Designation:D 1505–03
Standard Test Method for
Density of Plastics by the Density-Gradient Technique 1DOS窗口
This standard is issued under the fixed designation D 1505;the number immediately following the designation indicates the year of original adoption or,in the ca of revision,the year of last revision.A number in parenthes indicates the year of last reapproval.A superscript epsilon (e )indicates an editorial change since the last revision or reapproval.This standard has been approved for u by agencies of the Department of Defen.
1.Scope*
1.1This test method covers the determination of the density of solid plastics.
1.2This test method is bad on obrving the level to which a test specimen sinks in a liquid column exhibiting a density gradient,in comparison with standards of known density.
N OTE 1—The comparable ISO document is ISO 1183–2.There has not been any data generated to date comparing the results of the ISO method with this method.
1.3The values stated in SI units are to be regarded as the standard.
1.4This standard does not purport to address all of the safety concerns,if any,associated with its u.It is the responsibility of the ur of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to u.
2.Referenced Documents 2.1ASTM Standards:2
D 941Test Method for Density and Relative Density (Spe-cific Gravity)of Liquids by Lipkin Bicapillary Pycnometer D 2839Practice for U of a Melt Index Strand for Deter-mining Density of Polyethylene
D 4703Practice for Compression Molding Thermoplastic Materials into Test Specimens,Plaques,or Sheets
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E 691Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method 2.2ISO Standard:
ISO 1183-2Methods for Determining the Density and Rela-tive Density of Noncellular Plastics 3
3.Terminology 3.1Definition:
3.1.1density of plastics —the weight per unit volume of material at 23°C,expresd as follows:
D 23C ,g/cm 3
(1)
N OTE 2—Density is to be distinguished from specific gravity,which is the ratio of the weight of a given volume of the material to that of an equal volume of water at a stated temperature.
4.Significance and U
4.1The density of a solid is a conveniently measurable property which is frequently uful as a means of following physical changes in a sample,as an indication of uniformity among samples,and a means of identification.
4.2This test method is designed to yield results accurate to better than 0.05%.
N OTE 3—Where accuracy of 0.05%or better is desired,the gradient tube shall be constructed so that vertical distances of 1mm shall reprent density differences no greater than 0.0001g/cm.3The nsitivity of the column is then 0.0001g/cm 3·mm.Where less accuracy is needed,the gradient tube shall be constructed to any required nsitivity.
5.Apparatus
5.1Density-Gradient Tube —A suitable graduate with ground-glass stopper.4
5.2Constant-Temperature Bath —A means of controlling the temperature of the liquid in the tube at 2360.1°C.A thermostatted water jacket around the tube is a satisfactory and convenient method of achieving this.
5.3Glass Floats —A number of calibrated glass floats cov-ering the density range to be studied and approximately evenly distributed throughout this range.
5.4Pycnometer ,for u in determining the densities of the standard floats.
5.5Liquids ,suitable for the preparation of a density gradi-ent (Table 1).
N OTE 4—It is very important that none of the liquids ud in the tube
1
This test method is under the jurisdiction of ASTM Committee D20on Plastic and is the direct responsibility of Subcommittee D20.70on Analytical Methods (Section D20.70.01).
Current edition approved November 1,2003.Published January 2004.Originally approved in 1957.Last previous edition approved in 1998as D 1505-98.2
For referenced ASTM standards,visit the ASTM website,www.astm,or contact ASTM Customer Service at rvice@astm.For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website.3
Available from American National Standards Institute (ANSI),25W.43rd St.,4th Floor,New York,NY 10036.
4
Tubes similar to tho described in Refs (6)and (12)may also be ud.
1
*A Summary of Changes ction appears at the end of this standard.
Copyright ©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.
exert a solvent or chemical effect upon the test specimens during the time of specimen immersion.
5.6Hydrometers —A t of suitable hydrometers covering the range of densities to be measured.The hydrometers should have 0.001density graduations.
5.7Analytical Balance ,with a nsitivity of 0.001g.
5.8Siphon or Pipet Arrangement ,for filling the gradient tube.This piece of equipment should be constructed so that the rate of flow of liquid may be regulated to 1065mL/min.
6.Test Specimen
6.1The test specimen shall consist of a piece of the material under test.The piece may be cut to any
shape convenient for easy identification,but should have dimensions that permit the most accurate position measurement of the center of volume of the suspended specimen (Note 5).Care should be taken in cutting specimens to avoid change in density resulting from compressive stress.
