ASTM D792-20

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Designation: D792 − 13 D792 − 20
Standard Test Methods for
Density and Specific Gravity (Relative Density) of Plastics
by Displacement
This standard is issued under the fixed designation D792; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 These test methods describe the determination of the specific gravity (relative density) and density of solid plastics in forms
such as sheets, rods, tubes, or molded items.
1.2 Two test methods are described:
1.2.1 Test Method A—For testing solid plastics in water, and
1.2.2 Test Method B—For testing solid plastics in liquids other than water.
1.3 The values stated in SI units are to be regarded as the standard.
1.4 Warning—Mercury has been designated by many regulatory agencies as a hazardous substance that can cause serious
medical issues. Mercury, or its vapor, has been demonstrated to be hazardous to health and corrosive to materials. Use caution
when handling mercury and mercury-containing products. See the applicable product Safety Data Sheet (SDS) for additional
information. The potential exists that selling mercury or mercury-containing products, or both, is prohibited by local or national
law. Users must determine legality of sales in their location.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
NOTE 1—This standard is not equivalent to ISO 1183–1 Method A. This test method provides more guidelines on sample weight and dimension. ISO
1183-1 allows testing at an additional temperature of 27 6 2°C.
NOTE 1—This standard is not equivalent to ISO 1183–1 Method A. This test method provides more guidelines on sample weight and dimension. ISO
1183-1 allows testing at an additional temperature of 27 6 2°C.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D891 Test Methods for Specific Gravity, Apparent, of Liquid Industrial Chemicals
D4968 Practice for Annual Review of Test Methods and Specifications for Plastics
D6436 Guide for Reporting Properties for Plastics and Thermoplastic Elastomers
E1 Specification for ASTM Liquid-in-Glass Thermometers
E12 Terminology Relating to Density and Specific Gravity of Solids, Liquids, and Gases (Withdrawn 1996)
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.70 on Analytical Methods
(Section D20.70.01).
Current edition approved Nov. 1, 2013July 1, 2020. Published November 2013July 2020. Originally approved in 1944. Last previous edition approved in 20082013 as
D792 - 08.D792 - 13. DOI: 10.1520/D0792-13.10.1520/D0792-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
*A Summary of Changes section appears at the end of this standard
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D792 − 20
E2251 Specification for Liquid-in-Glass ASTM Thermometers with Low-Hazard Precision Liquids
E2935 Practice for Conducting Equivalence Testing in Laboratory Applications
IEEE/ASTM SI-10 Practice for Use of the International System of Units (SI) (the Modernized Metric System)
3. Terminology
3.1 General—The units, symbols, and abbreviations used in these test methods are in accordance with IEEE/ASTM SI-10.
3.1 General—The units, symbols, and abbreviations used in these test methods are in accordance with IEEE/ASTM SI-10.
3.1.1 For terms relating to precision and bias and associated issues, the terms used in this test method are in accordance with
the definitions in Terminology E456.
3.2 Definitions:
3.2.1 specific gravity (relative density)—the ratio of the mass of a given volume of the impermeable portion of the material at
23°C to the mass of an equal volume of gas-free distilled or de-mineralized water at the same temperature; the form of expression
shall be:
Specific gravity~relative density!23/23°C
~or sp gr 23/23°C!
NOTE 2—This definition is essentially equivalent to the definition for apparent specific gravity and apparent density in Terminology E12, because the
small percentage difference introduced by not correcting for the buoyancy of air is insignificant for most purposes.
3.2.2 density—cubic metre of impermeable portion of the material at 23°C. The form of expression shall be:
23 3
D ,kg/m
3 3 3
NOTE 3—The SI unit of density, as defined in IEEE/ASTM SI-10, is kg/m . To convert density in g/cm to density in kg/m , multiply by 1000.
NOTE 4—To convert specific gravity 23/23°C to density 23°C, kg/m , use the following equation:
23 C 3
D ,kg/m 5 sp gr 23/23°C3997.5
Where 997.5 kg/m is the density of water at 23°C.
4. Summary of Test Method
4.1 Determine the mass of a specimen of the solid plastic in air. It is then immersed in a liquid, its apparent mass upon
immersion is determined, and its specific gravity (relative density) calculated.
5. Significance and Use
5.1 The specific gravity or density of a solid is a property that is conveniently measured to identify a material, to follow physical
changes in a sample, to indicate degree of uniformity among different sampling units or specimens, or to indicate the average
density of a large item.
5.2 Changes in density of a single material are due to localized differences in crystallinity, loss of plasticizer, absorption of
solvent, or to other causes. It is possible that portions of a sample differ in density because of their differences in crystallinity,
thermal history, porosity, and composition (types or proportions of resin, plasticizer, pigment, or filler).
5.3 Density is useful for calculating strength-weight and cost-weight ratios.
6. Sampling
6.1 The sampling units used for the determination of specific gravity (relative density) shall be representative of the quantity
of product for which the data are required.
6.1.1 If it is known or suspected that the sample consists of two or more layers or sections having different specific gravities,
either complete finished parts or complete cross sections of the parts or shapes shall be used as the specimens, or separate
specimens shall be taken and tested from each layer. The specific gravity (relative density) of the total part shall not be obtained
by adding the specific gravity of the layers, unless relative percentages of the layers are taken into account.
7. Conditioning
7.1 Conditioning—Condition the test specimens at 23 6 2°C and 50 6 10 % relative humidity for not less than 40 h prior to
test in accordance with Procedure A of Practice D618, unless otherwise specified by the contract or relevant material specifications.
In cases of disagreement, the tolerances shall be 61°C and 65 % relative humidity.
