1、Designation: D 792 08Standard Test Methods forDensity and Specific Gravity (Relative Density) of Plasticsby Displacement1This standard is issued under the fixed designation D 792; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 These test methods describe
3、 the determination of thespecific gravity (relative density) and density of solid plasticsin forms such as sheets, rods, tubes, or molded items.1.2 Two test methods are described:1.2.1 Test Method AFor testing solid plastics in water, and1.2.2 Test Method BFor testing solid plastics in liquidsother
4、than water.1.3 The values stated in SI units are to be regarded as thestandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and dete
5、rmine the applica-bility of regulatory limitations prior to use.NOTE 1This standard is not equivalent to ISO 11831 MethodA. Thistest method provides more guidelines on sample weight and dimension.ISO 1183-1 allows testing at an additional temperature of 27 6 2C.2. Referenced Documents2.1 ASTM Standa
6、rds:2D 618 Practice for Conditioning Plastics for TestingD 891 Test Methods for Specific Gravity, Apparent, ofLiquid Industrial ChemicalsD 4968 Guide for Annual Review of Test Methods andSpecifications for PlasticsD 6436 Guide for Reporting Properties for Plastics andThermoplastic ElastomersE1 Speci
7、fication for ASTM Liquid-in-Glass ThermometersE12 Terminology Relating to Density and Specific Gravityof Solids, Liquids, and Gases3E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodIEEE/ASTM SI-10 Practice for Use of the InternationalSystem of Units (S
8、I) (the Modernized Metric System)3. Terminology3.1 GeneralThe units, symbols, and abbreviations used inthese test methods are in accordance with IEEE/ASTM SI-10.3.2 Definitions:3.2.1 specific gravity (relative density)the ratio of themass of a given volume of the impermeable portion of thematerial a
9、t 23C to the mass of an equal volume of gas-freedistilled or de-mineralized water at the same temperature; theform of expression shall be:Specific gravity relative density! 23/23Cor sp gr 23/23C!NOTE 2This definition is essentially equivalent to the definition forapparent specific gravity and appare
10、nt density in Terminology E12,because the small percentage difference introduced by not correcting forthe buoyancy of air is insignificant for most purposes.3.2.2 densitycubic metre of impermeable portion of thematerial at 23C. The form of expression shall be:D23, kg/m3Notes 2-4!NOTE 3The SI unit of
11、 density, as defined in IEEE/ASTM SI-10,iskg/m3. To convert density in g/cm3to density in kg/m3, multiply by 1000.NOTE 4To convert specific gravity 23/23C to density 23C, kg/m3,use the following equation:D23 C, kg/m35 sp gr 23/23C 3 997.5Where 997.5 kg/m3is the density of water at 23C.1These test me
12、thods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.70 on AnalyticalMethods (Section D20.70.01).Current edition approved June 15, 2008. Published July 2008. Originallyapproved in 1944. Last previous edition approved in 2000 as D 792
13、 - 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1*A Summary of Changes section appears at th
14、e end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Test Method4.1 Determine the mass of a specimen of the solid plastic inair. It is then immersed in a liquid, its apparent mass uponimmersion is deter
15、mined, and its specific gravity (relativedensity) calculated.5. Significance and Use5.1 The specific gravity or density of a solid is a propertythat is conveniently measured to identify a material, to followphysical changes in a sample, to indicate degree of uniformityamong different sampling units
16、or specimens, or to indicate theaverage density of a large item.5.2 Changes in density of a single material are due tolocalized differences in crystallinity, loss of plasticizer, absorp-tion of solvent, or to other causes. It is possible that portions ofa sample differ in density because of their di
17、fferences incrystallinity, thermal history, porosity, and composition (typesor proportions of resin, plasticizer, pigment, or filler).5.3 Density is useful for calculating strength-weight andcost-weight ratios.6. Sampling6.1 The sampling units used for the determination of spe-cific gravity (relativ
18、e density) shall be representative of thequantity of product for which the data are required.6.1.1 If it is known or suspected that the sample consists oftwo or more layers or sections having different specificgravities, either complete finished parts or complete crosssections of the parts or shapes
19、 shall be used as the specimens,or separate specimens shall be taken and tested from eachlayer. The specific gravity (relative density) of the total partshall not be obtained by adding the specific gravity of thelayers, unless relative percentages of the layers are taken intoaccount.7. Conditioning7
