1、Designation: D7191 10Standard Test Method forDetermination of Moisture in Plastics by Relative HumiditySensor1This standard is issued under the fixed designation D7191; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st 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 quantitative determinationof water down to 20 ppm in plastics using a relative humiditysenso
3、r.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 is t
4、heresponsibility 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 known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reage
5、nt WaterD883 Terminology Relating to PlasticsD1600 Terminology for Abbreviated Terms Relating toPlasticsD6869 Test Method for Coulometric and Volumetric Deter-mination of Moisture in Plastics Using the Karl FischerReaction (the Reaction of Iodine with Water)E177 Practice for Use of the Terms Precisi
6、on and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 DefinitionsThe definitions used in this test method arein accordance with Terminology D883.4. Summary of Test Method4.1 A sample is loaded into a septum-ca
7、pped 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 vial as it enters the heater. A dry carrier gasthen flows into the vial and carries the evolved volatiles in theheadspace into the senso
8、r manifold. In the sensor manifold, thecarrier gas is cooled to allow high-boiling volatiles to condenseon a hydrophobic filter. The filters hydrophobic propertiesallow the moisture in the carrier gas to pass through and thenbe measured as an increase in potential at the relative humiditysensor. Thi
9、s 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 moisturecontent.4.2 This test method utilizes a sealed, airtight flow systemthat prevents contamination of the analyzer from water prese
10、ntin 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 the processability of plas-tics. It is possible that high moisture content will cause surfaceimperfections (that is, splay or bubbling) o
11、r degradation byhydrolysis. Low moisture (with high temperature) has beenknown to cause solid phase polymerization.5.3 The physical properties of some plastics are greatlyaffected by the moisture content.6. Interferences6.1 Elevated concentrations of some common solvents suchas methanol, ethanol and
12、 acetone will give biased high read-ings due to their polar characteristics and ability to permeatethe thermoset polymer layers of the relative humidity sensor.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.70 on Anal
13、ytical Methods.Current edition approved April 1, 2010. Published June 2010. Originallyapproved in 2005. Last previous edition approved in 2005 as D7191 - 05.DOI:10.1520/D7191-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
14、For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.7. Apparatus7.1 Moisture Analyzer3, an apparatus that consists of:7.
15、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.7.1.3 Manifold, which provides:7.1.3.1 A thermally stable port
16、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 high boiling volatiles.7.1.3.4 A port for mounting the coaxial needle, or twoneedle set.7.1.4 Coaxial Needle, a
17、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 through one needle and outflowfrom the sample vial through the second needle.7.1.5 Relative Humidity (RH) Sensor,
18、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 1C of the programmed tem-perature between 25C and 275C.7.1.7 Microcontroller, which provides:7.1.7.1 Capabilit
19、y 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 readability.8. Reagents and Materials8.1 Capillary TubesNIST-traceable at the desired totalmass of water, typically 1000
20、 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 indicated, references to watershall be understood to mean reagent water as defined by TypeII of Specification D1193
21、.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 specimen size, exercise care to ensurethat the specimen is representative of the sample.9.2 Due to the hygroscopic nat
22、ure 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 processing and testing shall be allowed to cool to roomtemperature in a sealed container prior to determination.9.4 Te
23、st 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 calibrated using a NIST-traceable temperaturecalibration interface, and the RH sensor shall be verified andcalibrated
24、 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 vial heater calibration in accordance withthe manufacturers instructions.10.3 If the results are not within the acc
25、eptable 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) filled with water (see 8.4) or other methodas specified by the instrument manufacturer.10.5 If the RH sensor veri
26、fication 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 (see 8.4) or other method asspecified by the instrument manufacturer.10.6 Repeat step 10.4 to verify RH sensor cal
27、ibration.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 flow in accordance with themanufacturers specifications.11.1.3 Program the analyzer with the appropriate test con-
28、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 described in Appendix X2 or bycontacting the analyzer manufacturer.11.1.4 Place a clean vial on the balance and
29、 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 back on the balance andreweigh.11.1.7 Record the sample weight.11.1.8 Cap the vial ensuring the PTFE-coated side of
30、 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 analyzer.11.1.11 Begin the program and follow the prompts forstarting the analysis.11.1.12 At the end of the test, th
31、e bottle will be very hot souse caution when handling.11.1.13 Record the result as displayed.3The sole source of supply of the apparatus known to the committee at this timeis Arizona Instrument, 1912 West 4thStreet, Tempe, AZ 85281. If you are aware ofalternative suppliers, please provide this infor
32、mation to ASTM InternationalHeadquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,1which you may attend.D7191 10211.1.14 Repeat steps 11.1.4-11.1.14 for subsequent tests.12. Calculation or Interpretation of Results12.1 If results are displa
33、yed 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.12.2 If results are displayed as percent of water present andconversion to parts per mill
34、ion (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 material, source, and manufacturers code,
35、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 The precision of this test method is based on aninterlaboratory study of D7191 - 05 conducted in 2009. Twelvelaboratories tested a total of four different ma
36、terials. Every testresult represents an individual determination. Each laboratoryreported triplicate test results. Practice E691 was followed forthe design and analysis of the data.14.1.1 Repeatability limit (r)Two test results obtainedwithin one laboratory shall be judged not equivalent if theydiff
37、er by more than 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.14.1.1.1 Repeatability limits are listed in Table 1.14.1.2
38、Reproducibility limit (R)Two test results shall bejudged not equivalent if they differ by more than the R valuefor that material; R is the interval representing the criticaldifference between two test results for the same material,obtained by different operators using different equipment indifferent
39、 laboratories.14.1.2.1 Reproducibility limits are listed in Table 1.14.1.3 The above terms (repeatability limit and reproduc-ibility limit) are used as specified in Practice E177.14.1.4 Any judgment in accordance with statements 14.1.1and 14.1.2 would have an approximate 95 % probability ofbeing cor
40、rect.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 were determined throughextensive tests that have been completed on these comm
41、on 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 specific material.TABLE 1 Moisture in Plastics by Relative Humidity Sensor (%)Mat
42、erial Average RepeatabilityStandardDeviationReproducibilityStandardDeviationRepeatabilityLimitAs % of Avg. ReproducibilityLimitAs % of Avg.x SrSRrrRRPolycarbonate 0.09059 0.00487 0.02240 0.01364 15.05 0.06272 69.23Polypropylene 0.01025 0.00149 0.00587 0.00418 40.80 0.01642 160.2Nylon 6 0.42595 0.017
43、02 0.05677 0.04764 11.19 0.15894 37.32ABS 0.26304 0.00617 0.02333 0.01729 6.57 0.06533 24.84D7191 103X2. DETERMINING OPTIMAL TEST CONDITIONSX2.1 When determining the optimal test conditions for amaterial, it is useful to have a Karl Fischer apparatus availableand test in accordance with Test Method
44、D6869. 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 needed to produce a result where the total mass of wa
45、terpresent 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 temperature 20C be-low the melting or decomposition tem
46、perature 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 CriteriaStart at a rate of 0.50 g/s. In-crease or decrease the
47、 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 volatiles present in the sample. It will also benecessary
48、 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 any item mentionedin this standard. Users of this stan
49、dard 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 technical 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 at
