1、Designation: D 3895 07Standard Test Method forOxidative-Induction Time of Polyolefins by DifferentialScanning Calorimetry1This standard is issued under the fixed designation D 3895; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he 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. Scope*1.1 This test method outlines a procedure for the determi-nation of oxidative-induction time (OIT) of polymer
3、ic materi-als by differential scanning calorimetry (DSC). It is applicableto polyolefin resins that are in a fully stabilized/compoundedform.1.2 The values stated in SI units are to be regarded as thestandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated
4、 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. Specific hazardsinformation is given in Section 8.NOTE 1This test method is similar to ISO 113576, but no
5、t equiva-lent. ISO procedure provides additional information not supplied by thistest method.2. Referenced Documents2.1 ASTM Standards:2D 4703 Practice for Compression Molding ThermoplasticMaterials into Test Specimens, Plaques, or SheetsE 473 Terminology Relating to Thermal Analysis and Rhe-ologyE
6、691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 967 Test Method for Temperature Calibration of Differ-ential Scanning Calorimeters and Differential ThermalAnalyzers3. Terminology3.1 DefinitionsDefinitions of terms applying to thermalanalysis appear in
7、 Terminology E 473.3.2 Description of Term Specific to This Standard:3.2.1 oxidative induction timea relative measure of amaterials resistance to oxidative decomposition; it is deter-mined by the thermoanalytical measurement of the timeinterval to onset of exothermic oxidation of a material at aspec
8、ified temperature in an oxygen atmosphere.3.2.2 Abbreviations:3.2.3 HDPEhigh-density polyethylene.3.2.4 LDPElow-density polyethylene.3.2.5 LLDPElinear low-density polyethylene.3.2.6 OIToxidative induction time.4. Summary of Test Method4.1 The sample to be tested and the reference material areheated
9、at a constant rate in an inert gaseous environment(nitrogen). When the specified temperature has been reached,the atmosphere is changed to oxygen maintained at the sameflow rate. The specimen is then held at constant temperatureuntil the oxidative reaction is displayed on the thermal curve.The time
10、interval from when the oxygen flow is first initiatedto the oxidative reaction is referred to as the induction period.4.1.1 The end of the induction period is signaled by anabrupt increase in the specimens evolved heat or temperatureand may be observed by a differential scanning calorimeter(DSC). Th
11、e OIT is determined from the data recorded duringthe isothermal test.4.2 The type of containment system used depends on theintended application use of the material being tested. Polyole-fins used in the wire and cable industry typically require copperor aluminum pans, whereas polyolefins used in geo
12、membraneand vapor-barrier film applications exclusively use aluminumpans.4.3 Unless otherwise specified, the analysis temperatureused in this test has been set arbitrarily at 200.0C. For samplesthat have relatively low or high stabilization levels, a different1This test method is under the jurisdict
13、ion of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.30 on Thermal Properties.Current edition approved April 1, 2007. Published April 2007. Originallyapproved in 1980. Last previous edition approved in 2006 as D 3895 06.2For referenced ASTM standards, visit the A
14、STM 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.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Bar
15、r Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.temperature may be selected (typically between 180 and220C) to yield a thermal curve that can be interpreted andanalyzed easily.5. Significance and Use5.1 The OIT is a qualitative assessment of the level (ordegree) of stabi
16、lization of the material tested. This test can beused as a quality control measure to monitor the stabilizationlevel in formulated resin as received from a supplier, prior toextrusion.NOTE 2The OIT measurement is an accelerated thermal-aging testand as such can be misleading. Caution should be exerc
17、ised in datainterpretation since oxidation reaction kinetics are a function of tempera-ture and the inherent properties of the additives contained in the sample.For example, OIT results are often used to select optimum resinformulations. Volatile antioxidants may generate poor OIT results eventhough
18、 they may perform adequately at the intended use temperature ofthe finished product.NOTE 3There is no accepted sampling procedure, nor have anydefinitive relationships been established for comparing OIT values on fieldsamples to those on unused products, hence the use of such values fordetermining l
