X-ray Fluorescence Analysis Of Polymers

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When results matterA WHITE PAPER FROMSPECTRO ANALYTICAL INSTRUMENTSX-ray fluorescenceanalysis of polymersIntroductionNowadays, plastics are used in all areas ofand Zn compounds, CuI, KI, KBr .) and flameour lives. Be it as packaging, in automobilesretardantsand above all in the electrical, electronics andphosphorus and inorganic flame retardants .).(brominecompounds,organo-toy industries. The properties of the plasticsare very different, from extremely rigid toIt is also often necessary to prove that aextremely flexible, everything is possible – andpart made of plastic complies with legalin the most diverse colors.requirements. The more well-known regulationshere are the directive on the restriction ofThese properties are achieved by blendingthe use of certain hazardous substances inadditivesDuringelectrical and electronic equipment (RoHS), themanufacturing the concentration of manydirective on packaging and packaging wasteadditives in the polymer can be controlled byand the directive on end-of-life vehicles ELV.totherawpolymer.the element content. Substances of interest aree.g. fillers (talc, chalk and limestone [CaCO3],kaolin, feldspar .), dyes (rutile or anatase[TiO2], ZnO, ZnS, Fe2O3 ), stabilizers (Ca

X-rayasTraditionally, in many cases WD-XRF is usedinstrumentalin process control and ED-XRF (especiallyanalysis is established as a fast method ofportable systems) for screening analysis.accurate elemental analysis and screeningHowever, this has changed with hodforThegenerations of devices: ED-XRF devices canadvantages here are in particular the speed ofoffer comparable performance characteristicsthe analysis as well as the low requirementsas WD-XRF systems, depending on thefor sample tallysamples.twodifferentOn the one hand, ED-XRF is distinguished bymethods of XRF; wavelength dispersivethe simultaneous multielement detection, but(WD-XRF) and energy dispersive (ED-XRF).also by the low thermal load on the sample.ED-XRF devices are available in a widerange of handheld systems, from portable tolaboratory instruments.Depending on the task, the analyzers arealso differentiated according to the samplesurface under test. If individual particles areto be localized in a plastic (for example fromabrasion) on a sample surface in a failureanalysis, analyzers with a small excitationspot (microanalysis on a scanning electronmicroscope, micro-XRF) are suitable.For process control, however, traditionallylarger sample areas (2 to 10 mm) areinvestigated.2X-ray fluorescence analysis of polymers

Analytical PrincipleX-ray fluorescence analysis is an analyticalmethod for identifying the different chemicalelements contained in a substance anddetermining their quantity. For this purpose,the substance is excited to emit elementspecific radiation, the spectral compositionof which contains this information. Figure 1shows this schematically.In ED-XRF, the X-ray fluorescence radiationis detected with the aid of a semiconductordetector and the signals are further processedFigure 1: Principle of X-ray fluorescenceinto a measurement spectrum. The principleis shown in Figure 2. The information inthe spectrum is used to determine elementconcentrations in the sample.Sample PreparationThe preparation of the sample is importantfor an accurate analysis. In order to achieveoptimal results with the analysis, the samplesshould be in the form of pellets, produced byinjection molding or compression molding.The same can also be achieved withhomogeneous materials by examining a partof the sample with a sufficiently good samplesurface when using the XRF device.Figure 2: Principle of ED-XRFX-ray fluorescence analysis of polymers3

For a fast screening analysis, it may besufficient if the sample is present as agranulate or as a powder after a grinding.Figure3showsmeasurementspectrarecorded with the SPECTRO XEPOS usingthe HAPG polarization crystal for a granulesample of the BCR 680 material comparedto a pellet produced by the compressionmolding process. The differences in thespectra are clearly visible, especially for theelements with low atomic numbers such asmass and sample diameter. For a screeningS and Cl.analysis this is usually sufficient; for processcontrol, samples of the same shape andSince fluorescence radiation of higher energythickness should be used for calibration.can also be detected from a greater depthof the sample, the thickness of the sampleThe effect is caused by the fact that theplays a role for the accuracy of the analysisexcitation radiation is absorbed by theof the concentrations of elements with asample matrix when entering the samplehigher atomic number. This is irrespective ofand the generated fluorescence radiationwhether the sample is examined as granulate,is absorbed as it emerges from the sample.fine powder or pellet. In order to reduce theSince the excitation radiation is a higher-effect, the device software can consider otherenergy radiation, the effect is smaller thanparameters from the spectrum (backscatterthat of fluorescence radiation. The intensityinformation) or the specification of sampleI0 generated in the sample is absorbed alongthe path d by the sample of the density ρ. Themass attenuation coefficient μ is dependenton the energy of the fluorescence radiation.This results in the following formula:I I0 * exp (- µ * ρ * d)If the value for the intensity I is determinedfor a thickness at which the fluorescenceintensity was absorbed by 63% (1/e), youcan determine a value which is generallyreferred to as “attenuation length”. Figure 4shows the value of the “attenuation length”for the example of a polypropylene matrixand a take-off angle of 45 degrees for thefluorescence radiation of different elementsFigure 3: Measurement spectra, taken with HOPG polarization crystal for a pelletsample (shown in blue) and a molding pellet (shown in red)with different atomic numbers.As you can see from the graph (Figure 4), theescape depth of the fluorescence radiation is4X-ray fluorescence analysis of polymers

