1、Designation: D6869 03 (Reapproved 2011)D6869 17Standard Test Method forCoulometric and Volumetric Determination of Moisture inPlastics Using the Karl Fischer Reaction (the Reaction ofIodine with Water)1This standard is issued under the fixed designation D6869; the number immediately following the de
2、signation indicates the year oforiginal adoption or, in the case of revision, the 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 Scope*1.1 This method uses the
3、reaction of Iodine (I2) with water (Karl Fischer Reaction) to determine the amount of moisture in apolymer sample.21.2 This test method is intended to be used for the determination of moisture in most plastics. Plastics containing volatilecomponents such as residual monomers and plasticizers are cap
4、able of releasing components that will interfere with the I2/waterreaction.1.3 This method is suitable for measuring moisture over the range of 0.005 to 100 %. Sample size shall be adjusted to obtainan accurate moisture measurement.1.4 The values stated in SI units are regarded as the standard.NOTE
5、1This standard is technically equivalent to ISO 15512 Method B.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental pract
6、ices and determine theapplicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Rec
7、ommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ISO Document:ISO 15512 PlasticsDetermination of Water Content33. Summary of Test Method23.1 Samples are heated to vaporize water that is transported by a nitrogen carrier gas to
8、the titration cell. The moisture collectedin the solution within the titration cell is determined using the reaction of water with I2.3.2 Endpoint detection is made by instrumented methods. Determination of the moisture present is made using the reaction ofI2 with water.3.3 Coulometric instruments u
9、se Faradays law to measure the moisture present with 10.71 Coulombs (C) of generating currentcorresponding to 1 mg of water (2I- I2 + 2e-). Volumetric instruments measure the volume of solution containing I2 that isrequired to keep the current constant.4. Significance and Use4.1 Moisture will affect
10、 the processability process ability of some plastics. High moisture content causes surface imperfections(that is, splay or bubbling) or degradation by hydrolysis. Low moisture (with high temperature) causes polymerization.1 This test method is under the jurisdiction of ASTM Committee D20 on Plastics
11、 and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Sept. 1, 2011Dec. 1, 2017. Published October 2011January 2018. Originally approved in 2003. Last previous edition approved in 20032011 asD6869 - 03.D6869 - 03 DOI:10.1520/D6869-03R11.(2011). DOI:1
12、0.1520/D6869-17.2 See Appendix X1, History of ReagentsAssociated With the Karl Fischer Reaction, for an explanation of coulometric and volumetric techniques as well as an explanationof the Karl Fischer Reaction and Karl Fischer Reagents.3 Available from American National Standards Institute (ANSI),
13、25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.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 technically possible to adequately depict al
14、l 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 1
15、00 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 The physical properties of some plastics are affected by the moisture content.5. Interferences5.1 Some compounds, such as aldehydes and ketones, interfere in the determination of moisture content using this method
16、.6. Apparatus6.1 Heating Unit, consisting of an oven capable of heating the sample to approximately 300C, a furnace tube, a temperaturecontrol unit, a carrier gas flow meter, and desiccating tubes for the carrier gas.6.2 Sample Pan (Boat), normally a glass sample boat or boat manufactured of a suita
17、ble material to transfer the oven heat tothe sample. It is permitted to use aluminum foil as a disposable liner for the sample pan.6.3 Titration Unit, consisting of a control unit, titration cell with a solution cathode, platinum electrode, and solution stirringcapability. This apparatus has the cap
18、ability to generate or deliver iodine to react stoiciometrically with the moisture present in thetitration cell. The current or volume required to generate the iodine converts to micrograms of water present. The percent moisturein the sample is then calculated based on the sample weight used and is
19、given as a direct digital readout.6.4 Analytical Balance, capable of weighing 0.1 mg (four decimal place balance).6.5 Glass Capillary (Micropipette), used to measure a known amount of water, typically 2 mg (2000 g).7. Reagents and Materials7.1 Anode (Generator) Solution, per manufacturers recommenda
20、tion.7.2 Cathode Solution, per manufacturers recommendation.NOTE 2Hydranal or similar anode and cathode solutions are recommended. These reagents do not contain pyridine, are less toxic, and have nooffensive odor.7.3 Silica Gel, granules, approximately 2 mm, desiccant for drying tube of titration as
21、sembly (if applicable).7.4 Special Grease, as supplied by manufacturer for ground glass joints.7.5 Molecular Sieve, or suitable desiccant (for drying the nitrogen carrier gas stream).7.6 Nitrogen Gas (N2),containing less than 5 g/g of water.7.7 Neutralization Solution, or check solution (per manufac
22、turers recommendation).8. Hazards8.1 Due to the low quantities of water measured, maximum care shall be exercised at all times to avoid contaminating thesample with water from the sample container, the atmosphere or transfer equipment. Hygroscopic resin samples shall be protectedfrom the atmosphere.
