1、Designation: D6474 99 (Reapproved 2006) D6474 12Standard Test Method forDetermining Molecular Weight Distribution and MolecularWeight Averages of Polyolefins by High Temperature GelPermeation Chromatography1This standard is issued under the fixed designation D6474; the number immediately following t
2、he designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method
3、 covers the determination of molecular weight distributions and molecular weight averages of linearpolyolefins by high temperature gel permeation chromatography (GPC). This test method uses commercially available polystyrenestandards and equipment and is applicable to polyethylenes (excluding high p
4、ressure low density polyethyleneLDPE) andpolypropylenes soluble in 1,2,4-trichlorobenzene (TCB) at 140C. This test method is not absolute and requires calibration.NOTE 1Size exclusion chromatography (SEC) often is used as an alternative name for gel permeation chromatography (GPC).NOTE 2Specific met
5、hods and capabilities of users may vary with differences in columns, instrumentation, applications software, and practicesbetween laboratories.NOTE 3One general method is outlined herein; alternative analytical practices can be followed and are attached in notes where appropriate.NOTE 4There is no s
6、imilar or equivalent ISO known ISO equivalent to this standard.1.2 The values stated in SI units, based on IEEE/ASTM S1-10, are to be regarded as the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the use
7、r of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD3016 Practice for Use of Liquid Exclusion Chromatography Terms and Relationsh
8、ipsD5296 Test Method for Molecular Weight Averages and Molecular Weight Distribution of Polystyrene by High PerformanceSize-Exclusion ChromatographyE685 Practice for Testing Fixed-Wavelength Photometric Detectors Used in Liquid ChromatographyE691 Practice for Conducting an Interlaboratory Study to D
9、etermine the Precision of a Test MethodIEEE/ASTM S1-10 Standard for Use of the International System of Units (SI): The Modern System (replaces ASTM E 380 andANSI/IEEE Standard 268-1992)3. Terminology3.1 DefinitionsDefinitions of terms applying to plastics appear in Terminology D883.3.2 Definitions o
10、f Terms Specific to This Standard:3.2.1 polyolefin, nused in this context, refers to PE (except LDPE) and PP thermoplastics.4. Summary of Test Method4.1 In this test method, a polyolefin sample is dissolved in a solvent and injected onto a chromatographic column(s) packed witha solid substrate, whic
11、h separates the molecules according to their size in solution. The separated molecules are detected and1 This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommitttee D20.70 on Analytical Methods.Current edition approved March 15, 2006
12、Dec. 15, 2012. Published April 2006December 2012. Originally approved in 1999. Last previous edition approved in 19992006as D6474D647499(2006).99 DOI: 10.1520/D6474-99R06.10.1520/D6474-XX.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at servi
13、ceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. B
14、ecauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section ap
15、pears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1recorded as they elute from the column according to concentration. Through calibration, retention times are converted to molecularweights. Average molecu
16、lar weight parameters and molecular weight distribution are determined from the molecular weightconcentration data.5. Significance and Use5.1 This test method measures the molecular weight distribution and molecular weight averages of polyethylene (except LDPE)and polypropylene resins. Differences i
17、n molecular weight and molecular weight distribution significantly affect physicalproperties, such as morphology, strength, melt flow etc., and as a result, the final properties of products made from these resins.6. Interferences6.1 A major interference is the presence of insoluble, highly entangled
18、, high molecular weight material that may be linear orcross-linked. A successful outcome of the test requires that the sample be dissolved completely prior to the chromatographicseparation. The presence of the above-described material often precludes the necessary dissolution step.6.2 A mismatch in
19、the antioxidant level in the dissolved sample and that of the TCB eluent (see 8.1).6.3 The accuracy of the molecular weight results decreases, that is, they become increasingly underestimated, as the -olefincomonomer content increases in linear low density polyethylene (LLDPE). For example, the resu
20、lts for an octene copolymercontaining 30 branches per 1000 carbon atoms will be about 6 % low.7. Apparatus7.1 Essential ComponentsThe essential components of the instrumentation are a solvent reservoir, a pump, a solvent degasser,a sample injection system, packed columns, and a solute mass detector.
