1、Designation: D 2839 05Standard Practice forUse of a Melt Index Strand for Determining Density ofPolyethylene1This standard is issued under the fixed designation D 2839; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers the preparation of a sample forpolyethylene density determination in accordance with TestMethod D
3、 1505. The sample consists of a strand produced byextrusion of the polyethylene in accordance with Test MethodD 1238, Condition 190/2.16 (Melt Index).1.2 The values stated in SI units are to be regarded as thestandard. The values given in brackets are for information only.1.3 This standard does not
4、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 determine the applica-bility of regulatory limitations prior to use.NOTE 1There is no similar or equivalent IS
5、O standard.2. Referenced Documents2.1 ASTM Standards:2D 1238 Test Method for Flow Rates of Thermoplastics byExtrusion PlastometerD 1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD 4703 Practice for Compression Molding ThermoplasticMaterials into Test Specimens, Plaques, or
6、 SheetsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 melt index strandthe extrudate produced when poly-ethylene is extruded in accordance with Test Method D 1238,Condition 190/2.16.4. Significance and Use4.1 This
7、practice has been found to be very useful forpreparing polyethylene samples suitable for determination ofdensity by Test Method D 1505, for quality control purposes,especially in a resin manufacturing facility where fast, repro-ducible, comparative results are needed. It is not necessarilyrecommende
8、d for resin specifications which may be a part of asales contract between the buyer and the seller.4.2 The density of a polyethylene sample is highly depen-dent on the preparation and thermal history of the specimens.The level of density results obtained by this practice of samplepreparation differs
9、 from that obtained by other methods asdescribed in Practice D 4703.4.3 Before proceeding with this practice, reference shouldbe made to the specification of the material being tested. Anytest specimen preparation, conditioning, dimensions, or testingparameters, or some combination thereof, covered
10、in thematerials specification shall take precedence over those men-tioned in this practice. If there are no material specifications,the default conditions apply.5. Apparatus5.1 Extrusion Plastometer, as described in Test MethodD 1238.5.2 Hot Plate, to boil water.5.3 Beakers, 250-mL low form, graduat
11、ed, with watch-glasscovers.6. Sample6.1 Polyethylene, in any form suitable for test in accordancewith Test Method D 1238.7. Procedure7.1 Prepare a Melt Index Strand by extruding the sample inaccordance with Test Method D 1238, Condition 190/2.16,dropping the strand on a cool metal plate after cuttin
12、g off.When Procedure B of Test Method D 1238 is used, cut off theextrudate at about the time the timer is actuated and discard.Save the portion extruded during the timed interval.NOTE 2The conditioning procedure as described in 7.2 and 7.3 maybe omitted, if desired; in such case, after a 10-min cool
13、ing period, cut off1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials(D20.15.01).Current edition approved July 1, 2005. Published July 2005. Originally approvedin 1969. Last previous edition appr
14、oved in 2002 as D 2839 - 02.2For 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.1*A Summary of Changes section ap
15、pears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the density specimen as described in 7.4 and determine the density inaccordance with Test Method D 1505.NOTE 3It has been shown that the measured densit
16、y of an extrudedstrand can be significantly affected by changes in the localized air velocitydue to external drafts, location in relation to HVAC outlets, and so forth.It is advisable to minimize any external airflow and to recognize this whenrelocating instruments or when comparing results from ins
17、truments indifferent locations.7.2 Drop the strand into a 250-mL beaker containing at least200 mL of briskly boiling water, and cover with a watch-glass.Keep a large beaker full of water boiling along with this so thatthe amount of water can be maintained at 200 mL for the wholeperiod without interr
18、upting the boiling. Let the strand conditionin the boiling water for 30 min.NOTE 4A time interval of 5 days at room temperature betweenextrusion of the strand and dropping into boiling water has not been foundcritical.7.3 At the end of the boiling time, remove the beaker fromthe hot plate, making su