N OTE 5—The equilibrium positions of film specimens in the thickness range from 0.025to 0.051mm (0.001to 0.002in.)may be affected by interfacial tension.If this affect is suspected,films not less than 0.127mm (0.005in.)in thickness should be tested.
6.2The specimen shall be free of foreign matter and voids and shall have no cavities or surface characteristics that will cau entrapment of bubbles.
7.Preparation of Density-Gradient Columns
7.1Preparation of Standard Glass Floats 5—Prepare glass floats by any convenient method such that they are fully annealed,approximately spherical,have a maximum diameter less than one fourth the inside diameter of the column,and do not interfere with the test specimens.Prepare a solution (400to 600mL)of the liquids to be ud in the gradient tube such that the density of the solution is approximately equal to the desired lowest density.When the floats are at room temperature,drop them gently into the solution.Save the floats that sink very slowly,and discard tho that sink very fas
t,or save them for another tube.If necessary to obtain a suitable range of floats,grind lected floats to the desired density by rubbing the head part of the float on a glass plate on which is spread a thin slurry of 400or 500-mesh silicon carbide (Carborundum)or other
appropriate abrasive.Progress may be followed by dropping the float in the test solution at intervals and noting its change in rate of sinking.
7.2Calibration of Standard Glass Floats (e Appendix X1):
7.2.1Place a tall cylinder in the constant-temperature bath maintained at 2360.1°C.Then fill the cylinder about two thirds full with a solution of two suitable liquids lected from Table 1,the density of which can be varied over the desired range by the addition of either liquid to the mixture.After the cylinder and solution have attained temperature equilibrium,place the float in the solution,and if it sinks,add the denr liquid by suitable means with good stirring until the float revers direction of movement.If the float ris,add the less den liquid by suitable means with good stirring until the float revers direction of movement.
7.2.2When reversal of movement has been obrved,re-duce the amount of the liquid additions to that equivalent to 0.0001-g/cm 3
density.When an addition equivalent to 0.0001-g/cm 3density caus a reversal of movement,or when the float remains completely stationary for at least 15min,the float and liquid are in satisfactory balance.The cylinder must be covered whenever it is being obrved for balance,and the liquid surface must be below the surface of the liquid in the constant-temperature bath.After vigorous stirring,the liquid may continue to move for a considerable length of time;make sure that the obrved movement of the float is not due to liquid motion by waiting at least 15min after stirring has stopped before obrving the float.
7.2.3When balance has been obtained,fill a freshly cleaned and dried pycnometer with the solution and place it in the 2360.1°C bath for sufficient time to allow temperature equilib-rium of the glass.Determine the density of the solution by normal methods (Test Method D 941)and make “in vacuo”corrections for all weighings.Record this as the density of the float.Repeat the procedure for each float.
7.3Gradient Tube Preparation (e appendix for details):7.3.1Method A —Stepwi addition.
7.3.2Method B —Continuous filling (liquid entering gradi-ent tube becomes progressively less den).
7.3.3Method C —Continuous filling (liquid entering gradi-ent tube becomes progressively more den).
8.Conditioning
8.1Test specimens who change in density on conditioning may be greater than the accuracy required of the density determination shall be conditioned before testing in accordance with the method listed in the applicable ASTM material specification.
9.Procedure
9.1Wet three reprentative test specimens with the less den of the two liquids ud in the tube and gently place them in the tube.Allow the tube and specimens to reach equilibrium,which will require 10min or more.Thin films of 1to 2mils in thickness require approximately 11⁄2h to ttle,and rechecking after veral hours is advisable (Note 4).
9.2Read the height of each float and each specimen by a line through the individual center of volume and averaging the
5
Glass floats may be purchad from American Density Materials,3826Springhill Rd.Staunton,V A 24401,Ph:(540)887-1217.
TABLE 1Liquid Systems for Density-Gradient Tubes
System
Density Range,
g/cm 3Methanol-benzyl alcohol 0.80to 0.92Isopropanol-water
0.79to 1.00Isopropanol-diethylene glycol 0.79to 1.11Ethanol-carbon tetrachloride 0.79to 1.59Toluene-carbon tetrachloride 0.87to 1.59Water-sodium bromide 1.00to 1.41Water-calcium nitrate
1.00to 1.60Carbon tetrachloride-trimethylene dibromide 1.60to 1.99Trimethylene dibromide-ethylene bromide 1.99to
2.18Ethylene bromide-bromoform
2.18to
2.89
three values.When a cathetometer is ud,measure the height of thefloats and specimens from an arbitrary level using a line through their center of volume.If equilibrium is not obtained, the specimen may be imbibing the liquid.
