1、Designation: F 2625 07Standard 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 F 2625; the number immediately followi
2、ng 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method d
3、iscusses 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.
4、 Itcan 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 as thestandard. The values given in parentheses are for informatio
5、nonly.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. Refere
6、nced Documents2.1 ASTM Standards:2D 3418 Test Method for Transition Temperatures of Poly-mers By Differential Scanning CalorimetryE 793 Test Method for Enthalpies of Fusion and Crystalli-zation by Differential Scanning CalorimetryE 967 Test Method for Temperature Calibration of Differ-ential Scannin
7、g Calorimeters and Differential ThermalAnalyzersE 968 Practice for Heat Flow Calibration of DifferentialScanning CalorimetersE 1953 Practice for Description of Thermal Analysis andRheology Apparatus3. Terminology3.1 Symbols:3.1.1 DHf, ntheoretical heat of fusion of 100 % crystallinematerial (J/g).3.
8、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 the melting endotherm(C).3.1.5 %X, npercentage of crystallinity of material.4. Summary of Test Method4.1 This test method consists o
9、f 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 reference pan. The area under themelting endotherm, indicative of the enthalpy of melting, isnormalized with the sample mass. This value i
10、s then normal-ized with the theoretical enthalpy of melting of 100 % crystal-line polyethylene to determine the percentage of crystallinity inthe test sample.5. Significance and Use5.1 The crystallinity of UHMWPE will influence its me-chanical properties, such as creep and stiffness. The reportedcry
11、stallinity will depend on the integration range used todetermine the heat of fusion, and the theoretical heat of fusionof 100 % crystalline polyethylene used to calculate the percent1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is
12、the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved Feb. 1, 2007. Published February 2007.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume in
13、formation, 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.crystallinity in an unknown specimen. Differential scanningcalorimetry is an effective means of accurately mea
14、suring bothheat of fusion and melting temperature.5.2 This test method 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 compone
15、nt if bulkmeasurements are desired.6.2 The integration range used 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
16、too tall, as temperature gradi-ents can then be generated in the 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 D 3418 and Practice E 1953.7.2 Aluminum DSC sample
17、pans, crimpable. Pans withventing holes are optional. The same type of pan must be usedfor the sample and reference pan.7.3 Analytical balance, accurate to 60.01 mg.NOTE 1According to Test Method E 793, the repeatability standarddeviation for the enthalpy of fusion of a polyolefin is 1.2 % when usin
18、g abalance resolution of 0.01 mg.8. Sampling, Test Specimens, and Test 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
19、 used to cut a slice. The specimenmust not be cut with a tool that generates 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
20、a minimum of three specimensper test location are tested.NOTE 2“Test 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
21、. The same rate and gas should be used for all calibrationsand tests. 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 E 967 and Practice E 968,respectively. Typically, pure indiu
22、m is used as a referencematerial. Both onset of the melting endotherm 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 var
23、y with the lot of the indium byas much as 3 %. Users should refer to the 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
24、specimens should all bewithin 62 mg of each other.11.2 Place the specimen 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 iti
25、s flat. If it is not flat, prepare another sample.11.4 Place the sample 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
26、 be performedif desired.12. Calculation or Interpretation of Results12.1 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 rep
27、ort thechange. The area will depend on the integration range selected.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 t
28、ransition (DHs) by dividing the calculated enthalpy in12.2 by the mass 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=
29、289.3 J/g.412.5 Calculate the peak melting temperature (Tp) and onsettemperature (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 Han
30、dbook of Chemistry and Physics, 76th ed, CRCPress, Boca Raton, 1995.4Wunderlich, B. and Cormier, C. M., “Heat of fusion of polyethylene,” J. Polym.Sci., Vol A-2, No. 5, 1967, pp. 987988.F262507213. Report13.1 Report the following information:13.1.1 Description of the raw material and material prepa-
31、ration. This information should include any annealing cycles ormechanical 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 E 1953.13.1.5 Peak melting temperature, on
32、set temperature, heat offusion (J/g), and the percentage of crystallinity. 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 A round robin study will be conducted
33、 on samples ofUHMWPE to determine a precision and bias statement.15. Keywords15.1 crystallinity; differential scanning calorimetry; heat offusion; melting temperature; thermal analysis; UHMWPEAPPENDIX(Nonmandatory Information)X1. RATIONALEX1.1 Theoretical Enthalpy of FusionX1.1.1 Although new estima
34、tes 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 percent crystallinitydetermined with this standard w
35、ith newer estimates of DHf.When doing so, users shall indicate what value of DHfwasused.5See, for example, Wunderlich, B., Thermal Analysis, Academic Press, 1990,p.418, where DHf= 293 J/g for polyethylene.NOTEThe peak integration range was 50 to 160C. The sample showed an onset temperature of 126.9C
36、, a peak temperature of 134.9C, and a DHf=163.2 J/g.FIG. 1 Representative DSC Thermal Curve Showing Melting EndothermF2625073ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are ex
37、pressly 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 not revi
38、sed, 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, which you ma
39、y 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,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).F2625074