23、8.2 Due to the high temperatures and the chemicals involved in this test method, safe lab practices must be followed at all times.9. Sampling, Test Specimens, and Test Units9.1 Unless otherwise agreed upon by interested parties or described in a specification, the material shall be sampled statistic
24、allyor the sample shall come from a process that is in statistical control.9.2 Samples that will determine the moisture of a larger lot of material must be taken in such a manner that the moisture contentwill not change from the original material. Sample containers must be adequately dried and the e
25、nvironment in which samplingis performed must not add additional moisture to the sample. Most normal plant or lab operating conditions are adequate forsampling. The sample container shall be properly sealed to prevent moisture pick-up before testing.9.3 Samples in many forms, such as molded powder,
26、molded shapes, or re-grind are permitted. It is recommended that moldedspecimens be cut into smaller parts prior to testing (recommended maximum size 4 by 4 by 3 mm)9.4 Transfer samples quickly from sealed container to balance to instrument to prevent moisture pick-up.10. Preparation of Apparatus10.
27、1 Assemble the apparatus according to the manufacturers instructions. Molecular sieve or suitable desiccant must be usedin the drying tubes for the nitrogen carrier gas.10.2 Pour approximately 200 mL (or an amount specified by the manufacturer) of generator (anode) solution into the titrationcell.10
28、.3 Add 10 mL of cathode solution to the cathode cell.NOTE 3The condition of both anode and cathode solutions are determined by the appearance of the fluids. The solutions must be light amber in color.As solutions age, viscosity will increase and solution color will turn dark. The instrument will ind
29、icate solution integrity by the “background” valueD6869 172titration rate. Do not analyze samples containing low moisture content if the “background” value is greater than 0.10 g/s.10.4 Turn the cell power switch on. If the cell potential shows a negative value, indicating that the anode solution co
30、ntainsexcess iodine, add approximately 50 to 200 L of neutralization solution or check solution.10.5 Disconnect the tube connecting the vaporizer unit to the titration cell. Set nitrogen flow rate to achieve steady bubblingof nitrogen to the titration cell. (A flow rate of 200 to 300 mL/min is recom
31、mended.)10.6 Lift the titration cell and agitate the solution by gently swirling the cell to remove any residual water from the walls. Stirthe solution for a minute in the Titration Mode to dry and stabilize the inner atmosphere.10.7 Reconnect the tube from the vaporizer unit to the titration cell.
32、Keep the carrier gas flow on during the whole titration. Theinstrument is now ready for sample analysis.10.8 Set the oven and furnace tube temperature as required to obtain accurate results for the plastic to be tested. The temperatureis set so that the analysis is completed in a short time period,
33、yet eliminating the generation of water from thermal degradationof the sample. Selection of Optimum Heating Temperature is discussed below.10.9 Selection of Optimum Heating Temperature:10.9.1 Select optimum heating temperature for material to be tested by carrying out tests in several different temp
34、eratures tomake a curve as shown in Fig. 1.10.9.1.1 In the range from 1 to 2, the water in the sample is not vaporized sufficiently so that the water content indicatedincreases in proportion to the temperature.10.9.1.2 Between 2 and 3, the water content measured appears nearly constant and is consid
35、ered the optimum heatingtemperature range for determining moisture content.10.9.1.3 Water content appears to increase between 3 and 4. This is probably caused by the generation of water due to thermaldecomposition or solid phase polymerization of the sample.10.9.1.4 Measurement time is also a consid
36、eration in selection of the optimum heating temperature.11. Calibration and Standardization11.1 The apparatus is verified for proper operation by either analysis of a known quantity of water or analysis of a hydratesample that will release moisture upon heating. Two methods of checking the instrumen
