BS EN ISO 4629-1:2016 pdf free
BS EN ISO 4629-1:2016 pdf free.Binders for paints and varnishes一Determination of hydroxyl value
The hydroxyl groups contained in a test portion are acetylated with acetic anhydride. The excess acetic anhydride is hydrolysed and the resulting acetic acid is titrated with potassium hydroxide solution,either in the presence of a colour indicator or potentiometrically.
NOTE Primary and secondary amines, if present, will also be acetylated. In such cases, this will have to be allowed when calculating the hydroxyl value.
Add 5 ml of ethyl acetate (5.2) to the contents of the conical flask and shake, if necessary, with gentle warming, until the test portion (8.2) is dissolved.
If the test portion is not soluble in ethyl acetate, another solvent may be 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 min, shaking every 5 min.
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 min at room temperature. Add 30 ml of the toluene/ butanol mixture (5.3) from the top of the condenser and use a further 30 ml of the toluene/ butanol mixture to rinse the condenser/flask joint.
Titrate with potassium hydroxide solution (5.6)
一either in the presence of a colour indicator (see Note 2), a few drops of phenolphthalein solution (5.7) or mixed-indicator solution (5.8), or
一determining the end point potentiometrically (see Note 3), using the potentiometric titration apparatus (6.6).
NOTE 1 The tolerance of 0,02 ml on the volume of the acetylating reagent is necessary to obtain the required precision of the test result.BS EN ISO 4629-1 pdf free download.