Attenuation length in µm100000100001000100101102030405060atomic numbervery much dependent on the atomic numberFigure 4: Escape depth of fluorescence radiation of different elements in a polyethylene matrixof the element (more precisely on the energyof the fluorescence radiation). If, for thedetection of the element Na, the intensityis obtained from a depth of a few μm, thisvalue for the element Cd is in the range of2-3 cm in a polymer matrix.Figure5showsmeasurementspectrarecorded with the SPECTRO XEPOS fortwo pellets of different thicknesses. Thedifferences in the spectra are clearly visible,especially for the elements with higheratomic numbers such as Br and Pb.Figure 5: Measurement spectra for two molding pellets of different thickness(thick sample shown in red, thin sample shown in blue)X-ray fluorescence analysis of polymers5

Figure 6: Measurement spectra recorded for four plastic compacts with different Ti contents (0, 0.3, 1.0, and 7.7 mg/kg), measuring time: 150 secFigure 8: Measurement spectra recorded for three polyamidesamples with Cu contents between about 1.6 and 5%Analyticsshows measurement spectra recorded withFor accurate analysis of the samples, athe SPECTRO XEPOS for four plastic pelletsmethod that has been calibrated with revisedwith different titanium contents.standards is used. These standards shouldinclude a matrix comparable to the unknownThe detection limit for Ti in such a plasticsamples, and the pellets should be ofmatrix is 0.1 mg/kg. Comparable lowcomparable size and thickness.detection limits are achieved for otherimportant elements, too.If low contents are examined in polymers,a calibration is often used which assumesIn many cases, the concentrations of thea linear relationship between intensity andelements to be analyzed tend to be in theconcentration. Other elements in the sample% range. The following example shows theor higher contents can be taken into accountanalysis of Cu in polyamide in which copperby corresponding correction terms. Figure 6iodide was added as a stabilizer.Copper content in %Withtheintensities,measuredtheXRFSample R011.635Sample R021.638calibrated and a goodSample R031.638reproducibilitySample R041.637accuracy of the analysisSample R051.642can be achieved.Average1.638Std dev(standard deviation)0.002spectrometercanbeandThe concentrations ofother stabilizers (e.g., CaFigure 9: Calibration for Cu in polyamideTable 1: Precison of a repeatmeasurement of Cu in polyamide6X-ray fluorescence analysis of polymers

Figure 10: Measurement spectra recorded for ABSsamples with different TiO2 contentsFigure 12: Measurement spectra recorded for polystyrene samples with different Br contentsand Zn compounds, KI, KBr .) in plastics canreproducibility and accuracy of the analysisbe analyzed in the same way.can be achieved.Also, the contents of dyes, e.g. rutile orAn additional example is the analysis ofanatase (TiO2), ZnO, ZnS, Fe2O3 . can beBr from brominated flame retardants. Thedetermined by X-ray fluorescence analysis ofmethod corresponds to that described above.the elements Ti, Zn, Fe . Figure 10 shows theThe spectra in Figure 12 show measurementsanalysis of TiO2 in ABS. Of course, the TiO2of polystyrene samples with different Brcontent could also be determined indirectlycontent. With the measured intensities, theby incineration. However, if there are fillers inXRF spectrometer can be calibrated and athe ABS, for example, then this method doesgood reproducibility and accuracy of thenot give an accurate statement.analysis can be achieved.With the measured intensities, the XRFspectrometer can be calibrated and a goodCorrela on TiO2 in ABS12R² 0.9981TiO2 analyzed in %1086420024681012TiO2 reference concentra on in %Figure 11: Calibration for TiO2 in ABSX-ray fluorescence analysis of polymersFigure 13: Calibration for Br in polystyrene7