9.3Old samples can be removed without destroying the gradient by slowly withdrawing a wire screen basket attached to a long wire(Note6).This can be conveniently done by means of a clock motor.Withdraw the basket from the bottom of the tube and,after cleaning,return it to the bottom of the tube.It is esntial that this procedure be performed at a slow enough rate(approximately30min/300-mm length of column) so that the density gradient is not disturbed.
N OTE6—Whenever it is obrved that air bubbles are collecting on samples in the column,a vacuum applied to the column will correct this.
10.Calculation
10.1The densities of the samples may be determined graphically or by calculation from the levels to which the samples ttle by either of the following methods:
10.1.1Graphical Calculation—Plotfloat position versus float density on a chart large enough to be read accurately to 61mm and the desired precision of density.Plot the positions of the unknown specimens on the chart and read their corre-sponding densities.
10.1.2Numerical Calculation—Calculate the density by interpolation as follows:
Density at x5a1[~x2y!~b2a!/~z2y!#(2) where:
a and b=densities of the two standardfloats,
y and z=distances of the two standards,a and b,respec-tively,bracketing the unknown measured from
an arbitrary level,and
x=distance of unknown above the same arbitrary level.
11.Report
11.1Report the following information:
11.1.1Density reported as D23C,in grams per cubic centimetre,as the average for three reprentative test speci-mens,
11.1.2Number of specimens tested if different than three, 11.1.3Sensitivity of density gradient in grams per cubic centimetre per millimetre,
11.1.4Complete identification of the material tested,and 11.1.5Date of the test.12.Precision and Bias6
12.1Specimens Molded in One Laboratory and Tested in Several Laboratories—An interlaboratory test was run in1981 in which randomized density plaques were supplied to22 laboratories.Four polyethylene samples of nominal densities of0.92to0.96g/cm3were molded in one laboratory.The data were analyzed using Practice E691,and the results are given in Table2.
12.2Specimens Molded and Tested in Several Laboratories: 12.2.1Samples Prepared Using Practice D4703in Each Laboratory—Table3is bad on a round robin9conducted in 1994in accordance with P
ractice E691,involving ven materials tested by7to11laboratories.For each material,all of the samples were prepared by each laboratory,molded in accordance with Procedure C of Annex A1of Practice D4703, and tested using this test method.The data are for comparison with the data of the same samples tested by Practice D2839. Each test result is an individual determination.Each laboratory obtained six test results for each material.
12.2.2Samples Prepared Using Practice D2839in Each Laboratory—Table4is bad on a round robin9conducted in 1994in accordance with Practice E691,involving ven materials tested by10to15laboratories.For each material,all of the samples were prepared by each laboratory in accordance with Practice D2839.Each test result is an individual deter-mination.Each laboratory obtained six test results for each material.
12.3Concept of r and R—Warning—The following expla-nations of r and R(12.3-12.3.3)are only intended to prent a meaningful way of considering the approximate precision of this test method.The data in Table1should not be rigorously applied to acceptance or rejection of material,as tho data are specific to the round robin and may not be reprentative of other lots,conditions,materials,or laboratories.Urs of this test method should apply the principles outlined in Practice E691to generate data specific to their laboratory and materi-als,or between specific labor
atories.The principles of12.3-12.3.3would then be valid for each data.
If S r and S R have been calculated from a large enough body of data,and for test results that were averages from testing one specimen:
12.3.1Repeatability Limit,r(Comparing two test results for the same material,obtained by the same operator using the 6Supporting data are available from ASTM Headquarters.Request RR:D20-1123.
TABLE2Precision Data Summary—Polyethylene Density
Material Average Density,g/cm3S r A S R B r C R D
10.91960.000290.001060.000820.0045
20.93190.000120.000800.000340.0023
30.95270.000330.001160.000930.0033委曲求全
40.96230.000620.001140.001800.0033
A S
r
养肝喝什么茶=within-laboratory standard deviation for the indicated material.It is obtained by pooling the within-laboratory standard deviations of the test results from all of the participating laboratories.如何挑榴莲
B S
R =between-laboratories reproducibility,expresd as standard deviation,for the indicated material.
C r=within-laboratory repeatability limit=2.8S
r .
