ASTM D5629-23

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Designation: D5629 − 16 D5629 − 23
Standard Test Method for
Polyurethane Raw Materials: Determination of Acidity in
Low-Acidity Aromatic Isocyanates and Polyurethane
Prepolymers
This standard is issued under the fixed designation D5629; 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 acidity, expressed as ppm of hydrochloric acid (HCl), in aromatic isocyanate or polyurethane
prepolymer samples of below 100 ppm acidity. The test method is applicable to products derived from toluene diisocyanate and
methylene di(phenylisocyanate) (see Note 1). Refer to Test Method D6099 for determination of acidity in moderate- to high-acidity
aromatic isocyanates.
1.2 The values stated in SI units are to be regarded as the standard.
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 healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
NOTE 1—This standard is equivalent to ISO 14898, Method B.
1.4 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
D6099 Test Method for Polyurethane Raw Materials: Determination of Acidity in Moderate to High Acidity Aromatic
Isocyanates
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(Withdrawn 2009)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
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, 2016March 1, 2023. Published April 2016March 2023. Originally approved in 1994. Last previous edition approved in 20112016 as
D5629 - 11.D5629 - 16. DOI: 10.1520/D5629-16.10.1520/D5629-23.
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 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.
*A Summary of Changes section appears at the end of this standard
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D5629 − 23
2.2 ISO Standards:
ISO 14898 Plastics—Aromatic Isocyanates for Use in the Production of Polyurethane—Determination of Acidity
3. Terminology
3.1 Definitions—The terminology in this test method follows the standard terminology defined in Terms used in this 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, 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 n-propanol, a cosolvent and a known amount of HCl. Additional acid is released
into the solvent system during urethane formation. The acid is then titrated potentiometrically with methanolic KOH. The same
procedure is performed with a blank solution and the difference in titer is used to calculate the acidity present in the isocyanate
sample.
5. Significance and Use
5.1 This test method is suitable for research or for quality control to characterize aromatic isocyanates and low-acidity
prepolymers. Acidity correlates with performance in some polyurethane systems.
6. Apparatus
6.1 Disposable Beakers, 250 mL.
6.2 Repipet, pipet or buret, 50 mL.
6.3 Pipet, 100 mL, class A volumetric; or a 100-mL buret with a dosing unit; or a 100-mL repipet, class A volumetric.
6.4 Potentiometric Titrator:
6.4.1 Reference Electrode, bridge-type electrolyte (double junction), sleeve-type diaphragm, having saturated LiCl/ethanol
solution in both chambers, or equivalent.
6.4.2 pH Glass Electrode (see Note 2).
NOTE 2—A combination pH electrode with internal reference is acceptable.
6.5 Magnetic Stirrer.
6.6 Polytetrafluoroethylene-Coated Stir Bars.
6.7 Watch Glasses.
6.8 Analytical Balance, capable of weighing to the nearest 0.1 mg.
7. Reagents and Materials
7.1 0.01 N KOH in Methanol, for example, 0.66 g 87.7 % KOH/1000 mL methanol, standardized with potassium hydrogen
phthalate (KHP).
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
D5629 − 23
7.2 Toluene or THF (dried for 24 h over 5 A molecular sieves).
7.3 n-Propanol, acidified with 120 μL concentrated hydrochloric acid per 4-L bottle. Allow this solution to stand for at least 24
h before use to allow equilibration. The solution is to be mixed well before dispensing.
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. 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 7 aqueous buffers.
10. Test Conditions
10.1 Since isocyanates react with moisture, keep laboratory humidity low, preferably around 50 % relative humidity. For further
information, see 8.1.
11. Procedure
11.1 Make a blank determination in conjunction with each series of samples. Prepare the blank in the same manner as a sample,
only omitting the sample. All samples and blanks are to be
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