1、Designation: D 6247 98 (Reapproved 2004)Standard Test Method forAnalysis of Elemental Content in Polyolefins By X-rayFluorescence Spectrometry1This standard is issued under the fixed designation D 6247; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, the 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.1. Scope1.1 This test method covers a general procedure for thedetermination of elemental content
3、 in polyolefins by X-rayfluorescence spectrometry, in concentration levels typical ofthose contributed by additives and reactor processes.NOTE 1Specific methods and capabilities of users may vary withdifferences in interelement effects and sensitivities, instrumentation andapplications software, and
4、 practices between laboratories. Developmentand use of test procedures to measure particular elements, concentrationranges or matrices is the responsibility of individual users.NOTE 2One general method is outlined herein; alternative analyticalpractices can be followed, and are attached in notes, wh
5、ere appropriate.1.2 The values stated in SI units are to be regarded as thestandard. The inch-pound units given in brackets are forinformation only.1.3 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 st
6、andard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in Section 10.NOTE 3There is no similar or equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:2C 1118 Guid
7、e for Selecting Components for Wavelength-Dispersive X-ray Fluorescence (XRF) SystemsD 883 Terminology Relating to PlasticsD 4703 Practice for Compression-Molding ThermoplasticMaterials into Test Specimens, Plaques or SheetsE 135 Terminology Relating to Analytical Chemistry forMetals, Ores, and Rela
8、ted MaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 1361 Guide for Correction of Interelement Effects inX-ray Spectrometric AnalysisE 1621 Guide for X-ray Emission Spectrometric Analysis3. Terminology3.1 Definitions:3.1.1 Definitions of ter
9、ms applying to XRF and plasticsappear in Terminology E 135 and Terminology D 883, respec-tively.3.2 Definitions of Terms Specific to This Standard:3.2.1 elementused in this context, refers to any chemicalelement that can be determined by XRF; and is often usedsynonymously with the term metal.3.2.2 i
10、nfinite thicknessor critical thickness: the thicknessof specimen which, if increased, yields no increase in intensityof secondary X-rays, due to absorption by the polymer matrix.This thickness varies with secondary X-ray energy, or wave-length.3.2.3 polyolefinused in this context, refers to PE and P
11、Pthermoplastics.4. Summary of Test Method4.1 The test specimen is compression molded or injectionmolded into a plaque having a clean, uniform surface.4.2 The plaque is irradiated in the WDXRF with a beam ofprimary X-rays, that causes each element to fluoresce atspecific wavelengths (lines). Choice o
12、f appropriate lines andspectrometer test conditions can vary according to each ele-ment, and with factors such as detector response, concentrationrange, and other elements present in the sample matrix.4.3 These secondary X-rays are dispersed with diffractioncrystals of appropriate spacing, and measu
13、red by appropriatedetectors configured at angles specific to lines of interest.Additional considerations appear in Guides C 1118 andE 1621.4.4 Analyte concentration is determined by relation/comparison of line intensity with a calibration curve.1This test method is under the jurisdiction of ASTM Com
14、mittee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved July 1, 2004. Published July 2004. Originally approvedin 1998. Last previous edition approved in 1998 as D 6247 - 98.2For referenced ASTM standards, visit the ASTM website, ww
15、w.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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NOTE
16、 4An alternative method utilizes a fundamental parameters typecalibration.5. Significance and Use5.1 X-ray fluorescence spectrometry is an accurate andrelatively fast method to determine multielement concentra-tions in polyethylene or polypropylene materials, or both. Itcan be used as a quality cont
17、rol measure for post-reactorstudies, for additive levels in formulated resins, and forfinished products.5.2 Further elaboration appears in Guide E 1621.6. Interferences6.1 Potential interferences are explained in Guide E 1621.7. Apparatus7.1 Calibration Standards Formulation:7.1.1 Batch Compounding
