ASTM D5523-21

Standard Test Method for Polyurethane Raw Materials: Acidity by Argentometric Determination of Hydrolyzable Chlorine in Monomeric, Aromatic Isocyanates

SIGNIFICANCE AND USE
5.1 This test method is suitable for research or for quality control to characterize TDI and MDI.  
5.2 This test method was developed to overcome problems with low-level acidity determinations that use glass electrodes in the presence of reagent alcohol solvents. Reagent alcohols contain acidic and basic species, which complicate the glass electrode methods at low levels of acidity.
SCOPE
1.1 This test method measures the hydrolyzable chlorine content of monomeric, aromatic isocyanates used as polyurethane raw materials and expresses it as HCl acidity. The test method is applicable to toluene diisocyanate (TDI) and monomeric methylene di(phenylisocyanate), known as MDI. The main sources of hydrolyzable chlorine and, therefore, acidity in monomeric aromatic isocyanates are carbamyl chlorides, acid chlorides, and dissolved phosgene. All of these compounds react with alcohols and water to form hydrochloric acid.  
1.2 This test method applies only to monomeric isocyanates in which all of the acidity is derived from species that generate HCl on solvolysis.  
1.3 The values stated in SI units are to be regarded as the standard.  
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
Note 1: There is no known ISO equivalent to this standard.  
1.5 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: 14-Jan-2021
• ICS: 83.080.20 - Thermoplastic materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.22 - Cellular Materials - Plastics and Elastomers

Relations

• 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 D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM E2935-17 - Standard Practice for Conducting Equivalence Testing in Laboratory Applications
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e1 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM E456-13A(2017)e3 - Standard Terminology Relating to Quality and Statistics
• Effective Date: 01-Oct-2017
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM E2935-16 - Standard Practice for Conducting Equivalence Testing in Laboratory Applications
• Effective Date: 15-Nov-2016
• Refers: ASTM E2935-15 - Standard Practice for Conducting Equivalence Testing in Laboratory Applications
• Effective Date: 01-Oct-2015

Overview

ASTM D5523-21: Standard Test Method for Polyurethane Raw Materials: Acidity by Argentometric Determination of Hydrolyzable Chlorine in Monomeric, Aromatic Isocyanates is an essential standard developed by ASTM International. It provides a reliable test method for measuring the hydrolyzable chlorine content in monomeric, aromatic isocyanates-namely toluene diisocyanate (TDI) and methylene di(phenylisocyanate) (MDI). This acidity, expressed as hydrochloric acid (HCl), is critical for the characterization and quality control of polyurethane raw materials. The test addresses specific analytical challenges associated with low-level acidity determinations, particularly in the presence of reagent alcohol solvents.

Key Topics

• Scope and Applicability

  • Measures hydrolyzable chlorine as HCl in monomeric, aromatic isocyanates used for polyurethane production.
  • Applicable to TDI and MDI, where acidity primarily originates from carbamyl chlorides, acid chlorides, and dissolved phosgene.
  • Applicable only for acids that yield HCl upon solvolysis.
  • Uses SI units as the standard for reporting results.

• Testing Method

  • Utilizes an argentometric titration (potentiometric titration with methanolic silver nitrate) after reaction with 2-propanol and methanol.
  • Addresses limitations in glass electrode methods due to interfering acidic and basic species in reagent alcohols.
  • Procedures require careful control of humidity and avoidance of chloride contamination.

• Precision and Bias

  • Repeatability and reproducibility data are provided for typical laboratory usage, with guidelines for expected variation in results.

• Safety and Handling

  • Emphasizes precautions for sampling and handling isocyanates to prevent hazardous exposure.
  • Details the responsibility of the user to ensure compliance with safety, health, and regulatory requirements.

Applications

• Quality Control and Certification

  • Ensures that polyurethane raw materials such as TDI and MDI meet required specifications regarding hydrolyzable chlorine content, impacting the performance and stability of end-use polyurethane products.

• Research and Development

  • Used in R&D settings to investigate the purity and reactivity of isocyanates, facilitating the development of new polyurethane formulations.

• Manufacturing Assurance

  • Integral for continuous process monitoring and improvement in the polyurethane supply chain, minimizing risks associated with excessive acidity or chlorine residues.

• Compliance and Reporting

  • Recognized approach for regulatory compliance and technical documentation in the global polyurethane industry, ensuring traceability and consistency in test results.

Related Standards

• ASTM D883 – Terminology Relating to Plastics

  • Standard terminology document providing definitions relevant to plastics including isocyanates and polyurethanes.

• ASTM E456 – Terminology Relating to Quality and Statistics

  • Outlines quality and statistical terminology applicable to test methods and laboratory data.

• ASTM E2935 – Practice for Conducting Equivalence Tests for Comparing Testing Processes

  • Guidance on evaluating the equivalence of different testing processes, relevant to lab accreditation and inter-laboratory studies.

Keywords:

acidity, hydrolyzable chlorine, isocyanates, TDI, MDI, polyurethane, titration, argentometric determination, quality control, raw materials, ASTM D5523-21

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ASTM D5523-21 sets the benchmark for accurately determining acidity by measuring hydrolyzable chlorine in aromatic isocyanates, thereby supporting the reliability, safety, and performance of polyurethane manufacturing and research worldwide.

