1、Designation: D 7191 05Standard Test Method forDetermination of Moisture in Plastics by Relative HumiditySensor1This standard is issued under the fixed designation D 7191; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、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 quantitative determinationof water down to 20 ppm in plastics using a relative humidityse
3、nsor.1.2 Values stated in SI units are to be regarded as standard.1.3 Specimens tested in this test method can reach or exceed250C, use caution when handling them after testing hascompleted.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It i
4、s 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.NOTE 1There is no similar or equivalent ISO standard.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reag
5、ent WaterD 883 Terminology Relating to PlasticsD 1600 Terminology for Abbreviated Terms Relating toPlasticsD 6869 Test Method for Coulometric and Volumetric De-termination of Moisture in Plastics Using the Karl FischerReaction (the Reaction of Iodine with Water)3. Terminology3.1 DefinitionsThe defin
6、itions used in this test method arein accordance with Terminology D 883.4. Summary of Test Method4.1 A sample is loaded into a septum-capped glass vial thatis moved into a heater to evolve the volatiles from the sampleinto the headspace. A coaxial needle, or two needle set, piercesthe septum of the
7、vial as it enters the heater. A dry carrier gasthen flows into the vial and carries the evolved volatiles in theheadspace into the sensor manifold. In the sensor manifold, thecarrier gas is cooled to allow high-boiling volatiles to condenseon a hydrophobic filter. The filters hydrophobic propertiesa
8、llow the moisture in the carrier gas to pass through and thenbe measured as an increase in potential at the relative humiditysensor. This sensor signal is integrated over time to provide ameasurement of the total mass of water in the sample. The totalmoisture is then divided by sample mass to yield
9、moisturecontent.4.2 This test method utilizes a sealed, airtight flow systemthat prevents contamination of the analyzer from water presentin the atmosphere.5. Significance and Use5.1 This test method is intended for use as a control,acceptance, and assessment test.5.2 Moisture can seriously affect t
10、he processability of plas-tics. It is possible that high moisture content will cause surfaceimperfections (that is, splay or bubbling) or degradation byhydrolysis. Low moisture (with high temperature) has beenknown to cause solid phase polymerization.5.3 The physical properties of some plastics are
11、greatlyaffected by the moisture content.6. Interferences6.1 Elevated concentrations of some common solvents suchas methanol, ethanol and acetone will give biased high read-ings due to their polar characteristics and ability to permeatethe thermoset polymer layers of the relative humidity sensor.7. A
12、pparatus7.1 Moisture Analyzer3, an apparatus that consists of:7.1.1 Flow Regulator, capable of maintaining the carrier gasflow rate within the manufacturers specified conditions.7.1.2 Flow Meter, capable of measuring the carrier gas flowrate in accordance with the manufacturers specified condi-tions
13、.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved November 1, 2005. Published November 2005.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orconta
14、ct ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The sole source of supply of the apparatus known to the committee at this timeis Arizona Instrument, 1912 West 4thStreet, Tempe, AZ 85281
15、. If you are aware ofalternative suppliers, please provide this information to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700,
16、West Conshohocken, PA 19428-2959, United States.7.1.3 Manifold, which provides:7.1.3.1 A thermally stable port for mounting and operationof the relative humidity sensor.7.1.3.2 Inlet and outlet ports for the carrier gas.7.1.3.3 A cold trap filter loop which filters out particulatesand re-condensed h
17、igh boiling volatiles.7.1.3.4 A port for mounting the coaxial needle, or twoneedle set.7.1.4 Coaxial Needle, a needle which has a dual flow pathallowing the carrier gas to flow into the sample vial and thenback into the manifold, or a two needle set configured to allowinflow into the sample vial thr
18、ough one needle and outflowfrom the sample vial through the second needle.7.1.5 Relative Humidity (RH) Sensor, a capacitive sensingelement that measures the relative humidity of the carrier gascoming into the manifold.7.1.6 Sample Vial Heater, capable of maintaining thesample vial temperature within
