BS ISO 4629-3:2018 pdf download – Binders for paints and varnishes — Determination of hydroxyl value Part 3: Rapid test
This document specifies a titrimetric method for determining the hydroxyl groups in resins and binders for paints and varnishes.
This method is primarily suitable for neutral media. Acidic products provide higher values; neutral products provide, through neutralization of the acidic carbamates, lower values. For these products, preliminary tests are performed to ensure the applicability of the method.
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 4618, Paints and varnishes — Terms and definitions
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at
— IEC Electropedia: available at
hydroxyl value
number of milligrams of potassium hydroxide (KOH) corresponding to hydroxyl groups that have been acetylated under specified test conditions in 1 g of the product tested
[SOURCE: ISO 4629‑1:2016, 3.1]
4 Principle
The primary and secondary hydroxyl groups of the sample are converted to acidic carbamate groups using toluene‑4‑sulfonyl‑isocyanate. The carbamate can then be titrated with the strong base tetrabutylammonium hydroxide (TBAOH) under non‑aqueous conditions, i.e. in an organic solvent.
5 Reagents
During the analysis, use only reagents of recognized analytical grade and only water of at least grade 3 purity as specified in ISO 3696.
5.1 Solution of tetrabutylammonium hydroxide (TBAOH) in isopropanol/methanol,c(TBAOH) = 1,0 mol/l.
5.2 Reaction solution.
Place approximately 250 ml acetonitrile in a 500 ml volumetric flask and titrate with 20 ml toluene4‑sulfonyl‑isocyanate. Make up the solution to the mark with acetonitrile and mix thoroughly. The reaction solution has a shelf life of approximately 1 month.
5.3 Acetonitrile, HPLC‑Grade.
5.4 Toluene, analytical grade.
6 Apparatus
Ordinary laboratory equipment and glassware, together with the following.
6.1 Conical flask, capacity about 250 ml.
6.2 Watch glass.
6.3 Burette.
6.4 Potentiometric titration apparatus.
7 Sampling
Take a representative sample of the product to be tested, as specified in ISO 15528.
8 Procedure
Depending on the expected hydroxyl number, weigh out 1 g to 15 g 1) of the product under test in the conical flask (6.1), dissolve with 3 ml toluene and 7 ml acetonitrile and heat to 30 °C to 35 °C.
Add 10 ml reaction solution (5.2) and cover the flask with the watch glass (6.2). Allow the reaction to proceed for 5 min under gentle stirring. Then add 1,5 ml distilled water (to hydrolyse the excess reaction solution) and stir for an additional 3 min.
Add 30 ml acetonitrile (5.3) and titrate the mixture with the tetrabutylammonium hydroxide solution (5.1) until after the second point of change.
The electrode should be immersed in the solution immediately before the measurement. The electrode and burette shall be rinsed with acetone before each use.
After each titration rinse the electrode and burette tip with acetone followed by distilled water. Then place the electrode in distilled water for 1 min.
10 Precision
No precision data are currently available.
11 Test report
The test report shall contain at least the following information:
a) all details necessary to identify the product tested;
b) a reference to this document, i.e. ISO 4629‑3:2018;
c) the result of the test as indicated in Clause 9;
d) any deviation (by agreement or otherwise) from the test method specified;
e) any unusual features (anomalies) observed during the test;
f) the date of the test.BS ISO 4629-3 pdf download.