18、Equipment, with temperatureregulation capabilities, for melt homogenization of elementalcompounds or additives into polyolefin reference standards.Equipment can range from small scale torque rheometersequipped with mixing head, to larger-scale batch mixers.Nitrogen purge capabilities are recommended
19、.NOTE 5An alternative method requires a single-screw or twin-screwlaboratory-scale extruder in place of the melt-fusion head, however, morematerial is required for formulation. Dry homogenization techniqueswhich do not require the use of melt-compounding apparatus have beenused, however, such are no
20、t recommended.7.1.2 Analytical Balance, 0.1-mg sensitivity7.2 Specimen Preparation:7.2.1 Thermal Press, for compression-molding of plaques,and capable of obtaining temperatures, pressures and coolingrates, as recommended for PE and PP in Practice D 4703 andin Section 11 of this test method.7.2.2 Fla
21、sh Type Mold, picture-frame type, described inPractice D 4703: stainless-steel chase to mold test plaques 3.2mm 0.125 in. thick, uncoated Mylar3(polyester film) partingsheets, and smooth, stainless steel backing plates of minimum2.5 mm thickness.NOTE 6Injection molding apparatus have also been emplo
22、yed, inplace of the thermal press and flash mold.NOTE 7The recommended thickness of 3.2 mm may vary with userpreference. Other material may be used for parting sheets, provided it doesnot adhere to the polymer under such thermal conditions. Some techniquesuse polished steel backing plates, with chro
23、med surfaces, and no partingsheets. The apparatus used should not introduce contamination of ele-ments of interest, and should yield specimens with a plane surface ofadequate smoothness.7.3 Excitation Source, Spectrometer, and MeasuringSystemRequirements for a wavelength-dispersive XRF areoutlined i
24、n Guides C 1118 and E 1621.8. Reagents and Materials8.1 P-10 Gas, a mixture of 90 % argon and 10 % methane,ultra-high purity or equivalent, for use with gas-flow propor-tional detectors.8.2 Nitrogen, prepurified grade or equivalent, for purgingthe melt fusion chamber.8.3 Elemental StandardsCompounds
25、 or additives, orboth, to be melt homogenized into polymer calibration stan-dards. Material should be certified as to elemental purity andshould be dried and desiccated prior to use.9. Reference Materials9.1 Reference Materials, can be prepared by users, as inSection 11.9.2 Other Materials, appear i
26、n Guide E 1621.9.3 Monitor SamplesTo account for instrument drift (forexample, electronic variations or long term X-ray sourcedegradation).NOTE 8Monitor samples are selected for their long-term durability,and should ideally contain elements near to high and low ends ofanalytical range(s) of interest
27、. Prefabricated glass discs outside range(s) ofinterest are often used. They are measured before measurement ofcalibration standards, and are remeasured periodically (for example,daily). Any drift from original measurements can be accounted for, andnecessary corrections can be applied to maintain ca
28、librations relative toinitial conditions.10. Safety Precautions10.1 Occupational Health and Safety Standards for X-rays,and ionizing radiation shall be observed. It is also recom-mended that proper practices be followed, as shown in GuideE 1621.NOTE 9X-rays are dangerous and can cause serious person
29、al injury.X-ray beams can be very narrow and difficult to detect. Precautions takenminimize potential radiation exposure include an increase in protectiveshielding, an increase of distance, and a decrease of time near anysuspected source of leakage.10.2 ChemicalAppropriate precautions for chemical h
30、az-ards shall be observed for any chemicals and materials used inpreparing calibration standards. Consult the suppliers MaterialSafety Data Sheets for specific hazards and safety practices.10.3 Pressurized Gas requires safe and proper handlingpractices.10.4 Specimen PreparationFollow appropriate pre
31、cau-tions when using hot equipment for homogenization andspecimen preparation. Consult manufacturers recommenda-tions for specific practices.11. Preparation of Reference Materials and TestSpecimens11.1 Specimen PlaquesConsistent preparation of refer-ence materials and test specimens is essential. Va
32、riations insample thickness, surface finish and homogeneity can affectreliability of results.11.1.1 Reference MaterialsA technique that offers consis-tent elemental dispersion throughout the calibration standardshould be followed. Melt homogenization to ensure uniformityis recommended; see Annex A1.
