not require additional solvents. Propylene is both a reactive monomer and a suspension medium. Ethylene-propylene rubber products are suspended in the propylene because it is insoluble in propylene and becomes a polymer liquid propylene slurry. The characteristics of suspension polymerization are that the polymer concentration in the polymerization reaction solution can reach 33% to 40%; the reaction heat is removed by the evaporated monomer; the evaporated propylene can be recycled; the polymer particles are large and need to be washed after being crushed; Solvent-free, eliminating the need for solvent recovery and refining steps; using wet condensation; the third monomer is evenly distributed in the molecular chain, and the utilization rate is high, which is conducive to improving product processing performance. At present, the only manufacturers in the world that use suspension polymerization to produce ethylene-propylene rubber are Germany's Bayer and Italy's Enichem. Their production capacity only accounts for about 11% of the world's total ethylene-propylene rubber. The method has few product grades and the products are mainly used for polyolefin modification.

The gas-phase process was successfully developed by the UCC (United Carbide) Company in the United States. In 1998, the world's first production unit (91kt / a) was built at the DuPont Dow Chemical Company in the United States. The production capacity accounts for about 9% of the world's total ethylene-propylene rubber capacity. Compared with the solution polymerization method and the suspension polymerization method, the gas phase polymerization method does not use a solvent, and does not require removal, recovery, and drying steps of the solvent. Not only the process is simple, but also the energy consumption can be greatly reduced, almost no three waste emissions, less investment, and low cost. The disadvantage of the gas phase polymerization method is that because the product contains carbon black, the product has poor versatility, and the rubber properties do not meet the needs of some uses. Therefore, there are limitations that cannot be widely promoted. In 2008, Dow's 91kt / a gas phase unit closed.

Main properties of ethylene-propylene rubber

Ethylene-propylene rubber low density and high filling

Ethylene-propylene rubber is a lower density rubber with a density of 0.87. In addition, a large amount of oil can be added and fillers can be added, which can reduce the cost of rubber products, make up for the shortcomings of the high price of ethylene-propylene rubber raw rubber, and for high Mooney ethylene-propylene rubber, physical and mechanical properties after high filling are reduced The magnitude is small.

Ethylene-propylene rubber aging resistance

Ethylene-propylene rubber has excellent weather resistance, ozone resistance, heat resistance, acid and alkali resistance, water vapor resistance, color stability, electrical properties, oil repellency, and fluidity at room temperature. Ethylene-propylene rubber products can be used for a long time at 120 , and can be used briefly or intermittently at 150-200 . Adding a suitable antioxidant can increase its use temperature. EPDM rubber crosslinked with peroxides can be used under more severe conditions. EPDM rubber can be cracked for more than 150 hours under the conditions of 50pphm ozone and 30% stretching.

Ethylene-propylene rubber corrosion resistance

Due to the lack of polarity and low saturation of ethylene-propylene rubber, it has good resistance to various polar chemicals such as alcohols, acids, alkalis, oxidants, refrigerants, detergents, animal and vegetable oils, ketones and fats. ; But poor stability in aliphatic and aromatic solvents (such as gasoline, benzene, etc.) and mineral oil. Under the long-term effect of concentrated acid, the performance will also decline.

Water vapor resistance of ethylene-propylene rubber

Ethylene-propylene rubber has excellent water vapor resistance and is superior to its heat resistance. In 230 ° C superheated steam, there is no change in appearance after nearly 100 hours. However, under the same conditions, fluorine rubber, silicone rubber, fluorosilicone rubber, butyl rubber, nitrile rubber, and natural rubber have a noticeable deterioration in appearance after a short period of time.

Ethylene-propylene rubber resistance to overheating

Ethylene-propylene rubber also has better resistance to hot water, but it is closely related to the vulcanization system used. Ethylene-propylene rubber with dithiodimorpholine and TMTD as the vulcanization system, after soaking in 125 ° C hot water for 15 months, the mechanical properties change little, and the volume expansion rate is only 0.3%.

Electrical properties of ethylene-propylene rubber

Ethylene-propylene rubber has excellent electrical insulation and corona resistance, and its electrical properties are better than or close to those of styrene-butadiene rubber, chlorosulfonated polyethylene, polyethylene, and cross-linked polyethylene.

Ethylene-propylene rubber elasticity

Because there is no polar substituent in the molecular structure of ethylene-propylene rubber, the molecular cohesion energy is low, and the molecular chain can maintain flexibility in a wide range, second only to natural rubber and butadiene rubber, and it can be maintained at low temperature.

Ethylene-propylene rubber adhesion

Ethylene-propylene rubber has low cohesive energy due to the lack of active groups in the molecular structure, and the rubber compound is easy to bloom, and the self-adhesion and mutual adhesion are poor.

