ASTM D4672-00
(Test Method)Standard Test Methods for Polyurethane Raw Materials Determination of Water Content of Polyols
Standard Test Methods for Polyurethane Raw Materials Determination of Water Content of Polyols
SCOPE
1.1 These test methods measure water content of polyols and many other organic compounds.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Note 1--ISO Standard 14897 is equivalent to these test methods.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation:D4672–00
Standard Test Methods for
Polyurethane Raw Materials: Determination of Water
Content of Polyols
This standard is issued under the fixed designation D 4672; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Summary of Test Methods
1.1 These test methods measure water content of polyols 4.1 Test MethodsAand B are based essentially on volumet-
and many other organic compounds. ric or coulometric titrations that follow the reduction of iodine
1.2 The values stated in SI units are to be regarded as the by sulfur dioxide in the presence of water. This reaction
standard. The values given in parentheses are for information proceeds quantitatively when methanol or another alcohol
only. (ROH) and pyridine (C H N) or a similar amine (R8N) are
5 5
1.3 This standard does not purport to address all of the present to react with the sulfur trioxide (SO ) and hydriodic
safety concerns, if any, associated with its use. It is the acid (HI) produced according to the following reactions:
responsibility of the user of this standard to establish appro- ROH+SO +R8N→ [R8NH]SO R
2 3
priate safety and health practices and determine the applica- H O+I +[R8NH]SO R+2R8N→ [R8NH]SO R + 2[R8NH]I
2 2 3 4
bility of regulatory limitations prior to use. 4.2 To determine water, Karl Fischer reagent (a solution of
iodine, sulfur dioxide, imidazole, and pyridine or a pyridine
NOTE 1—ISO Standard 14897 is equivalent to these test methods.
substitute) is added to a solution of the sample in methanol or
other alcohol until all the water present has been consumed.
2. Referenced Documents
2 The titrant can either be added by buret (volumetry) or
2.1 ASTM Standards:
generated electrochemically in the titration cell (coulometry).
D 1193 Specification for Reagent Water
Coulometric titrations eliminate the need for standardizing the
D 883 Terminology Relating to Plastics
reagent.
E 180 Practice for Determining the Precision of ASTM
Methods for Analysis and Testing of Industrial and Spe-
5. Significance and Use
cialty Chemicals
5.1 These test methods are suitable for quality control, as a
specification test, and for research. The water content of a
3. Terminology
polyol is important since isocyanates react with water.
3.1 Definition:
3.1.1 polyurethane, n—a polymer prepared by the reaction
TEST METHOD A: MANUAL PROCEDURE
of an organic diisocyanate with compounds containing hy-
NOTE 2—Commercially available automated Karl Fischer titrators are
droxyl groups.
used extensively.
3.1.1.1 Discussion—Polyurethanes, or urethanes, as they
5.2 The description of the manual systems presented below
are sometimes called, may be thermosetting, thermoplastic,
is for reference purposes and has been included in order to
rigid or soft and flexible, cellular or solid. (See Terminology
better define the principles of the Karl Fischer measurement.
D 883.)
6. Apparatus
6.1 Titration Vessel—A vessel of approximately 300-mL
These test methods are under the jurisdiction of ASTM Committee D20 on
capacity, such as a tall-form, lipless beaker, provided with a
Plastics and are the direct responsibility of Subcommittee D20.22 on Cellular
tight-fitting closure to protect the reaction mixture from atmo-
Plastics. It was recommended to ASTM by the American Plastics Council.
spheric moisture.The vessel shall also be fitted with a nitrogen
Current edition approved Nov. 10, 2000. Published February 2001. Originally
published as D 4672 – 91. Last previous edition D 4672 – 95.
inlet tube, a 10-mLburet, a stirrer (preferably magnetic), and a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
port that may be opened momentarily for sample and solvent
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
addition or removal of electrodes. It is convenient to provide a
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. vacuum line leading to a 1-L trap bottle for drawing off the
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D4672–00
titrated solution. Pass the nitrogen through a drying tube 8. Sampling
containing anhydrous calcium sulfate before it enters the
8.1 It is essential to avoid changes in the water content of
titration vessel.
