BS EN ISO 4629-1:2016 pdf download

BS EN ISO 4629-1:2016 pdf download.Binders for paints and varnishes- Determination of hydroxyl value Part 1: Titrimetric method without using acatalyst (IS0 4629-1:2016).
4 Principle
The hydroxyl groups contained in a test portion are acetylated with acetic anhydride. The excess acetic anhydride is hydralysed and the resulting acetic acid is titrated with potassium hydroxide solution. either in the presence of a colour Indicator or potentiornetrically.
NOTE Primary and secondary amines, if present, will also be acetylated. In audi cases, this will have to be allowed when calculating the hydroxyl value.
S Reagents
l)uring 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 PotassIum hydrogen phthalate IC6H4 (COOl-I) (COOK)].
5.2 Ethyl acetate, anhydrous.
5.3 Toluene/butanol mixture, I + 2 by volume.
5.4 Pyrldine/water mixture, 3 • I by volume.
5.5 Acetylating reagent
Dissolve 4,0 gnfp-toluenesulfnnicacid monohydrate (CH3C6I-LçSO3H’l-IzO) in 100 ml of ethyl acetate (52). preferably using a magnetic stirrer.
To this solution, add slowly, while stirring. 33 ml of acetic anhydride. Check that 5 ml of this reagent requires on titration a volume of between 40 ml and 50 ml of potassium hydroxide solution (56) for neutralization.
5.6 Potassium hydroxide. standad volumetric solution, cIKOH) s 0,5 mol/l, in methanol. Ethanol may also be used if the product to be tested is soluble in ethanol.
5.6.1 PreparatIon
Weigh, to the nearest 0,05 g, 28 g of potassium hydroxide, dissolve In the minimum quantity of water In a 1 000 ml one-mark Flask, dilute to the mark with methanol and mix well.
5.6.2 Standardization
Weigh, to the nearest 0.01 g, 2,5 g of potassium hydrogen phthalatc (51). previously dried at about 120 °C to constant mass and allowed to cool in a desiccator, into a 250 ml flask. Add 150 ml freshly boiled and cooled water and swirl until dissolved.
Titrate the potassium hydroxide solution prepared in 6J… using pheriolphthalein solution (Z) as indication, until a red coloration that remains for at least lOs appears.
Calculate the actual concentration, c, in moles of hydroxyl ions (OH) per litre, of the potassium hydroxide solution, using:
Weigh to the nearest 1 rng. the test portion Into the conical flask (J).
8.3 Determination
Add 5 ml of ethyl acetate (52) to the contents of the conical flask and shake, if necessary, with gentle warming, until the test portion (82) is dissolved.
If the test portion is not soluble in ethyl acetate, another solvent may he used.
Allow to cool to room temperature, add (5.00 * 0.02) ml (see Note 1) of the acetylating reagent (5.5) by means of the microburette or pipette (6.3) and fit the reflux condenser (6.2) on the conical flask.
Heat the flask in the heating apparatus (6.5), maintained at (50± 1) C, for 20 mm. shaking every 5 mm.
Cool the contents of the flask to room temperature, remove the condenser, add 2 ml of water, replace the condenser and vigorously shake the flask. Add 10 ml of the pyridine/water mixture (5.4) from the top of the condenser so as to rinse down the condenser tube. Mix the contents of the flask and allow to stand for 5 mm at room temperature. Add 30 ml of the toluene/butanol mixture (52) from the top of the condenser and use a further 30 ml of the toluene/butanol mixture to rinse the condenser/flask loint.
Titrate with potassium hydroxide solution (5k)
— either In the presence of a colour indicator (see Note 2). a few drops of phenolphthaleln solution (51) or mixed-indicator solution (5.8). or
— determining the end point potcntioini’trically (see Note 3), usIng the potentlometric titration apparatus (oh).
NOTE 1 The tolerance of 0.02 nil on the volume of the acetylating reagent is necessary to obtain the required precision of the test result.
NOTE 2 The colour changes are as follows:
— phenolphthaleln: colourless (acld)/red (alkaline);
— mixed Indicator; yellow acld)/blue (alkaline).