The temperature range over which the physical properties of plastics are important is not larger than 550 C, from -100 C to +450 C. A reasonable lower limit of temperature at which plastics are used is -100 C, and +450 C is the upper limit of fabrication temperatures. For most other materials of construction, for example glass, ceramics, and steel, the corresponding temperature range is much larger, from -100 C to about +1000 C. These materials are fabricated at temperatures which are normally several hundred degrees above the temperatures at which they are used. Plastics are used at temperatures which are considerably closer to their fabrication temperatures. As a result, the effects of temperature on the physical properties are relatively much larger for plastics than for most other materials of construction.
This sensitivity of plastics to temperature is important to the manufacturer and consumer alike. The manufacturer must control the uniformity of his existing products and make every effort to produce new materials having superior thermal properties. The consumer must use plastics at temperatures within which their properties are suitable. To meet the needs of both the manufacturer and consumer, accurate description of the effects of temperature on the physical properties of plastics is required.
Description of the effects of temperature on the physical properties requires test equipment and test methods. Ideally, each method should measure a single, fundamental property. Practically, two types of tests appear to be required: rapid tests which often do not provide fundamental data and have as their principal virtue, characterization; and more elaborate tests, the principal purpose of which is measurement of fundamental properties. In this paper the existing standard ASTM tests for measuring the effects of temperature on the physical properties of plastics will be discussed. Deficiencies in these methods will be pointed out and current efforts toward their improvement, which are under study by Subcommittee III on Thermal Properties, of ASTM Committee D-20 on Plastics, will be described. The need for additional test methods will be discussed as the basis for probable future development.