ISO 14900:2023

INTERNATIONAL ISO
STANDARD 14900
Third edition
2023-12
Plastics — Polyols for use in the
production of polyurethanes —
Determination of hydroxyl number
Plastiques — Polyols pour la production de polyuréthanne —
Détermination de l'indice d'hydroxyle
Reference number
© ISO 2023
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Interferences . 2
6 Reagents . 2
7 Apparatus . 4
8 Method A — Acetylation . 5
8.1 Procedure . 5
8.2 Expression of results . . 7
8.3 Precision and bias . 8
8.4 Test report . 8
9 Method B — Phthalation . 9
9.1 Procedure . 9
9.2 Expression of results . . 10
9.3 Precision and bias . 10
9.4 Test report . 11
Bibliography .12
iii
Foreword
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 12,
Thermosetting materials.
This third edition cancels and replaces the second edition (ISO 14900:2017), which has been technically
revised.
The main changes are as follows:
— the title has been changed to plural form to read: "Plastics — Polyols for use in the production of
polyurethanes — Determination of hydroxyl number";
— in 7.13, hotplate has been added as heating device;
— in 8.1.3, an oil bath has been added, in addition to a hot plate, as a heating device;
— in 8.3.1 and 9.3.1, precision and bias information have been updated;
— in 9.1.3, the information on hydrolysis of excess phthalic anhydride, and the water addition process
have been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
International Standards which deal with the determination of hydroxyl values of unsaturated-
polyester resins (ISO 2554), non-ionic surface active agents (ISO 4326, ISO 4327), binders for paints
and varnishes [ISO 4629 (all parts)] and industrial polyglycols (ISO 6796) have been published. The
two methods in this document are improved versions of imidazole-catalyzed procedures specifically
tailored to the determination of the hydroxyl number of many types of polyol, including those used in
the production of polyurethanes. Method A is especially suited to the determination of the hydroxyl
number of polyether polyols that may have steric hindrance, or are otherwise difficult to determine
by phthalation. Method B is a general method based on phthalation and is applicable to a wide range of
polyol types. Both of these methods are similar to procedures found in ASTM D4274.
v
INTERNATIONAL STANDARD ISO 14900:2023(E)
Plastics — Polyols for use in the production of
polyurethanes — Determination of hydroxyl number
WARNING — Persons using this document should be familiar with normal laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its
use. It is the responsibility of the user to establish appropriate safety and health practices and to
determine any national regulatory conditions prior to use.
1 Scope
This document specifies two methods for the measurement of the hydroxyl number of polyols used as
polyurethane raw materials.
The hydroxyl content of polyols are determined to properly formulate polyurethane systems. Method A
is primarily applicable to readily esterified polyether polyols. It is also intended for polyols which have
significant steric hindrance, such as those based on sugars. Method B is intended for polyether polyols,
polymer polyols and amine-initiated polyols, but can give low results for sterically hindered polyols.
Other polyols can be analysed by these methods if precautions are taken to verify applicability. These
methods can be used for research and for quality control and specification purposes.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 385, Laboratory glassware — Burettes
ISO 648, Laboratory glassware — Single-volume pipettes
ISO 760, Determination of water — Karl Fischer method (General method)
ISO 835, Laboratory glassware — Graduated pipettes
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4788, Laboratory glassware — Graduated measuring cylinders
ISO 6353-1, Reagents for chemical analysis — Part 1: General test methods
ISO 6353-2, Reagents for chemical analysis — Part 2: Specifications — First series
ISO 6353-3, Reagents for chemical analysis — Part 3: Specifications — Second series
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
polyurethane
polymer prepared by the reaction of an organic di- or polyisocyanate with compounds containing two
or more hydroxyl groups
3.2
hydroxyl number
hydroxyl value
number of milligrams of potassium hydroxide equivalent to the hydroxyl content of 1 g of a test portion
4 Principle
4.1 Method A (Acetylation): A test portion is refluxed in a solution of acetic anhydride in pyridine
to acetylate the hydroxyl groups present; the reaction is catalyzed by imidazole. The excess reagent is
hydrolyzed with water and the resulting acetic acid is titrated with standardized sodium hydroxide
solution. The hydroxyl content is calculated from the difference in titration of the test portion and a
blank solution.