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: D5523 − 21
Standard Test Method for
Polyurethane Raw Materials: Acidity by Argentometric
Determination of Hydrolyzable Chlorine in Monomeric,
Aromatic Isocyanates
This standard is issued under the fixed designation D5523; 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* E456 Terminology Relating to Quality and Statistics
E2935 Practice for Conducting Equivalence Tests for Com-
1.1 This test method measures the hydrolyzable chlorine
paring Testing Processes
content of monomeric, aromatic isocyanates used as polyure-
thane raw materials and expresses it as HCl acidity. The test
3. Terminology
method is applicable to toluene diisocyanate (TDI) and mono-
meric methylene di(phenylisocyanate), known as MDI. The
3.1 Definitions—Terms used in this standard are defined in
mainsourcesofhydrolyzablechlorineand,therefore,acidityin
accordance with Terminology D883, unless otherwise speci-
monomeric aromatic isocyanates are carbamyl chlorides, acid
fied. For terms relating to precision and bias and associated
chlorides, and dissolved phosgene. All of these compounds
issues,thetermsusedinthisstandardaredefinedinaccordance
react with alcohols and water to form hydrochloric acid.
with Terminology E456.
1.2 This test method applies only to monomeric isocyanates
3.2 Definitions of Terms Specific to This Standard:
in which all of the acidity is derived from species that generate
3.2.1 acidity—the acid strength of a sample expressed as
HCl on solvolysis.
parts per million hydrochloric acid (HCl) present.
1.3 The values stated in SI units are to be regarded as the
3.2.2 hydrolyzable chlorine—the amount of chlorine re-
standard.
leased as chloride ion under the conditions of the test,
expressed as parts per million chlorine.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
4. Summary of Test Method
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
4.1 The sample reacts with 2-propanol to form urethanes
mine the applicability of regulatory limitations prior to use.
and hydrochloric acid, which is liberated from the labile
carbamyl chlorides, acid chlorides, and dissolved phosgene.
NOTE 1—There is no known ISO equivalent to this standard.
The chlorides of the liberated acid are then determined
1.5 This international standard was developed in accor-
potentiometrically using standard methanolic silver nitrate
dance with internationally recognized principles on standard-
solution and calculated as parts per million HCl.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
5. Significance and Use
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
5.1 This test method is suitable for research or for quality
control to characterize TDI and MDI.
2. Referenced Documents
2 5.2 This test method was developed to overcome problems
2.1 ASTM Standards:
with low-level acidity determinations that use glass electrodes
D883 Terminology Relating to Plastics
in the presence of reagent alcohol solvents. Reagent alcohols
contain acidic and basic species, which complicate the glass
This test method is under the jurisdiction ofASTM Committee D20 on Plastics
electrode methods at low levels of acidity.
and is the direct responsibility of Subcommittee D20.22 on Cellular Materials -
Plastics and Elastomers.
Current edition approved Jan. 15, 2021. Published January 2021. Originally
6. Interferences
approved in 1994. Last previous edition approved in 2015 as D5523 - 15. DOI:
10.1520/D5523-21.
6.1 Acidic species that do not generate chloride ions under
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the conditions of this test method will not be determined
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
because acidity is determined indirectly from the chloride ion
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. concentration.
*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
D5523 − 21
6.2 Acidic species that do not produce chloride ions are Diisocyanates can cause skin and respiratory sensitization
expected to be negligible at low levels of acidity and for the (asthma)insomepeople.Oncesensitized,itisessentialtolimit
monomeric isocyanates in this test method. further exposure to diisocyanates. Use a combination of
engineering controls and personal protective equipment, in-
6.3 Care must be taken to avoid chloride contamination of
cluding respiratory, skin and eye protection, to prevent over-
glassware and sample containers.
exposure to diisocyanates. Consult the product suppliers’
Safety Data Sheet (SDS) for more detailed information about
7. Apparatus
potential health effects and other specific safety and handling
7.1 Potentiometric Titrator.
instructions for the product.)
7.2 Combination Silver Billet Electrode (Note 2).
10. Test Conditions
7.3 Oven, 70°C (Note 3).
10.1 Since isocyanates react with moisture, keep laboratory
7.4 Magnetic Stirrer.
humidity low, preferably around 50 % relative humidity. See
NOTE 2—The combination silver billet electrode is to be stored in 0.01
warning statement in 9.1.
N methanolic silver nitrate solution in order to keep the electrode
conditioned properly. The use of chloride containing solutions must be
avoided during storage and maintenance of the apparatus.
11. Procedure
NOTE 3—Monomeric MDI samples can be solid when received in the
11.1 Weigh10.0gofthesampleintoabeakerandrecordthe
laboratory.An oven is to be used to melt the sample prior to beginning the
test procedure.
weight to the nearest 0.0001 g (Note 4).
11.2 Add100mLof2-propanoltothebeaker,cover,andstir
8. Reagents and Materials
the sample for 10 min.
8.1 Purity of Reagents—Reagent grade chemicals shall be
11.3 Add 100 mL of methanol, cover, and continue stirring
used in all tests. Unless otherwise indicated, it is intended that
the sample solution for an additional 20 min (Note 5).
all reagents conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society where
11.4 Add ten drops of concentrated nitric acid solution to
such specifications are available. Other grades can be used,
the sample solution.
provided it is first ascertained that the reagent is of sufficiently
11.5 Cool the sample solution to room temperature in an ice
high purity to permit its use without lessening the accuracy of
bath if necessary.
the determination.
8.2 Methanol. 11.6 Titrate the sample solution potentiometrically with the
appropriate methanolic silver nitrate solution (Note 6).
8.3 2-Propanol.
11.7 Recordthevolume
...

