EPDM rubber is one of the most common synthetic rubbers today. Its superior properties, wide range of applications, and grades have largely contributed to its popularity. Primarily, this type of rubber is used in applications where ozone protection is a major concern. In this article, you will learn about the properties, grades, and use cases of EPDM rubber.
What is EPDM Rubber?
EPDM is an acronym that stands for Ethylene Propylene Diene Monomer. This tells you that the compound is made up of ethylene, propylene, and diene monomers. Ethylene, propylene, and diene are natural elements found in oils and natural gas.
Like all rubbers, EPDM is a polymer. Its polymer is made up of monomers of ethylene and propylene. This polymerization is achieved through copolymerization, a chemical reaction that involves two or more different monomer compounds.
Here is a little more about the three monomers that make up EPDM rubber;
- Ethylene (E) is a simple hydrocarbon. It is known to provide the weather-resistance properties of EPDM rubber
- Propylene (P) is also a hydrocarbon monomer. It is responsible for the elasticity and flexibility of cured EPDM rubber.
- Diene monomer (DM) is technically not a hydrocarbon, although it contains hydrogen and carbon atoms. It is responsible for unsaturation, a property that is required for crosslinking of the polymer structure.
This synthetic rubber was first developed by DuPont in the 1950s. Back then, EPDM was used as a roofing material. While it is still used for roofing today, this application does not take advantage of all the properties of the compound.
Other rubber manufacturers were able to improve this material over the years and make it more capable of handling diverse environmental conditions. Moreover, manufacturers have made several grades of the compound with specific properties for specific use cases. These are among the factors that have led to the widespread use of EPDM rubber.
Properties of Vulcanized EPDM Rubber
Vulcanization is the process by which rubber is processed in numerous ways to improve its underlying properties. This process involves the addition of additives, accelerators, and other agents known for improving rubber properties. Then, this compound is heated to a specific temperature to activate the crosslinking which brings out these properties.
Some of the common mechanical properties of EPDM rubber that arise from vulcanization include the following;
High Resistance to UV Radiation
UV or ultraviolet is a form of electromagnetic radiation that exists freely in the atmosphere and is emitted by the sun and other heavenly bodies. If uncontrolled, UV has damaging effects on living and non-living things.
EPDM is among the compounds that can resist the damaging effects of UV radiation. This resistance is in part due to the compound’s chemical composition and molecular structure. Carbon and its bonds are particularly known to support this resistance. Also, during the vulcanization process, additives that absorb or reflect UV rays are added to its molecular structure.
Several experiments to show this resistance have been conducted. In one example, EPDM rubber was left exposed to sunlight for over two decades (over 20 years). When retrieved, the rubber showed no signs of cracking, even at the molecular level. This shows you that you can use products made from EPDM rubber in outdoor environments for at least twenty years.
Poor Resistance to Oils
The resistance of EPDM to oils with a hydrocarbon backbone is relatively poor compared to other synthetic rubbers. The obvious reason for this is that the compound is made from hydrocarbon-based monomers.
EPDM has shown signs of swelling when it comes into contact with mineral oils for extended periods. This is because the compound absorbs these oils and they become part of their molecular composition.
After swelling, EPDM loses its elasticity, hardness, and overall mechanical properties. You would not want this to happen since it can present a hazard. Still, some manufacturers have been able to formulate EPDM rubbers that can withstand oils to a certain extent. This is achieved by adding certain additives during the vulcanization process.
30 – 90 Shore A Durometer
A durometer is the measurement of the hardness of a material. This hardness is indicated using a range of values. For EPDM rubber this range falls anywhere between 30 and 90. However, a durometer is technically not a unit of measurement. It is more of a comparison scale of the hardness of a material based on the hardness of another material.
Shore A durometer is used to indicate the hardness of softer materials such as rubber. Compounds that possess this scale have elasticity and stiffness at the same time. Therefore, they can be used in applications where both hardness and elasticity are required.
In the lower scale, that is anything between 0 and 30, the material is considered soft. Then anything above 70 is considered hard. EPDM falls in the range of 30 to 90 because it can exist in both foam and hard sheets.
A high Degree of Elasticity
Elasticity is quite essential for rubber. It means that the material cannot be deformed or has a high resistance to deformity when it is stretched. This degree is measured in what is called elastic modulus. The elasticity modulus of EPDM is about 7Mpa. This value is measured for unfilled EPDM, which means rubber that has not been reinforced using fillers. Carbon black is a common filler.
