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 https://www.iso.org/obp — IEC Electropedia: available at http://www.electropedia.org/ 3.1 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...
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