21、NOTE 5Complete high temperature GPC units with a maximum operating temperature of 210C are commercially available.7.2 Solvent ReservoirThe solvent reservoir shall hold sufficient TCB to ensure consistency of composition for a number ofruns. The TCB should be is protected from exposure to water in th
22、e air and the reservoir material shall be inert to the solvent.7.3 PumpThe principal requirement of the pump is production of a relatively constant flow, with minimum pulsations, ofsolvent through the columns. In general, the rate should be is adjustable between 0.1 and 5.0 cm3/min and back pressure
23、s shouldarenot to exceed limits specified by the column manufacturer. Flow rate precision shall be at least 60.3 % as measured under theconditions and time interval for a typical analysis.7.4 Sample Injection SystemThe purpose of the injection system is to introduce the solution containing the sampl
24、e into theflow stream as a sharply defined zone. Either a six-port valve with an attached sample loop or a variable volume injector can beused for this purpose in conjunction with an autosampler. Requirements include minimal contribution to band spreading, injectorability to operate at the back pres
25、sure generated by the columns, repeatability of injection volume, and no carryover.7.5 ColumnsStainless steel columns with uniform and highly polished inside walls are recommended for high temperatureGPC. Columns with lengths ranging from 20 to 50 cm with fittings, frits, and connectors designed to
26、minimize dead volume andmixing are recommended. Generally, the packing materials, typically styrene divinylbenzene copolymers, have narrow particle sizedistributions in the 3 to 20 m range. Packing materials are available in a variety of shapes and pore sizes. Columns may be arepacked with particles
27、 of relatively uniform pore size or with a “mixed bed” of particles to produce a broad range of pore sizes.If a set of columns with uniform pore size is used, it is recommended that the columns be connected in order of increasing poresize towards the low pressure detector side.NOTE 6Packed high temp
28、erature GPC columns are available from a number of manufacturers.7.6 DetectorThe detector provides a continuous measure of the concentration of solute eluting from the column(s). Thedetector shall be sufficiently sensitive and respond linearly to the solute concentration, independently of molecular
29、weight, andshall be of low internal volume so as not to distort the concentration gradient during elution. For this test method, the detector cellvolume should be 30 L or less. The most commonly used concentration detectors for high temperature GPC are refractive indexor infrared. The former has mod
30、erate sensitivity and general utility. When testing detector performance, follow the recommen-dations of the instrument manufacturer.NOTE 7For polyolefins, the refractive index (dn/dc) increment is essentially constant above molecular weights of 5 000 g/mol. The response of thecomponents below 5 000
31、 g/mol should be corrected prior to the molecular weight calculations using a pre-established dn/dc molecular weight calibration.The principal disadvantage of the differential refractometer is that the temperature within the detector cell shall be controlled to within 0.0001C.7.7 Tubing and Fittings
32、All tubing between the sample injector and the detector shouldmust be no greater than 0.25 mm (0.01in.) internal diameter and rated for pressures up to 42 MPa. Connecting column tubing shouldmust be kept as short as possibleand all fittings and connectors shall have low dead volumes to prevent mixin
33、g.7.8 Data Acquisition/Handling SystemMeans shall be provided for determining chromatographic peak heights or integratedarea segments at prescribed time intervals and for handling and reporting data. This is best accomplished using a computer withappropriate software.D6474 122NOTE 8Data acquisition
34、and handling systems for high temperature GPC have not been standardized. However, a number of different manufacturersprovide GPC specific computer software.8. Reagents and Materials8.1 Solvent1,2,4-trichlorobenzene (TCB) is recommended as the solvent for this test method; however, any solvent that
35、hasa boiling point higher than the operating temperature, is considered a good solvent for polyolefins, and is compatible with the GPCcomponents, may be used. method. With a refractive index detector, the solvent shall have a refractive index different than thatof the polyolefins analyzed. Solvent p