20、.1 ConditioningCondition the test specimens at23 6 2C and 50 6 5 % relative humidity for not less than 40h prior to test in accordance with Procedure A of PracticeD 618, unless otherwise specified by the contract or relevantmaterial specifications. In cases of disagreement, the tolerancesshall be 61
21、C and 62 % relative humidity.7.2 Test ConditionsConduct tests in the standard labora-tory atmosphere of 23 6 2C and 50 6 5 % relative humidity,unless otherwise specified in this specification or by thecontract or relevant material specification. In cases of disagree-ment, the tolerances shall be 61C
22、 and 62 % relative humid-ity.TEST METHOD A FOR TESTING SOLID PLASTICSIN WATER (SPECIMENS 1 TO 50 g)8. Scope8.1 This test method involves weighing a one-piece speci-men of 1 to 50 g in water, using a sinker with plastics that arelighter than water. This test method is suitable for plastics thatare we
23、t by, but otherwise not affected by water.9. Apparatus9.1 Analytical BalanceA balance with a precision of 0.1mg or better is required for materials having densities less than1.00 g/cm3and sample weights less than 10 grams. For allother materials and sample weights, a balance with precision of1 mg or
24、 better is acceptable (see Note 5). The balance shall beequipped with a stationary support for the immersion vesselabove the balance pan (“pan straddle”).NOTE 5The balance shall provide the precision that all materialstested have three significant figures on density. In case that materials withdiffe
25、rent densities are tested on one single balance, use the balance thatprovides at least three significant figures for all materials concerned.NOTE 6To assure that the balance meets the performance require-ments, check on zero point and sensitivity frequently and perform periodiccalibration.9.2 Sample
26、 Holder, corrosion-resistant (for example, wire,gemholder, etc.).9.3 SinkerAsinker for use with specimens of plastics thathave specific gravities less than 1.00. The sinker shall: (1)becorrosion-resistant; (2) have a specific gravity of not less than7.0; (3) have smooth surfaces and a regular shape;
27、 and (4)beslightly heavier than necessary to sink the specimen. Thesinker shall have an opening to facilitate attachment to thespecimen and sample holder.9.4 Immersion VesselA beaker or other wide-mouthedvessel for holding the water and immersed specimen.9.5 ThermometerA thermometer readable to 0.1C
28、 orbetter.10. Materials10.1 WaterThe water shall be substantially air-free anddistilled or de-mineralized water.NOTE 7Air in water can be removed by boiling and cooling the water,or by shaking the water under vacuum in a heavy-walled vacuum flask.(WarningUse gloves and shielding.) If the water does
29、not wet thespecimen, add a few drops of a wetting agent into the water. If thissolution does not wet the specimen, Method B shall be used.11. Test Specimen11.1 The test specimen shall be a single piece of materialwith a size and shape suitable for the testing apparatus,provided that its volume shall
30、 be not less than 1 cm3and itssurface and edges shall be made smooth. The thickness of thespecimen shall be at least 1 mm for each1gofweight. Aspecimen weighing 1 to 5 g was found to be convenient, butspecimens up to approximately 50 g are also acceptable (seeNote 8). Care shall be taken in cutting
31、specimens to avoidchanges in density resulting from compressive stresses orfrictional heating.NOTE 8Specifications for certain plastics require a particular methodof specimen preparation and should be consulted if applicable.11.2 The specimen shall be free from oil, grease, and otherforeign matter.1
32、2. Procedure12.1 Measure and record the water temperature.D79208212.2 Weigh the specimen in air. Weigh to the nearest 0.1 mgfor specimens of mass 1 to 10 g and density less than 1.00g/cm3. Weigh to the nearest 1 mg for other specimens.12.3 If necessary, attach to the balance a piece of fine wiresuff
33、iciently long to reach from the hook above the pan to thesupport for the immersion vessel. In this case attach thespecimen to the wire such that it is suspended about 25 mmabove the vessel support.NOTE 9If a wire is used, weigh the specimen in air after hanging fromthe wire. In this case, record the
34、 mass of the specimen, a = (mass ofspecimen + wire, in air) (mass of wire in air).12.4 Mount the immersion vessel on the support, andcompletely immerse the suspended specimen (and sinkers, ifused) in water (see 10.1) at a temperature of 23 6 2C. Thevessel must not touch sample holder or specimen. Re
