ASTM D792, ISO 1183 Specific Gravity and density

ASTM D792, ISO 1183 Specific Gravity and density Scope:

ASTM D792 test is used for the determination of the specific gravity (relative density) and density of solid plastics in the form of sheets, rods, tubes, or molded items. Specific gravity means a measure of the mass ratio of a given substance volume at 23 °C of the same deionized water volume. Density is the mass of a substance per unit volume. Specific gravity and density are particularly important when plastic is sold at a cost per pound and a lower density or specific gravity means more material per pound or varying weight of the component.

Test Procedure:

The determination of specific gravity and density for solid plastic items is carried out using ASTM D792 and ISO 1183 test techniques. It is convenient to measure a solid’s specific gravity or density to determine its composition, track physical changes in a sample, assess the degree of homogeneity between several sampling units or specimens, or estimate the typical density of a huge object. 

There are two basic test methods for the ASTM D792 test:  method A and method B. Method A can be used for the sheets, rods, tubes, and moulded articles. For the test method A, the sample is measured in air and then weighed after immersing in distilled water. The temperature is maintained at 23°C using a sinker and wire, to keep the sample completely submerged. Finally, the density and specific gravity calculations are carried out.

A single material’s density can change for a variety of reasons, including localised changes in crystallinity, the loss of a plasticizer, solvent absorption, or other factors. It’s possible that different regions of a sample have different densities due to changes in its composition, porosity, thermal history, and crystallinity.

It should be noted that the ISO 1183-1 Method A is not equivalent to this standard. Additional instructions on sample weight and dimension are provided by this test procedure. Testing is permitted at a temperature of 27 2°C per ISO 1183-1.

Video 01: ASTM D792 & ASTM D1505 Density of HDPE Geomembranes

Sample size: 

Any suitable size.

Data: 

Specific gravity =  a/[(a + w)-b]

Where

a = mass of specimen in air.
b = mass of specimen and sinker (if used) in water.
W = mass of totally immersed sinker if used and partially immersed wire.

Density, kg/m³ = (specific gravity)(997.6)

Conclusion

ASTM D792 test method is important to assess the average density, or specific gravity, of a bigger sample or product by evaluating the physical changes in a plastic sample related to the degree of uniformity relative to other samples.