D R=between-laboratories reproducibility limit=2.8S
R
.
same equipment on the same day)—The two test results should be judged not equivalent if they differ by more than the r value for that material.
12.3.2Reproducibility Limit,R (Comparing two test results for the same material,obtained by different operators using different equipment in different laboratories)—The two test results should be judged not equivalent if they differ by more than the R value for that material.
12.3.3Any judgment in accordance with 12.2.1or 12.2.2would have an approximate 95%(0.95)probability of being correct.
12.3.4Bias —There are no recognized standards by which to estimate the bias of this test method.
13.Keywords
13.1density;film;gradient;plaque;polyolefins;polyeth-ylene;polypropylene;preparation
APPENDIXES
(Nonmandatory Information)
X1.FLOAT CALIBRATION—ALTERNATIVE TEST METHOD
X1.1This test method of float calibration has been found by one laboratory to save time and give the same accuracy as the standard test method.Its reliability has not been demon-strated by round-robin data.
X1.1.1Prepare a homogeneous solution who density is fairly clo to that of the float in question.
X1.1.2Fill a graduate about 3⁄4full with the solution,drop in the float,stopper,and place in a thermostatted water bath near 23°C.Fill a tared two-arm pycnometer (Test Method D 941,or equivalent)with the solution.Place the pycnometer in the bath.
X1.1.3Vary the bath temperature until the solution density is very near to that of the float.(If the float was initially on the bottom of the graduate,lower the bath temperature until the float ris;if the float floated initially,rai the bath tempera-ture until the float sinks to the bottom.)
X1.1.4Change the bath temperature in the appropriate direction in increments corresponding to solution density increments of about 0.0001g/cm 3until the float revers direction of movement as a result of the last change.This must be done slowly (at least 15-min intervals between incremental changes on the temperature controller).Read the volume of liquid in the pycnometer.
X1.1.5Change the bath temperature in increments in the opposite direction,as above,until a change in the float position again occurs.Read the volume of liquid in the pycnometer.
N OTE X1.1—The float should ri off the bottom of its own volition.As a precaution against surface tension effects when the float is floating,the float should be pushed about halfway down in the liquid column and then obrved as to whether it ris or falls.For this purpo,a length of Nichrome wire,with a small loop on the lower end and an inch or so of length extending above the liquid surface,is kept within the graduate throughout the cour of the run.To push a floating float down,the cylinder is unstoppered and the upper wire end grasped with tweezers for the manipulations.The cylinder is then quickly restoppered.
X1.1.6Remove the pycnometer from the bath,dry the outside,and t aside until the temperature reaches ambient temperature.Weigh and calculate the “in vacuo”mass of solution to 0.0001g.Using the average of the two obrved solution volumes,calculate the density of the solution to 0.0001g/cm 3.This solution density is also the float density.X1.1.7The pycnometer ud should be calibrated for vol-ume from the 23°C calibration,although the reading is taken at a different temperature.The alternative test method is bad on a number of unsupported assumptions but generally gives the same results as that described in 7.2within the accuracy
TABLE 3Precision Data—Density,g/cm 3
Material Number of
Laboratories
Density,g/cm 3S r A S R B r C R D
B 70.91390.000290.000880.000810.00245F 80.91770.000180.000790.000510.00221G 80.92200.000280.000710.000780.00197A 110.93560.000360.001050.001000.00294E 110.95280.000460.001180.001290.00331
C 100.96190.001000.001000.001030.00281D
9
0.9633
0.00036
0.00137
0.00101
0.00384
A
S r =within-laboratory standard deviation for the indicated material.It is obtained by pooling the within-laboratory standard deviations of the test results from all of the participating laboratories.B
S R =between-laboratories reproducibility,expresd as standard deviation,for the indicated material.C
r =within-laboratory repeatability limit =2.8S r .D
R =between-laboratories reproducibility limit =2.8S R .
TABLE 4Density,g/cm 3,Samples Prepared in Accordance With
Practice D 2839
Material
Number of
Laboratories
Density,g/cm 3S r A S R B r C R D B 100.91390.000260.000780.000720.00219F 120.91790.000200.000780.000550.00220G 130.92220.000300.000730.000850.00206A 150.93570.000410.000800.001150.00225E 140.95300.000390.000920.001090.00258C 110.96150.000300.000730.000850.00206D
10
0.9626
0.00053
0.00109
0.00148
0.00305
A南充冬菜
S r =within-laboratory standard deviation for the indicated material.It is obtained by pooling the within-laboratory standard deviations of the test results from all of the participating laboratories.B
烂泥巴
S R =between-laboratories reproducibility,expresd as standard deviation,for the indicated material.C
r =within-laboratory repeatability limit =2.8S r .D
R =between-laboratories reproducibility limit =2.8S R
.
required.In ca of disagreement,the method described in7.2
shall be the referee method.
