ASTM D5155-96

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: D 5155 – 96
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Methods for
Polyurethane Raw Materials: Determination of the
Isocyanate Content of Aromatic Isocyanates
This standard is issued under the fixed designation D 5155; 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 D 1193 Specification for Reagent Water
E 180 Practice for Determining the Precision of ASTM
1.1 These test methods measure the isocyanate content of
Methods for Analysis and Testing of Industrial Chemicals
aromatic isocyanates used as polyurethane raw materials.
1.1.1 Test Method A—Unheated toluene-dibutylamine de-
3. Terminology
termines the amount of toluene diisocyanate in refined toluene-
3.1 Definitions:
2,4-diisocyanate and toluene-2,6-diisocyanate, or mixtures of
3.1.1 polyurethane, n—a polymer prepared by the reaction
the two. Other isomers, if present, will be included in the
of an organic diisocyanate with compounds containing hy-
determination. This test method may also be applied to other
droxyl groups.
isocyanates of suitable reactivity and solubility.
3.1.1.1 Discussion—Polyurethanes or urethanes, as they are
1.1.2 Test Method B—Heated toluene-dibutylamine deter-
sometimes called, may be thermosetting, thermoplastic, rigid
mines the amine equivalent of crude or modified isocyanates
or soft and flexible, or cellular or solid (see Terminology
derived from toluene diisocyanate, methylenebis-(4-
D 883).
phenylisocyanate), and polymethylene polyphenylisocyanate.
3.2 Definitions of Terms Specific to This Standard:
1.1.3 Test Method C—Unheated trichlorobenzene-toluene-
3.2.1 amine equivalent—the weight of sample that will
dibutylamine determines the isocyanate content of crude or
combine with 1.0-g equivalent weight of dibutylamine.
modified isocyanates derived from toluene diisocyanate,
3.2.2 assay—the percent by weight of toluene diisocyanate
methylene-bis-(4-phenylisocyanate), and polymethylene
present in the sample.
polyphenylisocyanate. This test method can also be used to
3.2.3 isocyanate (NCO) content—the weight percent of the
assay isomer mixtures of toluene diisocyanate and methylene-
NCO groups present in the sample.
bis-(phenylisocyanate).
1.2 This standard does not purport to address all of the
4. Summary of Test Methods
safety concerns, if any, associated with its use. It is the
4.1 All three test methods react the isocyanate sample with
responsibility of the user of this standard to establish appro-
an excess of dibutylamine to form the corresponding urea. The
priate safety and health practices and determine the applica-
NCO content is determined from the amount of dibutylamine
bility of regulatory limitations prior to use. For specific
consumed in the reaction. Each test method varies solvent or
warning and precautionary statements, see Note 2.
heating times to yield accurate assays of the sample in
NOTE 1—There is no equivalent ISO standard.
question.
4.1.1 Test Method A—The sample is added to an excess of
2. Referenced Documents
dibutylamine in toluene and allowed to stand at room tempera-
2.1 ASTM Standards:
ture for 15 min. The reaction mixture is diluted with isopropyl
D 841 Specification for Nitration Grade Toluene
alcohol, and the excess dibutylamine is back-titrated colori-
D 883 Terminology Relating to Plastics
metrically with hydrochloric acid.
4.1.2 Test Method B—The sample is added to an excess of
dibutylamine in toluene and stirred for 20 min. The resulting
These test methods are under the jurisdiction of ASTM Committee D-20 on
solution is then heated rapidly to 100°C, removed from the
Plastics and are the direct responsibility of Subcommittee D20.22 on Cellular
Plastics. These test methods were recommended to ASTM by the Society of the
heat, and allowed to stand for 30 min. The reaction mixture is
Plastics Industry Polyurethane Raw Materials Analysis Committee.
diluted with isopropyl alcohol, and the excess dibutylamine is
Current edition approved Nov. 10, 1996. Published January 1997. Originally
back-titrated potentiometrically with hydrochloric acid.
published as D 5155 – 91. Last previous edition D 5155 – 91.
Revisions to this edition include the addition of Note 1 as well as the lowering 4.1.3 Test Method C—The sample is added to a solution of
of the normal acidity level of crude isocynates from 0.3 % to 0.05 %. The
dibutylamine in toluene and trichlorobenzene. The resulting
designation of pH in a nonaqueous mixture was changed to “apparent pH.” Section
24, Report, was added, and Precision and Bias, Sections 14, 19, and 25, were
rewritten to reflect the statistical significance of the data available.
2 4
Annual Book of ASTM Standards, Vol 06.03. Annual Book of ASTM Standards, Vol 11.01.
3 5
Annual Book of ASTM Standards, Vol 08.01. Annual Book of ASTM Standards, Vol 15.05.
