What’s the Difference Between Elastomers and Silicones

Elastomers and silicones are two versatile materials commonly used in machinery, but do you really understand the key differences between them?

Choosing the wrong material for your application can lead to premature part failure, unplanned downtime, and ballooning maintenance costs.

In this article, we’ll dive into the critical differences between elastomers and silicones, including their composition, properties, and best-fit applications.

What Are Elastomers

Elastomers are polymeric materials that exhibit rubber-like elasticity. They can stretch and deform under stress but return to their original shape once the stress is removed. This reversible deformation is due to the cross-linked structure of elastomer molecules.

The term “elastomer” is derived from “elastic polymer.” Elastomers consist of long polymer chains with intermolecular crosslinks. These crosslinks allow the material to be stretched to high strains and spring back to its original dimensions when the stress is released.

What Are Silicones

Silicones, also known as polysiloxanes, are synthetic polymers that contain a repeating siloxane (Si-O) backbone with organic groups attached to the silicon atoms. The siloxane backbone provides silicones with unique properties compared to carbon-based polymers.

The most common silicone is polydimethylsiloxane (PDMS), where two methyl groups are attached to each silicon atom. However, other organic groups can be used to modify the properties of silicones for specific applications.

The Difference Between Elastomers and Silicones

Backbone Composition

The primary difference between elastomers and silicones lies in their polymer backbones. Elastomers are based on carbon-carbon backbones, similar to other organic polymers. In contrast, silicones have a siloxane (Si-O) backbone with organic groups attached to the silicon atoms.

Chemical Resistance

Silicones generally show better resistance to chemicals compared to elastomers. The siloxane (Si−O) bonds in silicones are more stable and less reactive than the C−C bonds in elastomers when exposed to oils, solvents, and other aggressive chemicals.

Heat Resistance

Silicones provide superior heat resistance compared to most elastomers. Silicone rubber can maintain its properties at temperatures up to 300°C (572°F) for extended periods.

Most elastomers have lower heat resistance, with maximum service temperatures around 150-200°C (302-392°F).

Cold Resistance

Silicones maintain flexibility and elasticity at extremely low temperatures, down to -100°C (-148°F) or lower. The flexible siloxane backbone allows silicone molecules to move and bend easily, even when cooled.

Elastomers tend to stiffen and lose elasticity at low temperatures due to the reduced motion of the polymer chains. The glass transition temperature (Tg) of elastomers varies widely. Some elastomers like silicone rubber and fluorosilicone rubber have very low Tg values and maintain flexibility at low temperatures.

UV Resistance

Silicones provide excellent resistance to UV degradation. The siloxane bonds are stable under UV light exposure, allowing silicones to retain their properties outdoors for extended periods.

Many elastomers are susceptible to UV degradation unless specifically formulated with UV stabilizers. UV light can break chemical bonds in elastomer molecules, leading to cracking, discoloration, and loss of mechanical properties over time.

Durability

Elastomers generally have higher tensile strength, abrasion resistance, and tear resistance than silicones. This makes elastomers more suitable for dynamic sealing applications and where high mechanical strength is required. Silicones are preferred for static seals and applications where extreme temperature or chemical resistance is crucial.

Compression Set

Silicones typically have lower compression set values compared to elastomers, meaning they recoverbetter and retain their original shape after prolonged compression. This property makes silicones ideal for sealing applications where long-term stress is applied. Elastomers may suffer from higher permanent deformation under similar conditions.

Cost

Elastomers are generally less expensive than silicones. The raw materials and processing costs for elastomers are lower, making them a more cost-effective choice for many applications. Silicones have a higher cost due to the more expensive raw materials and specialized manufacturing processes required.

Recyclability

Elastomers are more easily recyclable compared to silicones. Many elastomers, such as natural rubber and thermoplastic elastomers (TPEs), can be reprocessed and reused. Silicones, on the other hand, are thermoset polymers that are difficult to recycle due to their cross-linked structure. Recycling silicones often involves downcycling into lower-value products.

Applications

Elastomers find widespread use in tires, conveyor belts, hoses, seals, gaskets, and shock absorption components. They are preferred for applications requiring high mechanical strength, abrasion resistance, and dynamic sealing.

Silicones are commonly used in medical devices, food processing equipment, electrical insulation, sealants, adhesives, and high-temperature applications. They excel in areas where biocompatibility, chemical inertness, wide temperature stability, and weathering resistance are essential.