ing of plastics for the detection of regulatedsubstances (e.g., RoHS: DIRECTIVE 2002/95/ECOF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of January 27, 2003 on the restriction of the useof certain hazardous substances in electrical and electronic equipment and DIRECTIVE 2011/65/EU OF THEEUROPEAN PARLIAMENT AND OF THE COUNCIL ofJune 8, 2011 on the restriction of use of certain hazardous substances in electrical and electronic equipment(amended version), ElektoG, AltfahrzeugV, VerpackV).In test methods of international institutionssuch as IEC (IEC 62321-3-1) and ASTM, XRFis described as the method of choice for afast screening analysis.For this purpose, it is particularly importantto achieve correspondingly low detectionFast Screening Analysislimits for the relevant elements in order toFor a fast screening analysis, methods withhave sufficient safety that the limit values areautomatic matrix correction considering flu-undershot even at short analysis times. Fig-orescence and scattering, so-called Turbo-ures 14a, b, and c show measurement spec-Quant methods are suitable.tra of the European reference materials ERMRC 680 m and 681 m in comparison.Today, one of the most important applications for fast screening analysis is the screen-Figure 14a:Comparison of measurement spectra of the samplesERM EC 680m and 681m forthe elements As, Hg and Pb8X-ray fluorescence analysis of polymers

Figure 14b: Comparison of measurement spectra of the samples ERM EC 680m and 681m for the elementCdFigure 14c: Comparison of measurement spectra of the samples ERM EC 680m and 681m for the elementCrX-ray fluorescence analysis of polymers9

Table 2:Cr in mg/kgZn in mg/kgAs in mg/kgBr in mg/kgCd in mg/kgSn in mg/kgSb in mg/kgHg in mg/kgPb in mg/kgAnalysis 19.3201.05.2189.120.819.79.43.211.2Analysis 29.4200.65.1189.121.220.010.02.711.4Analysis 39.4201.35.2190.321.520.79.22.511.4Analysis 49.4201.35.2189.221.120.410.02.911.4Analysis 59.4201.35.1189.921.620.810.02.511.2Analysis 69.4200.85.3189.221.420.410.22.910.8Analysis 79.3201.65.0189.820.920.29.73.111.9Analysis 89.3201.55.1189.121.220.29.52.611.5Analysis 99.3201.05.2189.421.620.49.22.711.5Analysis 109.5201.25.2189.421.420.38.92.911.59.4 0.1201.2 0.35.2 0.1189.5 0.421.3 0.320.3 0.39.6 0.42.8 0.311.4 0.3AverageTable 2 shows the results of a 10-fold repeathere. The total mapping time for an examinedmeasurement of the sample ERM 680m witharea of 1.6 2.8 cm was about 40 minutes.a total analysis time of 10 min per sample us-When looking at the measurement spectraing the SPECTRO XEPOS HE.Failure AnalysisFor failure analyses (for example in the caseof debris particles on a plastic surface), XRFdevices with a small excitation spot anda mapping function can be used. The testsample is positioned on a movable sampletable and the sample is then “scanned”.While doing this, mapping images are createdas shown in Figures 15 through 17. As anexample, a “spiked sample” was examinedFigure 15: Distribution image of Cr on a plastic surface caused by abrasive particlesFigure 16: Distribution image of Ni on a plastic surfacecaused by abrasive particles10X-ray fluorescence analysis of polymers

Figure 17: Superimposed distribution imagesof Fe, Cr and Ni on a plastic surface caused byabrasive particlesat the two points, recorded with a longermeasurement time, the differences in theFigure 18: Spectra taken at two locations of the sample containing aparticleelement composition become clear.If the detected points are then subjected toa quantitative examination, the followingresults are obtained.Summary1.8550SpecificationFe in %1.2379Point analysisSpecification94.55Point analysis87.59Cr in %1.5 - 1.81.7Ni in %0.85 - 1.151.65Mo in %0.15 - 0.250.180.6 - 0.80.20-0.080.9 - 1.11.230.4 - 0.70.640.15 – 0.450.41V in %Mn in %11.0 - 12.09.95 0.01Table 3: Results of analyzes of “spiked” abrasive particles on a plastic sampleIn the characterization of element content incalibrating the analyzer, the sample matrixpolymers, XRF has proved to be an excellentmust be observed. The selection of the rightanalytical technique.analytical system depends on the analyticaltasks.When preparing samples for an XRF analysis,a number of parameters must be considered.For trace element determinations, a highThese include the sample shape, the samplesensitivity to detection is required; thesurfaceresolution of the spectrometer may beandsamplethickness.WhenX-ray fluorescence analysis of polymers11