Ethylene-propylene rubber modified varieties

Since the successful development of diethylene-propylene and ternary ethylene-propylene rubbers in the late 1950s and early 1960s, various modified ethylene-propylene rubbers and thermoplastic ethylene-propylene rubbers (such as EPDM / PP) have appeared in the world. The extensive application of ethylene-propylene rubber provides a large variety and grades. Modified ethylene-propylene rubber is mainly brominated, chlorinated, sulfonated, maleic anhydride, maleic anhydride, silicone modified, nylon modified. Ethylene-propylene rubber also has grafted acrylonitrile, acrylate and the like. Over the years, many good polymer materials have been obtained by means of blending, copolymerization, filling, grafting, reinforcement and molecular compounding. Ethylene-propylene rubber has also been greatly improved in performance through modification, thereby expanding the application range of ethylene-propylene rubber.

Brominated ethylene propylene rubber is processed on a mill with a brominating agent. After bromination, ethylene-propylene rubber can improve its vulcanization speed and adhesive properties, but its mechanical strength is reduced. Therefore, brominated ethylene-propylene rubber is only suitable as an intermediary layer between ethylene-propylene rubber and other rubbers.

Chlorinated ethylene propylene rubber is made by passing chlorine gas through a solution of ethylene propylene diene rubber. Ethylene-propylene rubber can improve vulcanization speed and compatibility with unsaturated rubber, flammability, oil resistance, and adhesive properties after chlorination.

Sulfonated ethylene-propylene rubber is made by dissolving EPDM rubber in a solvent and treated with a sulfonating agent and a neutralizing agent. Due to the properties of thermoplastic elastomers and good adhesion properties, sulfonated ethylene-propylene rubber will be widely used in adhesives, coated fabrics, building waterproof materials, anti-corrosion linings, etc.

Acrylonitrile-grafted ethylene-propylene rubber uses toluene as a solvent and perchlorobenzyl alcohol as an initiator, and acrylonitrile is grafted to ethylene-propylene rubber at 80 ° C. Acrylonitrile modified ethylene-propylene rubber not only retains the corrosion resistance of ethylene-propylene rubber, but also obtains oil resistance equivalent to that of nitrile-26, and has good physical and mechanical properties and processing properties.

Thermoplastic ethylene-propylene rubber (EPDM / PP) is based on EPDM rubber and polypropylene. At the same time, the ethylene-propylene rubber is the product of the desired degree of crosslinking. It not only retains the inherent characteristics of ethylene-propylene rubber in performance, but also has significant thermoplastic injection, extrusion, blow molding and calendering process performance.

In addition, modified ethylene-propylene rubber also includes chlorosulfonated ethylene-propylene rubber, acrylate-grafted ethylene-propylene rubber, and the like.

Ethylene-propylene rubber application

Due to the saturated structure of the ethylene-propylene rubber molecular chain, it exhibits valuable properties such as excellent weather resistance, ozone resistance, electrical insulation, low compression set, high strength and high elongation. Its applications are extremely extensive, and its consumption is increasing year by year. . According to the characteristics of different series and molecular structure of ethylene-propylene rubber, the application types of ethylene-propylene rubber are general application, mixed application, fast vulcanization, easy processing and combined use of diene rubber. From the analysis of actual application, ethylene-propylene rubber has been widely used in non-tires.

Ethylene-propylene rubber automotive industry

Ethylene-propylene rubber is the most widely used in the automobile manufacturing industry. It is mainly used in automotive seals, radiator hoses, spark plug jackets, air conditioning hoses, rubber pads, and hoses. In the automotive weather strip industry, EPDM's elasticity, ozone resistance, and weather resistance are mainly used. Its ENB EPDM rubber has become the main material of automotive weather strips. The annual consumption of raw rubber in China has exceeded 10,000 tons. Half of the variety relationship depends on imports. Due to the characteristics of thermoplastic EPDM / PP, such as high strength, good flexibility, high gloss coating, and easy recycling, it has become the leading material in the production of automobile bumpers and automobile instrument panels at home and abroad. It is estimated that by 2010, there will only be two products of automobile bumpers and dashboards, and the annual domestic consumption of EPDM / PP will reach 45,000 tons. The main process methods used for the recycling of such products are: firstly remove the coating on the product surface-crushing-cleaning-re-granulation-add new materials to produce new products. In this way, in the production of bumpers and dashboards, a large number of raw materials can be saved to achieve better economic benefits. The amount of ethylene-propylene rubber used in the automobile industry in China accounts for 42% -44% of the total amount of ethylene-propylene rubber used in the country, which does not include the amount of ethylene-propylene rubber used in ship, train and container seals. Due to the poor adhesion of ethylene-propylene rubber, the use of ethylene-propylene rubber cannot be promoted in the tire body and tread parts of a large number of materials in the automotive tire industry. Only a small amount of ethylene-propylene rubber is used in inner tires, white tire sidewalls, and tires. C rubber.

Ethylene-propylene rubber construction industry

Because ethylene-propylene rubber has excellent water resistance, heat resistance, cold resistance, weather resistance, and easy construction, ethylene-propylene rubber is mainly used in the construction industry for plastic sports fields, waterproof membranes, house door and window seals, and glass curtain walls. Seals, sanitary equipment, and pipe seals. The largest amount of ethylene-propylene rubber in the construction industry is also the number of plastic sports fields and waterproof coils. In terms of domestic use, it has accounted for 26% -28% of the total amount of ethylene-propylene rubber. EPDM waterproof membranes have gradually replaced waterproof membranes made of other materials (such as CMS), especially waterproof membranes for underground construction.

