At CRGI, customers are always bringing forward new and exciting applications for us to help service. Every application has its challenges, not the least of which is the inevitable degradation that rubber compounds undergo as they are put to use. While some products, like fine wine, often improve with age, rubber is one material that usually undergoes some deterioration with time. While the effects of ageing can seem to be a fact of life where rubber is concerned, these effects can often be mitigated if the right material is chosen at the outset.
Ageing is a term often used in the rubber industry to describe the degradation of rubber that can occur over time without the action of chemicals. Three main agents contribute to the ageing of rubber compounds: oxidation from atmospheric oxygen; ozone; and ultra-violet (UV) light. Symptoms of degradation due to ageing include softening and embrittlement of the compound, cracking, and rotting, all of which lead can lead to breakdown and failure of the compound in-use.
When selecting a rubber compound, users should consider the extent to which the compound will be subject to ageing from oxidation, ozone, and UV light. Applications where the end-product is in-use either completely or partially outdoors should be given particular attention. In these types of applications, the rubber compound is more exposed to the forces of ageing – a fact that is often overlooked when selecting materials.
Oxidation of a rubber compound can occur over time as the material is exposed to atmospheric oxygen. Oxidation can cause molecular chain cleavage in some compounds, where the molecular network of the material is loosened, leading to degradation and softening. Oxidation can also cause cross-linking in some rubber compounds, causing hardening and embrittlement of the compound. Compounds that are resistant to oxidation include Neoprene (moderate resistance) and EPDM (high resistance).
Ozone, another gas present in the atmosphere, causes ageing of rubber by breaking the double bonds in a compound, leading to cracking. Whereas oxidation tends to occur slowly over time, ageing due to ozone occurs more quickly and may be increased by stress. Again, both Neoprene and EPDM exhibit resistance to ozone damage.
Sunlight, made up of both visible, infrared and UV light, causes ageing in rubber by promoting the development of free radicals on the surface of a compound. UV light is particularly aggressive, as it causes degradation of the polymers making up the compound. The net result is discolouration and cracking of the material. EPDM, Fluoroelastomers such as Viton®, Chloropene, Urethane, and silicone rubbers offer good resistance to UV ageing.
While the above highlights some the preferred materials for countering the effects of ageing, customers should consider ageing together with the degradation from other sources that is likely to occur when the final product is in-use. For example, while Neoprene, and especially EPDM, are inherently ozone-resistant, a specific application may call for an oil-resistant compound that may also be subject to attack by ozone. In this case, we would advise selecting a specially formulated Nitrile-Butadiene Rubber (NBR) compound that is blended with ozone-resistant ingredients to address this application.
What this example shows is that to ensure fitness for purpose in the end-product, it is vitally important that the application detail be communicated by the customer, and that the application requirements be understood by the supplier. In this example, if the application requirements were neither communicated nor understood, and were a non-ozone-resistant NBR compound to be selected, this compound could break down in less than 72 hours when in-use, causing the entire application to fail.
At CRGI, we are well-versed in helping customers to select the optimal material to counter degradation due to ageing and other factors. Whether the application is general industrial use or automotive, our sales representatives will be pleased to help you select the preferred material for your application.
Paul Carey is CRGI’s Automotive Sales Manager. Contact Paul directly at email@example.com.