ASTM D4672-00(2006)e1
(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
SIGNIFICANCE AND USE
These test methods are suitable for quality control, as a specification test, and for research. The water content of a polyol is important since isocyanates react with water. TEST METHOD A: MANUAL PROCEDURE Top
Note 2—Commercially available automated Karl Fischer titrators are used extensively.
The description of the manual systems presented below is for reference purposes and has been included in order to better define the principles of the Karl Fischer measurement.
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.
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.
These test methods are equivalent to ISO 14897.
General Information
Relations
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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
´1
Designation: D4672 − 00(Reapproved 2006)
Standard Test Methods for
Polyurethane Raw Materials: Determination of Water
Content of Polyols
This standard is issued under the fixed designation D4672; 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 (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Removed non-mandatory language throughout in March 2006.
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
by sulfur dioxide in the presence of water. This reaction
1.2 The values stated in SI units are to be regarded as the
proceeds quantitatively when methanol or another alcohol
standard. The values given in parentheses are for information
(ROH) and pyridine (C H N) or a similar amine (R8N) are
only. 5 5
present to react with the sulfur trioxide (SO ) and hydriodic
1.3 This standard does not purport to address all of the
acid (HI) produced according to the following reactions:
safety concerns, if any, associated with its use. It is the
ROH+SO +R8N→ [R8NH]SO R
2 3
responsibility of the user of this standard to establish appro-
H O+I +[R8NH]SO R+2R8N→ [R8NH]SO R + 2[R8NH]I
2 2 3 4
priate safety and health practices and determine the applica-
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—These test methods are equivalent to ISO 14897.
substitute) is added to a solution of the sample in methanol or
2. Referenced Documents
other alcohol until all the water present has been consumed.
The titrant is either added by buret (volumetry) or generated
2.1 ASTM Standards:
electrochemically in the titration cell (coulometry). Coulomet-
D1193 Specification for Reagent Water
ric titrations eliminate the need for standardizing the reagent.
D883 Terminology Relating to Plastics
E180 Practice for Determining the Precision of ASTM
5. Significance and Use
Methods for Analysis and Testing of Industrial and Spe-
cialty Chemicals (Withdrawn 2009)
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 Definitions:
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
used extensively.
droxyl groups.
3.1.1.1 Discussion—Polyurethanes,orurethanes,astheyare
5.2 The description of the manual systems presented below
sometimes called, may be thermosetting, thermoplastic, rigid
is for reference purposes and has been included in order to
or soft and flexible, cellular or solid. (See Terminology D883.)
better define the principles of the Karl Fischer measurement.
These test methods are under the jurisdiction of ASTM Committee D20 on
6. Apparatus
Plastics and are the direct responsibility of Subcommittee D20.22 on Cellular
Materials - Plastics and Elastomers.
6.1 Titration Vessel—A vessel of approximately 300-mL
Current edition approved March 15, 2006. Published June 2006. Originally
capacity, such as a tall-form, lipless beaker, provided with a
approved in 1991. Last previous edition approved in 2000 as D4672 - 00. DOI:
tight-fitting closure to protect the reaction mixture from atmo-
10.1520/D4672-00R06E01.
spheric moisture.The vessel shall also be fitted with a nitrogen
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
inlet tube, a 10-mLburet, a stirrer (preferably magnetic), and a
Standards volume information, refer to the standard’s Document Summary page on
port that may be opened momentarily for sample and solvent
the ASTM website.
3 addition or removal of electrodes. It is convenient to provide a
The last approved version of this historical standard is referenced on
www.astm.org. vacuum line leading to a 1-L trap bottle for drawing off the
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D4672 − 00 (2006)
titrated solution. Pass the nitrogen through a drying tube nol until the solution is a pale yellow.A100-mLportion of the
containing anhydrous calcium sulfate before it enters the treated solvent requires 1 to 10 mL of dilute Karl Fischer
titration vessel. reagent.