19、 1C of the programmed tem-perature between 25C and 275C.7.1.7 Microcontroller, which provides:7.1.7.1 Capability of integrating and converting the RHsensor signal.7.1.7.2 Capability of controlling the temperature of thesample vial heater and sensor manifold.7.2 Balance, external, with 1-mg readabili
20、ty.8. Reagents and Materials8.1 Capillary TubesNIST-traceable at the desired totalmass of water, typically 1000 g, or other qualified waterstandard devices.8.2 Sample Vials70-mm tall and 25-mL capacity.8.3 Sample Vial Septapolytetrafluoroethylene (PTFE)-coated silicone.8.4 WaterUnless otherwise indi
21、cated, references to watershall be understood to mean reagent water as defined by TypeII of Specification D 1193.8.5 Carrier GasAny dry gas with water content less than3 ppm including but not limited to dry air, nitrogen, helium orargon.9. Sampling and Test Specs and Units9.1 Due to the small specim
22、en size, exercise care to ensurethat the specimen is representative of the sample.9.2 Due to the hygroscopic nature of many plastics, samplesshall be stored in airtight containers made of glass or otherqualified or suitable material.9.3 Samples that have been heated to remove moisture priorto proces
23、sing and testing shall be allowed to cool to roomtemperature in a sealed container prior to determination.9.4 Test specimens in the form of liquid, powders, pellets, orground material.10. Calibration and Standardization10.1 To maintain the integrity of the test results, the vialheater shall be calib
24、rated using a NIST-traceable temperaturecalibration interface, and the RH sensor shall be verified andcalibrated using NIST-traceable capillary tubes. Alternatively,other suitable instrument calibration methods and standardscan be used as specified by the instrument manufacturer.10.2 Perform the via
25、l heater calibration in accordance withthe manufacturers instructions.10.3 If the results are not within the acceptable range,contact the analyzer manufacturer.10.4 Perform the RH sensor verification daily in accordancewith the manufacturers instructions by way of using a capil-lary tube (see 8.1) f
26、illed with water (see 8.4) or other methodas specified by the instrument manufacturer.10.5 If the RH sensor verification result is not within theacceptable range, perform the RH sensor calibration in accor-dance with the manufacturers instructions using a capillarytube (see 8.1) filled with water (s
27、ee 8.4) or other method asspecified by the instrument manufacturer.10.6 Repeat step 10.4 to verify RH sensor calibration.10.7 If results are not within the acceptable range, contactthe analyzer manufacturer.11. Procedure11.1 Sample Analysis:11.1.1 Turn on the analyzer.11.1.2 Establish carrier gas fl
28、ow in accordance with themanufacturers specifications.11.1.3 Program the analyzer with the appropriate test con-ditions.NOTE 2Suggested test conditions are listed in Appendix X1. If testconditions for a specific material are not listed in Appendix X1, they willhave to be determined experimentally as
29、 described in Appendix X2 or bycontacting the analyzer manufacturer.11.1.4 Place a clean vial on the balance and tare it.11.1.5 Refer to Table X2.1 and place the appropriate amountof sample in the vial keeping in mind that the vial must remainless than half full.11.1.6 Place the vial with sample bac
30、k on the balance andreweigh.11.1.7 Record the sample weight.11.1.8 Cap the vial ensuring the PTFE-coated side of theseptum is facing the inside of the vial.11.1.9 With the vial on its side, ensure the sample is evenlydistributed in the vial.11.1.10 Place the vial in the testing position in the analy
31、zer.11.1.11 Begin the program and follow the prompts forstarting the analysis.11.1.12 At the end of the test, the bottle will be very hot souse caution when handling.11.1.13 Record the result as displayed.11.1.14 Repeat steps 11.1.4-11.1.14 for subsequent tests.12. Calculation or Interpretation of R
32、esults12.1 If results are displayed in total micrograms (g) ofwater present, then calculate percent moisture content of thesample as follows:Moisture content,%5 R 3 10 4/W (1)where:R = total water result for sample, g, andW = sample weight, g.D719105212.2 If results are displayed as percent of water