36、urity and consistency shall be considered when choosing a solvent. For example, unlessfreshly distilled, and subsequently, kept in a glass container under an inert gas, TCB will react with water to form hydrochloricacid that will attack tubing walls and degrade column packing. The TCB reservoir shou
37、ldmust be protected against exposure tomoisture, or be replaced frequently with fresh solvent, or both. An antioxidant, such as 2,6-di-tert-butyl-4-methylphenol (BHT)shouldmust be added to the solvent reservoir at the same concentration, that is, about 250 mg/L, as in the solvent used to dissolvethe
38、 polymer to minimize any interference due to an antioxidant mismatch peak.NOTE 9Several laboratories are successfully recycling TCB using partial vacuum distillation.NOTE 10Any solvent that has a boiling point higher than the operating temperature, is considered a good solvent for polyolefins, and i
39、s compatiblewith the GPC components, can be used8.2 Polymer StandardsNarrow MWD (MW/Mn 0.3 %) in the flow rate between the time of calibration and sample analysis will causesignificant, systematic errors in MW values calculated. Users should determine the average flow rate of their system by measuri
40、ngthe volume of solvent eluted over a specified time period. When flow rate variations in excess of 0.3 % are observed, replace or3 “Modern Size Exclusion ChromatographyPractice of Gel Permeation and Gel Filtration Chromatography,” W.W. Yau, J.J. Kirkland, and D.D. Bly, John Wiley andSons, 1979.D647
41、4 124service the pump or correct for flow variations by addition of a flow measuring device or use a flow rate marker such as for examplethe air peak or toluene, that is, internal standard.14. Calibration14.1 Selection of Polystyrene StandardsPrepare solutions of polystyrene calibration standards as
42、 outlined in 12.2. A minimumnumber of three standards per decade of MW need to be used to adequately define the calibration curve over the MW range coveredby the columns.14.2 Injection of Polystyrene StandardsMake injections with the instrument autosampler at the same temperature as thecolumn oven t
43、emperature, that is, typically 140C. Add the internal standard, if used, to the solution prior to injection. The injectionvolumes of all standards shallmust be identical regardless of concentration. The recommended volume is 300 L for columns withinternal diameters of 0.8 to 1.0 cm. For diameters of
44、 0.8 cm, use a smaller volume should be chosen.volume.14.3 Data AcquisitionDetermine the elution peak maxima and the corresponding elution volumes (or times) for the variouspolystyrene standards (and internal standard). Usually, this is accomplished with a data acquisition software package.14.4 Gene
45、ration of Calibration CurveConvert the polystyrene peak molecular weights to polyolefin molecular weights. Thisis accomplished using the following equation:log10M25$1/112!%3log10 K1/K2!1$111!/112!%3log10M1 (3)where:M2 = the molecular weight of the polyolefin,2, K2and 1, K1 = Mark-Houwink constants f
46、or the polyolefin and polystyrene, respectively, andM1 = molecular weight of the polystyrene. The above equation is derived from the empirical Mark-Houwinkequation:#5K 3M (4)where: = intrinsic viscosity and the universal calibration concept4 which states that the product of intrinsic viscosity and m
47、olecularweight for any polymer is proportional to its hydrodynamic volume, which in turn defines the elution volume of thepolymer. Values for Ks and s may be determined with an on-line viscometer or obtained from the literature. Thefollowing values are recommended for polystyrene (PS), polyethylene
48、(PE), and polypropylene (PP) in TCB at 140C:KPS 51931023 mL/g PS 50.655 (5)KPE 53931023 mL/g PE 50.725KPP 51931023 mL/g PP 50.72514.4.1 Generate the polyolefin GPC calibration curve by plotting the logarithm of the peak molecular weight values versus themeasured peak elution volumes (or times). The
49、calibration curve generally assumes an s-shape that asymptotically approaches totalpermeation at low MW and total exclusion at high MW. It is recommended that a third or fifth order polynomial be used to fit thecalibration data. A number of software packages are available to do this.15. Procedure15.1 Preparation for AnalysisPrepare polymer sample solutions as described in Section 12. An internal standard may be isadded to each sample solution before injection. Alternatively, a “stock” solution containing an internal st