35、move anybubbles adhering to the specimen, sample holder, or sinker, byrubbing them with a wire. Pay particular attention to holes inthe specimen and sinker. If the bubbles are not removed by thismethod or if bubbles are continuously formed (as fromdissolved gases), the use of vacuum is recommended (
36、see Note10). Determine the mass of the suspended specimen to therequired precision (see 12.2) (see Note 11). Record thisapparent mass as b (the mass of the specimen, sinker, if used,and the partially immersed wire in liquid). Unless otherwisespecified, weigh rapidly in order to minimize absorption o
37、fwater by the specimen.NOTE 10Some specimens may contain absorbed or dissolved gases,or irregularities which tend to trap air bubbles; any of these may affect thedensity values obtained. In such cases, the immersed specimen may besubjected to vacuum in a separate vessel until evolution of bubbles ha
38、ssubstantially ceased before weighing (see Test Method B). It must also bedemonstrated that the use of this technique leads to results of the requireddegree of precision.NOTE 11It may be necessary to change the sensitivity adjustment ofthe balance to overcome the damping effect of the immersed speci
39、men.12.5 Weigh the sample holder (and sinker, if used) in waterwith immersion to the same depth as used in the previous step(Notes 12 and 13). Record this weight as w (mass of the sampleholder in liquid).NOTE 12If a wire is used, it is convenient to mark the level ofimmersion by means of a shallow n
40、otch filed in the wire. The finer thewire, the greater the tolerance is permitted in adjusting the level ofimmersion between weighings. With wire Awg No. 36 or finer, disregardits degrees of immersion and, if no sinker is used, use the mass of the wirein air as w.NOTE 13If the wire is used and is le
41、ft attached to the balance armduring a series of determinations, determine the mass a with the aid of atare on the other arm of the balance or as in Note 9. In such cases, caremust be taken that the change of mass of the wire (for example, fromvisible water) between readings does not exceed the desi
42、red precision.12.6 Repeat the procedure for the required number ofspecimens. Two specimens per sample are recommended.Determine acceptability of number of replicate test specimensby comparing results with precision data given in Tables 1 and2. Use additional specimens if desired.13. Calculation13.1
43、Calculate the specific gravity of the plastic as follows:sp gr 23/23C 5 a/a 1 w 2 b!where:a = apparent mass of specimen, without wire or sinker, inair,b = apparent mass of specimen (and of sinker, if used)completely immersed and of the wire partially im-mersed in liquid, andw = apparent mass of tota
44、lly immersed sinker (if used) andof partially immersed wire.13.2 Calculate the density of the plastic as follows:D23C, kg/m35 sp gr 23/23C 3 997.513.3 If the temperature of the water is different than 23C,use the density of water listed in Table 3 directly, or use thefollowing equations to calculate
45、 the density of water at testingtemperature:M 5DD/Dt (1)Dconversion to 23C!, kg/m35 sp gr ta/tw3 997.5 1 tw23! 3 M (2)andsp gr 23/23 5 D conversion to 23C!/997.5 (3)where:M = slope,DD = difference between the lowest and highest tempera-ture tolerance for the standard density of water (D 21C D 25C),D
46、t = difference between the highest and lowest tempera-ture tolerance recommended, (21C25C),ta= temperature of air, andtw= temperature of water.14. Report14.1 Report the following information:TABLE 1 Test Method A Specific Gravity Tested in WaterMaterial Mean SrASRBrCRDPolypropylene 0.9007 0.00196 0.
47、00297 0.00555 0.00841Cellulose Acetate Butyrate 1.1973 0.00232 0.00304 0.00657 0.00860Polyphenylene Sulfide 1.1708 0.00540 0.00738 0.01528 0.02089Thermoset 1.3136 0.00271 0.00313 0.00767 0.02171Polyvinyl Chloride 1.3396 0.00243 0.00615 0.00688 0.01947ASr= within laboratory standard deviation for the
48、 individual material. It is obtained by pooling the within-laboratory standard deviations of the test results from all of theparticipating laboratories:Sr= (s1)2+(s2)2.+(sn)2/n1/2BSR= between-laboratories reproducibility, expressed as standard deviation: SR=Sr2+SL21/2where SLis the standard deviatio
49、n of laboratory means.Cr = within-laboratory critical interval between two test results = 2.8 3 Sr.DR = between-laboratories critical interval between two test results = 2.8 3 SR.D79208314.1.1 Complete identification of the material or producttested, including method of specimen preparation and condi-tioning,14.1.2 Average specific gravity (relative density) for allspecimens from a sampling unit corrected to 23.0C (Table 3)are reported as sp gr 23/23C = _, or average densityreported as D23C= _ kg/m3,NOTE
