Plastics -- Polyols for use in the production of polyurethane -- Determination of hydroxyl number

ISO 14900:2017 specifies two methods for the measurement of the hydroxyl number of polyols used as polyurethane raw materials. It is necessary to know the hydroxyl content of polyols 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 may 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.

Plastiques -- Polyols pour la production du polyuréthanne -- Détermination de l'indice d'hydroxyle

General Information

Status
Published
Publication Date
01-Mar-2017
Current Stage
6060 - International Standard published
Start Date
30-Jan-2017
Completion Date
02-Mar-2017
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INTERNATIONAL ISO
STANDARD 14900
Second edition
2017-03
Plastics — Polyols for use in the
production of polyurethane —
Determination of hydroxyl number
Plastiques — Polyols pour la production du polyuréthanne —
Détermination de l’indice d’hydroxyle
Reference number
ISO 14900:2017(E)
ISO 2017
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ISO 14900:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
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ISO 14900:2017(E)
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 ................................................................................................................................................................................ 7

8.4 Test report ................................................................................................................................................................................................... 8

9 Method B — Phthalation .............................................................................................................................................................................. 8

9.1 Procedure .................................................................................................................................................................................................... 8

9.2 Expression of results .......................................................................................................................................................................... 9

9.3 Precision and bias .............................................................................................................................................................................10

9.4 Test report ................................................................................................................................................................................................10

Bibliography .............................................................................................................................................................................................................................12

© ISO 2017 – All rights reserved iii
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ISO 14900:2017(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,

as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the

Technical Barriers to Trade (TBT) see the following URL: www . i so .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 12,

Thermosetting materials.

This second edition cancels and replaces the first edition (ISO 14900:2001), of which it constitutes a

minor revision. It also incorporates the Technical Corrigendum ISO 14900:2001/Cor. 1:2005. The

changes compared to the previous edition are as follows:
— in Clause 2, the normative references have been updated;

— in Clause 4, it has been clarified that Method A refers to “acetylation” and Method B refers to

“phthalation”.
iv © ISO 2017 – All rights reserved
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ISO 14900:2017(E)
Introduction

International Standards have been published 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). 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.
© ISO 2017 – All rights reserved v
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INTERNATIONAL STANDARD ISO 14900:2017(E)
Plastics — Polyols for use in the production of
polyurethane — 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

ensure compliance with any national regulatory conditions.
1 Scope

This document specifies two methods for the measurement of the hydroxyl number of polyols used

as polyurethane raw materials. It is necessary to know the hydroxyl content of polyols 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

may 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 terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
© ISO 2017 – All rights reserved 1
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ISO 14900:2017(E)
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, it is intended

that all reagents 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).

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.

NOTE 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 has to be taken that

sufficient reagent is present to complete the reaction quantitatively. See also 8.1.2.

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ISO 14900:2017(E)

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 the note to 6.1).

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 as follows:

Water to add, in ml = 4,0 − 9A
where A is the percent water already in the pyridine.
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 performed by the following:

c = c + F(θ − θ )
θ2 θ1 1 2
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ISO
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