At 7Mpa, EPDM is quite stiff, but way lower than other rubbers. The modulus of elasticity is related to the tensile strength of the material. To clarify, the tensile stress of the material is what informs the elasticity. If the compound can withstand high elastic modulus, it translates to a high degree of elasticity.
The elasticity of EPDM makes it suitable for applications where factors like tension are expected. In practice, this includes most applications in industries such as automotive and aerospace.
Moderate Tensile Strength
Having established that Young’s modulus of EPDM is subpar, it should not be surprising that the compound has a low tensile strength.
Tensile strength is the amount of pull force any given material can withstand without breaking. Most rubber compounds have a high tensile strength, which is why they are quite elastic. This property is measured in PSI or pounds per inch. In that case, the tensile strength of EPDM falls in the range of 500 – 2,000 PSI.
The tensile strength of compounds like rubber is measured in relation to elongation at break and tear strength. This is because the three properties are all related to one thing — tension stress.
Elongation at break is the measure of the length of stretch that EPDM maintains before it breaks. In other words, how much can the material stretch before it snaps? This property is measured in percentages. For EPDM, the elongation is within the range of 100 – 700 %. This range of elongation is generally considered high.
Tear strength represents the resistance of the material to tearing. It is measured in kilonewtons per meter (kN/m). EPDM has a tear strength of anything from 10 – 50 kN/m. Technically, this is considered moderate resistance, meaning the compound can withstand tear.
High Chemical Resistance
Provided that there are thousands of chemicals in the environment, it can be challenging to test the resistance of EPDM to most of the chemicals. However, there have been many tests that have shown that this compound has an excellent resistance to chemicals.
Resistance to chemicals means the ability of the material to remain unchanged in both chemical and physical states when it comes into contact with chemicals. Unlike hydrocarbon chemicals that are found in oils, EPDM can resist the degrading effects of the majority of chemicals. This means that the compound can be used in applications where you expect these chemicals.
Synthesis of EPDM Rubber
EPDM is made in the lab like most synthetic polymers. This means that you cannot find this compound freely in nature. This is unlike natural rubber that comes from the tree sap of a specific group of trees. However, its monomers, ethylene, propylene, and diene monomers, are found in natural gas. These monomers are transformed into rubber through polymerization.
Polymerization of Ethylene and Propylene
The copolymerization of base monomers of EPDM rubber produces either EPM or EPDM copolymers. This means that the synthesis produces either of the two types of ethylene-propylene copolymers.
EPM is the first type of copolymer. This copolymer contains only ethylene and propylene monomer compounds. On the other hand, EPDM is a copolymer of ethylene and propylene, with small amounts of diene monomer. Two of the common dienes used are 1,4-hexadiene and ethylidene norbornene, both of which are organic compounds.
The two types of copolymers are made using a polymerization reaction. In this reaction, the gaseous forms of ethylene and propylene are dissolved in organic solvents in the presence of catalysts such as Ziegler-Natta.
Ziegler-Natta catalysts are primarily responsible for facilitating the opening of the double bonds that exist in the ethylene and propylene compounds. In return, this opening facilitates the bonding of one of the carbon bonds to another molecule of the compounds. This bonding continues to happen until a long-chain polymer of multiple monomers is made.
The end product of this reaction is a thermoplastic elastomer (TPE). In this form, the compound is unstable and it needs to undergo vulcanization to reinforce its properties. Vulcanization is an example of a rubber-curing method.
Vulcanization of EPDM Rubber
As a TPE, EPDM exhibits both thermoplastic and elastomeric properties. In other words, it can have the properties of plastics and those of rubber. Vulcanization is performed to ensure that it has only rubber-like properties.
Vulcanization is the process by which reinforcement agents, also known as fillers, are mixed with the TPE compound to enhance the properties of rubber. For EPDM, the most common vulcanizing agents are sulfur and peroxide. The primary goal of these agents is to facilitate the cross-linking of the polymer.
Sulfur Vulcanizing System
Sulfur is the most commonly used element for vulcanizing rubber. It exists freely and in abundance in most parts of the world. Also, sulfur is cost-effective, and that is why it is highly used. This element is used alongside heat, where the element is added to the TPE under heat.
This element facilitates the cross-linking of EPDM polymer compounds. In technical terms, it transforms EPDM from a thermoplastic into a thermoset. That is to say from plastic-like to rubber-like.
Peroxide vulcanization system
Primarily, peroxide is used as a substitute when the rubber manufacturer wants to produce sulfur-free EPDM. This consideration is made especially when manufacturing food-grade EPDM rubber. Peroxide performs the same function as sulfur.