the material during sampling operations. Many polyols are
6.2 Instrument Electrodes—Platinum with a surface equiva-
quite hygroscopic and errors from this source are particularly
lent of two No. 26 wires, 4.762 mm (0.19 in.) long. The wires
significant in the determination of the small amount of water
should be 3 to 8 mm apart and inserted in the vessel so that 75
usually present. Use almost-filled, tightly capped containers
mL of solution will cover them.
and limit as much as possible contact of the sample with air
6.3 Instrument Depolarization Indicator—Having an inter-
when transferring the sample to the titration vessel. Avoid
nal resistance of less than 5000 V and consisting of a means of
intermediate sample containers, if possible. If several different
impressing and showing a voltage of 20 to 50 mV across the
analyses are to be performed on the same sample, determine
electrodes and capable of indicating a current flow of 10 to 20
the water first and do not open the sample prior to the actual
µA by means of a galvanometer or ratio tuning circuit.
analysis.
6.4 BuretAssembly—ForKarlFischerreagent,consistingof
a 10-mL buret with 0.05-mL subdivisions connected by means
9. Standardization of Reagent
of glass or polyethylene (not rubber) connectors to a source of
9.1 Standardize the Karl Fischer reagent daily using the
reagent. Several types of automatic dispensing burets may be
same procedures as used for titrating the sample.
used. Since the reagent loses strength when exposed to moist
9.1.1 Add 100 mLof titration solvent to the flask and titrate
air,allventsmustbeprotectedagainstatmosphericmoistureby
theresidualmoistureasdescribedinSection10.Tothistitrated
adequate drying tubes containing anhydrous calcium sulfate.
solvent, immediately add 1 drop of water from a weighing
All stopcocks and joints should be lubricated with an inert
pipet. Weigh the pipet to 60.1 mg. Complete the titration with
lubricant.
Karl Fischer reagent as described in Section 10. It may be
necessary to refill the buret during the titration.
7. Reagents
9.1.2 Calculate the equivalence factor, F, in terms of milli-
7.1 Purity of Reagents—Use reagent-grade chemicals in all
grams of water per millilitre of reagent as follows:
tests. Unless otherwise indicated, it is intended that all reagents
equivalency factor, F 5 A/B (1)
shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society where
such specifications are available. Other grades may be used,
where:
provided it is first ascertained that the reagent is of sufficiently
A = water added, mg, and
high purity to permit its use without lessening the accuracy of
B = Karl Fischer reagent required, mL.
the determination.
7.2 Purity of Water—Unless otherwise indicated, references
10. Procedure
to water shall be understood to mean reagent water as defined
10.1 Adjust the nitrogen valve so that dry nitrogen flows
by Type I of Specification D 1193.
into the titration vessel at a slow rate (20 to 50 mL/min).
7.3 Karl Fischer Reagent—Equivalent to 2.5 to 3.0 mg of
Introduce approximately 100 mL of titration solvent into the
water/mL. Dilute commercially available stabilized Karl Fis-
titration vessel, making sure that the electrodes are covered
cher reagent (6 mg of water/mL) with an equal volume of
withsolvent.Adjustthestirrertogiveadequatemixingwithout
anhydrous ethylene glycol monomethyl ether (containing less
splashing. Titrate the mixture with Karl Fischer reagent to the
than 0.1 % water). (See Note 3.)
end point. (See Note 4.)
NOTE 3—Improved, pyridine-free Karl Fischer reagents have been 10.2 To the prepared titration mixture, add the amount of
made available and are now highly recommended as a replacement for the
sample as indicated in Table 1. Exercise care when the sample
previous reagents. See Section 14, under Test Method B, Automated
is transferred so that water is not absorbed from the air,
Procedure.
particularly under conditions of high humidity. Allow the
7.4 Titration Solvent, Anhydrous Methanol—Unless the
solution to stir 1 or 2 minutes until dissolution is complete.
methanol is extremely dry it will require a large amount of
10.3 Titrate the mixture again with Karl Fischer reagent to
dilute Karl Fischer solution to react with its residual water. For
thesameendpointpreviouslyemployed.Recordtheamountof
this reason the solvent shall be further dried by adding
reagent used to titrate the water in the sample.
undiluted Karl Fischer reagent (6 mg of
...
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