ASTM D6099-24

Standard Test Method for Polyurethane Raw Materials: Determination of Acidity in Moderate to High Acidity Aromatic Isocyanates

SIGNIFICANCE AND USE
5.1 This test method can be used for research or for quality control to characterize aromatic isocyanates and prepolymers of moderate to high acidity. Acidity correlates with performance in some polyurethane systems.
SCOPE
1.1 This test method determines the acidity, expressed as parts per million (ppm) of HCl, in aromatic isocyanate samples of greater than 100–ppm acidity. The test method is applicable to products derived from toluene diisocyanate and methylene-bis-(4–phenylisocyanate) (see Note 1).
Note 1: This test method is equivalent to ISO 14898, Test Method A.  
1.2 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jan-2024
• ICS: 83.040.01 - Raw materials for rubber and plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.22 - Cellular Materials - Plastics and Elastomers

Relations

• Replaces: ASTM D6099-18 - Standard Test Method for Polyurethane Raw Materials: Determination of Acidity in Moderate to High Acidity Aromatic Isocyanates
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM E456-13a(2022)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Refers: ASTM E456-13a(2022) - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Apr-2022
• Referred By: ASTM D5629-23 - Standard Test Method for Polyurethane Raw Materials: Determination of Acidity in Low-Acidity Aromatic Isocyanates and Polyurethane Prepolymers
• Effective Date: 01-Feb-2024

Overview

ASTM D6099-24, titled “Standard Test Method for Polyurethane Raw Materials: Determination of Acidity in Moderate to High Acidity Aromatic Isocyanates,” provides a standardized procedure for measuring the acidity of aromatic isocyanates used in polyurethane production. Key isocyanates addressed include toluene diisocyanate (TDI) and methylene-bis-(4-phenylisocyanate) (MDI). The method specifically applies to samples exhibiting acidity greater than 100 ppm, expressed as HCl. The standard method is widely adopted in quality control and research to help assess material suitability and predict performance in polyurethane systems.

Key Topics

• Scope and Applicability

  • Suitable for TDI and MDI raw materials and prepolymers with moderate to high acidity (>100 ppm HCl).
  • Correlates acidity with performance in polyurethane manufacturing.
  • Equivalent to ISO 14898, Test Method A, ensuring international alignment.

• Test Method Summary

  • Acidity is determined by mixing the isocyanate sample with methanol and a cosolvent.
  • The sample is titrated potentiometrically using methanolic KOH.
  • The result is calculated and reported as ppm HCl.

• Precision and Repeatability

  • The method includes standard practices to ensure reproducibility and repeatability of results.
  • Guidance on calibration, sampling, and handling is provided to guarantee accurate acidity measurements.

• Safety and Handling

  • Emphasizes the need for special sampling strategies to prevent moisture contamination.
  • Details health and safety precautions for handling diisocyanates, including skin, eye, and respiratory protections.

Applications

The ASTM D6099-24 test method is used across various phases of polyurethane production and research:

• Quality Control in Manufacturing

  • Ensures raw materials meet specified acidity limits, preventing downstream issues in polyurethane foam or elastomer production.
  • Detects batch-to-batch variability that could affect product performance.

• Research and Development

  • Supports evaluation of novel isocyanate formulations or additives by quantifying acidity profiles.
  • Helps investigate the impact of acidity on physical and mechanical properties of polyurethane products.

• Supply Chain Assurance

  • Provides a benchmark for vendors and customers to align on material quality specifications using internationally recognized tests.

• Regulatory and Compliance

  • Ensures companies meet international requirements in the trade of polyurethane raw materials by adhering to harmonized procedures, reducing technical barriers.

Related Standards

• ISO 14898

  • Equivalent to ASTM D6099-24 for determining acidity in aromatic isocyanates.

• ASTM D883

  • Provides terminology relating to plastics and underpins definitions used in D6099-24.

• ASTM E691

  • Practice for conducting interlaboratory studies, relevant for laboratories seeking to validate their D6099-24 results.

• ASTM E2935

  • Offers procedures for evaluating test method equivalence, applicable to comparisons with D6099-24.

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Keywords: aromatic isocyanates, acidity determination, polyurethane raw materials, TDI, MDI, titration, quality control, ASTM D6099-24, parts per million HCl, polyurethane industry standards

