1、Designation: D7191 10D7191 18Standard 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 ye
2、ar 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. Scope1.1 This test method covers the quantitative determination of water down to 20 ppm in plastics using a relative humi
3、dity sensor.1.2 Values stated in SI units are to be regarded as standard.1.3 Specimens tested in this test method can reach or exceed 250C, use caution when handling them after testing hascompleted.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its
4、use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.NOTE 1There is no known ISO equivalent to this standard.1.5 This international standard wa
5、s developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced
6、Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD883 Terminology Relating to PlasticsD1600 Terminology for Abbreviated Terms Relating to PlasticsD6869 Test Method for Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction (theReaction of Io
7、dine with Water)E177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method3. Terminology3.1 DefinitionsThe definitions used in this test method are in accordance with Terminology D883.4.
8、Summary of Test Method4.1 A sample is loaded into a septum-capped glass vial that is moved into a heater to evolve the volatiles from the sample intothe headspace.Acoaxial needle, or two needle set, pierces the septum of the vial as it enters the heater.Adry carrier gas then flowsinto the vial and c
9、arries the evolved volatiles in the headspace into the sensor manifold. In the sensor manifold, the carrier gas iscooled to allow high-boiling volatiles to condense on a hydrophobic filter. The filters hydrophobic properties allow the moisturein the carrier gas to pass through and then be measured a
10、s an increase in potential at the relative humidity sensor. This sensor signalis integrated over time to provide a measurement of the total mass of water in the sample. The total moisture is then divided bysample mass to yield moisture content.4.2 This test method utilizes a sealed, airtight flow sy
11、stem that prevents contamination of the analyzer from water present inthe atmosphere.1 This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved April 1, 2010Dec. 1, 2018. Publis
12、hed June 2010December 2018. Originally approved in 2005. Last previous edition approved in 20052010 asD7191 - 05.D7191 - 10. DOI:10.1520/D7191-10.DOI:10.1520/D7191-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual B
13、ook of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be tech
14、nically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO
15、Box C700, West Conshohocken, PA 19428-2959. United States15. 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 plastics. It is possible that high moisture content will cause surfaceimperf
16、ections (that is, splay or bubbling) or degradation by hydrolysis. Low moisture (with high temperature) has been known tocause solid phase polymerization.5.3 The physical properties of some plastics are greatly affected by the moisture content.6. Interferences6.1 Elevated concentrations of some comm
17、on solvents such as methanol, ethanol and acetone will give biased high readings dueto their polar characteristics and ability to permeate the thermoset polymer layers of the relative humidity sensor.7. Apparatus7.1 Moisture Analyzer3, an apparatus that consists of:7.1.1 Flow Regulator, capable of m
18、aintaining the carrier gas flow rate within the manufacturers specified conditions.7.1.2 Flow Meter, capable of measuring the carrier gas flow rate in accordance with the manufacturers specified conditions.7.1.3 Manifold, which provides:7.1.3.1 A thermally stable port for mounting and operation of t
19、he 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 particulates and re-condensed high boiling volatiles.7.1.3.4 A port for mounting the coaxial needle, or two needle set.7.1.4 Coaxial Needle, a needle which has a dual flow
20、 path allowing the carrier gas to flow into the sample vial and then backinto the manifold, or a two needle set configured to allow inflow into the sample vial through one needle and outflow from thesample vial through the second needle.7.1.5 Relative Humidity (RH) Sensor, a capacitive sensing eleme
21、nt that measures the relative humidity of the carrier gas cominginto the manifold.7.1.6 Sample Vial Heater, capable of maintaining the sample vial temperature within 1C of the programmed temperaturebetween 25C and 275C.7.1.7 Microcontroller, which provides:7.1.7.1 Capability of integrating and conve
22、rting the RH sensor signal.7.1.7.2 Capability of controlling the temperature of the sample vial heater and sensor manifold.7.2 Balance, external, with 1-mg readability.8. Reagents and Materials8.1 Capillary TubesNIST-traceable at the desired total mass of water, typically 1000 g, or other qualified
23、water standarddevices.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 water shall be understood to mean reagent water as defined by Type II ofSpecification D1193.8.5 Carrier GasAny dr
24、y gas with water content less than 3 ppm including but not limited to dry air, nitrogen, helium or argon.9. Sampling and Test Specs and Units9.1 Due to the small specimen size, exercise care to ensure that the specimen is representative of the sample.9.2 Due to the hygroscopic nature of many plastic
25、s, samples shall be stored in airtight containers made of glass or other qualifiedor suitable material.9.3 Samples that have been heated to remove moisture prior to processing and testing shall be allowed to cool to roomtemperature in a sealed container prior to determination.9.4 Test specimens in t
26、he form of liquid, powders, pellets, or ground material.3 The sole source of supply of the apparatus known to the committee at this time is Arizona Instrument, 1912 West 4th Street, Tempe, AZ 85281. If you are aware ofalternative suppliers, please provide this information to ASTM International Headq
27、uarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee,1 which you may attend.D7191 18210. Calibration and Standardization10.1 To maintain the integrity of the test results, the vial heater shall be calibrated using a NIST-traceable temperatureca