D 5155
solution is allowed to stand until it has cooled to room 10.2 Cooling Bath—Any container approximately 50 mm
temperature. The reaction mixture is diluted with methanol and deep filled with ice and water.
back-titrated potentiometrically with hydrochloric acid.
11. Reagents
5. Significance and Use
11.1 Bromcresol Green Indicator Solution—Using 1.5 mL
of 0.1 N sodium hydroxide, extract the bromcresol green from
5.1 These test methods can be used for research or for
0.100 g of bromcresol green indicator-grade powder, stirring
quality control to characterize isocyanates used in polyurethane
vigorously until the amount of insoluble residue remains
products.
constant. Decant the aqueous portion into a 100-mL volumetric
6. Interferences
flask and dilute to the mark with water.
11.2 Dibutylamine Solution (260 g/L)—Dilute 260 g of dry
6.1 Phosgene, the carbamyl chloride of the isocyanate,
dibutylamine to 1 L with dry toluene. Dry the solution with a
hydrogen chloride, and any other acidic or basic compounds
drying agent.
will interfere. In refined isocyanates, these impurities are
11.3 Hydrochloric Acid (1 N)—Prepare 1 N HCl (hydro-
usually present in such low amounts that they do not affect the
chloric acid) and standardize frequently enough to detect
determination. While some crude or modified isocyanates
changes of 0.001 N.
contain acidities of up to approximately 0.05 %, the NCO
11.4 Isopropyl Alcohol.
content is not normally corrected.
11.5 Toluene, dry, conforming to Specification D 841 with a
7. Reagents and Materials
drying agent.
7.1 Purity of Reagents—Reagent grade chemicals shall be
12. Procedure
used in all tests. Unless otherwise indicated, it is intended that
12.1 Run sample and blank determinations side by side.
all reagents shall conform to the specifications of the Commit-
Run the blank determination exactly as described as follows,
tee on Analytical Reagents of the American Chemical Society,
6 but without adding the sample.
where such specifications are available. Other grades may be
12.2 Add a magnetic stirring bar and 40 mL of dry toluene
used, provided it is first ascertained that the reagent is of
to a 500-mL Erlenmeyer flask that has been rinsed successively
sufficiently high purity to permit its use without lessening the
with water, alcohol, and high-purity acetone, dried at 100°C,
accuracy of the determination.
and allowed to cool in a desiccator. Accurately add, by pipet or
7.2 Purity of Water—Unless otherwise indicated, references
buret, 50 mL of dibutylamine solution and mix carefully.
to water shall be understood to mean reagent water as defined
12.3 While stirring the contents of the flask, slowly add 6.5
by Type I of Specification D 1193.
to 7.0 g of the sample weighed to the nearest 0.001 g (Note 3).
8. Sampling Wash down the sides of the flask with 10 mL of dry toluene,
then stopper the flask loosely and allow it to stand at room
8.1 Since organic isocyanates react with atmospheric mois-
temperature for 15 min.
ture, take special precautions in sampling (see Note 2). Usual
sampling methods (for example, sampling an open drum with
NOTE 3—If spattering is anticipated, cool the flask and contents in the
a thief), even when conducted rapidly, can cause contamination cooling bath before adding the sample and continue to cool until the heat
of reaction is dissipated. Add 10 mL of dry toluene, stopper the flask
of the sample with insoluble urea. Therefore, blanket the
loosely, and allow the contents to come to room temperature.
sample with dry air or nitrogen at all times.
12.4 Add 225 mL of isopropyl alcohol from a 250-mL
NOTE 2—Warning: Organic isocyanates are toxic when absorbed
graduated cylinder and 0.8 mL of bromcresol green indicator
through the skin, or when the vapors are breathed. Precaution: Provide
solution from a graduated 1-mL pipet. Titrate with 1 N HCl
adequate ventilation and wear protective gloves and eyeglasses.
solution in a 50 or 100-mL buret while stirring the flask
9. Test Conditions
contents with the magnetic stirring bar. Near the end point,
9.1 Since isocyanates react with moisture, keep the labora- slowly add the HCl dropwise. The end point is reached when
the blue color disappears and a yellow color appears that
tory humidity low, preferably below 50 % relative humidity.
persists for at least 15 s (Note 4).
TEST METHOD A—UNHEATED TOLUENE-
NOTE 4—Alternatively, the end point may be determined using a
DIBUTYLAMINE
potentiometer and electrodes. When using this apparatus, it may be
10. Apparatus
10.1 Lunge Pipet, or any weighing device that can weigh a
The Linde 4A Molecular Sieve, or its equivalent, has been found suitable. The
Linde 4A Molecular Sieve is available from Union Carbide Corp., Specialty
liquid by difference to the nearest 0.001 g.
Gas-Linde Division, 2 Greenway Plaza, Suite 901, Houston, TX 77046, or from
other Union Carbide locations nationwide.
