Rubber is probably one of humanity’s greatest inventions, it is a very useful & malleable material but chances are something made of rubber has let you down at some point in your life. Like most elastomers rubber will also undergo significant changes over time when exposed to heat, light and ozone. These changes can have a dramatic effect on the service life and properties of the rubber products also can impair the functionality of critical rubber parts, like seals, O-rings, washers, gaskets etc. and could lead to machine failure which can of course have potentially catastrophic consequences. Read on to find out more about typical rubber deterioration causes and practical ways to prevent rubber deterioration.
What is Rubber Deterioration?
Natural rubber and synthetic elastomers deteriorate on aging as a result of the contribution of a number of factors. It has been generally recognized for many years that the changes in properties on aging are due primarily to the deteriorating effects of one or more of the following factors: heat, light, oxygen, and ozone. Some non oxidative thermal changes are involved but the effects of heat and light are for the most part a result of their effect upon the oxidation reaction. Oxidative and thermal ageing of rubber are accelerated by stress and reactive gases, like ozone, resulting in cracking, charring and color fading. However, the addition of antioxidants, UV stabilizers and antiozonants can slow or prevent these types of issues.
Oxidative rubber degradation can cause hardening or softening, depending on the structure of the elastomer. Hardening is more common because free radicals produced due to heat, oxygen and light combine to form new crosslinks, which reduces the flexibility of the rubber. Although the general mechanism of autoxidation is well understood, the actual chain scission and crosslinking steps are often unknown. They depend on the composition of the rubber including concentration of accelerators, activators, and fillers as well as on the temperature and composition of the atmosphere.
How does Rubber Products deteriorate?
Natural rubber and synthetic elastomers deteriorate on aging as a result of the contribution of a number of factors. It has been generally recognized for many years that the changes in properties on aging are due primarily to the deteriorating effects of one or more of the following factors: heat, light, oxygen, and ozone. Some non oxidative thermal changes are involved but the effects of heat and light are for the most part a result of their effect upon the oxidation reaction. Thus oxygen in the form of O2 or O3 is the primary cause of deterioration of elastomers. Rapid combination with ozone is a characteristic reaction of unsaturated organic compounds.
The two main forms of rubber degradation are: hardening (or embrittlement) and softening. From a molecular perspective, these chemical processes are known as “chain hardening” and “chain scission” respectively. The chemical makeup of the polymer will determine which type of deterioration will ultimately occur. For instance, the polymer polybutadiene and its copolymer derivatives – such as styrene-butadiene-styrene (SBS) and nitrile rubber (NBR) – is developed using a process called cross-linking, which involves joining polymer chains together to form one single molecule. Free radicals produced by heat, oxygen and light combine to form new crosslinks, which reduces flexibility and leads to hardening. This is chain hardening.
Natural rubber (polyisoprene) and other isoprene polymers, on the other hand, are susceptible to chain scission. These types of rubber are developed using polymerization, which entails bonding multiple identical molecules – or monomers – to form a polymer. As such, their polymer main chain is liable to degrade, which is the act of chain scission, and leads to the softening of the rubber material.
How can we prevent rubber products from deterioration ?
Even before a rubber product is manufactured, a technique known as DMA ( Dynamic Mechanical Analysis ) can be used to predict a rubber material’s response to stress-strain conditions. DMA stress analysis illustrates whether a proposed design will function to design specifications prior to manufacturing a mould tool.
After Ageing Properties:
Apart from DMA Ageing properties were tested according to the ASTM D573-99 Standard Test Method for Rubber – Deterioration in an Air Oven. The tensile and physical properties namely hardness, tensile strength, elongation at break, modulus 300%, tear strength were measured before and after ageing for each aging time. This can help to prevent rubber deterioration in the long-term and provide significant cost-savings.
When ozone comes in contact with rubber, the double and triple chemical bonds are attacked causing the cracking that is commonly seen on the surface of some rubber products. Conducting controlled, laboratory Ozone Testing of material samples against industry standards also provide us critical information needed to make formulation decisions.
Rubber compounds are complex mixtures of polymers, reinforcing fillers, oils / plasticizers, curatives, stabilizers, and other additives that are combined in relatively quick mixing processes. Durability is impacted by all these ingredients, their interactions, and the quality of the mixing. By Compounding Designing we are able to find out the correct proportion & composition of mixing various compounds in order to prevent the deterioration of our sealing products such as Seals, O Rings, Gaskets, Washers, Grommets, Bellows etc.
To know more in depth about the essential considerations before designing a rubber products read our another blog- http://www.kesaria.com/5-essential-considerations-before-designing-rubber-products/
Addition Of Antiozonants & Other Additives:
Apart from above methods & techniques the problem can be prevented by adding antiozonants to the rubber before vulcanization. With the help of additives rubber deterioration can be prevented. A common and low cost antiozonant is a wax which bleeds to the surface and forms a protective layer, but other specialist chemicals are also widely used.
On the other hand, the problem does recur in unprotected products such as rubber tubing and seals, where ozone attack is thought to be impossible. Unfortunately, traces of ozone can turn up in the most unexpected situations. Using ozone-resistant rubbers is another way of inhibiting cracking. EPDM rubber and butyl rubber are ozone resistant, for example. For high value equipment where loss of function can cause serious problems, low cost seals may be replaced at frequent intervals so as to preclude failure.
With the right rubber restoring techniques, and a sufficient level of care and maintenance, rubber seals or products of certain polymer types can often be brought back from the brink of failure and restored to functionality.
To know more in depth about how to improve service life of rubber parts read our another blog– http://www.kesaria.com/how-to-improve-serviceife-of-rubber-parts/
At Kesaria Rubber, we have spent decades developing innovative rubber products which are capable of resisting the most challenging sealing environments. We request you to please check our product range. If you would like further assistance, please contact our Sealing Experts who will be happy to help, diagnose the problem and suggest possible solutions.
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