Grades of EPDM Rubber
After the rubber compound has been vulcanized, it undergoes drying to form sheets and other forms of rubber. Right before or after this, the rubber needs to be graded.
Grading is the classification of rubber compounds according to their chemical composition, properties, and physical appearance. This classification is done in various ways including chemical analysis and visual inspection. For EPDM rubber, the most common grades are commercial and food-grade rubber. Special grades are also manufactured in some instances.
Commercial-grade EPDM rubber
The term commercial grade is an umbrella term that represents all basic grades of EPDM. These grades have no additives apart from the regular ones. In other words, it can be considered the standard grade of EPDM rubber.
Commercial-grade EPDM rubber exhibits the majority of the properties we have listed above. As such, they are suitable for general applications and use cases where these properties are desired. This grade of rubber can be vulcanized using either peroxide or sulfur.
FDA-approved EPDM rubber
The Food and Drugs Administration (FDA) is a US-based international regulatory body that oversees the production of products that are considered for human consumption. Its responsibility is to ensure that the public health of the masses is protected. Therefore, it sets standards for materials like rubber used to produce food containers and such likes.
With that in mind, FDA-approved EPDM rubber is a grade of EPDM that has been approved for use with food substances. There are minimum requirements that rubbers in this category must have for them to be certified as food-grade.
One of the core requirements of FDA-approved or food-grade EPDM is non-toxicity. This one should be a no-brainer. To achieve this, the TPE needs to be vulcanized with peroxide instead of sulfur. Food-grade EPDM also has several specific properties such as high flex fatigue resistance and wide temperature range.
What is the Lifespan of EPDM Rubber?
The lifespan of rubber varies depending on several factors. One, different grades degrade at different rates. This means some will reach their lifespan faster than the rest. Also, the lifespan is affected by the underlying usage conditions. When used in harsh conditions, EPDM rubber will degrade faster than in moderate conditions.
With these parameters, you can see that it would be almost impossible to put a number into the lifespan of this compound. The most we can do is make a general estimate based on conditions and other factors. For instance, we can estimate that in regular conditions, EPDM rubber can last at least 20 years before it starts wearing off.
For applications such as roofing, EPDM can last at least 50 years. This is because the specific formulation of EPDM rubber used for roofing is enhanced to sustain conditions that are expected on a roof. Also, EPDM is quite resistant to UV and ozone which are expected in a roof.
Why EPDM Rubber is Used for Roofing
When DuPont introduced people to roofing using EPDM rubber, several contractors adopted the material. This widespread adoption was a result of several reasons. Some of these reasons include;
Resistance to UV Radiation, Heat, and Weather
The roof is always exposed to the atmosphere, a layer of the earth that contains UV, heat, moisture, and other elements. Its function is to shield us from these elements. As such, it would be expected for a roof to have a high resistance to these elements. Since EPDM has demonstrated the ability to resist these elements, it is among the most common roofing materials.
Environmental Friendly
The environment is also a factor that is considered when choosing roofing materials. While the compound is not biodegradable, it has other factors that classify it as eco-friendly.
On one hand, EPDM is 100% recyclable. This is good for the environment since old roofs can be repurposed and used in other applications. More so, its non-toxic nature ensures that it does not pollute rainwater. If this was not the case, rainwater that passed through EPDM roofs would be hazardous to plants and animals.
It Requires Little Maintenance
Little to no maintenance is another reason why EPDM is ideal for roofing. Once it is installed, it does not require painting, cleaning, or patching. This is thanks to its excellent physical properties such as abrasion and corrosion resistance.
Moderate Flame Retardation
Flame retardation is the ability of the material to stop the spread of fire. Materials that have this property burn slowly when ignited and eventually contain the fire. This is helpful in reducing the spread of accidental fires. EPDM has consistently demonstrated this capability, making it an ideal roofing material.
Easy Installation
Technicians that specialize in EPDM roofing perform this process in record time. This is because the material does not require a lot of modification. In most cases, the only thing required is heat to activate the material. Also, the roofing material is packaged in long sheets that are rolled on the top of the roof during the roofing.
Benefits of EPDM Rubber
If you consider the properties of this compound, you can easily tell that this material is quite beneficial. Let us make that clear by singling out these benefits.
