1、Designation: D 7426 08Standard Test Method forAssignment of the DSC Procedure for Determining Tgof aPolymer or an Elastomeric Compound1This standard is issued under the fixed designation D 7426; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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 covers the assignment of the glasstransition temperatures (Tg) of materials
3、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 operating temp
4、erature range is from 120 to500C. 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 advised that all suc
5、hinstruments 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 as thestandard. The values given in parenthe
6、ses 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 limitations
7、prior to use.2. Referenced Documents2.1 ASTM Standards:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 473 Terminology Relating to Thermal Analysis and Rhe-ologyE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 967 Test Me
8、thod for Temperature Calibration of Differ-ential Scanning Calorimeters and Differential ThermalAnalyzersE 1142 Terminology Relating to Thermophysical Properties2.2 ISO Standard:3ISO 113572 Differential Scanning Calorimetry (DSC)-Part2 Determination of Glass Transition Temperature3. Terminology3.1 D
9、efinitions:3.1.1 The following terms are applicable to this test methodand can be found in Terminology E 473 and TerminologyE 1142: differential scanning calorimetry (DSC), differentialthermal analysis (DTA), glass transition, glass transitiontemperature (Tg), and specific heat capacity.3.2 Definiti
10、ons 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 the ex
11、trapolated 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 on the
12、thermal 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 differenceb
13、etween the extrapolated onset and extrapolated end.3.2.5.1 DiscussionThe inflection point temperature (Ti)ismost 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
14、 defined as follows:1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.14 on Time and Temperature-Dependent Physical Properties.Current edition approved Jan. 1, 2008. Published February 2008.2For referenced ASTM standards,
15、visit the ASTM website, 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.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New Y
16、ork, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.7 temperature of first deviation (To), C, nthe point offirst detectable deviation from the extrapolated baseline prior tothe transition.3.2.8 tempe
17、rature of return to baseline (Tr), C, nthepoint of last deviation from the extrapolated baseline beyondthe transition.4. Summary of Test Method4.1 This test method involves continuously monitoring thedifference in heat flow, or temperature between, a referencematerial and a test material when they a
18、re 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 scanning calorimetry provides a rapid testmethod for determining changes in spe
19、cific 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 temperature may lead to important infor-mation about their thermal history, proce
20、ssing 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 can affect theresults. The presence of impurities will affect the transiti
21、on,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 be of the same domain size.6.2 In some cases the specimen may react with ai
22、r 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 glass transition region, caremust be taken to distinguish between degradation
23、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 Scanning CalorimeterThe essential in-strumentation required to provide the mi
24、nimum 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 constant rate over the temperaturerange from 120 to 500C, a temperature sen
25、sor 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 environment of a purge gas of 10 to100 mL/min within 4 mL/min, and a temperature con
26、trollercapable 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.7.2 Recording Device, capable of recording and displayingany fraction of the heat flow signal (including no
27、ise) on theY-axis and any fraction of the temperature signal (includingnoise) on the X-axis.FIG. 1 Glass Transition Region Measured TemperaturesD 7426 0827.3 Containers (pans, crucibles, vials, etc.), inert to thespecimen and reference materials and of suitable structuralshape and integrity to conta
28、in 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 anempty specimen capsule or tube.7.5 Nitrogen, or other inert purge gas supply, of pur
29、ity 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 preliminarythermal cycle as outlined in 10.2 is not performed. Grinding,microtoming, or similar t
30、echniques 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, razor blade, paper punch, or cork borer (size No. 2or 3) to appropriate size in t
31、hickness 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 orpunch disks, if circular specimen pans are used.8.4 Report any mechanical or thermal
32、 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 Method E 967.10. Procedure10.1 Use a specimen mass appropriate for the material to
33、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 two cycles of heating and controlled or notcontrolled cooling between the two cyc
34、les. 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 the Tgisbelow ambient temperature.NOTE 3Other, preferably inert, gases may be use
35、d, 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 instrument is at equilibrium.10.6 Repeat heating at same rate as in 10.4, and record the
36、heating 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 onset temperature, C, andTm= midpoint temperature, C.10.8 Increasing the heating ra
37、te 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 temperature range andis known to be affected by time dependent phenomena, such as t
38、he 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 glasstransition takes place. The particular temperature chosen must be agreedon by
39、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 those who construct therespective tangents by hand.(3) Tm(preferred) or Tiis more l
40、ikely 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 onset of thetemperature range over which the glass transition occurs. Any compariso
41、nof 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 thematerial tested.11.1.2 Description of instrument used for the test.11.1.3 The scan
42、 rate in C/min.11.1.4 Identification of the specimen environment by pres-sure, gas flow rate, purity, and composition, including mois-ture, if applicable.11.1.5 Results of the transition measurements using tem-perature parameters (Ti) cited in Fig. 1.Ti(used as Tg)ispreferred.11.1.6 Any side reactio
43、ns (for example, crosslinking, ther-mal degradation, oxidation) shall also be reported and thereaction identified, if possible.12. Precision and Bias412.1 The precision of this test method is based on aninterlaboratory study conducted in 2006. The testing wasperformed using the methods described in
44、Practices E 177 andE 691. 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 individual laboratories (Table 2).Each “test result” was an individual dete
45、rmination. 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 if they differ by morethan the “r” value for that material; “r” is the in
46、tervalrepresenting the critical difference between two test results for4Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR: D11-1097.D 7426 083the same material, obtained by the same operator using thesame equipment on the same day
47、in the same laboratory.12.1.1.1 The average repeatability limit calculated 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-tw
48、een two test results for the same material, obtained bydifferent operators 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 ap
49、proximate 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 552 results, from 12 laboratories, on 4materials.13. Keywords13.1 differential scanning calorimetry (DSC); differentialthermal analysis (DTA); glass transition; specific heat capacityASTM International takes no position respecting the validity o
