What are the factors contributing to the aging of O-ring materials?

  O-rings are widely used for sealing in various mechanical equipment. They perform sealing functions under static or dynamic conditions in specific temperatures, pressures, and different liquid and gas media, while also possessing resistance to high and low temperatures. When manufacturing rubber sealing ring products, it is necessary to control the ambient temperature to maintain good sealing elasticity, as well as the advantages of ozone resistance and weather aging resistance.

Additionally, rubber sealing materials offer excellent properties such as non-toxicity, odorlessness, water resistance, flame retardancy, heat resistance, wear resistance, and oil resistance. They can be made into thermal insulation, insulation products, and medical silicone products, making them environmentally friendly standard seals. So, what are the factors contributing to the aging of O-ring rubber materials?

1, Oxidation mechanism: Oxygen undergoes free radical chain reactions with rubber molecules in O-ring rubber materials, leading to molecular chain scission or excessive crosslinking, which changes the properties of silicone rubber products. Oxidation is one of the key causes of rubber seal aging.

2,Light mechanism: Ultraviolet (UV) light with high energy is responsible for damaging rubber sealing materials, as shorter light wavelengths carry higher energy. In addition to causing rubber molecular chain scission and crosslinking, rubber absorbs light energy to generate free radicals, thereby accelerating the oxidative chain reaction process. External light also exerts a heating effect. Another characteristic of light (different from heat) is that it primarily acts on the rubber surface. For samples with high rubber content, mesh cracks may appear on both sides, a phenomenon known as "photo-oxidative cracking" (or "surface cracking due to light exposure").

3,Ozone effect: Ozone is much more chemically reactive than oxygen and highly destructive. It also breaks molecular chains, but its effect on O-ring materials varies with rubber deformation.

4,High temperature: Elevated temperatures can cause thermal cracking or thermal crosslinking of O-ring rubber products, but the main role of heat is activation. It increases oxygen diffusion rate and active oxidation reactions, accelerating the rubber oxidation process—a common aging phenomenon known as thermo-oxidative aging.

5,Mechanical stress: Under repeated mechanical stress, rubber sealing rings undergo molecular chain scission, generating free radicals that trigger oxidative chain reactions, forming a mechanochemical process. This involves both mechanical molecular chain breakage and mechanically activated oxidation. Furthermore, ozone cracking is likely to occur under stress.

6,Moisture effect: Moisture impacts aging in two ways. Firstly, silicone rubber products are prone to damage when exposed to humid air, rain, or immersion in water, as water-soluble substances and hydrophilic groups in the rubber are leached and dissolved by water. Secondly, hydrolysis or moisture absorption—especially under the alternating effects of water immersion and atmospheric exposure—accelerates the deterioration of rubber sealing materials.

7,Other factors: Chemical media (such as oils), variable valence metal ions, high-energy radiation, electricity, and biological agents can also affect the aging degree of O-ring rubber materials.

8,Material-specific considerations: Different rubber materials have varying requirements for operating pressures, so the aging of O-ring materials must be treated differently. Nitrile rubber (NBR) exhibits good oil resistance and hydrolysis resistance; fluoroelastomers (FKM/Viton) resist various chemical substances; and EPDM (ethylene propylene diene monomer) offers excellent UV resistance.