EPDM Rubber: Properties, Applications, and Curing Processes

EPDM rubber, or ethylene propylene diene monomer rubber, is a synthetic elastomer material that is well-known for its excellent weather and ozone resistance. It was first developed in the 1960s and has since been used in a wide range of applications due to its unique properties. In this blog, we will take a closer look at EPDM rubber and its various applications.

Properties of EPDM Rubber

EPDM rubber has several unique properties that make it an ideal material for a wide range of applications, including:

1. Excellent Weather and Ozone Resistance: EPDM rubber has excellent resistance to weathering and ozone, making it an ideal material for outdoor applications.
2. Good Chemical Resistance: EPDM rubber has good resistance to many chemicals, including certain acids and alkalis.
3. Good Heat Resistance: EPDM rubber has good heat resistance and can withstand relatively high temperatures and relatively low temperatures without degrading or losing its properties. Most EPDM materials can handle temperatures ranging from -67°F to 300°F (-55°C to 150°C), but can vary depending on cure type and use case. Some specialty blends can even handle temperatures up to 555°F (290°C).
4. Good Electrical Insulation Properties: EPDM rubber has good electrical insulation properties, making it an ideal material for manufacturing electrical components.

Applications of EPDM Rubber

EPDM rubber has a broad range of applications across various industries, including:

1. Automotive Industry: EPDM rubber is widely used in the automotive industry for manufacturing various components, including seals, O-rings, hoses, and weather-stripping, that require excellent weather and ozone resistance.
2. Drinking Water Industry: EPDM rubber is commonly used in applications where NSF 61 certified materials are required.
3. Construction Industry: EPDM rubber is used in the construction industry for manufacturing various products, including roofing membranes, gaskets, and seals, that require excellent weather and ozone resistance.
4. Electrical Industry: EPDM rubber is used in the electrical industry for manufacturing various components, including electrical waterproofing seals, insulation and cable jackets, that require excellent electrical insulation properties.
5. Consumer Goods Industry: EPDM rubber is used in the consumer goods industry for manufacturing various products, including garden hoses, boots, and weather-stripping, that require excellent weather and ozone resistance.

Curing Types

One critical aspect of EPDM rubber is the curing process. Curing is the process of transforming the raw rubber material into a solid, usable product. There are several different types of EPDM rubber cure types, each with its advantages and disadvantages. In this blog post, we will discuss the two most common types of EPDM rubber cure types.

1. Sulfur Cure: Sulfur cure is a widely used EPDM rubber curing process. This process involves mixing the raw rubber material with sulfur, which acts as a curing agent. The sulfur cure process requires a lower curing temperature and has a shorter curing time than peroxide cure, but it results in lower mechanical properties and heat resistance. Sulfur cured EPDM parts can sometimes experience excretions of a dusty white substance called “bloom”. Read more in the “bloom” section below.
2. Peroxide Cure: Peroxide cure is the most common type of EPDM rubber curing process. This process uses peroxide chemicals, which are mixed with the raw rubber material before molding. The peroxide chemicals act as a catalyst, initiating the cross-linking of the rubber molecules. This curing process requires high-temperature molds and has a longer curing time, but it results in excellent mechanical properties and heat resistance. Peroxide cured EPDM is generally considered “cleaner” and does not bloom.

Bloom

Bloom is a phenomenon that occurs in sulfur-cured EPDM rubber (and some other materials) where a powdery film appears on the surface of the rubber. The film can be white or brown in color and can be wiped off easily with a cloth or a soft brush.

Bloom occurs because of the migration of inert, unreacted sulfur or wax to the surface of the rubber. During the sulfur curing process, excess sulfur can remain on the surface of the rubber, where it reacts with oxygen to form sulfur dioxide gas. The sulfur dioxide then reacts with moisture in the air to form sulfuric acid, which causes the powdery film to appear on the surface of the rubber.

Bloom is more common in sulfur-cured EPDM rubber that has been stored for a long time or in conditions where the rubber is exposed to high humidity or heat. While bloom does not affect the mechanical properties of the rubber, it can affect the appearance of the finished product and may cause surface contamination or adhesion issues if the rubber is to be painted, glued, or coated.

To prevent bloom, manufacturers may add anti-blooming agents to the rubber compound or use alternative curing methods such as peroxide cure. Proper storage conditions, such as low humidity and moderate temperatures, can also help to prevent bloom from occurring.

Conclusion

EPDM rubber is a highly versatile elastomer material that offers excellent weather and ozone resistance, as well as good chemical resistance and electrical insulation properties. Its unique properties make it an ideal material for a wide range of applications across various industries, including the automotive, construction, electrical, and consumer goods industries. If you require a material that offers excellent weather and ozone resistance for your application, EPDM rubber may be an excellent choice for you. If you are interested in learning more, see our EPDM page!

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Sources:

[1] All about EPDM rubber - properties, applications and uses. (2021, October 27). https://www.thomasnet.com/articles/plastics-rubber/all-about-epdm-rubber-properties-applications-and-uses/

[2] Shamsabadi, A. A., Farahani, A., Shirkavand, M. J., Hafezi, M., & Tohidian, M. (2023). Carbon black/ethylene propylene diene monomer (EPDM) rubber as polymer electrolyte membrane fuel cell gaskets: mechanical and chemical assessment. Iranian Polymer Journal. https://doi.org/10.1007/s13726-023-01239-9

[3] Wang, Y., Liu, H., Li, P., & Wang, L. (2022). The effect of Cross-Linking type on EPDM elastomer dynamics and mechanical Properties: A Molecular Dynamics Simulation study. Polymers, 14(7), 1308. https://doi.org/10.3390/polym14071308

[4] Colom, X., Carrillo-Navarrete, F., Saeb, M. R., Marín-Genescà, M., Formela, K., & Cañavate, J. (2023). Evaluation and rationale of the performance of several elastomeric composites incorporating devulcanized EPDM. Polymer Testing, 121, 107976. https://doi.org/10.1016/j.polymertesting.2023.107976