OVERVIEW

The term thermal properties is open to more than one interpretation. Specific heat, thermal conductivity and diffusivity clearly come under this heading but the term can be taken to also include heat ageing, low temperature tests and fire resistance. However, these are more properly dealt with, as in this volume, under Effect of Temperature. Thermal analysis is a group of techniques in which a property of a sample is monitored against temperature, or time at a temperature, and, therefore, is also generally concerned with measuring the effect of temperature. Nevertheless, for convenience, a brief overview of thermal analysis is given here.

The thermal properties of rubber are of very great importance, particularly in the processing stages, but there is a remarkable dearth of reliable data. Traditionally, the approach to heating and cooling problems was empirical rather than by careful analysis. The data needed for such analysis was not available, largely because of the undoubted experimental difficulties to be overcome but, even with data, somewhat complicated calculation is required.

In the last two or three decades, the value of an analytical approach to heat transfer problems has been increasingly realised and considerable effort has been devoted to developing measuring techniques and convenient methods of calculation to produce the data needed as input to process simulation software. However, the measurement of thermal properties remains a very specialised subject, there is little evidence of standard procedures and the tests are carried out in relatively few laboratories. As was said of another specialised...