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How to Identify Plastics

Here is a preliminary guide that will help you to identify many of the basic types of plastics using simple techniques and readily available tools.

Naturally, these tests should be used only for tentative identification because some complex plastic compounds require a rigorous analysis for identification.

To initially determine whether a material is thermoset or thermoplastic, heat a stirring rod (to about 500°F/260°C, the material is a thermoplastic; if not, it is probably a thermoset.

Next, hold the sample to the edge of a flame until it ignites. (Hold in the flame for about 10 seconds if no flame is produced immediately.) If the material burns, note the nature of the smoke, the presence of soot in the air and, if while burning, the sample drips.

Next, extinguish the flame and cautiously smell the fumes. (In identifying the odor, a known sample is most helpful for comparison.) Finally, check your observations against the known characteristics of each plastic given on page 93.

Once you have made a tentative identification, it is usually desirable to make one additional test to confirm the results of the original identification. Remember additives may affect results; for example, flame retardants would mask the polymer’s normal burning characteristics.

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