33、 present andconversion to parts per million (PPM) is desired, calculate asfollows:PPM 5 Moisture content %! 3 10,000 (2)12.3 No further calculation or interpretation is necessary.13. Report13.1 Report the following information:13.1.1 Complete identification of the sample tested, includ-ing type of m
34、aterial, source, and manufacturers code,13.1.2 Date of test,13.1.3 Individual specimen size,13.1.4 Individual specimen moisture, and13.1.5 Average moisture.14. Precision and Bias14.1 Precision and bias statements will be established fol-lowing completion of round robin analyses in accordance withAST
35、M requirements. See Table 1 for information on repeat-ability of this test method.15. Keywords15.1 moisture determination; plasticsAPPENDIXES(Nonmandatory Information)X1. MOISTURE ANALYZERX1.1 Suggested test conditions for selected plastics aregiven in Table X1.1.NOTE X1.1These suggested conditions
36、were determined throughextensive tests that have been completed on these common plastics. It isnot intended to be inclusive of every grade of every plastic and it willpotentially be necessary to contact the analyzer manufacturer for assis-tance with determining the best test conditions for your spec
37、ific material.TABLE 1 Repeatability and Correlation for Moisture Content by Relative Humidity Sensor vs. Karl Fischer Titration (Single LaboratoryResults)AMaterialBRelative HumiditySensor MeanStandardDeviationCoefficient ofVariationKarl FischerTitration MeanStandardDeviationCoefficient ofVariationPO
38、M 0.0269 0.0015 5.75 0.0237 0.0023 5.20ABS 0.0389 0.0008 2.14 0.0360 0.0017 4.56ABS + PC 0.0055 0.0008 15.05 0.0047 0.0008 17.24EVOH 0.0823 0.0062 7.54 0.0803 0.0108 13.48PA 6 0.0608 0.0086 14.07 0.0623 0.0063 10.21PA 6/6 0.0558 0.0043 7.75 0.0562 0.0052 9.23PBT 0.0061 0.0006 10.48 0.0059 0.0004 6.4
39、2PC 0.0103 0.0004 3.47 0.0106 0.0010 9.09PEI 0.0159 0.0009 5.79 0.0158 0.0008 5.24PET 0.0086 0.0004 4.06 0.0088 0.0008 9.06PS 0.0218 0.0006 2.86 0.0211 0.0015 7.17PVC 0.0173 0.0004 2.28 0.0173 0.0006 3.38TPE 0.0122 0.0003 2.61 0.0119 0.0008 6.97TPU 0.0640 0.0024 3.80 0.0640 0.0018 2.74AAll Results g
40、iven in percent (%). Results are based on five consecutive tests.BDefinitions for the following abbreviations can be found in Terminology D 1600.D7191053X2. DETERMINING OPTIMAL TEST CONDITIONSX2.1 When determining the optimal test conditions for amaterial, it is useful to have a Karl Fischer apparat
41、us availableand test in accordance with Test Method D 6869. Optimizationof test conditions may include adjustment of the sample size,test temperature, ending criteria or vial purge. Use the follow-ing guidelines for optimizing test conditions:X2.1.1 Sample SizeIncrease or decrease the sample sizeas
42、needed to produce a result where the total mass of waterpresent is 1000 g. See Table X2.1 for recommended samplesizes keeping in mind that the sample vial must remain lessthan half full to prevent the sample coming in contact with thecoaxial needle during testing.X2.1.2 Test TemperatureStart at a te
43、mperature 20C be-low the melting or decomposition temperature of the material,or both. Increase or decrease the temperature in increments of5C to achieve the desired results. If no significant change inthe test result occurs, proceed to rate adjustment for furtheroptimization.X2.1.3 Ending CriteriaS
44、tart at a rate of 0.50 g/s. In-crease or decrease the rate in increments of 0.05 g/s to achievethe desired result.X2.1.4 Vial Purge TimeIncrease or decrease the vialpurge time as needed to minimize interferences from atmo-spheric moisture present in the sample vial or the presence oflow boiling vola
45、tiles present in the sample. It will also benecessary to decrease the vial purge in some cases to zero whentesting materials with high moisture content or where themoisture evolves quickly.ASTM International takes no position respecting the validity of any patent rights asserted in connection with a
46、ny item mentionedin this standard. Users of this standard are expressly 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 technica
47、l committee and must be reviewed every five years andif not revised, 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
48、at a meeting of theresponsible technical committee, which you may 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
49、 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).TABLE X1.1 Suggested Test Conditions for Selected PlasticsMaterial Test Temp (C) Ending Criteria (g/s) Sample Size (g) Vial Purge (s)ABS 230 Rate = 0.75 1-2 45ABS + PC 200 Predict 5-7 45EVOH 215 Rate = 0.75 1-2 45POM 150 Predict 2-3 45PA 6 200
