1、Designation: D7426 08 (Reapproved 2013)Standard Test Method forAssignment of the DSC Procedure for Determining Tgof aPolymer or an Elastomeric Compound1This standard is issued under the fixed designation D7426; the number immediately following the designation indicates the year oforiginal adoption o
2、r, 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 covers the assignment of the glasstransition temperatures (Tg
3、) of materials using differentialscanning calorimetry.1.2 This test method is applicable to amorphous materials,including thermosets or semicrystaline materials containingamorphous regions, that are stable and do not undergo decom-position or sublimation in the glass transition region.1.3 The normal
4、 operating temperature range is from 120to 500C. The temperature range may be extended, dependingupon the instrumentation used.1.4 Computer or electronic-based instruments, techniques,or data treatment equivalent to this test method may also beused.NOTE 1Users of this test method are expressly advis
5、ed that all suchinstruments or techniques may not be equivalent. It is the responsibility ofthe user of this standard to determine the necessary equivalency prior touse.1.5 ISO 113572 is equivalent to this test method.1.6 The values stated in SI units are to be regarded asstandard. The values given
6、in parentheses are for informationonly.1.7 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 l
7、imitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE473 Terminology Relating to Thermal Analysis and Rhe-ologyE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE967
8、Test Method for Temperature Calibration of Differen-tial Scanning Calorimeters and Differential Thermal Ana-lyzersE1142 Terminology Relating to Thermophysical Properties2.2 ISO Standard:3ISO 113572 Differential Scanning Calorimetry (DSC)-Part2 Determination of Glass Transition Temperature3. Terminol
9、ogy3.1 Definitions:3.1.1 The following terms are applicable to this test methodand can be found in Terminology E473 and TerminologyE1142: differential scanning calorimetry (DSC), differentialthermal analysis (DTA), glass transition, glass transitiontemperature (Tg), and specific heat capacity.3.2 De
10、finitions of Terms Specific to This Standard:3.2.1 There are commonly used transition points associatedwith the glass transition region. (See Fig. 1.)3.2.2 extrapolated end temperature (Te), C, nthe point ofintersection of the tangent drawn at the point of greatest slopeon the transition curve with
11、the extrapolated baseline followingthe transition.3.2.3 extrapolated onset temperature (Tf), C, nthe pointof intersection of the tangent drawn at the point of greatestslope on the transition curve with the extrapolated baselineprior to the transition.3.2.4 inflection temperature (Ti), C, nthe point
12、on thethermal curve corresponding to the peak of the first derivative(with respect to time) of the parent thermal curve. This pointcorresponds to the inflection point of the parent thermal curve.3.2.5 midpoint temperature (Tm), C, nthe point on thethermal curve corresponding to12 the heat flow diffe
13、rencebetween the extrapolated onset and extrapolated end.3.2.5.1 DiscussionThe inflection point temperature (Ti)is1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.10 on Physical Testing.Current edition approved Nov. 1, 20
14、13. Published January 2014. Originallyapproved in 2008. Last previous edition approved in 2008 as D7426 08. DOI:10.1520/D7426-08R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume inform
15、ation, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Un
16、ited States1most easily determined from the first derivative curve and willbe used as the glass transition temperature (see Fig. 1).3.2.6 Two additional transition points are sometimes iden-tified and are defined as follows:3.2.7 temperature of first deviation (To), C, nthe point offirst detectable
17、deviation from the extrapolated baseline prior tothe transition.3.2.8 temperature of return to baseline (Tr), C, nthe pointof last deviation from the extrapolated baseline beyond thetransition.4. Summary of Test Method4.1 This test method involves continuously monitoring thedifference in heat flow,
18、or temperature between, a referencematerial and a test material when they are heated or cooled ata controlled rate through the glass transition region of the testmaterial and analyzing the resultant thermal curve to providethe glass transition temperature.5. Significance and Use5.1 Differential scan
19、ning calorimetry provides a rapid testmethod for determining changes in specific heat capacity in ahomogeneous material or domain. The glass transition ismanifested as a step change in specific heat capacity. Foramorphous and semi-crystalline materials the determination ofthe glass transition temper
