Materials
EPDM Rubber
Molded EPDM
Product Description
EPDM (Ethylene Propylene Diene Monomer) Rubber has outstanding resistance to aging, weathering, ozone, oxygen and many chemicals. It offers excellent high and low temperature stability, plus steam and water resistance. In general, EPDM has dynamic and mechanical properties between natural rubber and SBR.
EPDM products can be used in the production of extruded rubber or molded rubber products and are used in many static and dynamic applications including:
- Automotive weather-stripping and seals
- EPDM Tubing
- Belts
- Electrical insulation
- Rubber mechanical goods
- Washing machines/dishwashers
- Hydraulic brake systems
NOTE: EPDM should not be used where continual contact with petroleum based products is required.
EPDM Rubber Material Properties
| Common Names | EPDM, EPR, EPT |
| ASTM D-2000 Classification | CA |
| Military (MIL-STD 417) | RS |
| Chemical Definition | Ethylene Propylene |
| General Characteristics | |
|---|---|
| Durometer Range (Shore A) | 30-90 |
| Tensile Range (P.S.I) | 500-2500 |
| Elongation (Max %) | 600 |
| Compression Set | Good |
| Resilience – Rebound | Good |
| Abrasion Resistance | Good |
| Tear Resistance | Fair |
| Solvent Resistance | Poor |
| Oil Resistance | Poor |
| Low Temperature Usage (F°) | -20° to -60° |
| High Temperature Usage (F°) | Up to 350° |
| Aging Weather – Sunlight | Excellent |
| Adhesion to Metals | Fair to Good |
Comment – Ethylene Propylene is a polymer that exhibits outstanding properties. It has exceptionally good weather aging resistance as well as resistance to water, chemicals, and ozone. EPDM also shows an excellent resistance to gas permeability and aging due to steam exposure. It is an excellent polymer to use in high temperature applications as it is heat resistant up to 350°F. Ethylene Propylene provides poor resistance to oil and solvents; however it is fairly good in its resistance to ketones and alcohols. EPDM is not recommended for usage in food applications or those that expose it to aromatic hydrocarbons.
EPDM Rubber Applications
EPDM's properties allow it to be a widely used, highly versatile, synthetic rubber in both specialty and general purpose applications. Since EPDM can be processed to meet a number of different requirements, it has been adopted by many industries for a number of applications including:
- Automotive weatherstripping
- Glass-run channels
- EPDM Grommets
- Automotive seals
- Radiator, garden and appliance EPDM hoses
- EPDM Tubing
- Electrical insulations and stinger covers
- Roofing membranes
- EPDM belts
- Plastic impact modification
- Rubber mechanical goods
- Water system O rings and hoses
- Ozone exposure applications
- Automotive cooling systems
Chemistry and Compounding
Ethylene-propylene elastomers share the same monomers as the thermoplastic polymers polyethylene (PE) and polypropylene (PP). Depending on polymer composition and how the individual monomers are combined, ethylene-propylene rubbers can be produced in a wide range of families ranging from amorphous, non-crystalline to semi-crystalline structures. These polymers can also be produced in a wide range of Mooney viscosities.
When compounded and combined, the ethylene and propylene monomers of EPDM form a chemically saturated, stable backbone that provides excellent resistances to ozone, heat, oxidation and weathering. From here, a third non-conjugated monomer of diene can be terpolymerized to the polymer to maintain a saturated backbone and subsequently place the reactive unsaturation in a side chain, making it available for vulcanization or polymer modification chemistry. The resulting terpolymers created are referred to as EPDM.
Structure of EPDM containing ENB
The two most commonly used diene termonomers in the creation of EPDM are ethylidene norbornene (ENB) and dicyclopentadiene (DCPD). These respective dienes will incorporate with the polymer differently, each with their own tendency for introducing long chain branching (LCB), or polymer side chains, that will ultimately influence the vulcanization rates by sulfur or peroxide cures. The following table summarizes the characteristics of the cures using both the ENB and DCPD termonomers.
| Termonomer | Cure & Property Features | Long Chain Branching |
|---|---|---|
| ENB | Fastest and Highest state of cure Good tensile strength Good compression set resistance |
Low to Moderate |
| DCPD | Slow Sulfur Cure Good compression set resistance |
High |
Features of EPDM Elastomers
The different properties of a finished EPDM compound will be largely controlled by the ethylene and diene content, the Mooney viscosity and the molecular weight distribution. Example – Lowering ethylene content will decrease crystallinity and thus decrease hardness and modulus. The follow table highlights some of the general features in compounding EPDM and the results of having higher or lower levels of specific attributes.
| Characteristics | High | Low |
|---|---|---|
| Ethylene Content | Flow at High Extrusion Temps. High tensile strength, modulus Good Green Strength High Loading (Reducing Cost) |
Fast Mixing Calendering and Milling Low Hardness and Modulus Low Temp. Flexibility |
| Diene Content | Acceleration Versatility High Modulus, Low Set Good Compression Set Cure Degree and Fast Rate |
High Heat Stability Low Hardness and Modulus Scorch Resistance |
| Molecular Weight | Good Modulus and Set High Loading and Oil Extension Good Green Strength Good Tensile and Tear Resistance Collapse Resistance |
High extrusion rates Low Viscosity, Scorch Resistance Good Calendering Fast mixing |
| MWD | Good overall processing Collapse Resistance Good Milling and Calendering Extrusion feed and smoothness |
Fast extrusion rate High Cure Low Die Swell Good Physicals |
Manufacturing Processes
EPDM can be manufactured commercially in three major processes, solution, slurry (suspension), and gas-phase.
The Slurry process of polymerizing EPDM is a modification of bulk polymerization wherein the monomers and catalyst system are injected into a propylene filled reactor. The polymerization reaction is immediate and cubs of polymer are formed that are not soluble in the propylene. This process of slurry polymerization reduces the needs for solvents and solvent handling equipment. The low viscosity of the slurry also allows for more stable temperature controlling and easier handling of the product. The process is not limited by solution viscosity, meaning a high molecular weight polymer can still be produced through slurry polymerization without a penalty to production.
The process of solution polymerization is a widely used method which is highly versatile in making a wide range of polymers. In this process, polymerization of the ethylene, propylene and catalyst systems takes place in an excess of hydrocarbon solvent. If the compound requires stabilizers and oils, they are added directly after polymerization. Following this, the solvent and unreacted monomers are flashed of by mechanical devolatilization or by using hot water or steam leaving only the EPDM compound. The remaining polymer, which is in crumb form, is next dried using either mechanical press, drying ovens, or dewatering in screens. From here, the crumb can be formed into bales or extruded into pellets.
Gas-phase polymerization was developed for the manufacturing of ethylene-propylene rubbers. It involves a reactor that consists of a vertical fluidized bed into which the monomers, catalysts and nitrogen in gas form are fed, and solid product is removed. The intense heat of the reaction is removed through the use of circulating gas which also will serve to fluidize the polymer bed. In gas-phase polymerization, solvents are not used thus eliminating the needs for solvent stripping, washing and drying. However, when engaging in this process, continuous injection of a substantial amount of carbon black is necessary. This additive acts as a partitioning aid which prevents the polymer granules from sticking to each other and the reactor walls. To enable rapid mixing, products are made in granular form.
