ISO 4327:1979 Preview
Non-ionic surface active agents -- Polyalkoxylated derivatives -- Determination of hydroxyl value -- Phthalic anhydride method
This standard was last reviewed and confirmed in 2013. Therefore this version remains current.
The hydroxyl groups are esterified by phthalic anhydride in pyridine solution. The excess of phthalic anhydride is hydrolyzed with water containing in the sodium hydroxide solution used for the neutralization. The acidity which appears during the esterification and of the phthalic acid formed during the hydrolysis is neutralized by sodium hydroxide solution in the presence of phenolphthalein as indicator. The hydroxyl value is calculated from the difference between the volumes of sodium hydroxide solution used for the titration of the blank and of the test solution.
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