CAUTION — Acetic anhydride and pyridine are toxic and flammable. In addition, acetic anhydride
is corrosive. Take proper precautions when handling these reagents.
4.2 Method B (Phthalation): The hydroxyl groups in a test portion are esterified by refluxing with a
solution of phthalic anhydride in pyridine; the reaction is catalyzed by imidazole. The excess anhydride
is hydrolyzed with water and the phthalic acid formed is titrated with standardized sodium hydroxide
solution. The hydroxyl content is calculated from the difference in titration of the test portion and a
blank solution.
5 Interferences
5.1 Excess water will interfere by destroying part of the esterification reagent. If the sample contains
more than 0,2 % water, dry the sample with a reagent that will not add acidity or basicity to the sample.
5.2 Primary and secondary amines and long-chain fatty acids react with the reagent to form stable
compounds that will be included in the result.
6 Reagents
Reagent-grade chemicals shall be used in all determinations. Unless otherwise indicated, all reagents
shall conform to the specifications of ISO 6353-1, ISO 6353-2 and ISO 6353-3, although other grades
may be used provided that it is first determined that the reagent is of sufficiently high purity to permit
its use without lessening the accuracy of the determination.
Unless otherwise indicated, references to water shall be understood to mean grade 2 reagent water as
defined by ISO 3696.
6.1 Acetylation reagent (for method A).
6.1.1 Mix 127 ml of acetic anhydride with 1 000 ml of dry pyridine (6.7). Add 16 g of imidazole (6.3)
and swirl carefully to dissolve. Prepare the reagent fresh daily and keep it in a dark bottle. Do not use it
if it is darker than pale yellow.
6.1.2 Some laboratories have reported that dark, resinous solids have formed when the mixture
of pyridine and esterification reagent is heated. In that event, it has been found that preparing the
acetylation reagent with the addition of 0,4 % water in the pyridine (6.8) will correct the problem.
However, care should be taken that sufficient reagent is present to complete the reaction quantitatively.
See also 8.1.2.
CAUTION — Acetic anhydride and pyridine are eye, skin and respiratory irritants. Avoid bodily
contact with these reagents and use only in a well-ventilated area.
6.2 Phthalation reagent (for method B).
Weigh 116 g of phthalic anhydride into a 1 l brown bottle. Add 700 ml of pyridine (6.7) and shake
vigorously until dissolved. Add 16 g of imidazole and swirl carefully to dissolve. The reagent shall stand
overnight before use. Avoid prolonged exposure of the reagent to moisture in the air. Discard reagent
that develops a colour. In the blank titration as described in the procedure for method B, exactly 25 ml
of this reagent shall consume between 95 ml and 100 ml of 0,500 mol/l sodium hydroxide.
6.3 Imidazole, reagent grade or equivalent.
6.4 Hydrochloric acid, standard solution, 0,1 mol/l.
Prepare and standardize to four significant figures in accordance with good practice, using potassium
acid phthalate (6.6) as a primary standard. Determine and record the temperature at which the
standardization was performed. The concentration of the solution shall be corrected to the temperature
at which the determination is performed, as described in 6.9. This solution is required only if a
correction is to be applied for the presence of strong base in the sample being analysed.
6.5 Phenolphthalein indicator solution, 10 g/l.
Prepare a solution of 1 g of phenolphthalein in 100 ml of pyridine (6.7).
6.6 Potassium acid phthalate.
Use a certified primary standard.
6.7 Pyridine, reagent grade, containing less than 0,1 % water.
If purification is required, distil from phthalic anhydride, discarding the fraction boiling below 114 °C
to 115 °C.
6.8 Pyridine, containing from 0,30 % to 0,45 % water (used for special cases: see 6.1.2).
Determine the water content of the pyridine using ISO 760. Add the required amount of water. The
required volume of water to add per litre of pyridine may be calculated using Formula (1):
W = 4,0 − 9A (1)
where
W is the water to add, in ml;
A is the percent water already in the pyridine, in mass %.
6.9 Sodium hydroxide, standard solution, 0,5 mol/l.
Prepare and standardize to four significant figures in accordance with good practice. Determine and
record the temperature at which the standardization was performed. The factor for thermal expansion
of this solution is 0,000 14. For calculation of the hydroxyl content, the concentration of the solution
shall be corrected to the temperature at which the determination was calculated using Formula (2):
C = C + F (θ − θ) (2)
θ2
...