important if many elements are present inFor the detection of abrasion particles andthe sample (due to possible line overlaps),their quantitative analysis, XRF systems withand the device s software should providea small excitation spot and a mapping optioncorresponding calibration models for largeare suitable.concentration ranges. High precision is, ofcourse, essential for high accuracy.The following table gives a good overviewof which XRF system is suitable for whichIn addition to process control, XRF is alsoapplication:suitable for rapid screening of samples tomonitor regulated substances.12ApplicationBest suitedWell suitedCompliance ScreeningSPECTRO XEPOS(XEP05HE)SPECTRO XEPOS,SPECTROSCOUT,SPECTRO xSORTSPECTRO MIDEX(F), Na Cl in polymersSPECTRO XEPOS(XEP05C, XEP05P,XEP05HE)SPECTRO XEPOS (XEP05D),SPECTROSCOUT,SPECTRO MIDEXTraces of K-Mnin polymersSPECTRO XEPOS(XEP05P, XEP05HE)SPECTRO XEPOS(XEP05D, XEP05C)Process control ofelements in the range ofatomic numbers 19 92SPECTRO XEPOS(all versions)SPECTROSCOUT,SPECTRO MIDEXAnalysis of inclusions,element mappingsSPECTRO MIDEXX-ray fluorescence analysis of polymers

Contact UsCONTACT USREQUEST A QUICK QUOTEREQUEST A FREE DEMORESOURCE LIBRARYwww.spectro.comGERMANYSPECTRO Analytical Instruments GmbHBoschstrasse 10D-47533 KleveTel.: 49.2821.892.0Fax: 49.2821.892.2202spectro.sales@ametek.comUSASPECTRO Analytical Instruments Inc.91 McKee DriveMahwah, NJ 07430Tel.: 1.800.548.5809 1.201.642.3000Fax: TEK CommercialEnterprise (Shanghai) CO., LTD.Part A1, A4 2nd Floor Building No.1 Plot SectionNo.526 Fute 3rd Road East; Pilot Free Trade Zone200131 ShanghaiTel.: 86.21.586.851.11Fax: idiaries: uFRANCE: Tel 33.1.3068.8970, Fax 33.1.3068.8999, spectro-france.sales@ametek.com, uGREAT BRITAIN: Tel 44.1162.462.950,Fax 44.1162.740.160, spectro-uk.sales@ametek.com, uINDIA: Tel 91.22.6196 8200, Fax 91.22.2836 3613, sales.spectroindia@ametek.com,uITALY: Tel 39.02.94693.1, Fax 39.02.94693.650, spectro-italy.sales@ametek.com, uJAPAN: Tel 81.3.6809.2405, Fax 81.3.6809.2410,spectro-japan.info@ametek.co.jp, uSOUTH AFRICA: Tel 27.11.979.4241, Fax 27.11.979.3564, spectro-za.sales@ametek.com,uSWEDEN: Tel 46.8.5190.6031, Fax 46.8.5190.6034, spectro-nordic.info@ametek.com.uSPECTRO operates worldwide and is present in more than 50 countries. For SPECTRO near you, please visit www.spectro.com/worldwide 2018 AMETEK Inc., all rights reserved, subject to technical modifications A-18, Rev. 0 Photos: SPECTRO, Corbis, Adobe Stock, iStockphoto Registeredtrademarks of SPECTRO Analytical Instruments GmbH : USA (3,645,267); EU (005673694); “SPECTRO”: EU (009693763);“SPECTRO XEPOS”: Germany (39851192), USA (2,415,185)X-ray fluorescence analysis of polymers

X-ray fluorescence analysis of polymers 5 very much dependent on the atomic number . of the element (more precisely on the energy of the fluorescence radiation). If, for the . The spectra in Figure 12 show measurements of polystyrene samples with different Br content. With the measured intensities, the

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