Chemical Resistance of TPE 

Why the Interplay between Material, Medium, and Component Design is Crucial

Seals come into contact with cleaning agents, handles with oils and greases, automotive components with fuels or operating fluids, and components in industrial applications with a wide variety of process media. Thermoplastic Elastomers (TPE) are regularly exposed to chemical substances in many applications.

A key and entirely valid question that my colleagues in sales and development often hear is: “How resistant is your TPE to this or that medium?” But there is no one-size-fits-all answer to this question. 
The chemical resistance of a TPE does not depend only on the material or the chemical. Factors such as material composition, medium, temperature, duration of contact, type of contact, and component geometry are decisive. Equally important is the question of what happens at the molecular level during contact.

Generally speaking, two types of interaction can be distinguished: physical and chemical effects. In the case of a physical effect, the medium does not react chemically with the polymer. Instead, it can, for example, influence the structure of the TPE. In some cases, such processes are reversible: if the medium is removed, the material can—depending on the material, medium, and stress—return to its original state, at least to a large extent. A typical phenomenon is swelling: molecules from the contacting medium penetrate the material, causing its volume to increase and its mechanical properties to change.

Other possible consequences of physical effects include changes in weight or volume, softening, as well as irreversible embrittlement or changes and defects on the surface.

A fundamental principle from chemistry helps in assessing resistance: like dissolves like. Put simply, this means that substances with similar polarity often interact more strongly with one another. For example, a nonpolar polymer is more sensitive to certain nonpolar media, whereas polar media exhibit different behavior when in contact with nonpolar polymers.

This consideration is particularly relevant for thermoplastic elastomers, as this is a highly diverse class of materials. The polymer base, additives, plasticizers, fillers, and other formulation components determine—in terms of their proportions and combinations—how polar or nonpolar a compound is and how it reacts to a specific medium. 

Therefore, chemical resistance can under no circumstances be assessed in a blanket manner for “TPE.”

Even a material that is fundamentally suitable can exhibit different behavior under changed operating conditions. Two of the most important influencing factors are temperature and duration of contact.

As temperature rises, diffusion processes can be accelerated. Media may penetrate the material more quickly or more deeply under certain circumstances, while chemical reactions may proceed more rapidly. A TPE that shows virtually no changes at room temperature over a short period of time may react significantly differently at higher temperatures or with prolonged exposure.

Therefore, information on media resistance should always be considered in conjunction with the actual operating conditions. The statement “resistant to medium X” is of limited significance without information on temperature and time.

In addition to the material itself and its environmental conditions, another factor is often underestimated: the geometry of the component. Wall thickness, in particular, influences the extent to which a medium can affect a component. Thin-walled areas can be completely penetrated more quickly than solid areas.

Corners, edges, notches, and transitions also deserve special attention. Mechanical stresses can become concentrated in these areas. When chemical or physical influences act on areas that are already under high stress, the effects can reinforce one another. Chemical resistance is therefore not exclusively a matter of material properties, but always also a matter of component design.

Tables and resistance lists are a helpful starting point for the preliminary selection of a material. However, they can only partially reflect the actual operating conditions of a component. For a reliable material evaluation, several factors must therefore be considered together: What medium is used? At what concentration? At what temperature? How long and in what manner does contact occur? What is the component’s geometry, and what mechanical stresses is it simultaneously exposed to?

In our certified laboratory, we have the capability to conduct a wide range of tests and simulations and provide you with the best possible advice. And as we’ve already mentioned in our recent newsletters, it’s always beneficial to involve material suppliers as early as possible in project phases.

This is because, particularly with TPE, one fundamental principle of material selection becomes especially clear: chemical resistance is not an isolated material property. It is the interplay of the polymer base, formulation, environmental conditions, design, and processing that ultimately determines how a material will perform over the long term in a specific application.

Which media and operating conditions pose the greatest challenges for you when selecting TPE? We look forward to your comments.