19、re the water level is at approximately200 mL, and allow to stand on the bench at standard laboratorytemperature for 1 h.7.4 Remove the strand from the water and cut off a 5-mm14-in. length from the thicker end of the strand. Discard thisportion, and, from the next 10 mm 12 in. of strand, cut at leas
20、tthree short pieces of convenient size for density determination.If the sample whitens when cutting, use a very sharp razorblade, and cut very slowly. Cutting under water may avoidwhitening. This whitening appears to affect sample density andshould be avoided. Discard any specimens with bubbles orvi
21、sible roughness.7.5 Determine the density of the specimen in accordancewith Test Method D 1505 within 24 h of the conditioningdescribed in 7.2 and 7.3.NOTE 5Considerable periods of time at room temperature betweenconditioning and density determination have little effect on results, butshould be held
22、 to less than a day.8. Report8.1 Report the following information:8.1.1 Any deviations from the procedure, including omis-sion of the conditioning.8.1.2 The density according to the Report Section of TestMethod D 1505.9. Precision and Bias9.1 PrecisionTable 1 is based on a round robin conductedin 19
23、94, in accordance with Practice E 691, involving sevenmaterials tested by 10 to 15 laboratories. For each material, allof the samples were prepared by each laboratory in accordancewith this practice. Each test result is an individual determina-tion. Each laboratory obtained six test results for each
24、 material.(WarningThe following explanations of r and R (9.2-9.2.3)are only intended to present a meaningful way of consideringthe approximate precision of this practice. The data in Table 1should not be rigorously applied to acceptance or rejection ofmaterial, as those data are specific to the roun
25、d robin and maynot be representative of other lots, conditions, materials, orlaboratories. Users of this practice should apply the principlesoutlined in Practice E 691 to generate data specific to theirlaboratory and materials, or between specific laboratories. Theprinciples of 9.2-9.2.3 would then
26、be valid for such data.)9.2 Concept of r and RIf Srand SRhave been calculatedfrom a large enough body of data, and for test results that wereaverages from testing one specimen:9.2.1 Repeatability Limit, r (Comparing two test resultsfor the same material, obtained by the same operator using thesame e
27、quipment on the same day)The two test results shouldbe judged not equivalent if they differ by more than the r valuefor that material.9.2.2 Reproducibility Limit, R, (Comparing two test resultsfor the same material, obtained by different operators usingdifferent equipment in different laboratories)T
28、he two testresults should be judged not equivalent if they differ by morethan the R value for that material.9.2.3 Any judgement in accordance with 9.2.1 or 9.2.2would have an approximate 95 % (0.95) probability of beingcorrect.9.3 BiasAt the 95 % confidence level, there is no evi-dence of difference
29、 between the mean values of density testsprepared by this practice and those prepared using PracticeD 4703, Annex 1, Procedure C.10. Keywords10.1 density; melt index strand; PE; polyethyleneTABLE 1 Precision DataMaterial N Average SrASRBrCRDB 10 0.9139 0.00026 0.00078 0.00072 0.00219F 12 0.9179 0.00
30、020 0.00078 0.00055 0.00220G 13 0.9222 0.00030 0.00073 0.00085 0.00206A 15 0.9357 0.00041 0.00080 0.00115 0.00225E 14 0.9530 0.00039 0.00092 0.00109 0.00258C 11 0.9615 0.00030 0.00073 0.00085 0.00206D 10 0.9626 0.00053 0.00109 0.00148 0.00305ASr= within-laboratory standard deviation for the indicate
31、d material. It isobtained by pooling the within-laboratory standard deviations or the test resultsfrom all of the participating laboratories.BSR= between-laboratories reproducibility, expressed as standard deviation,for the indicated material.Cr = within-laboratory repeatability limit = 2.8 Sr.DR =
32、between-laboratories reproducibility limit = 2.8 SR.D2839052SUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this practice since the last issue, D 2839 - 02,that may impact the use of this practice. (July 1, 2005)(1) Added Note 3 regarding external air flow effects.
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36、ee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D2839053
