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R., P. Brown, T. Butler, "Natural Ageing of Rubber - Changes in Physical Properties Over 40 Years"

A unique collection of long term ageing data, available for the first time, from Rapra Technology Limited.

This report is an output from the Weathering of Elastomers and Sealants project which forms part of the UK government’s Department of Trade and Industry’s Degradation of Materials in Aggressive Environments Programme.

Rapra Technology Limited has just completed a comprehensive natural ageing and physical testing programme on 19 rubber compounds, stored in controlled conditions, for a period of 40 years. This is believed to be the most extensive such study ever carried out. Now, for the first time, all the results of this unique programme have been published in this report.

The properties of natural and synthetic rubbers suit them to a diverse range of applications, many of which demand a prolonged service life, and the retention of some or all of their mechanical properties for years or even decades. When the ageing programme was conceived in the 1950s, rubber product manufacturers were faced with a wider range of raw rubbers than had ever been available before. The relatively recent development of some of these materials also meant that there was little information available regarding their longevity. Thus the need was identified for a systematic programme of storage and testing.

Rubber formulations were selected to represent those used in a wide range of applications, including general purpose and ‘good ageing’ grades. Remarkably, most of these formulations are still representative of compounds being specified today. The following rubbers were studied:

* Natural rubber

* Styrene-butadiene rubber

* Butyl rubber

* Polychloroprene

* Nitrile rubber

* Acrylate rubber

* Chlorosulphonated polyethylene

* Polysulphide rubber

* Silicone rubber

Samples were stored under temperate and tropical climatic conditions, and at various intervals the following properties were measured:

* Hardness

* Volume change

* Resilience

* Volume and surface resistivity

* Tensile strength

* Elongation at break

* Modulus at 100% and 300% elongation

* Long and short term compression set

* Low temperature stiffness

The results of all these tests are presented graphically in this report, allowing the rate of deterioration of properties and the influence of the environment to be clearly seen. Properties after 40 years are also tabulated, together with calculations of percentage change. This information will prove invaluable to anyone specifying or supplying rubber materials or components.

Further work is now being carried out on the properties of the same formulations after accelerated ageing. If you would like to be informed when this programme is complete, please contact Rapra Technology Ltd for further information.

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