37、t are listed here, a micro-capillary methodand a sodium citrate method.11.2 Micro-capillary Method:11.2.1 A glass capillary (micropipette) is used to measure a known amount of water, typically 2 mg (2000 g). Prepare theinstrument as detailed in Section 12.11.2.2 Fill the micropipette by holding it a
38、t its midpoint with a pair of tweezers and dipping the tip into distilled ordemineralized water. Take care not to get excess moisture on the outside surface of the capillary.11.2.3 Place the capillary in the sample boat through the furnace tube port. An oven temperature of 150C or greater shall beus
39、ed.11.3 Sodium Citrate Method:11.3.1 This method uses sodium citrate dihydrate (C6H5Na3O72H2O) with theoretical water content of 12.24 %.11.3.2 Weigh 0.0100 to 0.0200 g of sodium citrate to the nearest 0.0001 g. Record the sample weight.11.3.3 Analyze the moisture content using an oven temperature o
40、f 225C or greater.FIG. 1 Optimum Heating Temperature Selection for MaterialD6869 173NOTE 4Another permissible method, which uses a micro syringe, is described in section 4.5.3.1 of ISO 15512. It is permissible to use similar hydratesto check instrument performance.12. Procedure12.1 If the oven is at
41、 the selected operating temperature before the analysis begins, pre-heat the sample boat to eliminate anymoisture present. Heat the boat in the oven for 2 min, and then allow the boat to cool for 2 min prior to the introduction of samples.12.2 Weigh the sample to be tested and record the weight to t
42、he nearest 0.1 mg. Sample weight to be used is dependent on theamount of moisture expected in the sample. The following table lists recommended sample weights for various moisture ranges:Expected Moisture Content (w) Sample Weight (m)w 1 % 0.2 g m $ 0.1 g1 % $ w 0.5 % 0.4 g m $ 0.2 g0.5 % $ w 0.1 %
43、1 g m $ 0.4 g0.1 % $ w m $ 1 g12.3 Place the sample in the sample boat through the furnace tube port. Move the sample boat into the oven and begin analysis.12.4 At completion of the sample analysis, the instrument will automatically report the result or display g of moisture titrated.12.5 Remove the
44、 sample boat and empty the contents, then prepare the sample boat for next analysis. Removal of the previoussample will provide more accurate results.13. Calculation or Interpretation of Results13.1 Most commercial coulometric instruments will perform calculations automatically based on the microgra
45、ms of waterdetected.13.2 If the moisture is not calculated automatically, calculate the water content in the test portion (expressed as a percentageby mass) as follows:%moisture5micrograms of watergrams of water 31024%moisture5 grams of watergrams of sample310014. Report14.1 Report the sample type,
46、oven temperature, sample weight, and % moisture.15. Precision and Bias15.1 The precision of this test method is not known because inter-laboratory data are not available. If and when inter-laboratorydata are obtained, a precision statement will be added at a subsequent revision.15.2 A “ruggedness” t
47、est was run at three labs using nylon 6,6 with the following results:LabNumber DayAnalysisTemp. (C)FirstAnalysisSecondAnalysis1 1 190 0.2323 0.22981 2 190 0.2047 0.23231 1 200 0.2491 0.22501 2 200 0.1842 0.19272 1 240 0.308 0.3162 2 240 0.314 0.3042 1 200 0.264 0.2632 2 200 0.285 0.2973 1 220 0.25 0
48、.243 2 220 0.24 0.233 1 200 0.23 0.243 2 200 0.25 0.2416. Keywords16.1 moisture content; moisture determination; plasticsD6869 174APPENDIX(Nonmandatory Information)X1. HISTORY OF REAGENTS ASSOCIATED WITH THE KARL FISCHER REACTIONX1.1 History of Reagents Associated with the Karl Fischer ReactionX1.1.
49、1 The Karl Fischer chemical reaction is:I212H2O1SO22HI1H2SO4X1.1.2 This reaction takes place in the presence of a base and a solvent. Karl Fischers original combination of reagents, whichcontained pyridine, was first used in 1935. It was not widely used because of the objectionable odor of pyridine.X1.1.3 Wider use of the Karl Fischer reaction did not take place until the early 1980s when reagents were offered where pyridinewas replaced with methanol. This eliminated the odor problem associated with pyridine. Halogenated alcohols (especiallytrifluoroetha
