BS ISO 14900:2017 pdf download – Plastics Polyols for use in the production of polyurethane – Determination of hydroxyl number 4 Principle 4.1 Method A (Acetylation): A test portion is reflllxed in a so lution of acet ic anhydr i de in pyr id ine to acetylate the hydroxyl grollps pr esen t; the reaction is cata lyzed by imidazole. The excess reagent is hydrolyzed with water and the res lllting acetic acid is titrated with standardized sodium hydroxide solution. The hydroxyl content is calcul ated from the difference in titration of the test port i on and a blank solution. CAUTION – Acetic a nhydrid e and pyridine are toxic and f1 amm a ble . In addition , ac e tic anhydride is corrosive . Take prop er pre c aution s when handling these reagents . 4.2 Method B (Phthal a tion): The hydroxyl groups in a test portion are esterified by refluxing with a solution of phthalic anhydride in pyridine; the r eaction is catalyzed by imidazole. The excess anhydride is hydrolyzed with water and the p hthalic acid formed is ti trated with standardized sodíum hydroxide solution. The hydroxyl content ís calculated from the difference in títratíon ofthe test portíon and a blank solution. 5 Interferences 5.1 Excess water will i nterfere by destroyíng part of the esterifícatíon reagen t. If the samp le contains more than 0 , 2 % water , dry the sample with a r eagent th at will n ot add acidity or basicity to the sam ple. 5.2 Pri mary and seco n da ry amin es and long-chain fa tty acids react with the reagent to f orm st ab le compo u nds th at will be included in th e res ult. 6 Reagents Reagent-grade chemicals sha ll be used in all determinations. Un l ess otherwise indicated , it is inte n ded that all reagents conform to the specifications of I SO 6353 -1, ISO 6353-2 and ISO 6353-3, although ot h er grades may be used provided that it is first determined that the reagent is of sufficiently high purity to permit its use without lesseni ng 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 re ag e nt (for method A). Mix...
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