1、Designation: F2625 10Standard Test Method forMeasurement of Enthalpy of Fusion, Percent Crystallinity,and Melting Point of Ultra-High-Molecular WeightPolyethylene by Means of Differential Scanning Calorimetry1This standard is issued under the fixed designation F2625; the number immediately following
2、 the 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. Scope1.1 This test method disc
3、usses the measurement of the heatof fusion and the melting point of ultra-high-molecular weightpolyethylene (UHMWPE), and the subsequent calculation ofthe percentage of crystallinity.1.2 This test method can be used for UHMWPE in powderform, consolidated form, finished product, or a used product. It
4、can also be used for irradiated or chemically-crosslinkedUHMWPE.1.3 This test method does not suggest a desired range ofcrystallinity or melting points for specific applications.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandar
5、d.1.5 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 standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced
6、 Documents2.1 ASTM Standards:2D3418 Test Method for Transition Temperatures and En-thalpies of Fusion and Crystallization of Polymers byDifferential Scanning CalorimetryE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE793 Test Method for Enthalpies of
7、Fusion and Crystalli-zation by Differential Scanning CalorimetryE967 Test Method for Temperature Calibration of Differen-tial Scanning Calorimeters and Differential Thermal Ana-lyzersE968 Practice for Heat Flow Calibration of DifferentialScanning CalorimetersE1953 Practice for Description of Thermal
8、 Analysis andRheology Apparatus3. Terminology3.1 Symbols:3.1.1 DHf, ntheoretical heat of fusion of 100 % crystallinematerial (J/g).3.1.2 DHs, nmass normalized heat of fusion of the testsample (J/g).3.1.3 Tp, nmelting temperature at the peak of the meltingendotherm (C).3.1.4 To, nonset temperature of
9、 the melting endotherm(C).3.1.5 %X, npercentage of crystallinity of material.4. Summary of Test Method4.1 This test method consists of placing a known mass ofUHMWPE in a sample pan and heating the sample pan at acontrolled temperature while measuring the heat flow to thesample pan and an empty refer
10、ence pan. The area under themelting endotherm, indicative of the enthalpy of melting, isnormalized with the sample mass. This value is then normal-ized with the theoretical enthalpy of melting of 100 % crystal-line polyethylene to determine the percentage of crystallinity inthe test sample.5. Signif
11、icance and Use5.1 The crystallinity of UHMWPE will influence its me-chanical properties, such as creep and stiffness. The reportedcrystallinity will depend on the integration range used to1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices a
12、nd is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved Dec. 1, 2010. Published December 2010. Originallyapproved in 2007. Last previous edition approved in 2007 as F2625 07. DOI:10.1520/F2625-10.2For referenced ASTM standards, visit the ASTM website,
13、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.de
14、termine the heat of fusion, and the theoretical heat of fusionof 100 % crystalline polyethylene used to calculate the percentcrystallinity in an unknown specimen. Differential scanningcalorimetry is an effective means of accurately measuring bothheat of fusion and melting temperature.5.2 This test m
15、ethod is useful for both process control andresearch.6. Interferences6.1 As machining processes can affect the crystalline struc-ture of UHMWPE, care should be taken to obtain a represen-tative sample away from the surface of a component if bulkmeasurements are desired.6.2 The integration range used
16、 to measure the area of themelting endotherm will affect the measured value, as canheating rate. Therefore, the same ranges and test conditionsmust be used to ensure comparative results between laborato-ries.6.3 The sample must not be too tall, as temperature gradi-ents can then be generated in the
17、sample, leading to erroneousresults. It is suggested that the sample height should be lessthan 2 mm.7. Apparatus7.1 Differential scanning calorimeter (DSC), as described inTest Method D3418 and Practice E1953.7.2 Aluminum DSC sample pans, crimpable. Pans withventing holes are optional. The same type
18、 of pan must be usedfor the sample and reference pan.7.3 Analytical balance, accurate to 60.01 mg.NOTE 1According to Test Method E793, the repeatability standarddeviation for the enthalpy of fusion of a polyolefin is 1.2 % when using abalance resolution of 0.01 mg.8. Sampling, Test Specimens, and Te
19、st Units8.1 The UHMWPE test specimen can be in the form ofpowder, flake, film, or pellet.8.2 If a specimen is to be cut from a larger piece ofpolyethylene, it is recommended that a clean, sharp razor bladeor other equivalent tool is used to cut a slice. The specimenmust not be cut with a tool that g
20、enerates enough heat to meltthe UHMWPE. A core borer or punch can also be used to cuta sample from a film of UHMWPE.8.3 The specimen should be fairly flat to ensure goodthermal contact with the sample pan.8.4 It is recommended that a minimum of three specimensper test location are tested.NOTE 2“Test
21、 location” is defined as the location on the sample wherethe DSC analysis is performed.9. Preparation of Apparatus9.1 The DSC test chamber should be purged with drynitrogen, argon, or helium at a controlled flow rate during alltests. The same rate and gas should be used for all calibrationsand tests
22、. A purge rate of 10 to 50 ml/min is recommended.10. Calibration and Standardization10.1 Calibrate the temperature and heat flow signals of theDSC according to Test Method E967 and Practice E968,respectively. Typically, pure indium is used as a referencematerial. Both onset of the melting endotherm
23、of the referencestandard and the heat of fusion shall be reported and comparedwith published values (To= 156.6C, DHf= 28.57 J/g).3TheDSC calibration should be verified on at least a monthly basis.NOTE 3The value of the DHfwill vary with the lot of the indium byas much as 3 %. Users should refer to t
24、he certificate of analysis for theDHfof their specific lot of indium.11. Procedure11.1 Weigh an UHMWPE specimen on an analytical bal-ance to a resolution of 0.01 mg. The specimen weight shouldbe between 5 and 10 mg. The replicate specimens should all bewithin 62 mg of each other.11.2 Place the speci
25、men into an aluminum DSC sample pan,cover with an aluminum lid, and crimp to seal the sample. Ifthe DSC software allows compensation for the pan weight,record the weight.11.3 Inspect the bottom of the sample pan to ensure that itis flat. If it is not flat, prepare another sample.11.4 Place the sampl
26、e pan into the DSC chamber, along withan empty reference pan.11.5 Equilibrate the sample at ambient temperature for atleast 3 min.11.6 Heat the sample from ambient to 200C at 10C/min.An additional cooling cycle and heating run can be performedif desired.12. Calculation or Interpretation of Results12
27、.1 Construct a straight baseline by connecting points from50 to 160C on the heating cycle. If the melting endotherm isnot complete by 160C, the user can change the position of thebaseline construction on the high end, but must report thechange. The area will depend on the integration range selected.
