1、Designation: D3895 14Standard Test Method forOxidative-Induction Time of Polyolefins by DifferentialScanning Calorimetry1This standard is issued under the fixed designation D3895; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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. Scope*1.1 This test method outlines a procedure for the determi-nation of oxidative-induction time (OIT) of polymeric
3、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 wi
4、th 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 standard and ISO 113576 2013 address the same s
5、ubjectmatter, but differ in technical content.2. Referenced Documents2.1 ASTM Standards:2D4703 Practice for Compression Molding ThermoplasticMaterials into Test Specimens, Plaques, or SheetsE473 Terminology Relating to Thermal Analysis and Rhe-ologyE691 Practice for Conducting an Interlaboratory Stu
6、dy toDetermine the Precision of a Test MethodE967 Test Method for Temperature Calibration of Differen-tial Scanning Calorimeters and Differential Thermal Ana-lyzers3. Terminology3.1 DefinitionsDefinitions of terms applying to thermalanalysis appear in Terminology E473.3.2 Definitions of Terms Specif
7、ic 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 aspecified temperature in an oxygen atmosphere.3.2.2 A
8、bbreviations: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 at a constant rate in an inert gaseous environmen
9、t(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 OIT is determined from the data recorded during theiso
10、thermal period. The time interval from when the oxygenflow is first initiated to the oxidative reaction is referred to asthe induction period.4.1.1 The end of the induction period is signaled by anabrupt increase in the specimens evolved heat or temperatureand will be recorded as an exothermic event
11、 by a differentialscanning calorimeter (DSC).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 geomembraneand vapor-barrie
12、r 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, it ispossible to adjust the temperature (typically between 180 and220C) to
13、yield a thermal curve that can be interpreted andanalyzed easily.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.30 on Thermal Properties.Current edition approved Dec. 1, 2014. Published January 2015. Originallyapprove
14、d in 1980. Last previous edition approved in 2007 as D3895 07. DOI:10.1520/D3895-14.2For referenced ASTM standards, 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 p
15、age onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 The OIT is a qualitative assessment of the level (ordegree) of stabiliz
16、ation of the material tested. This test has thepotential to be used as a quality control measure to monitor thestabilization level in formulated resin as received from asupplier, prior to extrusion.NOTE 2The OIT measurement is an accelerated thermal-aging testand as such can be misleading. Caution s
17、hould be exercised 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 resu
18、lts eventhough 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 fo
19、rdetermining life expectancy is uncertain and subjective.6. Apparatus6.1 Differential Scanning CalorimeterAs a minimumrequirement, the thermal analysis equipment shall be capableof measuring heat flow of at least 10-mW full scale. Theinstrument recorder shall be capable of displaying heat flow ortem
20、perature differential 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 re
21、sins, stabilizers, 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
22、 a flow rate 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 Electronic Mass Flow Controller, Rotometer (Cali-brate
23、d) or Soap-Film Flowmeter, for gas-flow calibration.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
24、are commercially available. Alternatively,the 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 t
25、he OIT test result significantly (that is, including any associatedcatalytic effects).6.9 Compression-Molding Device with Heated Platens.6.10 Spacer Plates, Shim Stock, Caul Plates, etc.6.11 Polyethylene Terephthalate Film (PET) or Polytetra-fluoroethylene (PTFE) Coated Cloth, for sample-plaque prep
26、a-ration.6.12 Thickness Gauge.6.13 Laboratory Gas Burner, for 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-
27、high-purity grade (extra dry).7.3 NitrogenUltra-high-purity grade (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 orco
28、ntaining oxygen.8.2 The use of pressurized gas requires safe 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 wei
29、ght. Specimen disks(6.4-mm diameter) cut from the sheet will 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
30、precision adversely.9.1.1 Obtain the required mass of the sample and place thematerial in the center of the appropriately sized spacer betweentwo sheets of Polyethylene Terephthalate or PTFE coated clothand two caul plates.9.1.2 Place the assembly into the compression-moldingdevice. The preheat and
31、pressing temperature is 160C forpolyethylene and 190C for polypropylene.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 ambienttem
32、perature. Alternatively, quench the plaque in ice water.9.1.5 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 appro
33、priate pan type.Use an identical empty pan as the reference. (Do not crimp orseal the pans.)NOTE 9If controlled cooling is not necessary, the option to prepare theD3895 142test sample using Practice D4703, Annex 1 (Procedure C), is acceptable.10. Procedure10.1 Instrumental CalibrationThis procedure
34、uses 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. Calibrate the ins
35、trument at leastonce per month or before use if longer than one 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 referenc
36、e pansinto their respective 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
37、 240C at1C/minNOTE 10The 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 E967) for indium and tin, respectively. Themelting point of the calibrant is defined as the
38、 intercept of theextended 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 cal
39、ibration step. (After one 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 an
40、y residual oxygen.Commence 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 temp
41、erature. Turn on the recorder. 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 equilib
42、rium time has expired, change 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 en
43、tire exotherm. (see Fig. 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 specificati
44、on havebeen met.10.2.6 Upon 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 is sufficient to avoid anypremature thermal oxidation of the sample.10.2.7
45、 Test frequency is established by the user. As aminimum requirement, samples are tested in duplicate with themean 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-tion
46、s.FIG. 1 Indium and Tin Melting Thermal CurvesD3895 14310.3 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. Expand the x-axis as muchas possible to facilitate analysis.10.3.1 Extend the recorded base
47、line 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 pref
48、erred 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 the
49、 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 t
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