1、Designation: D 792 00Standard 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 (e) 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 describ
3、e 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.NOTE 1Alternatively, Test Method D 1505 may be applied to manysuch forms, as well as to films and sheeting.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 t
5、heresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 2This standard is not equivalent to ISO 1183 Method A.2. Referenced Documents2.1 ASTM Standards:D 618 Practice for Conditio
6、ning Plastics and ElectricalInsulating Materials for Testing2D 891 Test Methods for Specific Gravity, Apparent, ofLiquid Industrial Chemicals3D 1505 Test Method for Density of Plastics by the Density-Gradient Technique2D 1622 Test Method for Apparent Density of Rigid CellularPlastics2D 1898 Practice
7、 for Sampling of Plastics4D 4968 Guide for Annual Review of Test Methods andSpecifications for Plastics2E 1 Specification for ASTM Thermometers5E 12 Terminology Relating to Density and Specific Gravityof Solids, Liquids, and Gases6E 380 Practice for Use of the International System of Units(SI) (the
8、Modernized Metric System)7E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method73. Terminology3.1 GeneralThe units, symbols, and abbreviations used inthese test methods are in accordance with Practice E 380.3.2 Definitions:3.2.1 specific gravity (relative
9、density)the ratio of themass in air of a unit volume of the impermeable portion of thematerial at 23C to the mass in air of equal density of an equalvolume of gas-free distilled water at the same temperature; theform of expression shall be:Specific gravity relative density! 23/23Cor sp gr 23/23C!NOT
10、E 3This definition is essentially equivalent to the definition forapparent specific gravity and apparent density in Terminology E 12,because the small percentage difference introduced by not correcting forthe buoyancy of air is insignificant for most purposes.3.2.2 densitythe mass in air in kilogram
11、s per cubic metreof impermeable portion of the material at 23C. The form ofexpression shall be:D23, kg/m3Notes 3-5!NOTE 4The SI unit of density, as defined in Practice E 380 is kg/m3.To convert density in g/cm3to density in kg/m3, multiply by 1000.NOTE 5Specific gravity 23/23C can be converted to de
12、nsity 23C,kg/m3, by use of the following equation:D23 C, kg/m35 sp gr 23/23C 3 997.51These test methods 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 Dec. 10, 2000
13、. Published March 2001. Originallypublished as D 792 44. Last previous edition D 792 98.2Annual Book of ASTM Standards, Vol 08.01.3Annual Book of ASTM Standards, Vol 15.05.4Discontinued. See 1998 Annual Book of ASTM Standards, Vol 08.01.5Annual Book of ASTM Standards, Vol 14.03.6Discontinued. See 19
14、95 Annual Book of ASTM Standards, Vol 15.05.7Annual Book of ASTM Standards, Vol 14.02.1*A Summary of Changes section appears at the 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 Dete
15、rmine the mass of a specimen of the solid plastic inair. It is then immersed in a liquid, its apparent mass uponimmersion is determined, and its specific gravity (relativedensity) calculated.5. Significance and Use5.1 The specific gravity or density of a solid is a propertythat can be measured conve
16、niently to identify a material, tofollow physical changes in a sample, to indicate degree ofuniformity among different sampling units or specimens, or toindicate the average density of a large item.5.2 Changes in density of a single specimen may be due tochanges in crystallinity, loss of plasticizer
17、, absorption ofsolvent, or to other causes. Portions of a sample may differ indensity because of difference in crystallinity, thermal history,porosity, and composition (types or proportions of resin,plasticizer, pigment, or filler).NOTE 6Reference is made to Test Method D 1622.5.3 Density is useful
18、for calculating strength-weight andcost-weight ratios.6. Sampling6.1 The sampling units used for the determination of spe-cific gravity (relative density) shall be representative of thequantity of product for which the data are required, inaccordance with Practice D 1898.6.1.1 If it is known or susp
19、ected 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 shall be used as the specimens,or separate specimens shall be taken and tested from eachlayer. The specific gravity (rel
20、ative density) of the total partcannot be obtained by adding the specific gravity of the layers,unless relative percentages of the layers are taken into account.7. Conditioning7.1 ConditioningCondition the test specimens at23 6 2C and 50 6 5 % relative humidity for not less than 40h prior to test in
21、 accordance with Procedure A of PracticeD 618, unless otherwise specified by the contract or relevantmaterial specifications. In cases of disagreement, the tolerancesshall be 61C and 62 % relative humidity.7.2 Test ConditionsConduct tests in the standard labora-tory atmosphere of 23 6 2C and 50 6 5
22、% 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 and 62 % relative humid-ity.TEST METHOD A FOR TESTING SOLID PLASTICSIN WATER (SPECIMENS 1 TO 50 g)8. Scope8.1 This test me
23、thod 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 wet by, but otherwise not affected by water.9. Apparatus9.1 Analytical BalanceA balance with a precision within0.1 mg, accura
24、cy within 0.05 % relative (that is, 0.05 % of themass of the specimen in air), and equipped with a stationarysupport for the immersion vessel above the balance pan (“panstraddle”).NOTE 7Assurance that the balance meets the performance require-ments should be provided by frequent checks on adjustment
25、s of zero pointand sensitivity and by periodic calibration for absolute accuracy, usingstandard masses.9.2 Sample Holder, corrosion-resistant (for example, wire,gemholder, etc.).9.3 SinkerA sinker for use with specimens of plastics thathave specific gravities less than 1.000. The sinker shall: (1)be