33、NOTE 10Resins from actual production runs have been used forcalibration standards, after verification by independent analytical methods.11.1.2 Test SpecimensIf elemental dispersion is poor,homogenize the sample according to Annex A1, Section 2. Ifelemental dispersion is acceptable, proceed to 11.2.3
34、Mylar is a registered trademark of DuPont.D 6247 98 (2004)211.2 Compression MoldingBoth calibration standards andtest specimens are pressed into plaques having a suggestedthickness of 3.2 mm 0.125 in. Each plaque should have asmooth, plane surface, and no voids. Refer to Practice D 4703.NOTE 11Techn
35、iques using no polymer-based calibration have beenused.NOTE 12Some users employ a laboratory-scale injection moldingtechnique as an alternative to this suggested compression moldingmethod.NOTE 13A thickness of 3.2 mm is commonly used, however, somelaboratories employ lesser or greater thicknesses (f
36、or example, 6 mm, tomore closely approach infinite thickness; or extruded thin films andsheets). The convenience of making a plaque of one thickness for allelements, versus infinite thickness may be a factor for user consideration.NOTE 14Plaques may be molded in the proper dimensions to fit theinstr
37、ument, or may be of a larger size, from which the specimen plaque ispunched out.11.2.1 Weigh the required mass of plastic and place into thehollow chase of the picture frame flash mold assembly, whichis sandwiched between Mylar3parting sheets, and supportedby smooth backing plates.11.2.2 Place the a
38、ssembly into the press, which has beenpreheated to 175C for PE and 200C for PP. Heat the sampleunder appropriate pressure and time settings to obtain asuitable specimen plaque.11.3 Cooling Rate is chosen to yield a uniform, smoothplaque. User preferences vary.11.3.1 Programmed CoolingAfter a pre-pro
39、grammeddwell time at high pressure, initiate cooling at a recommendedrate of 15 6 2C per minute, or:11.3.2 Quick CoolingRemove the hot assembly and pres-surize in a water-cooled press, or equivalent, and allow it tocool to ambient temperature.11.4 It is recommended to clean specimen surfaces withiso
40、propyl alcohol (or methyl alcohol), immediately prior tomeasurement. Operator experience may show this need to varywith the element or additive to be measured.11.4.1 Care should be taken to handle only the sides, not thesurface of the specimen following molding or cleaning so thatoils and salts from
41、 the skin do not contaminate the specimen.Disposable cotton gloves may be worn when handling speci-mens to prevent inadvertent contamination.12. Preparation of Apparatus12.1 A description of considerations is included in GuideE 1621.NOTE 15Measurement of Ka lines is recommended, where possible.NOTE
42、16A reduction of X-ray tube power used (for example -10 %current) can result in an overall increase in tube life.13. Calibration and Standardization13.1 Considerations are covered in Guide E 1621.NOTE 17Background subtraction is a suggested correction method forpolyolefins. A linear calibration curv
43、e was suitable for the elementalconcentrations listed in the annex. Higher concentrations may requiremathematical corrections covered in Guide E 1361.NOTE 18One alternative calibration method, using fundamental pa-rameters software, required measurements of only one polymer blank andone standard per
44、 element (for example, 0.5 % analyte element in mineraloil).14. Procedure14.1 Refer to Guide E 1621.NOTE 19The effects of poor surface finish on test accuracy canbecome more adverse at longer wavelengths (lower atomic numbers) andat lower analyte concentrations. The use of a sample spinner is recom-
45、mended.14.2 It is recommended to measure monitor sample(s) daily,for elements of interest, and to apply any required driftcorrections to sample measurements.14.3 Participating laboratories preferred a fixed countingtime over a fixed number of counts.15. Interpretation of Results15.1 Refer to Guide E
46、 1621.16. Precision and Bias16.1 Instrument RepeatabilityRepeatability of one instru-ment in one laboratory measuring one single specimen of anexperimental formulation 30 times is shown in Table 1.16.2 Round Robin Study:16.2.1 Precision and bias statements are currently underevaluation. Data were ob
47、tained in a round robin study con-ducted in 1992, in accordance with Practice E 691, involvingtwo groups of commercial grade materials (one group ofpolyethylene, one group of polypropylene), with each groupcontaining three materials (that is a total of six materials). Thegrades were selected on the
48、basis of their relative elementalcontent levels, from low ( 200 and 5000 ppm); as contributed by catalystresidues or additives. Each grade was relatively free ofinterferences and interelemental effects. Reference values forthe elements selected for testing in each of the round robinsamples were dete
49、rmined by neutron activation analysis.16.2.2 To minimize variations in elemental dispersion, eachsample material was homogenized by triple extrusion passes.Polyethylene and polypropylene sample groups were preparedby each of two laboratories respectively, and distributed toeach round robin participant under cover of these respectivelabs. Twelve laboratories participated in this study. Each roundrobin participant had the option to analyze either one, or bothgroups of materials. The polyethylene sample group was testedfor a total of nine eleme
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