Both density and specific gravity are significant physical characteristics that dictate both the mechanical, thermal and processing characteristics of plastic materials. The ASTM D792, the name of the former being Standard Test Methods of Density and Specific Gravity of Plastics by Displacement, outlines the standard practices that ensure the accuracy of measuring these two aspects. The technique is especially significant as even the slight differences in the density may hint at the variations of the formulation, filler content, or processing conditions. Compliance with the ASTM D792 will help the laboratories to make sure that measurements of densities are valid, reproducible and comparable even across batches and suppliers. This criterion is typically applied in studies, product design, and quality control of plastic material of a routine.
Principle and Methodology
The principle of ASTM D792 is founded on the principle of Archimedes, whereby a principle of buoyancy of a specimen in a fluid is utilized to identify its volume. It is conducted by weighing the plastic specimen in air followed by weighing in liquid that is appropriate in most cases in distilled water. The calculation of the density and specific gravity of the material is done by using the difference between these weights. To preserve the accuracy the method considers the effects of temperature on the immersion fluid. To guarantee reliable results according to this standard, it is important to ensure that the specimen is properly conditioned and all the air bubbles are removed.