Ethylene-propylene rubber electrical and electronics industry

In the electrical and electronic industries, the excellent electrical insulation, weather resistance, and corrosion resistance of ethylene-propylene rubber are mainly used. Such rubbers are used in many electrical components. For example, using ethylene-propylene rubber to produce cables, especially submarine cables using EPDM or EPDM / PP instead of PVC / NBR to make cable insulation, the cable's insulation performance and service life have been greatly improved. A large number of ethylene-propylene rubbers are also used in transformer insulation pads and electronic insulation jackets.

The combined use of ethylene-propylene rubber and other rubbers is also a large area for the application of ethylene-propylene rubber. The combination of ethylene-propylene rubber and other rubbers in performance can complement each other and improve process and reduce costs. However, due to the different affinity of various compounding agents for different polymers, the co-vulcanizability depends on the crosslinking efficiency of each polymer. It is impossible to achieve molecular-level compatibility by blending different polymers and using Phase heterogeneity. This uneven phase distribution of the compounding agent has a significant impact on the performance of the ethylene-propylene rubber. Here is a brief introduction:

Ethylene propylene rubber has good compatibility and co-vulcanizability with butyl rubber. The physical and mechanical properties of the two rubbers are additive. Butyl rubber can improve the air tightness and tear of ethylene propylene rubber. And sound insulation; while ethylene-propylene rubber improves the ozone resistance and aging resistance of butyl rubber, improves the gloss of the butyl rubber extrusion surface, and improves the deformation resistance of the semi-finished product when it is parked.

Ethylene propylene rubber can be used with neoprene in different proportions to improve the oil resistance of ethylene propylene rubber. After the use of ethylene-propylene rubber and neoprene, the two rubbers have complementary properties. Ethylene-propylene rubber has improved oil resistance, flame resistance, and adhesion; chloroprene rubber has also improved ozone resistance, chemical resistance, heat resistance, steam resistance, and low temperature flex resistance, and improved processing of chloroprene rubber Oil and carbon black loadings reduce costs.

(3) After the use of ethylene-propylene rubber and silicone rubber, the heat resistance, weather resistance, low-temperature compliance and electrical properties are further improved; the mechanical properties of silicone rubber are also greatly improved. Ethylene-propylene-diene rubber is used in combination with fluororubber. The low-temperature properties of fluororubber and the medium resistance of ethylene-propylene rubber are improved, and the cost of the rubber compound is reduced.

Modification of SBR, NR, etc. of ethylene-propylene rubber improves the aging resistance and high temperature resistance of this rubber, and also improves the adhesion of ethylene-propylene rubber.

The EPDM rubber used for automotive weatherstrips has been used in combination with LDPE, SBR, etc. to meet the sealing requirements of various parts of automobiles, and has achieved ideal results. It can be used with LDPE or liquid polybutadiene rubber to obtain high hardness (Shore A hardness of 96) EPDM rubber. Such high hardness EPDM is mostly used in the production of automotive water tank and trunk seals. Especially the high-hardness EPDM rubber used in combination with liquid polybutadiene rubber has good extrusion processability.

In addition to the combined use of ethylene-propylene rubber and other types of rubber, the application of ethylene-propylene rubber as a modifier for thermoplastic engineering plastics is not only small, but also widely used. For example, the modification of ethylene-propylene rubber to PVC, PP, PE, etc. mainly improves the performance requirements of weather resistance, resilience, and low temperature brittleness resistance of these thermoplastic engineering plastics.

In addition to the above, ethylene-propylene rubber is used in daily necessities, sports equipment, machinery and chemical equipment, lubricant modification and various rubber products production fields.

Although the price of raw rubber of ethylene-propylene rubber is relatively high, especially the price of imported raw rubber of ethylene-propylene rubber is higher, it makes full use of its high oil-filling and filling properties, and uses the characteristics that can be used with other rubbers to reduce the mixing The production cost is practical and the actual material production cost will not be much higher than other rubbers.

Ethylene-propylene rubber recycling

Ethylene-propylene rubber is more and more widely used. How to recycle vulcanized waste rubber and waste products is a subject worthy of research and development. Abandoned everywhere, causing great pollution to the environment. The traditional method of desulfurization regeneration is not good. In the world, the research and development of the recovery and utilization of vulcanized ethylene-propylene waste rubber by microwave desulfurization has been successful, but it is still in the research stage in China. Once this method is successfully researched and developed in China, the economic and social benefits of waste ethylene-propylene rubber recycling will be enormous.

Ethylene-propylene rubber

As long as we know more about the properties and characteristics of ethylene-propylene rubber, make full use of the unique properties of ethylene-propylene rubber, better solve the problem of recycling waste vulcanized rubber, reduce the raw rubber price of ethylene-propylene rubber, and the application fields and needs of ethylene-propylene rubber Volume will achieve greater development.