26、corrosion-resistant; (2) have a specific gravity of not less than7.0; (3) have smooth surfaces and a regular shape; and (4)beslightly heavier than necessary to sink the specimen. Thesinker should have an opening to facilitate attachment to thespecimen and sample holder.9.4 Immersion VesselA beaker o
27、r other wide-mouthedvessel for holding the water and immersed specimen.9.5 ThermometerA thermometer with an accuracy of60.1C is required.10. Materials10.1 WaterThe water shall be substantially air-free anddistilled or demineralized water.NOTE 8Water may be rendered substantially air-free by boiling
28、andcooling or by shaking under vacuum in a heavy-walled vacuum flask.(Precaution: Use gloves and shielding.) If the water does not wet thespecimen, a few drops of a wetting agent shall be added. If this solutiondoes not wet the specimen, Method B shall be used.11. Test Specimen11.1 The test specimen
29、 shall be a single piece of the materialunder test of any size and shape that can conveniently beprepared and tested, provided that its volume shall be not lessthan 1 cm3and its surface and edges shall be made smooth. Thethickness of the specimen should be at least 1 mm for each 1g of weight. A spec
30、imen weighing 1 to 5 g usually will befound convenient, but specimens up to approximately 50 g maybe used (Note 9). Care should be taken in cutting specimens toavoid changes in density resulting from compressive stresses orfrictional heating.NOTE 9Specifications for certain plastics require a partic
31、ular methodof specimen preparation and should be consulted if applicable.11.2 The specimen shall be free from oil, grease, and otherforeign matter.12. Procedure12.1 Measure and record the water temperature.12.2 Weigh the specimen in air to the nearest 0.1 mg forspecimens of mass 1 to 10 g or to the
32、nearest mg for specimensof mass more than 10 to 50 g.12.3 If necessary, attach to the balance a piece of fine wiresufficiently long to reach from the hook above the pan to thesupport for the immersion vessel. In this case attach theD792002specimen to the wire such that it is suspended about 25 mmabo
33、ve the vessel support.NOTE 10If a wire is used the specimen may be weighed in air afterhanging 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, andcompletely immerse the suspended
34、specimen (and sinkers, ifused) in water (10.1) at a temperature of 23 6 2C. The vesselmust not touch sample holder or specimen. Remove anybubbles adhering to the specimen, sample holder, or sinker,paying particular attention to holes in the specimen and sinker.Usually these bubbles can be removed by
35、 rubbing them with awire. If the bubbles cannot be removed by this method or ifbubbles are continuously formed (as from dissolved gases), theuse of vacuum is recommended (Note 12). Determine the massof the suspended specimen to the required precision (12.2)(Note 11). Record this apparent mass as b (
36、the mass of thespecimen, sinker, if used, and the partially immersed wire inliquid). Unless otherwise specified, weigh rapidly in order tominimize absorption of water by the specimen.NOTE 11It may be necessary to change the sensitivity adjustment ofthe balance to overcome the damping effect of the i
37、mmersed specimen.NOTE 12Some 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 hassubst
38、antially 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.12.5 Weigh the sample holder (and sinker, if used) in waterwith immersion to the same depth as used in the previous step(Notes 13 and 14
39、). Record this weight as w (mass of the sampleholder in liquid).NOTE 13If a wire is used, it is convenient to mark the level ofimmersion by means of a shallow notch filed in the wire. The finer thewire, the greater the tolerance which may be permitted in adjusting thelevel of immersion between weigh
40、ings. With wire Awg No. 36 or finer,disregard its degrees of immersion and, if no sinker is used, use the massof the wire in air as w.NOTE 14If the wire is used and is left attached to the balance armduring a series of determinations, the mass a may be determined eitherwith the aid of a tare on the
41、other arm of the balance or as in Note 12. Insuch cases, care must be taken that the change of mass of the wire (forexample, from visible water) between readings does not exceed thedesired precision.12.6 Repeat the procedure for the required number ofspecimens. Two specimens per sample are recommend
42、ed.Determine acceptability of number of replicate test specimensby comparing results with precision data given in Tables 1 and2. Additional specimens may be required to give the desiredprecision.13. Calculation13.1 Calculate the specific gravity of the plastic as follows:sp gr 23/23C 5 a/a 1 w 2 b!w
43、here: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 totally immersed sinker (if used) andof partially immersed wire.13.2 Calculate the densit
44、y 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,the following equations will be used:M 5DD/Dt (1)D conversion to 23C!, kg/m35 sp gr ta/tw3 997.5 1 tw23! 3 M (2)sp gr 23/23 5 D conversion to 23C!/997.5 (3)where:M = slope,DD = dif
45、ference between the lowest and highest tempera-ture tolerance for the standard density of water (D 21C D 25C),Dt = difference between the highest and lowest tempera-ture tolerance recommended,ta= temperature of air, andtw= temperature of water.14. Report14.1 Report the following information:14.1.1 C
46、omplete 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)TABLE 1 Test Method A Specific Gravity Tested in WaterMaterial Mean
47、 SrASRBrCRDPolypropylene 0.9007 0.00196 0.00297 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= wi
48、thin laboratory standard deviation for the 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:
49、 SR=Sr2+SL21/2where SLis the standard deviation 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.D792003are reported as sp gr 23/23C = _, or average densityreported as D23C= _ kg/m3,14.1.3 A measure of the degree of variation of specificgravity or density within the sampling unit such as the standarddeviation and number of determinations on a homogeneousmaterial or the averages plus