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: D5523 − 15 D5523 − 21
Standard Test Method for
Polyurethane Raw Materials: Acidity by Argentometric
Determination of Hydrolyzable Chlorine in Monomeric,
Aromatic Isocyanates
This standard is issued under the fixed designation D5523; 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 measures the hydrolyzable chlorine content of monomeric, aromatic isocyanates used as polyurethane raw
materials and expresses it as HCl acidity. The test method is applicable to toluene diisocyanate (TDI) and monomeric methylene
di(phenylisocyanate), known as MDI. The main sources of hydrolyzable chlorine and, therefore, acidity in monomeric aromatic
isocyanates are carbamyl chlorides, acid chlorides, and dissolved phosgene. All of these compounds react with alcohols and water
to form hydrochloric acid.
1.2 This test method applies only to monomeric isocyanates in which all of the acidity is derived from species that generate HCl
on solvolysis.
1.3 The values stated in SI units are to be regarded as the standard.
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
NOTE 1—There is no known ISO equivalent to this standard.
1.5 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
E456 Terminology Relating to Quality and Statistics
E2935 Practice for Conducting Equivalence Tests for Comparing Testing Processes
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 April 1, 2015Jan. 15, 2021. Published May 2015January 2021. Originally approved in 1994. Last previous edition approved in 20102015 as
D5523 - 10.D5523 - 15. DOI: 10.1520/D5523-15.10.1520/D5523-21.
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.
*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
D5523 − 21
3. Terminology
3.1 Definitions—For definitions of terms Terms used in this test method, see standard are defined 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:
3.2.1 acidity—the acid strength of a sample expressed as parts per million hydrochloric acid (HCl) present.
3.2.2 hydrolyzable chlorine—the amount of chlorine released as chloride ion under the conditions of the test, expressed as parts
per million chlorine.
4. Summary of Test Method
4.1 The sample reacts with 2-propanol to form urethanes and hydrochloric acid, which is liberated from the labile carbamyl
chlorides, acid chlorides, and dissolved phosgene. The chlorides of the liberated acid are then determined potentiometrically using
standard methanolic silver nitrate solution and calculated as parts per million HCl.
5. Significance and Use
5.1 This test method is suitable for research or for quality control to characterize TDI and MDI.
5.2 This test method was developed to overcome problems with low-level acidity determinations that use glass electrodes in the
presence of reagent alcohol solvents. Reagent alcohols contain acidic and basic species, which complicate the glass electrode
methods at low levels of acidity.
6. Interferences
6.1 Acidic species that do not generate chloride ions under the conditions of this test method will not be determined because
acidity is determined indirectly from the chloride ion concentration.
6.2 Acidic species that do not produce chloride ions are expected to be negligible at low levels of acidity and for the monomeric
isocyanates in this test method.
6.3 Care must be taken to avoid chloride contamination of glassware and sample containers.
7. Apparatus
7.1 Potentiometric Titrator.
7.2 Combination Silver Billet Electrode (Note 2).
7.3 Oven, 70°C (Note 3).
7.4 Magnetic Stirrer.
NOTE 2—The combination silver billet electrode is to be stored in 0.01 N methanolic silver nitrate solution in order to keep the electrode conditioned
properly. The use of chloride containing solutions must be avoided during storage and maintenance of the apparatus.
NOTE 3—Monomeric MDI samples can be solid when received in the laboratory. An oven is to be used to melt the sample prior to beginning the test
procedure.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such
D5523 − 21
specifications are available. Other grades can be used, provided it is first ascertained that the reagent is of sufficiently high purity
to permit its use without lessening the accuracy of the determination.
8.2 Methanol.
8.3 2-Propanol.
8.4 Nitric Acid, concentrated, 70 %.
8.5 Silver Nitrate.
8.6 Methanolic Silver Nitrate Solution (0.01 N)—Prepare by dissolving 1.70 g AgNO /L of solution. Potentiometrically
standardize with titration-grade sodium chloride frequently enough to detect changes of 0.00005 N.
8.7 Methanolic Silver Nitrate Solution (0.001 N)—Prepare by dissolving 0.170 g AgNO /L of solution. Potentiometrically
standardize with titration-grade sodium chloride frequently enough to detect changes of 0.000005 N.
9. Sampling
9.1 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.
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.)
10. Test Conditions
10.1 Since isocyanates react with moisture, keep laboratory humidity low, preferably around 50 % re
...