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6099 − 24
Standard Test Method for
Polyurethane Raw Materials: Determination of Acidity in
Moderate to High Acidity Aromatic Isocyanates
This standard is issued under the fixed designation D6099; 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.
1. Scope* 3. Terminology
1.1 This test method determines the acidity, expressed as 3.1 Definitions—Terms used in this test method are in
parts per million (ppm) of HCl, in aromatic isocyanate samples accordance with Terminology D883, unless otherwise speci-
of greater than 100–ppm acidity. The test method is applicable fied. For terms relating to precision and bias and associated
to products derived from toluene diisocyanate and methylene- issues, the terms used in this standard are defined in accordance
bis-(4–phenylisocyanate) (see Note 1). with Terminology E456.
3.2 Definitions of Terms Specific to This Standard:
NOTE 1—This test method is equivalent to ISO 14898, Test Method A.
3.2.1 acidity, n—the acid strength of a sample expressed in
1.2 This international standard was developed in accor-
ppm HCl.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
4. Summary of Test Method
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
4.1 The isocyanate is mixed with an excess of methanol and
Barriers to Trade (TBT) Committee. a cosolvent. Additional acid is released into the solvent system
during urethane formation. The acid is titrated potentiometri-
2. Referenced Documents
cally with methanolic KOH, and the acidity present in the
isocyanate sample is calculated from the titer.
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
5. Significance and Use
E180 Practice for Determining the Precision of ASTM
Methods for Analysis and Testing of Industrial and Spe-
5.1 This test method can be used for research or for quality
cialty Chemicals (Withdrawn 2009) control to characterize aromatic isocyanates and prepolymers
E456 Terminology Relating to Quality and Statistics
of moderate to high acidity. Acidity correlates with perfor-
E691 Practice for Conducting an Interlaboratory Study to mance in some polyurethane systems.
Determine the Precision of a Test Method
E2935 Practice for Evaluating Equivalence of Two Testing 6. Apparatus
Processes
6.1 250-mL Beakers.
2.2 ISO Standards:
6.2 50-mL Pipet or Repipet, Class A volumetric.
ISO 14898 Plastics—Aromatic isocyanates for use in the
6.3 100-mL Pipet or Repipet, Class A volumetric.
production of polyurethane—Determination of acidity
6.4 Automatic Titration Equipment, capable of inflection
detection and stirring the sample while, titrating, such as:
This test method is under the jurisdiction of ASTM Committee D20 on Plastics 6.4.1 Commercially-available Automatic Titration
and is the direct responsibility of Subcommittee D20.22 on Cellular Materials -
Apparatus,
Plastics and Elastomers.
6.4.2 Reference Electrode, with saturated LiCl/ethanol so-
Current edition approved Feb. 1, 2024. Published February 2024. Originally
lution in both chambers.
approved in 1997. Last previous edition approved in 2018 as D6099 - 18. DOI:
10.1520/D6099-24.
6.4.3 pH Glass Electrode, (see Note 2).
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
NOTE 2—A combination pH electrode with internal reference also may
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on be used.
the ASTM website.
6.5 Magnetic Stirrer.
The last approved version of this historical standard is referenced on
www.astm.org.
6.6 Stir Bars.
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. 6.7 Watch Glasses.
*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
D6099 − 24
TABLE 1 Round–Robin Acidity Data in Accordance With Practice
6.8 Analytical Balance, capable of weighing to the nearest 1
E180
mg.
Values, ppm HCl
A B C D E F
Average S S r R n df
7. Reagents and Materials r R
Rubinate M 189 5.8 13.5 16.2 37.9 11 23
7.1 0.02 N KOH in Methanol—1.32 g KOH pellets (85 %
Mondur MR 414 3.4 27.5 9.5 76.9 11 20
A
KOH)/1000 mL methanol, standardized with potassium hydro-
S = within-laboratory standard deviation of the replicates.
r
B
S = between-laboratory standard deviation of the average.
gen phthalate (KHP).
R
C
r = within-laboratory repeatability limit = 2.8 × S .
r
D
7.2 Toluene or 1,2,4–Trichlorobenzene (TCB), dried for 24 h
R = between-laboratory reproducibility limit = 2.8 × S .
R
E
n = number of laboratories contributing valid data for this material.
over molecular sieves.
F
df = degrees of freedom in the data after incorporating multiple data sets from
7.3 Anhydrous Methanol. most laboratories due to different combinations of solvent and electrode.
8. Sampling
8.1 Since organic isocyanates react with atmospheric
NOTE 5—If results indicate a drift in the data or a slow electrode
response, clean or replace the pH electrode.
moisture, take special precautions in sampling. Usual sampling
methods, even when conducted rapidly, can cause contamina-
11.7 Record the titrant volume for the potentiometric end
tion of the sample with insoluble urea. Therefore, blanket the
point. If more than one potentiometric end point is found,
sample with dry air or nitrogen at all times. (Warning—
record the one at highest apparent pH less than 7.
Diisocyanates are eye, skin and respiratory irritants at concen-
NOTE 6—The inflection point typically is at apparent pH between 4 and
trations above the occupational exposure limit (TLV or PEL).
5.
Diisocyanates can cause skin and respiratory sensitization
11.7.1 If no clear end point can be identified, calculate
(asthma) in some people. Once sensitized, it is essential to limit
results using the end point at apparent pH
...