7.2 Test Conditions—Conduct tests in the standard laboratory atmosphere of 23 6 2°C and 50 6 10 % relative humidity, unless
otherwise specified in this specification or by the contract or relevant material specification. In cases of disagreement, the
tolerances shall be 61°C and 65 % relative humidity.
D792 − 20
TEST METHOD A FOR TESTING SOLID PLASTICS IN WATER (SPECIMENS 1 TO 50 g)
8. Scope
8.1 This test method involves weighing a one-piece specimen of 1 to 50 g in water, using a sinker with plastics that are lighter
than water. This test method is suitable for plastics that are wet by, but otherwise not affected by water.
8. Scope
8.1 This test method involves weighing a one-piece specimen of 1 to 50 g in water, using a sinker with plastics that are lighter
than water. This test method is suitable for plastics that are wet by, but otherwise not affected by water.
9. Apparatus
9.1 Analytical Balance—A balance with a precision of 0.1 mg or better is required for materials having densities less than 1.00
g/cm and sample weights less than 10 grams. For all other materials and sample weights, a balance with precision of 1 mg or better
is acceptable (see acceptable. Note 5). The balance shall be equipped with a stationary support for the immersion vessel above the
balance pan (“pan straddle”).
NOTE 5—The balance shall provide the precision that all materials tested have three significant figures on density. In case that materials with different
densities are tested on one single balance, use the balance that provides at least three significant figures for all materials concerned.
9.1.1 The balance shall provide the precision that all materials tested have three significant figures on density. In case that
materials with different densities are tested on one single balance, use the balance that provides at least three significant figures
for all materials concerned.
NOTE 5—To assureensure that the balance meets the performance requirements, check on zero point and sensitivity frequently and perform periodic
calibration.
9.2 Sample Holder, corrosion-resistant (for example, wire, gemholder, etc.).
9.3 Sinker—A sinker for use with specimens of plastics that have specific gravities less than 1.00. The sinker shall: (1) be
corrosion-resistant; (2) have a specific gravity of not less than 7.0; (3) have smooth surfaces and a regular shape; and (4) be slightly
heavier than necessary to sink the specimen. The sinker shall have an opening to facilitate attachment to the specimen and sample
holder.
9.4 Immersion Vessel—A beaker or other wide-mouthed vessel for holding the water and immersed specimen.
9.5 Thermometer—A thermometer readable to 0.1°C or better.
10. Materials
10.1 Water—The water shall be substantially air-free and distilled or de-mineralized water. If this solution does not wet the
specimen, Method B shall be used.
NOTE 6—Air in water can be removed by boiling and cooling the water, or by shaking the water under vacuum in a heavy-walled vacuum flask.
(Warning—Use gloves and shielding.) If the water does not wet the specimen, add a few drops of a wetting agent into the water. If this solution does
not wet the specimen, Method B shall be used.
11. Test Specimen
11.1 The test specimen shall be a single piece of material with a size and shape suitable for the testing apparatus, provided that
its volume shall be not less than 1 cm and its surface and edges shall be made smooth. The thickness of the specimen shall be
at least 1 mm for each 1 g of weight. A specimen weighing 1 to 5 g was found to be convenient, but specimens up to approximately
50 g are also acceptable (see Note 87). Care shall be taken in cutting specimens to avoid changes in density resulting from
compressive stresses or frictional heating.
NOTE 7—Specifications for certain plastics require a particular method of specimen preparation and should be consulted if applicable.
11.2 The specimen shall be free from oil, grease, and other foreign matter.
12. Procedure
12.1 Measure For density calculation, measure and record the water temperature. This is not needed for specific gravity
calculation.
12.2 Weigh the specimen in air. Weigh to the nearest 0.1 mg for specimens of mass 1 to 10 g and density less than 1.00 g/cm .
Weigh to the nearest 1 mg for other specimens.
12.3 If necessary, attach to the balance a piece of fine wire sufficiently long to reach from the hook above the pan to the support
for the immersion vessel. In this case attach the specimen to the wire such that it is suspended about 25 mm above the vessel
support.
D792 − 20
NOTE 9—If a wire is used, weigh the specimen in air after hanging from the wire. In this case, record the mass of the specimen, a = (mass of
specimen + wire, in air) − (mass of wire in air).
12.3.1 If a wire is used, weigh the specimen in air after hanging from the wire. In this case, record the mass of the specimen,
a = (mass of specimen + wire, in air) − (mass of wire in air).
12.4 Mount the immersion vessel on the support, and completely immerse the suspended specimen (and sinkers, if used) in
water (see 10.1) at a temperature of 23 6 2°C. The vessel must not touch sample holder or specimen. Remove any bubbles
adhering to the specimen, sample holder, or sinker, by rubbing them with a wire. Pay particular attention to holes in the specimen
and sinker. If the bubbles are not removed by this method or if bubbles are continuously formed (as from dissolved gases), the
use of vacuum is recommended (see Note 108). Determine the mass of the suspended specimen to the required precision (see 12.2)
(see Note 119). Record this apparent mass as b (the mass of the specimen, sinker, if used, and the partially immersed wire in liquid).
Unless otherwise specified, weigh rapidly in order to minimize absorption of water by the specimen.
NOTE 8—Some specimens may contain absorbed or dissolved gases, or irregularities which tend to trap air bubbles; any of these may affect the density
values obtained. In such cases, the immersed specimen may be subjected to vacuum in a separate vessel until evolution of bubbles has substantially ceased
before weighing (see Test Method B). It must also be demonstrated that the use of this technique leads to results of the required degree of precision.
NOTE 9—It may be necessary to change the sensitivity adjustment of the balance to overcome the damping effect of the immersed specimen.
12.5 Weigh the sample holder (and sinker, if used) in water with immersion to the same depth as used in the previous step (Notes
1210 and 1311). Record this weight a
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