The hydroxy groups present in a test portion are esterified with phthalic anhydride. The excess phthalic anhydrids is hydrolyzed and the phthalic acid formed is neutralized with standard volumetric sodium hydroxide solution. If the sample contains free acidity or alkalinity a corresponding correction is made. From the corrected hydroxyl number, the apparat relative molecular mass may be calculated by a formula given.
PUBLISHED
ISO 6796:1981
90.93
Standard confirmed
Jul 19, 2019