Pipets and burets shall conform to National Institute of Standards and
Reagent Chemicals, American Chemical Society Specifications, American Technology tolerances, as given in Peffer, E. L., and Mulligan, G. C., “Testing of
Chemical Society, Washington, DC. For suggestions on the testing of reagents not Glass Volumetric Apparatus,” NIST Circular C 434, 1941, available from the
listed by the American Chemical Society, see Analar Standards for Laboratory Superintendent of Documents, U.S. Government Printing Office, Washington, DC
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia 20025.
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, If an isocyanate other than TDI is used, substitute the equivalent weight of the
MD. material being analyzed.
D 5155
necessary to transfer the solution to a 600-mL beaker prior to titration.
16.2 Hydrochloric Acid (1 N)—Prepare 1 N hydrochloric
After transfer, rinse the Erlenmeyer flask with 25 mL of isopropyl alcohol
acid (HCl) and standardize frequently enough to detect changes
and add the rinse to the 600-mL beaker. To titrate, immerse the calomel
of 0.001 N.
and glass electrodes of the pH meter (standardized with pH 4.0 standard
16.3 Isopropyl Alcohol, 99 % minimum purity.
buffer) and titrate the sample to the break that occurs at approximately pH
16.4 Toluene, dry, in accordance with Specification D 841,
4.2 to 4.5 with 1.0 N HCl while stirring the solution with a stirring bar.
and dried by a drying agent.
13. Calculation
17. Procedure
13.1 Calculate the assay, %, as follows:
17.1 Add 50 mL of dry toluene to a dry 600-mL beaker.
Assay 5 ~B 2 S!~N!~87.08!~100!/1000 W (1)
Pipet 25 mL of the dibutylamine solution into the beaker.
When constants are combined, this equation reduces to
Swirl the beaker to mix the contents.
Assay 5 8.708 N~B 2 S!/W (2) 17.2 Transfer to the beaker 0.02 to 0.03 equivalents of the
sample weighed to the nearest 0.001 g. Start the magnetic
where:
stirrer carefully and rinse the sides of the beaker with an
B 5 HCl required for titration of the blank, mL,
additional 10 mL of dry toluene. Cover the beaker and continue
S 5 HCl required for titration of the sample, mL,
mixing for an additional 20 min.
N 5 normality of the HCl, meq/mL,
17.3 Place the beaker on a hot plate with the − 10 to 100°C
W 5 sample used, g,
10 thermometer in the sample. Heat the sample mixture rapidly
87.08 5 equivalent weight of TDI, mg/meq,
with stirring, so that the solution reaches a temperature of 95 to
1000 5 conversion from g to mg, and
1 1
100°C in 3 ⁄2 to 4 ⁄2 min. Do not overheat. Quickly remove the
100 5 conversion to percent.
beaker from the hot plate, cover it with a watchglass, and allow
14. Precision and Bias it to stand for 30 min.
17.4 Cool the beaker and contents to room temperature and
14.1 Attempts to develop a precision and bias statement for
add 225 mL of isopropyl alcohol.
this test method have not been successful due to the limited
17.5 Titrate potentiometrically with 1.0 N HCl to the break
number of laboratories participating in round-robin tests. Data
that occurs at approximately apparent pH 4.2 to 4.5.
on precision and bias cannot be given for this reason. Anyone
17.6 Titrate a blank exactly as described in 17.5, but without
wishing to participate in the development of precision and bias
adding the sample.
data should contact the Chairman, Subcommittee D20.22
(Section D20.22.01), ASTM, 100 Barr Harbor Drive, West
18. Calculation
Conshohocken, PA 19428.
18.1 Calculate the amine equivalent as follows:
14.2 A limited round robin was conducted.
14.2.1 It has been estimated that duplicate results by the
1000~W!
amine equivalent 5 (3)
same analyst should be considered suspect if they differ by
N~B 2 S!
0.4 % TDI.
18.2 Calculate the NCO, %, as follows:
14.2.2 It has been estimated that results reported by different
4.202~B 2 S!N
laboratories should be considered suspect if they differ by
NCO 5 (4)
W
0.8 % TDI.
14.3 There are no recognized standards by which to esti-
where:
mate the bias of this test method.
B 5 HCl required for titration of blank, mL,
S 5 HCl required for titration of sample, mL,
TEST METHOD B—HEATED TOLUENE-
N 5 normality of HCl, meq/mL,
DIBUTYLAMINE
W 5 sample used, g, and
4.202 5 constant combining the equivalent weight of NCO
15. Apparatus
(42.02) mg/meq, conversion of g to 1000 mg, and
15.1 Potentiometric Titrator, or pH meter.
conversion to 100 %.
15.2 Calomel Electrode.
42.02~B 2 S!~N!~100! 4.202~B 2 S!N
15.3 Glass Electrode.
NCO 5 5 (5)
1000 W! W
~
15.4 Lunge Pipet, or any weighing device suitable for
weighing a liquid sample by diff
...