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. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6099 − 18 D6099 − 24
Standard Test Method for
Polyurethane Raw Materials: Determination of Acidity in
Moderate to High Acidity Aromatic Isocyanates
This standard is issued under the fixed designation D6099; 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.
1. Scope*
1.1 This test method determines the acidity, expressed as parts per million (ppm) of HCl, in aromatic isocyanate samples of greater
than 100–ppm acidity. The test method is applicable to products derived from toluene diisocyanate and methylene-bis-
(4–phenylisocyanate) (see Note 1).
NOTE 1—This test method is equivalent to ISO 14898, Test Method A.
1.2 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
E180 Practice for Determining the Precision of ASTM Methods for Analysis and Testing of Industrial and Specialty Chemicals
(Withdrawn 2009)
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2935 Practice for Evaluating Equivalence of Two Testing Processes
2.2 ISO Standards:
ISO 14898 Plastics—Aromatic isocyanates for use in the production of polyurethane—Determination of acidity
3. Terminology
3.1 Definitions—Terms used in this test method are in accordance with Terminology D883, unless otherwise specified. For terms
relating to precision and bias and associated issues, the terms used in this standard are defined in accordance with Terminology
E456.
3.2 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.22 on Cellular Materials - Plastics
and Elastomers.
Current edition approved Aug. 1, 2018Feb. 1, 2024. Published August 2018February 2024. Originally approved in 1997. Last previous edition approved in 20132018 as
D6099 - 13.D6099 - 18. DOI: 10.1520/D6099-18.10.1520/D6099-24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
*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
D6099 − 24
3.2.1 acidity, n—the acid strength of a sample expressed in ppm HCl.
4. Summary of Test Method
4.1 The isocyanate is mixed with an excess of methanol and a cosolvent. Additional acid is released into the solvent system during
urethane formation. The acid is titrated potentiometrically with methanolic KOH, and the acidity present in the isocyanate sample
is calculated from the titer.
5. Significance and Use
5.1 This test method can be used for research or for quality control to characterize aromatic isocyanates and prepolymers of
moderate to high acidity. Acidity correlates with performance in some polyurethane systems.
6. Apparatus
6.1 250-mL Beakers.
6.2 50-mL Pipet or Repipet, Class A volumetric.
6.3 100-mL Pipet or Repipet, Class A volumetric.
6.4 Automatic Titration Equipment, capable of inflection detection and stirring the sample while, titrating, such as:
6.4.1 Commerically-availableCommercially-available Automatic Titration Apparatus,
6.4.2 Reference Electrode, with saturated LiCl/ethanol solution in both chambers.
6.4.3 pH Glass Electrode, (see Note 2).
NOTE 2—A combination pH electrode with internal reference also may be used.
6.5 Magnetic Stirrer.
6.6 Stir Bars.
6.7 Watch Glasses.
6.8 Analytical Balance, capable of weighing to the nearest 1 mg.
7. Reagents and Materials
7.1 0.02 N KOH in Methanol—1.32 g KOH pellets (85 % KOH)/1000 mL methanol, standardized with potassium hydrogen
phthalate (KHP).
7.2 Toluene or 1,2,4–Trichlorobenzene (TCB), dried for 24 h over molecular sieves.
7.3 Anhydrous Methanol.
8. Sampling
8.1 Since organic isocyanates react with atmospheric moisture, take special precautions in sampling. Usual sampling methods,
even when conducted rapidly, can cause contamination of the sample with insoluble urea. Therefore, blanket the sample with dry
air or nitrogen at all times. (Warning—Diisocyanates are eye, skin and respiratory irritants at concentrations above the
occupational exposure limit (TLV or PEL). Diisocyanates can cause skin and respiratory sensitization (asthma) in some people.
D6099 − 24
Once sensitized, it is essential to limit further exposure to diisocyanates. Use a combination of engineering controls and personal
protective equipment, including respiratory, skin and eye protection, to prevent over-exposure to diisocyanates. Consult the product
suppliers’ Safety Data Sheet (SDS) for more detailed information about potential health effects and other specific safety and
handling instructions for the product.)
9. Calibration
9.1 Calibrate the electrodes using pH 4 and pH 7 aqueous buffers.
10. Test Conditions
10.1 It is essential that moisture be excluded from the sample by all means possible to ensure the accuracy of measurements in
this standard. See Section 8 of this standard for guidance on how to keep moisture out of the sample.
11. Procedure
11.1 All samples shall be done in duplicate.
11.2 Accurately weigh to the nearest 1 mg, 10 g of sample into a 250-mL beaker.
11.3 Add 50 mL of dried toluene or TCB.
NOTE 3—THF has been used as a solvent for prepolymers.
11.4 Add 100 mL of methanol into the solution.
11.5 Add a stir bar, cover with a watch glass, and stir for 20 min.
NOTE 4—Samples must be at room temperature before titration. Warm samples cause more frequent electrode clogging.
11.6 With uniform stitrringstirring of the sample, automatically titrate the mixture with 0.02 N methanolic KOH through the
potentiometrically-determined inflection end point between apparent pH 4 and 9. Follow manufacturer’s instructions for
instrument-specific parameters for set-up, calibration and analysis of samples.
NOTE 5—If results indicate a d
...