20、ature may lead to important infor-mation about their thermal history, processing conditions,stability of phases, and progress of chemical reactions.5.2 This test method is useful for research, quality control,and specification acceptance.6. Interferences6.1 Achange in heating rates and cooling rates
21、 can affect theresults. The presence of impurities will affect the transition,particularly if an impurity tends to plasticize or form solidsolutions, or is miscible in the post-transition phase. If domainsize has an effect upon the detected transition temperature, thespecimens to be compared should
22、be of the same domain size.6.2 In some cases the specimen may react with air duringthe temperature program causing an incorrect transition to bemeasured. Whenever this effect may be present, the test shallbe run under either vacuum or an inert gas atmosphere. Sincesome materials degrade near the gla
23、ss transition region, caremust be taken to distinguish between degradation and glasstransition.6.3 Since milligram quantities of sample are used, it isessential to ensure that specimens are homogeneous andrepresentative, so that appropriate sampling techniques areused.7. Apparatus7.1 Differential Sc
24、anning CalorimeterThe essential in-strumentation required to provide the minimum differentialscanning calorimetric capability for this method includes a testchamber composed of a furnace(s) to provide uniform con-trolled heating (cooling) of a specimen and reference to aconstant temperature or at a
25、constant rate over the temperaturerange from 120 to 500C, a temperature sensor to provide anindication of the specimen temperature to 60.1C, differentialsensors to detect heat flow difference between the specimenand reference with a sensitivity of 650 W, a means ofsustaining a test chamber environme
26、nt of a purge gas of 10 to100 mL/min within 4 mL/min, and a temperature controllercapable of executing a specific temperature program by oper-ating the furnace(s) between selected temperature limits at arate of temperature change of up to 10C/min constant to60.5C/min.FIG. 1 Glass Transition Region M
27、easured TemperaturesD7426 08 (2013)27.2 Recording Device, capable of recording and displayingany fraction of the heat flow signal (including noise) on theY-axis and any fraction of the temperature signal (includingnoise) on the X-axis.7.3 Containers (pans, crucibles, vials, etc.), inert to thespecim
28、en and reference materials and of suitable structuralshape and integrity to contain the specimen and references.7.4 Inert Reference Material, with a heat capacity approxi-mately equivalent to that of the specimen may be used, for easeof interpretation. The inert reference material may often be anemp
29、ty specimen capsule or tube.7.5 Nitrogen, or other inert purge gas supply, of purity equalto or greater than 99.9 %.7.6 Analytical Balance, with a capacity greater than 100 mg,capable of weighing to the nearest 0.1 mg.8. Specimen Preparation8.1 Powders or GranulesAvoid grinding if a preliminarytherm
30、al cycle as outlined in 10.2 is not performed. Grinding,microtoming, or similar techniques for size reduction oftenintroduce thermal effects because of friction or orientation, orboth, and thereby change the thermal history of the specimen.8.2 Molded Parts or PelletsCut the samples with amicrotome,
31、razor blade, paper punch, or cork borer (size No. 2or 3) to appropriate size in thickness or diameter, and lengththat will approximate the desired mass in the subsequentprocedure.8.3 Films or SheetsFor films thicker than 40 m, see 8.2.For thinner films, cut slivers to fit in the specimen tubes orpun
32、ch disks, if circular specimen pans are used.8.4 Report any mechanical or thermal pretreatment.9. Calibration9.1 Using the same heating rate, purge gas, and flow rate asthat to be used for analyzing the specimen, calibrate thetemperature axis of the instrument following the proceduregiven in Test Me
33、thod E967.10. Procedure10.1 Use a specimen mass appropriate for the material to betested. In most cases a 10 to 40 mg mass is satisfactory. Anamount of reference material with a heat capacity closelymatched to that of the specimen may be used. An emptyspecimen pan may also be adequate.10.2 Perform t
34、wo cycles of heating and controlled or notcontrolled cooling between the two cycles. The first cycle oftenis useful to provide thermal history information, the secondcycle provides information on the material with previousthermal history erased.NOTE 2Two cycles are not needed for elastomers, since t