Long-lasting Performance
In a previous section, we established that, generally, EPDM can last at least 20 years under normal circumstances. It is also worth mentioning that this lifespan is guaranteed with minimal or no maintenance. Such a performance can be considered long and suitable. This is because you will have gotten more than enough value from the material.
Weather-proof
The weather is usually quite unpredictable in most areas. However, something that remains constant is that weather can have damaging effects on compounds like rubber.
We saw that EPDM has excellent resistance to ozone and its counterparts. This means that the material is weather-proof. As such, it opens up the material to a whole range of applications and so on. This is why EPDM is mostly used in roofing services.
Wide Range of Applications
In another section, we will detail the applications of EPDM and you will be able to see how useful this compound is. Applications span across different industries, with most of them being in harsh conditions of the environment.
Flexible over a wide range of temperatures
Having a wide range of operating temperatures is a good thing for rubber. This means it can be exposed to low or high temperatures and still remain functional. This is unlike most synthetic elastomers that can only sustain either low or high temperatures.
Low maintenance
Requiring minimal to no maintenance except for regular checkups, EPDM makes the list of low-maintenance rubber compounds. Maintenance is generally expensive. Therefore, since this material requires low maintenance, it translates to low costs in the long run. Occasionally, you might be required to replace components due to natural wear and tear.
Non-toxic
Toxicity is dangerous for the environment. EPDM has low toxicity levels, which can be removed during the vulcanization process. As we said earlier, the best approach to ensure the lowest levels of toxicity is to use peroxide during the vulcanization process.
Good electrical insulation
Electrical insulation is required in several applications across many industries. EPDM has demonstrated good insulation due to its high resistivity and low dielectric constant. Due to its molecular structure, it hinders the flow of electrons, thereby making it a bad conductor of electricity.
Limitations of EPDM Rubber
On top of all the praise, EPDM has its fair share of limitations. This is because the material is by no means indestructible. For the most part, its limitations are related to some of its poor properties. These limitations include;
Poor rubber-metal bonding capabilities
EPDM is not among the rubber compounds used in rubber-to-metal bonding, a process that is used to create rubber-metal hybrids. One of the main reasons for this is because the material is non-polar. Polarity is required for forming strong bonds with metals, which are usually polar in nature.
High compression set
When rubber is said to have a low compression set, it means that the compound decreases in size when compressed. Typically, rubber is expected to return to its form after the compression force is retracted. Elastomers like silicone demonstrate this property perfectly. EPDM, on the other hand, cannot return to its natural form after this compression.
Easily degrades when exposed to oils
We discussed this when looking at the properties of EPDM rubber. Being unable to sustain oil degradation is a huge disadvantage for rubber. This is because most rubbers are primarily meant to be used in oil-prone environments.
Poor compatibility with aggressive chemicals
Aggressive chemicals are known to be so hostile that they can degrade even the strongest elements on Earth. They include strong acids, strong alkalis, halogens, and so on. These compounds contain elements that can cause corrosion or complete dissolution of the material. EPDM is unable to remain unchanged when it comes into contact with these chemicals.
Applications of EPDM Rubber
The uses of EPDM rubber span across multiple industries. Right now, you might be in possession of something made from this material and you would never tell. Several manufacturers use this compound for its unmatched properties.
Some of the common uses of the material include;
- Roofing – As we saw earlier, there are many reasons why this compound is the go-to roofing material. For over 50 years, construction companies have relied on it to add an extra layer of protection to roofs.
- Automotive parts – In the automotive industry, rubber is an inseparable commodity. You will see being used in engine parts, wheels, dashboards, and so on. EPDM is among the rubber materials used to make these parts.
- Construction equipment – Apart from roofing, EPDM is also used in other construction equipment. These are mostly equipment that are used in the open such as mats, tools, and so on.
- HVAC equipment – Due to its excellent proofing qualities, EPDM rubber is relied on in the HVAC industry. Components include seals, o-rings, and gaskets are common.
- Industrial rubber products – This is a broad category representing all components used in multiple industries. They include bushings, gaskets, flooring material, and rollers. Most of these components are made of EPDM rubber.
This list of applications is not exhaustive since it does not consider grades of EPDM rubber. That means there could be more applications that we have not mentioned here. All in all, you have gotten a sense of how reliable this synthetic rubber is.
Conclusion
Everything about EPDM points to its versatility as a synthetic rubber. It has exceptional properties and characteristics that build on those of natural rubber. Pushing the limits of natural rubber is at the heart of synthesizing rubber-like materials in the lab. It is accurate to say that the applications of EPDM rubber have demonstrated this goal in totality.