6.2 Instrument Electrodes—Platinum with a surface equiva-
8. Sampling
lent of two No. 26 wires, 4.762 mm (0.19 in.) long. The wires
8.1 It is essential to avoid changes in the water content of
are to be 3 to 8 mm apart and inserted in the vessel so that 75
the material during sampling operations. Many polyols are
mL of solution will cover them.
quite hygroscopic and errors from this source are particularly
6.3 Instrument Depolarization Indicator—Having an inter-
significant in the determination of the small amount of water
nal resistance of less than 5000 V and consisting of a means of
usually present. Use almost-filled, tightly capped containers
impressing and showing a voltage of 20 to 50 mV across the
and limit as much as possible contact of the sample with air
electrodes and capable of indicating a current flow of 10 to 20
when transferring the sample to the titration vessel. Avoid
µA by means of a galvanometer or ratio tuning circuit.
intermediate sample containers, if possible. If several different
6.4 Buret Assembly—For Karl Fischer reagent, consisting of analyses are to be performed on the same sample, determine
a 10-mL buret with 0.05-mL subdivisions connected by means the water first and do not open the sample prior to the actual
of glass or polyethylene (not rubber) connectors to a source of analysis.
reagent. Several types of automatic dispensing burets may be
9. Standardization of Reagent
used. Since the reagent loses strength when exposed to moist
air,allventsmustbeprotectedagainstatmosphericmoistureby
9.1 Standardize the Karl Fischer reagent daily using the
adequate drying tubes containing anhydrous calcium sulfate.
same procedures as used for titrating the sample.
All stopcocks and joints are to be lubricated with an inert
9.1.1 Add 100 mLof titration solvent to the flask and titrate
lubricant.
theresidualmoistureasdescribedinSection10.Tothistitrated
solvent, immediately add 1 drop of water from a weighing
7. Reagents
pipet. Weigh the pipet to 60.1 mg. Complete the titration with
Karl Fischer reagent as described in Section 10. It may be
7.1 Purity of Reagents—Use reagent-grade chemicals in all
necessary to refill the buret during the titration.
tests. Unless otherwise indicated, it is intended that all reagents
9.1.2 Calculate the equivalence factor, F, in terms of milli-
shall conform to the specifications of the Committee on
grams of water per millilitre of reagent as follows:
Analytical Reagents of the American Chemical Society where
such specifications are available. Other grades may be used, equivalency factor, F 5 A/B (1)
provided it is first ascertained that the reagent is of sufficiently
high purity to permit its use without lessening the accuracy of
where:
the determination.
A = water added, mg, and
7.2 Purity of Water—Unless otherwise indicated, references
B = Karl Fischer reagent required, mL.
to water shall be understood to mean reagent water as defined
10. Procedure
by Type I of Specification D1193.
10.1 Adjust the nitrogen valve so that dry nitrogen flows
7.3 Karl Fischer Reagent—Equivalent to 2.5 to 3.0 mg of
into the titration vessel at a slow rate (20 to 50 mL/min).
water/mL. Dilute commercially available stabilized Karl Fis-
Introduce approximately 100 mL of titration solvent into the
cher reagent (6 mg of water/mL) with an equal volume of
titration vessel, making sure that the electrodes are covered
anhydrous ethylene glycol monomethyl ether (containing less
withsolvent.Adjustthestirrertogiveadequatemixingwithout
than 0.1 % water). (See Note 3.)
splashing. Titrate the mixture with Karl Fischer reagent to the
NOTE 3—Improved, pyridine-free Karl Fischer reagents have been
end point. (See Note 4.)
made available and are now highly recommended as a replacement for the
previous reagents. See Section 14, under Test Method B, Automated
10.2 To the prepared titration mixture, add the amount of
Procedure.
sample as indicated in Table 1. Exercise care when the sample
7.4 Titration Solvent, Anhydrous Methanol—Unless the is transferred so that water is not absorbed from the air,
methanol is extremely dry it will require a large amount of particularly under conditions of high humidity. Allow the
dilute Karl Fischer solution to react with its residual water. For solution to stir 1 or 2 minutes until dissolution is complete.
this reason the solvent shall be further dried by adding
10.3 Titrate the mixture again with Karl Fischer reagent to
undiluted Karl Fischer reagent (6 mg of water/mL) to a bottle
thesameendpointpreviouslyemployed.Recordtheamount
...
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