19、ife expectancy is uncertain and subjective.6. Apparatus6.1 Differential Scanning CalorimeterAs a minimum re-quirement, the thermal analysis equipment shall be capable ofmeasuring heat flow of at least 10-mW full scale. Theinstrument recorder should be capable of displaying heat flowor temperature di
20、fferential on the Y-axis and time on the X-axis.The time base must be accurate to 61 % and be readable to 0.1min.NOTE 4The OIT test is a function of a particular compoundsstabilizer system and should not be used as a basis of comparison betweenformulations that might contain, different resins, stabi
21、lizers, or additivepackages, or all of these.6.2 Gas-Selector Switch and Regulators, for high-puritynitrogen and oxygen.The distance between the gas-switchingpoint and the instrument cell shall be such that the timerequired to transition to an oxygen environment is less than oneminute. At a flow rat
22、e of 50 mL/min, this equates to amaximum switching volume of less than 50 mL.6.3 Analytical Balance, 0.1-mg sensitivity.6.4 Bore-Hole Cutter, 6.4-mm diameter.6.5 Specimen-Encapsulating Press.6.6 Forceps, Scalpel, and Cutting Board.6.7 Rotometer (Calibrated) or Soap-Film Flowmeter, forgas-flow calibr
23、ation.6.8 Specimen HoldersDegreased aluminum or oxidized-copper pans (6.0 to 7.0-mm diameter, 1.5-mm height). Use theappropriate pan type for the material being tested.NOTE 5Aluminum lids are required for temperature calibration.NOTE 6Both types of pans are commercially available. Alternatively,the
24、copper pans can be fabricated manually. Details on copper panpreparation and oxidation as well as instructions for aluminum panconditioning (degreasing) are given in Annex A2-Annex A4.NOTE 7The material composition of the specimen holder can influ-ence the OIT test result significantly (that is, inc
25、luding any associatedcatalytic effects).6.9 Compression-Molding Device with Heated Platens.6.10 Spacer Plates, Shim Stock, Caul Plates, etc.6.11 Mylar3(Polyester Film) or Teflon3(Polytetrafluoroet-hylene) Coated Cloth, for sample-plaque preparation.6.12 Thickness Gage.6.13 Laboratory Gas Burner, for
26、 copper-pan oxidation.6.14 Boiling Flask, with condenser and heating mantle.6.15 Forced-Air Oven.7. Reagents and Materials7.1 All chemical reagents used in this procedure shall beanalytical grade unless otherwise specified.7.2 OxygenUltra-high-purity grade (extra dry).7.3 NitrogenUltra-high-purity g
27、rade (extra dry).7.4 Aluminum Pan Degreasing Solvent.7.5 Indium (99.999 % purity).7.6 Tin (99.999 % purity).8. Hazards8.1 Oxygen is a strong oxidizer that accelerates combustionvigorously. Keep oil and grease away from equipment using orcontaining oxygen.8.2 The use of pressurized gas requires safe
28、and properhandling.9. Sampling9.1 The following sample preparation procedures are rec-ommended: the test sample is compression molded into sheetformat (thickness of 250 6 15 m) prior to analysis to yieldconsistent sample morphology and weight. Specimen disks(6.4-mm diameter) cut from the sheet will
29、have a weight ofapproximately 5 to 10 mg, depending on sample density.NOTE 8If the sample requires homogenization prior to analysis, themelt compounding procedure given in Appendix X1 is recommended.Poor sample uniformity will affect test precision adversely.9.1.1 Meter out the required mass of the
30、sample and placethe material in the center of the appropriately sized spacerbetween two sheets of Mylar3or Teflon3coated cloth and twocaul plates.9.1.2 Place the assembly into the compression-moldingdevice. The preheat and pressing temperature should be 160Cfor polyethylene and 190C for polypropylen
31、e.9.1.3 Heat the sample with appropriate pressure and timesettings to obtain a plaque with uniform thickness.9.1.4 Remove the plaque assembly and place it between twothick steel plates (heat sink) and cool the plaque to ambienttemperature. Alternatively, the plaque can be quenched in icewater.9.1.5
32、Determine the average thickness of the sheet to ensurethat it is within the allowable tolerances.9.1.6 Use the bore-hole cutter to punch out a disk from theplaque and record the specimen weight.9.1.7 Place the specimen disk into the appropriate pan type.Use an identical empty pan as the reference. (
33、Do not crimp orseal the pans.)3Mylar and Teflon are registered trademarks of DuPont.D 3895 072NOTE 9The test sample may also be prepared using Practice D 4703,Annex 1 (Procedure C), with the exception that controlled cooling is notnecessary.10. Procedure10.1 Instrumental CalibrationThis procedure us
34、es a two-point calibration step. Indium and tin are used as the calibrantssince their respective melting points encompass the specifiedanalysis temperature range (180 to 220C). Calibrate theinstrument in accordance with the manufacturers instructionsusing the following procedure. The calibration ste
