OVERVIEW

Distinction can be made between the short term and long term effects of temperature. In general, short term effects are physical and reversible when the temperature is returned to ambient, whilst the long term effects at elevated temperature are mostly chemical and not reversible. The long term chemical effects are usually referred to as the results of ageing.

All physical properties of rubber vary in the short term when the temperature is changed, some to a greater extent than others. Throughout this book the need has been emphasised to measure properties over a range of temperatures in order to fully characterise the material. In principle, almost any property could be used to monitor the general temperature sensitivity of a rubber but obviously some properties are more satisfactory than others. In practice, the simpler mechanical tests are frequently chosen to give experimental simplicity, but these are not necessarily the most sensitive. It is most sensible, where possible, to monitor the properties which are most relevant to the service applications, and this principle also applies when measuring the ageing effects of long term exposure. The British standard for acquisition and presentation of multi-point data for rubbers ^[1] is largely concerned with data obtained as a function of temperature. Various methods of thermal analysis, as mentioned in Chapter 14, are a particularly efficient way of scanning properties over a range of temperatures. Particular types of test for the short term effect of temperature which require individual comments are thermal expansion, the...