28、An example is shown in Fig. 1.12.2 Integrate the area under the fusion endotherm from theheating cycle to yield the enthalpy of the transition in units ofJoules (J).12.3 Calculate the mass normalized sample heat of fusionmelting transition (DHs) by dividing the calculated enthalpy in12.2 by the mass
29、 of the sample in units of grams (g).12.4 Calculate the percentage of crystallinity (%X)bydividing the mass normalized sample heat of fusion in 12.3 bythe heat of fusion of 100 % crystalline polymer:%X 5DHs/DHf3 100 (1)where:DHf= 289.3 J/g.412.5 Calculate the peak melting temperature (Tp) and onsett
30、emperature (To) as indicated in Fig. 1. The onset temperatureis determined from the line drawn from the peak temperaturetangent to the melting endotherm and its intersection with theconstructed baseline.3Linde, D. R., ed., CRC Handbook of Chemistry and Physics, 76th ed, CRCPress, Boca Raton, 1995.4W
31、underlich, B. and Cormier, C. M., “Heat of fusion of polyethylene,” J.Polym. Sci., Vol A-2, No. 5, 1967, pp. 987988.F2625 10213. Report13.1 Report the following information:13.1.1 Description of the raw material and material prepa-ration. This information should include any annealing cycles ormechan
32、ical deformation used on the material.13.1.2 Description of the calibration material.13.1.3 Description of the sample pans.13.1.4 Description of instrument and software package perPractice E1953.13.1.5 Peak melting temperature, onset temperature, heat offusion (J/g), and the percentage of crystallin
33、ity. If multiplepeaks were observed within the integration limits, the peak andonset temperatures of these peaks should be reported.13.1.6 Date of ASTM standard used.14. Precision and Bias14.1 PrecisionA round robin study was conducted on twosets of samples of UHMWPE to determine a precision and bia
34、sstatement. The samples were GUR 1020 and GUR 1050(Ticona), compression molded by Orthoplastics. Seven labora-tories worldwide participated in the round robin. Due toequipment difficulties, the data from one of the laboratorieswas excluded from the analysis. Metrics of repeatability andreproducibili
35、ty between different institutions were calculatedas outlined in Practice E691. The data is summarized in Table1, showing melting onset temperature (Tonset), peak meltingtemperature (Tpeak), and percent crystallinity, as well as repeat-ability standard deviation (Sr) and reproducibility standarddevia
36、tion (SR).14.2 BiasNo statement may be made about the bias of thistest method, as there is no standard reference material orreference test method that is applicable.15. Keywords15.1 crystallinity; differential scanning calorimetry; heat offusion; melting temperature; thermal analysis; UHMWPENOTEThe
37、peak integration range was 50 to 160C. The sample showed an onset temperature of 126.9C, a peak temperature of 134.9C, and a DHf=163.2 J/g.FIG. 1 Representative DSC Thermal Curve Showing Melting EndothermTABLE 1 International Interlaboratory Study Test ResultsTonsetC Uncertainty, TonsetTpeakC Uncert
38、ainty, Tpeak% crystallinity Uncertainty, %crystallinitySample mean sr(%) sR(%) mean sr(%) sR(%) mean sr(%) sR(%)GUR 1050 127.57 0.49 0.42 136.68 0.27 0.87 58.24 2.61 8.57GUR 1020 127.13 0.61 0.71 136.63 0.13 0.72 60.24 3.32 10.25F2625 103APPENDIX(Nonmandatory Information)X1. RATIONALEX1.1 Theoretica
39、l Enthalpy of FusionX1.1.1 Although new estimates of theoretical heats offusion of 100 % crystalline polyethylene have been reported,5DHf= 289.3 J/g has been historically used for UHMWPE. Forconsistency with values reported previously, this value willcontinue to be used. Users may recalculate percen
40、t crystallinitydetermined with this standard with newer estimates of DHf.When doing so, users shall indicate what value of DHfwasused.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standa
41、rd are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif
42、 not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, whi
43、ch you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee 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,U
44、nited 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). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).5See, for example, Wunderlich, B., Thermal Analysis, Academic Press, 1990,p.418, where D Hf= 293 J/g for polyethylene.F2625 104
