Aging of Elastomers

In the case of elastomers, aging describes the gradual process by which they lose their physical and chemical properties over time, particularly their elasticity and flexibility. This process, which - like abrasion - has a significant impact on the performance and service life of elastomer components, results on the one hand from a combination of external influences. These include temperature, UV radiation, ozone or chemical substances. On the other hand, the intrinsic properties of the material also drive the aging process - for example the molecular structure or the additives in the material.

Causes of aging

The aging of elastomers is a complex process. Understanding these aging mechanisms is crucial for the selection and use of elastomers in demanding applications. From material selection to compounding and component design, targeted measures can be taken to extend the service life of elastomer components over their entire service life.

Thermal stress plays a key role in aging. Increased temperatures accelerate chemical reactions in the elastomer, particularly thermal oxidation. This leads to degradation of the polymer chains, which manifests itself in a deterioration in mechanical properties. This aspect must be given particular consideration when designing seals or molded parts for high-temperature applications.

Oxidative processes , triggered by contact with atmospheric oxygen, pose a further challenge. These reactions attack the polymer chains and can break them, leading to significant material weakening. Unsaturated elastomers such as NR or SBR are particularly susceptible to this and often require the use of special antioxidants.

UV radiation triggers photochemical reactions in elastomers that lead to the formation of free radicals. These radicals can in turn break or cross-link polymer chains, which in practice leads to embrittlement and material degradation. UV resistance is therefore a critical factor in outdoor applications, such as profile seals or bellows.

Ozone exposure and its consequences are also often underestimated. It leads to accelerated aging, particularly in unsaturated elastomers such as NR, SBR or BR. Ozone attacks the double bonds in the polymer chains, which leads to cracking and embrittlement. This phenomenon, known as ozone cracking, is particularly important for elastomer components used outdoors and often requires the use of special ozone protection agents or the choice of ozone-resistant materials such as EPDM or FKM .

Chemical influences from aggressive media such as acids, alkalis or solvents can cause lasting damage to the polymer structure. The selection of an appropriately chemically resistant elastomer, for example FKM for mineral oil environments or EPDM for use in environments exposed to brake fluids, is essential for the long-term stability of the material.

Mechanical stresses , particularly cyclical stresses, lead to fatigue in the elastomer. The formation of microcracks that grow over time can ultimately lead to failure of the component - for example in dynamically loaded components such as bellows. These must withstand repeated stretching and compression, so the correct choice and design of materials, taking mechanical aging into account, is crucial for a long service life and reliable function.

Signs and Effects of Aging in Elastomers

What is true for human life also applies to elastomers to a certain extent: aging does not happen overnight - it is a progressive process. It manifests itself in various forms that can affect the functionality and reliability of the components.

One of the most common effects is an increase in the hardness of the material. The elastomer loses its flexibility, becomes more brittle and shows a reduced ability to adapt to deformation. This can be particularly problematic in sealing applications, as the sealing effect decreases.

In parallel with hardening, a decrease in tear strength and elongation at break often occurs. The material becomes more susceptible to cracking and can break more easily under stress. Fine cracks can form on the surface, which can spread over time and lead to material failure.

Another visible consequence of aging is color changes. These can range from slight discoloration to significant yellowing or browning. Although color changes do not always directly affect the mechanical properties, they are an indicator of chemical changes in the material.

Many elastomers also tend to change dimensions as they age . They can shrink or swell, which can lead to significant problems in precision applications. In addition, components subject to dynamic stress can experience increased abrasion, which further shortens the service life.

Methods for delaying aging in elastomers

Fortunately, elastomers are not immune to the aging process - the right handling makes the difference. For example, the correct storage of the components : cool, dry and dark environments slow down the aging process considerably. Extreme temperature changes and direct sunlight should be avoided. Controlling the humidity is just as important. This should be neither too high nor too low in order to protect the material from drying out or from promoting oxidation processes. In addition, elastomer components must be kept away from chemical substances and ozone sources during storage - such as engines, welding equipment or UV lamps.

Where contact with chemicals or other aggressive media is unavoidable during use of the elastomer product, special coatings or the choice of more resistant elastomer types can provide a remedy. In some cases, the use of protective housings or shields is also useful in order to minimize the impact of harmful environmental influences.

Measures can also be taken during the compounding of the elastomer: The use of anti-aging agents such as antioxidants, UV stabilizers or ozone protection agents can significantly increase resistance to various aging mechanisms. The choice and dosage of these additives must be carefully tailored to the application. One example of an additive that can be added during compounding is special ozone protection waxes. The wax migrates to the surface of the elastomer and forms a protective layer there. This layer then reacts preferentially with ozone and thus absorbs most of the ozone pollution, protecting the underlying elastomer from direct ozone attack. The wax thus bears the brunt of the ozone reaction and ultimately extends the service life of the elastomer.

For critical applications, regular monitoring of components is recommended . Cyclical inspections and measurements allow signs of aging to be detected early and countermeasures to be initiated. This can range from simple visual inspections to complex material-technical investigations.