28、libration interface, and the RH sensor shall be verified and calibrated using NIST-traceable capillary tubes. Alternatively, otherOther suitable instrument calibration methods and standards canshall be used as specified by the instrument manufacturer.10.2 Perform the vial heater calibration in accor
29、dance with the 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 accordance with the manufacturers instructions by way of using a capillarytube (see 8.1) filled with water (see 8.4) o
30、r other method as specified by the instrument manufacturer.10.5 If the RH sensor verification result is not within the acceptable range, perform the RH sensor calibration in accordance withthe manufacturers instructions using a capillary tube (see 8.1) filled with water (see 8.4) or other method as
31、specified by theinstrument manufacturer.10.6 Repeat step 10.4 to verify RH sensor calibration.10.7 If results are not within the acceptable range, contact the analyzer manufacturer.11. Procedure11.1 Sample Analysis:11.1.1 Turn on the analyzer.11.1.2 Establish carrier gas flow in accordance with the
32、manufacturers specifications.11.1.3 Program the analyzer with the appropriate test conditions.NOTE 2Suggested test conditions are listed in Appendix X1. If test conditions for a specific material are not listed in Appendix X1, they will haveto be determined experimentally as described in Appendix X2
33、 or by contacting 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 amount of 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 and re
34、weigh.11.1.7 Record the sample weight.11.1.8 Cap the vial ensuring the PTFE-coated side of the septum is facing the inside of the vial.11.1.9 With the vial on its side, ensure the sample is evenly distributed in the vial.11.1.10 Place the vial in the testing position in the analyzer.11.1.11 Begin th
35、e program and follow the prompts for starting the analysis.11.1.12 At the end of the test, the bottle will be very hot so use 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 Results12.1 If resu
36、lts are displayed in total micrograms (g) of water present, then calculate percent moisture content of the sampleas follows:Moisture content,%5R 31024/W (1)where:R 5 total water result for sample, g, andW 5 sample weight, g.12.2 If results are displayed as percent of water present and conversion to
37、parts per million (PPM) is desired, calculate asfollows:PPM5Moisture content %!310,000 (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, including type of material, source, and manufactur
38、ers code,13.1.2 Date of test,13.1.3 Individual specimen size,13.1.4 Individual specimen moisture, and13.1.5 Average moisture.D7191 18314. Precision and Bias14.1 The precision of this test method is based on an interlaboratory study of D7191 - 05 conducted in 2009.Twelve laboratoriestested a total of
39、 four different materials. Every test result represents an individual determination. Each laboratory reported triplicatetest results. Practice E691 was followed for the design and analysis of the data.14.1.1 Repeatability limit (r)Two test results obtained within one laboratory shall be judged not e
40、quivalent if they differ bymore than the r value for that material; r is the interval representing the critical difference between two test results for the samematerial, obtained by the same operator using the same equipment on the same day in the same laboratory.14.1.1.1 Repeatability limits are li
41、sted in Table 1.14.1.2 Reproducibility limit (R)Two test results shall be judged not equivalent if they differ by more than the R value for thatmaterial; R is the interval representing the critical difference between two test results for the same material, obtained by differentoperators using differ
42、ent equipment in different laboratories.14.1.2.1 Reproducibility limits are listed in Table 1.14.1.3 The above terms (repeatability limit and reproducibility limit) are used as specified in Practice E177.14.1.4 Any judgment in accordance with statements 14.1.1 and 14.1.2 would have an approximate 95
43、 % probability of beingcorrect.15. Keywords15.1 moisture determination; plasticsAPPENDIXES(Nonmandatory Information)X1. MOISTURE ANALYZERX1.1 Suggested test conditions for selected plastics are given in Table X1.1.NOTE X1.1These suggested conditions were determined through extensive tests that have
44、been completed on these common plastics. It is not intendedto be inclusive of every grade of every plastic and it will potentially be necessary to contact the analyzer manufacturer for assistance with determiningthe best test conditions for your specific material.TABLE 1 Moisture in Plastics by Rela
45、tive Humidity Sensor (%)Material Average RepeatabilityStandardDeviationReproducibilityStandardDeviationRepeatabilityLimitAs % of Avg. ReproducibilityLimitAs % of Avg.x Sr SR r r R RPolycarbonate 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.
46、01642 160.2Nylon 6 0.42595 0.01702 0.05677 0.04764 11.19 0.15894 37.32ABS 0.26304 0.00617 0.02333 0.01729 6.57 0.06533 24.84D7191 184X2. DETERMINING OPTIMAL TEST CONDITIONSX2.1 When determining the optimal test conditions for a material, it is useful to have a Karl Fischer apparatus available and te
47、stin accordance with Test Method D6869. Optimization of test conditions may include adjustment of the sample size, testtemperature, ending criteria or vial purge. Use the following guidelines for optimizing test conditions:X2.1.1 Sample SizeIncrease or decrease the sample size as needed to produce a
48、 result where the total mass of water present is1000 g. See Table X2.1 for recommended sample sizes keeping in mind that the sample vial must remain less than half full toprevent the sample coming in contact with the coaxial needle during testing.X2.1.2 Test TemperatureStart at a temperature 20C bel
49、ow the melting or decomposition temperature of the material, or both.Increase or decrease the temperature in increments of 5C to achieve the desired results. If no significant change in the test resultoccurs, proceed to rate adjustment for further optimization.X2.1.3 Ending CriteriaStart at a rate of 0.50 g/s. Increase or decrease the rate in increments of 0.05 g/s to achieve the desiredresult.X2.1.4 Vial Purge TimeIncrease or decrease the vial purge time as needed to minimize interferences from atmospheric moisturepresent in the sample vi
