Application of EPDM
The abbreviation EPDM means ethylene propylene diene M-class rubber. The key advantage of the compounds, which ensures their widespread use, is the availability and low cost of precursors (ethylene and propylene monomers). Other important characteristics for application are listed below:
- ozone resistance;
- resistance to weathering;
- chemical and thermal stability;
- excellent dielectric properties;
- ability to keep color.
The intensive use of ethylene-propylene copolymers is associated with the low cost of the feedstock. EPDM rubbers can replace expensive elastomers.
Elements of pipelines
Another area of use for ethylene-propylene rubbers is water supply. On the basis of copolymers, rubber expansion joints are produced in several versions:
- increased flexibility.
Compensators have a wide operating temperature range (from -40 to 100°C), the ability to dissipate electrical power. The environmental friendly rubber based on EPDM allows the use of expansion joints in pipelines with drinking water. The chemical resistance of rubbers makes it possible to transport though pipelines a variety of liquid medium from ketones and salt solutions to technical alcohols.
Copolymers of ethylene and propylene are in demand in mechanical engineering. Materials based on EPDM are used as sealants for various car modules – windows, doors, trunk, bonnet. The most engine components – gaskets and tubes – are also made from EPDM rubber. EPDM crumb production includes:
- pedal covers and mats;
- transmission belts;
- conveyor belts;
- hoses with a special inner layer of cellular rubber;
- cable sheaths.
Among the potential applications remains the production of automobile tires. Now this is prevented by the stickiness of rubbers: the adhesion of synthetic elastomers to steel wire and polyester cord. Tires made entirely of EPDM thermopolymer are already being produced, but the technology continues to improve. In addition, generated by friction heating prevents the operation of ethylene-propylene tires on trucks. So far, the potential application is limited to passenger car tires.
Household and construction areas
EPDM rubbers are used to make:
- seals for glass, entrance doors, heating radiators;
- garden and household hoses;
- solar thermal collectors;
- gaskets and belts;
- electrical insulating materials;
- speaker membranes.
Rubbers are in demand in waterproof cable connections. Similar properties of EPDM copolymers have found application in residential construction. Elastomers are used in the production of roofing and waterproofing materials. In particular, rubbers are used to make geomembranes that do not pollute rainwater runoff.
In road construction EPDM granules are embedded in a polyurethane base and applied to various types of coatings – concrete, asphalt, wood, tile or brickwork. The result is a non-slip, safe surface for wet areas, playgrounds, mall entrances etc.
EPDM rubbers are gradually replacing silicone. A good example is the production of respirators for painting work in a confined space. With the usage of ethylene-propylene copolymers, impact-resistant plastics are created, rubberized fabrics and sleeves are produced. The scope of EPDM operation continues to expand. Periodically, new areas of application for ethylene-propylene copolymers emerge.
EPM copolymers – methods for producing rubbers with special properties
Modern production produces two basic varieties of high-molecular rubbers with special properties. These are binary (EPM) and ternary (EPDM) copolymers of ethylene propylene.
Some facts about EPDM history
The classical technology of copolymerization was developed by Ziegler and Natta in the middle of the last century. In 1953 a group of German chemists patented titanium-based catalysts. Further development of technology led to a whole group of complex organometallic compounds. They were called Ziegler-Natta catalysts. Subsequently, for work on the synthesis of stereoregular polymers, including olefins, German scientists received the Nobel Prize.
The latter fact reflects the importance of creating a technology for the copolymerization of ethylene with propylene on Ziegler-Natta catalysts. Both types of high molecular structures EPM and EPDM are produced using a similar technology. The difference is the addition of acyclic unsaturated hydrocarbons (dienes) in the synthesis of ternary rubbers.
Detailed description of copolymerization
The synthesis is carried out in heavy hydrocarbon solvents. An alternative option is also used – copolymerization in liquid propylene. Ziegler-Natta catalysts are usually vanadium compounds and various aluminum alkyls. Taking into account the higher activity of ethylene, the content of this monomer in the copolymer is higher. This is worth paying attention when preparing the initial mixture. The diene introduced to facilitate vulcanization is often chosen as ethylidenenorbornene, less often as a dimer of cyclopentadiene. Hydrogen is used as a molecular weight regulator.
The polymerization technology depends on the choice of medium. For heavy hydrocarbon solvents usually set temperature of 30°C and a cascade system of 2–5 reactors. An alternative solution is a polymerization reactor with a stirrer and cooling. Monomers and a catalyst are fed into it.
Polymerization in liquid propylene takes place at temperatures ranging from -20 to 40°C. The reaction components are fed separately as solutions. The resulting suspension of rubber in propylene is then sent to water degassing. Finally, the resulting mass is dehydrated on special presses.
High molecular weight compounds synthesized during the copolymerization process are similar to natural unvulcanized rubber, but do not always have elastomeric properties. In fact, the first stage of the synthesis ends with the production of an amorphous crystalline substance with a static distribution of monomers over the macromolecule.
Vulcanization is necessary for the production of elastomers. The saturated nature of the synthesized ethylene-propylene copolymers (EPR) does not allow vulcanize in the standard way – using sulfur complexes and accelerators. In some cases the problem is solved by cross-linking with organic peroxides. Another universal solution is the introduction of a multiply saturated cyclo or aliphatic hydrocarbon into the EPR macromolecule. As a result, double bonds are formed in the polymer structure, which are necessary for the crosslinking reaction. The compounds obtained by the described technology, in contrast to pure copolymers, are called EPDM or EPT.
Nuances of synthesis
To date, various proportions of ethylene/propylene have been tested in the copolymerization process. If the components are in equal proportion, a soluble amorphous copolymer is formed. The significant predominance of one of the monomers radically changes the picture. The result of the synthesis is the production of crystalline copolymers, the proportion of amorphous substances is sharply reduced.
It remains to be added that the introduction of dienes to facilitate copolymerization has been practiced since 1962. This is the first, but by no means the last, improvement in synthesis. To date, many patents have been issued for various modifications of the classical copolymerization technology. An illustrative example is thermoplastic polyolefin rubbers (TPO). The material has elastomeric properties and is obtained in the process of high-temperature dynamic vulcanization. The reagents are isotactic polypropylene and EP, EPD rubbers.