X2.GRADIENT TUBE PREPARATION
X2.1Method A—Stepwi Addition:
X2.1.1Using the two liquids that will give the desired
density range,and nsitivity(S)in grams per cubic centimetre
per millimetre,prepare four or more solutions such that each
differs from the next heavier by80S g/cm3.The number of
solutions will depend upon the desired density range of the
column and shall be determined as follows:
Numbers of solutions to prepare density2gradient(X2.1)
column~Note X2.1!5~11D22D1!/80S(X2.1)
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where:
D2=upper limit of density range desired,
D1=lower limit of density range desired,and
S=nsitivity,in grams per cubic centimetre per milli-
metre.
N OTE X2.1—Correct the value of(1+D
2−D
1
)/80S to the nearest
whole number.To prepare the solutions,proceed as follows:Using the hydrometers,mix the two liquids in the proportions necessary to obtain the desired solutions.Remove the dissolved air from the solutions by gentle heating or an applied vacuum.Then check the density of the solutions at2360.1°C by means of the hydrometers and,if necessary,add the appropriate air-free liquid until the desired density is obtained.
N OTE X2.2—Where aqueous mixtures are ud,0.5%aqueous sodium acetate should be ud to prepare the mixture.This reduces the formation of bubbles from dissolution.
N OTE X2.3—In order to obtain a linear gradient in the tube,it is very important that the solutions be homogeneous and at the same temperature when their densities are determined.It is also important that the density difference between the solutions concutively introduced into the tube be equal.
X2.1.2By means of a siphon or pipet,fill the gradient tube with an equal volume of each liquid starting with the heaviest, taking appropriate measures to prevent air from being dis-solved in the liquid.After the addition of the heaviest liquid, very carefully and slowly pour an equal volume of the cond heaviest liquid down the side of the column by holding the siphon or pipet against the side of the tube at a slight angle. Avoid excess agitation and turbulence.In this manner,the “building”of the tube shall be completed.
N OTE X2.4—Density gradients may also be prepared by reversing the procedure described in X2.1.1and X2.1.2.When this procedure is ud, the lightest solution is placed in the tube and the next lightest solution is very carefully and slowly“placed”in the bottom of the tube by means of a pipet or siphon which just touches the bottom of the tube.In this manner the“building”of the tube shall be completed.
X2.1.3If the tube is not already in a constant-temperature bath,transfer the tube,with as little agitation as possible,to the constant-temperature bath maintained at2360.1°C.The bath level should approximately equal that of the solution in the tube,and provision should be made for vibrationless mounting of the tube.
X2.1.4For every254mm of length of tube,dip a minimum offive clean calibratedfloats,spanning the effective range of the column,into the less den solvent ud in the preparation of the gradient tube and add them to the tube.By means of a stirrer(for example,a small coiled wire or other appropriate stirring device)mix the different layers of the tube gently by stirring horizontally until the least den and most denfloats span the required range of the gradient tube.If,at this time,it is obrved that thefloats are“bunched”together and not spread out evenly in the tube,discard the solution and repeat the procedure.Then cap the tube and keep it in the constant-temperature bath for a minimum of24h.
X2.1.5At the end of this time,plot the density offloats versus the height offloats to obrve whether or not a fairly smooth and nearly linear curve is obtained.Some small irregularities may be en,but they should be slight.Whenever an irregular curve is obtained,the solution in the tube shall be discarded and a new gradient prepared.
N OTE X2.5—Gradient systems may remain stable for veral months. X2.2Method B—Continuous Filling with Liquid Entering Gradient Tube Becoming Progressively Less Den:
X2.2.1Asmble the apparatus as shown in Fig.X2.1,using beakers of the same diameter.Then lect an appropriate amount of two suitable liquids which previously have been carefully deaerated by gentle heating or an applied vacuum. Typical liquid systems for density-gradient tubes are listed in Table1.The volume of the more den liquid ud in the mixer (Beaker B shown in Fig.X2.1)must be equal to at least one half of the total volume desired in the gradient tube.
An FIG.X2.1Apparatus for Gradient Tube
Preparation