35、he Tgisbelow ambient temperature.NOTE 3Other, preferably inert, gases may be used, and other heatingand cooling rates may be used, but must be reported.10.3 Hold temperature until the instrument is at equilibrium.10.4 Program cool at a rate of 10C/min to 100C.10.5 Hold temperature until the instrume
36、nt is at equilibrium.10.6 Repeat heating at same rate as in 10.4, and record theheating curve until all desired transitions have been completed.Other heating rates may be used but must be reported.10.7 Determine temperature TiTii, (see Fig. 1),where:Ti= inflection temperature, C,Tf= extrapolated ons
37、et temperature, C, andTm= midpoint temperature, C.10.8 Increasing the heating rate produces greater baselineshifts thereby improving detectability. In the case of DSC thesignal is directly proportional to the heating rate in heatcapacity measurements.NOTE 4The glass transition takes place over a tem
38、perature range andis known to be affected by time dependent phenomena, such as the rate ofheating (cooling). For these reasons, the establishment of a single numberfor the glass transition needs some explanation. Either Tfor Tmor Timaybe selected to represent the temperature range over which the gla
39、sstransition takes place. The particular temperature chosen must be agreedon by all parties concerned. In selecting which value should be taken as,the reader may wish to consider the following:(1) Tmwas found to have higher precision than Tf(see 12.3).(2) The measurement of Tfis often easier for tho
40、se who construct therespective tangents by hand.(3) Tm(preferred) or Tiis more likely to agree with the measurementof Tgby other techniques since it is constructed closer to the middle of thetemperature range over which the glass transition occurs.(4) Tfmay be taken to more closely represent the ons
41、et of thetemperature range over which the glass transition occurs. Any comparisonof glass transition temperatures should contain a statement of how the testwas run and how the value was obtained.11. Report11.1 Report the following information:11.1.1 A complete identification and description of thema
42、terial tested.11.1.2 Description of instrument used for the test.11.1.3 The scan rate in C/min.11.1.4 Identification of the specimen environment bypressure, gas flow rate, purity, and composition, includingmoisture, if applicable.11.1.5 Results of the transition measurements using tem-perature param
43、eters (Ti) cited in Fig. 1.Ti(used as Tg)ispreferred.11.1.6 Any side reactions (for example, crosslinking, ther-mal degradation, oxidation) shall also be reported and thereaction identified, if possible.TABLE 1 Tg, Glass Transition Temperature (C): Distributor-Prepared SamplesMaterialAveragexStandar
44、dDeviationRepeatabilityLimit (r)ReproducibilityLimit (R)CR 66.123 1.975 2.484 5.975FKM 16.221 2.349 1.246 6.675HNBR 41.437 2.096 1.918 6.124ECO 63.252 2.115 1.893 6.168AVERAGE 1.885 6.236D7426 08 (2013)312. Precision and Bias412.1 The precision of this test method is based on aninterlaboratory study
45、 conducted in 2006. The testing wasperformed using the methods described in Practices E177 andE691. Twelve laboratories received 4 different polymers in 2different states of preparation: fully prepared and weighed bythe distributor (Table 1); and specimens that were to beprepped and weighed at the i
46、ndividual laboratories (Table 2).Each “test result” was an individual determination. Participat-ing laboratories tested 6 replicate samples for both the preparedand unprepared specimens of each material.12.1.1 RepeatabilityTwo test results obtained within onelaboratory shall be judged not equivalent
47、 if they differ by morethan the “r” value for that material; “r” is the intervalrepresenting the critical difference between two test results forthe same material, obtained by the same operator using thesame equipment on the same day in the same laboratory.12.1.1.1 The average repeatability limit ca
48、lculated from thematerials in this study is 1.9225.12.1.2 ReproducibilityTwo test results should be judgednot equivalent if they differ by more than the “R” value for thatmaterial; “R” is the interval representing the difference be-tween two test results for the same material, obtained bydifferent o
49、perators using different equipment in different labo-ratories.12.1.2.1 The average reproducibility limit calculated fromthe materials in this study is 5.948.12.1.3 Any judgment in accordance with these two state-ments would have an approximate 95 % probability of beingcorrect.12.2 BiasAt the time of the study, no accepted referencematerial suitable for determining the bias for this test methodwas utilized, therefore no statement on bias is being made.12.3 The precision statement was determined through sta-tistical examination of 5
