Specific Gravity Test Lab
This test method describes the determination of the specific gravity (relative density) of solid plastics in forms such as sheets, rods, tubes, or molded items.
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Significance & Use
a. The specific gravity or relative density of a solid is a property that can be measured conveniently to identify a material, to follow physical changes in a sample, to indicate degree of uniformity among different specimens, or to indicate the average density of a large item.
b. Changes in density of a single specimen may be due to changes in crystallinity, loss of plasticizer, absorption of solvent, or to other causes. Portions of a sample may differ in density because difference in crystallinity, thermal history, porosity, and composition (types or proportions of resin, plasticizer, pigment, or filler.
c. Density is useful to calculate strength-weight ratio and cost-weight ratios.
Summary of Test Methods
a. The mass of a specimen in air (Ma) is determined.
b. Then the specimen is immersed in water; upon immersion its apparent mass (Mb) is determined; and, its specific gravity
(SG = Ma / Ma- Mb) is calculated.