Ageing - change in the polymer structure
What is ageing?
Ageing refers to the time-dependent degradation of the physical, chemical and mechanical properties of a material due to environmental influences and operational stresses. In the case of elastomers such as natural rubber (NR), EPDM, NBR or silicone rubber (VMQ), ageing leads to changes in the Polymer structure, which manifests itself in brittleness, loss of elasticity, Cracking, discolouration or swelling.
What factors influence the ageing of rubber parts?
- Thermal influences: high temperatures accelerate chemical reactions such as oxidation or post-crosslinking
- Oxidation: Oxygen splits or cross-links polymer chains, which changes hardness and flexibility
- Ozone: Ozone also has a chain-splitting effect and causes fine surface cracks, especially in components that are already pre-stressed and stretched
- UV radiation: photochemical decomposition of the polymer chains, which leads to mechanical weakening and embrittlement. Often becomes visible as yellowing or chalking
- Contact with media: Oils, solvents, acids or alkalis can swell or decompose materials
- Dynamic load: cyclical elongation or compressive loads promote micro-crack formation and fatigue
Ageing can affect the function of seals, vibration dampers, diaphragms and. Moulded rubber parts, Silicone moulded parts and Joint parts can be severely impaired by reducing or losing tightness, flexibility or strength. In safety-critical applications such as aerospace or medical technology, ageing resistance is therefore a decisive selection criterion.
What measures are there for ageing resistance?
The service life of elastomers can be extended by using suitable anti-ageing agents, selecting resistant materials (e.g. FKM or EPDM), protective coatings, storage under optimum conditions and design measures (e.g. avoiding permanent expansion in ozone-laden air).