35、p should beperformed at least once per month.10.1.1 Place 5 6 0.5 mg of indium/tin into an aluminumsample pan. Place an aluminum cover over the pan, and sealusing the encapsulating press. Prepare an empty sealed pan tobe used as the reference. Place the specimen and reference pansinto their respecti
36、ve locations in the instrument cell.10.1.2 Turn on the nitrogen-gas flow at a rate of 50 mL/min(with an absolute pressure of 140 kPa).10.1.3 Use the following melting profiles:Indium: = ambient to 145C at 10C/min, 145 to 165C at1C/minTin: = ambient to 220C at 10C/min, 220 to 240C at1C/minNOTE 10The
37、specified heating rates are for calibration use only.10.1.4 Adjust the temperature-calibration software (or po-tentiometer) to set the melting point at 156.63 and 231.97C(see Practice E 967) for indium and tin, respectively. Themelting point of the calibrant is defined as the intercept of theextende
38、d baseline and the extended tangent to the first slope ofthe endotherm (that is, the onset). See Fig. 1.NOTE 11An inadequate melting thermal curve is occasionally ob-tained due to poor surface contact of the calibrant material to the pansurface. If this occurs, repeat the calibration step. (After on
39、e melting/crystallization cycle the calibrant material should coat the bottom of thepan evenly.)10.2 Instrument Operation:10.2.1 Load the specimen and reference pans into the cell.10.2.2 Allow 5 min for a nitrogen prepurge prior to begin-ning the heating cycle to eliminate any residual oxygen.Commen
40、ce programmed heating of the specimen (under nitro-gen flow of 50 6 5 mL/min) from ambient temperature to200C (set point) at a rate of 20C/min.10.2.3 When the set temperature has been reached, discon-tinue programmed heating and equilibrate the sample for 5 minat the set temperature. Turn on the rec
41、order. If the instrumentbeing used does not have an isothermal temperature-control-mode feature, follow the alternate procedure outlined in AnnexA1 or alternatively ensure accurate temperature control bymonitoring and adjusting continually, as required.10.2.4 Once the equilibrium time has expired, c
42、hange thegas to oxygen at a flow rate of 50 6 mL/min. (Record thisevent.) This changeover point to oxygen flow is considered thezero time of the experiment.10.2.5 Continue isothermal operation until the maximumexotherm has been reached to allow a complete examination ofthe entire exotherm. (see Fig.
43、 2 and Fig. 3). At the testersdiscretion, it is acceptable to terminate the test at a predeter-mined heat flow change provided that data are available tosupport the alternative. It is also acceptable to terminate the testif time requirements stated in the products specification havebeen met.10.2.6 U
44、pon completion of the test, switch the gas selectorback to nitrogen and cool the instrument to ambient tempera-ture. If additional testing is being conducted, cooling theinstrument cell below 60 to 70C should be sufficient to avoidany premature thermal oxidation of the sample.10.2.7 Test frequency i
45、s established by the user. As aminimum requirement, samples should be tested in duplicatewith the mean value reported.10.2.8 Clean the DSC cell of contamination by heating to500C for 5 min in air (or oxygen) prior to conductingmeasurements and between the testing of different formula-tions.FIG. 1 In
46、dium and Tin Melting Thermal CurvesD 3895 07310.3 Thermal Curve AnalysisThe data is plotted with theheat-flow signal normalized to sample mass (that is, W/g) onthe y-axis, versus time on the x-axis. The x-axis should beexpanded as much as possible to facilitate analysis.10.3.1 Extend the recorded ba
47、seline beyond the oxidativereactive exotherm. Extrapolate the steepest linear slope of thisexotherm to intercept the extended baseline (see Fig. 3).10.3.2 The OIT is measured to within 60.1 min from zerotime to the intercept point.10.3.3 The tangent method used to measure the oxidationtime is the pr
48、eferred method, but the selection of the appropri-ate tangent to the exotherm sloped line is, at times, difficult ifthe exothermic peak has a leading edge. It is possible thatexothermic peaks with leading edges occur if the oxidationreaction is slow.NOTE 12The oxidation thermogram is indicative of t
49、he additives usedin the polymer. Thus, oxidation may not occur as a smooth transition andmultiple steps or slopes may be produced. When this occurs, resamplingand retesting is recommended to ensure that the testing is representative ofthe oxidation process.NOTE 13If multiple slopes result from the oxidation process, OITneeds to be defined to accurately reflect the oxidation of the polymer. It isup to the user to determine which slope best represents the materialproperty for an application. It must be noted in the report if the tang
