Elastomers in Product Development: Material Properties

Elastomers. Generated by Midjourney

Elastomers are the hard-working hero of many a product design. In this series of posts, we’re exploring the flexible properties and use cases for a range of elastomers and examining their use in new product development.

Porticos has extensive knowledge and experience with the integration of elastomers into physical devices. We’re here to help; please get in touch!

Read Previous Post: Elastomer Fabrication Processes

The first article in this series, Introduction to Elastomers, listed several properties that set elastomers apart from other engineering materials. When designing a product, these materials offer specialization that is often required for mission-specific applications. The priority of a toothbrush grip is cost, for example, whereas the priorities of a car tire are traction and wear resistance.

Hundreds of elastomers have been developed to fit the many niche needs encountered in product development. In this article, we’ll consider the elastomer properties most commonly used and differentiate their benefits.

Elastomer cable jacket comparison at room temperature and -30°C (-22°F)
Elastomer cable jacket comparison at room temperature (left) and -30°C (-22°F) (right).

Environmental Suitability

“Where will it be used?” is the first question one should ask when designing an elastomeric component. This answer informs the range of temperatures, chemicals, and solar radiation the elastomer must withstand.

Temperature range is especially critical. Above a certain temperature, thermoplastic elastomers will melt (by design) and thermosets will chemically degrade. Below a certain temperature (known as the glass transition temperature) they will lose much of their elasticity (see example, right). Only a few elastomers are suitable for bitterly cold temperatures.

Hardness

Hardness refers to a material’s ability to resist localized deformation at its surface, i.e., withstand exterior indentations. 

Elastomers are so soft that they have their own set of hardness scales. Product designers can use a hardness specification to indirectly control other properties of an elastomer, such as modulus (flexibility) and conformability. 

Harder elastomers are frequently used in applications where good abrasion resistance is required, such as vehicle tires. Softer elastomers are commonly used to create ergonomic grips and provide cushioning. TPEs (thermoplastic elastomers) are particularly useful in these applications since they can be insert-molded or over-molded onto more rigid materials like plastic or metal.

Deformation Characteristics

Generally, elastomers will return to their original shape after being deformed. However, they have some additional behaviors that should be considered.

First, many elastomers are somewhat viscoelastic. That viscosity means they tend to resist rapid deformation, a property that makes them useful in vibration-dampening applications.

Second, all elastomers experience compression set and stress relaxation when deformed for long periods of time. “Compression set” is a plastic (permanent) deformation of the elastomer after deformation. Stress relaxation is a reduction in “push back” force at a fixed amount of deformation. Both of those behaviors can degrade elastomer materials and lead to issues in products, particularly when used for sealing applications.

Reduction in Push-Back Force” over 45 seconds
Reduction in “Push-Back Force” over 45 seconds.

Friction and Wear

Elastomers are known for having a high coefficient of friction, meaning they typically add high frictional force. This property facilitates their use in tires, shoe soles, and non-slip socks. Most of those applications also benefit from increased wear resistance, which makes some elastomers more suitable than others. Elastomers can also be modified with additives to improve their wear resistance, or to reduce friction in sliding applications such as dynamic seals.

Permeability and Outgassing

When creating a seal, it is crucial that the fluid being contained does not seep through, or permeate, the material(s) containing it. Elastomers make very effective liquid seals due to their low liquid permeability.

More care must be taken when selecting a seal material for gasses. For example, many elastomers are susceptible to permeation by hydrogen and helium.

The use of elastomers for vacuum applications requires careful testing and consideration. Most elastomers will outgas at low absolute pressure. This will change the chemical and mechanical properties of the elastomer over time, possibly rendering it brittle or porous.

Biocompatibility

Some elastomers (particularly silicone) are acceptable for use in medical and food-handling applications. Most, however, are not used in these applications unless specifically designed and tested to meet rigorous safety standards. It is also worth noting that natural rubber (latex) can cause allergic reactions.

Next Up

In this article, we have discussed the properties used to differentiate elastomers. But which elastomers perform the best in each category? Which elastomers are best for combinations of goals? 

In our next article, we will discuss some of our favorite elastomers and suggest where and when they should (and should not) be used.

XL200P Exploded View

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